Update: Leak at D.C. Cook nuclear plant not serious safety concern, NRC says

BRIDGMAN, MI -- The D.C. Cook Nuclear Plant notified the Nuclear Regulatory Commission of an unusual event that resulted in reactor coolant leaking into a relief tank exceeding 10 gallons per minute.

The NRC said the notification is under "emergency action level S8," and was caused due to actuation of the letdown relief valve that resulted in reactor coolant system leakage to the pressurizer relief tank exceeding 10 gpm.

The NRC sent a news release about the event at 8 a.m. Wednesday, Sept. 13.

The plant was making preparations to proceed to cold shutdown to support their refueling outage, the NRC said.

Operators were in the process of reducing reactor coolant system letdown from 120 gpm to 45 gpm when the letdown system relief valve lifted. The relief discharged to the pressurizer relief tank at approximately 12 gpm. Operators isolated the letdown line which reduced the leakage to approximately 1 gpm, the NRC said.

Plant staff is in the process of determining where the 1 gpm leakage is from and evaluating the basis for terminating the unusual event, according to the NRC.

A call to the NRC seeking comment on the emergency notification was not immediately returned.