POWER November 2012 - 36

NUCLEAR POWER
tained damage. Cracks even appeared in the
Washington Monument in the nation's capital,
and the rumbling of the initial shock and
aftershocks were felt throughout the MidAtlantic
and Northeast U.S.
It is important to recall that the Central
Virginia temblor occurred six months after
the devastating earthquake and tsunami that
crippled Japan's Fukushima Daiichi nuclear
station. The Japanese accident caused governments
around the world to reevaluate their
nuclear energy policies, and public interest in
nuclear energy greatly intensified. This was
new and unexplored territory for Dominion
and the NRC. There was never any doubt that
the company's first priority was to ensure public
safety. But Dominion also knew that in this
time of extreme sensitivity to nuclear energy,
the company's response could very well set the
tone for the future of nuclear energy policy.
Dominion soon realized the company
would need to develop and obtain approval
from the NRC for the appropriate process to
restart the two units. (See the sidebar for a
summary of the steps taken to restart the two
units.) Dominion also knew that the NRC
had little experience in dealing with a nuclear
plant shutting down as a result of a beyonddesign-basis
earthquake. In fact, no nuclear
unit in U.S. history had ever experienced a
shutdown caused by a temblor.
Recovery and Restoration
Within 24 hours, the company's North Anna
Power Station restored off-site power and
exited the emergency plan after completing
all walkdown inspections of equipment most
susceptible to seismic damage. This was in
keeping with the company's formal Corporate
Emergency Response Plan, which includes an
extensive public communications program.
No damage was reported to systems required
to maintain the station in a safe condition.
While the ground force accelerations
from the earthquake did exceed North Anna's
licensed design basis for about 3 seconds,
the station-built with multiple layers
of safety-sustained no functional damage
to safety systems, structures, or components.
In fact, the extensive engineering
analysis completed by the company demonstrated
that it could have safely withstood a
quake well above that experienced.
Using an NRC-endorsed document prepared
by the Electric Power Research Institute (EPRI),
the company assessed the overall impact on the
station. On a scale from zero (where no functional
damage is observed) to three (where very
significant damage has occurred), the company's
detailed inspections determined that the
earthquake ranked as zero impact for North
Anna. However, to be extra thorough and safe,
the company proceeded to evaluate the station
36
2. Rigorous inspections. Dominion visually inspected 100 feet of safety-related buried
pipe with wall thickness verified by ultrasonic measurements. Courtesy: Dominion Generation
3. Minor repairs required. The minor damage experienced by the two stations cracked
mortar and concrete. The necessary repairs were completed prior to restart. Courtesy: Dominion
Generation
4. Short trip. The dry casks holding spent nuclear fuel moved from 1 to 4½ inches during
the earthquake. Courtesy: Dominion Generation
as if the quake had an impact of one on the scale.
This required far more extensive engineering inspections,
testing, and analysis. That decision
went a long way to establish up front that the
company would be conservative and systematic.
Dominion has since been lauded by nuclear
safety experts as a prime example of an excellent
nuclear safety culture.
Additionally, the company immediately
brought in some of the top external seismic
experts to walk down the station and put eyes
on important adjacent structures to make sure
the station was safe and that the company
was not overlooking anything.
In the days and weeks that followed, a special
NRC inspection team, with full cooperation
from Dominion, thoroughly evaluated
the company's response to the earthquake,
including initial actions by control room operators
to place the unit in a safe and stable
condition. They concluded that:
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■ Control room operators and station employees
responded to the quake as trained.
■ Safety systems engaged as designed and
expected.
■ No significant damage occurred to safetyrelated
systems at the power station.
Additional inspections and analysis were performed
by the NRC, and the company thoroughly
documented its own inspections and analysis
and responded to every question posed to it by
NRC inspectors, engineers, and seismic experts.
Before the NRC allowed the units to restart, the
company had provided the NRC with more than
1,000 pages of documentation (Figure 2).
Examples of minor damage included nonstructural
concrete cracking, insulation that
was shaken off some pipes, and broken seals on
electrical insulators attached to the main station
transformers. These were repaired or replaced
prior to restarting the units (Figures 3 and 4).
POWER | November 2012

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POWER November 2012

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