Fission Stories #25: Please Don’t Flush the Toilet While the Reactor is Running

, former director, Nuclear Safety Project | December 21, 2010, 7:49 am EDT
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A sign on the bathroom door at the University of Florida’s research reactor contained this warning:

       Please Don’t Flush the Toilet While the Reactor is Running.

The normal cooling water system for the reactor was connected to the city water main. This connection also supplied water to the toilets. The reactor automatically shut down at least five times when a flushing toilet adversely affected its cooling water flow.

The interim solution was to hang the warning sign on the bathroom door. How could a conscientious person in the bathroom really tell whether the reactor was running? It’s not like the bathroom had windows into the reactor area or gauges indicating current reactor parameters. To flush or not to flush, that’s the question.

Similar problems have been found at nuclear power reactors. For example, the system used to monitor power within the reactor core at the Grand Gulf nuclear plant in Mississippi  began acting erratically in the early 1980s. One output would show expected results while a repeated output for the same location in the core moments later would show entirely different results. The problem was eventually tracked down to a wiring error that allowed operation of the freight elevator in another building at the site to vary the voltage going to the core monitoring system.

Our Takeaway

Nuclear power plants feature many complex systems interconnected by common power supply, ventilation, and cooling water systems. Neither rest rooms nor freight elevators can be dismissed as having no possible interface with safety systems. Anything is possible and a good safety culture trains workers to consider every option until definitive proof eliminates it.

“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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