Monitoring of soil radiation doses from contaminated soil buried in a paddy field in Iitate Village, Fukushima

Abstract

Radiocesium released from Fukushima Daiichi nuclear power plant in March 2011 was accumulated in paddy fields within 5 cm of the surface soil layer. In order to remove this radiocesium, Japanese government carried out decontamination work to strip off surface layer soil. For this reason, the paddy fields of Iitate Village of Fukushima Prefecture are filled with a lot of flexible container bags packed with contaminated soil. On the other hand, based on the nature that radiocesium is fixed to clay minerals, we conducted an in situ burial experiment of contaminated soil at a paddy field in Iitate Village, Fukushima Prefecture, and have been testing rice cultivation every year at the paddy field where soil contaminated with radiocesium was buried. However, there remains fear that radiocesium might be released again to the environment. In order to prove that radiocesium will not leak from the paddy field, we are measuring the soil radiation doses in the well from March 2015. As a result of measurement of soil radiation doses every half year, we found that the soil radiation doses have a Gaussian distribution with a peak of which depth has not changed for 3 years. This indicates that radiocesium is unlikely to leach further through the contaminated soil even under conventional rice production in a paddy field.