SEABROOK, N.H. — An unexpected reactor shutdown happened at New Hampshire’s Seabrook nuclear power plant as the plant was shutting down for planned refueling and maintenance early Tuesday, a Nuclear Regulatory Commission spokesman said.

Neil Sheehan, a spokesman for the commission, said the plant’s turbine/generator had been taken offline in preparation for testing early Tuesday. The refueling and maintenance generally lasts several weeks.

The reactor shutdown happened shortly before 12:30 a.m. when an electrical problem impacted the plant’s reactor coolant pumps, knocking them out of service. Sheehan said backup systems activated, as designed, to safely cool down and shut down the reactor. The electrical problem is being investigated.

Sheehan said the NRC’s senior resident inspector was in the control room observing the plant shutdown at the time, and did not identify any concerns with operator or equipment response with the reactor shutdown.

He said it would be too soon to determine whether the incident could lead to any NRC performance action.

The plant had the fewest number of safety violations in the Northeast from 2000 to 2012 among facilities with only one reactor, according to a report by the federal Government Accountability Office. The GAO reported that the plant, which is owned by NextEra Energy, had three higher-level violations and 85 lower-level violations over the 12 years. Seabrook was granted a 40-year license to operate in 1990.

NextEra is seeking an extension of the plant’s operating license until 2050.