The March 11, 2011, Great East Japan Earthquake and tsunami created a humanitarian and material disaster in northeastern Japan. These natural events caused extensive damage to coastal communities in Iwate, Miyagi, and Fukushima Prefectures (Figure 1.1) and were responsible for about 15,900 deaths and 2,600 missing persons (National Police Agency of Japan , 2014); untold human suffering, especially of injured and displaced persons; and physical infrastructure losses exceeding $200 billion1 (~¥17 trillion).
The earthquake and tsunami were also responsible for initiating a severe nuclear accident at the Fukushima Daiichi Nuclear Power Station2 (Figure 1.2) located in east-central Fukushima Prefecture about 180 km southwest of the earthquake hypocenter (see Figure 1.1). The accident was rated as a Level 7 (major accident) event on the International Nuclear and Radiological Event Scale of the International Atomic Energy Agency, on par with the 1986 Chernobyl accident. However, releases of radioactive material to the atmosphere (mainly noble gases, iodine-131, and cesium-134/cesium-137) from the Fukushima Daiichi accident were less than 15 percent of the Chernobyl releases.3
1 Cabinet Office of Japan: http://www.meti.go.jp/english/earthquake/nuclear/japan-challenges/pdf/japan-challenges_c.pdf. Accessed on June 3, 2014.
2 When the formal names of nuclear plants are used in this report they are capitalized, for example the Fukushima Daiichi Nuclear Power Station. Lower case is used for informal names, for example, the Fukushima Daiichi plant.
3 Based on TEPCO release estimates. See http://www.tepco.co.jp/en/press/corp-com/release/betu12_e/images/120524e0201.pdf. Accessed on June 3, 2014.
FIGURE 1.1 Map of the Tohoku region of Japan (northern Honshu) showing the epicenter of the Great East Japan Earthquake (yellow star) and location of the Fukushima Daiichi Nuclear Power Station.
FIGURE 1.2 Oblique aerial photo of the Fukushima Daiichi Nuclear Power Station prior to the March 11, 2011, Great East Japan Earthquake and tsunami. Locations of reactor units are indicated by their numbers (i.e., Units 1-6). Locations of the turbine buildings, seawall, and common spent fuel storage (pool and dry) are also indicated. SOURCE: Courtesy of TEPCO.
Three of the six reactors at the Fukushima Daiichi plant sustained severe core damage during the accident and released hydrogen and radioactive materials. Explosion of the released hydrogen in three reactor buildings (Figure 1.3) caused severe structural damage and impeded onsite emergency response efforts. Offsite transport of the released radioactive materials by winds contaminated parts of Fukushima Prefecture and smaller regions of neighboring prefectures (Chiba, Gunma, Ibaraki, Miyagi, and Tochigi Prefectures) (Figure 1.4). About 78,000 residents were evacuated from a 20-km-radius exclusion zone established around the station and 62,000 from a 20- to 30-km-radius from the plant (UNSCEAR, 2013b). A large portion of this exclusion zone will likely remain off-limits to full-time reoccupation for the foreseeable future.
At the time of the Fukushima Daiichi accident, the Blue Ribbon Commission on America’s Nuclear Future was completing an assessment for the U.S. Secretary of Energy of options for managing spent nuclear fuel and high-level radioactive waste in the United States. In the weeks following the accident, concerns were raised about the condition of the spent fuel pools
FIGURE 1.3 March 16, 2011, photo of the Fukushima Daiichi Nuclear Power Station showing damaged Units 1 (foreground), 3, and 4 reactor buildings. SOURCE: Courtesy of TEPCO (http://photo.tepco.co.jp/library/110316/110316_1f_chijou_2.jpg).
in the damaged reactor buildings at the Fukushima Daiichi plant and the potential for large-scale releases of radioactive materials from the stored spent fuel.
In view of these concerns, the Blue Ribbon Commission recommended that the National Academy of Sciences (NAS) conduct an assessment of lessons learned from the Fukushima Daiichi accident (BRC, 2012, pp. xii-xiii):
[T]he [Blue Ribbon] Commission recommends that the National Academy of Sciences (NAS) conduct a thorough assessment of lessons learned from Fukushima and their implications for conclusions reached in earlier NAS studies [NRC, 2004b4] on the safety and security of current storage arrangements for spent nuclear fuel and high-level waste in the United States. This effort would complement investigations already under way by the [U.S. Nuclear Regulatory Commission] and other organizations.
