Dose estimation in the recycling of removed soil for land reclamation

Dose estimation for workers and the public was conducted to use the recycled soil removed from the Fukushima prefecture for land reclamation. The land was availed to the public as a greenery-covered area. In the case of revegetation with trees, the absorption of Cs by the trees was considered. The exposure from trees, trimmed or thinned trees, and the organic deposits from litter fall were evaluated. From the results, the concentration levels of radiocesium, 134Cs and 137Cs, for which the annual effective exposure dose does not exceed 1 mSv/y was calculated. Moreover, the thickness of the cover soil required to maintain the exposure dose lower than 10 μSv/y for the public during servicing was ascertained. Furthermore, disasters were considered; for instance, by considering that tsunamis, fires, and intense heavy rain can increase the exposure doses based on the changes in the conditions of the reclamation land. We confirmed that the additional exposure dose during the disaster and rehabilitation of the area was lower than 1 mSv/y. From these evaluation results, we determined the amenable concentration levels for recycling.