Because of the accident at the Fukushima Daiichi Nuclear Power Station, large area of east Japan was contaminated by radiocesium. Decontamination of the contaminated soil was conducted not only at Fukushima prefecture but also at Iwate, Miyagi, Ibaraki, Tochigi, Gunma, and Chiba prefectures. Decontamination soil taken at Fukushima prefecture is going to be stored in interim storage facilities and disposed of within 30 y at outside of Fukushima prefecture after reduction volume and concentration treatments. On the other hand, how to treat and dispose decontamination soil generated at the outside of Fukushima prefecture is not determined yet.

In order to provide technical information to treat the decontamination soil which size is varied and stored many places, external effective dose conversion factors were calculated using MCNP5 code for various decontamination soil volumes, distance from the decontamination soil, and thickness of the cover soil. The decontamination soil volume was changed from 4 m^3^ to 400000 m^3^. The maximum amount is comparable to the total amount of decontamination soil generated at the outside of Fukushima prefecture. The evaluation point was set at the center of the decontamination soil and changed from 1 to 100 m from the edge of the decontamination soil and the height was all 1 m from the ground. At the disposal site, the surface of the decontamination soil must be covered by non-contaminated soil or material to avoid dissipation. However, cover soil thickness was changed from 0 to 50 cm to evaluate the effect of the cover soil. Finally, external exposure doses for resident near the site and public entering the site was evaluated for the radiocesium concentration of 700 Bq/kg and 2500 Bq/kg, which are 50 percentile and 95 percentile radioactivity concentrations of decontamination soil, respectively.

The external exposure dose was exponentially decreased with an increase of the cover soil thickness in the simulated range. If there is no cover soil, the external exposure dose was over 10 μSv/y for resident 1 m from the site and the public entering the site, even the decontamination soil volume was 4 m^3^ and the concentration was 700 Bq/kg. On the other hand, external exposure dose was less than 10 μSv/y for all cases when the surface was covered by 30 cm non-contaminated soil.

This research was funded by the Ministry of Environment, Japan.


Sensitivity Analysis of External Exposure Dose for Future Burial Measures of Decontamination Soil Generated Outside Fukushima Prefecture

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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