Workers incorrectly opened and shut certain valves, causing water to flood from a massive storage tank to an area of the reactor known as the torus. The torus plays a role in depressurizing and cooling down the reactor in case of a serious accident.
“This was a breakdown in the process that shows lack of adherence to procedure,” according to a spokesman for the Nuclear Regulatory Commission. He said there were no immediate safety concerns.
At noon on Friday, Pilgrim operators were flushing pipes in the reactor’s cooling system in preparation for an upcoming refueling. They opened a valve on the torus without first closing the valve on the water storage tank. Water being drained into the torus, setting off an alarm in the control room.
“This volume of water placed the torus level above the administrative limit for readiness should an unplanned event occur,” a spokesman for plant owner Entergy Corp. told the Cape Cod newspaper. “Station personnel appropriately responded to close the valves and processed and filtered the water from the torus back to the condensate storage tanks.”
Friday’s flood was the second recent serious incident involving operator error. On March 27, workers triggered the wrong switch, causing the temporary shutdown of a coolant injection system that is essential to cool the plant in a severe emergency.
Federal regulators in 2015 labeled Pilgrim as one of the three worst performers in the country and placed under increased oversight for safety violations and unplanned shutdowns.
Soon thereafter, Entergy announced it would close Pilgrim permanently in mid-2019 due to poor market conditions and increased operational costs. The closure will remove 680 megawatts of capacity from the New England power grid.