The operator of the Fukushima No. 1 nuclear power plant found the radiation level of the building housing the No. 1 reactor stood as high as 700 millisieverts per hour, the government’s nuclear agency said Monday, citing the need for radiation shielding to proceed with work to bring an end to the nuclear crisis.
The radiation level, which was around 10 millisieverts per hour at its lowest, was measured as Tokyo Electric Power Co. workers and agency officials entered the No. 1 reactor building early Monday as part of preparations to start full-scale work to create a stable system to cool the damaged fuel inside.
“An area with a double-digit millisievert level, let alone three-digit figures, is quite tough as a working environment. So we have to do the work by using some shielding,” Nuclear and Industrial Safety Agency spokesman Hidehiko Nishiyama said.
Tepco officials said the high radiation level is so far unlikely to affect the utility’s schedule to stabilize the plant’s troubled reactors around October at the earliest, but it is uncertain whether things will go as planned because of the difficult working environment.
Workers dealing with the crisis triggered by the March 11 quake and tsunami are allowed to be exposed to radiation levels no higher than 250 millisieverts in total. So they can only stay for 20 minutes in the most contaminated area of the No. 1 reactor building. Still, Tepco believes that restoration work is possible inside the reactor building because the radiation level in areas where workers need to stay is between 10 to 70 millisieverts per hour.
The latest move came after Tepco opened the doors linking the reactor building to its adjacent turbine building Sunday, and confirmed the resultant release of radioactive materials into the air had not raised radiation levels on the premises and nearby areas as of 5 a.m. Monday, according to the firm.
By opening the double-entry doors, air containing about 500 million becquerels of radioactive substances is believed to have been released into the atmosphere from the upper part of the No. 1 reactor building, which was damaged in a hydrogen explosion that occurred in the early days of the nuclear crisis.
Seven Tepco workers and two nuclear regulatory officials went into the reactor building around 4:20 a.m. and measured radiation inside for about 30 minutes. They were exposed to radiation between 2.7 millisieverts and 10.56 millisieverts, the agency said.
Tepco plans to fill the No. 1 reactor’s primary containment vessel with water to a level above the nuclear fuel inside, and start operating by June an air-cooling device aimed at reducing the temperature of the water circulating around the reactor. Now that workers have entered the reactor building, Tepco plans to have them install and adjust instruments to measure the water levels in the reactor’s containment vessel, and place a heat exchanger.
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