nuclear-news

Radiation so high, even robots cannot approach Fukushima No. 1 nuclear reactor

Reactor 2 radiation too high for access March 29, 2012 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 amonth, 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 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 Institute.

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.

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 difficult….
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. http://www.japantimes.co.jp/text/nn20120329a1.html

March 29, 2012 Posted by Christina Macpherson | Japan, safety | Leave a comment

Fukushima nuclear plant is far from safe

 Still critical: radiation levels at Fukushima can kill in minutes Latest readings from tsunami-stricken nuclear plant overturn claims that reactors have been made safe The Independent, DAVID MCNEILL   TOKYO  THURSDAY 29 MARCH 2012      A lethal level of radiation has been detected inside one of the reactors at the Fukushima nuclear power plant, throwing fresh doubts over the operator’s claims that the disabled complex is under control. Continue reading →

March 29, 2012 Posted by Christina Macpherson | Japan, safety | Leave a comment

Alarming news about the state of Fukushima’s nuclear reactors today

Very high radiation, little water in Japan reactor, Sydney Morning Herald, MARI YAMAGUCHI, March 28, 2012 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……
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…. http://news.smh.com.au/breaking-news-technology/very-high-radiation-little-water-in-japan-reactor-20120328-1vxxz.html

March 28, 2012 Posted by Christina Macpherson | Japan, safety | Leave a comment