At the Hanford Nuclear Reservation in Richland, Washington first steps are being taken toward mitigation of the threat posed by hydrogen buildup in a milliongallon tank of radioactive waste. Shown in the photograph is a 64‐foothigh pump being lowered on 4 July through a 40‐inch‐diameter pipe into tank 101‐SY, which is buried below ground. Of the 177 tanks of high‐level waste stored at Hanford, 101‐SY is the most notorious, because of the high concentrations of hydrogen that are produced by its mixture of radioactive materials and organic chemicals. (See PHYSICS TODAY, March 1992, page 17.) The material in the tank forms a viscous slurry at the bottom, covered by a liquid layer and topped by thick pieces of crust. As the hydrogen is generated, it is trapped in the slurry, and about every three months it is released in a giant “burp.” Hydrodynamic models have indicated that the pump should be able to stir the tank contents enough to promote a continual release of hydrogen gas and prevent the accumulation of explosive concentrations.

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