Dose Estimation in Recycling of Decontamination Soil Resulting From The Fukushima NPS Accident For Road Embankments

Abstract

Since the Fukushima nuclear power station accident, large quantities of radiocesium-contaminated soil generated from decontamination activities have been stored in Fukushima prefecture. To complete the final disposal of decontamination soil, reducing the disposal volume through recycling can prove effective. The Ministry of the Environment of Japan has developed a policy of handling low-activity decontamination soil as recycled materials under the management of public authority. The recycling is limited to civil engineering structures in public projects, such as road embankments and coastal levees. However, there has been no practical review or safety assessment of decontamination soil recycling. In this study, to contribute to guideline development for decontamination soil recycling by the Ministry of the Environment, dose estimation was considered as a way of ensuring that the use of recycled decontamination soil for road embankments was safe. First, based on Japanese construction standards, additional doses to workers and the public in construction and service (e.g., use of a road embankment) scenarios were evaluated. From the result, the radioactive cesium concentration level of recycled materials that would result in all additional doses meeting the radiation criterion of 1 mSv y was derived to be 6,000 Bq kg. Then, construction conditions were reviewed to reduce additional doses to the public in a service scenario. To confine doses to the public to below 10 μSv y based on the derived radioactivity level, an additional layer of soil slope protection of 40 cm or more was needed. Finally, additional doses expected in a disaster scenario were confirmed to be below 1 mSv y based on the derived radioactivity level, an additional layer of soil slope protection of 40 cm or more was needed. Finally, additional doses expected in a disaster scenario were confirmed to be below 1 mSv y based on the derived radioactivity level.

Effectiveness of landscape decontamination following the Fukushima nuclear accident: a review

“…This result was confirmed by Yamashita et al (2014), who showed that 99 wild plants grown in paddy and upland fields had a very low phytoextraction efficiency. Tamaoki et al (2016) reached the same conclusions, although they suggested Kochia (Bassia scoparia) as a potential candidate for phytoremediation even though its efficiency in removing 137 Cs would require numerous cultivation rounds. Accordingly, given the low efficiency of phytoextraction, the main remediation strategy consists of removing the surface layer of soils with the majority of radiocesium.…”

“…As 22 million m 3 of decontamination soil (i.e. 90 % of the total) and incineration ash waste (10 %) is expected to be produced through remediation of the fallout-impacted region, recycling may be instrumental for reducing this volume (Takai et al, 2018). The Japanese Ministry of Environment developed a policy to separate decontamination soil into low-and high-activity soils, the former being "recycled" in public projects.…”

“…Overall, the recycling of decontaminated soil is limited to civil engineering structures in public projects, such as road embankments and coastal levees. Takai et al (2018) evaluated the associated additional doses to workers and the public using these structures and demonstrated that additional dose rates would remain below the 1 mSv yr −1 threshold corresponding to 6000 Bq kg −1 .…”

“…Therefore, more than half of the total decontamination soil should become recyclable in at least 5 years. Through the use of pre-treatment activities, such as classification processing, even more decontaminated soil may become recyclable in the not-too-distant future (Takai et al, 2018).…”

Strategies and effectiveness of land decontamination in the region affected by radioactive fallout from the Fukushima nuclear accident: A review

“…In general, owing to the strong and nearly irreversible bond of radiocesium to fine soil particles, the majority of FDNPP derived 137 Cs is stored within the topsoil (i.e. the top 5 cm) in undisturbed soils (Lepage et al, 2014;Matsunaga et al, 2013;Takahashi et al, 2015;Mishra et al, 2015;Matsuda et al, 2015). Mishra et al (2015) reported that for these undisturbed soils, the vertical migration of radiocesium down the soil profile was slower in forest soils compared to grassland soils.…”