Progress Energy's Brunswick nuclear reactors in Eastern North Carolina are among several dozen U.S. reactors that could fail to shut down automatically during an earthquake, potentially risking the safety of the power plant.
GE Hitachi Nuclear Energy, based in Wilmington, this week advised Raleigh-based Progress and other power companies to conduct tests to determine what conditions would prevent their reactors from shutting down safely during a temblor.
Affected by the potential glitch are 35 boiling water reactors designed by General Electric and built between the late 1960s and the early 1990s. The twin-reactor Brunswick plant near Southport has been generating electricity since the mid-1970s. GE's nuclear division formed a joint venture with Hitachi in 2007.
The Shearon Harris nuclear reactor in Wake County is of a different design - by Westinghouse - called a pressurized-water reactor. Duke Energy's seven reactors in North and South Carolinas also are pressurized-water reactors. None are General Electric designs.
GE Hitachi noted that the probability of not shutting off properly is very low, and plant operators could override automatic emergency systems to shut down reactors manually. Reactors are designed to automatically shut off during a serious earthquake.
GE Hitachi said it has been studying the problem for about a year and knew about its potential before an earthquake-spawned tsunami in March disabled GE reactors in Japan.
"This preceded the Fukushima event by several months," said GE Hitachi spokesman Michael Tetuan.
The potential impact for Raleigh-based Progress is not clear. The company is reviewing GE Hitachi's advisory, Progress spokesman Mike Hughes said.
Tetuan said most nuclear plants could fix the problem with "minor tweaking."
In a worst case scenario, a nuclear plant would have to replace fuel channels in which the uranium is held, Tetuan said. A typical boiling water reactor has between 400 and 800 such channels.
The Nuclear Regulatory Commission has been notified of GE Hitachi's reviews but has not required any measures.
The malfunctions are caused by a complex interaction of factors.
Fuel channels can bow slightly when the nuclear core is super-heated through the nuclear reaction.
Even when bowed, the channels can accommodate a control rod inserted to deactivate the fission process.
But bowed channels, compounded by movements of the earth's surface, could be impassable for a control rod, Tetuan said. For that to happen, though, the reactor has to be under low pressure, which is also rare.
"We've proactively identified a very unique set of conditions in which a plant rarely operates where this is a concern," Tetuan said. "With the guidance provided to our customers, they will be able to monitor potentially affected fuel channels and avoid a safety concern."
