Oyster Creek went dark early this morning due to a loss of off site power, causing the plant's reactor to be shut down as a precaution.

Nuclear Regulatory Commission Region 1 spokesperson Neil Sheehan says at 3:41 in the morning the plant lost a 230 kilovolt line -presumable due to a loss of ground or electrical fault, causing the reactor's to "scram"-where all the control rods get inserting rapidly into the reactor, halting fission immediately and shutting down the reactor.

He notes the plant's emergency diesle generators kicked in after the off site power was lost, providing power to safety systems.

"The plant also had to declare an 'unusual event' which is the lowest of four levels of emergency classification used by the NRC, because they had a loss of off site power greater than fifteen minutes."

He says all of the safety systems operated as they should have, and off site power was restored by 5:14 am - exiting the 'unusual event' designation.

The plant will remain in cold shutdown, which is where the reactor is completely cooled down, depressurized, and shut off, while safety officials trouble shoot what happened and make any necessary repairs.

After a cold shut down more time is required to restart operations, than after a quicker "hot shut down"- where the reactor is left pressurized and heated. However because a reactor coolant pump was tripped the cold shut down was necesarry.

Sheehan could not give a specific time of when the reactor would be turned back on.

Sheehan says the two full time inspectors working within Oyster Creek responded immediately, and were satisfied with the response of the plant.