LACEY TOWNSHIP -- The operators of the Oyster Creek nuclear power plant intend to shut down as soon as weather permits so they can investigate two broken pumps used to cool its reactor.

One of the five large pumps, which circulate cool water through the reactor, shut down just before 9 a.m. Wednesday; the other shut down last summer.

The malfunction is believed to be caused by a short in power to pump ground cables, Neil Sheehan, a spokesman for the Nuclear Regulatory Commission, told The Press of Atlantic City for Saturday's newspapers.

"They're not going to know that for certain until they shut the plant down and get into the containment building and get a closer look," Sheehan said.

The 630-megawatt plant in Lacey Township is the oldest commercial nuclear power plant in the United States.

The plant can operate at full power with one pump down, but with two down it was running at about 53 percent power last week.

Pete Resler, a spokesman for AmerGen, the energy company that operates Oyster Creek, said Saturday that he would not disclose when the plant is shutting down because it could affect energy market prices.

Plant operators will slowly shut the plant down so that the discharge temperature drops by about one degree an hour -- a process that could take up to 12 hours, said Rachelle Benson, Oyster Creek spokeswoman.

Meanwhile, the plant is working with aquariums, fishery experts and state agencies to reduce the environmental impacts from the shutdown, according to a statement the plant released Friday.