Environmental Engineering Reference
In-Depth Information
have occurred in Japan, and caused a huge amount of local
damage, including damage to the region
s power grid.
The Fukushima reactors were immediately isolated from
outside sources of power. The reactors came through the
earthquake with very little damage, shut down properly,
and all emergency power systems turned on as designed.
Forty minutes later a huge tsunami struck the coast.
It killed roughly
'
people, displaced nearly a million,
and came over the Fukushima sea wall which was only
s
emergency generators and the switch-gear to connect
them properly were in the basements of the generator
buildings and all were drowned out. The site was left only
with batteries which were designed to last only a few
hours. Thus, in a very short time it was impossible to
circulate cooling water through the reactor core
feet high while the wave was
feet high. The plant
'
-
an
extremely dangerous situation.
The problem was that although the reactors were prop-
erly shut down, that meant only that no nuclear
fission
reactions were taking place. The radioactivity in the core
was, however, still generating a great deal of power.
At the moment of shutdown, a reactor continues to gen-
erate about
% of its thermal power from radioactivity.
A reactor that produces
megawatts of electricity has
a thermal power of about
megawatts, so immediately
after shutdown it still produces about
megawatts of
heat, more than enough to melt its core unless there is
some way to cool it. With no electricity at Fukushima, no
cooling water could be circulated; as the water in the
reactor boiled away, no new water could be pumped in
and part of the core began to be exposed; and as hydrogen
