COLUMBIA, S.C. - Federal regulators said Wednesday that they would be increasing oversight at a South Carolina nuclear power plant after a leak forced the shutdown of one of the facility's three reactors last fall.

The increased monitoring announced in a statement by the U.S. Nuclear Regulatory Commission comes with a citation to Duke Energy for failing to identify and correct a crack in a safety system at the Oconee Nuclear Station.

Last November's shutdown at the plant near Seneca, about 30 miles west of Greenville came after engineers detected flaws in the airtight, steel-lined concrete containment building designed to prevent radiation from leaking into the air or ground.

Officials said at the time there was no threat to employees or the public, and the crack was quickly repaired. But in a news release issued Wednesday, NRC officials said they determined the method Oconee used to check for cracks was inadequate and failed to find the crack before it began leaking.

Regulators inspected the facility in June and, last month, met with Duke officials, who said site operators didn't take all possible precautions to prevent the leak. In a statement, Duke spokeswoman Amanda Dow said Wednesday the company respects regulators' decision.

"We have long since completed inspections of piping in all three of the Oconee units to ensure there were no other piping flaws," Dow said. "Oconee is operating safety, and our number one priority every day is safe operation of the plant."

Oconee began operating in 1973 and is Duke's second-oldest nuclear plant. One of its three reactors was already offline for refueling before the shutdown of Unit 1. On Wednesday, all three reactors were listed as fully operational.

Several weeks before the November incident, Oconee's Unit 3 was shut down when engineers discovered a faulty control valve was causing changes in the flow of water in a different system that generates steam to turn the turbines and create power. That reactor started generating power again three days later and was quickly fully operational.

In October, a Government Accountability Office report found that, since 2000, the Oconee Nuclear Station reported the most safety violations of any nuclear plant in the Southeast, with 163 lower-level violations and 14 higher-level violations.

Lower-level violations pose very low risk, such as improper upkeep of a transformer, while higher-level violations range in significance, like an electrical system that caused a fire.