To avoid the kind of complacency over safety that led to the March 2011 disaster at the Fukushima Daiichi Nuclear Power Station in Japan, U.S. nuclear plant operators and regulators must be prepared to take timely action to upgrade plant safety features in line with advances in the understanding of natural hazards, states a report released today.
The report, Lessons Learned from the Fukushima Nuclear Accident for Improving Safety of U.S. Nuclear Plants, was written by a committee of the National Academy of Sciences. The panel drew on Japanese and international investigations into the causes of the Fukushima disaster, precipitated by the magnitude-9 earthquake and tsunami of 11 March 2011.
Like previous assessments, the academy’s report cites as a key contributing factor to the disaster the "failure of the plant owner [Tokyo Electric Power Co.] and the principal regulator [the Nuclear and Industrial Safety Agency] to protect critical safety equipment at the plant from flooding in spite of mounting evidence that the plant’s current design basis for tsunamis was inadequate." The earthquake cut power from the electrical grid and the tsunami swamped the plant’s emergency generators, which were located in basements in the complex. The total loss of power deprived plant operators of reliable data on conditions within the reactors. They could not control key equipment, and therefore could not cool the reactors. Three of the plant’s six reactors suffered core meltdowns, hydrogen explosions damaged the facility, and the release of radioactive plumes led to the evacuation of about 100,000 nearby residents, many of whom remain in temporary housing.
The report notes that plant personnel were inadequately trained and lacked sufficient manpower to cope with simultaneous crises at several reactors. The situation was exacerbated by the loss of communication lines between the plant and the headquarters in Tokyo.
The report’s authors describe the disaster as a beyond-design-basis event, because several factors were more severe than anticipated by designers—particularly the earthquake and tsunami hazards. "The overarching lesson learned from the Fukushima Daiichi accident is that nuclear plant licensees and their regulators must actively seek out and act on new information about hazards that have the potential to affect the safety of nuclear plants," the report concludes, adding that plant operators "must take timely actions to implement countermeasures when such new information results in substantial changes to risk profiles at nuclear plants." The report cites a need to strengthen capabilities "for identifying, evaluating, and managing the risks from beyond-design-basis events," including large earthquakes or floods that occur very infrequently.
During a dial-in press conference to discuss the report, committee member B. John Garrick, a consultant in Laguna Beach, California, explained that there is also a need to assess how a severe accident, simultaneously affecting multiple reactors at one site and within a region, can complicate crisis management at a time when electricity, support, and emergency services from off-site could be disrupted, as happened at the Fukushima plant. In such circumstances, plant personnel must be trained to respond in an ad hoc manner to circumstances that are nearly impossible to completely predict, the report states.
Among a number of specific lessons, the report identifies the need to ensure a continuing source of power for instrumentation and safety system control and to cool and depressurize reactors; to improve monitoring of radiation levels both on-site and in the surrounding community; and to provide more robust communication links between on-site and off-site support facilities.
Robert Bari, a physicist at Brookhaven National Laboratory in Upton, New York, noted that plant operators and regulators in the United States and other countries are already taking steps to upgrade plant systems, operating procedures, and operator training in response to the Fukushima disaster. But "it is too soon to evaluate their comprehensiveness, effectiveness, or status," he said.
Norman Neureiter, acting director of the Center for Science, Technology, and Security Policy of AAAS, which publishes Science and ScienceInsider, chaired the committee of 21 experts.