November 07, 2013
By TOSHIO KAWADA/ Staff
Writer
OKUMA, Fukushima
Prefecture--The 1,533 nuclear fuel assemblies were lined up in neat
rows in the storage pool of the No. 4 reactor building amid new
equipment and a clean environment.
But in stark contrast was the
scene around the No. 4 reactor building at the Fukushima No. 1
nuclear power plant.
Concrete walls were still
missing from the third and fourth floors of the No. 4 reactor
building, raising questions among onlookers if the structure could
withstand a huge earthquake.
On the sea side of the
building, a piping system and metal rods were exposed behind
collapsed walls of a former boiler building.
A truck swept up by the 2011
tsunami remained upside down by the side of the turbine building.
Amid these surroundings,
Tokyo Electric Power Co. plans to start removing the nuclear fuel
assemblies from the No. 4 storage pool as early as next week. The
work would represent a new stage in the overall plan to end the
nuclear crisis that started 32 months ago.
“It is a big step in the
process to decommission the reactor,” Nuclear Regulation Authority
Commissioner Toyoshi Fuketa said.
The entire decommissioning
plan for the plant is expected to take 30 to 40 years to complete,
and the strategy could change at any moment.
Workers still do not know the
location of melted nuclear fuel in the No. 1, No. 2 and No. 3
reactors. High radiation levels are preventing entry to some areas.
And contaminated water leaks continue to plague the site.
And removing the nuclear fuel
from the No. 4 pool will require delicate procedures, considering the
state of the building and the dangers involved.
NRA Chairman Shunichi Tanaka
told TEPCO President Naomi Hirose to use extreme caution in removing
the assemblies.
“The process involves a
very large risk potential,” Tanaka told Hirose. “In a sense, it
is more risky than the radioactive water crisis.”
TEPCO on Nov. 6 allowed
reporters to see the spent fuel storage pool of the No. 4 reactor
building and other areas of the stricken nuclear plant.
An elevator took the
reporters to the top floor of the five-story building. A steel frame
had been assembled near the pool, and a new fuel hoist and a new
crane had been installed.
The No. 4 reactor building
itself was covered by a canopy to replace the roof that was blown off
in an explosion on March 15, 2011.
TEPCO plans to transfer the
1,533 nuclear fuel assemblies to a “storage pool for common use”
100 meters west of the No. 4 reactor.
The removal and transfer is
expected to be completed at the end of next year.
The assemblies contain both
spent and unused fuel. Some bundles were moved to the pool from the
reactor core because the No. 4 reactor was undergoing a regular
safety check when the Great East Japan Earthquake and tsunami struck
the plant on March 11, 2011.
The disaster knocked out the
cooling system for the storage pool, sparking fears that it would dry
up, leaving the fuel exposed and allowing huge amounts of radioactive
substances to spew into the air.
That didn’t happen.
However, the explosion four days after the tsunami left large chunks
of debris in the storage pool.
Those chunks have been
cleared, but a number of smaller pieces remain in the storage pool.
The fuel removal process will
use a cask receptacle that is 5.5 meters long, weighs 91 tons and can
hold 22 fuel assemblies. It will be submerged in the pool and receive
one fuel assembly at a time to prevent a nuclear reaction from
occurring.
A crane will lower the
receptacle to the ground, where a vehicle will pick it up and take it
to the common-use storage pool.
TEPCO plans to use two
receptacles to speed up the transfer process and finish removing all
the fuel in just over a year.
In addition to uranium, spent
nuclear fuel contains highly toxic plutonium and other radioactive
substances, which could be released if the fuel assemblies are
damaged during the removal or transfer process.
TEPCO has taken measures to
check for deformed fuel assemblies and to prevent the remaining
debris from causing damage when the fuel is pulled out.
The company has also decided
to use double wires to ensure the receptacles are not dropped by
mistake.
The canopy covering the No. 4
reactor building is designed to contain radioactive materials in the
event of an accident. The bottom of the storage pool has also been
strengthened with concrete and other materials.
The reinforced storage pool
could withstand shaking as strong as the magnitude-9.0 Great East
Japan Earthquake, TEPCO officials said.
MYSTERIES REMAIN AT
NO. 1 TO NO. 3 REACTORS
The government and TEPCO
announced the three-stage road map for decommissioning the Fukushima
reactors in December 2011.
The first stage involves
preparatory work, such as clearing debris, followed by the
second-stage program that includes the removal of nuclear fuel from
the pool in the No. 4 reactor building.
According to the road map,
work to remove spent nuclear fuel from the pool in the No. 3 reactor
building should start in the first half of fiscal 2015. But high
radiation levels have prevented workers from approaching the No. 3
reactor, meaning that remote-control equipment will be needed to
assess the situation.
The road map does not specify
when the removal work will be completed there.
Removing the melted nuclear
fuel from the No. 1 to No. 3 reactors is part of the third stage, and
it is expected to start in fiscal 2020 at the earliest.
Engineers will first study
methods to deal with the melted fuel, followed by the installation of
equipment for the task. Currently, remote-control robots are being
developed to study the situation and reduce workers’ exposure to
radiation.
The locations and the
condition of the melted fuel for these reactors remain a mystery. It
apparently dropped to the containment vessels through the inner
pressure vessels housing the reactor cores.
In addition, TEPCO has not
determined the extent of damage to the pressure and containment
vessels.
TEPCO plans to insert a small
remote-control device equipped with a camera into the suppression
pool in the bottom part of the containment vessel of the No. 1
reactor on Nov. 13 at the earliest to get an idea of the internal
situation.
The road map for
decommissioning work could drastically change depending on the
conditions of the melted nuclear fuel and the damage to the
containment vessels.
ONGOING CONTAMINATED
WATER PROBLEM
One obstacle in the
decommissioning plan is the continuous leaks of water contaminated
with radioactive materials.
The Alps system that can
remove 62 types of radioactive materials, including strontium, from
water is scheduled to be put into full operation within this month.
It is considered a key piece
of equipment to cut down the workers’ risk of exposure to
radiation.
On Nov. 6, the Alps system
was still not operational.
Under a tent the size of a
gymnasium, where the Alps equipment is stored, workers were
inspecting tanks and piping while using cranes hanging from ceilings
to relocate containers.
Test runs of Alps started in
March. But the operations were suspended in June after water was
found leaking from some of the tanks in the system.
On Sept. 27, Alps operations
were restarted, only to be shut down the same day due to a different
problem.
Contaminated water is
increasing by about 400 tons every day at the plant due to the
continuing cooling of the reactors and groundwater entering cracks in
the buildings and mixing with radioactive water.
TEPCO has removed only cesium
from about 380,000 tons of contaminated water so far. And since even
the Alps system cannot remove tritium, TEPCO has no choice but to
store the radioactive water at the site.
In April, radioactive water
was found to have leaked from an underground storage tank. In August,
300 tons of highly contaminated water had spilled from a tank and
likely reached the ocean.
Other leaks have also taken
place, spreading soil contamination in the plant’s compound.
Workers on Nov. 6 were seen
heightening barriers and embankments to prevent radioactive water
from spilling over the encasements surrounding tanks holding
contaminated water.
About 200 workers have been
assigned to monitor the tanks for possible leaks.
“The division to deal with
contaminated water is different from the one to remove nuclear fuel.
So we will be able to sufficiently carry out work for the two
issues,” said Akira Ono, director of the Fukushima No. 1 nuclear
power plant.
However, TEPCO Vice President
Zengo Aizawa was not so optimistic.
“From the mid- and
long-term perspective, I have concerns,” Aizawa said.
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