Hazardous Materials

CHAPTER 16 Radioactive Materials

-- 01/07--03/07 :· .

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Covrte-sy of Lilnd;, u , r, Inc.. Glen wood, /J/l no1s.

airborne radioactivity area, p . 703 alpha particle, p . 689 alpha decay, p . 689 alpha radiation , p . 690 atmospheric fallout. p. 706 background radiatio n, p . 698 becquerel (Bq), p . 697 beta decay, p . 690 beta radiation, p. 691 breeder reactor, p . 710 chain reaction, p . 707 Comprehensive Nuclear-Test-Ban Treaty ccren, p . 113 critical mass, p . 707 criticality, p . 707 criticality safety Index (CSI), p . 715 curie (Ci), p . 697 depleted uranium (DUF6), p . 71Z deute rium, p . 686 deuteron. p. 686 dirty bomb, p. 729 dry cask, p. 716

684

electromagnetic radiation, p . 692 electron volt (eV), p. 689 enriched uranium, p. 712 excepted package, p . 721 exclusive use, p . 721 fissile nuclei, p . 706 fission product. p. 704 fuel rod, p . 712 gamma decay, p . 693 gamma radiation, p. 692 gamma ray (photon), p . 691 gray (Gy), p . 698 green salt, p. 711 half-life, p. 687 high-radiation area, p . 703

~~i~~;,YP~o; 2 t;-controlled quantity

inverse square law of radiation, p . 726 ionizing radiation, p. 689 irradiation, p. 694 Isomeric transition (IT), p . 693 low specific activity material (LSA),p. 720 mas s number, p . 686 meltdown, p . 710

metastable state (isomeric state),p. 693 mixed oxide fuel (MOX}, p . 711 negatron, p . 690 normal form class 7 material (non-special-form class 7 materi,1ij, p , 724 nuclear fission, p . 704 nuclear reactor, p . 704 orange oxide, p . 711 positron, p. 691 protlum, p . 686 radiation absorbed dose (rad), p. 698 radiation area, p . 703 radiation level, p . 699 radiation sickness, p . 698 radioactive material, p. 685 radioactive materials area, p. 702 radioactivity, p. 686 radioisotope (radionuclide), p. 687 radiological dispersal device, p. 729 radlolysls, p . 703 reportable quantity (RQ), p. 718 resldential radon , p . 727 roentgen, p . 698 roentgen equivalent man (rem), p. 69B

-

staled source, p. 693 sievert (Sv), p . 698

surface contaminated object (SCO),p. 720

type B package, p . 722

special form class 7 materlal, p . 723 eciflc activity, p . 697

:~rateglc Reduction Arms Treaty (START), p . 713

transport Index, p. 719 tritium, p . 686

uranium enrichment process, P- 71 1

very high radiation area, P- 703 yellowcake, p . 711

triton, p . 686 type A package, p. 722

1 Describe the phenomenon of radioactivity and the concept of a half-life for a give n radioisotope.

1 Describe the na ture of each mode by whic h a radioisotope ma y decay. 1 Describe the differentiating features of alpha, beta, and gamma radiation. 1 Describe the nature of a sea led radiatio n sou rc e and the features of the ionizing

radiation symbol used to identify its presence. 1 Identify rhe units used for the measurement of activity and radiation dose. 1 Identify the ge ne ral aspects of OSHA regulations req uiring employers to limit

radiation exposure in the workplace, including the posting of signs in areas where radioactive materials a re stored or used. Describe the phenomenon of nuclear fission, incl ud ing sponta neous fission. Iden tify the primary health concern posed by the presence of rad o n within residen- tial dwellings. Identify the label s, markings, and placards that DOT requi res on packaging of radioactive mat erials and the transport \'e hicles used for their s hipment. Identify the response actions to be executed when radioactive materials a re released from their packaging into the environment. Describe the response action to be executed whe n a radiological dirty bomb ha s been activated a nd discharged into the environment.

W hen we hear the te rm radioactive, two fearsome incidents generally come t o mind: the accidenta l release of material fro m a nuclear power plant and the deployment of nuclear weapons. 1 We discover in this chapter that both events are associated with the occ urrence of o ne o r more nuclear processes. The forms of matter that display chem are called radioactive materials.

We a lso lea rn in this c hap ter that serious health ri sks are linked wit h exposure t o radioactive materials. To eliminate or minimize rhe impact of these risks, the U.S. Con- gre ss delegated the following responsibilities to the reg ulat ory bodies listed:

• The U.S. Nuclea r Regulatory Commission (N RC ) re gulates the civilian nuclear cnerg)' industry by licensing th e construction and operation of the nation's nuclear power plants.

• The U.S. Department of Energy (DOE) oversees the research and d evelo pment of new a nd creat ive means for reducing the burgeoning supply of nuclear was te . In add ition, it oversees the construction a nd operation of nuclear waste disposal sites and responds to re lea ses of radioactive material from any source. DOE a lso certifies the integrity of the unique packages in which radioactive material is transported, provided t he y a re fo r the purpose of national security.

1 Nuclear wea pon s. o r nucl ear bombs, in iti.ill y were called aro mic bo mb5. Th e renn 1111 c fr a r is pre fe ra ble to

atom rc, bec au se the phe nom enon res pon sible fo r th ei r detonation is a nucl ea r one.

ra d io a ctive m a t e ria l A material containing

an Isotope that sponta - n e o usly emits ionizin g ra d iatio n; for DOT pu r- po ses, a materlal whose speci fic activity and t otal activity In a con- sig nment exceed valu es pu bl is hed for liste d ra dioisoto pes at 49 C.F.R. §173 .436

Chapter 16 Radioactive Materials 685

mass number • The tota l nu mber of pro- tons and neutrons in a given nu cl eus

protiu m • The hydro- ge n isotope com posed of one proton and no neutrons deuteriu m• The hy dro- gen isotope co mposed of one proton and one neutron

EPA es{abl ishes r.idi.ation-exposure limir_s to p~o rect publi c he_alt.h. These limi ts appJ to ra dia tion arisi ng m the env1ron_menc, mcludmg natural r~d1at1on and the radiatio~ from spent radioactive m:iten ~ds m storage. EPA :ilso momtors the levels of rad rivi ry in ai r, preci pitatio n, drinking waler, and milk al 164 monitoring stations s;::~ throughout rh e 50 srates. OS HA estab lishes radi:iri on-expos ure limit s that protect employees who use rad ' tfre mat erials wirhin those wo rkplaces that are not regulated by NRC or DOE. ioac- DOT ensu res th ~tr shi.Ppers and c~ rr iers ~dop~ proced~res to eliminate or minimize the ris ks associated wuh rransportmg rad1oact1ve materials.

In combination, these age ncies serve to prov_ide a_degree o ~ protectio n against the hazards associated with inad ve rtent exposure to rad1oam ve materials.

16. 1 FEATURES OF ATO M IC NUCLEI In Senion 4.4, we noted chat the atomic nucleus ha s two primary constituents: protons and neutrons. Although the nuclei of all atoms of the same element have the same number of protons, they m:i y have different numbers of neutrons. These nuclei are called isoropes.

The number of protons found in rhe nucleu s of an atom is its atomic number. The number of protons equals the number of electrons in a neutral atom. Because the atomic nwnbers of the elements are compiled in the periodic table, we may use a periodic table to re:idily identify the number of protons in a gi ven nucleus. The tora l number of protons and neutrons in a particular isotope is called its mass number.

Hydrogen has an atomic number of 1; rhis means that every hydrogen atom has one proton. Each hydrogen atom has one electron, but when a hydrogen atom is ionized, it is stripped of its electron , and only its nucleus remains.

Hydrogen atoms exist in an y of three isotopic forms having the following unique names and compositions:

Protiu m is the simplest of the hydrogen isotopes and, in fact, the simplest of all nuclei. Protium ha s a single proton as irs nucleus. When a protium atom is ionized, only a proton remains. Deuterium is the second hydrogen isotope. Deuterium has a nucleus consisting of a proron and a neutron. When a deuterium atom is ionized , the remaining nudeu5 is composed of one proton and on e neutron and is called a deuteron. Tritium is the third hydrogen isotope. Tritium has a nucleus consisting of a proton and rwo neutrons. The nucleus of an ionized tritium atom is called a triton. deuteron • The nucl eus

of the deute ri um atom Each isotope is designated by the symbol 2X, where z and t\ are the atomic num be r tri ti um • The hydrogen and ma ss number, respecti vel y; X is the element's chemical symbol. Using chis format, rh e isotope composed of three hydrogen isotopes are designated by the symbols !H, fH, and {H, rcspectivdr: For one proton and two each , the symbol Z equals l, the number of proton s. The number of neutrons is the differ- neutrons ence between the superscript and the subscript: for prorium, the number is O; for deu ie- trito n • The nuc leus of rium, the number is l; and for tritium, the number is 2. Deuterium and tritium are al so the tr itium atom represe nted as D and T, respectively. radioactivity , The prop- Only the isotopes of hydrogen have unique names. The isotopes of other elements are erty associ ated with the n:imed by identifying the name or symbol of rh e element and the mass number of th e :i;;~~~;ta~:~~on of isot~pe at iss ue. Thu s, nuclei designated as l£C, ~l1 U and iSK are named carbon-12, gamma rad iation from uramum-235., and pota ssium-40, or ~ -12, U-235, and K-40, respectively. . , cain rad ioisotopes, their cap- . All nucle~ ~an have three or more 1so1opes, many of which are stable; that 1s, the) re clei ture of extran uclear their c~mposmons and do nor undergo spontaneous changes. Howe\'er, many ot~.er n~dis- eleetrons, or their spon- are subJ ect to spontaneo us tran sformati ons. They are sa id to "transform" "decay, or . taneous fi ss ion integrate.,.. The phenomenon is called radioactivity, and the intrinsically' unstable nuclei are 68 6 Chapter 16 Rad ioactive Materials

•Jid ro be radioactive. ~hey ~re ~ailed radioisotopes, or radionuclides. Protium and deute- ;iulll are srab_k _, nonradioac_uve isotopes of hydrogen, but tritium is a radioisotope.

Rad1oacu v1t}' generally IS not affected by any physical or chemical change in a substance. Hence, when radioacti\•e mat~~ls are ~ubjecred to changes in pressure, temperature, or chemi- cil n:twre, the sr:o~1aneous d1smregrat10n of the ~levanr radioisowpe usually is not altered . .

When a rad101sotope undergoes a change, it usuall y emits a particle; less commonly, 1t absorbs an electron. Both processes fr~quend y are accompanied by the simultaneous emi s- . of energy. When the transformauon occurs, the radioisotope is converted inro a new ~ 1 ~~eus, which is either stable or radioactive itself. Radioisotopes often undergo several nsformations before 1hey are convened into stable nuclei.

ira Each radioactive transformation is associated with a specific period of time. The time during which an arbitrary number of nuclei are reduced to half the number is called the half-life of that radioisotope. For instance, suppose a volume of tritium gas containing S00.000 molecules is set aside for 12.32 years. Because the tritium molecule is diatomic, there are I million atoms of tritium in this volume. After a 12.32-year lapse, only 500,000 iritium :iroms remain; and after another 12.32 -year lapse, on ly 250,000 tritium atoms remain. Hence, 12.32 years is the half-life of tritium.

A half-life is typically symbolized as t½ and is one of the characteristic properties of a r.1dioisotope. Its value may range from nanoseconds to billions of years. Each element has at least one radioisotope. The hundred or so elements collectively have nearly 3100 kno wn radioisotopes. Table 16.1 shows that few radioisotopes are present in nature. If they were present when Earth was initiall y formed, most disappeared long ago, because the planet is 3.6 billion years old.

Some commercially available radioisotopes are listed in Tab le 16.2. Although rher have man y potentia l purposes , most commercia l radioisotopes are used to image the

lfr1!iiii AADIOISOTOPE

Tri tium Ca rbon-14 Potassium-40 Rubidium -87 lridium-115 lanth an um -138 Neody mi um -144 Sa mari um-147

~ 87 Platinum- 190 Rad ium -226 Thor ium -232

Some Naturally Occurring Radioisotopes"

HALF-LIFE (y) I RELATIVE ISOTOPIC

ABUNDANCE(%) I MODE OF DECAYb 12 .32 0.00013 ~- 5700 ~-

1.248 X 109 I 0.012 p-, EC,~• 4.81 X ,olO 27.8 ~-

4.41 X 10 14 958 p-

1.02 X 10 11 0.089 p,-, EC

2.29 x 10 15 23.9

1.06x10 11 15.1

3.76 X 10 10 2.60 p-

4.33 X 10 10 62.9 ~-

6.5 X 10 12 I 0.012

1600 1.40 X 1010 100

0.72 7.04 x 108

4.468 X 109 99.28 Uran ium-235 --_ i..,'.:'.:::..:..:.:...,,-----t~ ;;-- Uran ium -238 :Chan of Nu cl ldes, National Nu clear Data Center, srookhaven Nation al l abor atory, Long Isl an d, New York {l012). S~ctlon 16.2.

radioisotope {radion ucl ide)• An atom ic nucleus that undergoes a spontane· ous change by emitting a particle, absorb ing an extranuclear electron, or undergoing sponta- neous fission

half- li fe • The time period during which an arbitrary amount of a rad ioisotope is trans- formed into half that amount

Chapter 16 Radioactive Materials 687

MilhiiN Some Commercially Available Radioisotopes RADIOISOTOPE --- Amer icium -241

Cesium-137

Chrom,um -51

Co ba lt-57

Cobalt-60

Fluorine-18

Gado lin ium- 153

Ga ll iu m-67

Ind ium-t i t

lodin e-123

tod ine-- 125

lodine-131

lrid ium-192

lron-59

Pa ll ad iu m-103

Phosphorus-32

Pluto ni u m-238

Pot a ssium-40

Rad ium -223

Rad ium -226

Rhen ium- 187

Se le ni um-75

Sod ium -24

Stro nt iu m-90

Techne ti um -99m

HALF-LIFE• APPLICATION OR USE --- Smoke dete cto rs 432 .6y

3008y

27.7025 d

271.74d

~ diat io n so urce for treatment of cance r; sealed rad iat ion sou~ food s

Ra~ e fo rdete ~ ofred ~l1 volumea~ b~ ----1-R,- d-ia-t ion source fo r in_stru~ent ca li brat ion and determ ina~

t he body 's uptake of vi tamin Biz

5.27 y

109.77 min

240.4d

3 .2617 d

2.8047 d

13.2235 hr

59.407 d

8.0252 d

73 .829d

44.495 d

16.991 d

14.262 d

87.7y

1.248 X 109 y

11.43 d

1600 y

4JJ X 10 10 y

I 119.79d

1S.997 hr

28.90 y

6.0067h r

Sea ted source for industr ial radiograp hy; sealed source for treatment of cancer irrad iat ion of foods, and induc ing cross-l ink ing w ith in polyethylene and rubbe~ macromo lecu les; determ inat ion of the effectiveness of the body's uptake of vitam ins; ste rili zat ion o f medical de vi ces

Bra in- and bone-i mag ing drug ; rad iat ion source for tumor imaging using pos itron em iss ion tomography

Rad iat ion source for determ in ing bone density and the enent of bone mineral ization

Diagnost ic drug for tumor detection

Diagnost ic drug tor tumor detection; rad iation source for imaging the gastr ic and cardiac systems

Rad iation source for imag ing the bra in, thyroid, and renal systems

Cancer therapeut ic drug ; brain , blood, and metabolic-function diagnostic drug; surg ically implanted as a component of • seeds" for the internal treatment of prostate

Bra in, pulmonary, and thyro id diagnostic drug ; thyro id -cancer chemotherapeutic drug

Sealed source for industrial radiography ; surgically implanted as brachytherapy needles into organ for internal cancer treatment

Radiat ion source for measuring the rate of format ion and lifetime of red blood cells

Rad iation source for detect ion of skin cancer

Power source for the thermoe lectric generators used in equipment for planetary stud ies, incl ud ing the Mart ian rover, Curiosity Dat ing geolog ical format ions

Rad io immunotherapeut ic drug

Rad iat ion source for treatment of cancer

Dat ing meteor ites

I Pancrea ti c cancer d iagnostic drug I Radiat ion source for detect ion of obstruct io ns with in the circulatory system \ Industrial gauges; thermoelectr ic generators

I Ra d iat ion source for imag ing the brain, thyro id, live r, kidney, lung, and card iova~u lar systems ___ Th a lliu m-201 3.042 1 d

Trit ium,orH-3 12.32 y ~ + :::--::~ ----11---,ea::_:,d:..:i•:...'d:...i•:.,9:..."o:.:st:...i<:..:d:::'":.,9 _____________ __

Rad iation source for determ ination of total body water Yttrium 90 64.053 hr Rad 10 1mmunotherapeut1c drug

•Ch art of NuclidM, Nationa l Nucl ea r Data c,n1er, Brookhaven Nationa l La borat ory, Long isla nd. New Yo rk (2012).

688 Chapter 16 Radioactive Materials

org:i ns in pa~ie~1ts having diseases in the heart , bones, and elsewhere. Generally, to pro- diic e a graphic ~m age of the st ructure or m~tabolic activity of an organ , radiologists inject l rJdi oisorope into the bloodstream and film the activity of the radioisotope as it move s

,oncentrates. or Some radioi sot0pe~ are u.scd to treat cancer patients. The radiation source delivers a hii;h dose fo~ <:7onsecu~1 ve da_1ly tre_atments to a specific location in the body. Less com-

nly. a rad101sotope 1s surgically implanted to deliberately radiate an organ over a long mo e period. During the treatment of prostate cancer, for example, a surgeon may implant tin~in c- 125 or palladium-103 encased in tiny pellets or " seeds " within the proscate. The 10

dioisotope kills cells in the nearby region, including those that are malignant. Once ::e:itment is completed, the seeds are surgically removed.

fi·itiH&HiMlll-11 r:-e,ium• 137 1s a rad101sotope often used a'> a sealed source (Section 16 3) of gamma rad•atJon for the tfeatm e nt

of cance r 11 a cl inic pu rchas es a sour ce conta,n ,ng 7 60 x 1015 atoms of cesium-137 today, hOIN ma ny atoms w,11 rema1n ,n 121 yea rs '

Solutlon: The ha ll -hie of ces,um-137 ts listed 1n Table 16 2 as 30 08 yea r, The number of half-lives in 12 1 yea rs 1s then detei min ed by d1v1s 1on:

Number of half- lives~ 121 y/ 3008y = 4 0 This me-ans that afte r the passage of 12 1 ye ars . cesi um-137 will have disintegrated through four hali-hves, hence, one-skXteent h of th e ato ms will re main

½ X ½ x Yi X ½ = (1/1)• ,., 1/1 6

~•u•t1 olym g 7 60 x 101s by 1/1 6 gives 4 75 x 10 14 atoms 7 60 x 101~ atoms x 1/ 16 = 4.75 x 101' atoms

Thus, after the passage of 12 1 yea rs, 4 75 x 1014 atoms of cesium -137 rem ai n ,n the sealed sourc e

16.2 MODES OF RADIOISOTOPIC DECAY Nuclear transformations of radioisotopes principally occur by means of one or more of the modes illustrated in figure 16.1: alpha decay, beta decay (nega.tr~n emission, positron emission, and electron capture), gamma decay, and spontaneous hss1on .. t\l.pha: b~ta, ~md ga mma decay gives rise to a specific cype of radiation: B:c~usc th ~ r~d1at1on 1omzes the matter through which it passes, each is an example of 1onizmg rad1at1on. We shall exam- ine them in Sections 16.2-A, 16.2-B, and 16.2-C.

The unit used to express the energy associated ,~ith alpha , beta , and gamma. dee:? typical\}' is the electron volt or eV. One electron volt 1s the amount of ene~gy ac~mred b) an electron when it is accel~rated by an electric potential of one ~·oh. It 1s equ_1vale_nt_ to 1.602 X 10~19 J. The energy typically emitted by r~diois~topes IS express;~ l~/r11l1on electron volts. One million electron volts, or l MeV, 1s cqlllvalent to 1.602 10 J.

16,2-A A LPHA D ECAY .\fany radi - - 11 , those ha ving atomic numbers grea1er than 83 , disi.nt ~grate b msotopes, especia ) . d of two proto ns and two neutrons. rhese Y spontaneously emitting particles compose - lied alpha decay Alpha particles

Panicles are called alpha particles, a~d the process/ ca symbolized as either ~He or the are the nuclei of doubly ionized hehum atoms an are

ioniz ing radiation Types of rad iation

that ionize matter upon impact

e le ctron volt (e V) The amou nt of energy acquired by an electron when It is accelerated by an e lectric potential of one volt

alpha A par- ticle emitted from cer• tain radio isotopes and having the properties of a doubly ion ized hel ium atom

a lpha d t!ca y A mode of radioisotopic decay associated with the em ission of an alpha part icle by a nucleus

Chapter 16 Radioactive Materials 689

r

alpha radiation • The coll ect ive com bination of th e alpha particles em in ed from certa in rad ioisotopes

beta dKay A mode of radioisotopic decay associ ated w ith the spontaneous emiss ion of a negatron or posi• tron from a nucleus or th e capture of an orbital electron by the nucl eus

negatro n • A particle hav in g the pr ima ry propert ies of an el ectron

FI GURE 16.1 The modes by wh ,ch rad•OISO· tooes decay, wherein the open circles represent protons, and thesol, o red circ les rep resent neutrons Th e most common modes of decay are those associa ted with the production of beta and gamma rad1at1on Tht> ra rest mode of decay 1ssocntaneous fiss ion

-y-decay

Gree k letter o:. When man y nucle i decay b y alpha emiss io n, the combination of alpb.i particl es is called alpha radiation.

