On March 17, Environment and Public Works Committee Chairman Barbara Boxer (D-CA) asked for a thorough review and posed a number of questions to the Nuclear Regulatory Commission on US nuclear power plants. Chairman Jaczko responded on April 8 (the pdf was posted on 4/15). Below are a few highlights from the letter:
1. Please identify all U.S. nuclear facilities subject to significant seismic activity and/or tsunamis.
Although we often think of the US as having "active" and non-active" earthquake zones, earthquakes can actually happen almost anywhere. Seismologists typically separate the US into low, moderate and high seismicity zones. The NRC requires that every nuclear plant be designed for site-specific ground motions that may be expected at their locations. In addition, the NRC has specified a minimum ground motion level to which all nuclear plants must be designed. The designation of the general type of seismic zone that may apply at any specific site is subject to interpretation but a conservative interpretation -meaning a larger zone-might include the following plants, based upon a preliminary estimate:
High Seismicity -Diablo Canyon, SONGS [San Onofre]
Moderate Seismicity -Brunswick, Robinson, Summer, Vogtle, Hatch, Clinton, Watts Bar, Sequoya, North Anna
Low Seismicity -all other plants
2. What extra safety features does the NRC currently require for facilities that have a credible threat of an earthquake or tsunami?
… With regard to the type of containment design used by the most heavily damaged plants in Japan, the NRC initiated a Boiling Water Reactor (BWR) Mark I Containment Improvement Program in the late 1980. This led to installation of hardened vent systems for containment pressure relief, as well as enhanced reliability of the automatic depressurization system.
Additionally, following the 9/11 events, reactor licensees have been required to develop strategies to maintain and restore core cooling, containment, and spent fuel pool cooling capabilities under the circumstances associated with the loss of large areas of the plant due to explosions or fire. Licensees are required to develop strategies for fire fighting, operations to mitigate fuel damage, and actions to minimize radiological release.
4. What increased risk is associated with exposure to mixed oxide fuel?
… NRC has evaluated the use of MOX fuel and concluded that the design basis accidents consequences were within the acceptance criteria and the differences between MOX and uranium fuel were within the dose consequences calculation uncertainties. The staff has concluded that the presence of a small number of MOX fuel assemblies in Fukushima Daiichi Unit 3 constitutes an insignificant change from non-MOX fuel in core operating conditions and accident consequences.
There are a few other answers worth checking out so be sure to stop by (pdf).