Few nuclear power plants in the U.S. have updated or conducted adequate risk assessments since the 1990s, the Government Accountability Office found in a new report, and the Nuclear Regulatory Commission should analyze whether all plants should be required to develop new plans to assess natural hazards that could threaten the safety of the plants.
When the nation's 104 operating reactors were originally licensed before 1997, the Commission (NRC) required licensees to assess natural hazards using "deterministic analysis." Informed by historical experience, test results, and expert judgment. Deterministic analysis considers a specific set of potential accidents and how the consequences of those accidents can be prevented and mitigated," the Government Accountability Office (GAO) report said. California's Diablo Canyon and San Onofre nuclear plants presumably are among those 104 plants.
Subsequent to most of these initial licenses being issued, NRC has endorsed another assessment method called "probabilistic risk assessment" (PRA) — a systematic method for assessing what can go wrong, its likelihood, and its consequences, resulting in quantitative estimates of risk, seen as a means to enhance and extend traditional deterministic analysis, the report said.
In 1991, the report said, NRC requested that licensees voluntarily examine their reactors' vulnerability to natural hazards and suggested PRA as one of several possible methods for licensees to use in their examinations. However, most licensees opted to use other methods. NRC officials and nuclear power industry representatives — and reflected in data GAO obtained from five licensees that together operate 25 reactors — found few licensees are likely to have developed or updated since the 1990s the PRAs that address natural hazards. NRC would have to conduct an analysis to determine whether or not to require licensees to develop PRAs that address natural hazards. NRC officials said the agency has not conducted such an analysis.
On March 11, 2011, the report said, an earthquake triggered a tsunami wave that exceeded the seawall at Japan's Fukushima Daiichi nuclear power plant, leading to the release of radioactive material into the environment. The disaster raised questions about the threats that natural hazards, such as earthquakes and floods, may pose to U.S. commercial nuclear power reactors. NRC licenses and regulates U.S. nuclear power reactors. NRC criteria for licensees to assess natural hazards were developed using an approach that required reactors to be designed according to a set of potential accidents using deterministic analysis. Since the 1990s, NRC has been encouraging the use of PRA as part of a risk-informed, performance-based approach.
The GAO report explained the report's findings this way:
"The experts in assessing natural hazards and/or nuclear reactor risks that GAO interviewed offered a range of views on (1) the overall adequacy of NRC processes for assessing the threats that natural hazards pose to operating U.S. nuclear power reactors and (2) what, if any, changes to those processes are warranted. Several experts said they believe NRC processes are generally adequate for assessing the threats that natural hazards pose to operating reactors. However, more than half of the experts GAO interviewed suggested expanding the use of PRA for assessing natural hazards as a complement to traditional deterministic analyses to provide a more robust approach. Those experts cited a number of advantages to doing so, including that PRA can help identify vulnerabilities that might otherwise be overlooked by relying on traditional deterministic analyses alone. Several experts also identified challenges to expanding the use of PRA for assessing natural hazards, including the limited number of experts qualified to develop PRAs and the costs of doing so."
The GAO said it was asked to (1) determine the extent to which PRA is applied to natural hazards at operating U.S. reactors and (2) describe expert views on and suggested changes, if any, to NRC processes for assessing natural hazards at such reactors.
GAO recommended that NRC analyze whether licensees of operating reactors should be required to develop PRAs that address natural hazards. The report said the NRC agreed with the recommendation and stated it will conduct the analysis in the context of ongoing initiatives.
Talk Radio News Service reported (GAO - More Safety Precautions Needed for Nuclear Reactors) that "Senator Barbara Boxer (D-CA), chair of the Senate Environmental and Public Works Committee, slammed the NRC, stating, 'There is absolutely no excuse for the NRC's failure to require the most up to date methods to asses the threat posed by natural disasters . . . action is needed now to ensure standards are in place that best protect the health and safety of the American public.'"
"Echoing that sentiment, U.S. Rep. Ed Markey (D-MA), ranking member of the House Natural Resources Committee, explained, 'we know what happened at Fukushima could happen here in the U.S., and we should utilize the best and latest information available to asses vulnerabilities. Markey referenced the tsunami in Japan last year damaged numerous nuclear power plants releasing harmful radiation.' "