Alp ha radiation is associated wit h a ~elatively large a_mo_unt of ~nergy tha t rangts from 4 to 8 MeV; but because a lpha parnc_les a re dou~l y ionized, th1 ~ en~rgy is readily di ss ipated by its passage thro ugh a few centimeters of atr or by absorption ma thin piece of matter. For instance, alpha rad iation is absorbed b y the thickness of this page.

When alpha decay occu rs, th e at0mic numb er a nd mass number of th e as sociated n uclei decrease by 2 and 4 , re spec tiv el y. An example of a radioisotope that disintegrates by a lpha decay is uranium-238. This phenomenon is repr ese nted by either of the follow. ing equations:

! J~U --+ !:MiTh + 1He 1 J~U --+ .!Jt Th + u

Both equations represent the chan ge that th e uranium-238 nucleus undergoes by emitti ng a n alpha particl e. The sy mbol o f the particle is written to the right of the arrow ro designate th a t th e a lpha particle ha s been emitted from the uranium -238 nucleus.

Equations d enot in g nuclear phenomena a re n o t balanced in the chemical se nse. Inst ead, a nucl ea r equation is balanced when each of th e following is fulfilled: The sums of th e aromic numbers and th e s um s of th e ma ss numbers are the sa me on each side of the a rrow.

16 .2-8 BETA DECAY The seco nd m ode of radioactive disintegration is ca ll ed beta decay. This process occurs w hen a radi oisot0pe eit her emi t s a ncga tron or positron or combines with an ex1ranude3r electron. These individu al ty pes of beta decay may occ ur individually or in combination.

Neg a tron Emission The first rype of beta d ecay is equiva lent in res ult 10 th e emission o f an electron from the nucleus. W hen electrons a re di scussed in nucl ea r phenom ena , the)' ordinaril)' a~e ~all:~ negatrons a nd are de signa ted as fr, o r -1e. W hen beta deca y occurs by ch e en11ssion . negatrons, the mass numbers o f th e associa ted radioisotopes remain unchanged, bu! rhe,r ato mic numbers increase by I. 2

. ~n example of a radi oisotop e th a t disintegrates by nega1ron emissio_n !s thorium·,!!;: Thi s 1s th e nucleu s p roduced w hen uranium•238 di si nte grates . On emntmg a nega

2 T he types of lxrJ •decay a re al~o J~~o,1Jtcd with th e produc tion of neu trJI subJtom ic p JCficle~ calkd ,witfl/l(i,$

an d a11tmei <1m105. Th,:-sc part icl,:-s Mt' of no lnter es r he1t.

690 Chapter 16 Rad ioactive Mate ri als

honu m-234 becon~es protoactinium-234. This phenomenon is represe nted by either of :he fo llowing equation s:

!~6Th - 1 J~ Pa + - ~" .!ttTh - 1{~ Pa + p-

The emi ssio n of a nega tron from a nucleus rai ses a basic que stion: How ca n it be emi tt ed fro m the nucl e~s when the elect~on is not a component of the nucle~ s? ~he pro·

. • a ppa rentl y more involved th an a smgl e equation represents. N ucl ea r sc1e nt1 sts ha ve ~:~: ~~lin ed that during n egatro n emission, eac h neutron wi thin th e un stabl e nucleus

forms into a proron and an elec1ron. The proton then becomes part of the new ~~~:us, a nd the electron is si ~ulra_neously emitted. This conversion of the neutron (6 11 ) in to a prow n a nd an electron 1s designated as follows:

611- \1-! + _1(' N . uon s possess a range of energi es, but these energi es generally arc n o greater th a n~

The y us uall y are absorbed by a 1--cent imet er-thick sheet o f aluminum. The combt- ~a:i~ n of multiple negatron-deca)' processes rep rese nts one type of beta radiation.

Positro n Emi ssio n . . The second rype of beta decay invol\'es the emission of a positron from a nu~lcus. A p~s1tron is 3 particle like an electron in most features, but it is positively charged. It ts sy ~1boltzed a~ .1e, or 13" . When a radioi sotope emits positrons, the ma ss numbers of the assoc.1a1ed nuclei remain unchanged, but their atomic numbers decrease by 1. Each nucl ea r event involves th e con\'ersion of a proton into a neutron and posi tron, expressed as follows:

\H - ~11 + .1e Sodium-22 is a n exa mple of a radi oisotope that deca)'S b y emining positrons. This

nucleu s spo ntaneousl y tran sfo rms into neon-22. The event is denot ed by either of the fol- lowi ng equations:

HN :-. - fijNe + .1e 11 ~.1 ---4- 1ij Ne + ~ .

Like neg:nrons, positrons possess :1 range of energies, but gc nerall_y the y ar~ no greater than 3 McY. Like negatrons, the y usuall y are absorbed by a t -ce_numcter-th1ck sh:er of aluminum. The combination of multiple positron-decay processes 1s also represe ntauvc o f beta radiation.

Electro n Ca p ture . The phenomenon associated with th e third type of beta decay involves the caprure of a n unstable nucleus a nd an orbital electron. A radioi sotope that undergoes clec1ron ca pture dec reases in atomic numb er by I but its mass numb er remain ~ unchanged. Eac h _electron ca ptu red by ihe nucleus re ac t s with a proto n, 1here by fornung a neutron, w hi ch then becomes pa rt of th e s trucrnre of the new nucleus. T his nucl ear event is represented b y the fo llowi ng cq ua 1ion :

\H ,.. ~c--+ ~n

b@t a rad iatio n The collective comb ination of the negatrons or positrons emitted from certa in radio isotopes

The counterpart of an electron, having an electric charge of +1

Argon-37 is an exa mple of a radioisotope th a t under goes electron ca pture . The ph eno menon is rep re se nted as follows:

;;Ar + -1e FCI In 1h · · h b I f he electron is written to the lcfl of th e arrow to d esignate 1s msra nce, c e sy m o o t

1 that the el ect ron h as combined with th e argon-3 7 nuc eu s. Chapter 16 Rad ioactive Materials 6 91

Ii

SOLVED EXERCISE 16.2

electromagnetic ra diation The ent ire ra nge of e ne rgy t ha t trave ls as waves through space

gamma The co llect ive com bination o f ga mm a rays emitt ed from a nucl eus

ga mma ray (photo n) • A massl ess pack et of e lectromagnet ic energy e mitted by certa in rad io isotopes

u:~i ~~;ae~~ct1~1:s0t ;u;:ial d1ag nost1c dr ug an d fo r gas tru: an o ca rd,ac irnag!og f•l How many protons and neutrons a re pres ent 1n the in d,um-111 nu cl e us ? (b) •dent·fy tne product of ,ts rad, oactive trans format ion (<} What percen tage of ,n d,um -11 1 1ema ns 1n the bloodstream 8 4 days after adm ,n, str,mon of the drug ,

Solution: Referring to either Figur e 4 3 or Appe ndix Ba t the bac k of this text , we see that the ch em, :~~:•c_number of in d-um are determined to be In an d 49, re spectively Thu s, the sy mbol for the ,;;,iu~~ f•l ~:,:~;1~~u~:,; ::5~u;,~I~ ;;~t~~.s ;~:;~:aan~t the ,nd,um-l J l

nucleus Is 111 The number of neu trons ,n 1·••n is 111 - 49 or 62 neutrons 1n ths lb) 'ndium-11 t captures an orb,tal e1ectron, a pr0<ess represen~ed as fo ll ows

The product of this tramform at1on 1s cad m1um- 111 (c) r:;i°r~~:1~:1~::r;:;~:~~a:

1,:e1~a~f~:~ves Aft er that time , the percenta ge olthf Final perce nta ge = 100 % x Vi x Yl x ½ = 12 5%

16.2 -C GAMMA DECAY Alpha an d beta decay f~ equ e~d ~ a re accompanied by che simultaneous emission of the fo rm ':'f electr_o"_"agnet1c rad1at~o~ called gamma radiation. Like X-ray, infrared, and ulrrav1o ler rad1 ~t1on, ga mma rad ia ti o n has neither ma ss nor charge.

ln che P? rti o n o f th e elec tro mag neti c spectrum shown in Figure 16.2, the various fo ri:n s of ra dia nt en_ergy a re cha racteriz ed by their wa velength s. Ultra violet, infrared, and rad~ o _waves are sa id to ha ve " lo ng" wa vele ngths, whereas gamma radiation and X-ray rad1 ano n have " sho rt " wave length s. Vi sible li ght is th e bala nce point between long and sho rr wave len~h s, and rh e ~nl y fo rm rh a t is detected by our eyes. The components of the ~le~tromag net1 c spectrum with short wa velengths are ve ry energetic, so much so that they 1omz_e the matter thr~ugh which rh 7y pass, bu t th e co mponents with Jong wa velengths,m rela n vely nonenerge nc a nd do nor io ni ze ma n er.

~ch indi vi dual compo nent o f g:rnmrn rad ia ti o n is ca lled a gamma ray , or photon, ~nd 1s re prese nr ed by rh e sym bol -y . Beca use it does not possess a c harge, a gamma r3y ;f ~:~~~m el y penetrating a nd abso rbed o nl y by dense fo rms o f ma rter such as thick blocks

Rad ar

X rays c, 3: Gamm a L __J 2i l (Nea r) (Fa r)/ §

5 • ray , J Uiii'a~,ofc l Jt Infrar ed :.E

j FM ra di o AM ra dio

3 ,,:, 10 18 3 :,, 10 13 3 :,, ,o 10 3000 300 3 0

1~:ef:~~~ontnhts of the e'emomag net1 c spectrum as a funct ,on of radiation frequency Gamma

fr ea~e nc1es Beca use gam O t e s~e mu m, are fo rms of energy as soc iated with short wavelength s and high ionizing rad rauon ma rays ave sufficient ene rg ies 10 1ono ze matte r, gam ma radiation 1s a fo rm 01

692 Chapter 16 Rad ioactive Materials

The process in.v~ lvi ng rh e emission of gamma rays from a nucleus 1s ca ll ed gamma decaY. When a radio isotope un~ergoes ga _m'!la decay, no change in ei1her its atomi c num - ~er or ma ss ~um_ber occ urs. With the em1 ss1on of each gamma ra y, some frac tion of the energ)' of exc1t:H10~ ~hat ca uses rh e ~ucleus to be unstable is removed.

Im agi ne a ra d 101sotope chat exms in o nl y two energy stares. The mo re en ergetic fo rm- ih e excited st~te-ma y emit one or more ga mma ra ys from the nucleu s. The pheno meno n ma y b~ illu srra ted by the foll owing equation, wh ere the exci ted state is rep- rescnc ed by a n as teri sk:

(Q X)• ---,. ) X - -y In thi s process, the radioi sotope gi ves up a fraction of its excitati o n energy to become a mo re sta ble form of the same radio isotope.

Excited stat es that deca y by emitting gamma ra ys generally ha ve especially shon half-lives i<< I0-8 s), but some excited states have half-liv es in th e range o f -10-8 second to several }ears. In the latter case, the long- li ved excited state is referred to as a metastable state, or isomeric state, of the radioi so tope. The metastable state is designated by adding an m foJlow - ing the iso tope's mass number. For example, tcchnetium-99m is an excited state of techne- uu m-99 that has a half-life of 6.0067 hours. h deca ys by gamma-ra y emission as follows:

994"JT C ---,. ~';'re + -y The deca y of a metastable stal e of a radioisoto pe like technetium-99m is called an

isomeric transition, o r IT. Table 16.2 notes that , the gamma ra ys emitted from techne - tium -99m ca n be specifically used br radiologists to image the organs of the body.

The phenomenon of gamma-ray emi ssion is not alwa ys represented by means o f a n equation . It also is represe nted by 1he follo wing genera l diagra m, where eac h hor izontal ]me designates a discrete energy state of the atomic nucleus :

16.3 SEALED RADIATI ON SOURCES Se \'Cr:il radioisotopes listed in Table 16.2 a re encou ntered as sealed sources. Typica ll y, a man ufa cturer sea ls high level s of th ese radio isotopes wi thin do uble-skmned Steel rubes, whic h then are ho used wi thin a medi cal or other devi ce . The radioisoto pes rema in sea led wi th in rh ese rubes througho ut the period of th ei r use.

Co ba. lt-60 is an example of a ra dioi so tope th at is used as a sea led source. As it decays, negntro ns and gamma ra ys a. re emined to the environment. Fi rst, each nucle us emits a ncga - tron and transform s into an excited state of nickcl-60, which then emits two ga mma ra ys ha ving energies o f l. t 73 MeV and I.3 32 MeV. We represe nt this phe nomeno n as foll ows:

527 -y WCo

µ

\~---lr1 = 1.173 MeV I ln 1 332 MeV

gam ma d eca y • A spontaneous mode o f rad lo isotop lc decay assoc iated w ith the emiss ion of gamma rays from a nu cl eus, often accompany ing alpha and beta decay

me ta sta b le st at e (i some ric sta te)• An exc ited state of a radioisotope that has a half-life ln the range of <10 - 8 second to several years

iso me ric tra n siti on The decay of a

rad ioisotope by the emiss ion of a photon from an excited state t o a less energetic state

seal ed so urce • An encapsulate d ra d io isoto pe u sed in irrad iati on e q u ipment an d elsewh e re

Chapter 16 Ra d lo a ct ive M ater ia ls 693

zrrad i.l t i on • The mtent1ona l exposure

When co b.ilc -60. ,s used for a sp~c!fic purpose, 1he sca le~ so urce is posit ioned s

of matter to 1on1zmg rad iat ion, usually X rc1y~ or gamm a r ays, for med ical treatment. ste nl,za t1 on or preser - vation of foods. and other purposes

r~ e garnm.1 ray s emmed br che rad101soco~e pass th ro ugh us steel co ntai ner a nd O tha1 non,tlly penerratt.' :l m.1terial. This process 1s referre d to ~s i~radiation. Ga mm a r lntcn. used to irrndiate polyethrlene or rubber IO mduce cross- lmk mg with in their ars are cu les. They :ire :il~o used w irradiau: spices :1.11d o th er harvested f~o ds a nd~:c:;~le. medical devices. Smee 2008, w hen ant hrax- ta inted l_cu er~ we re ma il ed 10 U.S. 5 enhie (Secuon 10.2 1-E), the government has rero ute d a nd 1rrad 1a1ed ma il to th e Wh· ena tors Congression.11 offices, and oc her federal government offices in ce rt ain zi p it~ Houst, befo re its deliver y. co e areas

\'fhen gamma rays or ot her for ms of io mzl ng radia tio n are used to irrad· the y disrupt the fast-growing ce ll s of insects, mo lds, an d mic ro bes o n peris h

1 ~ ~ food~

poultry, ~nd produ ce. Irra d iati o n also d~stro~·s th e mic ro ~rga ni sms t hat cause lll e~t, age. burn does not rende r th e food rad1 oacuve o r ca use n to lose its nu t riti ve I SpotJ. . p!i mary advantage assoc iated_ wi th irradia tmg foods is irs success :n kill ing :~t·

ri a wuh m raw mea t an d prod uce. It 1s th e only kn own met ho d o f eliminating th e b~ctt- dea dl y bacte ri a Escherichia co l, , Salm o nella, an d Campylobact er fro m ra w fru iJ'°t~ntla.l]y rab!cs. _Typi~a ll y, fruits and vege tabl es t~lcra te an irra diat io n o f 1.0 kGy (Sccriona~6 \·~ c-whic h macava rcs 99.999% of the baccen a. .S B),

Al th oug h ga mm a-ray irradi atio n elimi nac es pes ts in fresh foods and ex tends h • Li fe, irradia ti o n also creates free ra dica ls, th e presence of w hic h could ncgari vcl t ~u- shdf inhe rem quality o f foods by produci ng small a mo unts o f und esi rabl e substa nce: ~ f the the re !s no tec hnical basis for concludin.g th a_r c~ ese irra dia ted _foods a re un safe t~ co~:~ the wi desp rea d use o f ga mma rays fo ~ 1rrad1 atm g foo ds rema ms a co ntroversial b' '

. FDA's appro va l is rcq~ired to sell irradiat ed foo~s i~ America n stores. As a c~::~m of us arpr<:'va l, FDA reqmrcs m.:muf~c tur~rs an d d1 smburors to affix th e Radura symbol show n m Fig ure 16.3 on packages of 1rrad1 a tcd foods . FDA also requ ires food di scr·b to ma rk packa ges of irra dia ted foo ds wi th ei th er of th e foll o wing statements:

1 utors

TREATED WITH RADI ATION TREATED BY IRRADIATION

. Sca led ra d iatio n sour ces a re highly dange ro us if th ey beco me un sea led. Ac kn owledg- ing th e need to wa rn people of th e prese nce of ra di oisoto pes in sea led sources the Uni ted ~atio ns' lnrcrn ati~ na l. Atomic Ener~y Age ncy, o r IAEA, and th e Intern a ti o n; I Organiia- n_o n fo r Srand a rd1zat1o n, or ISO, int ro du ced the io nizing rad ia ti o n sy mb ol shown in F,g u~e 16.4. The symbol shows waves ra di ati ng fro m a thr ee- bla d ed propell er ca lled a trefo il, a skull-a nd-crossbones sym bol, a nd a ru nni ng pe rso n .

. l ~EA an~ ISO reco mmend a ffi xi ng this sy mbo l to d ev ices th a r ho use a hig h-ltvd radw1soto pe ma sealed so urce, ex posure to w h ic h co ul d ca use d ea th or se rio us injury. The sea led so urce us uall y is a sea led caps ul e rh a1 co nt ai ns th e ra di o isoto pe. ft is funhcr sealed be t ween laye rs of non rad ioactive ma teria l o r firm! )' fi xed ro a no nr adioactive sur- face by electropla ting o r o cher mea ns to preve nt lea kage o r esca pe of th e radioisotope.

FI GU RE 16. 3 At 2 1 C FR §179 26(c.). FDA req uires th is international Radura symbo l to be poste d on 1rrad1ated pack.aged foods, bulk con- t.Mers of unpackaged foods, on placards at the point of pu rcha se for fresh produce , and on ,nvo rces for 1rrad 1ated 1ngred ren 1s and prod ucts so ld to food processors The logo 1s da1k green and displayed o n a w hrt e back.ground (Cou nesy of FDA-food and Dn.ig Admm,srra1,on l

694 Chapter 16 Rad ioactive Ma terials

FIGU RE 16 .4 The lAEA/ISO 1o n,z,n g rad,at1on symbol u~ed to warn 1nd,v1 dua ls that a dangerous le~ el of ,on - 1w19 rao ,a1,on 1n a sealedra01oact,vesource 1s nearby The tnangular sym bol ,s red w ith a black border and has black.andwh1tewavesr ad•at,ngfromat1 efo 1l, ask ull- and<rossbones symbol, and a runn ,ng person

l'\o rnia ll y th e radio iso 1o pe is vis ibl e o nl y when attempts ar c ma d e to di sa sse mble th e ~q uipment in wh ic h ir is maintai ned. The intent of th e io ni zi ng ra d ia ti o n symbo l is to wa rn people 10 di sta nce themselves from the radi ation so urce. Because it is no t a ffixe d to bui ld ing• access d oors, co nt a iners, o r tran spo rt ve hicles, th is sy mbol suppl e me nts rhe warni ng trefoil requir ed by NRC, O SH A and DOT o n signs, labels, a nd placa rd s.

16.4 DETECTION OF RADIOACTIVITY Seve ral ra di a tion detec tio n instruments arc commercia ll y ava il able. The ty pe sho w n in figure 16. 5 o ft en is used by emergency res po nders for detec ting th e prese nce o f a ra d ia· cion source . T he o perator may specificall y dc1erminc w heth er a r.i di ;1 cio n so urce is nea rb y, how close it is, its ident ity, and it s intensity.

The to tal ra diat io n to whi ch an indi vidual has been exp osed, includin g the o ccupa- tiona l rad ia tio n d ose, is determ ined thro ugh th e use o f perso na l-mo nitor ing equ ipment like t he o pti ca ll y stimula ted luminesce nt do si meters sho w n in Figur e 16. 6(a ) and th e pocket o r pe n d osimeters illustrated in Fi gure 16.6 (b ).

