Fission Stories #161
Good News: Workers removed a valve from the piping of a cooling water system at the Indian Point nuclear plant in New York on August 13, 1984, for maintenance. The cooling water system had two redundant loops of pumps, pipes, and heat exchangers. The loop the workers removed the valve from had been shut down for maintenance and inspections. The other loop remained in service. A pipe cross-connected the two loops, but three separate valves within the connecting pipe prevented water from the running loop from entering the idle loop.
Source: NRC
Bad News: Other workers discovered the room containing the cooling water system pumps filling with water that poured from the ends of the pipe where the valve had been removed. The water leaked from the pipe faster than it left via drains in the floor. It was later determined that all three valves in the cross-connect pipe had failed, allowing water from the running loop to reach the idle loop’s piping and from there reach the floor. The workers could not stop the room’s flooding.
Good News: The rising water levels submerged the electric motors for the cooling water system pumps. The motors shorted out and the pumps stopped running. Leakage of water into the room stopped and the floor drains slowly emptied water from the room.
Bad News: The rising flood waters shorted out all the cooling water system pumps, idling both loops. The plant lost all cooling water for its emergency equipment.
Good News: The reactor was shut down for refueling at the time of the incident. If there’s ever a good time for the electric motors for all the cooling water pumps to be underwater, it’s when no accident is underway.
Our Takeaway
Three valves had been purchased and installed to prevent water from the running loop from getting into the idled loop. But all three valves failed.
A corrective action for this problem might be to purchase and install a fourth valve. After all, what are the chances that all four valves fail? About the same odds of three valves failing, if their reliability is low.
A better corrective action involves improving the reliability of the existing valves by upgrading their maintenance and testing protocols. Three reliable valves can beat four less reliable ones.
“Fission Stories” is a weekly feature by Dave Lochbaum. For more information on nuclear power safety, see the nuclear safety section of UCS’s website and our interactive map, the Nuclear Power Information Tracker.