COVERT, MI --

Palisades nuclear power plant was shut down shortly before 7 p.m. Tuesday to repair a leak in the plant's safety injection/refueling water tank, according to a release from Entergy Corporation, the plant's owner.

The tank holds up to 300,000 gallons of borated water that floods the reactor during refueling outages. It is also the source for the safety injection system to remove heat from the reactor when there is a loss of coolant.

According to Palisades spokesman Mark Savage, the leak was first discovered several weeks ago.

The Palisades operations department has been monitoring and analyzing tank leakage twice every day over the past several days, according to a press release. But this afternoon around 1:41 p.m. the tank was declared inoperable.

The plant was removed from service at 6:49 p.m.

Savage declined to speculate as to when the plant will be back up running.

Repair work will include draining the tank, locating the leak, repairing the leak, refilling the tank and returning the plant to service.

In the past year, Palisades has been downgraded by the NRC, which has classified it as one of the four worst performing nuclear plants in the United States and prompted increased inspections in recent months.