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Fission Stories #114: Rub a Dub Dub, Three Pumps in a Tub: A Flood at Hatch

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Core spray pump at Hatch nuclear plant

RHR pump

On December 21, 1985, the Unit 1 reactor at the Hatch nuclear plant south of Vidalia, Georgia was shut down for a refueling outage. Workers performed a test simulating the loss of the electrical grid for the plant. As designed, the unit’s emergency diesel generators automatically started and supplied power to essential equipment.

A closed maintenance valve on the residual heat removal (RHR) pump suction piping opened when it lost electrical power. This valve contained a spring that pushed the valve open unless compressed air was supplied that overcame the spring force to close the valve. The air compressors supplying air flow to the valve were not powered from the emergency diesel generators, so they stopped functioning when the normal power was turned off.

The normal supply of water to the RHR pumps comes from the torus, a large metal cylinder inside the reactor building holding nearly two million gallons. Water from the torus flowed through the open valve through a disassembled RHR pump suction valve into the pump room. The pump room quickly flooded to a depth of 14 feet. Key equipment in the room, including both RHR pumps and one core spray pump were disabled when they became submerged.

Our Takeaway

Nuclear power plants are very complex. The technology can be intimidating. But a relatively simple concept involves keeping water on the inside of the pumps and piping, not on the outside. Don’t run with scissors. Don’t spit into the wind. Don’t go swimming for at least a half hour after eating. And don’t keep water on the outside of pumps and piping.

“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.

 

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About the author: Mr. Lochbaum received a BS in Nuclear Engineering from the University of Tennessee in 1979 and worked as a nuclear engineer in nuclear power plants for 17 years. In 1992, he and a colleague identified a safety problem in a plant where they were working. When their concerns were ignored by the plant manager, the utility, and the Nuclear Regulatory Commission (NRC), they took the issue to Congress. The problem was eventually corrected at the original plant and at plants across the country. Lochbaum joined UCS in 1996 to work on nuclear power safety. He spent a year in 2009-10 working at the NRC Training Center in Tennessee. Areas of expertise: Nuclear power safety, nuclear technology and plant design, regulatory oversight, plant license renewal and decommissioning

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  • Martin Trenz

    Yes, this IS complex technology, I agree, and I can’t blame the engineers and designers for missing this unfortunate combination of events. But I also have to ask myself: IF the equipment in the pump-room is important to the running of the plant (and which equipment isn’t…) AND it’s known that this equipment will not work when submerged (which is probably standard unless it is “hardened”) then why was there no mechanism to drain the pump room, like an actual drain? Or even inform someone that the pump room was flooding? This is not the first time I’ve seen this pattern: A does not belong into B, but there is no sensor to detect A in B. It might be hard to detect the exact level of hydrogen in the containment building, but finding the water-level of a room is basically washing-machine “technology”…