High accumulations of radioactive cesium-134 and cesium-137 have been detected in the town of Minami-Aizu, which lies 138 kilometers west-southwest of the stricken Fukushima No. 1 nuclear power plant.
High accumulations of radioactive cesium-134 and cesium-137 have been detected in the town of Minami-Aizu, which lies 138 kilometers west-southwest of the stricken Fukushima No. 1 nuclear power plant.
The science ministry released maps on Sept. 12 indicating the ground surface concentrations of the elements measured by aircraft.
High accumulations were also found in the town of Tadami, about 152 km west of the plant.
The maps evaluated airborne measurements across Fukushima Prefecture, including the Aizu district, the western part of the prefecture where no data had previously been available. The measurements were made between Aug. 16 and 28.
Concentrations of cesium-137 were found at 30,000 becquerels per square meter or more--about the same level as the threshold used to delineate contaminated zones after the 1986 Chernobyl accident--in Minami-Aizu, Tadami, Yugawa and other municipalities.
Meanwhile, the science ministry also released the same day the results of high-sensitivity reanalysis of seawater sampled off the Fukushima Prefecture coast that was earlier reported as free of "detectable" cesium-137 content. The reanalysis revealed up to 268 times the cesium-137 concentration prior to the accident at the Fukushima No. 1 plant, the ministry said.
The science ministry has been inspecting radioactive contamination of seawater off the coastlines of Miyagi, Fukushima and Ibaraki prefectures. Before Sept. 12, however, the ministry set a minimum detection limit of 9 becquerels of cesium-137 per liter, and made the designation "not detectable" for all values below that.
But the Nuclear Safety Commission of Japan and other parties called for high-sensitivity analysis to gain a clearer understanding of the actual state of seaborne contamination.
Picked up for reanalysis were seawater samples collected in late July from three locations, about 30-60 km from the Fukushima No. 1 plant, where earlier analysis said that cesium-137 was "not detectable."
Reanalysis produced cesium-137 concentrations of between 0.51-0.0092 becquerel per liter, or up to 268 times the maximum concentration (0.0019 becquerel per liter) detected during the science ministry's 2009 annual survey at a location about 25 kilometers from the Fukushima No. 1 plant. All concentrations were less than 1 percent of the safety standard of 90 becquerels per liter.