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Impact of Fukushima Daiichi Nuclear accident on U.S. code of federal regulations

Before discussing the Post Fukushima activities lets discuss the Fukushima accident in short. On March 11, 2011, a 9.0-magnitude earthquake struck Japan about 231 miles (372 kilometers) northeast of Tokyo off the Honshu Island coast. Eleven reactors at four sites (Fukushima Daiichi, Fukushima Daini, Onagawa, and Tokai) along the northeast coast automatically shut down after the quake. Fukushima Daiichi lost all power from the electric grid, with diesel generators providing power for about 40 minutes. At that point, an estimated 45-foot-high (14 meter) tsunami hit the site, damaging many of the generators. Four of six Fukushima Daiichi reactors lost all power from the generators. The tsunami also damaged some of the site's battery backup systems. Units 1, 2 and 3 at Fukushima Daiichi were operating when the earthquake hit. Units 4, 5 and 6 were shut down for routine refueling and maintenance. One of Unit 6's diesel generators continued working, providing power to keep both Units 5 and 6 (at right in the photo) safely shut down. Steam-driven and battery-powered safety systems at Units 1, 2 and 3 worked for several hours (and more than a day in some cases). Those systems eventually failed and all three reactors overheated, melting their cores to some degree. The conditions in the reactors generated extreme pressure, causing leaks of radioactive gas as well as hydrogen. The hydrogen exploded inside the reactor buildings of Units 1, 3 and 4, damaging the buildings and releasing more radioactive material from Units 1 and 3. Radioactive contamination spread over a large area of Japan, requiring the relocation of tens of thousands of people. The Japanese government has reopened limited areas for residents to return to, but many communities remain off-limits. Japanese authorities eventually stabilized the damaged reactors with alternate water sources. Work continues to isolate the damaged reactors and radioactive contamination from the environment.

After the Fukushima accident, a task force of senior NRC staff reviewed the causes, consequences and effects of the accident to determine what lessons could be imbibed regarding safety of the Nuclear Reactors presently stationed in US. In July 2011, the senior level task force referred to as Near Term task force (NTTF) provided recommendations to enhance U.S. reactor safety, and these became the foundation of the NRC's post-Fukushima activities. The Commission then approved a three-tiered prioritization of the recommendations. In SECY-11-0137, the NRC staff prioritized the Near-Term Task Force (NTTF) recommendations (SECY-11-0093) into three tiers. The activities were broadly divided into Tier 1 activities and post Fukushima Tier 2, Tier 3 And Non-Tiered activities. Here we are going to discuss Tier 1 activities only.

Tier 1 activities consisted mainly of Mitigation strategies, Containment venting systems, Spent fuel pool instrumentation, Seismic reevaluations, Flooding hazard reevaluations, Seismic and flooding walk downs, Emergency preparedness –staffing and communications, Station blackout mitigation strategies, Onsite emergency response capability, and Filtration and Confinement Strategies. Out of the above mentioned activities orders were passed for mitigation strategies, Containment Venting systems, and Spent fuel pool instrumentation some of these orders were then codified into US Code of federal regulations.

1. Mitigation Strategies: The primary function of mitigation strategies is to enhance the capability to maintain plant safety during prolonged power loss. At Fukushima, flooding from the tsunami disrupted the power systems after the earthquake had cut off external power sources, leaving the plants with insufficient worth of battery power. Nuclear power plants need electrical power 24 hours per day, even when the nuclear reactors are shut down, to run equipment that cools the reactor core and spent nuclear fuel. The NRC issued a Mitigation Strategies Order on March 12, 2012, requiring all U.S. nuclear power plants to implement strategies that will allow them to cope without their permanent electrical power sources for an indefinite amount of time. These strategies must keep the reactor core and spent fuel cool, as well as protect the thick concrete containment buildings that surround each reactor. The mitigation strategies are expected to use a combination of currently installed equipment (e.g., steam-powered pumps), additional portable equipment that is stored on-site, and equipment that can be flown in or trucked in from support centers. Following this NRC passed orders namely NRC Order on mitigation strategies (EA-12-049) (March 2012). NRC-issued guidance for mitigation strategies order (JLD-ISG-2012-01), Revision 2(Feb, 2017) and finally the last one Industry issued guidance for mitigation strategies Order (NEI 12-06), Revision 4 (December 2016) the link for them are given below;

