NRC Cites Limerick Nuke Plant

Exelon's Limerick Unit 2 nuclear power plant's breakdown in safety was "unacceptable," a Nuclear Regulatory Commission official said in a news release on Thursday.

An NRC inspection earlier this year found "inadequate procedures" related to the operation of two main feed water system valves.

The issue -- classified as a low to moderate safety significance -- will bring additional NRC oversight to the plant.

According to the release, during a start-up on April 22, valves failed to close, which made one of the plant’s safety systems, known as the Reactor Core Isolation Cooling system, inoperable from April 23 to May 23, 2011.

"Specifically, the partially open valves created a flow path that would have prevented the majority of water flow from the RCIC system from reaching the reactor during an accident and thereby helping to mitigate the event," the release states. "Because nuclear power plants are equipped with multiple safety systems, the reactor still could have been cooled and the plant safely shut down despite the condition."

Additionally, a primary containment isolation valve was inoperable during the same period.

The valves are used during an accident to close off the plant’s containment building and prevent release of radioactivity into the environment.

"Once the problem was identified by plant operators, they fully closed the valves and restored the operability of the RCIC system and the primary containment isolation valve," the release states.

“Because the valves in question failed to fully shut, the majority of the cooling water from one of the plant’s safety systems would have diverted to the condenser rather than flow to the reactor,” NRC Region I Administrator Bill Dean said via the release. “While other systems would help ensure safe shutdown of the reactor during an emergency, the NRC considers any degradation of plant safety margins to be unacceptable. It is important that Exelon takes actions to fully and satisfactorily address this problem, and the NRC will conduct necessary inspections to ensure this has taken place.”

The NRC will inspect the Limerick Unit 2 plant's corrective measures pertaining to the problems.

"We're okay with the finding," Exelon Spokeswoman April Schilpp said on Thursday. "(The NRC) will examine the actions that we've taken and the plans we have in place ... It is of very low safety significance." 

Editor's note: This article was updated at 5:30 p.m. Dec. 8.