NRC still unclear why inspectors missed 'flaw' spot at Harris Nuclear Plant
By Emery P. Dalesio, Associated Press
Harris Nuclear Plant will undergo more frequent inspections, federal regulators said Thursday night in Holly Springs.
HOLLY SPRINGS, N.C. -
An outside contractor
hired to look for flaws in a Duke Energy nuclear reactor near Raleigh
last year missed a quarter-inch spot of corrosion and cracking near the
reactor core that forced a full shutdown last month after new eyes
reviewing year-old data found the problem, federal regulators said
Four smaller spots were fixed during a refueling last
year, but the flaw that forced the May 15 shutdown at the Shearon Harris
nuclear plant wasn't found until new contractors reviewed ultrasonic
tests from last year, Nuclear Regulatory Commission inspectors said
during a public meeting.
The NRC said there was never radiation
leakage from the reactor vessel, which contains the heat and pressure
produced by the nuclear core's energy. The plant returned to full power
"The reason why they shut down was because they could not
confirm that there was no leakage," said Robert Williams, an NRC reactor
inspector who led a team looking into why the flaw was missed last
year. "Once they shut down and were able to perform the needed and
required examinations, they were able to confirm there was no leakage."
there been a leak from the reactor vessel as a result of such cracking,
it would have been contained by backup safety systems, the NRC said.
said they're still trying to figure out why a pair of expert-level
outside analysts independently failed to spot the problem, and why the
spot wasn't caught by later reviews of the data last year. A final NRC
inspection report will be released by July 11.
Duke Energy "is
taking actions to correct the failure of the personnel to identify the
defect," the NRC said in a summary distributed at the meeting.
cap on top of the reactor vessel, called a vessel head, will now be
checked for similar cracks every time the reactor is refueled, NRC
inspectors said. That's done every 18 to 24 months, the company said.
"They're looking at it every single time," Williams said.
a third of all U.S. pressurized water reactors like Harris have
similarly had cracking show up on a nozzle in the vessel head, the NRC
said. The cracks are caused by the extreme temperatures of the water
heated by the nuclear reaction and acid that results from boron mixed
with the water to extend the life of the fuel, said Joe Austin, the
senior NRC inspector stationed at the Harris plant.
took over the Harris plant after it acquired Raleigh-based Progress
Energy Inc. last year, which made it the country's largest electric
company. Duke Energy's two resulting operating subsidiaries in the
Carolinas each have territories that serve parts of North Carolina and
South Carolina that depend heavily on nuclear energy.