Nontraditional and Nuclear Energy Solutions

Botkin, Daniel B. Environmental Science: Earth as a Living Planet, 9th Edition. Wiley, 2013-12-23.

17.1 Current role of Nuclear power plants in World Energy production

Today, nuclear power provides about 14% of the world’s electricity and 4.8% of the world’s total energy. In the United States, 104 nuclear power plants produce about 20% of the country’s electricity and about 8% of the total energy used. Worldwide, there are 435 operating nuclear power plants.4,5 Nations differ greatly in the amount of energy they obtain from these plants. France ranks first, with about 78% of its electricity produced by nuclear en- ergy. The United States ranks seventeenth in the percent- age of electricity it obtains from nuclear power plants, but is the world leader in total energy produced from nuclear power (Figure 17.3). The United States produces more than 30% of the nuclear power produced in the world today.4,5

Most of the world’s nuclear power plants are in North America, western Europe, Russia, China, and India. Most of the U.S. nuclear power plants are in the eastern half of the nation. The very few west of the Mississippi River are in Washington, California, Arizona, Nebraska, Kansas, and Texas. The last nuclear plant to be completed in the United States went online in 1996. In 2012 two new reac- tors in Georgia at an existing site (Vogtle) were approved to begin construction. Worldwide, 65 new reactors were

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being constructed in 2012. China is the leader with 26, followed by Russia with 10, and India with 7.6

17.2 What Is Nuclear Energy?

Hard as it may be to believe, nuclear energy is the energy contained in an atom’s nucleus. Two nuclear processes can be used to release that energy to do work: fission and fu- sion. Nuclear fission is the splitting of atomic nuclei, and nuclear fusion is the fusing, or combining, of atomic nu- clei. A by-product of both fission and fusion is the release of enormous amounts of energy. (Radiation and related terms are explained in A Closer Look 17.1. You may also wish to review the discussion of matter and energy in Chapter 14’s A Closer Look 14.1.) (Note that at this time no fusion power reactor exists; research to develop such a power plant, which started in the middle of the twentieth century, continues—so far without success.)

Nuclear energy for commercial use is produced by splitting atoms in nuclear reactors, which are devices that produce controlled nuclear fission. In the United States, almost all of these reactors use a form of uranium oxide as fuel. Despite decades of research to try to develop it, nuclear fusion remains only a theoretical possibility.

Conventional Nuclear Reactors

The first human-controlled nuclear fission, demonstrated in 1942 by Italian physicist Enrico Fermi at the University of Chicago, led to the development of power plants that could use nuclear energy to produce electricity. Today, in addition to power plants to supply electricity for homes and industry, nuclear reactors power submarines, aircraft carriers, and icebreaker ships.

Nuclear fission produces much more energy per ki- logram of fuel than other fuel-requiring sources, such as biomass and fossil fuels. For example, 1 kg (2.2 lb) of ura- nium oxide produces about the same amount of heat as 16 metric tons of coal.

Three types—isotopes—of uranium occur in nature: uranium-238, which accounts for approximately 99.3% of all natural uranium; uranium-235, which makes up about 0.7%; and uranium-234, about 0.005%. However, uranium-235 is the only naturally occurring fissionable (or fissile) material and is therefore essential to the pro- duction of nuclear energy. A process called enrichment increases the concentration of uranium-235 from 0.7% to about 3%. This enriched uranium is used as fuel.

The spontaneous decay of uranium atoms emits neutrons. Fission reactors split uranium-235 by neutron bombardment. This releases more neutrons than it took to create the first splitting (Figure 17.4). These released neutrons strike other uranium-235 atoms, releasing still more neutrons, other kinds of radiation, fission products, and heat. This is the “chain reaction” that is so famous, both for nuclear power plants and nuclear bombs—as the process continues, more and more uranium is split, releas- ing more neutrons and more heat. The neutrons released are fast moving and must be slowed down slightly (mod- erated) to increase the probability of fission.

All nuclear power plants use coolants to remove ex- cess heat produced by the fission reaction. The rate of gen- eration of heat in the fuel must match the rate at which heat is carried away by the coolant. Major nuclear acci- dents have occurred when something went wrong5 with the balance and heat built up in the reactor core. The well-known term meltdown refers to a nuclear accident in which the coolant system fails, allowing the nuclear fuel to become so hot that it forms a molten mass that breaches the containment of the reactor and contaminates the outside environment with radioactivity.

The nuclear steam supply system includes heat ex- changers (which extract heat produced by fission) and primary coolant loops and pumps (which circulate the coolant through the reactor). The heat is used to boil wa- ter, releasing steam that runs conventional steam-turbine electrical generators (Figure 17.5). In most common reac- tors, ordinary water is used as the coolant as well as the moderator. Reactors that use ordinary water are called “light water reactors” because there is also “heavy water,” which combines deuterium with oxygen.6

Most reactors now in use consume more fissionable material than they produce and are known as burner reactors. Figure 17.6 shows the main components of a reactor: the core (consisting of fuel and moderator), con- trol rods, coolant, and reactor vessel. The core is enclosed in the heavy, stainless steel reactor vessel; then, for safety and security, the entire reactor is contained in a reinforced concrete building.

In the reactor core, fuel pins—enriched uranium (uranium dioxide)—are fabricated into strong ceramic pellets capable of withstanding operating temperatures and intense radiation in the reactor. Pellets are loaded into hollow tubes (3–4 m long and less than 1 cm, or 0.4 in., in diameter). These tubes are packed together (40,000 or more in a reactor) in fuel subassemblies. A minimum fuel concentration is necessary to keep the reactor critical— that is, to achieve a self-sustaining chain reaction. A stable fission chain reaction in the core is maintained by control- ling the number of neutrons that cause fission. Control rods, which contain materials that capture neutrons, are used to regulate the chain reaction. As the control rods are moved out of the core, the chain reaction increases; as they are moved into the core, the reaction slows. Full insertion7of the control rods into the core stops the fission reaction.

You may recall from Chapter 7 that isotopes are at- oms of an element that have the same atomic number (the number of protons in the nucleus) but that vary in atomic mass number (the number of protons plus neutrons in the nucleus). For example, two isotopes of uranium are 235U92 and 238U92. The atomic number for both isotopes of ura- nium is 92 (revisit A Closer Look 7.1); however, the atomic mass numbers are 235 and 238. The two different uranium isotopes may be written as uranium-235 and uranium-238 or 235U and 238U, respectively.