https://www.nrc.gov/reading-rm/doc-collections/nuregs/brochures/br0523/

https://www.nrc.gov/docs/ML1700/ML17005A188.pdf

https://www.nrc.gov/docs/ML1635/ML16354B421.pdf

Diverse and flexible coping strategies were introduced which were named as FLEX programs which were a set of prepositioned capabilities designed to extend the coping period in event of an extended AC power loss and other adverse situations such as occurred at the Fukushima Daiichi Plant. The FLEX implementation guide contains these elements and was endorsed in USNRC Interim Staff Guidance (USNRC, 2012c) as being an acceptable means of complying with the Mitigation Strategies Order. The link for this is given below;

https://www.ncbi.nlm.nih.gov/books/NBK253949/#

Severe accident management guidelines (SAMG) are intended to address “beyond-design-basis” situations in which the core has become or is becoming damaged. The goals of the SAMG are to stabilize a degraded core, maintain containment, and minimize the release of the core's fission products. Following the post Fukushima accident mitigation strategies The Electric Power Research Institute commissioned a revision to the severe accident management guidance technical basis report (EPRI, 2012b). New material addresses using seawater injection for reactor core cooling, common-cause failures due to external events, cooling spent fuel pools, setting priorities in multiunit events, containment isolation failure, and hydrogen combustion within plant buildings.

https://www.ncbi.nlm.nih.gov/books/NBK253949/#

2. Containment Venting System: The primary function of containment venting system is to provide a reliable hardened containment vent system for boiling water reactors (BWRs) with Mark I or Mark II containment designs. The Fukushima accident suspended the plants' ability to cool their reactor cores, causing heat and pressure to build within the concrete containment buildings that surround the reactors. This buildup damaged the buildings and which made it easier for radioactive material to reach the environment. The NRC issued an Order on March 12, 2012, requiring all U.S. nuclear power plants with the Fukushima-style containment design to install a reliable, hardened vent that can remove heat and pressure before potential damage to a reactor core occurs. This not only helps preserve the integrity of the containment building, but can also help delay reactor core damage or melting.  NRC issued order on reliable hardened vents (EA-12-050) (March 2012) ,Order on containment venting system (EA-13-109), Order on NRC guidance for reliable hardened vents order (JLD-ISG-2012-02)(Aug 2012), NRC-issued guidance for original Reliable Hardened Vents Order (JLD-ISG-2012-02) (August 29, 2012), and so on. The links for some of them are provided below,

https://www.nrc.gov/docs/ML1314/ML13143A321.pdf

https://www.nrc.gov/docs/ML1222/ML12229A475.pdf

https://www.nrc.gov/reading-rm/doc-collections/commission/secys/2012/2012-0157scy.pdf

https://www.nrc.gov/docs/ML1330/ML13304B836.pdf

https://www.nrc.gov/docs/ML1330/ML13304B836.pdf

3. Spent fuel pool instrumentation: The primary function of this is to provide a reliable wide range indication of water level in spent fuel storage pools. During the accident at Fukushima, the plants lost their ability to cool the spent fuel pools. Plant operators couldn't determine how much water was in the pools during the accident, which was a problem. If enough water boiled away or was otherwise lost, the spent fuel rods could emerge from the receding water and potentially release significant amounts of radiation. The NRC issued an Order on March 12, 2012, requiring all U.S. nuclear power plants to install water level instrumentation in their spent fuel pools. The instrumentation must remotely report at least three distinct water levels: 1) normal level; 2) low level but still enough to shield workers above the pools from radiation; and 3) a level near the top of the spent fuel rods where more water should be added without delay. US NRC passed order NRC Order on Spent Fuel Pool Instrumentation (EA-12-051) (March 12, 2012), NRC-issued guidance for Spent Fuel Pool Instrumentation Order (JLD-ISG-2012-03) (August 29, 2012), Industry-issued guidance for Spent Fuel Pool Instrumentation (NEI 12-02) (August 2012).

