Workers at the Peach Bottom nuclear power plant near Delta, Pa., temporarily weakened a key safety system designed to prevent a reactor meltdown -- and didn't realize it, federal regulators say.
The safety system at the plant north of the Maryland line in the Harford County area was fully restored in less than an hour, but the incident on Aug. 3 has prompted an inquiry by the Nuclear Regulatory Commission.
The action could result in a fine against PECO Energy Co., the utility that operates the twin-reactor plant on the Susquehanna River.
Bill Jones, a PECO spokesman, said the company would not comment until the NRC has completed its inquiry. PECO executives met behind closed doors last week with officials of the NRC's regional headquarters in King of Prussia, Pa.
Thomas T. Martin, the NRC's regional administrator, said in a Sept. 29 letter to PECO that plant operators committed "apparent violations" of federal rules resulting in a "significant degradation in plant safety."
It will be four to six weeks before the NRC decides whether to cite PECO, according to the agency.
The problem occurred when maintenance workers closed a valve that discharges water from the plant's emergency water system into the Susquehanna. The plant takes water from the river to help cool pumps and backup diesel generators that would be needed to keep the reactors from overheating in a serious accident.
By closing the discharge valve, Peach Bottom workers reduced by 50 percent the flow of cooling water available to keep the
emergency pumps and generators from overheating, according to documents and Wayne L. Schmidt, the NRC's senior resident inspector at the plant.
No emergencies occurred that day. PECO engineers contend that the reduced flow was still sufficient to prevent a meltdown.
But NRC officials are troubled by the apparent failure of plant operators to realize the risk they were taking by shutting the valve, the inspector said. And the utility staff did not analyze the potential consequences or take any precautions to reopen the valve in case of emergency, the NRC administrator said in his letter.
Even though closing the valve had caused an overflow of the plant's emergency cooling tower, the company did not recognize the potential safety problem until it was noticed by NRC inspectors.
"We had to find this and point it out to them," Mr. Schmidt said, noting that nuclear plant operators are expected to identify their mistakes and report them to the NRC.