A problem with the filter of a Wake County nuclear power plant's emergency cooling system may increase the chances of a serious accident, although officials at the plant said the probability remains low.
The Shearon Harris Nuclear Plant, located 22 miles southwest of Raleigh and owned by Progress Energy, is one of 69 nuclear reactors in the country that uses pressurized water for cooling. Earlier in the year, the Nuclear Regulatory Commission sent a bulletin to all plants alerting them to the design flaw common to their cooling systems and requiring them to address the issue.
"The plants were given 60 days to respond," said Ken Clark, spokesperson for the NRC. "All 69 plants have already responded." The problem involves the possibility of a pipe rupturing, which could loosen paint chips, insulation material and other debris that would collect at the floor of the plant and clog a sump drain, which acts as a filter. If the drain gets clogged, the water needed to keep the reactor core cool would not be able to recirculate.
"If you don't keep the reactors cool, they will self-ignite and could create a Chernobyl," said Stan Goff of NC WARN, a nuclear watchdog group in North Carolina.
The exact chances of an accident occurring at Shearon Harris or any other plant is not widely known. At the request of the NRC, the Los Alamos National Laboratory studied all 69 plants and ranked them in order of core damage risk. Although the NRC did not identify the exact risk of each plant, the Union of Concerned Scientists, another watchdog group, used details from the study to determine the chances of an accident at each plant.
The UCS report said the drainage flaw increases the risk of a serious accident occurring from one chance in 20,000 years to as low as one in every 400 years. The NRC considers as acceptable any rate above one in 10,000 chances per year for any plant.
The chance of a mishap at Shearon Harris is estimated at one in 869 years, which makes it less susceptible than the estimated industry average, at one in 704 years.
Progress Energy officials said, however, the Los Alamos study incorrectly reported the size of the screens on the sump drains, which made the plant seem more at risk than it really is. In addition, Los Alamos evaluated a 'leak before break' scenario where a pipe would show some leaking before completely failing.
"In that scenario, which is more realistic, Shearon Harris' probability was one in 25,000-plus years," said Sharon Hall, site communications director of the plant. "The industry average was one in 6,800 years."
Overall, the UCS reports there is a 34 percent chance of a serious accident occurring somewhere in the U.S. in the next three years. While neither the NRC nor Progress Energy would comment on this percentage, Clark said the NRC does not consider the issue an immediate safety threat.
"It's still a theoretical problem, [and] the chance of a pipe breaking is very remote," Clark said.
Nonetheless, Progress officials said they are taking the problem seriously. While there is currently no clear solution to the problem, the NRC bulletin requires all plants to examine the plant design, determine their susceptibility and implement some measures, which Progress is doing.
"Initially, we've been doing a lot of training," Hall said. "Our operators spend 20 percent of their time running through various scenarios on our control room simulator, and they've trained for the scenario [of a pipe rupturing]. If we did have a blockage, we have other options [to keep the reactor cool]."
Hall also said they have very strict policies about not allowing any foreign material into areas in the plant where they could get caught in the drain. Furthermore, Progress is conducting additional inspections of the plant and is looking at possible design changes. Yet Goff believes the Shearon Harris plant should be closed until the problem is fixed.
"The plant needs to be shut down, which is pricey," Goff said. "But it's a lot less pricey than a meltdown." Progress officials, however, insisted that all decisions are based on nuclear safety and not on cost.
The NRC is currently monitoring the situation at all 69 power plants across the nation. Since it does not look like the closing of the Shearon Harris plant is likely, watchdog groups like NC WARN are turning their attention to pressuring the NRC to issue stricter mandates.
"Our concern right now is NRC is a little slow [in making plants fix the problem]," Goff said. "The NRC has long been an industry advocate that encourages a compliance-only mentality."
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