In the past two years, Dominion Virginia Power's four nuclear power reactors experienced 12 unplanned shutdowns.

Then, the Aug. 23 earthquake in Louisa County forced two more shutdowns at the North Anna Power Station.

"That's too many trips for us," said David A. Heacock, president and chief nuclear officer of Dominion Nuclear. "And we're going to ensure it's not going to continue."


Unplanned shutdowns - also called "trips" or "scrams" - of the utility's most important electric generating stations could potentially cause dangerous safety issues and lead to an increase in the cost of power.

Dominion Virginia Power is the state's largest electric utility, serving 2.3 million customers, and is the only nuclear power plant operator in Virginia.

The Richmond-based company's plants at North Anna and Surry carry its base load of customer demand for electricity, essentially running all the time unless they're out of service for refueling, maintenance or an unplanned shutdown. The company's four nuclear reactors account for 18 percent of the company's electric capacity in the state but produce 40 percent of the electricity it generates.

"An excessive number of unplanned scrams can indicate particular problems in maintenance or certain other areas," said Joey Ledford, spokesman with the Nuclear Regulatory Commission in Atlanta. "That's a signal that there are things that need to be looked at.

"That's why we pay attention to them."

The North Anna 2 plant's performance drew special attention from NRC inspectors in September 2010 because the reactor had four unplanned outages within the past four quarters, an issue of low to moderate safety significance, according to the agency. In March, the NRC inspector determined that, in general, the company's problem identification, root-cause analyses and corrective actions were adequate.

Excluding the earthquake shutdowns, four of Dominion Virginia Power's unplanned shutdowns since October 2009 were due to pipe leaks, two were due to lighting strikes, two to a tornado, one to a mechanical failure and three to human errors. In the 12 months prior to October 2009, the company had gone a year with no unplanned outages, Heacock said.

Dominion Virginia Power investigated the events to learn their root cause, said Daniel G. Stoddard, the company's senior vice president for nuclear operations, and made corrections to avoid shutdowns for similar reasons.

But, Stoddard said of the spate of outages, "there is no common thread, no common cause."

The company's "record is acceptable," said the NRC's Ledford, with the incidents investigated and causes corrected. "The books have been closed on them."

Nationally, nuclear reactors have been averaging less than one unplanned shutdown per unit annually, according to the NRC.

"North Anna and Surry were well above the industry average," said David Lochbaum, a nuclear engineer with the Union of Concerned Scientists.

Last year, three of Dominion Virginia Power's nuclear units also performed below the national average using a measure called the "capacity factor," which is the time a nuclear station operates compared with running 100 percent of the time.

In 2010, for instance, Dominion Virginia Power's Surry 1 unit had a capacity factor of 87.65 percent, North Anna 1's capacity factor was 84.31 percent, and North Anna 2's was 79.3 percent.

Nationally, the average availability of nuclear units was 92.1 percent, according to the U.S. Energy Information Administration. Only Surry 2, at 98.76 percent, was above the national average.

Company officials point out that the capacity factor is also affected by outages for refueling, as well as maintenance and upgrade work.

In 2009, all four of Dominion Virginia Power's reactors operated above the national average capacity factor of 90.3 percent, the federal EIA said.

Despite Dominion Virginia Power's recent nuclear plant difficulties, said Lochbaum with the Union of Concerned Scientists, "they look very aggressively for problems and very aggressively act to correct problems."

"They don't have anything to hide," Lochbaum said. "They want to do it right."

Twenty-one different systems can signal one of Dominion Virginia Power's reactors to shut down, Heacock said.

"Our point is to make electricity safely," he said of the company's four nuclear reactors. "They're designed to fail safe. They're designed to default to shut down if there's a problem."

Across the U.S., "we've had more nuclear plant outages for natural events than historically this year," Heacock said. "That's why we have defense in depth," using multiple safety systems to guard against accidents at the power stations.

Three factors affect the safety of nuclear plants: events, something untoward happening at the plant; equipment; and people.

"It you have pre-existing weaknesses," Lochbaum said, "and then you have an earthquake, those pre-existing weaknesses can line up to create the perfect storm that turns a bad day into a catastrophic day."

Equipment and human failures tend to cluster at the beginning and end of a plant's life, he said.

Dominion Virginia Power's plants came online between 1972 and 1980. Originally licensed for 40 years, those licenses have been extended for an additional 20 years.

"I think they're unsafe," said Erica Gray of Henrico County, with the Coalition Against Nukes. "I think most of them are old and they're falling apart. I'm just scared that we're going to end up with an incident here that could render parts of our state uninhabitable."

Dominion Virginia Power officials, however, say the plants have to operate as well on the last day of the 60th year of their lives as they did on the first.

"They were designed safe," said David A. Christian, executive vice president and chief executive officer of Dominion Generation, a subsidiary of Dominion Resources Inc. "And we've done nothing but make them safer over the years."

"These plants, I can say very confidently, are safer today then they were when they were originally licensed."