[Marxism] Radiation in broken unit 2 too high for robots
lnp3 at panix.com
Thu Mar 29 07:40:57 MDT 2012
Thursday, March 29, 2012
Reactor 2 radiation too high for access
73 sieverts laid to low water; level will even cripple robots
By *MINORU MATSUTANI
Radiation inside the reactor 2 containment vessel at the Fukushima
No. 1 nuclear plant has reached a lethal 73 sieverts per hour and
any attempt to send robots in to accurately gauge the situation
will require them to have greater resistance than currently
available, experts said Wednesday.
Exposure to 73 sieverts for a minute would cause nausea and seven
minutes would cause death within a month, Tokyo Electric Power Co.
The experts said the high radiation level is due to the shallow
level of coolant water — 60 cm — in the containment vessel, which
Tepco said in January was believed to be 4 meters deep. Tepco has
only peeked inside the reactor 2 containment vessel. It has few
clues as to the status of reactors 1 and 3, which also suffered
meltdowns, because there is no access to their insides.
The utility said the radiation level in the reactor 2 containment
vessel is too high for robots, endoscopes and other devices to
Spokesman Junichi Matsumoto said it will be necessary to develop
devices resistant to high radiation.
High radiation can damage the circuitry of computer chips and
degrade camera-captured images.
For example, a series of Quince tracked robots designed to gather
data inside reactors can properly function for only two or three
hours during exposure to 73 sieverts, said Eiji Koyanagi, chief
developer and vice director of the Future Robotics Technology
Center of Chiba Institute of Technology.
That is unlikely to be enough for them to move around and collect
video data and water samples, reactor experts said.
"Two or three hours would be too short. At least five or six hours
would be necessary," said Tsuyoshi Misawa, a reactor physics and
engineering professor at Kyoto University's Research Reactor
The high radiation level can be explained by the low water level.
Water acts to block radiation.
"The shallowness of the water level is a surprise . . . the
radiation level is awfully high," Misawa said.
While the water temperature is considered in a safe zone at about
50 degrees, it is unknown if the melted fuel is fully submerged,
but Tepco said in November that computer simulations suggested the
height of the melted fuel in reactor 2's containment vessel is
probably 20 to 40 cm, Tepco spokeswoman Ai Tanaka said.
Tepco has inserted an endoscope and a radiation meter, but not a
robot, in the containment vessel. It is way too early to know how
long Tepco will need to operate robots in the vessel because it is
unknown what the devices will have to do, Tanaka said.
A Quince was exposed to radiation of 20 sieverts per hour for a
total of 10 hours, and the device worked fine, Koyanagi said. If
the team conducts further experiments, it may find out the robot
can resist even more radiation, he added.
According to experts, even though high radiation in the
containment vessel means additional trouble, it is not expected to
further delay the decommissioning the three crippled reactors, a
process Tepco said will take 40 years.
The experts noted, however, that removing the melted nuclear fuel
from the bottom of the containment vessels will be extremely
Tepco inserted a radiation meter into the containment vessel of
reactor 2 Tuesday for the first time, measuring atmospheric
radiation levels at several points inside the vessel. The readings
logged 31.1 and 72.9 sieverts per hour.
Tepco has not been able to gauge the water depths and radiation
levels of the containment vessels for reactors 1 and 3, as, unlike
unit 2, there is no access.
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