Plugging leaks will end crisis, not cold shutdown: analysts

Evacuees' health said at risk if they return home after 'Step 2' achieved

by

Staff Writer

Ever since the nuclear crisis
erupted six months ago, the public
has been clamoring to know
when the damaged reactors
at the Fu ku shi ma No. 1 power
plant will be brought under control
and when the nightmare will
end.

The government and Tokyo
Electric Power Co., which runs
the crippled plant, are working
to bring the three reactors into
cold shutdown by mid-January.

Cold shutdown means the temperature
at the bottom of the
pressure vessel, which holds the
core, has been lowered to less
than 100 degrees.

This critical milestone,
known as “Step 2″ in Tepco’s
road map for containing the
crisis, would limit the release of
radioactive materials from the
plant to less than 1 millisievert
per year, a level that poses no
health risks.

Since work at the plant is proceeding
relatively smoothly, it
appears likely the mid-January
target will be met.

But Fukushima No. 1 will still
have a long way to go before
the flooded plant’s reactors are
stable enough to be considered
safe, experts warn. The main reason
is the abundance of highly
radioactive water.

“There are about 110,00 tons
of contaminated water (in the
plant) and the situation is still
not completely under control
because coolant water is leaking
from the containment vessels.

There is no guarantee that the
irradiated water won’t leak from
the plant (and contaminate the
environment)” if another natural
disaster strikes, said Hisashi
Ninokata, a professor of reactor
engineering at the Tokyo Institute
of Technology.

After achieving cold shutdowns
of reactors 1, 2 and 3, the
government may declare parts
of the 20-km no-go zone around
the plant safe. It may even let
the evacuees return, as long as
the area is decontaminated and
crucial infrastructure restored.

But the longer the tainted water
leaks, the more the radioactive
waste will grow, leaving the
Fukushima plant vulnerable to
further disasters, Ninokata said.

Before the Fukushima crisis can
be said contained, the holes and
cracks from which the water and
fuel are escaping must be located
and sealed. But this extremely difficult
task could take years because
the radiation near the reactors is
simply too high to let workers get
near them.

“It’ll be too early to say that
the situation has reached a stable
phase even after Step 2 is completed,”
said Chihiro Kamisawa,
a researcher at Citizens’ Nuclear
Information Center, a nonprofit
group of scientists and activists
opposed to nuclear power.

When a reactor is in cold shutdown,
the water cooling its fuel
is still hot but no longer boiling,
which significantly reduces the
amount of radioactive emissions.

In late July, the temperature in
reactor No. 1’s pressure vessel fell
below 100 degrees. On Monday,
the same thing was achieved in reactor
3 after Tepco activated a system
that pumps water deep into
the containment vessel. But on
Friday, reactor No. 2 was still boiling
away with a reading of 112.6.

“Efforts seem to be making
smooth progress, and I think
Step 2 is likely to be achieved by
mid-January,” said Shinichi Morooka,
a Waseda University professor
and reactor expert.

Another reason for optimism
is the progress being made with
the water decontamination
system. The cleaning rate has
greatly improved in the past few
weeks and exceeded 90 percent
of capacity last week.

If the decontamination system
ever reaches its full potential, it
will allow Tepco to inject coolant
at a higher rate and bring the
melted cores to lower and stabler
temperatures.

The government also plans
to start decontaminating soil in
various hot spots so the evacuees
can return once the second step
is completed.

But some experts are questioning
whether residents should be
allowed to return so soon. The
cracks and holes in the leaking reactors
haven’t even been pinpointed
yet, let alone fixed, they say.

“As an engineer, I am worried
(about the plan to let residents
return) when it is still unclear
what is really going on inside the
reactors,” said Morooka.

For the time being, Tepco
can only guess where the water
is leaking from and which parts
need repair, because radiation
has prevented workers from fully
exploring the buildings.

Spokesman Junichi Matsumoto
said that since no extensive
damage to the reactors was
found during inspections of the
first and second floors of the
buildings, any holes or cracks are
probably at the basement level.

But with the basement floors
flooded, Tepco’s top priority is
just to get the water out. Plans to
fix the reactors aren’t even being
discussed yet, Matsumoto said.

Asked if the containment vessels
can take another quake, the
Tokyo Institute of Technology’s Ninokata
said he believes the impact
would likely be distributed evenly
through the structure without widening
existing cracks or holes.

But if the impact somehow focuses
on parts damaged by the
March 11 disasters, there could be
further damage, he said.

“The containment vessel is
what really ensures the safety
of a nuclear reactor,” Ninokata
said, warning that if radioactive
materials are still leaking out, allowing
residents to return would
risk harming their health.