SHIPPINGPORT, Pa. (AP) _ A leak in a coolant system at a nuclear power plant forced the shutdown of one of the plant's reactors and prompted a low-level emergency Monday.

Authorities said the leak at the Beaver Valley Power Station was contained within the building and there was no indication of a threat to public health or safety.

Reports from the plant, which is about 25 miles west of Pittsburgh, indicated there had not been a radioactive release from the building, said David Smith, director of the Pennsylvania Emergency Management Agency.

The emergency was declared at the plant's No. 2 reactor unit at 5:36 a.m. The leak was called an ``unusual event,'' the least serious of four classifications of power plant emergencies.

At one point, radioactive water was spilling onto the floor of the containment building at the rate of 12 to 20 gallons a minute, said Neil Sheehan, federal Nuclear Regulatory Commission spokesman. No workers were exposed.

Workers in protective suits went into the building to check the leak but were unable to reach the valve, Sheehan said. They were expected to try again after the reactor had been fully shut down Monday afternoon, he said.

The leak appeared to be coming from a line used to drain water from the reactor's coolant system, said Sheehan.

The other three classifications of nuclear plant emergencies are an alert, a site-area emergency and a general emergency. Only one general emergency has ever been declared at a U.S. nuclear plant, after the March 1979 accident at Three Mile Island near Harrisburg.