Fall 2014 Vol. 14 Number 1
Learning From Fukushima
Report Examines Lessons for the U.S.
On March 11, 2011, at 2:46 p.m. local time, a large earthquake struck off the northeast coast of Japan. Approximately 50 minutes later, a tsunami flooded parts of the Fukushima Daiichi Nuclear Power Plant, sparking a chain of events that resulted in the meltdown of three reactor cores and hydrogen explosions in three reactor buildings. Offsite releases of radioactive materials contaminated land in Fukushima and several neighboring prefectures, which prompted widespread evacuations of local populations, triggered large economic losses, and led to the eventual shutdown of all nuclear power plants in Japan.
The U.S. Congress requested that the National Academy of Sciences assess the causes of the accident and determine what could be learned and applied here in the United States.
The personnel at the Fukushima Daiichi plant responded to the accident with courage and resilience, said the committee that undertook the study, which found that the employees' actions likely reduced its severity and the magnitude of offsite radioactive material releases. However, several factors prevented plant personnel from achieving greater success and contributed to the overall severity of the accident. The overarching lesson learned from the accident, says the committee's report, is that nuclear plant licensees and their regulators must actively seek out and act on new information about hazards that can affect the safety of nuclear plants.
In response to the accident, nuclear plant operators and regulators in the U.S. and other countries are taking actions to upgrade nuclear plant systems, operating procedures, and training. As the U.S. nuclear industry and its regulator, the U.S. Nuclear Regulatory Commission (USNRC), implement upgrades, the report recommends particular attention to improving specific systems at nuclear plants: DC power for instrumentation and safety system control; tools for estimating real-time plant status during power losses; reactor heat removal and depressurization; 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; instrumentation for onsite and offsite radiation and security monitoring; and communications and real-time information systems. The report also recommends the U.S. nuclear industry and the USNRC improve resource availability and operator training and strengthen their capabilities for assessing risks from events that could challenge the design of nuclear plant structures and components. Part of this effort should focus on external 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. The USNRC should support these efforts by providing guidance and overseeing rigorous peer review, and eventually use these strengthened risk-assessment capabilities to further incorporate modern risk concepts into its nuclear safety regulations. The industry and its regulator should continuously seek to maintain a strong safety culture.
Four decades of analysis and operating experience have demonstrated that reactor core-damage risks are dominated by "beyond-design-basis events" -- such as equipment failures, loss of power, and inability to cool the reactor core -- that could impair critical safety functions, the report says. The Fukushima Daiichi, Three Mile Island, and Chernobyl accidents were all initiated by beyond-design-basis events. Current approaches for regulating nuclear plant safety are clearly inadequate for preventing core-melt accidents and mitigating their consequences, the committee found. 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.
-- Jennifer Walsh
The study was chaired by Norman Neureiter, senior adviser at the Center for Science Diplomacy and acting director of the Center for Science, Technology, and Security Policy of the American Association for the Advancement of Science. The study was sponsored by the U.S. Nuclear Regulatory Commission.