Serious rescue efforts for isolated people in destroyed
towns by tsunamis and quake are under way.
Another serious concern is of the stopped nuclear power
plants, Fukushima-I #II with 8 reactors total.
The Fukushima-I#1, 40 years old, has got the first trouble
after its automatic shut-down by the quake, which was caused
by no electricity (an emergency Diesel generator did not work
either) for driving circulation pumps of cooling water.
Consequently, decay heat of U-fuel pins could not be cooled
enough and temperature and steam pressure inside the reactor
vessel elevated continuously. Finally the melt-down of
reactor-core fuel started to happen, as detected by Cs and I
activities outside as the emergent value of reactor vessel
gas was opened to decrease the elevated steam pressure. It
happened an explosion, by mixing hydrogen-gas (generated by
H2O + high-temperature-metal interaction inside reactor) and
oxygen gas at the outside of the reactor steel-container,
which destroyed the concrete walls of the #1 plant building.
The reactor container vessel and reactor vessel were looked
not to be damaged.
TEPCO (Tokyo Electric Power Corp.) and NISA (Nuclear and
Industrial Safety Agency) decided to fill the inside and
outside of reactor vessel with seawater adding borated
acid to cool the reactor. The work was done. Radioactivity
monitors outside showed decrease of radiation level to about
ten times of natural BG, which was about several 100 times
just after the emergency gas-valve opening. Now the reactor
is confined stable. Citizens inside 20 km radius were
evacuated for safety.
(I think, the usage of sea water, emergent use, was chosen
by two reasons: 1) not enough pure-water was available
at the site, 2) NaCl contained in sea water, as well as
added borated acid (B-10) has significant thermal-neutron
absorption effect which may help avoiding a worst
critically accident of fallen debris of melt U-fuels into
water pool of container vessel, if happened.)
Probably the Fukushima-I#1 reactor will be closed
(disassembled) in near future. But we still need careful
watching what will be going on.
Now it is aired that Fukushima-I#3 reactor has got a similar
trouble. They might do similar treatment, not decided yet.