An important characteristic of a radioisotope is its half-life, the time required for one-half of a given amount of the isotope to decay to another form. Uranium-235 has a half-life of 700 million years, a very long time indeed! Ra- dioactive carbon-14 has a half-life of 5,570 years, which is in the intermediate range, and radon-222 has a relatively short half-life of 3.8 days. Other radioactive isotopes have even shorter half-lives; for example, polonium-218 has a half-life of about 3 minutes, and still others have half-lives as short as a fraction of a second.

There are three major kinds of nuclear radiation: alpha particles, beta particles, and gamma rays. An alpha particle consists of two protons and two neutrons (a helium nucleus) and has the greatest mass of the three types of radiation (Figure 17.7a). Because alpha particles have a relatively high mass, they do not travel far. In air, alpha particles can travel approximately 5–8 cm (about 2–3 in.) before they stop. However, in living tissue, which is much denser than air, they can travel only about 0.005–0.008 cm (0.002–0.003 in.). Because this is a very short distance, they can’t cause dam- age to living cells unless they originate very close to the cells. Also, alpha particles can be stopped by a sheet or so of paper.

Beta particles are electrons and have a mass of 1/1,840 of a proton. Beta decay occurs when one of the protons or neutrons in the nucleus of an isotope spontaneously changes. What happens is that a proton turns into a neutron, or a neutron is transformed into a proton (Figure 17.7b). As a result of this process, another particle, known as a neutrino, is also ejected. A neutrino is a particle with no rest mass (the mass when the particle is at rest with respect to an observer).a Beta particles travel farther through air than the more mas- sive alpha particles but are blocked by even moderate shield- ing, such as a thin sheet of metal (aluminum foil) or a block of wood.

The third and most penetrating type of radiation comes from gamma decay. When gamma decay occurs, a gamma ray, a type of electromagnetic radiation, is emitted from the isotope. Gamma rays are similar to X rays but are more en- ergetic and penetrating; of all types of radiation, they travel the longest average distance. Protection from gamma rays requires thick shielding, such as about a meter of concrete or several centimeters of lead.

Each radioisotope has its own characteristic emissions: Some emit only one type of radiation, whereas others emit a mixture. In addition, the different types of radiation have different toxicities (potential to harm or poison). In terms of human health and the health of other organisms, alpha radia- tion is most toxic when inhaled or ingested. Because alpha radiation is stopped within a very short distance by living tissue, much of the damaging radiation is absorbed by the tissue. When alpha-emitting isotopes are stored in a con- tainer, however, they are relatively harmless. Beta radiation has intermediate toxicity, although most beta radiation is ab- sorbed by the body when a beta emitter is ingested. Gamma emitters are dangerous either inside or outside the body; but when they are ingested, some of the radiation passes out of the body.

Each radioactive isotope has its own half-life. Isotopes with very short half-lives are present only briefly, whereas those with long half-lives remain in the environment for long periods. Table 17.1 illustrates the general pattern for decay in terms of the elapsed half-lives and the fraction remaining. For example, suppose we start with 1 g polonium-218 with a half-life of approximately 3 minutes. After an elapsed time of 3 minutes, 50% of the polonium-218 remains. After 5 elapsed half-lives, or 15 minutes, only 3% is still present; and after 10 elapsed half-lives (30 minutes), 0.1% is still present. Where has the polonium gone? It has decayed to lead-214, another radioactive isotope, which has a half-life of about 27 minutes. The progression of changes associated with the decay process is often known as a radioactive decay chain.

Now suppose we had started with 1 g uranium-235, with a half-life of 700 million years. Following 10 elapsed half-lives, 0.1% of the uranium would be left—but this process would take 7 billion years.

Some radioisotopes, particularly those of very heavy elements such as uranium, undergo a series of radioactive de- cay steps (a decay chain) before finally becoming stable, non- radioactive isotopes. For example, uranium decays through a series of steps to the stable nonradioactive isotope of lead. A decay chain for uranium-238 (with a half-life of 4.5 billion years) to stable lead-206 is shown in Figure 17.8. Also listed are the half-lives and types of radiation that occur during the transformations. Note that the simplified radioactive decay chain shown in Figure 17.8 involves 14 separate transforma-

tions and includes several environmentally important radio- isotopes, such as radon-222, polonium-218, and lead-210. The decay from one radioisotope to another is often stated in terms of parent and daughter products. For example, ura- nium-238 is the parent of daughter product thorium-234.

Radioisotopes with short half-lives initially have a more rapid rate of change (nuclear transformation) than do radio- isotopes with long half-lives. Conversely, radioisotopes with long half-lives have a less intense and slower initial rate of nuclear transformation but may be hazardous much longer.b

To sum up, when considering radioactive decay, two important facts to remember are (1) the half-life and (2) the type of radiation emitted.

17.3 Nuclear Energy and the Environment

The nuclear fuel cycle begins with the mining and pro- cessing of uranium, its transportation to a power plant, its use in controlled fission, and the disposal of radioactive waste. Ideally, the cycle should also include the reprocess- ing of spent nuclear fuel, and it must include the decom- missioning of power plants. Since much of a nuclear power plant becomes radioactive over time from exposure to radioisotopes, disposal of radioactive wastes eventually involves much more than the original fuel.

Throughout this cycle, radiation can enter and affect the environment (Figure 17.9).

Problems with the Nuclear Fuel Cycle

• Uranium mines and mills produce radioactive waste that can expose mining workers and the local environment to radiation. Radioactive dust produced at mines and mills can be transported considerable distances by wind and water, so pollution can be widespread. Tailings— materials removed by mining but not processed—are generally left at the site, but in some instances, radioac- tive mine tailings were used in foundations and other building materials, contaminating dwellings.

• Uranium-235 enrichment and the fabrication of fuel assemblies also produce radioactive waste that must be carefully handled and disposed of.

• Site selection and construction of nuclear power plants in the United States are highly controversial. The en- vironmental review process is extensive and expensive, often centering on hazards related to such events as earthquakes.

• The power plant or reactor is the site most people are concerned about because it is the most visible part of the cycle. It is also the site of past accidents, including partial meltdowns that have released harmful radiation into the environment.

