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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
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