When and what explosion? One of the nuclear test shots. If so which?
Remember Chernobyl was not a nuclear explosion, it was a steam explosion and graphite fire.
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to let the steam pass and avoid an explosion under some
undesireable circumstances.
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The only nuclear explosions in Japan were the two in WW2, on Hiroshima and Nagasaki.
However I believe you meant the Japanese nuclear reactorexplosion, which was not a nuclear explosion it was either a steam explosion and/or a hydrogen/oxygen chemical explosion. That occurred at Fukushima.
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A volcanic steam explosion was earlier believed to be the
cause.
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Hot oil is hotter than steam. When the water hits the oil, steam
is created instantaneously at the oil-water interface. The steam
expands violently, creating the apparent explosion.