• The United States at this time does not reprocess spent fuel from reactors to recover uranium and plutonium. However, many problems are associated with the han- dling and disposal of nuclear waste, as discussed later in this chapter.

• Waste disposal is controversial because no one wants a nuclear-waste-disposal facility nearby. The problem is that no one has yet figured out how to isolate nuclear waste for the millions of years that it remains hazardous.

• Nuclear power plants have a limited lifetime, usually estimated at only several decades, but decommissioning a plant (removing it from service) or modernizing it is a controversial part of the cycle and one with which we have little experience. For one thing, like nuclear waste, contaminated machinery must be safely disposed of or securely stored indefinitely.

Decommissioning or refitting a nuclear plant is very expensive (costing perhaps several hundred million dollars) and is an important aspect of planning for the use of nuclear power. It costs more to dismantle a nuclear reactor than to build it. At present, power companies are filing to extend the licenses of several nuclear power plants originally slated to be decommissioned. Recently, the Nuclear Regulatory Commission (NRC), in response to a U.S. Court of Appeals decision, has started a study of the environmental effects of storing used nuclear fuel at reac- tors around the country. The NRC will not make a final decision on relicensing any nuclear plant until the study is completed (about 2014). Other potential problems that may impact relicensing of reactors include the discovery of active faults. Active faults have been found near the Diablo Canyon Nuclear Power Station in southern Cali- fornia, and earthquake studies are underway there. Far- ther south in California, the San Onofre Nuclear Power Plant was shut down on January 31, 2011, following a small release of radiation that resulted from excessive wear of steam-generator tubes. Cost of repairs is extensive, and the future of the San Onofre Power Plant is uncertain. (Licenses for the San Onofre and Diablo plants expire in 2022 and 2024, respectively.)

In addition to the above list of hazards in trans- porting and disposing of radioactive material, there are potential hazards in supplying other nations with reac- tors. Terrorist activity and the possibility of irresponsible people in governments add risks that are not present in any other form of energy production. For example, Kazakhstan inherited a large nuclear weapons-testing fa- cility, covering hundreds of square kilometers, from the former Soviet Union. The soil in several sites contains “hotspots” of plutonium that pose a serious problem of toxic contamination. The facility also poses a secu- rity problem. There is international concern that this plutonium could be collected and used by terrorists to produce “dirty” bombs (conventional explosives that dis- perse radioactive materials). There may even be enough plutonium to produce small nuclear bombs.

Nuclear energy may indeed be one answer to some of our energy needs, but with nuclear power comes a level of responsibility not required by any other energy source.

17.4 Nuclear radiation in the Environment and Its Effects on human health

Ecosystem Effects of Radioisotopes

As explained in A Closer Look 17.1, a radioisotope is an isotope of a chemical element that spontaneously undergoes radioactive decay. Radioisotopes affect the environment in two ways: by emitting radiation that affects other materials and by entering the normal path- ways of mineral cycling and ecological food chains.

The explosion of a nuclear weapon does damage in many ways. At the time of the explosion, intense radiation of many kinds and energies is sent out, kill- ing organisms directly. The explosion generates large amounts of radioactive isotopes, which are dispersed into the environment. Nuclear bombs exploding in the atmosphere produce a huge cloud that sends radioiso- topes directly into the stratosphere, where the radio- active particles are widely dispersed by winds. Atomic fallout—the deposit of these radioactive materials around the world—was an environmental problem in the 1950s and 1960s, when the United States, the former Soviet Union, China, France, and Great Brit- ain were testing and exploding nuclear weapons in the atmosphere.

The pathways of some of these isotopes illustrate the second way in which radioactive materials can be dangerous in the environment: They can enter ecologi- cal food chains (Figure 17.10). Let’s consider an ex- ample. One of the radioisotopes emitted and sent into the stratosphere by atomic explosions was cesium-137. This radioisotope was deposited in relatively small concentrations but was widely dispersed in the Arc- tic region of North America. It fell on reindeer moss, a lichen that is a primary winter food of the caribou. A strong seasonal trend in the levels of cesium-137 in caribou was discovered; the level was highest in winter, when reindeer moss was the principal food, and lowest in summer. Eskimos who obtained a high percentage of their protein from caribou ingested the radioisotope by eating the meat, and their bodies concentrated the cesium. The more that members of a group depended on caribou as their primary source of food, the higher the level of the isotope in their bodies.

We are exposed to a variety of radiation sources from the sky, the air, and the food we eat (Figure 17.11). We receive natural background radiation from cosmic rays entering Earth’s atmosphere from space and from natu- rally occurring radioisotopes in soil and rock. The av- erage American receives about 2 to 4 mSv/yr. Of this, about 1 to 3 mSv/yr, or 50–75%, is natural. The differ- ences are primarily due to elevation and geology. More cosmic radiation from outer space (which delivers about 0.3–1.3 mSv/yr) is received at higher elevations.

Radiation from rocks and soils (such as granite and organic shales) containing radioactive minerals delivers about 0.3 to 1.2 mSv/yr. The amount of radiation deliv- ered from rocks, soils, and water may be much larger in ar- eas where radon gas (a naturally occurring radioactive gas) seeps into homes. As a result, mountain states that also have an abundance of granitic rocks, such as Colorado, have greater background radiation than do states that have a lot of limestone bedrock and are low in elevation, such as Florida. Despite this general pattern, locations in Florida where phosphate deposits occur have above-average background radiation because of a relatively high uranium concentration in the phosphate rocks.8

The amount of radiation we receive from our own bod- ies and other people is about 1.35 mSv/yr. Two sources are naturally occurring radioactive potassium-40 and car- bon-14, which are present in our bodies and produce about 0.35 mSv/yr. Potassium is an important electrolyte in our blood, and one isotope of potassium (potassium-40) has a very long half-life. Although potassium-40 makes up only a very small percentage of the total potassium in our bodies, it is present in all of us. In short, we are all slightly radio- active, and if you choose to share your life with another person, you are also exposing yourself to a little bit more radiation.

