The Nuclear Regulatory Commission’s latest analysis of faults near the Diablo Canyon nuclear power plant in California continues to conclude the plant’s design would withstand earthquakes near the site, NRC said 12 October.

The regulator had been focusing its efforts on trying to better understand a new zone of seismicity a ‘shoreline fault’ about a kilometer offshore from the plant. The fault was identified as a result of a collaborative research programme between PG&E and the US Geological Survey (USGS).

Pacific Gas & Electric (PG&E) informed the NRC of the shoreline fault in November 2008, and provided them with updated information in early 2011. A team of NRC staff visited the site in October 2011 and analyzed ground motion from earthquakes the Shoreline fault could potentially generate.

“All of those ground motions fell within Diablo Canyon’s existing design limits, which are based on ground motion associated with an earthquake from the larger Hosgri fault near the plant,” NRC concluded.

The NRC’s work is laid out in a 177-page Research Information Letter (RIL) 12-01, “Confirmatory Analysis Of Seismic Hazard At The Diablo Canyon Power Plant From The Shoreline Fault Zone” (ML121230035).

NRC said that Diablo Canyon must still carry out additional earthquake evaluations, as well as a “walkdown” to identify any near-term actions for enhancing earthquake resistance. These measures are included in the NRC’s recent information request to all U.S. nuclear power plants as the agency implements lessons learned from the Fukushima Dai-ichi nuclear accident.