Seabrook Nuclear Power Plant is back online after an unplanned shutdown this past weekend.
Officials with the plant and the Nuclear Regulatory Commission say the incident did not pose a safety risk, and a watchdog group agrees.
The malfunction involved Seabrook’s control rods, which are used to fine-tune the fission reaction that powers the facility.
A report to federal regulators says on Friday afternoon, a set of control rods moved into the reactor when they weren't supposed to.
This led operators to trip the reactor, or shut it down. The whole process is known as a manual scram.
"On Friday, our operators followed their procedures and training and initiated a manual shutdown of Seabrook’s reactor after an issue with a piece of equipment," says a spokesman for Seabrook's owner, NextEra, in a statement. "All systems responded normally and the equipment issue has been addressed."
The NRC says Seabrook resumed stable operations after the shutdown and began powering back up on Monday. The plant is now at full strength.
Seabrook watchdog group C-10 calls the outcome a "relief" in a statement.
"While it was disconcerting to learn that Seabrook Station had an unplanned event that resulted in the reactor being manually shut down, it sounds like safety mechanisms worked as they were supposed to work," says C-10 executive director Natalie Hildt Treat.
The incident came just before Seabrook hosts its annual safety meeting to update the public and answer questions. The event will take place virtually on Wednesday.
New England’s other nuclear plant, Millstone in Connecticut, operated normally throughout the scram. Together, the two facilities can supply about a third of the region’s electricity.
CORRECTION: An earlier version of this story referred to the shutdown as an emergency. It was not technically designated as an emergency by the NRC. This story has been updated.
