Radioactive materials released from the crippled No. 1, 2 and 3 reactors at the Fukushima No. 1 power plant are roughly one 10 millionth of contamination spewed at the beginning of the accident in March, based on readings taken in the past two weeks, Tokyo Electric Power Co. said Wednesday.
Tepco estimated the amount from July 26 to Aug. 12, saying the maximum reading logged was 200 million becquerels per hour. Based on this data, the radiation level around the plant is estimated at a maximum 0.4 millisievert per year, compared with the annual legal limit of 1 millisievert.
The estimated amount released March 15 was 2 quadrillion becquerels per hour, meaning the amount has decreased to one 10 millionth of that level.
But since the estimation was made based only on the amount of radioactive materials in the air around the west gate of the plant, “we think the degree of accuracy is still not that high,” Yoshinori Moriyama, a spokesman of the Nuclear and Industrial Safety Agency, said during a joint news conference by the government and Tepco.
The utility admitted the accuracy needs to be raised and said it will increase data-measuring spots, but “we don’t think it will be that different from this figure,” said Tepco Vice President Zengo Aizawa.
The figure revealed July 19 was about 1 billion becquerels per hour at most, and the surrounding area’s radiation level was estimated as a maximum 1.7 millisieverts per year.
During the briefing, the government and Tepco also updated the monthly progress of the second phase of the remedial road map, which aims for a cold shutdown of the reactors by mid-January.
They said the utility has already achieved stable cooling of the spent fuel pools of reactors 1 to 4, as it was able to launch circulation cooling systems in the pools of the four reactors this past month.
Cold shutdown is defined as bringing the temperature at the bottom of the pressure vessels to below 100 degrees, while reducing the radiation level around the plant to less than 1 millisievert per year.
Goshi Hosono, state minister in charge of the Fukushima crisis, said reducing the massive amount of radioactive contaminated water at the plant remains a major task. He also said the government will soon announce a basic plan for decontamination efforts around the plant.