To understand the effects of radiation, you need to be acquainted with the units used to measure radiation and the amount or dose of radiation that may cause a health problem. Sources of low-level radiation from our modern tech- nology include X rays for medical and dental purposes, which may deliver an average of 0.8–0.9 mSv/yr; nuclear weapons testing, approximately 0.04 mSv/yr; the burn- ing of fossil fuels, such as coal, oil, and natural gas, 0.03 mSv/yr; and nuclear power plants (under normal operat- ing conditions), 0.002 mSv/yr.9

Your occupation and lifestyle can affect the annual dose of radiation you receive. If you fly at high altitudes in jet aircraft, you receive an additional small dose of radia- tion—about 0.05 mSv for each flight across the United States. If you work at a nuclear power plant, you can re- ceive up to about 3 mSv/yr. Living next door to a nuclear power plant adds 0.01 mSv/year, and sitting on a bench watching a truck carrying nuclear waste pass by would add 0.001 mSv to your annual exposure. Sources of radia- tion are summarized in Figure 17.13a, assuming an annu- al total of 3 mSv/yr.10,11 The amount of radiation received at certain job sites, such as nuclear power plants and labo- ratories where X rays are produced, is closely monitored. At such locations, personnel wear badges that indicate the dose of radiation received.

Figure 17.13b shows some of the common sources of radiation to which we are exposed. Notice that exposure to radon gas can equal what people were exposed to as a result of the Chernobyl nuclear power accident, which occurred in the Soviet Union in 1986. In other words, in some homes, people are exposed to about the same radia- tion as that experienced by the people evacuated from the Chernobyl area.

Radiation Doses and Health

The most important question in studying radiation expo- sure in people is: At what point does the exposure or dose becomes a hazard to health? (See again A Closer Look 17.2.) Unfortunately, there are no simple answers to this seemingly simple question. We do know that a dose of about 5,000 mSv (5 sieverts) is considered lethal to 50% of people exposed to it. Exposure to 1,000–2,000 mSv is sufficient to cause health problems, including vomit- ing, fatigue, potential abortion of pregnancies of less than two months’ duration, and temporary sterility in males. At 500 mSv, physiological damage is recorded. The maxi- mum allowed dose of radiation per year for workers in industry is 50 mSv, approximately 30 times the average natural background radiation we all receive.12 For the gen- eral public, the maximum permissible annual dose (for infrequent exposure) is set in the United States at 5 mSv, about three times the annual natural background radia- tion.13 For continuous or frequent exposure, the limit for the general public is 1 mSv.

Most information about the effects of high doses of radiation comes from studies of people who survived the atomic bomb detonations in Japan at the end of World War II. We also have information about people exposed to high levels of radiation in uranium mines, workers who painted watch dials with luminous paint containing ra- dium, and people treated with radiation therapy for dis- ease.14 Starting around 1917 in New Jersey, approximately 2,000 young women were employed painting watch dials with luminous paint. To maintain a sharp point on their brushes, they licked them and as a result were swallow- ing radium, which was in the paint. Many of the women died of anemia or bone cancer.15 By 1924, dentists in New Jersey were reporting cases of jaw rot; within five years radium was known to be the cause.

Workers in uranium mines who were exposed to high levels of radiation have been shown to suffer a significant- ly higher rate of lung cancer than the general population. Studies show that there is a delay of 10 to 25 years be- tween the time of exposure and the onset of disease.

Although there is vigorous, ongoing debate about the nature and extent of the relationship between radia- tion exposure and cancer mortality, most scientists agree that radiation can cause cancer. Some scientists believe that there is a linear relationship, such that any increase in radiation beyond the background level will produce an additional hazard. Others believe that the body can handle and recover from low levels of radiation exposure but that health effects (toxicity) become apparent beyond some threshold. The verdict is still out on this subject, but it seems prudent to take a conservative viewpoint and ac- cept that there may be a linear relationship. Unfortunate- ly, chronic health problems related to low-level exposure to radiation are neither well known nor well understood.

Radiation has a long history in the field of medi- cine. Drinking waters that contain radioactive materials goes back to Roman times. By 1899, the adverse effects of radiation had been studied and were well known; and in that year, the first lawsuit for malpractice in using X rays was filed. Because science had shown that radiation could destroy human cells, however, it was a logical step to conclude that drinking water containing radioactive material such as radon might help fight diseases such as stomach cancer. In the early 1900s it became popular to drink water containing radon, and the practice was sup- ported by doctors, who stated that there were no known toxic effects. Although we now know that was incorrect, radiotherapy, which uses radiation to kill cancer cells in humans, has been widely and successfully used for a num- ber of years.15

17.5 Nuclear power plant Accidents

Although the chance of a disastrous nuclear accident is estimated to be very low, the probability that an accident will occur increases with every reactor put into operation. According to the U.S. Nuclear Regulatory Commission’s performance goal for a single reactor, the probability of a large-scale core meltdown in any given year should be no greater than 0.01%—one chance in 10,000. However, if there were 1,500 nuclear reactors (about three and a half times the present world total), a meltdown could be expected (at the low annual probability of 0.01%) every seven years. This is clearly an unacceptable risk.16 Increas- ing safety by about 10 times would result in lower, more manageable risk, but the risk would still be appreciable because the potential consequences remain large.

Three Mile Island

One of the most dramatic events in the history of U.S. radiation pollution occurred on March 28, 1979, at the Three Mile Island nuclear power plant near Harrisburg, Pennsylvania. The malfunction of a valve, along with hu- man errors (thought to be the major problem), resulted in a partial core meltdown. Intense radiation was released to the interior of the containment structure. Fortunately, the containment structure functioned as designed, and only a relatively small amount of radiation was released into the environment. Average exposure from the radiation emitted into the atmosphere has been estimated at 1 mSv, which is low in terms of the amount required to cause acute toxic effects. Average exposure to radiation in the surrounding area is estimated to have been approximately 0.012 mSv, which is only about 1% of the natural back- ground radiation that people receive. However, radiationlevels were much higher near the site. On the third day after the accident, 12 mSv/hour were measured at ground level near the site. By comparison, the average American receives about 2 mSv/year from natural radiation.

Next, we discuss the two most well-known and seri- ous nuclear accidents: the Chernobyl Nuclear Power Plant in 1986 and the Fukushima Nuclear Power Plant in 2011. It is important to understand that these serious accidents resulted in part from human error.

Chernobyl

Lack of preparedness to deal with a serious nuclear power plant accident was dramatically illustrated by events that began unfolding on Monday morning, April 28, 1986. Workers at a nuclear power plant in Sweden, frantically searching for the source of elevated levels of radiation near their plant, concluded that it was not their installa- tion that was leaking radiation; rather, the radioactivity was coming from the Soviet Union by way of prevailing winds. When confronted, the Soviets announced that an accident had occurred at a nuclear power plant at Cher- nobyl two days earlier, on April 26. This was the first no- tice to the world of the worst accident in the history of nuclear power generation.

