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Early
in the afternoon last August 23, people living near the small town of
Mineral, Va., felt a 5.8 magnitude earthquake. That earthquake also hit
the nearby
North Anna Nuclear Power Station.
The plant, operated by Dominion, automatically shut down and lost
electrical power from off site. The plant staff declared an Alert, the
second-lowest of four NRC emergency classifications, and shut down
safely.
The
NRC’s resident inspectors began reviewing the plant’s response to the
event immediately. A broader NRC inspection, called an Augmented
Inspection Team or AIT, was launched soon after the event and those
inspectors began assessing Dominion’s actions following the earthquake
and conducting an independent review.
That
inspection team found that the plant staff responded appropriately.
Although the ground motion exceeded some levels for which the plant was
originally licensed, there was no damage to safety equipment and safety
systems functioned during the quake. Another extensive NRC inspection
was later completed as part of reviewing the plant’s readiness to
restart.
The
NRC staff began that technical review to evaluate Dominion’s post-quake
inspections, steps required for restart and other long-term actions.
The inspections and technical review led the NRC to conclude in November
that both of the North Anna units could be operated following the
earthquake without undue risk to the public. The NRC also issued a
letter to Dominion that legally binds the company to its commitments,
such as incorporating analyses and information from the quake into
future plant license documents as well as continued reviews of equipment
and systems.
While
the North Anna Power Station survived an earthquake beyond its original
design with no significant damage, the NRC continues to
evaluate information from the earthquake and
the plant staff has installed additional seismic and backup equipment.
Despite the good news at North Anna, the NRC earthquake story does not
end there.
Six
years before the earthquake near North Anna, the NRC staff began
evaluating updated seismic models and methods for analyzing earthquake
hazards. That effort, which includes all nuclear plants, was rolled into
the lessons learned from the event at Japan’s Fukushima Daiichi nuclear
plant in March 2011. U.S. plants will use those updated methods to
determine if additional improvements to reduce seismic risk at some
plants are warranted.
Roger Hannah
Senior Public Affairs Officer
Region II, Atlanta
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