Inquiry to begin over Pilgrim nuclear plant’s ‘safe’ shutdown

The Pilgrim Nuclear Power Station in Plymouth went into automatic shutdown Saturday.David L. Ryan/Globe Staff/File

The Pilgrim Nuclear Power Station on Cape Cod Bay in Plymouth remains closed Sunday after going into an automatic shutdown Saturday afternoon, according to station and government officials.

“The plant is currently in a safe, stable shutdown condition and there is no impact on the health and safety of the public or plant employees,” said Lauren Burm, a spokeswoman for Entergy Corp., the company that operates Pilgrim, in a statement.

Officials for the Nuclear Regulatory Commission, an independent government agency overseeing the safety of nuclear plants, reiterated Sunday afternoon that there were no safety concerns regarding the state’s only operating nuclear power station.

“There were no complications during the shutdown and no increased risks to plant workers or the public,” said Neil Sheehan, an NRC spokesman.

The reactor and associated systems were cooled down to allow for an investigation into what caused the emergency shutdown, which is also called a scram.

Nuclear reactors use steam to make electricity, operating “like a giant tea kettle, turning water into steam which spins giant turbines that power generators to make electricity,” according to an explanation on Pilgrim’s website.

The shutdown occurred at about 4:30 p.m. Saturday while the reactor was at 100 percent power, triggered by the closure of a single main steam isolation valve, Burm stated, with all other plant systems responding as designed.

The valves “would be used in the event of an accident to halt the flow of steam from the reactor to the turbine building and thereby help ‘isolate’ radioactivity to the containment building surrounding the reactor,” said Sheehan.

A copper tube about a half-inch in diameter, called an air/nitrogen line, broke, triggering the valve closure, said Chip Perkins, a nuclear engineer and the regulatory assurance manager for Entergy. While the repair of the line shouldn’t be that complicated, the plant will do an investigation into what they call “extended circumstances,” followed by other independent investigations.

“Once we find a problem, we go in and look around to see if there are any other problems like it and any other areas where we have similar conditions,” said Perkins.

There was no information available about when the plant would reopen.

“Our senior resident inspector assigned to Pilgrim on a full-time basis traveled to the plant yesterday and today to independently verify that plant operators properly handled the shutdown and that there were no equipment performance issues,” Sheehan said. “No immediate concerns were identified. The NRC will continue to follow up on the company’s post-shutdown reviews.”

The shutdown follows an incident two weeks ago, on Aug. 9, in which the plant had to partially cut power. Sea water that flows into the plant had reached 75.09 degrees, exceeding the federally regulated temperature cap of 75 degrees, so power was cut by 10 percent for 3½ hours to cool the sea water.

Both Perkins and Sheehan said that Sunday’s shutdown was unrelated to elevated water intake temperatures. This is the Pilgrim station’s third automatic shutdown since Jan. 1.