• 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.