’Melt-through’ at Fukushima? / Govt report to IAEA suggests situation worse than meltdown
Nuclear fuel in three reactors at the Fukushima No. 1 nuclear plant has
possibly melted through pressure vessels and accumulated at the bottom
of outer containment vessels, according to a government report obtained
Tuesday by The Yomiuri Shimbun.
A “melt-through”—when melted nuclear fuel leaks from the bottom of
damaged reactor pressure vessels into containment vessels—is far worse
than a core meltdown and is the worst possibility in a nuclear accident.
The possibility of the situation at the plant’s Nos. 1 to 3 reactors was
raised in a report that is to be submitted to the International Atomic
Energy Agency.
If the report is released as is, it would be the first official
recognition that a melt-through has occurred.
It was revealed earlier that sections of the bottom of the pressure
vessels where control rods go through have been damaged. Highly
radioactive water from inside the pressure vessels was confirmed to have
leaked out of the containment vessels, even outside the buildings that
house the reactors.
The report also acknowledges problems with the vertical administrative
structure concerning nuclear safety regulations. As a result, the report
says, who was responsible for keeping people safe in the event of a
nuclear accident was not clear.
The report proposes separating the Nuclear and Industrial Safety Agency
from the Economy, Trade and Industry Ministry and making it an
independent organization. The report also proposes drastic reform of the
nation’s nuclear administration, including the Nuclear Safety Commission.
The Yomiuri Shimbun , June 8, 2011
http://www.yomiuri.co.jp/dy/national/T110607005367.htm
TEPCO faces prolonged battle against radioactive debris, water
As workers struggle to bring the Fukushima No. 1 nuclear power plant
under control, signs are increasing that the eventual cleanup of the
disaster will take much longer than previously thought.
Containers of rubble, unwanted and of unknown levels of contamination,
line the roadside near the plant. Pools of radioactive water at the
plant, a constant problem since the March 11 disaster, may pose even
longer-term challenges. And full studies on how to remove nuclear fuel
and eventually decommission the four troubled reactors have yet to start.
Tokyo Electric Power Co., the plant’s operator, started using
remote-controlled, unmanned heavy machinery in late April to put
radioactive debris into containers each with a capacity of about 4 cubic
meters.
By June 5, 279 containers had been filled.
“We don’t know where we can take the containers,” said a TEPCO spokesman.
In fact, the spokesman said the company has no idea about the aggregate
volume of the debris nor the amount of radiation for each container.
TEPCO planned to complete work to remove the rubble within three months,
but officials now say that no end is in sight.
One plausible receiver is Japan Nuclear Fuel Ltd., which accepts
low-level radioactive waste from electric power companies at its
facility in Aomori Prefecture.
But an official said the company cannot decide on whether to accept
radioactive debris unless the amount of radiation and the types of
radioactive materials are known.
The debris at the Fukushima plant includes concrete fragments of reactor
buildings that were blown off in hydrogen explosions as well as rubble
washed ashore by the March 11 tsunami.
Radiation levels of some pieces measured more than 1,000 millisieverts
per hour, a level that could cause acute disorders if workers are in
close proximity for a long time.
While workers at the Fukushima plant may be exposed to an accumulated
maximum of 250 millisieverts, radiation of up to 20 millisieverts per
hour was observed in the atmosphere around the No. 1 to 4 reactors as of
May 27.
What to do with highly radioactive water is also a growing concern for
TEPCO. Such water at the Fukushima plant is expected to increase to
200,000 tons in December, nearly double the 105,100 tons as of the end
of May.
The water currently contains radioactivity of 720,000 terabecquerels,
more than the 370,000-630,000 terabecquerels estimated to have been
released into the atmosphere.
The central waste treatment facility, which is capable of holding 14,000
tons of water, is nearly full.
The capacity at the facility and other containers will be increased by
4,300 tons, but the increased space will be filled by June 20.
TEPCO is injecting a huge amount of water to cool the reactors and the
storage pools for spent nuclear fuel rods. Radioactive water is believed
to be leaking from holes in the pressure vessels and containment vessels
of the reactors.
Using technology of France’s Areva SA, a system will be completed on
June 15 that can reduce the radioactivity of contaminated water to
one-1,000th by removing cesium and strontium. The water can then be
reused to cool the reactors or be stored at tanks for water with low
radioactivity.
But the system is capable of treating only up to 1,200 tons a day.
The water treatment system and another system to remove radioactive
materials, developed by Japanese and U.S. companies, are expected to
cost a total of 53.1 billion yen ($662 million).
However, it is still undecided how to dispose of the radioactive
substances removed from the water.
“We will consider treatment technology and regulations,” said Hidehiko
Nishiyama, a senior official at the Nuclear and Industrial Safety
Agency. “It will take years (to treat radioactive materials).”
Another huge challenge is how to dispose of nuclear fuel that remains in
the reactors and the storage pools.
The No. 1 to 3 reactors contained 1,496 fuel assemblies, or clusters of
fuel rods, while the storage pools for the No. 1 to 4 reactors held
3,108 fuel assemblies.
An estimated five to 10 years are needed to remove the nuclear fuel from
the reactors after they reach a stable cold shutdown state.
TEPCO said it plans to decommission the No. 1 to 4 reactors.
"We have not made full-fledged studies on how to decommission the
reactors," said Junichi Matsumoto, acting general manager of TEPCO’s
Nuclear Power and Plant Siting Division.
Toshiba Corp., which designed the Fukushima plant, announced plans in
April to remove fuel in five years and decommission reactors in slightly
more than 10 years.
But a paper carried in the online edition of Britain’s Nature magazine
soon after Toshiba’s announcement said decommissioning work would take
decades, even 100 years.
The paper quoted “veterans of cleanup operations” as saying that many
more years will be needed at Fukushima than the 11 years required to
remove fuel after the accident at the Three Mile Island nuclear power plant.
It also pointed out that following a fire in 1957 at a nuclear facility
in Sellafield, Britain, the reactor remained as it was for 20 years.
But TEPCO will be under pressure to remove the fuel quickly because
another major earthquake or tsunami could cause the release of
radioactive materials from the reactors.
TEPCO also must come up with new disposal measures because it is
difficult to transport damaged nuclear fuel to the reprocessing facility
in Aomori Prefecture.
Another problem is how to dispose of the pressure vessels, containment
vessels and piping systems that are all contaminated with high levels of
radioactivity.
(This article was compiled from reports by Shunsuke Kimura, Jin
Nishikawa, Eisuke Sasaki and Hidenori Tsuboya.)
Asahi Shimbun , June 7, 2011
http://www.asahi.com/english/TKY201106060179.html
Institute Wants Dosimeters Distributed to Fukushima Residents
Tokyo, June 7 (Jiji Press)—Japan’s National Cancer Center said
Tuesday dosimeters should be distributed to residents of areas with
relatively high levels of radiation emitted from a crippled nuclear
power plant.
The organization stressed the need to measure radiation doses of
those under 20 as well as farmers and other people who work outdoors.
The request comes as there is little available data on the risk of
cancer from exposure to radiation over long periods.
There are areas, known as “hot spots,” that have high levels of
radiation even though they are not close to the Fukushima No. 1 nuclear
power plant.
Dosimeters should be provided to residents—whether it is one for
each family or one for every 10 children—so as to trace patterns of
radiation exposure in everyday lives, National Cancer Center Chief
Director Takamasa Kayama said at a news conference.
Jiji Press, June 7, 2011
http://jen.jiji.com/jc/eng?g=eco&k=2011060700955