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Very high radiation, little water in Japan reactor
Datum: Mittwoch, 28. März 2012 07:46
Very high radiation, little water in Japan reactor
ENLARGE PHOTOIn this photo released by Tokyo Electric Power Co.
(TEPCO), a worker operates an endoscope to take photos of water in the
Unit 2 reactor’s primary containment vessel at the the tsunami-
crippled Fukushima Dai-ichi nuclear power plant in Okuma town,
Fukushima Prefecture, northeastern Japan, Monday, March 26, 2012.
TEPCO, the operator of the nuclear power plant, said the water level
of the reactor container is only 60 centimeters (about 2 feet) from
the bottom, indicating a large quantity of water injected to cool the
melted fuel is leaking from the vessel. (AP Photo/Tokyo Electric Power
Co.) EDITORIAL USE ONLY
ENLARGE PHOTOIn this photo taken by an endoscope and released by Tokyo
Electric Power Co. (TEPCO), a white thermometer, right, is seen
through the surface of water in the Unit 2 reactor’s primary
containment vessel at the the tsunami-crippled Fukushima Dai-ichi
nuclear power plant in Okuma town, Fukushima Prefecture, northeastern
Japan, Monday, March 26, 2012. TEPCO, the operator of the nuclear
power plant, said the water level of the reactor container is only 60
centimeters (about 2 feet) from the bottom, indicating a large
quantity of water injected to cool the melted fuel is leaking from the
vessel. (AP Photo/Tokyo Electric Power Co.) EDITORIAL USE ONLY
[?]
By MARI YAMAGUCHI
The Associated Press
Updated: 12:21 a.m. Wednesday, March 28, 2012
Posted: 8:41 a.m. Tuesday, March 27, 2012
http://www.palmbeachpost.com/news/world/very-high-radiation-little-water-
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TOKYO — One of Japan’s crippled nuclear reactors still has fatally
high radiation levels and much less water to cool it than officials
had estimated, according to an internal examination that renews doubts
about the plant’s stability.
A tool equipped with a tiny video camera, a thermometer, a dosimeter
and a water gauge was used to assess damage inside the No. 2 reactor’s
containment chamber for the second time since the tsunami swept into
the Fukushima Dai-ichi plant a year ago.
The data collected Tuesday showed the damage from the disaster is so
severe, the plant operator will have to develop special equipment and
technology to tolerate the harsh environment and decommission the
plant, a process expected to last decades.
The other two reactors that had meltdowns could be in even worse
shape. The No. 2 reactor is the only one officials have been able to
closely examine so far.
Tuesday’s examination with an industrial endoscope detected radiation
levels up to 10 times the fatal dose inside the chamber. Plant
officials previously said more than half of the melted fuel has
breached the core and dropped to the floor of the primary containment
vessel, some of it splashing against the wall or the floor.
Particles from melted fuel have probably sent radiation levels up to a
dangerously high 70 sieverts per hour inside the container, said
Junichi Matsumoto, spokesman for Tokyo Electric Power Co. The figure
far exceeds the highest level previously detected, 10 sieverts per
hour, which was detected around an exhaust duct shared by No. 1 and 2
units last year.
„It’s extremely high,“ he said, adding that an endoscope would last
only 14 hours in those conditions. „We have to develop equipment that
can tolerate high radiation“ when locating and removing melted fuel
during the decommissioning.
The probe also found that the containment vessel — a beaker-shaped
container enclosing the core — had cooling water up to only 60
centimeters (2 feet) from the bottom, far below the 10 meters (yards)
estimated when the government declared the plant stable in December.
The plant is continuing to pump water into the reactor.
Video footage taken by the probe showed the water inside was clear but
contained dark yellow sediments, believed to be fragments of rust,
paint that had been peeled off or dust.
A probe done in January failed to find the water surface and provided
only images showing steam, unidentified parts and rusty metal surfaces
scarred by exposure to radiation, heat and humidity. Finding the water
level was important to help locate damaged areas where radioactive
water is escaping.
Matsumoto said that the actual water level inside the chamber was way
off the estimate, which had used data that turned out to be
unreliable. But the results don’t affect the plant’s „cold shutdown
status“ because the water temperature was about 50 degrees Celsius
(122 Fahrenheit), indicating the melted fuel is cooled.
Three Dai-ichi reactors had meltdowns, but the No. 2 reactor is the
only one that has been examined because radiation levels inside the
reactor building are relatively low and its container is designed with
a convenient slot to send in the endoscope.
The exact conditions of the other two reactors, where hydrogen
explosions damaged their buildings, are still unknown. Simulations
have indicated that more fuel inside No. 1 has breached the core than
the other two, but radiation at No. 3 remains the highest.
The high radiation levels inside the No. 2 reactor’s chamber mean it’s
inaccessible to the workers, but parts of the reactor building are
accessible for a few minutes at a time — with the workers wearing full
protection.
Last year’s massive earthquake and a tsunami set off the worst nuclear
accident since Chernobyl, sending three reactor cores to melt and
causing massive radiation leaks. The government said in December that
the reactors are safely cooled and the plant has stabilized, while
experts have questioned its vulnerability.
During a recent visit by a group of journalists including The
Associated Press, the head of the plant said it remains vulnerable to
strong aftershocks and tsunami, and that containing contaminated water
and radiation is a challenge. Radioactive water had leaked into the
ocean several times already.
Workers found a fresh leak of 120 tons from a water treatment unit
this week from one of its hoses, with estimated 80 liters (20 gallons)
escaping into the ocean, Matsumoto said. Officials are still
investigating its impact.
Fukushima’s accident has instilled public distrust and concerns about
nuclear safety, making it difficult for the government to start up
reactors even after regular safety checks. All but one of Japan’s 54
reactors are now offline, with the last one scheduled to stop in early
May.