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Introduction

The U.S. Congress¹ asked the National Academy of Sciences (NAS) to conduct a technical study on lessons learned from the Fukushima Daiichi nuclear accident (Sidebar 1.1) for improving safety and security of commercial nuclear power plants² in the United States. Congress directed the U.S. Nuclear Regulatory Commission (USNRC) to contract with NAS for this study and also directed that the study “be conducted in coordination with the Department of Energy and, if possible, the Japanese Government” and “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 2004 NAS study was also the result of a congressional request made following the September 11, 2001, terrorist attacks on the U.S. homeland. That study examined the safety and security of spent fuel storage in pools and dry casks. Two reports were issued from that study: a classified report (NRC, 2004) and an abbreviated public version of that report (NRC, 2006³).

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¹ The request is contained in the Consolidated Appropriations Act of 2012 (P.L. 112-74).

² The terms nuclear power plant and nuclear plant are used interchangeably in this report.

³ Available for free download from The National Academies Press: http://www.nap.edu/catalog/11263/safety-and-security-of-commercial-spent-nuclear-fuel-storage-public.

The task for the present study is given in Sidebar 1.2⁴ and contains four specific charges:

• Study Charge 1 addresses the causes of the Fukushima Daiichi accident, focusing on the performance of safety systems at the Fukushima Daiichi plant and the responses of its operators following the earthquake and tsunami.
• Study Charge 2 calls for a reevaluation of the conclusions from the 2004 NAS report on spent nuclear fuel safety and security (NRC, 2004). It also calls for an evaluation of current storage arrangements for spent fuel (i.e., pool storage versus dry cask storage) in the context of the 2004 NAS study.
• Study Charges 3 and 4 focus on lessons learned from the Fukushima Daiichi accident for improving safety and security of plant sys-

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⁴ The statement of task for this study differs in wording from the congressional mandate. NAS shared the revised task with appropriate congressional staff to confirm its acceptability.

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.

This study is being carried out in two phases. The phase 1 study report, which was issued in July 2014 (NRC, 2014), addresses the causes of the Fukushima accident and lessons learned for nuclear plant safety. The present report, which provides the results of phase 2 of this study, addresses the following three issues:

1. Lessons learned from the accident for nuclear plant security.
2. Lessons learned from the accident for spent fuel storage safety and security.
3. Reevaluation of conclusions from previous Academies studies on safety and security of spent fuel storage.

1.1 STUDY PROCESS

Phase 2 of this NAS study was carried out by a subset of members from the phase 1 study committee (see NRC, 2014). The phase 2 committee has expertise and experience in several technical disciplines relevant to the study tasks, including geophysics, human factors, law and regulation, materials sciences, mechanical and structural engineering, nuclear engineering, nuclear safety and security, public health, and risk analysis. Biographical sketches of committee and staff members are provided in Appendix A.

The committee held 28 in-person and conference-call meetings during the course of this study to gather information and develop this report. A list of presentations made at the committee’s information-gathering meetings is provided in Appendix B. The committee visited several nuclear plants during the first phase of this study, including the Fukushima Daini, Fukushima Daiichi, and Onagawa plants in Japan and the Oyster Creek Generating Station and Edwin I. Hatch Nuclear Plant in the United States (see NRC, 2014, Appendix B). No additional plant visits were made during this

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⁵ 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. Such events are described in NRC (2014). See especially Section 5.2 in Chapter 5.

phase 2 study. The committee also received briefings from the USNRC on aspects of spent fuel safety and security during the first phase of this study.

1.2 STRATEGY FOR ADDRESSING THE STUDY CHARGE

This NAS study is one of many investigations/assessments initiated in the wake of the Fukushima Daiichi accident. Some key written products from these activities are listed in Table 1.1 of NRC (2014). Additional written products have been published since NRC (2014) was released. For example, the International Atomic Energy Agency (IAEA) released its comprehensive assessment of the Fukushima Daiichi accident on August 31, 2015 (IAEA, 2015); the government of Japan submitted an update of Japan’s comprehensive report on conditions at the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Station on September 30, 2015 (Government of Japan, 2015).

Investigations/assessments in the United States were led by the nuclear power industry, through the Institute of Nuclear Power Operations and Nuclear Energy Institute with technical support from plant operators and the Electric Power Research Institute, and also by the U.S. government, primarily through the USNRC with technical support from the Department of Energy and its national laboratories. The work of these groups is described in NRC (2014). The committee used the written products from these activities to inform its work. The peer-reviewed literature also served as an important source of information for this study.

The committee relied almost exclusively on English-language information sources for informing itself on the Fukushima Daiichi accident. English translations of key Japanese government and industry reports were readily available to the committee for this purpose (e.g., see Table 1.1 in NRC, 2014). However, the committee did not have access to the full range of Japanese-language papers, reports, and analyses of the Fukushima Daiichi accident.

There is still a great deal to be learned about the impacts of the accident on the Fukushima Daiichi plant, including impacts on spent fuel storage. Additional information will likely be uncovered as the plant is dismantled and studied, perhaps resulting in new lessons learned and revisions to existing lessons, including those in this report.

As noted in NRC (2014), NAS was asked to carry out a technical assessment of lessons learned from the Fukushima Daiichi accident. NAS was not asked to

• 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 com-

• mittee 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.

1.3 REPORT ORGANIZATION

This report is organized into seven chapters:

• Chapter 1 (this chapter) provides background information about this study.
• Chapter 2 describes the impacts of the March 11, 2011, Great East Japan Earthquake and tsunami on spent fuel storage at the Fukushima Daiichi plant and lessons learned for the United States.
• Chapter 3 identifies lessons that can be learned from the accident to improve commercial nuclear plant security systems, operations, and regulations.
• Chapter 4 provides a reevaluation of the findings and recommendations from previous NAS reports on spent fuel safety and security.

Chapters 5-7 provide supporting information for the reevaluation in Chapter 4:

• Chapter 5 focuses on security risk assessment.
• Chapter 6 focuses of loss-of-cooling events in spent fuel pools.
• Chapter 7 focuses on expedited transfer of spent fuel from pools to dry casks.

Findings and recommendations are provided in Chapters 2, 3, and 4. They are numbered using the format x.z, where x is the chapter number and z is a serial number (1, 2,…).

The appendixes provide committee and staff biographical sketches (Appendix A), a list of presentations made at the committee’s information-gathering meetings (Appendix B), conversions and units (Appendix C), and acronyms (Appendix D).