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Matsutani reports: "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 will require them to have greater resistance than currently available, experts said Wednesday."

Japanese medical personnel check a mother and son for radiation exposure in Kawamata village, Fukushima prefecture, Japan. (photo: Asahi Shimbun/EPA)
Japanese medical personnel check a mother and son for radiation exposure in Kawamata village, Fukushima prefecture, Japan. (photo: Asahi Shimbun/EPA)



Experts: Radiation at Fukushima Plant at Lethal Levels

By Minoru Matsutani, Japan Times

28 March 12

 

adiation 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 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. said.

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 function properly.

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 tracked Quince robots designed to gather data inside reactors can properly function for only two or three hours during exposure to 73 sieverts, said Eiji Koyanagi, the 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, nuclear 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 Institute.

The high radiation level can be explained by the low level of the water, which acts to block radiation.

"The shallowness of the water level is a surprise, and the radiation level is awfully high," Misawa said.

While the water temperature is 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 for Tepco, it is unlikely to affect the timing of decommissioning the three crippled reactors, which Tepco said will take 40 years.

The experts also said, however, that removing the melted nuclear fuel from the bottom of the containment vessels will be difficult.

Tepco inserted a radiation meter into the containment vessel of reactor 2 Tuesday for the first time, measuring aerial radiation levels at several points inside the vessel. The readings were for 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.

 

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+6 # Buddha 2012-03-28 16:48
And while Japan and Germany learn the lessons of Fukushima and start phasing away from old fission power plant designs, the US just onlined another nuke. Look, a properly designed Gen 3 (or soon Gen 4) reactor can actually be safe...if corners are not cut and every possible safety and training is done. But as we know, humans being humans, and corporations being penny pinching corporations, corners WILL be cut, mistakes will happen. And when bad things happen with nuclear power plants, particularly the old plant designs that require active functioning systems to prevent meltdown, they REALLY go wrong. This is why we need Gen 4 reactors for fission power, and to eventually get to working fusion power...both of which safely and automatically "shut down" in the case of malfunction and don't need the kind of active cooling reliant on continued power.
 
 
+3 # John Locke 2012-03-29 08:39
Nuclear power is NOT safe today at any level!
And yet, Obama has approved the construction of even more of these disasters waiting to happen.
Geo Thermal is the only safe and efficient form of energy use currently available, Wind is safe but still not profitable…Sola r is still something for the future but is still too expensive for the benefit derived, but it should be developed now with more economical units…We have to get away from Nuclear energy as a form of energy use. What will it take, an end to the planet before those fools in charge wake up?
 
 
+25 # Willman 2012-03-28 19:46
I hear that solar and wind is "TOO EXPENSIVE" from the fossils and nuke crowd.
Wonder what the final bill will be on this debacle.
 
 
+10 # lisamoskow 2012-03-28 22:48
The brainwashing we have gotten about the safety of nuclear power....

They started building a plant for nuclear disposal at the Hanford area (WA state)--suppose d to cost a few million--now it seems that it will cost 4 billion, or
even more.
 
 
+16 # Tazio 2012-03-28 22:59
When the Fukushima plants first started exploding, and people here were beginning to re-question American plans for new nuclear plants, Mitch McConnell said we shouldn't let problems in foreign countries affect our domestic energy policy decisions. (sic)
 
 
+7 # angryspittle 2012-03-29 07:22
So the coal/oil/nuke boys say wind and solar are too expensive. I wonder how expensive extinction would be.
 
 
+4 # Mamazon 2012-03-29 10:31
Nuclear Power plants = Armaggedon

In the pursuit of profit, human beings blew themselves to smithereens and destroyed the future of every species on the planet, except maybe cockroaches, How do I tell my 10 year old that people running corporations chose to mAke machines that kill us all -- no, it's not a movie son, it is the narcissism of our culture.
 

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