The current heat wave is threatening to shut down the nuclear power plant in Plymouth, as water used to cool the system nears limits on safe temperature.

The Nuclear Regulatory Commission requires that the water drawn from Cape Cod Bay to cool the Pilgrim Nuclear Power Station be below 75 degrees. On Tuesday afternoon, the water exceeded that mark for about 90 minutes, forcing the plant to reduce power output temporarily.

Water temperatures have not surpassed that mark again, but it is a possibility as the heat wave persists.

“Obviously, they are going to have to keep an eye on it,” said Neil Sheehan, a spokesman for the NRC, which oversees the plant. “They need to have sufficient heat transfer,” he said.


A reactor in Connecticut was shut down for two weeks last August due to water intake temperatures that exceeded the 75-degree limit, the NRC said.

When the limits were put into place, regulators never imagined that rising water temperatures would be a concern, Sheehan said.

“No one could envision a scenario where water temperatures would exceed these limits,” Sheehan said.

Peter Schworm can be reached at schworm@globe.com. Follow him on Twitter @globepete.