4 An abbreviated public version of this report was issued (NRC, 2006b).
FIGURE 1.4 Map showing cumulative ground deposition of cesium-134 and cesium-137 (becquerels per square meter) in northeastern Japan. The figure was produced by the Institut de Radioprotection et de Sûreté Nucléaire based on airborne surveys carried out in April 2011 and published by the Japanese Ministry of Education, Culture, Sports, Science and Technology. The concentric circles demarcate the 20- and 30-km-radius zones around the Fukushima Daiichi Nuclear Power Station. SOURCE: IRSN (2011, Figure 7 [http://hps.org/documents/irsn_fukushima_report.pdf]).
This recommendation was taken up by the U.S. Congress, which subsequently directed5 the U.S. Nuclear Regulatory Commission (USNRC) to contract with NAS for a study focused on five issues:
1. Causes of the crisis at Fukushima;
2. Lessons that can be learned;
3. Lessons’ implications for conclusions reached in earlier NAS studies on the safety and security of current storage arrangements for spent nuclear fuel and high-level waste in the United States, including an assessment of whether the amount of spent fuel currently stored in reactor pools should be reduced;
4. Lessons’ implications for commercial nuclear reactor safety and security regulations; and
5. Potential to improve design-basis threats assessment.
Congress directed that this study “be conducted in coordination with the Department of Energy and, if possible, the Japanese Government” and that the study “build upon the 2004 NAS study of storage issues and complement the other efforts to learn from Fukushima that have already been launched by the [US]NRC and industry.”
The formal statement of task for this NAS study is shown in Sidebar 1.1. It contains four study charges:
• Study Charge 1 addresses the causes of the Fukushima Daiichi accident, focusing particularly on the performance of safety systems at the Fukushima Daiichi plant and the responses of its operators following the earthquake and tsunami. This study charge maps directly to the first issue in the congressional mandate.
• Study Charge 26 focuses on a reevaluation of conclusions from the 2004 NAS report on spent nuclear fuel safety and security (NRC, 2004b, 2006b [public version]). This charge maps to the third issue of the congressional mandate. Moreover, it calls for an evaluation of current storage arrangements for spent fuel in the context of the 2004 NAS study, rather than a de novo assessment of current storage arrangements and whether they should be changed.
• The remaining two study charges map to the second, fourth, and fifth issues of the congressional mandate. They focus on lessons learned from the Fukushima Daiichi accident for improving safety and security of plant systems and operations (Charge 3) and regulations (Charge 4).
5 This directive was contained in the conference report from the Consolidated Appropriations Act of 2012 (Public Law 112-74).
6 For reasons explained later in this chapter, this task is not addressed in this report.
The National Research Council will provide an assessment of lessons learned from the Fukushima nuclear accident for improving the safety and security of nuclear plants in the United States. This assessment will address the following issues:
1. Causes of the Fukushima nuclear accident, particularly with respect to the performance of safety systems and operator response following the earthquake and tsunami.
2. Reevaluation of the conclusions from previous National Academy of Sciences studies on safety and security of spent nuclear fuel and high-level radioactive waste storage, particularly with respect to the safety and security of current storage arrangements and alternative arrangements in which the amount of commercial spent fuel stored in pools is reduced.a
3. Lessons that can be learned from the accident to improve commercial nuclear plant safety and security systems and operations.
4. Lessons that can be learned from the accident to improve commercial nuclear plant safety and security regulations, including processes for identifying and applying design-basis events for accidents and terrorist attacks to existing nuclear plants.
The study may examine policy options related to these issues but should not make policy recommendations that involve nontechnical value judgments.
a This task will be addressed in a subsequent report. It is not addressed in this report.
• An additional sentence was added to the end of the statement of task by NAS to preclude policy recommendations that involve nontechnical value judgments. Such nontechnical factors, for example, cost and public acceptability, can be as important as technical factors in the policy-making process. Policy recommendations are well beyond the technical scope of this study.
7 A “design-basis event” is a postulated event that a nuclear plant system, including its structures and components, must be designed and constructed to withstand without a loss of functions necessary to protect public health and safety.
Several terms are used throughout this report to describe accidents at nuclear power plants (referred to in this report as “nuclear plants”) and the events that initiate them. These terms have specific meanings when applied to nuclear plant safety as described in this sidebar.
Nuclear plant accidents are classified according to their implications for safety and the specific type of events that initiate them, known as an “accident sequence.” Nuclear plants are designed with extensive safety features and operators are trained to handle a wide range of normal and abnormal conditions, including accidents caused by equipment failure, loss of power, and loss of reactor core cooling capability.
