Rapid Response: AP Ignores Continuous Upgrading of Reactor Seismic Standards by Industry, NRC, Sept. 1, 2011
The Associated Press article “Gov’t Says 27 US Reactors Could Be More Vulnerable to Earthquakes; Review Planned” misconstrues the ongoing evaluations the U.S. Nuclear Regulatory Commission and the nuclear energy industry perform to ensure seismic safety at U.S. commercial nuclear reactors.
Below, we take a deeper look at the article’s claims.
The article says, “Federal scientists update seismic assessments every five to six years to revise building codes for some structures. But no similar system is in place for all but two of the nation’s 104 reactors.”
The nuclear energy industry and NRC continuously review seismic data and examine safety at U.S. reactors. In fact, some companies already have reviewed their plant’s ability to withstand earthquakes in the vicinity for their site using updated NRC data. These calculations show a low risk of damage to reactor fuel as a result of an earthquake.
We have learned new information about past earthquakes from reviewing additional written accounts of those events and by performing geological studies. Seismic source models are being updated to incorporate this data as well as that from other, more recent earthquakes that have occurred.
Also, NRC conducts ongoing studies of seismic risk to nuclear power plants, which the agency tracks as a generic issue (GI-199) because there are open issues pertaining to some reactors.
In 2010, the NRC issued information notice 2010-18 to inform operators of nuclear power plants and independent spent fuel storage facilities of its findings. The NRC’s updated assessment of seismic risk to nuclear power plants in the central and eastern United States showed that all operating reactors have sufficient safety margin for seismic events and remain consistent with the agency’s safety goals.
The article states, “Current regulations don’t require the NRC to make sure nuclear reactors are still capable of dealing with a new understanding of the [seismic] threats.”
Like many scientific and engineering issues that span decades, there is new information emerging about earthquakes, particularly in the central and eastern regions of the United States. The industry and the NRC are evaluating this data and this fall will discuss steps that may be taken to update seismic criteria.
“Although there is not an immediate safety concern, the NRC is focused on assuring safety during even very rare and extreme events. Therefore, the NRC has determined that assessment of updated seismic hazards and plant performance should continue,” the agency said.
As new seismic data becomes available, utilities will perform the necessary safety reviews to maintain nuclear energy facilities with safe operating and shutdown capabilities. As the industry continues to study the issue, plants will make investments to provide further assurance that the plant and public safety will be protected from seismic events.
The article states, “The risk that an earthquake would cause a severe accident at a U.S. nuclear plant is greater than previously thought, 24 times as high in one case, according to an AP analysis.”
The conclusions the article reaches are based on overly conservative calculations that tend to overpredict seismic hazards that might occur every 10,000 to 100,000 years.
As the NRC has said: “The NRC does not rank nuclear plants by seismic risk. The objective of the GI-199 Safety/Risk Assessment was to perform a conservative, screening-level assessment to evaluate if further investigations of seismic safety for operating reactors in the central and eastern US are warranted.” The results of the NRC’s safety risk assessment in GI-199 should not be interpreted as definitive estimates of plant-specific seismic risk because some analyses were conservative, making the calculated risk higher than in reality. The nature of the information used makes these estimates useful only as a screening tool.