It is speculated that the system that supplied cool- ing waters for the Chernobyl reactor failed as a result of human error, causing the temperature of the reactor core to rise to over 3,000°C (about 5,400°F), melting the ura- nium fuel, setting fire to the graphite surrounding the fuel rods that were supposed to moderate the nuclear reac- tions, and causing explosions that blew off the top of the building over the reactor. The fires produced a cloud of radioactive particles that rose high into the atmosphere. There were 237 confirmed cases of acute radiation sick- ness, and 31 people died of radiation sickness.17

In the days following the accident, nearly 3 billion people in the Northern Hemisphere received varying amounts of radiation from Chernobyl. With the excep- tion of the 30-km (19-mi) zone surrounding Chernobyl, the world human exposure was relatively small. Even in Europe, where exposure was highest, it was considerably less than the natural radiation received during one year.18

In that 30-km zone, approximately 115,000 people were evacuated, and as many as 24,000 people were esti- mated to have received an average radiation dose of 0.43 Sv (430 mSv). Studies have found that since the accident the number of childhood thyroid cancer cases per year has risen steadily in Belarus, Ukraine, and the Russian Federa- tion, the three countries most affected by Chernobyl. A total of 1,036 thyroid cancer cases have been diagnosed in children under 15 in the region. These cancer cases are be- lieved to be linked to the released radiation from the acci- dent, but other factors, such as environmental pollution, may also have played a role. It is predicted that a small percent of the roughly 1 million children exposed to the radiation eventually will contract thyroid cancer. Outside the 30-km zone, the increased risk of contracting cancer is very small and not likely to be detected from an ecological evaluation.18,19

To date, 4,000 deaths can be directly attributed to the Chernobyl accident, and according to one estimate, Chernobyl will ultimately be responsible for approximate- ly 16,000 to 39,000 deaths. Proponents of nuclear power point out that this is fewer than the number of deaths caused each year by burning coal. The World Health Or- ganization estimates there are several hundred thousand premature deaths worldwide annually as the result of air pollution from burning coal

Vegetation within 7 km of the power plant was ei- ther killed or severely damaged by the accident. Pine trees examined in 1990 around Chernobyl showed extensive tissue damage and still contained radioactivity. The dis- tance between annual rings (a measure of tree growth) had decreased since 1986.

Scientists returning to the evacuated zone in the mid- 1990s found, to their surprise, thriving and expanding animal populations. Species such as wild boar, moose, otters, waterfowl, and rodents seemed to be having a population boom in the absence of people. The wild boar population had increased tenfold since the evacuation. However, these animals may be paying a genetic price for living within the contaminated zone.

In areas surrounding Chernobyl, radioactive materi- als continue to contaminate soils, vegetation, surface wa- ter, and groundwater, presenting a hazard to plants and animals. The evacuation zone may be uninhabitable for a very long time (Figure 17.14) unless a way is found to remove the radioactivity. For example, the city of Prypyat, 5 km from Chernobyl, which had a population of 48,000 prior to the accident, is a “ghost city.” It is abandoned, with blocks of vacant apartment buildings and rusting ve- hicles. Roads are cracking, and trees are growing as new vegetation transforms the urban land back to green fields.

The final story of the world’s most serious nuclear ac- cident is yet to completely unfold.20 Estimates of the to- tal cost of the Chernobyl accident vary widely, but it will probably exceed $200 billion. Chernobyl is the most seri- ous nuclear accident to date; it certainly was not the first and is unlikely to be the last. Although the probability of a serious accident is very small at a particular site, the con- sequences may be great, perhaps posing an unacceptable risk to society. This is really not so much a scientific issue as a political one, involving values.

Japan’s Nuclear Accident, 2011

In 2011, a very large earthquake of magnitude 9 occurred offshore of Japan and displaced the ocean bottom, which generated a large set of tsunami waves that quickly reached the Japanese shore (Figure 17.15) where several nuclear power plants were located. (See this chapter’s opening case study.) When the earthquake occurred, the nuclear power plants immediately went into shutdown mode as a standard practice. What occurred shortly thereafter and produced a nuclear disaster more serious than anything that has occurred in the last several decades is a story with several lessons.

The Japanese have studied earthquakes and tsunamis for decades and were aware that large earthquakes in the region were possible. However, a magnitude 9.1 event was a surprise in that region, as was the extent of the tsunami, which overwhelmed sea walls protecting the plant and flooded the power stations. When the pumps that sent cooling water into the reactors (shut down but still very hot) failed, large amounts of heat and steam built up from water not circulating, and partial meltdowns at several re- actors took place. Steam explosions and subsequent fires damaged buildings and reactor confinement structures, and radioactive materials were released into the environ- ment. A number of other systems also failed, but the net result was that the people residing in the vicinity of the nuclear power plants were exposed to radiation sufficient to endanger human health.

The catastrophe could probably have been avoided. At the center of the controversy is the fact that some Japanese scientists had suggested that large tsunamis in the region were possible, and the tsunami protection barriers may not have been large enough. The possibility of very large tsunamis in the region with long return periods of about a thousand years was suggested as early as 2001. The prob- lem was that these scientific findings were not believed or not taken seriously. The Japanese nuclear industry sim- ply did not believe that the power plants were vulnerable. Even in the face of scientific evidence of the possibility of much larger tsunamis, the nuclear industry and govern- ment did not want to do the very expensive upgrades at the plants. In other words, warnings were ignored, per- haps to save money. It also has been suggested that the re- lationship between the nuclear industry and government is too closely aligned for proper regulation.21,22

If the nuclear power industry and government had taken heed of the warnings of their scientists, they might also have better protected the pumps and backup systems so that the plants would not flood should a tsunami over- top their defenses. In other words, steps could have been taken to locate the backup generators on higher ground.22

The Japanese catastrophe of 2011 is a lesson to us all that we are vulnerable to natural processes, and that we need to heed potential warnings of events that happen very infrequently. In the United States, we should learn from Japan’s catastrophe and ensure that our reactors are safer—in this case, by closely evaluating each reac- tor site for the possibility of flooding and damage to pumps and backup pumps that circulate cooling water.