FIGURE 16. 5 A portable handheld rad iat ion detector 1s commonly used by first-on -the-sce ne responders to measure the 1ntens1ty of alpha , beta , gamma. and X-ray rad iat ion Th,s model is know n as the inspector Its d1g1tal d is play provides 1ead1ngs ,n m1ll1roentgens pe r hour (mR/h), counts per m,nute (c/m1nl, or m,cros1eve rts pe r hour (µSv/h) (Cour-resyof S f ln tema r<OOJI, Inc . Sommeno-.-m, Tennessee )

Chapter 16 Radioactive Materials 695

r

I I

FI GU RE 16 .6 (a ) Ootr• c,f'y!itlmu lat ed lum,nes• centdosme:e rs and (b) pocl.e t or pen dos1me1e-s The use of these dos m- eters prc\ ces a measure- ment of the total amount of raoiauon to wh 1Ch an 1nc v o'u.:1J hasbeen ~ !COJt?PSy of

Ldl'lddl.lt'C/r>c,G~~ IUtnois.MT.JS. E ltltf'ma11MtJI, O:..~n. _ ,

lb!

,,,

696 Chapter 16 Radioactive Materials

16,5 UNITS OF RADIATION AND RADIATION DOSE fhe 1ntensi ry ~f rafois~ IO~c is called its activity, and the ac1iviry per unit mass is called its specific ~ct•v•ty : 5 sc ie n_ns~s developed radi atio n detection instruments, they simulta- n(OII SI}' defmed l~~ns of.r~dia uon meas~ remcnt to serve as a means of accounting for the JCllvit y of a specific rad101 sotopc. We cite them in the following sect ions.

16.s -A UNITS O F ACTIVITY Each type of ra~iation ?:rector provides the intensity of a radioisotop e by counting the nu mber of n~clei t~ a t dlSl~teg_~te duri~g a time period. The intensity of the radioisotope niaY be prov1~ed directl_y m d1smtegrat1ons per second, or it ma y be converted into mul - tiples or fracnon s of units called the curie and becquerel.

The curie (Ci) is a meas ure of the number of radioactive dis integrations occur- r11lg each seco nd in a sample. One curie is the amount of radiation equal to 3.7 X 10 10

disintegrations per seco nd. Because the curie is an extremely large unit, th e intensity of a sam ple of a radioactiv e mat erial usually is measured in millicuries (mCi), microcuries (µCi ), and picocuries (pCi ).

lmCi = 3.7 x 107 disimegrations/s 1µ.Ci = 3.7 x 104 disimegrarions/s lpCi = 3.7 X 10 - 2 disintegration s/s

T he becquerel (Bq) is the SI unit used to measure radioactive disintegrations per secon d. One Bq is equivalent to one nuclear disintegration per second, which can be writ- ten as follows:

!Ci= 3.7 X JO"Bq

Intensity of a radiation source

i peclfic act iv ity • The activity of a rad ioi so - tope per unit mass

curi e (Ci) • The amount of a rad io isotope that decays at the rate of 3 .7 x 1010 disintegra - tions per second

be cqu erel ( Bq) • The SI unit of radioactivity equivalent to 1 disinte- gration per second

The becquerel is a small amount of :ictivity; hence, it generally is used with a prefix lik e tera-. EPA, DOE, and NRC regulations usually list the activities of radioisotopes in tera- becquerels (TBq) and curies. One TBq equals a trillion becquerels or a trillion disintegra· tions per seco nd.

ITBq = 10 12 Bq

SOLVED EXERCISE 16.3

Te< hneti um -99m 1s used dunng diagnostic Imaging of th!! body's internal or gans When a rad,olog1cal technlaan ,n,em a patient intr avenously with 24 .5 mCI of t echnetium-99m , how many be<querels of the rad101sotope were rece ,vedbythe patient ?

Solution: One curie equals 3 7 x 1010 becqu etels, hence, by calcula1.1on, 24 5 mC 1 equals 9 x 10 8

Bq.

& 37 X 1010 Bq 24 5 rnCJ. X~X-- &--

= 9 X 101 Bq

16 .S-B UNITS O F RA DIATION DOSE When human ti ss ue is exposed to ionizing radiation, wear~ concerned with the quan~it)' ~f radiation absorbed per unit of mass. The a~ou?t of radi :.mon absorbed per bod)' we~ght is called the DOSE. It is measured by using umts !tkc the roentgen, rad, rem, grny, and s1 evert.

Chapter 16 Radioactive Materials 697

r

I

~ I --=-..

~ ntgen (R) • The a mount of rad ,.:1t ion that produces 21x 109 unrts of charge in 1 m 1ltih te r of dry air at standa rd atmospheric preuure

radi<1tion a bsorb~ dose The amount of rad iation absorb ed per gram o f body tissue

roe ntg en e-quiva lent man (rem) • The amount of ionizin g rad iation that prod uce s t he same biol og ical effect as 1 roe ntgen of X rays or gamm a rays

g ray (Gy) • Th e unit of an a bsorbed dose of rad iation equ ivalent to 1 joul e p er k il og ram of livi ng t issue

unit of dose-equ ivalen t. equal to 100 rem

ba ckground radiation • Cosmic ra diat ion and inesca pa ble low-level ionizing rad iat ion tha t is e mitted from natu- ra lly occurr in g a nd a rt i- fi cia lly produced rad io isotop e s; 300 mremly, or 3 mSvly

ra d iation Th e he a lth a il ment fo llow- ing short- or long -term exposure to rad iat ion

The roentge~ 1s symb~ hzed wj t h a cap u al lette r .. ..... O nce used as the •ntern;i,. uon al lllllt of r.1di:m on qu:mtLty ~o r_ X-ray and ga mma radt,mon, _1

4 R was defi ned as th

a mount of X-r;t y or ga mm a rad1at1on tha t produces 2.58 X 10 cou lombs of ch e 111 t kilog ram of dry air at 0°C and sta nd a rd atmosp_heric p r~ss ure . Althoug h its u~~e encountered in the o ld er literat ur e, 1he roe ntgen no w 1s essen n a ll y obsolete.

The term radiation absorbed dose , or rad , is th e amo~ nt of radia tio n a bso rbtd per gram o f bod y tis sue. T he roen tgen and ch e rad a re so close Ill mag nitu de that th e considered id entical. For prac tical pu rposes , I R = I rad. y arc

Rem 1s rhe acronym for ro~ntgen equ_ivale~t man . I~ is a _mt'as ure of the dose of an . ionizing radiation to body tissue m terms of its es runated b10\og1cal effect rela ti ve to 3 d

1 of I R of X rays or gamma .rays. T he rel a ti o n o_f the rem to ot her d~sc _unit s depend s on: bio logical effect und er cons1de rauon. One rem 1s the amo unt of rad1at1on that produce h same damage as I R of X rays o r ga mma _rays. T he mill irem (mrem ), o r one-t housa ~~t~ o f a rem, is a com monly encounte red frac tion of th e rem. T he ave rage American recciv :i round 620 mrem/y of radiatio n fr om natura l a nd :i rrifi cial radi:i ti on sources. cs

The gray (Gy) is t he amo unt of ra di atio ~ equi valent to th e tra nsfer o f I Joule of energy to 1 kilogram of liv ing riss ue. O ne gray 1s equ al to 100 rad.

The sievert (Sv) is th e pr~fe rred un i~ fo r me~s u.ring ex pos ur~ IO ion izing radiat ion, One sieve rr equals 100 rem. It 1s th e SI unn of rad1 au o n-dose•eq u1v a lent .

16.6 ILL EFFECTS CAUSED BY RADIATION EXPOSURE

All perso ns are co nsta ntl y exposed to cos mic rad ia ti o n a nd other inescapabl e low-l e\·cl ionizi ng radia tio n em ined from th e natura ll y occ urr ing rad io isotopes li sted in Table 16.1. Everyone is a lso exposed to art ificia ll y produ ced rad io iso topes in certain consum er prod• ucrs a nd when rad ioactive p ha rma ce utica ls are used to de tect the prese nce of tumors or to the rapeuticall y destro y th e cells wi1hin di seased ti ss ue.

The comb ination of io nizi ng ra dia tio n from natura l and artifi ci al sources in and around Ea rth is ca ll ed background radiation , th e so urces of wh ic h are noted in Figure 16.7. T he mos t sig nifica nt sources a re X rays, the nat ur all y occ urr ing radi oisotopes, and the radioisotopes use d to image 1he orga ns a nd ti ss ues of the bod y.

The acute ad verse hea lth effects result ing from ex posur e of the hum an organism to diffe rent doses o f ra dia ti o n are provided in Tabl e 16.3 . T hey :n e ma nifes1ed as th e illness called radiation sickness.

T he consequ ences to sp ecific bo dy o rga ns, es pecia ll y th e repro duct ivt' and acti\'e blood-fo rmi ng orga ns, a re li kel y to be ex peri enced as chronic effects. Radiati on scientists assert th at a ll ry pes of ion izi ng ra d iati o n are human carcinogens. The on se t o f cancer is li kely w hen an indivi du al is ex posed to io nizing ra diation, beca use th e radi a ti on damages cellu la r DNA. In 2006, the Natio nal Aca demy of Sciences es t ima ted th at one ou t of 100 indivi dua ls is likely to deve lop ca nce r from an acute dose o f 100 milli sieve rt s of radiation.

3

This o ne add itiona l cancer is in a dd itio n to the 4 2 th at no rm a ll y wo uld be expected in the same U.S. po pula tio n fr om all ot her ca uses of ca nce r. T he ca ncero us cells develop as rh c radiation-damaged cells inco rr ec tl y repair th emselves. Ca ncers of th e s kin , blood (leuk e· mia ), lun g, stomac h, esophag us, bo ne, th yroid, a nd bra in a re co mmon di seases ca used b)' expos ure to ion izing radia tio n. T he re is no thres ho ld o f ex pos ure below which a dose of ionizing radiat ion is ent irely ha rml ess- a hh o ugh rh e lik el ihood o f acquiring cancer fro m radiarion exposu re d iminis hes as t he dosage decl ines or w hen the to ta l dosage is broken into smalle r incremem s.

3 NJ rional Resc-a rch Co uncil of the Nat1onJ] Academi cs, Hta ft/1 R,sks fr om £yposurt to Low Ln•t/$ of Jom:.VI!

Radtation, BEIR B11 l'hase 2 (Washington. DC, NJt1onaJ Academi ts Prtis, 2006 ). 698 Chapter 16 Rad ioact iv e Materials

cornputed 1ornograph'r'

(m edical) 24%

Nuc lear med icine (m ed ica l)

12% 7% Consu mer

2%

flGU RE 16. 7 Sources of radiatio n to wh ich the U S. population 1s e)O.posed Computed tomography, mterven• ~onal fluorosco py, and conventio nal radiography are med ical procedures that use X rays to image parts of the body Theron 1s a synonym for radon -22 0, formed du nn g the stepwi~e decay of the nat urally occurring thorium ,adoiwtope , thor ium-232 . (Repnnttd with ~of~N.irion.,/Counclion RadldtlOl'l ProtectionaOO Me<1surem('(lts, Sfmestid, MJry/dnd, /on. t ing Rddiat,or, E.,;t)OSl,!reofthf' Popu/dtl0f1 ol rhe United Stitl.'5. NCRPReport No 160)

The radi ati on dose-equival ent rate is called the radiation level, whi ch is meas ured in millisieve rts per hour (mS v/hr ). ln mos t countrie s, the curr ent ma ximum permi ~si ble rad! - ation lev el to expo sed work ers is 20 mS v/y when it is averaged ove r 5 ye ars, w1th a maXI - mu m rad iatio n level of 50 millisiev crts in any one year.

The o fficial positio n of all federal agencies is chat ,m y exposu re to radiatio n ~rod.uc~s so me ris k of canc er; however, for exposur es at doses below legal limit s, th e ri sk 1s w1thm the range o f ot her ri sks co mm on1 y acce pted.

8/H!iiii Acute Rad1 a t1o n Effects Caused by a Single -Dose EKp os ure of Rad1 a t1 o n t o the Whole Bod y4 DOSE (Gy) _ SIGNS AND SYMPTOMS 0-0 75 No detectab le signs or symptoms in most exposed ind ividua ls although vomiting

(re tch ing) may occur in a few O 75--1 .5 Nausea , vom it ing (retching), anorex ia, fever, and infect ion 1 5--3 o Nausea , vom it ing (retching), anore xia, fatigue, weakness, bleed ing , fever, and

in fect ion; death rate <51/4 3 0- 5.3 Nau sea, vom iting (retch ing), anore xi a, fat igue, weakness, bleed in g, fever, infect ion,

and ul cerat ion; death rate <5--50 % 8.3-l l

O . . (retching) , anorex ia, fat igue, weak ness, bl.eed ing , fe ve r, Infect ion,

~:~~;:~;i~~. 1 ~~i iness, disor ientation , fluid los s/electr olyte imbala nc e, headache,

and faint ing; death rate 100 %

' A~ from NATO Handbook on tfl c M~ical Aspi"~r,0;::~t.o:!~"::;~:~~f~:~::~::~t(b), Cha pttr 6· G,neral Me d ltal Effects of Nuclea r Weapons. Diagnos 5·

radia tion level • The dose -equ iva lent to a person, expressed in mill isieverts per hou r (mSv/h r)

Chapter 16 Radioactive Materials 699

(, 0 o

Paper Aluminum Lead

FI GU RE 16.8 The relative penetrat ing power of alpha, beta, and gamma rad 1at1on Al pha rad iation 1~ a by a sheet of paper, beta rad 1auon by aluminum foi l, and gamma ra d,at 1on by a th ick block of lead

T he biological impact of radiation exposure depends on the type of radiation absor~d its energy. th e nature of specific radioisoto pes, and the age of the exposed indi vidual. w;' note the impact of the se facto rs se parately in the sections that immediately follow. e

16 .6 -A GENERAL EXPOSURE TO ION IZING RADIATION As demonstra ted in Fi gure 16 .8, a lph a, beta , and gamma radia1ion penetrate mattcrdif- fe renti )'. Th us , whe n eva lu:uing the potent ia l heahh effects re sulting from exposure to io niz ing radiation , it is important to know the specific 1ype of 1he radiation to which an individua l has been ex posed. These ill effects a re noted below:

Although alpha radiation is ve ry energetic, it is easily absorbed externally byrhc ep iderm is, the ou term os t la yer of th e skin . Beca use the epidermi s serves as a protect ive co vering of the unde rl yi ng li vi ng skin ce lls, ex ternal exposure to alpha radiation does not cause an ad ve rse health effec t. If it is inges ted, ho we ve r, the energetic alpha radia • tion may localize in a t iss ue or bone, where the subsequent biological damage ma)' be se\'ere.

Bera radi atio n pene trates deeper into ti ssue th an alpha radiation and ionizes the sub- stances it encou nters. A 2-MeV negatron, fo r insta nce, tra vels through 0.4 inch (10 mm) of tiss ue befo re being absorbe d. Beta radiation pa rticles equa l to or grea ter than 2 million electr on vohs ma y cause biologica l damage in exposed individual s.

Gamma rad ia tion also pa sses readil y through tiss ue and ionizes the substances ir encounte rs. Intern a l and ex ternal expos ure 10 gamma radiation usually causes more st• vere biological damage than ex pos ure to either olpha or bera radiation.

16 .6 -B EXPOSURE TO SPECIFIC RADIOISOTOPES As ide fr o m the general effects caused by radiati o n exposure, several radioisotopes_ca_n damage the human organi sm at specific locations w here they concentrate and mi_mi c the role of esse ntial nutrients. For example, the ra dioi so tope s of strontium and radiu ~ ma y replace ca lc ium in bo ne structures. This is potentially problematic because. t~ e) may become depo s ited in spaces ordinari l)' occ upied by marrow, a tissu e cont~inmg th e blood-forming cell s. The irradiation o f these cells can then cause an increase HI

th c

ho st victim's chances o f developing leukemia, myelofib rosis, or other diseases, 0

Loca lized dama ge ma y a lso occ ur w ithin the human o rganism from exposure 1d

iodine raclio iso tope s. This exposure specifically damages ihe thyroid , a butterfly-shape

700 Chapter 16 Rad ioactive Materials

d located near th e base of the neck Th h 'd ~I Jn onsiblc for re •ulatin h ' e t yro1 manufactures and s~c retes the hor· ~10nes res p . g .. g t e rate s of body growth and metabolism. Two such hormones arc th yroxme and tmodothyronine, whose molecular formulas a rc noted here:

I I I I

flO-b-o{)-CH,-T11 -<0 Ho-Q-o-Q- rn,-yH-<o 1 I NH2 OH y NH1 OH

Oi)rt• ~m~ Truodolh)ron1ne

The hum:111 bod~ a~qui res .i~dine ma in l)· from the diet (e.g., in seafood ). Iodized salt is used 10 prevent 1o~ me def1C1enc y, A suppl y of thyroxin e and triiodo1hyronin e rema ins scored in the 1hyro1d for use as the body demand s.

When th e body is exposed to iodine radioisotopes, th e 1hyroid gland ca ptures and stores the amount that is not secreted. The concentration of iodine radioisotopes in the chyroid and their _ low remova l rat~s incre;1.se an indi vidual's chance of developing th yroid ca nc er or other disorders. Approximately 40,000 people develop thyroid cancer eac h yea r.

16.6-C IMPACT OF AN INDIVIDUA L' S AGE O N RADIATION EXPOSURE

when human cells divide, their nuclear membran es di ssolve. Thi s then allows DNA to spread across the entire volume of the ce ll s and increases their likelihood of exposure to ihe free radicals produced by radiation. Under normal conditions, 1he nuclear membrane procec1s 1he DNA from exposure 10 free radicals; but, wh en cells frequ ently divide, 1heir DNA is likely to be damag ed. Because the ce ll s in unborn children, infants, and young- 51ers are dividing frequently 10 support growth, these individuals are more suscep1ible to 1he effects of radia ti on exposure compa red to adults.

16.7 WORKPLACE REGULATIONS INVOLVING RADIATION EXPOSURE

For activities not addressed by NRC or DOE, OSHA regulates emplo yee exposure to radiation in the workplace at 29 C.F.R. S 1910.96 by requiring 1he following:

No employer shall possess, use, or transfer sources of ionizing radiation in such J manner as to cause any individual to receive during one calenda r quarter (qtr ) a do se m ex ce ss of th e limits quo1cd in Table 16.4 from so urce s.in .th e em~loyer's possession or comrol. These radiati on doses are permissible exposure lmms (Secnon 10.6·D ).

iih!ii!i Penmssible Exposure L1m1ts in the Workplacea PERMISSIBLE (RADIATION) ~ POSURE LIMIT (mSv/ qtr)_ 125

1875

l5

'Ad ap~ from OSHA 19 CF.R. § 1910.96{b).

AREA OF THE BODY Whole body; head and trunk ; act ive blood -form ing organs; lens of the eyes; or gonad~

Hands and forearms ; feetan d ankles

I Sk in of th e whole body

Chapter 16 Radioact iv e Materlals 701

r.1d io.act ivem.1te ria ls area For purposes of NR C and OSH A reg ula- ti oris. any area with in a controlled area, acces- sibl e to in d ividua ls. in wh ich items or contain- er1 of radioamve mat e- ri al exist and the ir tot al activity exceeds th e threshold values pub- li~hed at 10 C.F.R §20, Appendi• E

An emp1o}Cr m J }' pcrnut an em ployee to recein~ a do se g reater th a n rhose prov in Tabk 16.4 as long a s: 1ded

a. The dose ro the whole body during an)' ca le nd ar quarter doe s no t exceed 3 and rem, b. The d ose to the w ho le bod )', wh e n _added to th e acc umulated occ upat io na l d

1he whole bod y, does not exceed ) x (N - 18) rem, w her e N is the indi vi~St' t? cu rrent age in rears. uals

T he exp ression .. dose to che whole bod(' incl udes a n y dose to th e e ntire body cific organ (gonads, active blood-forming o rgan s, head and trunk , or lens of th or a spe-

No e mpl oyer ma }' pe rm it an y emp loyee w ho is un de r 18 years of a ge toe eyeJ. anr one c:i.lendar quarter a dose in excess of 10 % of th e limits in Table 16.4. receive in

A r 10 C.ER. S835, che :'·Re establ is hes occ u pat ional ra d ia tio n protection stand fo r DOE employees, and OSHA s ubsequently adopte d th ~m. These standards ca n a;ds protec t on-dury emerge ncy responde rs. One common reqmrem ent is che posting f so in areas wh e re individuals work o r gat he r or w here a rad iatio n ha zard could po

O s_igns

exis t. At 10 C. F.R . §835. 603, N R C requires th e co ns picuous posting of the /enri;Uy rhose illus~ra red in Figure 16.9 in give n area s, each access ible to individuals. The ~!:/e each area 1s _defined a t 29 C.F. R. §19 10.1096 and 10 C.E R. §20.1003. These definirio of are s ummarized be low: ns

ra d io~ctive .m a~erials area is .any area w!thin a co ntrolled area, accessible to indi- ~·1dual s, m w~1 c h 1~ ems o r c~ nt a1 ners o f r.1d1oacti ve material exis t a nd th e total activ- lt}' of th e ra~1oacri ve ma1er1al exceeds th e a pplica bl e va lu es publis hed at lO C FR S20, Appendix ~· A. -_contro ll ed a rea .. is a n ar ea t? \~ hich access is managed by 0 ~ {0 ; DOE ro prorect md1v1duals from exposure to radi a ti o n an d/o r ra dioactive materi al.