There is extensive guidance from the U.S. Nuclear Regulatory Commission (USNRC) in the form of General Design Criteria (Title 10, Part 50, Appendix A, of the Code of Federal Regulations) to cover a specified set of failures or abnormal events, referred to collectively as “design-basis accidents.” A plant design must include specific engineering safety features such as emergency core cooling systems (see Chapter 2) so that the plant operators can recover the plant to a safe state following such accidents. The safety systems for design-basis accidents are designed to limit the damage to the fuel in the reactor core and minimize the release of radioactive material from the plant’s containment to levels that do not affect the health and safety of the general public.
Accidents that are not anticipated by the General Design Criteria specifications are known as “beyond-design-basis accidents.” Such accidents can be initiated
Because the final statement of task for this study differs in wording from the congressional mandate, NAS shared it with appropriate congressional staff prior to initiation of the study to confirm its acceptability.
Given the charge by Congress to focus on lessons learned from the Fukushima accident for U.S. nuclear plants, some explicit choices were made to narrow the study focus before the committee was assembled. In particular, an explicit decision was made not to focus the study on the geological and geophysical processes that produced the earthquake and tsunami. While these are no doubt important to Japan, they have limited relevance to nuclear plant safety in the United States.
The study was carried out using established NAS procedures. The committee appointments were designed to provide diverse expertise and
by a range of events originating inside the plant, referred to as “internal events,” or outside the plant, referred to as “external events.” Examples of internal events include equipment failures such as stuck valves (e.g., a stuck-open valve was the initiator of the 1979 Three Mile Island accident), pipe breaks, and human error (e.g., the 1986 Chernobyl accident was initiated by operator actions that had unforeseen consequences). Examples of external events include terrorist attacks as well as natural events such as large earthquakes and tsunamis (e.g., as discussed in Chapter 3 of this report, an earthquake and tsunami initiated the Fukushima Daiichi accident). Beyond-design-basis accidents can challenge the engineering safety systems at nuclear plants and require improvised operator actions and resources beyond the standard design features of the plant to recover a safe operational state.
If a beyond-design-basis accident results in excessive loss of reactor cooling and heatup of the reactor core, significant core damage can occur, resulting in a “severe accident.” The USNRC defines a severe accident as a “type of accident that may challenge safety systems at a level much higher than expected.” According to the International Atomic Energy Agency, a severe accident involves significant degradation of the reactor core (IAEA, 2007).
Severe accidents are associated with the release of fission products from the reactor fuel and the production of hydrogen from metal–water reactions in the reactor core. In the most extreme cases the fuel in the reactor core can melt, flow to the bottom of the steel vessel that holds the reactor core, and melt through the vessel onto the concrete floor of the plant’s containment. This can result in elevated temperatures, pressures, radiation levels, and combustible gas concentrations, such as hydrogen and carbon monoxide, inside containment.
experience in technical disciplines relevant to the study task; these include geophysics, health physics, human factors, law and regulation, materials sciences, mechanical and structural engineering, nuclear engineering, nuclear power plant operations, nuclear safety and security, public health, and risk analysis. The committee chair is an NAS member with demonstrated leadership capabilities and strong knowledge of Japan and its culture; however, he has no experience with the nuclear power industry. The vice chair, a member of the National Academy of Engineering, has devoted his career to the development and application of risk assessment to improve nuclear plant safety. Biographical sketches of the committee members are provided in Appendix A.
Committee members hold a range of views on the desirability of nuclear energy, as well as other energy-generating technologies, as energy sources for the United States. These views are not relevant to this study because it does not address energy policy issues.
The committee held 39 in-person and conference-call meetings during the course of this study to gather information and develop this report. Information about the committee’s information-gathering meetings is provided in Appendix B. One of these meetings was held in Tokyo, Japan, to enable in-depth discussions about the Fukushima Daiichi accident with Japanese technical experts from industry, academia, and government. The committee also visited the Fukushima Daini, Fukushima Daiichi, and Onagawa plants (see Figure 3.1 in Chapter 3) to learn about their designs, operations, and responses to the earthquake and tsunami. Additionally, subgroups of the committee visited two nuclear plants in the United States that are similar in design to the Fukushima Daiichi plant to learn about their designs and operations: Oyster Creek Generating Station in Forked River, New Jersey, and the Edwin I. Hatch Nuclear Plant in Baxley, Georgia.