https://www.nrc.gov/docs/ML1205/ML12056A044.pdf

https://www.nrc.gov/docs/ML1222/ML12221A339.pdf

4. Seismic Reevaluation: The primary function of this is to reanalyze potential seismic effects using present-day information to determine if safety upgrades are needed. Operating reactor sites are using present-day information to reevaluate the earthquake effects—or hazards—that could impact their site.  These newly reevaluated hazards, if worse than what the plant had originally calculated, will be analyzed to determine if plant structures, systems, and/or components need to be updated to protect against the new hazard.  The NRC will review each step in the analysis process and take action to require plant changes as necessary. The NRC is in information request phase and will take action as required.

5. Flooding Hazard reevaluations: The primary function to reanalyze potential flooding effects using present-day information to determine if safety upgrades are needed. Operating reactor sites are using present-day information to reevaluate the flooding effects—or hazards—that could impact their site.  These newly reevaluated hazards, if worse than what the plant had originally calculated, will be analyzed to determine if plant structures, systems, and/or components need to be updated to protect against the new hazard.  The NRC will review each step in the analysis process and take action to require plant changes as necessary.

6. Seismic and flooding walk downs: The primary function is to inspect existing plant protection features against seismic and flooding events, and correct any degraded conditions. In light of the effects from the extreme earthquake and tsunami of March 11, 2011, on the nuclear power plants at Fukushima, the NRC concluded U.S. nuclear power plants needed to reaffirm their existing ability to resist quakes and flooding.  On March 12, 2012, the NRC asked U.S. nuclear power plants to perform a detailed inspection, or "walk down," of their currently installed seismic and flooding protection features. The plants had to ensure the features met current requirements, and also identify, correct, and report any degraded conditions.  The plants completed their walk downs by November 2012; NRC inspectors have done follow-up inspections and the agency has issued plant-specific assessments of the licensee's walk down reports.

7. Emergency preparedness –staffing and communications: The primary function is to assess staffing needs and communications capabilities to effectively respond to an event affecting multiple reactors at a site. The accident at Fukushima highlighted how complicated emergency response can be if multiple reactors on the same site are affected at the same time and electrical power is unavailable. In response, the NRC asked U.S. nuclear power plants to assess how many emergency staff they will need to respond to a large accident that may affect multiple reactors at their site, and make changes to their emergency plans as necessary.  The NRC also asked the plants to assess and ensure that they can power the communications equipment these staff will need to effectively respond to such an accident. This includes power for radios for response teams, cellular telephones, and satellite telephones.

8. Station blackout mitigation strategies: The primary function is to enhance the capability to maintain plant safety during a prolonged loss of electrical power. This activity is under rulemaking process.

9. Onsite emergency response capabilities: The function of this capability is strengthen and integrate different types of emergency procedures and capabilities at plants. This activity is under rule making process.

10. Filtration and confinement strategies: The function of this strategy is to evaluate potential strategies that may further confine or filter radioactive material if core damage occurs. This activity is also under rule making process.

Finally, the safeguards for Nuclear Reactor given by the U.S. NRC are have proved to be the best by the standards of the world because after accident Tokyo Electric Power Company also proposed a program similar to FLEX. The strategies are to consider capability for accident control assuming situations where almost all station facilities used to control the accident lose their functions including situations like tsunamis which caused the Fukushima accident and taking complete countermeasure against it to prevent accidents from occurring. Also, the B.5.b requirements codified in 10 CFR § 50.54(h h)(2) were acknowledged to be the most important in mitigating strategies for responding to beyond design basis accident events. And following the Fukushima accident B.5.b capabilities and accident mitigation measures were recommended. Thus, it can be said that nuclear Reactor in the USA have an edge over the nuclear reactor in the other parts of the world when the safety criterion is considered.

Online References;

1. “What are the Lessons Learned from Fukushima?” U.S.NRC, United States Nuclear Regulatory Commission, https://www.nrc.gov/reactors/operating/ops-experience/japan-dashboard/priorities.html

2. “Appendix H Nuclear Plant Emergency Procedures and Guidelines”, NCBI, https://www.ncbi.nlm.nih.gov/books/NBK253949/