17.6 radioactive-Waste

Management

Examination of the nuclear fuel cycle (refer back to Figure 17.9) illustrates some of the sources of waste that must be disposed of as a result of using nuclear energy to produce electricity. Radioactive wastes are by-products of nuclear reactors. The U.S. Federal Energy Regulatory Commission (FERC) defines two main categories of ra- dioactive waste: low-level and high-level.

Low-Level Radioactive Waste

Low-level radioactive waste contains radioactivity in such low concentrations or quantities that it does not present a significant environmental hazard if properly handled. Low-level waste includes a wide variety of items, such as residuals or solutions from chemical processing; solid or liquid plant waste, sludges, and acids; and slightly contaminated equipment, tools, plastic, glass, wood, and other materials.

Low-level waste has been buried in near-surface burial areas in which the hydrologic and geologic conditions were thought to severely limit the migration of radioactivity. However, monitoring has shown that several U.S. disposal sites for low-level radioactive waste have not adequately protected the environment, and leaks of liquid waste have polluted groundwater. Of the original six burial sites, three were closed prematurely by 1979 due to unexpected leaks, financial problems, or loss of license, and as of 1995 only two remaining government low-level nuclear-waste repositories were still operating in the United States, one in Washington and the other in South Carolina. In addi- tion, a private facility in Utah, run by Envirocare, accepts low-level waste. Construction of new burial sites, such as the Ward Valley site in southeastern California, has been met with strong public opposition, and controversy con- tinues as to whether low-level radioactive waste can be disposed of safely.23

High-Level Radioactive Waste

High-level radioactive waste consists of commercial and military spent nuclear fuel; uranium and plutonium derived from military reprocessing; and other radioactive nuclear weapons materials. It is extremely toxic, and a sense of ur- gency surrounds its disposal as the total volume of spent fuel accumulates. At present, in the United States, tens of thou- sands of metric tons of high-level waste are being stored at more than a hundred sites in 40 states. Seventy-two of the sites are commercial nuclear reactors.24–26

These storage arrangements are at best a temporary so- lution, and serious problems with radioactive waste have occurred where it is being stored. Although improvements

in storage tanks and other facilities will help, eventually some sort of disposal program must be initiated. Some sci- entists believe the geologic environment can best provide safe containment of high-level radioactive waste. Oth- ers disagree and have criticized proposals for long-term underground disposal of high-level radioactive waste. A comprehensive geologic disposal development program should have the following objectives:26

• Identification of sites that meet broad geologic crite- ria, including ground stability and slow movement of groundwater with long flow paths to the surface.

• Intensive subsurface exploration of possible sites to posi- tively determine geologic and hydrologic characteristics.

• Predictions of the behavior of potential sites based on present geologic and hydrologic situations and assump- tions about future changes in climate, groundwater flow, erosion, ground movements, and other variables.

• Evaluation of risk associated with various predictions. • Political decision making based on risks acceptable to society.

What Should the United States Do with Its Nuclear Wastes?

For decades in the United States, the focal point for debates over nuclear wastes has been the plan to bury them deep in the earth at Yucca Mountain, Nevada. Extensive scientific evaluations were carried out, but the plan generated consid- erable resistance from the state and people of Nevada as well as from scientists not confident with the plan.26 Some of the scientific questions at Yucca Mountain have concerned natural processes and hazards that might allow radioactive materials to escape, such as surface erosion, groundwater movement, earthquakes, and volcanic eruptions.

In 2002, Congress voted to submit a license of applica- tion for Yucca Mountain to the Nuclear Regulatory Com- mission, but in 2010 the Obama administration rejected that plan, and then Secretary of Energy Steven Chu set up a blue ribbon panel to consider the alternatives. At pres- ent, there are 70,000 tons of radioactive waste from nuclear power plants, and federally authorized temporary storage facilities for these are said to be full. That is to say, there is no government-sanctioned and locally approved place to put any more nuclear wastes. Yet they continue to build up.

Why was the Yucca Mountain repository so contro- versial, and why has it finally been canceled, or at least put on hold? The Nuclear Waste Policy Act of 1982 initiated a high-level nuclear waste-disposal program. The Depart- ment of Energy was given the responsibility to investi- gate several potential sites and make a recommendation. The 1982 act was amended in 1987; the amendment, along with the Energy Power Act of 1992, specified thathigh-level waste was to be disposed of underground in a deep, geologic waste repository. It also specified that the Yucca Mountain site in Nevada was to be the only site evaluated. Costs to build the facility reached $77 billion, but no nuclear wastes have ever been sent there.26

Evaluation of the safety and utility of a new waste repository would have to consider factors such as the following:25–27

• Probability and consequences of volcanic eruptions. • Earthquake hazard. • Flood hazard from storms.

• Estimation of how long the waste may be contained and the types and rates of radiation that may escape from deteriorated waste containers.

• How heat generated by the waste may affect moisture in and around the repository and the design of the repository.

• Characterizationofgroundwaterflowneartherepository.

• Identification and understanding of major geochemi- cal processes that control the transport of radioactive materials.

• Possible rise of radioactive contaminated water to the surface after cracking in the bedrock from heat- generated radioactive wastes

One of the problems is just transporting the present amount of nuclear waste from power plants to any reposi- tory. According to previous U.S. government plans, be- ginning in 2010 some 70,000 tons of highly radioactive nuclear waste were going to be moved across the country to Yucca Mountain, Nevada by truck and train, one to six trainloads or truck convoys every day for 24 years. These train and truck convoys would have to be heavily guard- ed against terrorism and protected as much as possible against accidents.

A major question about the disposal of high-level radioactive waste is this: How credible are extremely long-range geologic predictions—those covering several thousand to a few million years?27 Unfortunately, there is no easy answer to this question because geologic processes vary over both time and space. Climates change over long periods, as do areas of erosion, deposition, and groundwa- ter activity. For example, large earthquakes even thousands of kilometers from a site may permanently change ground- water levels. The earthquake record for most of the United States extends back only a few hundred years; therefore, estimates of future earthquake activity are tenuous at best.

The bottom line is that geologists can suggest sites that have been relatively stable in the geologic past, but they cannot absolutely guarantee future stability. This means that policymakers (not geologists) need to evaluate the uncertainty of predictions in light of pressing political, economic, and social concerns.26 In the end, the geologic environment may be deemed suitable for safe contain- ment of high-level radioactive waste, but care must be taken to ensure that the best possible decisions are made on this important and controversial issue.