The initial strategy for this NAS study was to address all four charges of the study task (Sidebar 1.1) in a single report. However, NAS encountered unanticipated administrative delays in obtaining national security clearances for the committee. (These clearances are needed to address Charge 2 of the statement of task on spent fuel safety and security.) Additionally, once the necessary security clearances were obtained, the committee had to cancel two of its meetings (in April and November 2013) owing to the federal budget sequester and federal government shutdown. These meetings were to have been devoted to gathering information to address Charge 2.
NAS determined that it was not possible to complete the entire study on the original schedule because of these delays. However, because work on the other three study charges was proceeding on schedule, NAS decided to issue the results of that work in the present report and to negotiate a new schedule and budget with the study sponsor (USNRC) for addressing Charge 2 of the study task (Sidebar 1.1) and issuing the results in a separate report. Consequently, with one exception in Chapter 5 (see Section 22.214.171.124), the security portion of the study task is not addressed in this report.
This NAS study is one of many investigations or assessments initiated in the wake of the Fukushima Daiichi accident. Some key written products from these activities are listed in Table 1.1. They include, for example, four accident investigations in Japan: Two by the Japanese government (one each by the executive and legislative branches), one by a private organization, and one by Tokyo Electric Power Company, owner and operator of the Fukushima Daiichi plant. Nuclear plant operators and regulators in several countries have also conducted assessments to determine if operational or regulatory changes are needed to cope with extreme natural events (e.g., earthquakes and floods) that could occur at nuclear plants. The Interna-
TABLE 1.1 Selected Key Reports from Fukushima Daiichi Accident-Related Investigations and Assessments (as of June 2014)
Japanese Government and Related
- Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety (June 2011) (Government of Japan, 2011b)
- Additional Report of the Japanese Government to the IAEA—The Accident at TEPCO’s Fukushima Nuclear Power Stations (Second Report) (September 2011) (Government of Japan, 2011a)
- Investigation Committee on the Accident at Fukushima Nuclear Power Stations of Tokyo Electric Power Company (Established by Japanese Cabinet): Interim Report (December 2011) (Investigation Committee, 2011)
- Nuclear and Industrial Safety Agency, Technical Knowledge of the Accident at Fukushima Dai-ichi Nuclear Power Station of Tokyo Electric Power Co., Inc. (Provisional Translation) (March 2012) (NISA, 2012)
- Investigation Committee on the Accident at Fukushima Nuclear Power Stations of Tokyo Electric Power Company (Established by Japanese Cabinet), Final Report (July 2012) (Investigation Committee, 2012)
- National Diet of Japan Fukushima Nuclear Accident Independent Investigation Commission (NAIIC), The Official Report of the Fukushima Nuclear Accident Independent Investigation Commission (July 2012) (NAIIC, 2012)
- Japan Nuclear Technology Institute, Examination of Accident at Tokyo Electric Power Co., Inc.’s Fukushima Daiichi Nuclear Power Station and Proposal of Countermeasures (October 2011) (JANTI, 2011)
- TEPCO, Fukushima Nuclear Accident Analysis Report: Interim Report (December 2011) (TEPCO, 2011a)
- TEPCO, Fukushima Nuclear Accident Investigation Report: Interim Report, Supplementary Volume (December 2011) (TEPCO, 2011b)
- Tokyo Electric Power Company (TEPCO), The Nuclear Safety and Quality Assurance Meeting’s Accident Investigation Examination Committee’s Opinion of the Tokyo Electric Power Company’s “Fukushima Nuclear Accident Investigation Report” (Midterm Report) (November 2011) (TEPCO, 2011d)
- TEPCO, Mid-and-Long-Term Roadmap Towards the Decommissioning of Fukushima Daiichi Nuclear Power Units 1-4 (December 2011) (TEPCO, 2011c) [Note: this document was updated in 2012 and 2013.]