(a)

••• • CAUTION RADIOACTIVE

MATERIAL

••• • AIRBORNE (b )

RADIOACTIVITY AREA

(d )

CAUTION IQ•\iid•VI ••• • RADIATION AREA

(eJ

(c)

IQ·i•iit•l~ I ••• • GRAVE DANG ER

VERY HIGH RADIATION

AREA

••• • HIGH RA DIATION

AREA

~~GURE ~6.9 At IOC FR. §20 192, 29( FR §§1910 1096(eX2), 1910 1096(e)(3Xi ), 1910 1096{e)(4)(,i ), co~s~·~::~ex; :2~ 1:;ohT096(e)(6J, and 10 C FR . §835 603, OSHA and NRC respectively require the dose of iontzi~ raJau ese caution S•gns in areas where workers and other 1n d1v1duals coufd receive a imposed on a ierlow b:ck~~C:U~dwho le body The conventional co lor of the trefo,l 1s magenta or purple

702 Chapter 16 Rad ioacti ve Materials

1 r\ radiation ~ re~ i_s an y a rea_, ~ccess ibl c to individuals, 111 w hic h ra d 1a 1ion lev els cou ld result in ." 1.1 tn d i~•idual rece,vmg a n equi valent dose to th e w ho le body in excess of o.05 ru illi s~~ve ~t 111 1 ho ur at I l .8 inch es (30 cm ) from th e so urce o r fro m any surfac e i h:ll th e ra 1a tt on pene~rates.

• A high- radl~tion ~re~ ~s any area, access ibl e to indi vid ua ls, in which radiation leve ls co uld res.ul.t .111 a n 1.nd l\'ldual receivi ng a n equ iva le nt dose to the who le bod}' in excess 0 f 0. I m1ll 1s1ever t 111 an y 1 hour at t 1.8 inches (30 cm ) from th e radiati o n so urce or frolll a n y surfa ce th a t the radiation penetrates.

• An alrb~rne radi?activity area is any roo m, enclosure , or area in which a irborne rad ioactiv e mat e rial , compose d wholly or in part of li censed mate ria l ex is t in either of the following concentrations: ' (a) in excess of the deri ve d air concentrations (DACs) specified al 10 C.F.R. §20.100 I,

Appendix B; or (b) 10 such a degree that an individua l prese nt in the area w ith o ut respirat ory pro -

tec tion could exceed, during the hours an individual is prese nt in a week , a n intake of 0.6 % of th e annual limit or 12 DAC-hours.

" Li cense d mat e rial " m ea ns certain radioactive ma1 eria ls received, possesse d , u sed, tran sferre d, or di s posed of und er th e conditions of a license iss ued by the N RC.

1 A very high ra d iation are a is a n a rea, accessib le to individuals, in w hich r a diati o n levels co uld re sult in an individual rece iving an absorbed do se in excess of 5 gra y in any I hour at 3 9.37 inches ( I m ) fro m a radiati o n so urce or from an y surfac e that th e radi.11ion penetrates.

[:ic h sign in Fi g ure 16.9 bears a warning tr efoil and o ne of 1he following expressi ons:

CAUTION, RADIOACTIVE MATERIALS CAUTION, RADIATION AREA CAUTION, HIGH RADIATION AREA CAUTION, AIRBORNE RADIOACTIVITY AREA, o, DANGER, AIRBORNE RADIOACTIVITY AREA GRAVE DANGER, VERY HIGH RADIATION AREA

DO E and OSHA also requir e the conspicuous posting of la bels affixed to the contain• muse d to sto re certain quantiti es of radi oac ti ve materials. The la bels bea r the standard 11J rn ing trefoil and the word s CAUTION, RADIOACTI VE MATERIAL or DA N GER RADIOA CTI VE MATERIAL.

Al thoug h 1h e intention o f these signs and labels is to wa rn w orkers and other indi- 11du :1ls th a t radioactive mater ia ls are present at th e lo ca li o ns where 1hey are posted, the signs and lab e ls al so serve to inform emergenc y re sponders of the prese nce of radioactive ma terial s in 1h e specified areas .

16,8 EFFECTS OF IONIZING RAD IATION ON MATTER Whe n io ni z in g ra di a tion passes through matter, it s energy is di spersed among th e ato ms or mole c ul es of which th e rnart c r is co mpo se d. The process of irradiating th e matter is cal led radiolysls.

The initial action resulting from irradiating ma tt e r is the ionizatio n of 1he s ub sta nces through w hic h th e ra diation pa sses. The ioni zation is reprt>se nt ed for a molecule of an arbitrar)' sub stance A b y th e following equation:

A _______,-..A A .+ c1

rad iation a rea • For purposes of NRC and OS HA reg ul ation s, any area, accessible to 1ndi• viduals, in wh ich rad ia- t ion levels could result in an in dividual receiv· Ing an equ ivalent dose to the whole body in e•cess of 0 .05 mSv in 1 hour at 11 8 inches (30 cm) from the source or from any surface that the radiat ion penetrates

hig h-radi ation a rea For purposes of NRC

and OSHA regu lat ions, any area, access ible to ind ividua ls, in wh ich rad iat ion levels could result in an ind ividual receiv ing an equivalent dose to the whole body in e•cess of 0 . 1 mSv in any 1 hou r at 11.8 inches (30 cm) from the rad ia - tion source or from any surface that the rad ia - t ion penetrates

ai rborn e ra dioa ct iv ity a re a For purposes of NRC and OSHA regula - t io ns, any room , enclo- sure, or area in wh ich certain air borne rad io- act ive material elllst s at e ither concentration cited at 29 C.F.R. S 1910.1096 and 10 C.F.R. S20 .1 003 .

\/UY high ra di at ion a rea For purposes of NRC and OSHA regul a- tions, any area, access i- ble to individuals, in wh ich rad iation levels could result In an ind i- vidual rece ivi ng an absorbed dose in excess of 5 grays in any 1 hour at 39.37 inches (1 m) from a rad iation source or from any surfa rn that the radiat ion penetrates

rad iolysis The comb i- nat ion of chemical react ion s re sul ti ng from the exposure of a sub-

The wigg ly a rrow indicates that the rel evant reac tio n was indu~ed by ioni zlng radi a tion, ioniz ing r· sy mbo lizes an electron, and A + is the sy mbo l for a m o lecule-ion.

Chapt er 16 Radioactive Materials 703

nu cl ea r reactor • A

When such events occ ur repeatedly, the number _of ions a n~ electrons increases. Th en se\·er:.11 seco ndary phenomena usuall y occur. In particular, th e io n s may co mb ine With an}'. electron to form an excited state of A as follows:

Here. A .. refers to a molecule of A ~at has exc7ss e~e rgy. A ,. is an unsta ble molecule. BccaUSeii ~ssesses excessive energy, it ma y dissociate ennrel y mto molecules of new substa nces as follows:

A • ~ B-C The ions that form w hen radiation initially strikes a subst~m cc ma y also react with neu-

tra l molecules. Such reactions produce new io ns a n~ free radicals: The direct exPosure of a subsr:rnce to radiatio n also may res ult in ch e producuon _of free rad~cals. As noted before, frtt radica ls are highl y reactive chemi cal species that may tri gge r a va riety of chemical reactions.

Let's conside r specifica ll y th e phenomena associated with exposing wate r to gamma radi a tion . Water cons titut es thr ee-fou rth s of a ll the body's t iss u es; hence, considerable researc h effort s ha ve been devo ted to examining the nature o f the chemical species pro- duced w h en wa ter is exposed t o ra di at io n. When foreign s ub st a nces form by means of the ra dio lys is of water, the cellular b ioc hemistr y may be sign ificantl y altered, th ereby causing d amage o r dea th to th e affect ed cell s.

W hen wate r is exposed to gamma radiation, prima r y io nization of the water first occ urs, as fo ll ows:

l-l 20l/l~IH 20 i. (/I - e · Then, the wate r mo lecule-io n reacts with a neutral wa ter mole cul e to form a hydroxyl fr ee radical.

(1-1 00 1. (/ 1 - 1-1 10(/) W (aq ) + · 0 1-l (aq) The parenthetical expressio n "aq" on th e ri ght of t he a rrow accounts for the molecules of water listed on the left . The exposure of water to ga mma radiation ma y also produce h ydrogen atoms a nd hydro xy l free radica ls.

1-1 201/) --> H · (a q ) + · OH (aq ) The repeat ed occurrence of th is latte r eve nt ca u ses the conce ntration of hydroxyl radicals to increase. Ulrim,ael y two h)'droxyl radicals un ite to form hydrogen peroxide, a substanct kn own to damage living tissues.

2 · 0 1-i [aq) --> H , 0 2(/)

