March 28, 2012
Fukushima No. 2 reactor radiation level up to 73 sieverts per hour
TOKYO (Kyodo) -- The operator of the Fukushima Daiichi nuclear power plant said Tuesday that the radiation dose inside the crippled No. 2 reactor stood at an extremely high level between 31.1 and 72.9 sieverts per hour, underscoring the existence of radioactive substances from the melted fuel inside the structure.
Tokyo Electric Power Co. measured the radiation level by inserting a long dosimeter into the round-bottomed, flask-shaped primary containment vessel, where fuel is thought to be accumulating at the bottom following the nuclear accident last year.
Human beings could die within one month once exposed to 7 sieverts and within several days once exposed to 20 sieverts or more. Usually, when an ordinary reactor is not operating, the radiation level is low enough for workers to enter inside, according to the utility known as TEPCO.
The highest radiation dose was measured at about 4 meters from the bottom and about 1 meter away from the vessel's interior wall. The utility said it could not check a deeper area because the dosimeter had no camera attached.
The utility's spokesman Junichi Matsumoto said he cannot immediately tell whether the latest outcome will affect the current road map toward scrapping the Nos. 1 to 4 units, but added that the data can be used to study what kind of devices should be developed for the decommissioning work.
''One important challenge is resistance to radiation...If we are going to use electronic devices inside the primary containment vessel, we may have to consider shielding the devices, or use parts that can tolerate high levels of radiation,'' Matsumoto told a press conference
TEPCO carried out an industrial endoscope survey a day before, and found the vessel filled with water only 60 centimeters deep, a lower-than-expected height considering the amount of water injected into the reactor to keep the fuel inside cool.
The utility used the same hole to insert the endoscope and the dosimeter.
The No. 2 reactor is one of the plant's three reactors that have suffered meltdown in the nuclear accident, and its fuel is believed to have melted through the pressure vessel and accumulated in the outer primary container.
March 28, 2012
Lethal radiation detected inside Fukushima reactor
Tokyo Electric Power Company has detected extremely high levels of radiation inside one of the crippled reactors of the Fukushima Daiichi nuclear power plant.
TEPCO was able to place monitoring equipment directly inside the reactor for the first time since last year's accident.
A dosimeter lowered into the containment vessel of the No.2 reactor registered 72.9 sieverts, or 72,900 millisieverts per hour at maximum -- a level where a human is certain to die within about 7 minutes of exposure.
The utility hopes to determine the state of the vessels as it moves to decommission the reactors.
It says radiation levels increased as the dosimeter was lowered inside the reactor. This suggests the nuclear fuel melted down and collected at the bottom of the vessel.
The utility also learned the water level inside the vessel was only 60 centimeters, compared to the original estimate of about 3 meters.
TEPCO suspects the suppression chamber at the bottom of the vessel may have been destroyed.
The findings are a setback for plans to scrap the reactor. The utility has to pinpoint and repair damaged parts inside the vessel and fill it with water before extracting the fuel.
TEPCO says the development of devices that can withstand the extremely high levels of radiation is a pressing matter.