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News & Views item - April 2011 |
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.