No Need to Speed Up Transfer of Used Fuel to Dry Storage, NRC Staff Says
Jan. 9, 2014—Should the used nuclear fuel in storage pools at U.S. nuclear energy facilities be moved more quickly to dry cask storage systems? That’s a question the U.S. Nuclear Regulatory Commission and the nuclear energy industry have been giving significant attention since the magnitude 9.0 earthquake and tsunami in Japan that struck the Fukushima Daiichi nuclear plant in March 2011.
The industry and the NRC have undertaken a number of studies over many years to assess the safety of U.S. used fuel pools. Most recently, as part of the agency’s post-Fukushima lessons-learned activities, the NRC staff prepared two evaluations.
Beginning shortly after the accident in Japan, NRC staff assessed whether a severe, though highly unlikely, earthquake could damage a used fuel storage pool to the point of draining the water that cools and shields the fuel and whether the risks of such an event warrant expediting the transfer of used fuel out of the pools.
The study—“Consequence Study of a Beyond-Design-Basis Earthquake Affecting the Spent Fuel Pool for a U.S. Mark I Boiling Water Reactor”—evaluated whether an earthquake more severe than the one that struck the boiling water reactors in Japan would cause a U.S. used fuel pool of the same reactor type to lose the approximately 350,000 gallons of water it holds. The study was based on Peach Bottom reactor 3 in Pennsylvania, similar to the Fukushima Daiichi reactors.
The study also assessed 21 used fuel pools (20 in Japan and one in the U.S.) that, since July 2007, experienced earthquakes and were found to have suffered “no observed damage.”
Released last June, the results found that this type of used fuel pool is very likely to withstand severe earthquakes without leaking and that reducing the fuel loading density in storage pools would be of minimal value—the study noted the likelihood of a radiological release from the pool at the reference plant after the analyzed earthquake plant to be about one time in 10 million years or lower. Based on this study and previous studies, the staff concluded that used fuel pools protect public health and safety.
In November, the staff issued a regulatory analysis extending the results of the previous study to all U.S. reactors. The analysis―“Staff Evaluation and Recommendation For Japan Lessons-Learned Tier 3 Issue on Expedited Transfer of Spent Fuel”―sought to determine whether moving used fuel from pools would result in a “substantial increase in public health and safety” that would justify the additional cost.
The evaluation considered a broad history of NRC oversight of past studies of used fuel storage, used fuel pool operating experience―domestic and international―and past studies of pool safety. It concluded that expediting the transfer of used fuel to dry cask storage “would neither provide a substantial increase in the overall protection of public health and safety, nor sufficient safety benefit to warrant the expected implementation costs.”
At a Jan. 6 staff briefing for the NRC commissioners, the industry said it agrees with and supports the findings of both staff papers. David Heacock, Dominion Nuclear’s president and chief nuclear officer, commended the staff on what he called a “very thorough, conservative analysis.”
Heacock emphasized that the 21 reactor storage pools examined by the NRC staff all experienced actual earthquakes stronger than they were designed for and emerged without structural damage and minimal loss of water. The pool at Fukushima Daiichi reactor 4, he noted, remained largely intact after not only the fourth-largest earthquake in recorded history but also a major hydrogen explosion that damaged the entire building.
The conservatisms built into the analysis went much further than this experience, Heacock said. Even so, the results showed only an “extremely small chance” that the pool would leak. He said the study demonstrates the safety of used fuel pools using current operating practices, adding that the difference in public health risks between pool and dry storage can be characterized as “the small difference between extremely small values.”
The commission will now consider the staff recommendation and direct the staff appropriately.
Slide presentations from the Jan. 6 briefing are available on the NRC website.