17.7 the Future of Nuclear Energy

The United States would need 1,000 new nuclear power plants of the same design and efficiency as existing nuclear plants to completely replace fossil fuels. The International Atomic Energy Agency, which promotes nuclear energy, says a total of just 4.7 million tons of “identified” conven- tional uranium stock can be mined economically. If we switched from fossil fuels to nuclear today, that uranium would run out in four years. Even the most optimistic estimate of the quantity of uranium ore is not reassuring: It would last only 29 years.28

Nevertheless, nuclear energy as a power source for elec- tricity is now being seriously evaluated. Its advocates argue that nuclear power is good for the environment because:

• It does not contribute to potential global warming through release of carbon dioxide (see Chapter 20)

• It does not cause the kinds of air pollution or emit pre- cursors (sulfates and nitrates) that cause acid rain (see Chapter 21).

The argument against nuclear power is based on po- litical and economic considerations as well as scientific uncertainty about safety issues:

• Opponents emphasize that more than half the U.S. population lives within 75 miles of one of the nation’s 104 nuclear power plants.

• Converting from coal-burning plants to nuclear power plants for the purpose of reducing carbon dioxide emis- sions would require an enormous investment in nuclear power to make a real impact.

• Given that safer nuclear reactors are only just being developed, there will be a time lag, so nuclear power is unlikely to have a real impact on environmental problems—such as air pollution, acid rain, and poten- tial global warming—before at least the year 2050.

• Uranium ore to fuel conventional nuclear reactors is limited. The International Nuclear Energy Association estimates that at the 2004 rate of use, there would be 85 years of uranium fuel from known reserves, but if nations attempt to build many new power plants in the next decade, known reserves of uranium ore would be used up much more quickly.

• Some nations may use nuclear reactors as a path to nu- clear weapons. Reprocessing used nuclear fuel from a power plant produces plutonium that can be used to make nuclear bombs. There is concern that rogue na- tions with nuclear power could divert plutonium to make weapons or might sell plutonium to others, even terrorists, who would make nuclear weapons.30

Until 2001, proponents of nuclear energy were los- ing ground. Nearly all energy scenarios were based on the expectation that nuclear power would grow slowly or per- haps even decline in coming years. Since the Chernobyl and Japan accidents, many European countries have been reevaluating the use of nuclear power, and in most in- stances the number of nuclear power plants being built has significantly declined.

There is also a problem with present nuclear technol- ogy: Today’s light-water reactors use uranium very inef- ficiently; only about 1% of it generates electricity, and the other 99% ends up as waste heat and radiation. Therefore, our present reactors are part of the nuclear-waste problem and not a long-term solution to the energy problem.

One way for nuclear power to be sustainable for at least hundreds of years would be to use a process known as breeding. Breeder reactors are designed to produce new nuclear fuel by transforming waste or lower-grade uranium into fissionable material. Although proponents of nuclear energy suggest that breeder reactors are the future of nucle- ar power, only a few are known to be operating anywhere in the world. Bringing breeder reactors online to produce safe nuclear power will take planning, research, and ad- vanced reactor development. Also, fuel for the breeder re- actors will have to be recycled because reactor fuel must be replaced every few years. What is needed is a new type of breeder reactor comprising an entire system that includes reactor, fuel cycle (especially fuel recycling and reprocess- ing), and less production of waste. Such a reactor appears possible but will require redefining our national energy policy and turning energy production in new directions. It remains to be seen whether this will happen.

New Kinds of Fission Reactors

One design philosophy that has emerged in recent decades in the nuclear industry is to build less complex, smaller reactors that are safer. Large nuclear power plants, which produce about 1,000 MW of electricity (sufficient power for a medium-size city), require an extensive set of pumps and backup equipment to ensure that adequate cooling is available to the reactor. Smaller reactors producing 10 to 50 MW are much less expensive than large reactors and can be designed to be safer. Small reactors have an economy of scale and potentially could be mass-produced. A 10 MW reactor can provide the electricity needs of 8,000 homes and could hold sufficient fuel to run 30 years before need- ing refueling. Thus a single small nuclear (10 MW) reactor could provide power for a village, while several linked to- gether could power a small city. Small reactors can be de- signed with cooling systems that work by gravity and thus are less vulnerable to pump failure caused by power loss. Such cooling systems are said to have passive stability, and the reactors are said to be passively safe. Another approach is the use of helium gas to cool reactors that have specially designed fuel capsules capable of withstanding tempera- tures as high as 1,800°C (about 3,300°F). The idea is to design the fuel assembly so that it can’t hold enough fuel to reach this temperature and thus the reactor is self-limiting and will not experience a core meltdown.31

Several new designs for conventional nonbreeder fis- sion nuclear power plants are in development and the object of widespread discussion. Among these are the Advanced Boiling Water Reactor and the High Tempera- ture Gas Reactor.32,33 None are yet installed or operating anywhere in the world. The general goals of these designs are to increase safety, energy efficiency, and ease of op- eration. Some are designed to shut down automatically if there is any failure in the cooling system, rather than require the action of an operator. Although proponents of nuclear power believe these will offer major advances, it will be years, perhaps decades, until even one of each kind achieves commercial operation, so planning for the future cannot depend on them.

Fusion Reactors In contrast to fission, which involves splitting heavy nuclei (such as uranium), fusion involves combining the nuclei of light elements (such as hydrogen) to form heavier ones (such as bhelium). As fusion occurs, heat energy is released. Nuclear fusion is the source of energy in our sun and oth- er stars.

In a hypothetical fusion reactor, two isotopes of hydrogen—deuterium and tritium—are injected into the reactor chamber, where the necessary conditions for fu- sion are maintained. Products of the deuterium–tritium (DT) fusion include helium, producing 20% of the en- ergy released, and neutrons, producing 80%.

Several conditions are necessary for fusion to take place. First, the temperature must be extremely high (approximately 100 million degrees Celsius for DT fu- sion). Second, the density of the fuel elements must be sufficiently high. At the temperature necessary for fusion, nearly all atoms are stripped of their electrons, forming a plasma—an electrically neutral material consisting of pos- itively charged nuclei, ions, and negatively charged elec- trons. Third, the plasma must be confined long enough to ensure that the energy released by the fusion reactions exceeds the energy supplied to maintain the plasma.