- TEPCO, Estimation of the Released Amount of Radioactive Materials into the Atmosphere as a Result of the Accident in the Fukushima Daiichi Nuclear Power Station (May 2012) (TEPCO, 2012a)
- TEPCO, Fukushima Nuclear Accident Analysis Report (June 2012) (TEPCO, 2012b)
- TEPCO, Evaluation of the Situation of Cores and Containment Vessels of Fukushima Daiichi Nuclear Power Station Units-1 to 3 and Examination into Unsolved Issues in the Accident Progression: Progress Report No. 1 (December 2013) (TEPCO, 2013)
Other Japanese Organizations
- Atomic Energy Society of Japan (AESJ). Estimated Current Status of Fukushima-Daiichi Nuclear Power Plant Units 1-3 (April 18, 2011) (AESJ, 2011a)
- AESJ. Lessons Learned from the Accident at the Fukushima Daiichi Nuclear Power Plant (May 9, 2011) (AESJ, 2011b)
- Science Council of Japan, Report to the Foreign Academies from Science Council of Japan on the Fukushima Daiichi Nuclear Power Plant Accident (May 2011) (SCJ, 2011)
- Rebuild Japan Initiative Foundation, Independent Investigation Commission on the Fukushima Nuclear Accident (February 2012) (RJIF, 2014)
- International Atomic Energy Agency, IAEA International Fact Finding Expert Mission of the Fukushima Dai-Ichi NPP Accident Following the Great East Japan Earthquake and Tsunami (June 2011) (IAEA, 2011)
- International Atomic Energy Agency, International Nuclear Safety Advisory Group Annual Assessment Letters for 2011, 2012, and 2013 (INSAG, 2011, 2012, 2013)
- Nuclear Energy Agency, The Fukushima Daiichi Nuclear Power Plant Accident: OECD/NEA Nuclear Safety Response and Lessons Learnt (September 2013) (NEA, 2013)
U.S. Government and Related
- U.S. Nuclear Regulatory Commission (The Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident), Recommendations for Enhancing Reactor Safety in the 21st Century (July 2011) (USNRC NTTF, 2011)
- Blue Ribbon Commission on America’s Nuclear Future, Report to the Secretary of Energy (January 2012) (BRC, 2012)
- Sandia National Laboratories, Fukushima Daiichi Accident Study (Status as of April 2012) (July 2012) (Gauntt et al., 2012b)
- Government Accountability Office, Nuclear Safety: Countries’ Regulatory Bodies Have Made Changes in Response to the Fukushima Daiichi Accident (March 2014) (USGAO, 2014)
U.S. Industry and Related
- Institute of Nuclear Power Operations (INPO), Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station (November 2011) (INPO, 2011)
- Electric Power Research Institute (EPRI), Fukushima Daiichi Accident–Technical Causal Factor Analysis (March 2012) (EPRI, 2012a)
- EPRI, Summary of the EPRI Early Event Analysis of the Fukushima Daiichi Spent Fuel Pools Following the March 11, 2011 Earthquake and Tsunami in Japan (May 2012) (EPRI, 2012c)
- American Nuclear Society, Fukushima Daiichi: ANS Committee Report (June 2012) (ANS, 2012)
- INPO, Lessons Learned from the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station (August 2012) (INPO, 2012)
- EPRI, Fukushima Technical Evaluation Phase 1—MAAP5 Analysis (April 2013) (EPRI, 2013)
- Lochbaum et al., Fukushima: The Story of a Nuclear Disaster (February 2014) (Lochbaum et al., 2014)
Other Governments and Related
- Government of the United Kingdom, Japanese Earthquake and Tsunami: Implications for the UK Nuclear Industry Final Report (September 2011) (ONR, 2011)
- Canadian Nuclear Safety Commission, CNSC Fukushima Task Force Report (October 2011) (CNSC, 2011)
- Swiss Federal Nuclear Safety Inspectorate, Lessons Fukushima 11032011: Lessons Learned Checkpoints Based on the Nuclear Accidents at Fukushima (October 2011) (ENSI, 2011)
tional Atomic Energy Agency (IAEA) and Nuclear Energy Agency have organized meetings of member countries to share information and best practices from these assessments. The IAEA plans to issue a report in 2015 on the causes of the Fukushima Daiichi accident and lessons learned.
In the United States, the nuclear industry launched a fast-track effort to understand the Fukushima Daiichi accident and identify and implement appropriate countermeasures at U.S. nuclear plants. This effort is being led by the Institute of Nuclear Power Operations and Nuclear Energy Institute with technical support from plant operators and the Electric Power Research Institute.
The U.S. government, primarily through the USNRC with technical support from the Department of Energy and its national laboratories, launched a parallel effort to reevaluate nuclear plant safety regulations in light of the accident. Initially, the USNRC established a task force of senior agency staff to review current USNRC processes and regulations and make recommendations to improve them. The USNRC subsequently created the Japan Lessons-Learned Project Directorate,8 overseen by a steering committee of senior agency officials, to implement the task force’s recommendations. Several of the task force’s recommendations were implemented by the USNRC while this NAS study was under way and work to implement others was proceeding.
