Collaboration between administrative officers and risk researchers is important to solve effectively risk-related problems in the real world by applying risk studies. Therefore, a special session was organized at the 31th SRA-Japan Annual Meeting, titled “Possible interactions between policy formulations and risk studies”. In this session, first, the actual cases of risk measures were introduced by speakers from national and local governments. Next, we discussed (1) what could the risk researchers in the SRA-Japan could cooperate with administrative officers to develop innovative risk measures ?, and (2) what is necessary for both sides to apply the results of risk studies to policy formulations ? As a conclusion, we reaffirmed the importance of establishing a close relationship between administrative officers who consider policies and risk researchers who work at the SRA-Japan.

　福島第一原子力発電所事故から9年が経過し，これまでに除染等が進むとともに，一部の放射性物質が半減期を迎えたことなどから，福島県内の空間線量率は確実に低下している．その一方で，除染で生じた除去土壌等は，社会的受容性の課題もあって最終処分や，中間貯蔵施設での減容化処理後の再生利用の目途は立っていない．このような状況下で，福島県は，除染実施区域外で発生した放射性物質含有土に土壌洗浄工法を適用した試行的プロジェクトを実施し，減容化が可能なことを示した．しかし，その濃度に係わらず放射性物質含有土を生活空間で取り扱うことについては様々な議論が生じた．本研究は，この試行的プロジェクトの検証及び社会環境の分析から，土壌洗浄処理を施した放射性物質含有土の最終処分の実現に向けた社会的受容性の課題を明らかにした．

The purpose of this paper is to examine the current status and challenges to the final disposal of radiocesium-contaminated soil and to explore a theoretical framework for building shared knowledge and collaboration among a wide range of stakeholders. It is difficult to make effective solutions about the issues only by accountability from stakeholders. It is necessary to build common goals for cooperation among stakeholders.

Mechanochemical reaction applied to the radioactive Cs-contaminated soils, granitic and basaltic soils in Fukushima prefecture, for revealing the deconstruction of clay minerals in the soils and Cs-leaching behaviors. The reactions were conducted by a planetary-motion ball-milling machine for the desired durations up to 12 h at dry condition and wet conditions with ammonium chloride solution in the different solid to solution ratios. The Cs-leaching behaviors were depended on the type of soils, the milling duration and the dry or wet condition for milling. The Cs-leaching rate for the granitic soil was higher than that of the basaltic soil. The deconstruction of the clay minerals in soil was different between granitic and basaltic soil, but the deconstruction rates were dependent on the milling duration, and were consistent with the Cs-leaching rate. With the dry milling and Cs-leaching by ammonium chloride solution, the Cs-leaching rates were 29% and 13% after 1 h treatment, and then 48% and 32% after 3 h, for the granitic soil and the basaltic soil, respectively. For the wet milling of the granitic soil, the Cs-leaching rates were increased on the solid to solution ratio and the milling duration, 20% for 1 h, and up to 60% for 12 h (1 : 10 of solid to solution ratio). For the wet milling of the basaltic soil, the Cs-leaching rates were not clearly dependent on the solid to solution ratio and the milling duration, but up to 29% for 12 h (1 : 10 of solid to solution ratio). The results indicated that the mechanochemical reaction has the powerful potential for the increase of the Cs-leaching from the contaminated soils, and the volume-reduction after the classification.

In this study, we examined the mineralogical and chemical properties of the 11 soils weathered from different rock-types and Kanto loam, and their properties after heat treatment at 1550°C.

The constituent mineral of the weathered soils does not necessarily reflect the mineral and chemical compositions of the host rock. The sum of SiO₂, Al₂O₃, Fe₂O₃ in the weathered soil shares a considerable ratio as weathered materials while it's not necessarily reflect the chemical composition of the base material rock.With heat treatment of the 11 weathered soils and Kanto loam at 1550°C, the considerable weight loss and phase change was observed. The minerals produced after heating at 1550°C were mullite, cristobalite, hematite. While cristobalite is formed from all soils, mullite and hematite were existed after limited soil treatment. From this chemical weathering index (WI), the formation of mullite from the soil where the weathering is considerably advanced was clarified.The correlation between the formation of hematite and WI is not clear, but the dependence of the content of Fe₂O₃ is considered. After the heat treatment, significant weight loss was observed in the soils containing large amount of Fe₂O₃, weathered from andesite, basalt, gabbros, serpentinite, limestone as base materials and Kanto loam. It is thought that it depends on the difference of the content of clay minerals, the dehydration due to the change of clay minerals etc., and the reduction of iron (III) oxide. The basic data obtained in this study are considered to be important for future direction toward the heat treatment and volume reduction of the actual radioactive Cs-contaminated soil in Fukushima Prefecture.