BRATTLEBORO (AP) - Vermont Yankee nuclear power plant was forced to reduce its power output to about 36 percent late Sunday because of a problem with one of its recirculation pumps.

An electrical problem in a motor generator, which produces the force necessary to keep water flowing into the reactor vessel, caused the power-down, according to the Nuclear Regulatory Commission.

NRC spokesman Neil Sheehan said Yankee technicians working on the problem would have until 11 p.m. Monday to remedy the situation or the reactor would have to be shut down.

Even if the problem is fixed before the 24-hour period expires, the reactor won't go back up to 100 percent, he said.

At the time the problem was discovered, the plant was in a "coast down" mode in preparation for its upcoming refueling outage and was operating at 95 percent, he said.

Because this is a safety-related system, the NRC mandates that the repairs be completed within 24 hours or the plant be shut down.

There are two recirculation pumps that keep water moving in the reactor.

That water is boiled, turned into steam to drive the plant's turbine, which produces electricity, before being returned to the reactor.

The plant is currently operating with just one recirculation pump.

"There are no current safety issues associated with the problem," Sheehan stated in a press release.