Friday, Nov. 4, 2011
Find out true reactor conditions
http://www.japantimes.co.jp/text/ed20111104a1.html
Tokyo Electric Power Co. announced Wednesday that there is the
possibility that criticality, a sustained nuclear chain reaction, had
occurred "temporarily" and "locally" in the No. 2 reactor of the
stricken Fukushima No. 1 nuclear power plant. It detected radioactive
xenon-133 and xenon-135, products of uranium or plutonium fission, in
gases collected Tuesday from the reactor.
Because the half life of xenon-133 is 5.25 days and that of xeon-135 is
9.14 hours, criticality is very likely to have occurred just before the
gases were analyzed.
Although more than seven months have passed since the start of the
nuclear fiasco, clearly the reactor has not yet been stabilized. Tepco's
plan to achieve "cold shutdown" of the Nos. 1, 2 and 3 reactors by the
end of this year may face difficulty.
The fact that Tepco cannot deny the possibility of criticality
irrespective of its scale is a grave situation. The conditions are
similar in the Nos. 1, 2 and 3 reactors. It is thought that nuclear fuel
in them melted and has collected in the bottom of both the pressure and
containment vessels.
Tepco should make serious efforts to accurately grasp the conditions of
nuclear fuel inside the reactors.
Even after a reactor is shut down, nuclear fuel fissions occur bit by
bit inside cladding tubes without reaching criticality. Experts concur
that large-scale criticality will not occur in molten nuclear fuel. But
Tepco and the Nuclear and Industrial Safety Agency should take a serious
view of the fact that radioactive xenon pointing to criticality was
detected from the No. 2 reactor. What happened in it can happen in the
Nos. 1 and 3 reactors.
They should strictly watch the conditions of the three reactors and do
their utmost to prevent occurrence of criticality. They should not
forget the simple fact that a large amount of nuclear fuel exists in
these reactors.
Tepco injected 10 tons of a solution containing 480 kg of boric acid
into the No. 2 reactor shortly before 3 a.m. Wednesday to restrain
nuclear fission. This inversely shows that it has not been injecting a
boric acid solution into the reactors in continuously cooling them by
circulating water. Its laxness should be criticized. It wasn't till
after 7 a.m. Wednesday that NISA reported the criticality incident to
Prime Minister Yoshihiko Noda. NISA clearly lacked the ability to make a
correct judgment in this matter.
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