16.9 NUCLEAR FISS ION

~•~E~'.~:-:~~::~~~;' ~~~•;~i~:,~:~-l~ ybe~~:~:,~:~y:;~e,'~~•~~i~~0i!~~v:~ :;~~a~\n;~:~~l:1~;~~~;•,\::J :: in g fission to produc e tapes in nuclea r accelerators s uch as cyclotrons and be vatrons. Samples of such 1sotopts energ y. generally for ge n era ll y are radiated wi th a lpha particles, protons, deuterons, or other particles tha'. use as electricity ha ve bee n acc el erat ed to relativel y high ve locities. These high- velocity particles poss~) nu cl ear fi ss ion • The su~ stantia l energies . "Y~:n they are used to bombard nuclei, nuclear reac tions ofte\~:~:. nuc lear process dur ing This phenomenon art1hc1al\y trans forms one nucleus into another. Many of the ara 1

~~~~:/re produced radioisoto p es used in medicine are prepared in this fashion. 'thi mas s nuclei with the A seco nd method of production in vo lves using the nucl ear reactions that occur WI f ~a simulta neous emiss ion nuclear reactor, the heart o f a nuclear power plant. The reactor functions because O c of one or mo re neu- pheno menon called nuclear fission. As illustrated in Figure 16 10 nuclear fission is a proc~ss t rans and a substantia l ,~hereb y a nucleus splits into 1'.vo lighter-mass nuclei, accom~anied by the release of a amount of en ergy t1ve ly large amou nt of energy (-200 MeV ) and several neutrons (2.5 on the av erage). fission product • Any fragments that are produce_d by individual fission eve nts are called fission produ~- to e\cc· isotope pro duc ed when . In the nu~lear po we r in~usrry, engineers harness thi s energy and convert 11_ in f·,ss ion a fis1ion event occurs tn ca l energy m th e manner illustrated in Figu re 16 _ 11, The heat ge n erated durin g 704 Chapter 16 Radioactive Materials

Stack

Inside the steel vessel Steam generators

Waste tanks store dioactive waste in

r ii it is moved nd sto rag e.

FI GU RE 1 6 .10 The f,ss,on of a uran,um-235 nucleus induced by a low- velocity neutron 1hown at the up per left ,n this instance, banum-140, krypton-9 3, and three neu trons are produced

rage pond used

rods.

FIGURE 16.11 In a nu clear power plant. the energy generated by f1s- s1on is used to produce electricity. A nudear power plant does not generate air pollutan ts like a foss il -fuel-fired power plant. but it does generate spent fuel and h,gh-leve! radioaci.we waste, both of which require disposal.

Chapter 16 Radioactive Materials 705

fiss ile nuclei • Isotopes that ma y be initiated to unde rgo fission

atmospheric fa llo ut • Fission products pro- duced dur ing th e deto- nati on of a nuclear bomb and ca rried into t he atmosphe re where they move by air cur- rents from place to place, and ret urn to Earth's surface as dust or precipitation

is abso rbed by the water tha t is piped through ihe reacto r. Ne~t, the h~ated water is piped fro m th e reacto r ro a srea m generato r, where the water vapo rizes and 1s sem to a turb· The steam spins th e rurbine ~lades, whi ch generate electricity much like they do du::~ rhe opera tion of a fossi l-fuel -fired power plant.

T he neutrons generated by 0~s ~on m:i. y al s~ be us~d- to bombard ocher nuclei This process serves as a means of amftc1ally producing rad1msotopes tha t do not exist natu- r:i ll y. Many rad io isotopes listed in T:ible 16.2 are produced by _~e~tron bombardment in nuclea r re ac tors. Coba lr-60, for example, may be produc~d ar_uf~c1ally by radiating natu- ra ll y occurring cobalr-59 with the neutrons produced durmg f1s s1on.

i2Co + Jn ---+ 1QCo + 'Y Co balt-59 is the only naturally occurring stable isotope of cobalt.

The neutrons generated by fi ssion may also be used to induce other fission events. Overa dozen nuclei ma y be induced by neutrons to undergo fission, but uranium-233, uranium-235 and plutoniwn-239 are the only ones chat can be practically used for chis purpose. They~ said ro be fissile nuclei. Uranium-235 and plutonium-239 are used as the fissile material in bo th nuclear reactors and nuclear warheads. Plutonium-239 arguably is more desirable for use in nuclear bombs, because it can be produced from nonfissile uranium-238 and a smaller mass is needed as the nuclear fuel when compared to the mass of uranium-235.

For use in nuclear reactors and nuclear warheads, fissile nuclei are induced to undergo fi ss ion b}' exposing them to low-energy neutrons. Unstable uranium-236 first forms wh~n uranium-235 caprures a low-energy neutron. To achieve stability, most uranium-236 nuclei divide imo two other nuclei, simultaneously releasing energy and several neutrons. One such event is represented as follows, where the asterisk denotes the unstable nucleus:

1JJU + Jn ----. [ .!J1 U ] * ---+ ~! Br + 11iL3 + 2Jn + I 92MeY Dozens of these individual fission events occur as the fuel undergoes fission within a

reacto r. Several radioacti ve fission products are listed in Table 16.5. Their charge and ma ss are di stributed among the elements from zinc co terbium; that is, their Z values range from 30 to 65, and their A values range from 72 to 161. Mixtures of fission prod· ucts comprise one type of nuclear waste generated b}' a nuclear reactor. They are also the components of the atmosp he ri c fallout generated when a nuclear bomb is detonated.

ililiiliiililiiiiilliliL_ _______ _

706

The following equation desc nbes a fiss ion event that produces ban um-1 39 and anothe r isotope.

Identify th is second isotope

Solu ti on: A nudear equatio n is balanced when two co ndmons are fulfill ed: the su ms of the charges ar e ~~ same on each side of the arrow, and th e su ms of the mass num be rs are the same on each side of the arrow the left, the sum of the charges is 92 + 0 "' 92; on the ri ght, the sum is 56 + x + 0 == 56 + x, where xis the charge of the second isotope.

56 + X = 92 X = 36

Refebmng 1 10 ei th er Figure 4 3 or Appen dix 8 at the end of this text we see th at the element ha~,ng an atom ic

num er o 36 1s krypton ' wher~n th; left, the sum of the mass nu mbers is 235 + 1 = 23 6 on the righ t the su m is 139 + 3 + y "' 142 + 1

Y is e mass number of the second isotope · '

23 6 = 142 + y y = 36

Hence, the fission product prod uced by 1h1s event is krypton-94, or 1t Kr .

Chapter 16 Radioactive Materials

eli!ii!W Some Radioactive Fission Products ~ StON PRODUCT

sa ri um-140 cesium-134 cesium-137 (erium-141 Cerium-144 lodlne-131 iodine-132 i<rypton-85m Lanthanum-140 Niobium-95 Praseodymium-143 Praseodymium-144 Promethium-147 Rhodium-106 Ruthenium-103 Ruthenium-106 Strontium-89 Strontium-90 Technetium-99m Tellurium-129m Tellurium-132 Xenon-133m Zircon ium-95

I HALF-LIFE· MODE OF DECAY 12.5727 d ~- 2.0652 y ~- 30.0Sy p- 32 .508d p- 284.91 d ~- 8.0252 d p- 2.295 h ~- 4.480 hr p-, 1r 1.67855 d p- 34.991 d p- 13.57 d p- 17 .28 min p- 2.6234 y ~- 131 min p- 39 .247 d p- 371 .Sd p- 50.53 d p- 28.90y p- 6hr p-. IT 33 .6 d p-,IT 78 hr p- 5.2475 d IT 64 .032 d p-

'Chart of Nud ldes, Nat ional Nuclear Data Cent er, Brook lyn Nat ional L~boratory, Long Is land, New York (2012) .

, Natura l uranium is composed of the isotopes uranium-235 and uranium-238 in the ratio_of 1:138. This means that only 0.71 % by mass of naturally occurring uranium is uramum-235 . Uranium-238 is the more abundam uranium isotope, but it is not fissile .

The neutron-induced fission of uranium-235 is a particularly unique phenomenon, btcause for each single neutron that is consumed b}' reaction, additional neutrons are pro- duce~. These newl y formed neutrons are used to induce the fission of other uranium•235 n~iclei. The process thereby initiates a self-sustaining chain reaction like that illustrated in Figure 16. 12. The condition of sustaining the chain reaction is called criticality. In a nuclear reactor, the chain reaction is controlled by workers, and the energy is harnessed for the Ptaceful production of energy. By contrast, in the nuclear bomb or nuclea r-armed missile, the chain reaction builds at an explosive rate, and the energy is released into the environ- ment virtually at once.

16·9·A CRITI CALITY

chain reaction • A self- sustaining nuclear reaction in which the neutrons produced in one step trigger the next step, which in turn produces neutrons that trigger the next step, and so on

critica li ty • The condi• tion wherein a system is capable of sustaining a nuclear chain reaction by retaining at least as many neutrons from a fission reaction as are consumed in future fission events

C~n _the nuclear reactor at a power plant detonate like a ~uclear bo n~b or n~1clear-armed ~ 11

15_slle? Answering this question requires an understandmg of certam derail s about the critlcal mass • The Stan phenomenon. .. . smallest mass of fission -

A I I b f t able material that sup- o , certain minimum mass of fissile maceria must a w~ys_ c prcs~nc - or 1ss 1on to ports a self-sustaining

Ct.:ur; this is called the critical mass. When the nu ss of the fi ssile m:1tcm1\ is le ss than the chain reaction Chapter 16 Radioactive Materials 707

FIGU RE 16.12 A nucl ear cha in reaction The neutron (n ) ad1acent to the arrow is absorbed by a uranium-235 nucleus, which subsequently undergoes fission The fission by-produru (f) and add1t1onal neutrons are thus proouced. These neutrons induce the

-I , , u \ --09 -0 , I \

u

f~on of other ura- rnum -23 5 nucie1 The chain reaction is self- perpetua tin g until either the fuel 1s consumed or th e neutrons are absorbed by maner other than 0 the fuel

f

f n

- -------1 f

critical mass, most of rhe neutrons formed during fission events escape from the mass and do nor ind uce the fission of orher nuclei. The perpetuation of a chain reaction requires lhe system ro rerain at least as many neutrons as were consumed in the fission reaction from which the y were produced . In rhi s way, the neutrons may react in fu rther fiss ion events. Only then has the sys tem achieved criticality.

SOLVED EXERCISE 16.S

In 2006, researchers at the Unrven1ty of Utah showed that young childr en living m Utah and Neva da during the 1950s _and 1960s downwind from aboveground weapons-testing sites we re 7 .5 times more likely to devrlop th~ro-o neoplasms, the precursors to thyroid cancer, compared with individuals in the general populatJon IJ. L Lyon et al. '"Thyroid disease associated with exposure to the Nevada nuclear w eapons te st site radia tioo: A reevaluation based on corrected dosimetry and examination data, " Epidemiology, Vol . 14 (2006), pp 604-6ll]. What rs the most likely cause of th is childhood cancer?

Solution: Table 16 5 shows that 10d1ne-13 J and 1od1ne-13 2 are produced during fission When humans are e,:posed 10 a,rbome re

1 eas.es of these rad,orsotopes, localized damage to the thyroid occurs. Thyroid cancer is a commonly

observed abnormality associated with human exposu,e to airborn e rel eases of iodine ra dioisotopes produced dt,rll'lQ tne te5ting of nuclear weapons The 10d1ne radiois otopes are discharged into the air from which they are Sl,bSe- quentl/ removed by ra,r.water :n,e rain falls on pastures where grazing dairy cattl e co~ sume the grass and produce icd,ne-contam,nateo milk Ch,lcren who dnnk this milk are more likely to develop thyroid cancer than 1ndMduals whO do not dnnk iodine-contam,nated milk Thus those children who t1ve m areas where 1od1ne radioisotopes teod to accumulate are more hk.ety to develop thyr01d 'cancer than children who ltve in the general population.

708 Chapter 16 Radioactive Materials

To end World War II, the nuclear bombs sho wn in Figure 16.13 were detonated 1800 feet (550 ml over the Japanese cities of Hiroshima and Nagasaki. Their fissionable mate- ria l was first compressed into a relatively small volume by the detonation of a mantle of ex plosive charges that caused the nuclear fuel to increa se in densiry and achieve a super- critica l mass. Then, a chain reac tion occurred that released a cataclysmic amount of energy into the environment. The nuclear bomb that detonated over Hiroshima released an esLimated 6.3 x 10 13 joules of energy to the enviro nment. This is equivalent to the <ncrgy released during the deto natio n o f 15,000 tons (13,600 t ) of TNT. Abo ut ha lf o f it was released in the air blast, 35 % was heat, and 15% was nuclear radiation . The fir eba ll re sulting from the Hiroshima explosion was 50 % hotter than the surface of the sun.

FIGURE 16.13 Top " l.Jttle Boy, H the nuclear bomb detonated over Hiroshima, Japan , on August 6, 1945 This bomb contained fiss ile uranium-235, was 28 inches (71 cm ) 1n diameter, 120 inches (3 m) long, weighed about 9000 pounds (4100 kg), and kilted more than 200,000 people. Bottom HFat Man, " the nuclear bomb dropped on Nagasaki, Japan, on August 9, 1945 The bomb contained fissile plutomum-239, was 60 inches (1 SO cm) 1n diam- eter, 128 inches {3 2 m) long, weighed about 10,000 pounds (4500 kg ). an d killed more than 74,000 people (Courtesy of 1he los Alamos NatlOflallal>orarary, Las Alamos, New M e,l(ICO)

The amount of nuclear fuel in the bombs detonated over Hiroshima and Nagasaki contained far less fissionable material per uni t volume than the a mount used in a nuclea r reactor. Furthermore the number of neutrons available for future fission events is restricted in a reactor through \he use of control rods. These are long rods made from cadmium or boron steel that arc inserted into or near the fuel, o r withdrawn from the fuel. Both cad mium a.nd boron have naturally occurring isotopes that r~dily abs~r~ neutron~. Thus, the in ~e r- tton and withdrawal of control rods effectively mediate the fission reactions by absorbing cx:t ra neutrons and controlling their propagation. With their use, a nuclear explosion could never occur. Furthermore, even if all the control rods were removed, a nucl~ar po"'.er p~a nr could never explode in the same manner as a nuclear bomb . If the cham rea ~t1on m a nuclear reacror were to become uncontrollable, the energy generated by the reaction would

Chapter 16 Radioactive Materials 709

r m~~down • Seve re overheatmg o f a nucl ear rea cto r core, resu lt ing in the melt mg of t he nuclear fu el and itsc onta mm ent encai mg

bre-ede r re act or • A de vice in wh ich nonfis- sionable uran ium-238 is con verted into f ission- able p h..rton ium -239

o nly c:rn se a meltdown th a t co uld initiat c a h)' drogen or steam explo sion , but not a nu I explosio n . . . . c tar

No rwichsr:rn ding its impro~a b~liry, a di s:i stcr is h_kel y to o ccur whenever indi\'idu a re e xposed to fi ss iona ble matenal 111 an amount that 1s equal to or greater than its er· _als ma ss. Sixty inci dent s i~ vol ving the accmnubtion of a crici_cal mass o~ fi ssionable rna:;~~al h.1ve occ urred wo rldwide. generall y because safery practices were disregarded. 1 1

ta.I fo r exa m~l e. a c_r!tic ~I mass _of uranium -2 35 unintenti~nall y w~s accumulated at a u~nt:9: rep rocess ing fac il ity m Toka1mura, Japan that res ulted m exposing three workers to neutro Ill rw o of w hom s ub sequentl y died from the exposur e. ns,

16.9-B TERRORISTS' POTENTIAL M ISUSE OF FISSILE MATERIAL

During the pas t decnde, Americans have been subjected to a prevailing fear that ter . is t s ma y use fi ss ile materia l 10 construct a weapon of mass destruction.Weapons-gr: ura.nium and pl~tonium are reas~nably a~ailable for such use, although estimat:t

0 ;

their amounts differ. To clandesrmely build a nuclear bomb, terrorists need only 55

pound ~ (25 kg ) of weapons-grade uranium (Section 16.9-E ) or 18 pounds (8 kg) of plutornum-239.

A nuclear-armed terrorist attack could negatively impact our wa y of life in a man- ner worse than that encountered in an average war scene. This fact is emp hasized by a Rand Corporation stud y4 commissione_d by th e U.S . Dep~rtment of Homeland Security that concluded a nuclear-armed terrorist attack wou ld kill 60,000 people in San Jose, California, and cost as much as SI trillion in damages and cleanup. Ir is evident that eve n a small blas t in a heavil y populated city would cause an enormous numbu of casualties.

16.9-C PLUTONIUM-239 Prior w and through the years of the Cold War, va st amounts of fissile phuonium-239 w ere produced as plutonium (fV ) oxide (PuO2). Amassing pluronium-239 served as a deterrent to stabilize worldwide political power. The production was accomplished m breeder reactors from natural uranium (99 .3 % uranium-238 and 0.71 % uranium-235 ). The initial nuclear reaction produced uranium•239, which decayed in a stepwise process ro neprunium-239 and plutonium-239, as follows:

.!t!u + Jn ___. .! t}u -., 2~j u ___. 2~j~p + fr

.!J ji\p ___. 1JJ Pu T p- Even today, Pakistan and India , bitter arch rival s, continue ro breed pluconium-239 in reactors and stockpile it as a d eterrent for ca lm ing disputes that have existed for decadts. The U.S. arsenal of at lea st 90 ton s (82 t ) of plutonium-239 is stored within scaled bun · kers at th e Pantex DOE Plant near Armadillo, Texa s.

There are at least two reasons why the world's s upply 0 ( plutonium-239 may be troublesome:

As w e noted .in Section J 6.9- 8 , there is always rhe psychological fear that plutonium ma y be acquired by rogue nations and terrorists for clandestine purposes. Becau.se the ha lf-life of plutonium•239 is 24 , J JO years, it is evident tha t once rek :ise <l from JtS confinement, plutonium-239 poses a risk to Earth's inhabitants for cens of thou sands of ye ar s.

~Ch.t ries Meade and Roger C. Mol ande r (Ram.I Corpo r.111 on) "Consi dering th e [ff(' cts of 3 C3 cJ .irorh" Terr orm Ana ck"' (20061.

710 Chapter 16 Radioactive Materials

h onl y viable wa y 10 diminish supplies of plutonium-239 is to blend them with the l :~es o f natural or depleted uranium (Section 16.9-D) imo the mixed oxide fuel called

and use it to fuel nuclear reactors.

16_9.p URANIU M -ENR ICHMENT PROCES SES f iss ile uranium-235 is the primary fuel that serves as th e source of the power generated at niost nuclear power ~!ants, ~ur to effectively serve in this capacity, uranium mu~t ?e . topically enriched m uramum-235 to approximately 5 % by mass. (For use as f1ss1le ::,~rhead material, uranium-235 must be enriched to more than 80% by mass.) Although che basic nature. of the ~ranium-e_n_richment process is not secret, some features of the ngineering details are h1ghly classified. .

e An es sentia l element of the uranium-enrichment process is the producuon of ranium (VI) fluoride, frequently called uranium hexaf1uoride. Although i~ does not ~eact

~ppreciabl)' with oxygen, nitrogen, or ca~bon dioxide, uranium ~exafluonde reacts vigor- ousl y with water to produce uranyl fluoride and hydrogen fluoride.

UF6(g) + 2H20 (g) - U02F2(sJ + 4HF(g) Urdll1 um(VIJ n uondc Wai.·r Uran) l nu omk

Because the inhalation of hydrogen fluoride is highJ y dangerous m health (Section 8.11-B), uranium hexafluoride is considered hazardous primarily because of its corrosi~- ity, not its radioactive nature. _As first no~e_d in ~ecrion 6.6-B, ~OT acknowledges this property of ur a nium hexafluoride by reqmrmg shippers and came.rs to post _RADIOAC- TIVE and CORROSIVE placards on the transport vehicle or freight contamer used to uansport 1001 pounds (454 kg) or more of this substan~e. . .

The production of uranium hexafluoride occurs during the process1_ng of a uramum- bearing ore like pitchblende. Minerals containing uranium are nor rare m_ nat~re, bu~ the uranium is economica ll y recoverable only from deposits in which the uranmm ts relatively concentrated. These sources exist only in distinctive mines in Australia, Canada, and Kazakhstan.

Ura nium generally exists as a mixture of uranium (V) oxide _(U2O 5) and uranium (VI) oxide (UO ) collectively called triuranium octoxide (U 3O s) . It 1s recovered from the ore by sequenrfail y implementing the series of steps briefly summarized as fo ll ows:

I The ore is crushed and then mixed with nitric acid, resulting in the production of uranyl nitrate .

U3O8(s) l nuramu111oc lu \ 1,k N11neacid Ur..in) I mlrJtc N1tro gcnd1 0,ulc \\';i tcr

I Uranyl nitrate is thermall y decomposed to produce uranium (VI) oxide, commonly ca ll ed orange oxide.

+ + 0 2(gJ Unln) l llll r:J.ll· Urmuum(V l )O \ tdc N11 roge nd1 0,1 de

m ixed o xide fu el (MOX)• A blend of plutonium oxide with the oxide5 of natural or depleted uranium

uranium-enrichment pro ces5 es • Isolation techn iques for concen- trating f issile U-235

orang e oxide • Uranfum(VI) oxide (U0 3). an intermed iate in the production of uranium hexafluoride

I Uranium (Vl ) oxide is reduced with hydrogen , which produces uranium(!\! ) oxide, called yellowcake.

y ell owcake • Uranium(IV) oxide (U02), an intermediate in the production of uranium hexafluoride

UO ,(s ) + H 2(g l + H20 (g ) Ur:1.ni um{VI) o., 1de H) droge n UrJmum(I\ Jo , 1Jc

W.11e1

I Uranium(IV ) oxide is reacted with anhydrous hydrogen fluoride nt 932 0F (500oC ) forming uranium(IV ) fluoride, ca ll ed green salt.

+ 4HF(g ) UF,(s) Uramum (I V) o, 1Je H) drogc nnu omk

Crani u1n(I\' \ 1l1wmlc Wat<: r

green salt • Uranium(IV) fluoride (UF4), an intermediate in the production of uranium hexafluoride

Chapter 16 Radioactive Materials 711

tnri ch t d uranium • Uran ium and its compounds in which the concentration of uran ium-238 has been reduced or eliminated by processing

futl rod • A rod-shaped metal assembly often made of a zircon ium alloy and used to cont ain pe ll ets of nucl ea r fu el

dtpltttd uranium (DUFr,) uranium a nd its compound~ in wh ich the concentratio n of uran ium-235 has been red uced or elimi nated by processing

Ur.rnium (IV) fluoride is further fluorin:it~d a~ 482°F (250°CJ to prodlice Ura hex.ltluoride. which is a gas above 11 s sublunanon 1emperature of 14 70F (64 0C),n1uni

UF~(~) l 'r.uuu mt l\ ) lluund,: Fluonn.·

UFo(R) Ur.m1um(V h nuonik-

As it is produced, the ur:mium hexafluoride is an isotopic mix1ure of 235 UFb and Bs Ahhough these isotopic forms may be separa ted. by several means, the least expensive UF6. dure is a gas-centrihigation pr~ess that

1 ~ ke~ mto a

1 ~fu~u _,he mass di!ference of 1~roc~

componencs. In essence. the mixtu re of - UF6 and UF6 1s spun _a t hi gh speed h t\l. o creating a centrifuga l fo rce. As the ctntrifu ge opera tes, 1he heavier 2" 8UF6 concems, t ereby wa rd. The periodic removal of .ns UF6 leaves behind the fi ssile

135 UF6• It is ca\\edrat~ou,, uranium. For ~se as a re~ctor ~el,_ the uran_ium-235-enriched hexafl uoride gen:~:~ reduced to uramum(IV) oxide, which 1s ground 11110 a powder and pressed into cera . Y IS approxima tely 1.5 centimeters in diameter and 1.5 centimeters long. The pellets a:l~pellets into thin zi rconium rubes to form fuel rods, often as long as 13 feet (4 m). Approximat~ed sealed rods are then asse mbled in to bundles that comprise the core of the reactor. e y

200 When a process is conducted to reduce or eliminate the concentration of urani

in uranium metal or a uranium compound, the compound that remains is called d~~- 235

