Die Tanks mit abgebrannten Brennelementen auf dem Dach von Unit 4
sollen ab November geleert werden. Das Gebäude ist instabil und
könnte durch Tropenstürme, Erdbeben oder von allein einstürzen. Die
Risiken sind enorm.
(Reuters) - The operator of Japan's crippled Fukushima nuclear plant
is preparing to remove 400 tons of highly irradiated spent fuel from
a damaged reactor building, a dangerous operation that has never been
attempted before on this scale.
Containing radiation equivalent to 14,000 times the amount released
in the atomic bomb attack on Hiroshima 68 years ago, more than 1,300
used fuel rod assemblies packed tightly together need to be removed
from a building that is vulnerable to collapse, should another large
earthquake hit the area.
...
"They are going to have difficulty in removing a significant number
of the rods," said Arnie Gundersen, a veteran U.S. nuclear engineer
and director of Fairewinds Energy Education, who used to build fuel
assemblies.
The operation, beginning this November at the plant's Reactor No. 4,
is fraught with danger, including the possibility of a large release
of radiation if a fuel assembly breaks, gets stuck or gets too close
to an adjacent bundle, said Gundersen and other nuclear experts.
That could lead to a worse disaster than the March 2011 nuclear
crisis at the Fukushima plant, the world's most serious since
Chernobyl in 1986.
No one knows how bad it can get, but independent consultants Mycle
Schneider and Antony Froggatt said recently in their World Nuclear
Industry Status Report 2013: "Full release from the Unit-4 spent fuel
pool, without any containment or control, could cause by far the most
serious radiological disaster to date."
...
"The No. 4 unit was not operating at the time of the accident, so its
fuel had been moved to the pool from the reactor, and if you
calculate the amount of cesium 137 in the pool, the amount is
equivalent to 14,000 Hiroshima atomic bombs," said Hiroaki Koide,
assistant professor at Kyoto University Research Reactor Institute.
...
INADVERTENT CRITICALITY
"There is a risk of an inadvertent criticality if the bundles are
distorted and get too close to each other," Gundersen said.
He was referring to an atomic chain reaction that left unchecked
could result in a large release of radiation and heat that the fuel
pool cooling system isn't designed to absorb.
"The problem with a fuel pool criticality is that you can't stop it.
There are no control rods to control it," Gundersen said. "The spent
fuel pool cooling system is designed only to remove decay heat, not
heat from an ongoing nuclear reaction."
The rods are also vulnerable to fire should they be exposed to air,
Gundersen said.
The fuel assemblies are situated in a 10 meter by 12 meter concrete
pool, the base of which is 18 meters above ground level. The fuel
rods are covered by 7 meters of water, Nagai said.
...
Tepco has shored up the building, which may have tilted and was
bulging after the explosion, a source of global concern that has been
raised in the U.S. Congress.
...
Removing the rods from the pool is a delicate task normally assisted
by computers, according to Toshio Kimura, a former Tepco technician,
who worked at Fukushima Daiichi for 11 years.
"Previously it was a computer-controlled process that memorized the
exact locations of the rods down to the millimeter and now they don't
have that. It has to be done manually so there is a high risk that
they will drop and break one of the fuel rods," Kimura said.
Under normal circumstances, the operation to remove all the fuel
would take about 100 days. Tepco initially planned to take two years
before reducing the schedule to one year in recognition of the
urgency. But that may be an optimistic estimate.
"I think it'll probably be longer than they think and they're
probably going to run into some issues," said Murray Jennex, an
associate professor at San Diego State University who is an expert on
nuclear containment and worked at the San Onofre nuclear plant in
California.
...
And if another strong earthquake strikes before the fuel is fully
removed that topples the building or punctures the pool and allows
the water to drain, a spent fuel fire releasing more radiation than
during the initial disaster is possible, threatening about Tokyo 200
kilometers (125 miles) away.
...
(Additional reporting by James Topham and Mari Saito; Writing by
Aaron Sheldrick; Editing by Raju Gopalakrishnan)
Quelle:
> http://www.reuters.com/article/2013/08/14/us-japan-fukushima-insight-idUSBRE97D00M20130814
Online-Petitionen:
> http://petitions.moveon.org/sign/the-world-community-must
> http://www.avaaz.org/de/petition/Erneute_Katastrophe_mit_globalen_Folgen_in_Fukushima_verhindern/?copy
Interaktive Karte mit aktuellen Strahlungswerten für ganz Japan:
> http://jciv.iidj.net/map/
sollen ab November geleert werden. Das Gebäude ist instabil und
könnte durch Tropenstürme, Erdbeben oder von allein einstürzen. Die
Risiken sind enorm.
