Pilgrim employees preparing for this Sunday’s reactor refueling accidentally caused water to flood from a storage tank into the base of the reactor (the “torus”). The torus helps to depressurize and cool the reactor is an accident were to occur.

The workers were flushing out piping and working on some valves when they opened a valve out of sequence. This caused the flooding to occur and an alarm to sound in the control room. The water level in the torus made it so it would’t be useful if an accident would have happened. It took about 4 hours for workers to put the water back in the storage tank.

Read more about what happened in these media articles:

This is the second worker-caused error in the past week at Pilgrim. The Nuclear Regulatory Commission stated that it is continuing to assess the event.

The Union of Concerned Scientists (UCS) has developed a technical fact sheet to explain in more detail what happened and why the torus is important. Read the UCS fact sheet →