A Comment from Bob Park on Fukushima: Hydrogen Explosion in Reactor #4 Spent-Fuel Pool. (April 3, 2011)

It may be months before events at the Fukushima Daiichi nuclear power plant  are sorted out following the massive earthquake on 11 Mar 2011 at 14:46 JST  and the huge tsunami it caused. The major concern involves the fuel  storage pool for reactor No.4 which held the entire complement of fuel rods  from the reactor core and may yet melt down. The rods had been removed just  three months earlier. Reactors 4, 5 and 6 had been shut down prior to the  earthquake for scheduled maintenance. The remaining reactors shut down  automatically during the earthquake, but the 14 meter tsunami flooded the  plant, knocking out emergency generators needed to run the pumps that cool  and control the reactors; damage to transportation blocked help from elsewhere. It gets worse. Four days later, 15 March at about 06:00 JST, a hydrogen bubble that had collected above the spent fuel pond exploded,  heavily damaging the rooftop area of the Unit 4 reactor. At 09:40, the Unit 4 spent-fuel pool caught fire. It was extinguished by 12:00, but not  before huge amounts of radioactive contaminants had been released. That  should not have happened. A hydrogen bubble is explosive only when mixed  with a critical level of oxygen. During the 1979 Three-Mile Island  accident, it was feared that a large hydrogen bubble in the containment  dome would explode rupturing the building. It did not happen, but I have repeatedly urged that a tuft of "platinum wool" always be attached at the  high points of nuclear containment buildings where hydrogen bubbles would be expected to collect. The platinum would catalyse the oxidation of  hydrogen back to water before the mixture reaches an explosive level. The  one-time cost would be trivial.

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Bob Park, is emeritus professor of physics at the University of Maryland, College Park and a former Director of Public Information at the Washington office of the American Physical Society.