The potential energy available when and if fusion re- actor power plants are developed is nearly inexhaustible. One gram of DT fuel (from a water and lithium fuel sup- ply) has the energy equivalent of 45 barrels of oil. Deu- terium can be extracted economically from ocean water, and tritium can be produced in a reaction with lithium in a fusion reactor. Lithium can be extracted economically from abundant mineral supplies.

Many problems remain to be solved before nuclear fusion can be used on a large scale. Research is still in the first stage, which involves basic physics, testing of possible fuels (mostly DT), and magnetic confinement of plasma.

There have been some: In 1980, one of the plant’s two units filled with water (an operator’s mistake). In 1982, the piping of the same unit’s steam generator leaked and released radioac- tive water. In 1999, it shut down unexpectedly, but operators didn’t realize it until the next day, when the batteries that automatically took over ran down.

In April 2007, a transformer burned in the second unit, radioactive water leaked into groundwater, and the source of the leak was difficult to find. Most recently, in 2009, a leak in the cooling system allowed 100,000 gallons of water to escape from the main system. Uneasiness about the plant’s location increased after the terror attack on September 11, 2001. One of the hijacked jets flew close to the plant, and diagrams of unspecified nuclear plants in the United States have since been found in al Qaeda hideouts in Afghanistan.36

Proponents of nuclear power say these are minor prob- lems, and there has been no major one. As far as they can tell, the plant is safe. The Energy Policy Act of 2005 promoted nuclear energy, and the Obama administration is moving ahead with federal funding of nuclear power plants. Others, however, such as New York State’s attorney general Andrew Cuomo, believe the location is just too dangerous, and he has asked the Nuclear Regulatory Commission to deny Indian Point’s relicensing, saying that it has “a long and troubling history of problems.”

The conflict at Indian Point illustrates the worldwide debate about nuclear energy. Growing concern about fossil fuels has led to calls for increased use of nuclear power despite unanswered questions and unsolved problems regarding its use.

suMMaRy

• Nuclear fission is the process of splitting an atomic nu- cleus into smaller fragments. As fission occurs, energy is released. The major components of a fission reactor are the core, control rods, coolant, and reactor vessel.

• Nuclear radiation occurs when a radioisotope sponta- neously undergoes radioactive decay and changes into another isotope.

• The three major types of nuclear radiation are alpha, beta, and gamma.

• Each radioisotope has its own characteristic emissions. Different types of radiation have different toxicities; and in terms of the health of humans and other organisms, it is important to know the type of radiation emitted and the half-life.

• The nuclear fuel cycle consists of mining and processing uranium, generating nuclear power through controlled fission, reprocessing spent fuel, disposing of nuclear waste, and decommissioning power plants. Each part of the cycle is associated with characteristic processes, all with different potential environmental problems.

• The present burner reactors (mostly light-water reactors) use uranium-235 as a fuel. Uranium is a nonrenewable resource mined from the Earth. If many more burner reactors were constructed, we would face fuel short- ages. Nuclear energy based on burning uranium-235 in

light-water reactors is thus not sustainable. For nuclear energy to be sustainable, safe, and economical, we will need to develop breeder reactors.

• Radioisotopes affect the environment in two major ways: by emitting radiation that affects other materials and by entering ecological food chains.

• Major environmental pathways by which radiation reach- es people include uptake by fish ingested by people, up- take by crops ingested by people, inhalation from air, and exposure to nuclear waste and the natural environment.

• The dose–response for radiation is fairly well established. We know the dose–response for higher exposures, when illness or death occurs. However, there are vigorous de- bates about the health effects of low-level exposure to radiation and what relationships exist between exposure and cancer. Most scientists believe that radiation can cause cancer. But, ironically, radiation can be used to kill cancer cells, as in radiotherapy treatments.

• We have learned from accidents at nuclear power plants that it is difficult to plan for the human factor. People make mistakes. We have also learned that we are not as prepared for accidents as we would like to think. Some believe that people are not ready for the responsibility of nuclear power. Others believe that we can design much safer power plants where serious accidents are impossible.

• There is a consensus that high-level nuclear waste may be safely disposed of in the geologic environment. The problem has been to locate a site that is safe and not objectionable to the people who make the decisions and to those who live in the region.

• Nuclear power is again being seriously evaluated as an alternative to fossil fuels. On the one hand, it has

advantages: It emits no carbon dioxide, will not con- tribute to global warming or cause acid rain, and can be used to produce alternative fuels such as hydrogen. On the other hand, people are uncomfortable with nuclear power because of waste-disposal problems and possible accidents.

Botkin, Daniel B. Environmental Science: Earth as a Living Planet, 9th Edition. Wiley, 2013-12-23. VitalBook file.

Multimedia

1. energynownews. (2011, July 14). Energy 101: Light bulbs [Video clip]. Retrieved from http://www.youtube.com/watch?v=Pk60-D61h34

· Transcript

2. GOODMagazine. (2011, February 15). GOOD transparency: Electric vehicles [Video clip]. Retrieved from http://www.youtube.com/watch?v=QVgbESElP_I

· Transcript

3. U.S. Department of Energy. (2011, May 31). Energy 101: Daylighting [Video clip]. Retrieved from http://www.youtube.com/watch?v=-7EG4d-W4W8

· Captions are available by clicking the “CC” icon in the video window.

4. U.S. Department of Energy. (2011, January 25). Energy 101: Cool Roofs [Video clip]. Retrieved from http://www.youtube.com/watch?v=urbpBy_Z5lE

· Captions are available by clicking the “CC” icon in the video window.

5. U.S. Department of Energy. (2013, June 4). What is the smart grid? [Video clip]. Retrieved from http://www.youtube.com/watch?v=JwRTpWZReJk

· Captions are available by clicking the “CC” icon in the video window.

6. U.S. Department of Energy. (2013, June 10). Common sense and the next 30 seconds [Video clip]. Retrieved from http://www.youtube.com/watch?v=Ht4lEn3qHQI

· Captions are available by clicking the “CC” icon in the video window.

recommended Websites rESOURCES

1. Department of Energy. (n.d.). Nuclear. Retrieved from http://energy.gov/science-innovation/energy-sources/nuclear

2. U.S. Department of Energy | Energy Efficiency & Renewable Energy (http://www.eere.energy.gov/)