As the turbine in the Oyster Creek Nuclear Power Plant in Lacey resumes sending electricity to the PJM grid, inspectors of the Nuclear Regulatory Commission (NRC) are reviewing the circumstances that led to Monday's forced shutdown.

Operations restarted June 5, two days after the unplanned outage traced to a non-nuclear malfunction. The plant reached full power capacity today.

Exelon spokeswoman Suzanne D'Ambrosio explained that the problem was traced to reduced vacuum capacity in a condenser.

D'Ambrosio and Neil Sheehan, NRC spokesman, said that the condenser, which cools reactor-generated steam after it has driven the turbine, requires vacuum conditions to run at top efficiency.

According to Sheehan, inspectors traced the vacuum degradation to faulyu positioning of valves on the plant's augmented off-gas system.

NRC inspectors, assigned to full-time oversight of the generating station, watched operator actions during the shutdown, reviewed restart plans and the actual restart, and are conducting followup reviews of the outage, Sheehan said.

Plant operators are working through a period of low-to-moderate safety risk, desginated and defined by the NRC in response to a defect in one of several depressurization valves that are employed to deliver coolant to the reactor during shutdown procedures. That matter was rectfied, but had gone unnoticed for two years between refueling outages.

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