HOLLY SPRINGS, N.C. (AP) — 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 Thursday.
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 Sunday.
"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."
Had 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.
Inspectors 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.