Safety assessment of transportation and interim storage of rice straw contaminated by radioactive cesium due to the severe accident at the Fukushima Nuclear Plant

*Radioactive cesium in the rice straw was detected to be maximum value of 690,000Bq/kg after the severe accident of Fukushima Nuclear Plant. The straw was distributed to the market to feed beef cattle. The radiation exposure dose for the dairy farmer should be decreased based on prompt and suitable treatment such as moving and storage of contaminated straw. In order to provide the Japanese government with the technical information of the treatment, dose analyses for the scenarios on transportation and interim storage of contaminated straw were conducted in this study. As a result for transportation scenario, in the case of radioactive cesium concentration of 700,000Bq/kg, the annual dose for the transportation worker from remote place is calculated to be 1.3mSv/y, exceeding effective dose criterion of 1mSv/y for a worker. Therefore, it is suggested that the worker needs the measures to decrease the dose for the dominant external exposure pathway, namely, limiting transit time, reducing the straw volume and utilizing radiation shielding materials. The calculated results for interim storage scenario indicate that the distance to suppress the dose for an outside worker within 1mSv/y is 10m for 100,000Bq/kg and 30m for 500,000Bq/kg and 700,000Bq/kg.