The Ministry of the Environment formally decided on June 30 to allow limited use of radioactively contaminated soil in public works projects, but sidestepped estimates from a closed-door meeting that the soil may have to be monitored for up to 170 years.
The ministry decided that soil could be reused for embankments as long as the radioactivity of cesium it contained did not exceed 8,000 becquerels per kilogram. Under the Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors, contaminated soil can be used freely if the level of radioactivity is 100 becquerels per kilogram or less.
It earlier emerged that the ministry calculated in a closed-door meeting that some soil would have to be monitored for 170 years -- well beyond the life of embankments. However, in its basic policy the ministry simply stated, "Safety and administration methods will be examined during verification processes in the future."
It is expected that up to around 22 million cubic meters of waste contaminated with radioactive material from the Fukushima nuclear disaster will end up piled up at an interim storage facility straddling the border between the Fukushima Prefecture towns of Okuma and Futaba. The central government plans to dispose of the waste for good outside the prefecture by March 2045, but hopes to reuse as much of it as possible to reduce the amount.
Under the ministry's basic policy, reuse of the soil will be limited to public works where the body in charge of administering it is clearly established, and the radiation dose at a distance of 1 meter is no more than 0.01 millisieverts per year. When using contaminated soil with a level of radioactivity of 8,000 becquerels per kilogram, it would be placed under at least 50 centimeters of cover soil, which would then be covered with sand and asphalt.
During the closed-door meeting, it was calculated that it would take 170 years for the radioactivity of tainted soil to naturally decrease from 5,000 to 100 becquerels per kilogram -- much longer than the durability of soil mounds, at 70 years.