Dose estimation in recycling of removed soil as seaside protection forest (Contract research)

Sawaguchi, Takuma ; Takai, Shizuka ; Takeda, Seiji 

After the Fukushima Daiichi Nuclear Power Station accident, large quantities of radiocesium-contaminated soil were generated from decontamination activities in the Fukushima prefecture. The removed soil has been stored in the prefecture until its final disposal. To complete the final disposal outside Fukushima prefecture, reducing the disposal volume through recycling can prove effective. The Ministry of the Environment, Japan (MOE) has presented a policy to recycle low-radioactive removed soil as recycled materials under the management of public authority. The recycling is limited to civil engineering structures in public projects. In this study, to contribute to guideline development for removed soil recycling by MOE, dose estimation in recycling of removed soil as embankment materials of seaside protection forest was conducted. First, additional doses to workers and the public in construction and service scenarios were evaluated. From the result, the radioactive cesium concentration level of recycled materials, where all additional doses meet the radiation criterion of 1 mSv/y, was derived to be 5,000 Bq/kg. Then, construction conditions were reviewed to reduce additional doses to the public in a service scenario. With the derived radioactivity level of 5,000 Bq/kg, the covered soil thickness of 39 cm or more limited the doses to less than 10 Sv/y. Finally, additional doses in a disaster scenario were evaluated. The doses were confirmed to be below 1 mSv/y when the removed soil of 5,000 Bq/kg was used.