1 Septembre 2013
Radiation levels of up to 1,800 millisieverts per hour have been detected at four locations at the crippled Fukushima nuclear plant, as the operator checks storage tanks following a leak of 300 tons of radioactive water.
Tokyo Electric Power Co. said Aug. 31 it found between 70 and 1,800 millisieverts per hour around five tanks in three areas.
An exposure of 1,800 millisieverts per hour for about four hours is considered fatal to a human. But a worker can be shielded from the radiation with proper protection because it is mostly beta rays, which have weak penetrating power.
High radiation levels may be discovered at more locations as the utility continues to examine other storage tanks.
TEPCO detected between 220 and 1,800 millisieverts per hour around joints at the bottom of two tanks in an area called H3 on Aug. 31. Radiation levels between 70 and 100 millisieverts per hour had been found at the same locations on Aug. 22.
The utility also detected 230 millisieverts per hour at a section connecting two tanks in an H5 area and 70 millisieverts per hour around the bottom of a tank in an H4 area.
In the H5 area, a drop of water fell when a worker on patrol pressed insulation outside the connecting section of the tanks. A radiation level of 230 millisieverts per hour was measured on a section of the floor.
TEPCO officials said they believe radioactive water has not spread outside barriers surrounding tanks. They said water levels had not dropped in any of the five tanks, and drain valves on the barriers had been closed.
The five tanks are a so-called flange type that utilizes steel sheets connected by bolts. They are of the same design as the one from which TEPCO said on Aug. 19 an estimated 300 tons of radioactive water leaked.
The Nuclear Regulation Authority assessed the severity of the leakage at Level 3 (serious incident) on the eight-level International Nuclear and Radiological Event Scale (INES).
Flange-type tanks are said to be durable for about five years, and they account for 350 of the approximately 1,000 storage tanks at the Fukushima No. 1 plant.
TEPCO has announced plans to switch to tanks whose sheets are welded together, which are said to be more durable. But at least one month is required to complete a welded tank, while a flange-type tank can be installed in a week or so.
The company will have to continue to use flange-type tanks for the time being, which leaves the possibility that more radioactive water may escape them.
TOKYO (Kyodo) -- Very high radiation levels were observed Saturday at three tanks and one of the pipes connecting them at the troubled Fukushima Daiichi nuclear plant, pointing to the possibility that radioactive water may have newly leaked, Tokyo Electric Power Co. said.
The radiation readings were from 70 to 1,800 millisieverts per hour, although none of the tanks showed any visible fall in their water levels, the plant operator said, adding it is investigating the cause.
The tanks are built of steel plates held together by bolts in the same structure with the tank that was found last week to have leaked 300 tons of highly toxic water.
Traces of water leak were found below the pipe where 230 millisieverts per hour was measured, it said.
High radiation detected at Fukushima Daiichi tanks
The operator of the crippled Fukushima Daiichi nuclear power plant has detected extremely high levels of radiation on some of its storage tanks.
Tokyo Electric Power Company announced on Saturday that high levels of radioactivity were found in 4 areas in the complex where tanks containing contaminated water are located.
It has been monitoring more than 900 storage tanks since about 300 tons of radioactive wastewater leaked from a tank on August 20th.
TEPCO says one of Saturday's readings was 1,800 millisieverts per hour. Radiation at this level can kill a person in 4 hours.
The number is 18 times higher than the level of radioactivity at the same tank measured on August 22nd.
In another area, radioactivity of 230 millisieverts per hour was measured at a puddle underneath a pipe connecting tanks.
Although no change of water levels was detected at the tanks, TEPCO believes new leaks are possible. It is checking whether contaminated water has reached the ocean.