The Pilgrim Nuclear Power Station was shut down Tuesday morning because of a mechanical issue, the second such incident in recent weeks, officials said.
Neil Sheehan, a spokesman for the US Nuclear Regulatory Commission, wrote in an email that the Plymouth facility “experienced an unplanned shutdown” around 8:35 a.m.
Sheehan said the reactor shut down “due to a high water level resulting from an oscillating (fluctuating) feedwater regulating valve.” Water is pumped into the reactor vessel so it can be boiled, converted to steam, and sent to the turbine to generate electricity, Sheehan said.
Commission inspectors “will continue to keep a close eye on Entergy’s troubleshooting activities and any repair plans,” he said.
Entergy, the company that owns the plant, said in a statement that the shutdown “was due to unexpected fluctuations” in a feedwater regulating valve.
“All systems responded as expected during the shutdown and the plant is currently in a safe and stable condition,” the company said. “At no time was the health and safety of the public or plant challenged. A detailed investigation of the cause and subsequent repair plan is underway.”
It was not immediately clear when the plant will resume normal operations.
Tuesday’s shutdown followed an incident Aug. 21, when operations were halted “to allow for repairs to a main steam isolation valve,” Sheehan said.
“These valves are on the large steam lines that transport steam generated by the reactor to the turbine to spin it and produce electricity,” he wrote. “In the event of a severe accident, the MSIVs would be closed to prevent radioactivity from leaving the reactor containment building and reaching the environment. During testing of the valve, it did not close quickly enough to meet the performance criteria.”
The plant is scheduled to close in May 2019.David Abel and John R. Ellement of the Globe Staff contributed to this report.