The committee did not have the time to perform an in-depth evaluation of these industry, government, and international efforts. However, the committee used the written products from these activities to inform its
8 This directorate became the Japan Lessons-Learned Division effective June 1, 2014.
own work. The committee has provided a cross-walk between its findings and recommendations and key findings and recommendations from other investigations and assessments for the benefit of readers (see Appendix E).
The peer-reviewed literature also served as an important source of information for this study. This literature was particularly important for understanding, for example, the earthquake and tsunami; Japanese laws, regulations, and nuclear safety culture; human factors for responses to emergencies; and emergency preparedness and response.
The committee relied almost exclusively on English-language information sources for this study. Fortunately, English translations of key Japanese government and industry reports were readily available to the committee for this purpose (e.g., see Table 1.1). However, the committee did not have access to the full range of Japanese-language papers, reports, and analyses of the Fukushima Daiichi accident.
Most of the industry, government, and international activities described previously were undertaken under demanding schedules, typically a few months to a year, and were intended to implement safety improvements to existing nuclear plants on an accelerated schedule. This NAS study is being carried out on a longer (2-year) schedule and has a different scope: It is intended to be a broad-scope and high-level review of lessons learned from the Fukushima Daiichi accident to improve safety and security of U.S. nuclear plants, taking into account where possible the results of these other investigations and assessments (e.g., Table 1.1). This NAS study is intended to complement the efforts by industry and regulators to learn from the Fukushima Daiichi accident, as Congress directed when it issued the study mandate.
A great deal of additional information about the Fukushima Daiichi accident—for example, the status of currently inaccessible plant components, the location and characteristics of the damaged reactor cores, and pathways for hydrogen and radioactive material migration—will likely be uncovered as the reactors are dismantled and studied over the next four decades.9 As understanding of accident progression and phenomenology improve, new lessons will likely be learned and some existing lessons, including those in this report, may require revision.
The NAS was asked to carry out a technical assessment of lessons learned from the Fukushima Daiichi accident. NAS was not asked to:
• Assign blame for the accident. The reports from the Japanese accident investigations, which are referenced in Table 1.1, address this issue.
9 TEPCO’s roadmap for decommissioning the Fukushima Daiichi plant can be found at http://www.tepco.co.jp/en/nu/fukushima-np/roadmap/images/t120730_03-e.pdf. Accessed on June 3, 2014.
• Recommend changes to nuclear plant operations or regulations in Japan or other foreign countries. The mandate from Congress directed NAS to focus on U.S. nuclear plants. However, the committee hopes that the results of this NAS study will be useful to other countries.
• Recommend specific changes to U.S. laws or regulations, for example, to shut down or impose additional operating requirements on reactors in the United States. Such changes are the responsibility of the U.S. government, require the participation of affected stakeholders, and involve consideration of nontechnical factors that are beyond the scope of this study.
• Recommend specific changes to the designs or operations of U.S. nuclear plants. Such changes are the responsibility of the nuclear industry and its regulator, acting in response to their own assessments and with input from interested organizations and individuals, and require plant design-specific information that is unavailable to the committee.
• Assess whether U.S. nuclear plants are safe. The primary focus of this study is on how nuclear plant safety and security can be improved based on lessons learned from the Fukushima Daiichi accident. This focus should not be construed to suggest that nuclear plants are currently unsafe. Nuclear plant operators and regulators strive to make continuous improvements to nuclear plant safety (see Chapter 7).
The committee focused its information-gathering efforts on boiling water reactor (BWR) plants having designs similar to the Fukushima Daiichi plant. Some of the findings and recommendations in this report apply specifically to those plants. However, many of the findings and recommendations apply to both BWR and pressurized water reactor plants. Unless otherwise noted in individual findings and recommendations, they are intended to apply to both plant types.
This report is organized into seven chapters:
• Chapter 1 (this chapter) describes the study task and process.
• Chapter 2 provides information on nuclear plant design and operations in Japan and the United States. It is intended to provide background information to support the more detailed discussions of the Fukushima Daiichi accident that appear in Chapters 3 and 4.
• Chapter 3 describes the Great East Japan Earthquake and tsunami and their impacts on nuclear plants in Japan.
• Chapter 4 describes the accident at the Fukushima Daiichi plant.
• Chapter 5 presents the committee’s lessons learned from the Fukushima Daiichi accident for nuclear plant operations and regulations in the United States.
• Chapter 6 describes the offsite emergency response associated with the Fukushima Daiichi accident and lessons learned from that response for the United States.
• Chapter 7 describes the nuclear safety culture in Japan and lessons learned for the United States.
The appendixes provide additional information to support the discussions in the report chapters.