uranium. Depleted uranium hexafluoride , o r OUF6, is a waste product generated e~td the maniu m-enrichment process. In the United States, approximately 825 OOO unng (750,000 t ) of DUF6 is now stored in steel cylinders at three locations: Paducah, Kcnru:~n~ Portsmouth, Ohio; and East Tennessee Technology Park, Tennessee . The majority of J1 material was generated during past decades in connection with the U.S. military d f

I s

program. Its management is a responsibility of DOE. e ensc Peaceful nations are severel y limited in their use of fissile uranium for mliitary _

poses. No netheless, in contemporary times, they are obliged to implement approp~ur diplomatic steps aimed at preventing rogue nation s from acquiring nuclear fuel for ~ltt ta ry purposes. The_ fear is that r~gue na_tions ~per.a te nuclea_r ~o we r plants under the guise of energy producuon whe n their real mtennon 1s to max1 m1ze the production of fissile material fo r use in nuclear arms. The diploma1ic efforts of peaceful nations are directed at preventing them from conducting ura nium-enr ic hment processes or acquiring fissile mate- rial from other nations for military purposes .

Clandestine operatio ns associated with the production of uranium hexafluorid e ma y often be identified by inspecting the sites where the producti on is suspected. Such inspec- tions are conducted by representati ves of IAEA, which promotes the international develop- ment of peaceful uses of nuclear technology and discourages th ei r military applications.

16 .9-E SPONTANEOUS FI SSI ON As first noted in Section 16.2, spontaneous fissio n occurs onl y when cenain very heavy radio- isotopes deca y. These radioiso topes have an atomic number grea ter than 92. As their nuclei unde rgo sponta neous fission, they split into two nuclei and simultaneously generate neu1rons.

An exa mple of a radioisotope that decays by spo nt a neo us fis sion is wrium-250. When curium-250 undergoes spontaneo us fi ssio ns, ir splirs into two other nuclri. One such event is denoted as fo llows:

16.9-F THE GLOBAL FEAR OF USING NUCLEAR BOMBS DURING WARFARE

Th.roughout the hi sto ry of civiliza1ion 1

the use of nuclear weapo ns was required only twice-when the United States detonated them ove r Japan and ended World Wa r 11 · Thereafte r, especially through the yea rs of the Co ld War, it was the thr eat of nuc kar

712 Chapter 16 Radioactiv e Mate ri als

on deployment that facilitated rh e bal f r . i1·e.1: h that the United States and h ance o _PO 1t1 ~a l power. There w~s not a target 011 E~rt-a rined ballistic missi les. N/ e for_mer Sovm Union could not hit wuh lo ng-ra_nge nuclear· . h U . d K" ne nati ons now possess nucl ea r weapons: the United St:Jlt' S, Ru ss _ia, t b~i tel mgdom, F_rance, China, Israel, India , Pakistan, and No rth }(ore.1· Iran 1~ pro a . ose to possess ing nuclear weapons, and Pakistan and India ha ve 111

, reHed their ca pabi\1t1es to construct them. In r~ e J 99?s, the United States and the Russia n Federation engaged in mea sures aimed

.it reducing iheir nuclea r arse~als by mea ns of bilateral agreements formally known as Mea · sures for the Further Re~uction and Limitation of Strategic Offensive Arms, more com· 0100

\y ca ll ed _the Strat_eg1c Reduction Arms Treaty, or START. In 2011, each nation agreed IO red uce th ~1r respect1~e ~um.be_rs of deployable nuclear warheads co 1550 by 2018-eirher as inte rcontinental balhsnc mi ss tles or deployed submarine-launched ballistic missiles.5

Even wh~n START is completely implemented, however, both nations still will pos- sess subsra11t_1al_ n_u,~bers O~ nuclear warheads. Funhermore, while the United States and Russia are dmumshmg th ~tr arsenals, other nations are expanding chem. At the start of 20 13 , for exa mple, the Um1ed States and Ru ssia had reduced their nuclear warheads from 8000 to 7700, and from I 0,000 to 8000, respectively, but both China and Indi a had 1en 010 re wa rhea~s than they did at the stan of 2012.

6 In this regard, the United Sra.tes con· side rs the acnons of Iran co be the most fearsome. Although Iran insists chat its program is peaceful and me_ant on!~ to power a future generation of reactors, the United States and ot her Western nations believe that Iran intends to produce nuclear wea pons.

Paki stan's activities, too, are fearsome, because the country has taken steps to increase ics capacity to produce plu1onium. Pakistan's stockpile of over 100 deployable weapons is now esti mated to surpass India's stockpile. Both nations, who ha ve fought each other for decades, have launched initiatives to modernize their nuclear wa rh ead and deli ve ry sys· ccms. The all-pervading fear is chat the flagrant misuse of nuclear bombs by any nation would not only destabilize the immediate locality but could potentially decimate individ- ua l civili zatio ns and alter life on the entire planet.

To encourage international nuclear disarmament and reduce the further proliferation of nuclear wea pons, the United Na 1ions proposed a Comprehensive Nuclear-Test-Ban Treaty, or CTBT. One condition of this treaty prohibits the testi ng of a nuclear device of any size within any environment. As of 2011 , the CTBT was signed by 182 countries, of which 15 3 ha ve also ratified it. Included among the countries that ha ve ratified the treaty are France, the Russian Federation, and the United Kingdom, but China, Egypt, India , Iran, Israel, North Korea, Pakistan, Syria, and the United Scates ha ve not signed it.

Inspectors for the lAEA periodically monitor nuclear facilities co ensure that nuclea r mate• rial has not been di verted to military uses. Notwithstanding the responsibilities of the agency, th e proliferation of fuel for nuclear weapons continues as demons1ra1ed by the fo llowing:

I In 2006, 2007, and 2009, No rth Korea demonstrat ed that it could detonate a nuclear bomb.

I \''<'ithout IA EA's knowledge, Syria sec retl y constructed a nuclea. r reacto r to breed pluionium-239, but Israel destroyed the reactor in 2007 befo re it was activated.

I Iran has constructed a nuclear reactor, allegedly to use for the producti on of el ectrica l power, but the prevailing fear is that it actually plans 10 create pluconium-239 fo r military use.

1 Pakistan and India ha ve accelerated the breeding of plutonium-239 in reactors.

The combination of these incident s signals all too clearly that mass killing and destruc ti on from the deployment of nuclear weapons ma y again be rea lized. The energy

' ~otewonhy is th e fac t th:11 in 20 11, the United Sures rem ol'cd the uranium fue l from the IJsr 9,megaton BS3 bomb at the P:intex DOE l' lant nen ArmJd1ll0, Texas. E.ich BSJ bomb w.i s 600 tim es more powe rful thJ n rh ,:, bomb dropped 0l'c r Hiro ~h inu . Th e n.nion 's l~rges1 nuclear bomb 1s now the l.2-meg:n on B83. "Sll'R I Yearbook, Sto ckhol m Jnreml tion.1 1 Peace Re\em h JlO\J ).

Strate gic Redu ction Arm s Tru ty (ST ARD • A bilateral agreement between the Russia Federation and the United States to ach ieve nudear-arms - reduction goats by 2018

Compre he ns iv e Nucl ea r-Test-Ban Treaty (CTBn A treaty pro - posed by the United Nations, not yet a com- ponent of international law, that aims to pro- hib it the testing of all types of nuclear dev ice s

Chapter 16 Radioactiv e Materials 713

rele:m·d by ,he deronarion of a nucle:H bomb or ~he engag~ment of a ~uclear War head su rpJsses the e-nergy associ:ned with the deronauon of ordmary chemical ~xp losives. fa.r explosion of a nuclear bomb, fo r inst.:i.nce, re-leases more energy than that involved in~t de tonarion of approxi matel y l million tons (-909~000 t) o~ T~T. The relea se oft .e amou nt of energy rs globally fea rsome fo r the fo ll owmg comb111anon of rea sons: h15

Th is amount of energ y could insta nrl r ki ll ten s of thousands of people Within the immediate blast zo ne. The sur vivors of the init ial blast would not onl y suffer from the acute effects of d' tion exposure, but could acq uire long- term he~hh: rel ated problems like cancer.ta i,1. Climatic changes would occur. Computer modeling illustrates that the detonation of

1 Hiroshima-sized bombs, for example, would dim the sunlight reaching_ Ea rth for 10 : more years, red uce ra infall, and coo! the globe ro tempe ratu res resemblmg those expey;. enced during the Linle Ice (Secnon I0._12-B). The reduced tempera tures would also ca~ crop failures, malnutnt1on, and fanune throughout most of the wo rld and cause diseases to multiply.

16.9-G NUCLEAR POWER PLANTS AND THEIR HAZARDS fissile nuclei are used by the nuclear power industry as fuel for the generation of electric- ity. Four hundred thirry-five (435 ) nuclear power planes produce approximately 20% of rhe electrica l energy used worldwide. One hundred four, roughly one-fourth of the world's plants, operate within the United Sca tes, but mosc are approaching their projected operat- ing Ji ves of 40 yea rs, seven are 40+ yea rs old, and all but three have been operating for at least 20 years. 7 Thirty new plants are contemplated fo r construction during the next decade, wi th the first r.vo schedul ed co come onl ine in 2014 and 2015. In 2012, the NRC issued a license fo r construction of the first new nuclea r power plant in the United States since 1978.

If emissions from uranium mining and enrichment, fuel produccion, and spent-fuel production are ignored, the operation of nuclear power plants pro vi des certain environ- menta l benefits that compare fa vo rably over th e operation of fossil-fuel-fired power plants. In particular, operating nuclear power plants do nor emit the greenhouse gases blamed for climate change. They also ge nerate far less was te than do fossil-fuel-fired power plants.

No r.vi thstanding these benefits, a fear is perceived by rhe general public in connection with the siting and operation of nuclear power plants. A component of this fear is related with the longevity of the radia tion generated during their operation. A number of radio- isotopes ha vi ng very long half-li\·es are produced during the operation of nuclea r reactors. Examples incl ude neptuni um-237 and plu tonium-239, whose half-lives are 2,000,000 years and 24 , J 10 years, respecti ve ly. Whar ca n be done when radiation is released inad- vertentl y through mismanagement, the fai lure to follow established sa fety practices, cata- strophic natural disasters, or terro rist events?

NRC subjects nuclear power plants to especially ri gid regul atory controls and licens- ing requirements. Nonetheless, nuclea r power plants could release radioac ti vity from their confinement vessels into the enviro nment. Such events are not merely hypothetical possibilities, as there have been we ll-documented instances of airborne rel eases of rad io- activity from nucl ear power planes in th e United States, Russia, a nd Japan. Three occur· rences are nored here.

; In 20 12, the NRC gramed J license ro Sout hC'rn Com pan y to con mu ct and operate rwo nuclea r reactors 3 d)J• cent co rwo OpC'rac ing plants at irs fa cility ne3r Waynesboro, Geo rgia. Th is wa s the fi rst licens1: issued by thr '.'/ RC in 34 years.

714 Chapter 16 Rad ioactive Materials

cherr1o byl Nude~r Po we r Plant In April ! 986, series of opcra1or errors unlea shed a power surge ihat triggered an ex~lo· .0 11 .:ind a parual meltdown of the fuel at the Chernobyl nucl ear power plant in Ukrame,

: 1 Jt1Cniber countr_y of the fo r~er Soviet Uni on. Radioactive fu el and fission by- products . e di sch.:irged mto the env1ronmem, the majority of which ultimatel y spread over not M( Ukraine, but also Russia, Belarus, and parts of western Europe. The radiation level on he reactor sire ranged from 10,000 to 300,000 mSv/hr. Immediately afte r the disaster, at

I roxi mately 24 ,000 individuals living within 9 miles ( 15 km ) of the site received an

a~ Prage do se of 450 millisieverts before th ey were evacuated. ;t\C The Chernobyl disaster turned bustling vi ll ages and towns into unpopulated areas

d directl y threatened the hea lth of more chan 5 million peo ple. As of 2005, howeve r, r;:\,cr than 28 de?rhs had been directly att ribut ed to radiation exposure from the disaster, almos t all of _wh1ch we~e resc ue wor.kers. Afterwards, approximately 60?0 peop!e were diagnosed with ea rl y signs of t~ yro1d cancer caused in part br inhalauon of airborne io dine radioisotop.es. Many surv~ved ?wing to prompt medical rre~tme~t: Ev_en yea rs after he di saster, th yroid cancer was 1denufied as the most commonl y 1denttfied tll effect asso·

:iated with exposure to the ai rborne radiat io n from the Chernobyl reac tor. 8

Three-M il e-Isl and Nuclear Plant . In 1979, an accident occurred at the Three-Mile- Island plant in southeastern Pennsylv ~ma when the coolant used to modulate the generated heat was inadverte ntl y discharged mto the atmosphere and the Susquehanna River. 9 The operators quickl y shut down the power plan t, and all aux ili~ry equipmen.t remai ned opera_ti ve. A pa rtial n:1e!cdown occurred , resul ting in the venting of approximately 43,000 Ct of kr ypton rad101sotop es from the reactor building into the surrounding environment, but the confinement buildings were not des tro yed. The maximum dose recei ved by those livi ng wit hin 10 miles (16 km ) of the fac ility was 0.08 millisieverts. No one died as an immediate res ult of the accident, but the cancer rates in the region surrounding the plant remain points of fierce debate eve n today. Fukus hima Dai -lchi Nucl ear Power Station Jn 2011 a magnitude-9 earthquake occurred in Japa n, spawning a tsunami and disabling the el ec;rica l power system at the Fukushim:i. Dai-ichi Power Station. 10 Three of its six reactors we re operating at the time of the earthquake, and three others were undergoing main1enance. Without power, it was impossible to cool the three operating reacto rs. Within five hou rs of the onslaught, triple meltdowns occurred which, along with fires and h)·drogen explosions, ultimately damaged the integrity of four re ac tors and spread radio- ac tivity over an area of approximately 230 square mil es (596 km 2 ). .

The hydrogen explosions ca used radi oactive fiss ion product s to be spewe~ mto the atm osp here. These radioisotopes included iodine-13 I , iodine - I 32 , cesium-1_34 , cesium-1 37, tellurium-132, and xe non-1 33 . Japan~se water suppl ies, milk, vegetation, and seafood were tainted with iodine-t3l and cesmm-13 7 at unacce ptable le vels. The highest radiati on level recorded at the plant, obtained robotically, was 57 Sv/hr. lnd!vidu- als living 19 miles (31 km ) from the post-disaster plant experienced an annual maxim um concentration of 20 millisievcrts.

In the United States, iodine-131 and other radioisotopes were detecte~ at ve ry low concentratio ns, not only in Hawaii and the weste rn coastal states, bur also m Pennsy lva- nia and Massachusetts.

Chapter 16 Radioactive Ma terials 715

dry cas k A means of containment for spent nuclear fuel du ring its storage

16.9-H FUTURE USE OF NUCLEAR POWER PLANTS The diSJ.ster ar Fukushima DJ i-ic hi gt' nernted an international wake- l~p ca ll regard in smng. design, and opt'rarion of nucle~r po_wer plants. ~t leas~ one po_mr became obvfo'ht :--:- ucle:ir power plants should not be sited m se1smolog1cally nskr region s. us:

:--:onerheless., eve n with worries about the safc~y of nuclear technology, unanirniry is la mg among the countries of the world over the commued use of nuclear reactors. Genna ck. announcro th.:it it will discontinue use o~ its 17 nuclear_ reactors for the _generation of ety iry by 2022; Japan rumed off the last of its 50 ~eactors 111 2_012; and Sw1czerland discon~- useof its nudear power facilities in 1013. Also m 2013, twm react~rs at Co. lifomia'sSttn C:, fre•s nucl e-.1 r power facility were shut down permanentl y, following the detection of radiation leak. On the other hand, China an d 1n~!a :ippear to _have a~ _undiminished a~:~ for nuclear power plants, because they are posmon~d to ~mid addn1~nal ones. lndonesi Thailand, Somh Korea, and Viecnam also are proceedmg with construction of new plants. a.

In the United States. public support for nucl_ear reactors h_as . plu~meted, because expert designers, engineers, and regularors appea r incapable of d1:minaung or minirnizin rheir potential hazards. E\'e n so, four new reacrors probably wi ll be constructed using currenr technology during the next decade. g

The Fukushima Dai-ichi incidenr has also generated a rethinking about the storage requirements for spent nuclear fuel. In the future, rhe operators of nuclear power pl may be required ro transfer their spent fuel rod s into dry cas~s. (Spe?t fuel rods cont::: ing residual MOX (Section 16.9-B) were store~ at _t~e Fukush11:r1a J?a1-Ichi Power Plant in warer-filled pools.] A dry cask, one type of which 1s illustrated m Figu re 16.14, is a device th:it provides stand-alone containment of spent nuclear fuel and other high-level radioac- ti,·e wastes that ha ve first .. cooled " for one 10 five yea rs. The waste is robotica ll y insened into a I 0-inch-rhick steel canister that is vacuum-sea led, filled wit h an inert gas like helium to pre,•ent corrosion, and welded shut. Eac h canister is then placed inside a three-foot• th ic k co ncrete barrel rhat is equi pped wi th sma ll ve nts to keep its contents cool. This

FIGURE 16. 14 This steel and concre te "dry cask" rest ing on a concre te pad 1s a cylinder in wh ich high-level radi oactive waste such as spent nuclear fuel may be stored Each dry cask 1s routinely entombed 1n a concrete sior· age bun~ er unti l a permanent disposal fac1hty 1s avafable Approxima tely 1300 dry casks are now In use at 55 sites at nuclear power stations an d other locations nationwide Some have also been used for containment of radioac· t1ve materials du ring their t1ansp011at1on (Counesyof u 5 Mx.Irur Regularory Comm1S:S,on, wash,ngron, DC)

716 Chapter 16 Rad ioactive Materials

Je, igt1 and co~Sm_iction provides shi eld ing and performs 1he functions of confinement, r;1diological shieldin g, decay h~at removal, and physical protection of the spent fuel dur-

, 110 r111 al , abnorma l, and accident conditions. 111 g The di s~s ter at the Fukushima Dai -ic hi Nuclear Powe r Station also prompts lawmak-

ers ;111d pohC)' pla nners to develop a sa ti sfactory course of action fo r disposing uf the ;tion's most fearsome nuclear wastes. The production of ihese wastes is ongoing at the

~J uon ·s. nuclea r power plants, but nucl ea r wastes generated as ea rl y as the 1940s sti ll remai n 1n stor~ge: For exa mple, wastes formerly generated in conjunction with produc- uon of the

1 natton s nuclea~ w~apo ns are still stored at former defen se plants such as the

Ha nford Nuclear Rese~va tion. Ill Hanford, Washing1on. This site occupies an area of 560 ,qu:ire miles (1400 km- J and_1s located within the Columbia Ri ve r Basin in south-cenrral \Vashington, In 1943, when it was operational, the facility produced plutonium-239 for ihe U.S. nuclear weapons arsenal during World War II and through the Cold War. It now is rega rd ed as the nation's most seriously contaminated radioactive site, because the wastes in its 177 underground tanks are lea king into the surrounding soils.

Certain other nuclear wastes are now stored at temporary storage si tes in 35 sta te s. The)' were generated not only within the United States but outside the country as well. The latter wastes are stored to keep nuclear fuel from reaching international terrorist orga nizations or rogue nations.

Acknowledging the magnitude of the nuclear waste disposal problem , Congress directed the DOE to locate and construct a national site in which high-le ve l nuclear was tes cou ld be stored pe rm ane ntl y. An essential element of the site is an acceptable means for protecting th e next 25,000 generations of Americans from exposure to the nuclear waste generated contemporaneously.

The site initially selected by DOE and approved by Congress as a geologic repository for spe nt fuel and high-l evel radioactive wastes was a volcanic-rock ridge located within Yucca Mountain , approximately 100 miles (161 km ) northwest of Las Vegas, Nevada. However, in 2010, political pressures resulted in the issuance of a presidential order that essenti all y ceased the government's long-s tanding plan to di spose of these wastes at Yucca \fountain. After two decades of work, technica l problems, legal challenges, and political opposi tion caused a sc uttling of the project with the stroke of a pen.

In 201 3, DOE set a goal of locating an underground, permanent disposal si te by 2026, designing and licensing it by 2042, and constructing and accepting nuclear waste for buria l by 2048.

In the United Srntes, there are rwo active low-b·el nuclear waste storage sites:

Waste Isolation Pilot Project, or WIPP, nea r Carlsbad, New Mexico, which is used todar mainly for the temporary storage of plutonium wastes. WIPP is a m:issi ve geo- logic reposito ry in which wastes are stored in chambers excavated in vast salt beds nearly a half mi le underground.

I The Nevada National Security Site, approximately 65 mi les north of Las Vegas, is used to store the government's dregs associared with the cleanup of Cold War labora- tories and factories .

To date, no country has implemented a plan th~t addresses the lo~g-term disposal of nuclear waste. France is the only country that treats us spent fud , and F1?la~d and Sweden are the only countries that have selected locations as permanent depositories for nuclear waste.

16.10 TRANSPORTING RADIOACTIVE MATERIALS A stringent set of regulations app ly to the mmsp~rtation of a radioactive materi~I. The porrion of th ese regulations most immediately applicable to emergency responders ts sum- marized in the subsections that follow.

Chapter 16 Radioactive Materials 717

re po rta ble qu antity (RQ) The amoun t of a rad ioisoto pe list ed in Appe ndix Bat 40 C.F.R. §302.4 a n d 49 C. F.R. §1 72. 101, th e release of wh ich t rigge rs manda• to ry no t ifica t io n to th e Nat ional Response Ce nte r

8/Jj\iiii Spe<ifte Activity and Total Activity for Some Selected Rad101sotopes• RADIOISOTOPE TBq / g

Bismuth -207 ------, O x 10 1 ---+-- Coba lt -60 1.0 x 10 1

Ces ium -137 1 Q X 101

Molybd enum -99 1 0 X 102

Potass i um-40 1 Q X 102

' U:ct rptMfrom49C.F.R, § 1734)6

SPECIFIC ACTIVITY ----, Ci /g

~><1 06 2 7 X 10 "10

2 .7 X 1Q• IO 1. 0 X 106

2.7 X 10- IO 1 0 X 106

2.7 X 10"9 1 Q X 106

2.7 X 10 "9 1.Q X 106

TOTAL ACTIVITY

Cl

2. 7 X lQ -~

2 . 7 X 1Q ·5

2.7x 10-s

2.7 x1~ 2.7 x10 -s

W he n s hippe rs offe r a ra ~ioac tive ma t: rial for ~ransp~rt a tion, it is first necessary to dete rm ine wh ethe r DOT ap~hc s an cxe'.11 pt1 on th a t 1s :i~phcable to the potential consign. me nr. T he s hippe rs dete rmm e the acti vi t y conce ntra_t1 o n and the t?tal activity in the po te mi:;i l cons ign men t an d co mpa re th ese va lues wuh those publi shed at 49 C.F.R S 17 3 .4 36. T he DO T reg ul a tio ns appl y w hen th e act ivity co ncent ration and the totai activity in th e co nsignm e nt exceed th e published values. Table 16.6 lis ts some representa - tiv e val ues fo r severa l se lected radioi so tope s.

