Fission Stories #22: Graf Robinson

, director, Nuclear Safety Project | November 30, 2010, 8:02 am EDT
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Between the world wars, Germany built and operated a number of lighter-than-air passenger liners. These blimps, the Graf Zeppelin being the first and the Hindenburg being the most famous, used hydrogen gas for buoyancy. The downside of hydrogen is that it is extremely flammable. Newsreel cameras recorded Hindenburg’s demise as it burst into flames while attempting to dock at a mooring in Lakehurst, New Jersey.

At 2:36 am on January 7, 1989, operators at the Robinson nuclear plant in South Carolina declared an Unusual Event, the least severe of the NRC’s four emergency classifications. Hydrogen concentrations of six percent were detected in the turbine building, auxiliary building, and containment. Hydrogen concentrations greater than four percent are flammable.

Plant workers had been performing an air test of the main electrical generator. By mistake, the plant’s instrument and station air systems were connected to the hydrogen supply system. Hydrogen gas flowed in the instrument and station air system piping throughout the plant.

The mistake created the potential for explosive concentrations of hydrogen to be present in various buildings. Fortunately, the mistake was detected before the plant became the Graf Robinson.

Graf Hatch

On May 14, 1998, workers at the Hatch Unit 2 reactor in Georgia responded to a problem. It seems that hydrogen gas being injected into the water piping going to the condensate booster pumps was leaking back out into the turbine building. Monitors indicated a hydrogen concentration of 14 percent, well above the mixture needed for explosion.

Luckily, the source of the hydrogen leak was discovered and isolated before Graf Hatch was launched.

Our Takeaway

The Robinson event illustrates the point that, to the greatest extent possible, it should be physically impossible to accidentally connect a hydrogen supply to an air supply line. If the fittings were of different size, such mistakes would be impossible.

The Hatch event illustrates, once more, the point about safety gains sometimes having unintended consequences. Hydrogen was being injected to lessen the rate that pipe oxidize, or rust. That’s good. When that act results in an entire building reaching the flammable limit for hydrogen, that’s not so good. Salvaging pristine piping from within a demolished building offers little consolation.

“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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