2021 Fiscal Year Final Research Report

Research on deep groundwater components affecting actinide migration

Research Project

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Project/Area Number	19H02641
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Review Section	Basic Section 31010:Nuclear engineering-related
Research Institution	Tohoku University
Principal Investigator	Kirishima Akira 東北大学, 多元物質科学研究所, 教授 (00400424)
Co-Investigator(Kenkyū-buntansha)	宮川和也国立研究開発法人日本原子力研究開発機構, 核燃料・バックエンド研究開発部門幌延深地層研究センター, 研究副主幹 (90721225) 秋山大輔東北大学, 多元物質科学研究所, 助教 (80746751)
Project Period (FY)	2019-04-01 – 2022-03-31
Keywords	深部地下水環境 / 放射性核種移行 / 地層処分
Outline of Final Research Achievements	10 ppb or 100 ppb of La, Sm, Ho, and U were doped as the tracers into the sedimentary rock GW samples collected at Horonobe Underground Research Laboratory. Furthermore, the same tracers were doped into the crystalline rock groundwater samples collected at the Mizunami URL. The groundwater sample was sequentially filtered with a 0.2 micro meter pore filter, and 10 kDa NMWL ultrafilters. It was found from the experiment, that the solubility of the lanthanide was controlled by the phosphates in the Horonobe GW (sedimentary rock). Therefore, the solubility of MA, which have similar chemical behavior in an aqueous solution system, is also expected to be controlled by the formation of the phosphates. Besides in the Mizunami GW (crystalline rock), the result of this study indicated that a fraction of lanthanide and MA seemed to form hydroxide and/or hydroxo-carbonate. By contrast, the predicted U(VI) species were soluble carbonate complexes in both Horonobe and Mizumami GWs.
Free Research Field	放射性廃棄物
Academic Significance and Societal Importance of the Research Achievements	本研究では我が国の代表的な岩質である新第三紀堆積岩および結晶質岩の地下研究施設にて、深度300m以深の実際の処分深度の地下水を地下の還元雰囲気を維持した状態で採取した。ここにランタノイドやアクチノイドを添加し、定量分析および化学種分析によりこれら核種の溶解度を制限する地下水成分や移行を支配する地下水成分を明らかにした。これにより、現在、我が国の地層処分事業で進められている「閉鎖後長期の安全性の評価」の手法の科学的妥当性と改善が必要な点、あるいは実際に処分サイトが決定した際に試験研究により特に取得が必要となるサイト特有の化学データが何であるかの一端を示すことができた。