The Nuclear Regulatory Commission (NRC) should examine the benefits of mandating that nuclear plants in the U.S. add probabilistic risk assessment (PRA) to methods used to evaluate and prepare for natural hazards, the Government Accountability Office (GAO) finds in a new report.

PRA is a systematic method for assessing what can go wrong, its likelihood, and its potential consequences to determine quantitative estimates of risk in order to provide insights into the strengths and weaknesses of the design and operation of a nuclear power reactor. Companies licensed to operate nuclear power reactors already apply PRA to natural hazards—but only to a limited extent, the report finds. The 104 operating reactors in the U.S. that were originally licensed before 1997 were all required by the NRC to assess natural hazards using deterministic analysis. Through policy statements, the NRC has since endorsed PRA as a means to enhance and extend traditional deterministic analysis, and in 1991, the 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.

But “most licensees opted to use other methods,” the GAO report says. “According to NRC officials and nuclear power industry representatives—and reflected in data GAO obtained from five licensees that together operate 25 reactors—few licensees are likely to have developed or updated since the 1990s 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. According to agency officials, NRC has not conducted such an analysis.”

Several experts interviewed by the GAO told the congressional investigative arm that NRC processes are “generally adequate” for assessing threats that natural hazards could pose to operating reactors. But more than half the experts interviewed also suggested that expanding the use of PRA for assessing natural hazards as a complement to traditional deterministic analyses could provide a “more robust” approach, the report says.

“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,” it adds.

Rep. Edward J. Markey (D-Mass.) and Sen. Barbara Boxer (D-Calif.) asked the GAO to examine the NRC’s policies in March 2010 (Sen. Boxer joined the request in Feb. 2012).

“The threat of natural disasters to nuclear reactor safety is not theoretical,” said the lawmakers in a joint statement. They contend that eight nuclear reactors are on the “seismically active” West Coast, approximately 27 are near the New Madrid seismic zone in the Midwest, and five are in earthquake-prone South Carolina. Following the devastating Fukushima crisis in Japan in March 2011, several natural hazards have hit the U.S. and affected nuclear plants. Last summer, a magnitude 5.8 earthquake centered near Mineral, Va., caused the North Anna Nuclear Generating Station to shut down; summer flooding in Nebraska threatened the Fort Calhoun and Cooper nuclear power plants; Hurricane Irene caused the shutdown or otherwise impacted the emergency systems of at least nine nuclear reactors in August of 2011; and tornadoes caused the shutdown of several nuclear reactors in 2011.

“This report is yet another indication that while the NRC races ahead to issue or extend licenses for nuclear power plants, it has fallen behind inexcusably in addressing the safety of these very same facilities,” said Rep. Markey, top Democrat on the House Natural Resources Committee and senior member of the House Energy and Commerce Committee. “We know what happened at Fukushima could happen here in the U.S., and we should utilize the best and latest information available to assess vulnerabilities so we can ensure the safety of our operating nuclear reactors.”

Sources: POWERnews, GAO, Rep. Markey