The central government, responding to months of criticism from experts, has decided to measure levels of radioactive cesium in soil within the no-entry zone surrounding the stricken Fukushima No. 1 nuclear power plant, sources said Nov. 30.
The central government, responding to months of criticism from experts, has decided to measure levels of radioactive cesium in soil within the no-entry zone surrounding the stricken Fukushima No. 1 nuclear power plant, sources said Nov. 30.The government this summer examined soil within a radius of 100 kilometers of the Fukushima plant, but that did not include the area within the 20-kilometer no-entry zone. The government will survey an additional 100 locations, including those within the no-entry zone, by the end of the year by sampling soil to a depth of 10 centimeters. Depending on the results of the expanded survey, decontamination costs will likely increase, officials said.The science ministry carried out the initial surveys for a month from June to create a sufficient database for decontamination work. The University of Tokyo and Osaka University were among 94 organizations that cooperated with the program.Researchers stripped soil from a depth of 5 cm in 2,200 locations within the 100-km radius, and checked for levels of radioactive cesium. Based on the survey results, the ministry released a contamination map.The ministry also surveyed the depth that cesium had penetrated the soil. It took samples at a depth of 20 cm in about 300 locations within the 100-km radius. At that time, however, it did not carry out survey work in the no-entry zone.According to an analysis of samples by Osaka University, the penetration was within a depth of 5 cm in 90 percent of the 300 locations. In the remaining 10 percent, the deepest penetration reached 7 cm."We think the nature of soil in the no-entry zone is similar to that in surrounding areas," a science ministry official said. "So we expect the penetration level to be almost the same." The government has entrusted the gathering of soil in the no-entry zone to the Federation of Electric Power Companies of Japan, an industry organization."As workers were not accustomed to the job (for the survey), it took time," the ministry official said. "We also worried that they would be exposed to radiation."The government plans to conduct decontamination work in areas where radiation of 1 millisievert or more a year has been recorded.By checking the cesium contamination levels in the soil, it will decide how much topsoil has to be removed.Assuming that soil to a depth of 5 cm is removed, it will require stripping 15 million to 31 million cubic meters of dirt from Fukushima Prefecture alone.If cesium is found to have penetrated deeper into the soil in the no-entry zone, even more soil will have to be removed. That, obviously, would cause decontamination costs to increase.