The US Nuclear Regulatory Commission said 22 May, that it is launching a special inspection at Duke Energy’s Shearon Harris nuclear power plant in North Carolina, after a quarter-inch flaw was discovered on the reactor vessel head.

According to NRC, while the plant was shut down on May 15, further analysis of ultrasonic data gathered during an earlier refueling outage revealed an irregularity about one-quarter inch long near a nozzle on the vessel head.

"The flaw did not penetrate the vessel head wall and there was no evidence of leakage," NRC said. Duke Energy has already begun the repair process.

However, because the discovery is on the vessel head and was not seen in the original review, NRC said that it is sending the special inspection team "to analyze and understand all the details."

The team will, among other things, develop a timeline, review Duke’s actions leading up to the discovery of the flaw, examine the previous ultrasonic testing records for the vessel head, evaluate the company’s repair plans and determine if there are generic issues that should be communicated to other nuclear plants.

The results are expected to be issued within 45 days of the inspection being completed.

Photo: The single-unit Harris pressurized water reactor