(Reuters) - The operator of Japan's crippled Fukushima nuclear plant
is preparing to remove 400 tons of highly irradiated spent fuel from
a damaged reactor building, a dangerous operation that has never been
attempted before on this scale.
Containing radiation equivalent to 14,000 times the amount released
in the atomic bomb attack on Hiroshima 68 years ago, more than 1,300
used fuel rod assemblies packed tightly together need to be removed
from a building that is vulnerable to collapse, should another large
earthquake hit the area.
...
"They are going to have difficulty in removing a significant number
of the rods," said Arnie Gundersen, a veteran U.S. nuclear engineer
and director of Fairewinds Energy Education, who used to build fuel
assemblies.
The operation, beginning this November at the plant's Reactor No. 4,
is fraught with danger, including the possibility of a large release
of radiation if a fuel assembly breaks, gets stuck or gets too close
to an adjacent bundle, said Gundersen and other nuclear experts.
That could lead to a worse disaster than the March 2011 nuclear
crisis at the Fukushima plant, the world's most serious since
Chernobyl in 1986.
No one knows how bad it can get, but independent consultants Mycle
Schneider and Antony Froggatt said recently in their World Nuclear
Industry Status Report 2013: "Full release from the Unit-4 spent fuel
pool, without any containment or control, could cause by far the most
serious radiological disaster to date."
...
"The No. 4 unit was not operating at the time of the accident, so its
fuel had been moved to the pool from the reactor, and if you
calculate the amount of cesium 137 in the pool, the amount is
equivalent to 14,000 Hiroshima atomic bombs," said Hiroaki Koide,
assistant professor at Kyoto University Research Reactor Institute.
...
INADVERTENT CRITICALITY
"There is a risk of an inadvertent criticality if the bundles are
distorted and get too close to each other," Gundersen said.
He was referring to an atomic chain reaction that left unchecked
could result in a large release of radiation and heat that the fuel
pool cooling system isn't designed to absorb.
"The problem with a fuel pool criticality is that you can't stop it.
There are no control rods to control it," Gundersen said. "The spent
fuel pool cooling system is designed only to remove decay heat, not
heat from an ongoing nuclear reaction."
The rods are also vulnerable to fire should they be exposed to air,
Gundersen said.
The fuel assemblies are situated in a 10 meter by 12 meter concrete
pool, the base of which is 18 meters above ground level. The fuel
rods are covered by 7 meters of water, Nagai said.
...
Tepco has shored up the building, which may have tilted and was
bulging after the explosion, a source of global concern that has been
raised in the U.S. Congress.
...
Removing the rods from the pool is a delicate task normally assisted
by computers, according to Toshio Kimura, a former Tepco technician,
who worked at Fukushima Daiichi for 11 years.
"Previously it was a computer-controlled process that memorized the
exact locations of the rods down to the millimeter and now they don't
have that. It has to be done manually so there is a high risk that
they will drop and break one of the fuel rods," Kimura said.
Under normal circumstances, the operation to remove all the fuel
would take about 100 days. Tepco initially planned to take two years
before reducing the schedule to one year in recognition of the
urgency. But that may be an optimistic estimate.
"I think it'll probably be longer than they think and they're
probably going to run into some issues," said Murray Jennex, an
associate professor at San Diego State University who is an expert on
nuclear containment and worked at the San Onofre nuclear plant in
California.
...
And if another strong earthquake strikes before the fuel is fully
removed that topples the building or punctures the pool and allows
the water to drain, a spent fuel fire releasing more radiation than
during the initial disaster is possible, threatening about Tokyo 200
kilometers (125 miles) away.
...
(Additional reporting by James Topham and Mari Saito; Writing by
Aaron Sheldrick; Editing by Raju Gopalakrishnan)
Quelle:
> http://www.reuters.com/article/2013/08/14/us-japan-fukushima-insight-idUSBRE97D00M20130814
Online-Petitionen:
> http://petitions.moveon.org/sign/the-world-community-must
> http://www.avaaz.org/de/petition/Erneute_Katastrophe_mit_globalen_Folgen_in_Fukushima_verhindern/?copy
Interaktive Karte mit aktuellen Strahlungswerten für ganz Japan:
> http://jciv.iidj.net/map/