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What's Going On At Japan's Damaged Nuclear Power Plant?
http://www.emfnews.org
May 5 (Reuters) - Japanese engineers are struggling to gain
control of the Fukushima Daiichi nuclear power plant, 240 km
(150 miles) north of Tokyo, which was seriously damaged by a
March 11 earthquake and tsunami.
Two of the six reactors at the plant, operated by Tokyo
Electric Power Co (TEPCO), are considered stable but the
other four are volatile.
Following are some questions and answers about efforts to
end the world's worst nuclear crisis since the 1986
Chernobyl accident:
WHAT IS HAPPENING?
Workers are trying to fill the reactors with enough water to
bring the nuclear fuel rods inside to a "cold shutdown", in
which the water cooling them is below 100 degrees Celsius
and the reactors are considered stable.
TEPCO has been pouring water into the reactor vessels
containing the rods since the disaster to cool them as an
emergency measure. [ID:nL3E7FI0C7]
In a further step towards a cold shutdown, TEPCO is filling
the containment vessel -- an outer shell of steel and
concrete that houses the reactor vessel -- with water in a
procedure called water entombment. It has started by
increasing the amount of water being poured into the No.1
reactor.
At the same time, it will work to restore the reactors'
cooling system, which functions like a radiator on a car.
For the No.1 reactor, TEPCO is trying to install a separate
cooling system. On May 5, w orkers enter ed the No.1 reactor
building for the first time since a hydrogen explosion
ripped off its roof a day after the natural disaster. They
installed duct pipes to connect to ventilators t hat will
filter out 95 percent of the radioactive material in the
air.
Once the radiation level drops in a few days, TEPCO plans to
start installing the cooling system.
For reactors like No.2, which is suspected of having a
damaged containment vessel, TEPCO said it hopes to seal the
damaged sections with cement to prevent the water being
pumped in from leaking out.
WHAT IS HAMPERING OPERATIONS?
The large amounts of runoff from the water TEPCO has been
pumping in to prevent overheating of fuel rods and a nuclear
meltdown. The operator has estimated the amount of
contaminated water at the Daiichi plant at about 87,500
tonnes.
TEPCO plans to start operating in June a system to treat
this contaminated water. The system, developed by Toshiba ,
Hitachi-GE Nuclear Energy, Areva (CEPFi.PA) and U.S. firm
Kurion, would adsorb and isolate radioactive elements, then
the treated water would be re-used to cool down the
reactors.
The isolated radioactive materials would remain in the
nuclear plant for now.
For the time being, TEPCO has been transferring radioactive
water that has accumulated at the reactor buildings into
tanks and storage areas at the plant.
Many storage tanks on site were damaged by the tsunami and
authorities made a decision in April to pump contaminated
water with lower levels of radiation back into the ocean to
secure storage space. That has since stopped but could
resume if they run out of storage space again.
In the meantime, radiation continues to seep out of TEPCO's
nuclear complex into the sea and into the air, although at
far lower levels than at the peak of the crisis in
mid-March.
Soil containing radioactivity 10,000 times the normal level
was recently found at the bottom of the sea.
To contain contamination, workers have tried pouring liquid
glass to stop a leak and spraying the ground with sticky
resin to capture radiated dust. They are also injecting
nitrogen into reactors to prevent new hydrogen explosions
which would spread highly radioactive material into the air.
HOW LONG MIGHT THIS TAKE?
On April 17, TEPCO announced a timetable for its operations.
Within the first three months it plans to cool the reactors
and the spent fuel stored in some of them to a stable level
and reduce the leakage of radiation. [ID:nL3E7FH03J]
TEPCO then hopes to bring the reactors to a cold shutdown in
another three to six months.
But some experts said the process could take longer. TEPCO
said constant aftershocks, power outages, high levels of
radiation and the threat of hydrogen explosions were factors
that could hamper its work.
Weather conditions, such as the approaching rainy season and
typhoons and lightning during the summer, could also pose
problems.
WHAT ARE THE RISKS?
The main risk is radiation continuing to seep, or burst, out
each time a pipe leaks or rising pressure forces workers to
vent steam. Leaking water from within the nuclear pressure
vessels could find its way into soil and the ocean, while
spikes in radiation could contaminate crops over a wide
area.
The risk that the spent fuel pools could go into a chain
reaction is low, as long as temperature indicators are
accurate. But some more of the contaminated runoff may have
to be dumped into the sea, if workers run out of space to
store the water.
There is also a small risk of a corium steam explosion,
particularly in the No.1 reactor, which is the plant's
oldest and which is believed to have a weak spot.
If workers are unable to continue hosing operations, and if
the nuclear fuel manages to melt through the bottom of the
reactor and fall into a water pool below, this would result
in a burst of heat and a sudden release of a huge amount of
hydrogen that could breach the containment vessel.
Should either worst-case scenario happen, high levels of
radiation could be dispersed up to 20 km (12 miles) around
the site could be dispersed, making it impossible to bring
the reactors to a cold shutdown without great sacrifice.
WILL THE SITE BECOME A NO-MAN'S LAND?
Most likely, yes. Even after a cold shutdown there are
tonnes of nuclear waste sitting at the site.
Entombing the reactors in concrete would make them safe to
work and live a few kilometres away, but is not a long-term
solution for the disposal of spent fuel, which will decay
and emit radiation over several thousand years.
The spent nuclear fuel in Fukushima has been damaged by sea
water, so recycling it is probably not an option, while
transporting it elsewhere is unlikely because of the
opposition that would bring.
Experts say the clean-up will take decades.
by Mayumi Negishi, Shinichi Saoshiro and Yoko Kubota;
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