Earthquake Research Continues at Diablo Canyon

When you’re dealing with a topic as complex as California earthquakes (such as Sunday’s 5.3 quake near King City), it seems as if every answer only generates more questions. That’s the case with a recent NRC analysis of the area near the Diablo Canyon nuclear power plant, on the Pacific coast near San Luis Obispo.

Diablo Canyon’s owner, Pacific Gas & Electric, was working with the U.S. Geological Survey in 2008 when they discovered the “Shoreline Fault,” located just a few hundred yards offshore from the plant. This work stemmed from PG&E’s Long-Term Seismic Program; the company committed to the NRC in 1991 that it would continue the program to study seismic issues and perform periodic seismic reviews of the plant.

In 2011, PG&E submitted a detailed analysis of the Shoreline Fault to the NRC. Both PG&E’s analysis and the NRC’s just-published independent review reached the same conclusion – Shoreline’s shaking potential falls within what the Diablo Canyon reactors are already designed to withstand.

Even with that answer, both the state of California and the NRC have asked PG&E to do more work, although for different reasons.

California Assembly Bill 1632 in 2006 directed the California Energy Commission to assess the vulnerability of the state’s nuclear power plants to seismic hazards. As part of the assessment, PG&E proposed a multi-million dollar study that uses powerful air cannons for 3-D mapping of the offshore area near the plant.

Eighteen air guns would be towed behind a boat and used to emit 250-decibel blasts into the water over a 530-square nautical-mile area. The plan has drawn fire from biologists, environmentalists and fishermen who fear marine life from whales to sea otters and fish will be harmed. PG&E has pointed out that similar seismic surveys have been conducted elsewhere without adversely affecting marine life. PG&E has now decided to delay its seismic testing program until mid-November so it can make some changes to its work plan.

Separately from the state-mandated 3-D mapping, following the Fukushima nuclear accident in Japan the NRC sent a request for every U.S. nuclear power plant to re-analyze their earthquake hazards. So, in addition to meeting the requirements of the state, PG&E must also re-analyze the earthquake hazards for the NRC.

PG&E is now working with a team of independent experts to determine what should be included in its re-analysis for the NRC. The NRC doesn’t yet know if that group will also recommend the high-energy offshore surveys, which cannot be done without state approval.

If the offshore surveys are done, the NRC expects PG&E will include that information in its earthquake re-analysis. If not, the NRC expects PG&E will nonetheless assemble enough updated information to complete its re-analysis by early 2015. The results of all this work will ensure Diablo Canyon remains ready to safely shut down after an earthquake.

Scott Burnell
Public Affairs Officer