U.S. nuclear plant licensees should seek, act on nuclear plant hazards information
Nuclear plant operators and regulators in the United States and other countries are taking useful actions to upgrade nuclear plant systems, operating procedures, and operator training in response to the Fukushima Daiichi accident. As the U.S. nuclear industry and its regulator, the U.S. Nuclear Regulatory Commission (USNRC), implement these actions, the report recommends particular attention to improving the availability, reliability, redundancy, and diversity of specific nuclear plant systems:
- DC power for instrumentation and safety system control
- tools for estimating real-time plant status during loss of power
- reactor heat removal, reactor depressurization, and containment venting systems and protocols
- instrumentation for monitoring critical thermodynamic parameters — for example temperature and pressure — in reactors, containments, and spent-fuel pools
- hydrogen monitoring, including monitoring in reactor buildings, and mitigation
- instrumentation for both onsite and offsite radiation and security monitoring
- communications and real-time information systems
Further to improve the resilience of U.S. nuclear plants, the report also recommends:
- The U.S. nuclear industry and the USNRC should give specific attention to improving resource availability and operator training, including training for developing and implementing ad hoc responses to deal with unanticipated complexities.
- The U.S. nuclear industry and USNRC should strengthen their capabilities for assessing risks from events that could challenge the design of nuclear plant structures and components and lead to a loss of critical safety functions. Part of this effort should focus on events that have the potential to affect large geographic regions and multiple nuclear plants, including earthquakes, tsunamis and other geographically extensive floods, and geomagnetic disturbances. USNRC should support these efforts by providing guidance on approaches and overseeing rigorous peer review.
- USNRC should further incorporate modern risk concepts into its nuclear safety regulations using these strengthened capabilities.
- USNRC and the U.S. nuclear industry must continuously monitor and maintain a strong safety culture and should examine opportunities to increase the transparency of and communication about their efforts to assess and improve nuclear safety.
Until now, U.S. safety regulations have been based on ensuring plants are designed to withstand certain specified failures or abnormal events, or “design-basis-events”— such as equipment failures, loss of power, and inability to cool the reactor core — that could impair critical safety functions. However, four decades of analysis and experience have demonstrated that reactor core-damage risks are dominated by “beyond-design-basis events,” the report says. The Fukushima Daiichi, Three Mile Island, and Chernobyl accidents were all initiated by beyond-design-basis events. The committee found that current approaches for regulating nuclear plant safety, which have been based traditionally on deterministic concepts such as the design-basis accident, are clearly inadequate for preventing core-melt accidents and mitigating their consequences. A more complete application of modern risk-assessment principles in licensing and regulation could help address this inadequacy and enhance the overall safety of all nuclear plants, present and future.
The Fukushima Daiichi accident raised the question of whether offsite emergency preparedness in the United States would be challenged if a similar-scale event — involving several concurrent disasters — occurred here. The committee lacked time and resources to perform an in-depth examination of U.S. preparedness for severe nuclear accidents. The report recommends that the nuclear industry and organizations with emergency management responsibilities assess their preparedness for severe nuclear accidents associated with offsite regional-scale disasters. Emergency response plans, including plans for communicating with affected populations, should be revised or supplemented to ensure that there are scalable and effective strategies, well-trained personnel, and adequate resources for responding to long-duration accident/disaster scenarios. In addition, industry and emergency management organizations should assess the balance of protective actions — such as evacuation, sheltering-in-place, and potassium iodide distribution — for affected offsite populations and revise the guidelines as appropriate. Particular attention should be given to protective actions for children, those who are ill, and the elderly and their caregivers; long-term social, psychological, and economic impacts of sheltering-in-place, evacuation, and/or relocation; and decision making for resettlement of evacuated populations in areas that were contaminated by radioactive material.
The study was sponsored by the U.S. Nuclear Regulatory Commission.
— Read more in Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants (National Academies Press, 2014)