Some radi o iso tope s are tran sported as ~h aza rdou s s ub stanc es " within t he meaning of C ER C LA (Sect io n 6.2·B ), e xampl es of w hic h are pro vi ded in Table 16. 7 a long with their re p orta ble qu a ntiti es (RO). There are si x re po rt a ble quant itie s for radioi sotopes: 0.00037 TBq, 0.0037 TBq, 0.037 TBq, 0.37 TBq, 3.7 TBq, and 3 7 TBq.

16 .10-A SHIPPING DESCRIPTIONS W he n shippers offe r a radi oacti ve mat e rial for tran sportation, DOT requires them to includ e th e foll owi ng information in its sh ipp ing des cription:

Pro pe r shipping n:ime, haz a rd cla ss 7, a nd identification number. The proper shipping na mes of th e haza rdou s ma te ria ls in class 7 :ilwa ys begin w ith the wo rds .. Radioacti\-e mat eria l. ., So me exampl es a re lis ted in Append ix C.

Mhi!iiii Reportable Quant1t1es of Some Selected Ra d 101 soto p1 c Hazardous Substances• HAZARDOUS I RO [TBq] HAZARDOUS SUBSTANCE SUBSTANCE RQ ITBql Ar senic -77 37 I Pluto nium -23 9 00037 Coppe r-64 37 Pot ass ium-40 0.03 7 lodin e-131 0.000 37 1 Prome th ium -1 47 0.3 7 lridium -137 I " l Rad ium-22 8 0.0037 Lead-212 I o.37 Rad on- 222 0.0037 Mercu ry-195 3.7 7 St ro ntium -90 0.0037 Mo!ybdenum-99 3.7 Ura n ium-2 33 0.0037 Ph os phorus-32 I 00031 7 Ur an ium- 23 5 0.00 37 Platin um -189 I 3.7 1 Zinc-71 3.7 • r he report.tb le q uant i1oes of rad 101sotopes tha t a re haz a rd ou; su bst ances a re provided In Table 2 fo lJo~ lllg Occupa tion a l Sa fe ty a nd Health Ad mlnlwatlon Regu lation Standa rc11, 49 C.F.R. §172 . 10 1. Occupat ion al Sa et)' an d Heal t h Adm in istra tio n.

718 Chapter 16 Ra dioactive M at eri als

1 The c;i pira l letter s RQ , wh en a n acii \'it y equal 10 o r s rea ter th a n ihe repo rtabl e qu a n· 11 1y 1s o ffer ed for transportati on. Th e n.1111c o f the r:id ioi sotope.

: A J csc r~p '. ion o f th e ph.y~ ica l and chemica l form o f th e material. The ac t'. \''. t}' ~f the ra ~i oisoto pe : xpressed in becquerel s or it s multipl es or fract ions. The acti vity IS det ernuned by usmg ap propria1e radiation detec ti o n equipment. The .icll\'lt )' m .'.l )' :ilso be ex pressed in cur ies or oth er unit s and entered pare nth etical ly unrn e&11cly ne x1 to the measurement in becquerel s. Jde nofi c at1 o n of the label s that DOT require s to be aff ixed to th e rel e vant packa ging. . The 1ra nspo rt mdex, when DOT requir es e ither RADIOACTIVE YELLOW-II o r RAD IO ACTIV E YELLOW-Ill labels 10 be affixed to the packaging. The t ra nspo rt index is a d imensionless numb er used to des ignate the degree of co mrol to be exe r• cised during transportatio n of a nonfi ssile rad ioactive mate rial. It is determined by multipl ying the maximum radi a tion le vel in mS\'/hr at 3.3 fee t ( l m ) from the external surfa ce of the package by 100.

1 Th e criticality safety index (Sect ion 16.10-F), w hen DOT requ ires FISSILE 1:ibels to be affixed to the packaging.

1 Th e expression .. highway route-controlled quanury," or HR C Q, w hen shippers offer fo r transportation a "'highway route-cont ro ll ed quantit y" (Section 16 . 10-G ) of a class 7 h:i za rdous mat eri:il (49 C.F.R. S 172.203(d )( I O)j.

16.10-B LABELING REQUIREMENTS When shippers offer packages of radi oacti ve materia ls fo r transport a tion , DOT requ ires them to ,1ffi x on their opposite sides other th a n the bott om th e a pplica b le RAD IO ACTIVE WHITE-I, RADIOACTIVE YEL LOW-II , RADIO ACTIV E YEL LO W-Ill, o r FISSILE label s. RADIO ACTIVE YELLOW-III la bels a re al wa ys affix ed o n the o pposite s ides of packages containing a " highwa y ro ute-controlled qua ntity " of a class 7 ha za rdou s ma te- ria l and FISSILE labels are affi xed ad jacent to the :ipplicable RADIOACllVE YELLOW•II or RADIO ACTI VE YELLOW-III labels. The fea tures of th ese la bel s we re prev iously illus- tra ted in Fi gure 6.5.

DOT requires shippers to c hoose th e a pplica ble RAD IOACTIVE label by me asur- ing 1he radiati o n lev el at a ny po int o n the ext ernal sur face o f the pac kagi ng a nd d ete r- minin g the tr a nspo rt inde x. The a pplicable label is th en chose n from Tab le 16 .8 . DOT

1/li!iiii Categories of the DOT Class 7 labels•

trilnsport ind ex • For purposes of DOT regu - lation s, a d imensionless number that sh ip pers and carriers ass ign to certa in rad ioactive materials to designate the degree of control to be exercised during the ir t r ans it

TRANSPOR T INDEXb MAXIMUM RADIATION LEVEL AT A.N Y POINT ON A PACKAGE ' S EXTERN AL SURFACE LABEL CATEGORY

More th an O b ut not rnore t han 1

Mo re than 1 but not rnorethan 10

More t han 10

Less t han or equ al t o 0.005 mSv/h r (0 S mremlhr)

Gr eat er th an 0.005 mSv/hr (0.5 m rem/hr) but len t han or equ al t o 0.5 mSv/hr (SO mr em/hr) Gre at er th an 0.5 mSv/hr (50 mrem/hr) but l1m than or eq ual t o 2 mSv/h r (200 mr em/hr) Gre ater t han 2 mSv/h r (200 mrem/h r) but les s th an or equa l 10 10 mSv/hr (1000 mrem/hr,C

RADIOACTIV E W HITE -I

RAD IOACTIVE YEL LOW-I I

RAD IOACTIV E YELLOW -Ill

RADIOACTIVE Y EL LOW-Ill

~c.F.R. §l 72 403 . be lessthan OOS t he value lsco ns ld eredzero. ' DOTe~~~:c~~a~~ : ;~~~~e

1 ~ : ,':;~~~~.~s~ :r;:;0 ~ set fo rth at ,g'c.F R. §173.44 1 when t ra nspo rt ing radioae1lve materlal hav ing t his ma .1tlmum

•a~iatlon level

Ch ap ter 16 Radioactive Materi als 719

aim reqU1res shippers to ,nscnbe the following information within the contents-ent space: ry

The name of the rad,oiso tope to be transported and its acti vity on the a \' RADIOA CTIVE WHITE-I, RADIOACTIVE YELLOW-11, or RADJo~c'n~• YELLOW-111 label £ LSA·l material, or LSA-l (Semon 16.l0·C ), on the applicable RADIOACllv WHITE-!, RADIOACTIVE YELLOW-11, or RAD IOACTIVE YELLOW-IU lab,i when shippers offer LSA-1 matenal for transportation , The tr:mspo<t index on RADIOACTIVE YELLOW-11 and RADIOACTIVE YELLOW.m bbe\s The criti ca lit y safety index on the FISSILE label when shippers offer subcrir' I masses of _uran ium-233, uran ium-235, plutonium-239 or plutonium-24!

1:r transportation

low specific activi ty For

purposes of DOT regu- lations, certain rad ioac- tive material, includ ing uran ium and thorium oresandtritium - lab eledwater, that compl ieswiththe descriptions andactiv - itylimitatiom published at49 Cf.R §173.403

surface contami nated obj ect (SCO) for pur• poses of DOT regu la- tions, a solid object that is not itse lf radio- active but has radioac- t ive material distr ibuted on its surface

When shippers intend to offer packages that have been emptied of their class 7 con- rems fo r transportation , DOT ma y require them to affix EMPTY labels on opposite sides of the packages. The EMPTY label is a white sq uare with black lettering.

E] DOT requires EMPn' labels to be affixed to the packages when the exterior radiation levels re veal the presence of internal contamination following the removal of their radio- active contents.

16.10-C MARKING REQUIREMENTS At49 C.F.R. SS t 73.47 1 . 173.473, DOT requires shippers to mark each package contain· ing a class 7 hazardous material with the following information:

The name and address of the shipper and receiv er of the package The proper sh ipping name and UN identification number of the radioacti\"c material RQ, if the package contains an amount equal to or greater than the reportable quan·

tity of the radioacti ve material The gross mass when the package weighs over 110 pounds (50 kg ) Orientation arrows, if the contents are liquid " Radioacri ve-LSA" or .. Radioactive-SCO, " if applicable. low specific activity material (LSA) refers to radioactive material that complies with the DOT description5 and acti vity limitations provided in Table 16.9. Surface contaminated object_ (SC?) refers to a solid object that is not itself radioactive bur has radioactive material dis- tribu ted on its surface, The package types TYPE A or TYPE B, as appropriate (Section 16.10-E) The trefo il when the class 7 hazardous material is contained within a type B package USA, if destined fo r export For industrial packages (Section 16.10-E ), TIPE IP- I, TYPE IP-2, or TYPE~-~• a~ applicable, with the internationa l vehicle registration code of the country of origin° the de sign . le For type B packages (Section 16.10-E ), TYPE B(U) or TYPE B(M ), when apph_cab 1 and if desti ned for export, USA in conjunction with the specification marking or other package-cenificau identification

720 Chapter 16 Radioactive Mater ial s

jt-Hiiil low Specific Act1v1ty Materials• FEATURES GROUP

LSA•I Ura nium and _thorium ores, concentrates of uran ium and thorium ores, and other ores contain ing naturally occurr ing rad1onucl ides that are Intended to be processed for the use of the radionuclides, or

I Solid un irrad iated natural uran ium or thor ium or depleted uran ium or natural thorium or the ir solid or liqu id compounds or mixtures, or Rad ioactive mater ial other than fissile material for wh ich the Ai value is unl imited, or Other radioactive mater ial, exclud ing fissile materi al in quantities not excepted under §173.453, in which the rad ioactive mater ial is essentially un lformly dist ributed and the average specific activity does no.t exc~ed 30 times the values for activity concentration specif ied in §173 436, or 30 times the default values hsted 1n Table 8 of§173.433.

LSA•II Water with a tritium concentration of up to 0.8 TBq/l (20.0 Ci/I.), or Other radioactive material in which the act ivity is distributed throughout and the average specific ~ct ivity does not exceed 10 .... Ai/g for solids and gasts and 10-sAyg for liqu ids. The signifi cance of A2 is noted in Section 16.10-E .

LSA•III Sol ids (e.g., consolidated wastes, act iva ted materials), e1tclud ing certa in powders in which: The radio~cti_ve . material is distributed throughout a solid or a collection of sol id objects, or is essentially un iformly distributed m a solid compact bind ing agent such as concrete, bitumen, or ceramic; The rad ioactive material Is relatively insol uble, or it is intr ins ically contained In a relat ively insol uble material: so that, even under loss of packag ing, the toss of rad ioactive material per package by leach ing when placed in water for seven days would not exceed 0. 1 A2; and The estimated average specific activity of the solid, excluding any sh ield ing material, does not exceed 2 x 10-3A/g .

' Exm ptedfrom49C.F.R. §173.403.

16.10 -D PLACARDING REQUIREMENTS DOT requires carriers to post the RADIOACTIVE placard shown in Figure 6.13 on each side and each end of a transport ve hicle or freight container used to ship the following by highway or rail:

A package to which DOT requires RADIOACTIVE YELLOW-111 labels to be affixed .. Exclusive-use" LSA materials or SCOs within "excepted packages'' (Section 16.10-E) A "highwa y route-controlled quantity" of a class 7 hazardous materia l (Secrion 16. 10-G )

DOT prohibits carrie rs from displaying the UN/NA id en tification number of a radioac· nve material across the center face of a RADIOACTIVE placard.

16.1 0-E PACKAGING TYPES When shi ppers offer a radioactive material for transport~tion, DOT requires the~1 to co_n- tainerize it within one of th e following types of packagmg: excepted package, mdustnal package (I.P ), type A package, or type B package. These pa~kages ha~•e been d~signed _to protect workers, the public, and th e en\'ironme~t from the mherent nsks associated with transponing radioactive materials. Each is described next:

An excepted package refers to a type of packaging that DOT authorizes when LSA materials and SCOs are transported by an exclusive- use me~ns. Exclu~lve use ref~rs to the sole use b)' a single consignor of a conveyance or _a large freig?t conta~ner for wh1c~ all initial, intermediate, and final loading and unloa~mg are earned out 111 acco.rdancc with the written directions of the consignor or cons1g'.1ee. A~ example of a_n. exce pte_d package is a cardboard box that complies w!th cena.m specified ~est c?nd1t1ons. It 1s "exec led., from the routine labeling and markmg requtr em~nts but ts sub1ec t to other ~e- quirei~ems published at 49 C.F.R, SS I 73.42 1-1 73 .426. Shippers mu st also comply with

exce pted package purposes of DOT regu- lations, a package type in wh ichLSAmaterials and SCOs are trans- ported by exclusive-use means

e11d uslve For pur- poses of DOT and NRC regulations, the sole use by a single con- signor of a conveyance or a large fre ight con • talner for which all ini - tial, Intermediate, and final loading and unloading are carried out in accordance with the written directions of the consignor or consignee

Chapter 16 Radioactive Materials 721

type A package • For purposes of DOT reg ulations. a package designed to transport an A1 or A 1 quantity of rad ioact ive mater ial. as appropriate

ty~ B packa ge • For purposes of DOT regulations. a package designed to transport greaterthananA 1 or Ai quantrtyof rad ioactive material, as appro priate

FIGURE 15.15 wtienaradoact,vema terial s off ert>dfo r transportatonasanexcepteo ~ac,:;age shippers post this mar~mg on its pack· ag r,g The crosshatch ed border 15 typ1cally1ed onav.htebackground, andtheword1n9 1s cnnied , blac~

che ron~'eya~ce acti\•i~y l!mits publ ished at 49 .C.F.~ .. S 173.42 7(e). An e~cepted pack.a c of a rad1oacnve marerial rs gene rall y appa rent smce It 1s m~rked as shown m Figure 16,l1

An ind~strial package_ is anoc~~r type of au~homed ~ac~aging in which noT permits rhe shipment of cerram qu:mm1es of rad1oact1 ve material, rn strumencs, or arti 1 manufactured from natural or deplered uranium o~ natural thorium. The DOT reg:!: rions require shippers to use one of three types designated as IP-I, I P-2, and JP-3. Ea h type must be designed and fabricat ed to retain the incegriry of containment and shicldi~ whe~ it is su~jected ro normal co~ditions of transport . In addi ti on, IP-2 and IP-3 sarist certain prescnbed DOT tests publi shed at 49 C.F.R. SS 178.603 and 178.606 rrlating to their abi lity to remain intact when dropped and stacked, respectively.

A type A package has been designed to retain the integrity of containment and shield- ing when subjected to normal conditions of transport. Four examples of a type A package a re shown in Figure 16.16: a fiberboard box, wooden box, steel drum, and lead canister.

A type B package has been designed to retain the integrity of containment and shield ing when subjected to normal conditions of transport and to retain the integrity of containment and shielding when subjected to prescribed hypothetical accident-mt conditions. Three examples are shown in Figure 16.17: a steel outer drum with an inner container, a concrete and steel cask, and a massive tran spon container shielded with lead.

FIGURE 16.16 These typ1calformsoftypeA packag ,n g ha~e been shown1ow1thstandcer• ta1n DOT test procedures thatwered~1gned10 mamta rnthe 1n tegntyof contammemandsh1eld- 1ng undertli e norma!con• d•Mns of transport

Package must withstand normal conditions of transport only without loss or dispersal of the radioacti ve control contents.

DOT Specification fiberboard box

DOT Specification wooden box

Ii DOT Spocirlcation

steel drum

DOT Spocification typaApack89~

722 Chapter 16 Radioactive Materials

Packoge muSt stand both normal and acc ident test cond,t,ons w,thout loss of contents.

Exterior grade 3/4 in. Doug la s fir plywood

iJ 18 gauge steel drum or outer cover

\,,..,,,..--,= .... Inner

Stee l outer drum , shielded lnnerconta iner,

the rmal insulation between containers

31n. min imum all around

cop & bottom

Lag screws

Rods

FIG URE 16. 17 These typical forms of type 8 packag ing have been shown to withstand certain DOT test procedures that were des ,gned 10 rra1 n1a1n the integri ty of conta1nrnent and shie ld :ng under normal cond1t1orn of transport and the damag,ng cond itions of a transportatton awd~nt

When shippers offer a radioactive material for transportation, DOT requires them to selm a rype A or type B package based in part on the magnitude of rwo activity val ues, c.1 ll cd A1 and A2 ,

A1 is the maximum activity of a specia l-form class 7 ma1erial permitted in a type A package. A special form class 7 material refers to an indispersible solid radioactive mate- ria l that is ci1her a si ngle solid piece or a scaled capsule, at least one dimension of which is not less than 0.2 inch (5 mm), and in the case of th e capsule, contains radioactive material tha t may be opened only by dcstro)·i ng it. A radioactive ma1erial that is not a special-form elm 7 material is a normal form class 7 material, or nonspecial form class 7 material.

A2 is the maximum activiry of a class 7 material, other th an a specia l-form cla ss 7 mate ri al, LSA, or SCO, that is permitted for transportation within a type A package.

DOT publishes the A 1 and A2 values at 49 C.F.R. S 173.435, some excerpts of which are provided for several radioisotopes in Table 16.10.

ihjjj/Ji,i A1 and Ai Values fo r Some Selected Rad101sotopes41 ., ., SPECIFIC ACTIVITY RADIOISOTOPE TBq Cl TBq Ci TBq/g Cl/g

Bismuth-207 0.7 19 0.7 19 1.9 52

Cobalt•60 0.4 11 0.4 11 42 ,,oo

Cesiu m•137 2 54 0.6 16 l .2 87

Molybdenum•99 1.0 2.7 0.74 11 20' 1.8 x 104 4.8 x 105

Potass iu m-40 0.9 24 0.9 14 2.4 >< 10- 7 6.4 X 10-fi

I _,. EMcerptt d from 49 C.F.R. §lJ 3_4 35 and 10 C.f.R. Pan 71 , Apptnd1x. A. Tab e A boomenlcu$eOnly.

A, • For purposes of DOT regulations, the maximum activity of speci,11 form class 7 (rad ioactive) mater ial perm itted in a type A package

A2 For purposes of DOT regulat ions, the maximum activity of class 7 (radioactive) material, other th<1n specialformcl<1ss7 materi,11, LSA, andSCO, that is permitted in a type A package

speci al form cl ass 7 ma te ri al For purposes of DOT regulations, an indispersible, solid rad ioactive material that is either a single solid piece or a sealed capsule, at least one dimension of which is not less than 0.2 inch (S mm), and in the case of the capsule, contains rad ioactive material that can be opened only by destroying it

Chapter 16 Radioactive Materials 723

SOLVED EXERCISE 16.6

norm al fo rm d au 7 ma t eria l (no nspecia l form class 7 mate ria l)

For purp oses of DOT reg ulat ions, rad i oactive m ateri al that does not sat isfy th e definiti on of a special-form class 7 m ater ia l

.l. st- poer o•re~ for oomest·c iranspon at ,on a t} pe A package weigh ng 65 pounds (29 s kg) and ,. 13gged ,-0 ybdenum d ox.de having an act1v1ty o.f 2 9 TBQ The use of rad,at1on detection equ Prn;~nta n~g

a ma~ mum rad,at,on level or O 005 mS~/hr on tne su rrace of 1he pacl:age and a rad,at1on level of O OOo I r~"'" 1

a: 3 3 fee-1 (1 m) from ine s,.,rface What 1s the sh,ppmg descri ptJO n of this rad1oact1ve mate rial and 2 rn s~hii- /abeiS, mar ~•ngs anc placards, rf any, are requ11 ed when the package 1s transpon ed by means 0·, a rn; h,ch Dor on pub c n1ghways' Of veheft

Solution: It 1s first appropnate to de termin e th e transport index We ca lcula te 11 as 0 0002 Sv/hr x 1 oO td1m ens on1ess) Footnot e "b~ to Table 16 8 md·cates th at th,s calculated va 'ue may be token as O T · or 0 02 revt.>aJs that a max.mum surface rad•at1on le~·e/ of O 005 mSv/hr and a transport index of o require the ~ble 168 aff..x RADIOACTIVE WHITE-r labels on two oppo ~te sides other than the bottom of the packag e The s ~Poei to ence t o At,pendx c, Table 16 6, an d Se ction 16 10-A, the sh,pper prepares the following shipping de~ n ~tfei. enter on the accompanymg sh1pp1n g paper P Of1 !o

SHIPPING DESCRIPTION (IDENTIFICATION NUMBER, PROPER

SHIPPING NAME, PRIMARY HAZARD CLASS OR DIVISION, SUBSIDIARY HAZARD CLASS I ACTIV ITY

___ UN_ I_TS __ - H_ M_, __ O_R DIVISION, AND PACKING GRO _UP_l _/s-_..c(Tc:.Bq,:__) 1 steel drum we ,gh1ng UN 29 15. Radioacti ve material. Type A 2 9 65 lb (UN1A2 ) packa ge, 7 (Mofybden um -99, tagged In

so li d molybden um dioxide) (RAD IOACTIVE WHITE-I I.abel)

Fro m Tab1e 16 7, we determ ine that the sh pper Is not requ ired to enter t he letters RO In the sh ippin g descnptron since th e repo rtabl e q uan ti t y for molybde num -99 ,s 3 7 terabecque rels Then , fo ll ow in g infor mai ion

1 ~

Secti on 16 10-C, th e shipper ma rk s the packag e wi th the name and addr ess of th e sh ipper and receim the des1gna t1 on #Rad,oact 1ve ma1e r1 al, no s , H Type A pack ag e, an d the 1dent,f1c at1on number UN2 9JS , Becaus e th e pad age we ig hs less than 11 0 po un ds ( 50 kg), DOT does not req uiie th e sh ipper t o mark the wei g ht o n th e pac kage W hen DOT req ui res RAD IOACTIVE WHITE-I lab els to be affixed to the pac kag ,ng, th e ca m er 1s not ob li gated to p lacard the m otor ve h,cle used to tra nsp ort th e package

DOT uses A 1 and A 1 va lu es to define rype A and rype B packages. These dcfini!ions are paraphrased as follow s:

A "' rype A package" refers to a package designed to rran sporr an A 1 or A2 quami ry of radioactive marerial, as appropriare. T he purpose of rh e de sign is ro retain rh e im e-g - riry of conrainmenr and s rue/ding when subjected to normal conditions of transport. A ~ry pe B package" refers ro a package designed ro transport greater than an A1 or A2 quantiry of radioactive material, as appropriate. Th e purpose of rhe design is to rerain rh e integrity of con tainment and shielding when s ubjected to normal con di - tions of transpo rt and DOE-prescribed hypothetical accident-test conditions. A "' type B(U) package "' refers to a rype B package that together with its radioa cti\·e- conrents for internationa l shipment require s unilateral approval only of rhe package- design and of any sto wage provisions that may be neces sary for hear dissipation. A " type B(M ) .. package refers ro a type B package that rogerher wirh its radioacr_J ve conrents for international shipmenr requires unilateral approva l of rhe package design and ma y require approva l of the conditions of shipm ent. A type B(M ) package ha ~a maximum normal operating press ure of more than 100 psig (700 kPa/cm 2) or a relid de vice th at allows rhe release of class 7 radioa c tive material into the environme- nr under accident conditions.

When expo rring fissil e material, shippers a re required ro use th e package typts d~s;r: na ted as AF, B(UJF, a nd B(M )E These package rypes ha ve been design ed to meet especil } sr ringenr DOE criteria fo r s hipping fissile materi a l.

724 Chapter 16 Radioacti ve Materia ls

16,10-F CRITICALITY SAFETY INDEX >. !rhotigh D~)T and N RC r~quir_e th e use of th e cri ticality sa fety index for several pur- ~oses, 1he prima r}i ere 15 its use in connec ti on w1th th e rransporration of fi ssile 111 .i!crial. A_h~oug

1 • a rs th e res ponsibility of iss uing gene ra l licenses ro tho se who rr:i 11 sport fiss il e marrn _al, ~OT promulgates the regulatio ns ro which the licen sees musr adhe re whe n rrans_porung n.

