CHAPEL HILL – The unexpected shutdown of the Shearon Harris nuclear plant last week— just more than 25 miles southeast of Chapel Hill— has sparked an investigation by the Nuclear Regulatory Commission. The plant was closed due to the discovery of a crack in a nuclear reactor.

The NRC held an annual review meeting of the plant Monday and took questions from public about last week’s shutdown.

Jim Warren of the watchdog group NC WARN attended the meeting.

“One key concern is why did that crack remain unnoticed for at least a year?” Warren said.

Duke Energy spokesperson Valerie Patterson told WCHL following the incident that Duke Power performed the NRC-mandated inspections in 2012 during the plants scheduled refueling outage.

“However, as we were preparing for our upcoming refueling outage this fall, we reevaluated some inspection data that we had from that outage, and that reevaluation revealed a small flaw, which could affect one reactor vessel head penetration,” Patterson said.

She says the flaw was discovered during a review of ultrasonic data that showed a quarter-inch crack in the lid on top of the vessel that holds in superheated water under high pressure.

Warren says the NRC did not provide answers concerning the crack during its presentation.

“We want to see the NRC investigation go forward and try to make sure we find out when they knew about it, how did they know it, and did they cut corners causing them to miss this diagnosis of the crack,” Warren said.

Duke Energy took over the plant after its merger with Progress Energy last summer. The North Carolina Municipal Power Agency (NCEMPA) co-owns the plant as well.

Duke Energy maintains that no radioactive material was leaked from the plant.

“This was something that was in a part of the system where there have been problems at other problems around the county, and is a key safety issue,” Warren said. “Even on their best, running the plant is a challenge. When things go wrong, that creates more of a challenge.”

Shearon Harris will remain closed until the crack is repaired.