31 May (NucNet): The US nuclear regulator should analyse whether operators of nuclear reactors should be required to develop probabilistic risk assessments (PRAs) that address natural hazards, a report says.
The Government Accountability Office (GAO) report says companies licensed to operate nuclear plants apply PRA to natural hazards at operating US nuclear reactors “to a limited extent”.
The GAO said it carried out the study because the Fukushima-Daiichi accident “raised questions” about the threats that natural hazards such as earthquakes and floods might pose to US reactors.
The study says 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.
In 1991, the NRC requested that operators 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, the GAO report says. According to NRC officials and nuclear power industry representatives – and reflected in data the GAO obtained from five licensees that together operate 25 reactors – few licensees are likely to have developed or updated PRAs that address natural hazards since the 1990s.
The report says: “NRC documents and most experts we spoke with indicate that PRA offers the NRC and licensees a number of advantages that, as a complement to traditional deterministic assessments, can provide a more robust approach to assessing natural hazards.”
In a letter responding to the GAO report, the NRC said it agrees that it could analyse whether operators of nuclear plants should be required to develop and maintain PRAs that address natural hazards. It said it had already begun a number of initiatives “that are directly relevant to the issue”.
One initiative is that the NRC’s office for nuclear regulatory research is conducting a pilot PRA study at the Vogtle nuclear plant. The study will address the impact of natural hazards on reactors and spent fuel pools.
The report is online: www.gao.gov/assets/600/590431.pdf