As noted ea rli er, one DOT reg ulat ion is rhe requirem ent 10 inscribe the criticaliry s;1fer y index on .the FISSI~~ la~els that are affixed to opposite sides of packages co nra in- inS fiss ile material. The crit,cahty safety Index, or CSI, is a dimensionl ess number used to de-signa te th e d~gree_ 0 ~ control _over the accumulation of packages, ove rp:icks, or freight ,ontainers holding fissile material during th eir rr:in sporrarion. Shippers calculate th e CST using formulas a nd tables ~ublished at 10 C.F.R. SS 71.22 , 71.23 and 7 1.59.

DOT and reg~la_t10n s ar 10 C.ER. S7 I .59 requi re a shipper or carrier to con tr o l a package contammg fis~de material to assure that an array of such packages remains ,ubcritical. To ~nab!~ this control, the designer of th e package derives :i number .. N" based on the sansfac~1on of each of the following conditions, ass uming that the packages are stacked together m an y arrangement and with close full reflection on a ll sides of th e srnck by water:

Five rimes "N" undam aged packages with nothing betwee n them is subc ritical Two rimes "N"' damaged packages, if each package is subjected to hyporhe1ical acci- denl condirions specified at 10 C.F.R. S]I.73

1 The va lue of "N" cannot be less than 0.5

The CSI is determined by dividing th e- number 50 by the value of "N .. tha1 has been derived using th ese conditions. The value of rhe CSI may be zero provided that an unlim - ited number of packages are subcrirical, such that th e va lue of "N" is effectively equal to infi nity.

When a package containing fissile marerial is assigned a CSI value less than or equal ro 50, the package may be shipped in a non-exclusive-use conveyance, provided th a t rh e sum of the CS is is limited to le ss th an or eq ual co 50; or the package ma y be shipped in an ex clusive-use conveyance provided chat th e su m of the CSis is eq ua l to or less than 100. \'(1he- n rhe package containing fissile material is assigned a CS! va lue greater than 50, the package must be shipped by a carrier in an exclusive-use conveyance, pro vi ded char the sum of the CS!s is equal to or less rhan 100.

16. 10-G HIGHWAY ROUTE-CONTROLLED QUANTITY Un der ce rtain uniqu e circumstances, DOT allows carriers to transport a specified amo~nr of a radioactive material by a special route. Ir is called a highway route-<ontrolled quantity, or HRCQ. DOT defines HRCQ as 3000 times the A1 va lue for special-form cla ss 7 mate- ria l, 3000 tim es the A1 va lue for normal form class 7 rad ioac ti ve material, or 1000 TBq (27,000 Ci ), whichev er is less. _ .

When carriers intend to rransport a high w:iy route-controlled quantity of a radioac• ure material , DOT requires them ro ensure that the public's ri sk ~f ~adiation ex~osure is eliminat ed or minimized, by considering accident rar es, rhe ~rans1t ~,me, populauon d~n- Sit)•, anticipated activ ities, and the time of da)' and week_ dun_ng wh1ch_the transportation occu rs. DOT then directs rhe carrier to transport the rad10acuve marer.1al on the _Preferred route, or referred hi ghway (Section 15.4-F), DOT permits rhe earner to de~1.at e from using the preferred route or preferred highwa y only under em:rgency condmons that would mafe co ntinued use of the preferred route or preferred highwa y unsafe or, when

ne-ce~;~ry, to s t_op for : .sr, fu~I; 0 ~::~i;~:[ee:r:t~~ute or preferred highway, DOT require s h

en earners are arectVe E ol ds within squares ha ving a white background and

cri tica lity safety Ind ex (CSI) For purposes of DOT and NRC regula - t i ons, a d imens ionless number used to pro- vide control over the accumulation of pack- ages, overpacks, or freight conta iners hold - in g fissile materi al dur- ing the i r transportation

h i ghway r ou t e- con trolled q uanti ty ( HRCQ) For purposes of DOT reg ulalions, the least of th e follow ing amounu: 3000 t imes the A, value for a spec lal-formdass 7 (rad i oacti ve) materia l; 3000 times the A2 vatue for a norm al form class 7 material; or 1000 TBq (27,000 Ci)

r em to post RADIOACTI p acar Chapter 16 Radioactive Materials 725

invers e squ.i re J.i w of radiatio n • The obser- vation that the inten- sity of ra diat ion decreases as the inve rse squa re of the distance from its source increa ses

:1 bl.1ck bordu on ('.1ch sid e and c.1ch ('nd of the mo1or vehicle. The r .os1ing of thcse I .irds wirhm th e wh itt· squares sen t·s to designa te th ~H DOT has autho ri zed the ship rne~t;· a prefo rred ro urc. Y

When carriers tr:m spo rr a hig hwa y route-controlled quantity of a radioactiv rial in a motor vehicle,. freigh t container, o r ra ilca r, DOT als<:> requires r~ em to ;r:r: and implement a secu ri ty plan whose co mpon en ts comply wnh the requirements f C.F. R. S 172.801 . Motor ca rr ie rs are a_lso req_uired to obta in a haza rdo us materials :ft permit (Section 6. 1 OJ before t ranspomng a ~1ghw~y route-c ont r~ll ed quantity of a radiz acti ve m:nerial. Jssuan~e of ~he sa fety p~rmn requires motor ea rn ers to prepa re a wrinen route plan that complies wnh th e reqmrements of 49 C.F.R. §397. 101. Motor ca rriers ma r also be subject to other specia l cont rol s.

16. 11 RESPONDING TO INCIDENTS INVOLVING A RELEASE OF RADIOACTIVE MATERIALS

Whe n radiati on so urc es are loca ted nearby, gove r~m enr regulations require the autho- rized regulator y body to war n in di vi dual s of th eir presence. For example, NRC and OSHA requ ire the posting of the signs previousl y noted in Figure 16.9 in the workplace to warn employees that exposure to radia ti o n is likely. Emergency res ponders are also \varned of the prese nce of rad iatio n so urces when the y encounte r these signs .

A radioactive material ma y a lso be encountered at the scenes of cransporration mis- haps. Its presence is rapidl y verified by o bserving the following:

The number 7 as a co mpon ent of a shipping desc ription o f a ha za rdous material on a shipping paper The word RADIOACTIVE and th e numb er 7 o n yellow-and-white labels or the word FISSILE and th e n umbe r 7 on white-an d -black label s affixed to packages The word RADIOACTIVE a nd the numb er 7 on re llo w-a nd -w hit e placards posted on the rel e\'ant transport vehicl e

Once rhe presence of a radioacti ve ma teria l h;1 s been ve rified , how may responders protect th emselves from undu e ex pos ure to ionizing radiation? The answer to this ques• tio n requires the implementation o f three basic principles: shi elding, tim e, and distance.

Because moving behind a barrier or other s hield ma y be impractical during an emer· gency response action, th e best means of personal protectio n for responders is to limit th e rime of exposure and ro mainta in a position as far removed from the source as pracrica l so as to receive rhe min imum radi atio n dose.

Emergency re sponders may app reciate the impo rta nce of separa ti o n from a radioac· ri ve so urce by n oting the inverse square law of radiation. T hi s law is a rithm etically expressed as fo ll ows:

I =!.£_ ,., 1? th is equa tion, lo is th e original intensity of a ,;sma ll " radiation so urc e, and/ is th e inten- siry at a di sranc: r. Jc s umm ari zes the obse rva ti o n chat th e inten si ty of ionizing radiat~on dec~ease_s as the mverse square of the di stan ce from th e source increases. For exa mple, i( a rad1oacuve ma terial regist ers l000 co unr s/min on a Geige r counter held 1 foot (OJ ni) from a so urce, th e co unter will regis ter o nl y 250 co unc s/min when it is held 2 fe et (0.6 m)

726 Chapter 16 Ra d ioactive Materials

fr oJTl 1he source. Hence, _do.ubl ing th e di stan ce between a n ind ividual a nd th e so urce of rJdi;.1t ion rcduc_es th e radia no n exposu re. ro_ o n~-fo urth th e o rigina l valu e.

Use of 1hc in verse squa re la w of rad1at1on 1s limited to radi,u io n meas urements from :i :; ma ll so urce : The cl ~sest ~easurement mu st be a dista nce equal 1o or greater 1ha n th_ree tuiies the rn axnn um ~•mens1on o f th e so urce. The law ca nn ot be used w hen th e radi a 11on 15

sp rea d over a _relat_1ve ly larg~ area. When a ra d1 oa~uv: mate~1al has spilled, or when rhe package used for con tainment of

:i r:1di oac1iv e matenal 1~ lea king or damaged, emerge ncy responde rs sho uld consider pro· dure s co protect public health and the environment. Because special training in the ha n·

~~ing of radio~c_ti ve ~atcrial s is essential, the regi o nal offices of DOE's Na tional N uc.l~a t security Adm1~1.stratton (N NSA J_ or the appropriate sta re or local radio logica l autho_n11es hould be noufi cd when there 1s a need for an eme rgency res ponse effort involvmg a

;adioaccive material. ~NSA is prcp~red to res pond to any type of ra diologica l acci dent or te rroris t eve nt occurring anywhere m the world.

When firefighters and other emergency responders a rc called to suc h incidems, ca re should be exerci sed to avoid possible inhalation, ingestion, or contact w ith ra d ioacti~c rn:irerials. Loose radioactive material and its associated package sho uld be segrega ted m an area pending disposal instructions from EPA or res ponsi ble radiologica l authorities. If 3 fire is ongoing, it s hould be extinguished only from a distanc e that is considered suitable for protec ti o n of personnel. All appropriate meas ures should be exe rci sed to p reve nt the spread of radioactivity by minimi zing the quantity of run off wa ter.

16.12 RESIDENTIAL RADON Radioisotopes of radium continuously form dur ing the decay of na turall y occurring ura - ni um and thorium radioi soto pes. The y form in geologic areas where uranium a nd tho- rium are componentS of met a l-bea ring ores, granite, or bl ac k sh a le . For exn mple, radiu m-220 forms when the naturall y occ urring thorium -232 in a met a l-bea ring ore drcay s by th e following se ries of steps:

2JJTh - 1J3 R:1 - 2ij, Ac --+ !i~ Th - 1t; R:1 _____,,. 2j2Rn Althoug h geologic formations containing uranium and thorium arc relativel y uncom-

mon, 1hey do exis t below Earth's upper stratum in specific areas of th e world. In the Uni1ed States, the hi~ hest radon levels appear to occur along a geologic formation called rhe Reading Prong, 1 which exists across so utheas1ern Pennsy lvani a into north ern New Jersey and New York.

Buried deep beneath Earth's surface, 1he prese nce of radium radio isoto pes prese nts lit tle problem. However, th e decay of some radium radioisotopes produces th e colorless, odo rless noble gas radon, as illustrated b)' th e deca)' of radium-226.

2ijj Ra ---"' 2li Rn + o: Thus formed , radon slowly percolates upwa rd through ch_e rock and s~il a nd enters th e atm os phere, w here it di ss ipat es. The average atmospheric concentrauon of the radon radioi so topes is 0.4 pCi/L. ..

In the base mem of homes, radon may find its way through m?rtar Jo me s, th e crac ks in foundation floors , gaps betw een wall-10-wa ll _joi_nts, and pores m c~ncrete block ~ an~ 01her building ma terials. Radon also dissolves w1chm groundwater aquifers from which 11 may enter a ho me vi a the water supply and open sump pum ps. . . .

The radon char emers a dwelling is cal.led residential radon. It c~ns1sts pmnan_l),' of ra don-220 and radon-222, w hich have half-lives of 54.5 seconds and 3.8- da ys, respecrnely.

11 Thoma s M . Gerusky, " Th e r ennsy!vania Radon Story" (Pennsylvan ia Depa rt ment of Envi ronmental Prorrc1ion, 20 12).

res id ential radon • Th e radon that accumulates with in a dwelling from the decay of naturally occurring uranium and thor ium rad io isotopes

Chapter 16 Radioactive Materials 727

728

FIGURE 16. 18 Th€ so:< nostcormonrot.res:y wn -<h raoon i.'ntersa home (TJan open suMp pump, m the gaps betwet>n basi.'mem wa f. to,.,.va:t1oints; (3 ) rl'!e foundanon cra<XS 1n di e basi.'mem floor,(a!)tl- i.' oores 1n concre:e O:oc\s ~nc mor.arJOJ"lts , a,id(5 ) t.'lttresce n:iaJwater s.ro:, 'y

Each undergoes alpha decay. The producrs resulting from the decay are polonium radioiso- ropes, which also undergo alpha decay. The average year-round residential-radon concenrra- rion is approximately 1.3 pCi/L

Within rhe building shown in Figure 16.18, there is lirtle exchange between the inside and outside air. Under this condition, the residential -radon concentration may become so high thar irs presence poses an inhalation hea lth hazard. This is an especiall y serious siru- atio~ because there is compelling evidence, based primarily on studies of uran ium minm, showing that exposure ro radon causes lu ng cancer by mutating the genes of normal cells.

The risk of contracting cancer from exposure ro radon is proportional to the amount rhat emers a home and rhe length of time it remains within li ving areas. The majority of rad?~ rhar is inhaled is exha led back co the atmosphere immediately, but because the radon radioisotopes have short half-lives, some radon decays before it is exhaled. The polonium by-products rh.e~ lodge within lung tissue and radiate the nearby cells with alpha particles, The radon rad101sotopes ma y also decay in rhe air, whereupon the polonium radioisoropes adhere ro dust panic/es. Individuals are exposed to them when the dust is inhaled.

_ Se\•~ral rypes of radiarion derectors are designed ro determine the concentration of ~esident1al radon. Some are available for sale in hardware stores. The types used in dwell· mg~ and occuparional settings collect radon decay products on an air filter or charcoal camster for a pre-established rime. Then, rhe filter or canister is mai led ro a radiation laboratory where it is analyzed for its radiation content.

Be~ause the inha lation of radon has been shown to cause Jung cancer in humans, ra~on is denoted as a known human carcinogen. The specific radioisotopes radon-220 an radon-l22, ~re also denoted as human ca rcinogens. Radium-224, -226, a'nd -228 are also human carcmogens . _ The risk of developing lung cancer from exposure to a radon-enriched atmosphere is exacerbated for individuals who are smo kers; rhar is, in combination, radon and th e

Chapter 16 Radioactive Materials

-:i rc inogenic co mpo1~e_nts of tobacco smoke act synergistically. Smoking increases an indi - :id u:il's ri sk of acql~mng cancer from radon exposure by as much as 15 times. ~xposu re ro rJdon is rh ~ lead mg cause of lun~ cancer i~ nonsmokers and ,he second leading cause over.ill. Smoking tobacco products 1s the lead ing cause of lung cancer.

Ir is appa rent that to reduce the num ber of radon-induced deaths due 10 lung cancer, h levds of residential radon musr be minimized or eliminated within dwellings. EPA

1 t: mmends that home occupants use a concentration of 4 pCi per liter of air (4 pCi/L ) as

rccoccio n guideline. The World Health Organization's action guideline is set at 2.7 pCi/L. ~~on lev el s may be .reduced in ho~es by .sea ling base ment floors, increasing the air fl?w ·

ihroughour a residence by opemng windows and using fans, and when the dwellmgs :~.ea crawl space, keeping the venrs in 1his area open throughout rhe yea r. 1:he i!n~le-

rn ration of these measures assures the occupants that the radon concentration ms1de ~eir homes is no higher than that of the ambient air outside. r In the late 1990s, scientific re sea rchers 12 esrimated that residential-radon exp°.sur.e c;1uses 15,400 ro 21,800 cases of lung cancer each year. They also es_r i~ate~ that 260 md1 4 viduals die each year from the exposure to household wa1er conrammg dissolve~ rad~n. Approximately o~e-third of these incidents could have been pr~vente~ if .the res1dennal- r3don concentrauon had been reduced to a level below EPA's action gu1delme.

16.13 RADIOLOGICAL DISPERSAL DEVICE A dirty bomb may be regarded as any com,entional explosive dev_ice ~harged with a haz- ;1 rdous material that disperses into the environment as the explosive 1s deto~ated. In t~e- ory, the hazardous materia l could be a poisonou s gas, flammabl~ materi:11, co~r~s1ve materia l, biologica l or chemical warfare agent, or radioactive material. However, It IS by the widespread dissemination of a radioacti\'e ma1eria l 1har terrorists instill the highest degree of fear, massive panic, and chaos in. th.e affected popula~ion b~ca~se of misinto~ma- uon rega rding the basic principles of radiation exposure. This .devic.e 1s c?aractensc~c ~f the radiological dirty bomb. The threat of involvement in a rad1olog1cal 4 d1rty-bo.mb mc1- denr is highest in densely populated areas, such as during a sports event at which large numbers of people congregate. . . _

When a radiological dirty bomb is initially activated, the immed,a~e area of the mc~ - dem becomes contaminated with one or more radioisotopes. This area ttself could consti- tute :1 siza ble swath of land that would remain uninhabitable for years. Following th e dispersa l of radioact ive material by explosive action, the radioisotopes the~ cou~d diff~se throughout the air, where currents could carry chem to far.4 removed lo~atlo~s mclud1~g meet canyons, subway runnels, and inside buildings. In tlm.c, th ~ rad~oacnve m~tenal could even disperse worldwide. It is for this reason that a rad1olog1cal dirty bomb 1s also ca lled :1 radiological dispersal device . . .

The detonation of a radiologica l dispersal device could never produce the immediate mass casualties o r devastation that we associate with the detonation of nuclear weapons. Nonetheless th e level of radiarion cou ld induce regulatory agencies to cordon off sections of entire citi~s for long periods. . . . _ .

Experts fear that terrorists are most likely ro load a rad101sotope l!Sted m Table ~6_-11 into a radiological dispersal dev ice. These choices r.epres~nt the mosr co.rnm~n rad1.01s0• rop es used in industria l and medical settings. Also listed m Ta?le 16.1.1 1s a .quanmy of concern" for each radioisotope. Ir represents the activiry in curies th~t 1s wom~omc when rhe rad ioisorope is encounrered because the activi~ poses a hea lth nsk.1:hc third column in Table 16.11 provides the threshold concenrrat1?n nc~ded to contarr~mate 0.4 sq uare miles ( 1 km2 ). It is the activity of the radioisotope m CLmes that contammates th e area 10

11 Nariona! Academy of Scie nces , Biological Effuts of Jo11 i:i11g R11d1a11 011 VI (BEIR VIJ Report (Wa shin gton , DC: NJtion,11 Aca demic§ rre~s. !998 ).

d irty bo mb • A clandes- tine explosive dev ice charged with a radioac- tive or other hazardous material that is d issem i- nated into the environ- ment as the bomb detonates

ra dio log lca l d isp@rsa l d@vic@ • Any unconven • tiona l weapon used to deliberately d isperse radioact ive material in the environment to create terror or inf lict harm

Chapter 16 Radioactive Mate rials 729

r Fl+iiiiiii RADIOISOTOPE

Amencium-241

Ca liforn ium -252

Radioisot o p es M ost Li kel y t o aBe U sed b y Terrorists in a Rad1ol og1cal Dispersal Device

QUANTITY OF THRESHOLD (Ci) TO I CONCERN (Ci) CONTAMINATE 0.4 mi2 (1 kml) I 16.22 78 --I 5.41 4 9

----+- Ces ium -137

Coba lt-60

Cur ium -244

Gadolin ium -153

lndium -192

Pluton ium-238

Prometh ium -147

Rad ium -226

Selenium -75

Stront ium -90

Thul ium-1 70

Ytterb ium- 169

I I ' I I

2703 42

811 11

13.51 130

== 270 . 17 390 2162 100 16.22 220 10,810.81 410

10.81 ' 13 54.05 150

270.27 200

5405.41 2000

81 08 600

' Ada pted from Jon athan Meda Ila, " 'Dirty bombs'; Tech mcal backgrou nd. atta ck pr evention, and rfiponse, IS!uti fo r Co ng res5," Congression al Research Service, DRS Repo rt R41890 (June 24, 2011 ),

a level that a person living within it for a year wo uld receive a dose of 2 rem during the first year after the arrack. EPA and FEMA use this threshold as a protective action guide for relocation because personal damage from the radiation exposure is likely.

For illustrative purposes, suppose terrori sts load cesium chloride powder tagged with the radioisotope cesium-137 into a device. Because 1he powder is used as a scaled source to irradiate food, it is reasonably accessible to anyone. If terrorists load the cesi um chlo• ride into a bomb that is subsequentl y detonated, the ccsium-137 would readil y disperse into the immediate environment as a powder. Any cesium-137 activity equal to or greater than 27.03 Ci is considered a quantity of concern. The threshold concentration th:lt ca n po tentiall y contaminate an area of 0.4 square miles (1 km2) is 42 Ci. Any ccsi um-137 activity equal to or greater than this concentration causes EPA and FEMA to require the residents living in the contaminated area to relocate elsewhere.

Whar may an emergency response team do 10 best serve the public when terrorists have detonated a radiological dispersal device? The three basic tenets associated with radiation protection-shielding, rime, and distance--<ome into play when answering this qu estion. Tran slated into action, this means that the affected population should _be removed as quickl y as feasible from the areas where the concentrations of radioaCtll'C material arc hi ghesr. These individual s may then seek out official protective information from local radio and television broadcasts.

~PA _ ha s is~ ued protective-action guidelines for the personnel who respond to emer· genci es mvolv'.ng the activation of a radiologica l dispersal device. 13 Not only_ muS! resp~nders decide how to accomplish an action, they must also acknowledge that 1mple· mentmg a response action in volving radiation exposure cou ld jeopardize thei r own healr h.

11 Ma nu3 I of Pro trcti11e-Acu on Guides and Protrc t11·e Actions fo r Nuclea r Inci de nts {W:i shington, DC: U.S. 1:n,,.

ronmental Protrcrion Agency, ,\fa r 1992 ), EPA -400-R-92 -001; Fedrral Register 71 Uanuary 3, 20 06): 17,-96· 730 Chapter 16 Rad ioactive Materials

Th e adver se health effects that potentiaUy res ult from radiation exposure were previousl y , ,ted in Tables 1_6.3 an_d 16.4.' .

The protect1ve-act1on gu1dchncs arc based on th e nature of acti vities to be conducted at a site that is contaminated with various levels of radiation. They may be paraphrased as follow s:

When the prevailing radiation level is equal to or less than 5 rem, emergency respond- ers may initiate operations in a normal fa shion. When the radiation level ranges from 5 to 10 rem, careful consideration must be given to the relative importance of implementing response actions at once or waiting until the radiation level has subsided. Will multiple Lives be saved, or will large popu- lation s be protected only if the actions are conducted at once?

1 When the radiation level ranges from 10 to 25 rem, emergency responders are at risk of severe personal damage from radiation exposure, especially when executing the response action requires exposure over a significant time. Once again, the unique conditions of the incident at hand must be evaluated to decide whether the responders arc likely to immediately save multiple lives or protect large populations. When the level exceeds 25 rem, EPA recommends the use of robotic equipment to the maximum extent feasible. The use of robotic equipment minimizes the radiation- exposure period that ordinarily would be experienced by the emergency responders. This could prevent the onset of radiation sickness.

Chapter 16 Radioactive Materials 7 3 1