TOKYO (Kyodo) -- Tokyo Electric Power Co. said Wednesday that one of its female employees at the crisis-hit Fukushima Daiichi nuclear power plant was exposed to radiation doses exceeding three times the legal limit of 5 millisieverts in a three-month period, although she has not suffered any health problems.
The plant operator also started to increase the amount of water injected into the troubled No. 1 reactor core in preparation to flood the reactor's primary containment vessel to cool the fuel inside in a stable manner.
The utility known as TEPCO is trying to contain the country's worst nuclear disaster in line with a recently unveiled roadmap, which seeks to restore stable cooling to the reactors and spent fuel pools of the troubled Nos. 1 to 4 units in about three months.
But working conditions at the radiation-leaking plant are difficult, as seen in the latest revelation concerning the female TEPCO employee, who is in her 50s.
The government's nuclear safety agency said that two more female workers may also have been exposed to radiation in excess of the limit. The agency called on the utility to investigate the reason and take measures to prevent a recurrence.
Hidehiko Nishiyama, a spokesman for the Nuclear and Industrial Safety Agency, told a press conference the situation was "extremely deplorable," but added that all female employees had left the plant on March 23.
According to the plant operator and the agency, a total of 19 female TEPCO employees were working at the six-reactor complex in the days following the March 11 earthquake and tsunami that hit the plant, and one of them was exposed to a total of 17.55 millisieverts of radiation.
The woman was found to have suffered more internal than external radiation exposure, with the internal exposure reaching 13.6 millisieverts.
TEPCO and the agency said that the woman had been refueling fire trucks and working inside a building on site. She had been wearing a mask, but may have inhaled radioactive material when putting it on or taking it off.
A TEPCO official acknowledged during a separate press conference that its radiation-dose management should have been more stringent.
TEPCO has started checking the radiation exposure of the female workers from March 22, and the amount of exposure for the woman in question was confirmed Wednesday, the company said.
Under Japanese law, radiation workers cannot be exposed to more than 100 millisieverts over five years and more than 50 millisieverts in one year.
For female workers, the limit is 5 millisieverts in a three-month period, considering they may become pregnant. For the general public, the limit is 1 millisievert per year, excluding exposure from medical procedures.
As for efforts to restore the plant, TEPCO started in the morning to gradually increase the amount of water injected into the No. 1 reactor core from 6 tons per hour.
By temporarily increasing the rate to 14 tons per hour, TEPCO hopes to discover how far the reactor's primary containment vessel has filled up with water, which is currently not clear, according to Nishiyama.
"After looking at the outcome of the attempt, it will be decided whether TEPCO should take the action to fill water inside the vessel to the level above the reactor fuel," he said.
To prevent the release of radioactive substances in the event of an accident, reactor fuel is placed inside a pressure vessel, which is contained in a round-bottom flask-shaped primary containment vessel. A reactor building houses these vessels.
The agency, however, has earlier said that the water injected into the No. 1 reactor's pressure vessel is believed to be leaking out into the primary containment vessel.
The reactors and spent nuclear fuel pools of the Nos. 1 to 4 units need to be periodically injected with water from outside because they lost their cooling functions after the March 11 disaster. The units also suffered hydrogen explosions and fires.
The emergency measure to inject water has created vast pools of radiation-contaminated water inside the plant's reactor turbine buildings and other places on the premises.
(Mainichi Japan) April 27, 2011
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