New Perspective of Nuclide Immobilization Mechanisms in Mica Minerals for Further Confinement of Radioactive Waste

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K18916
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 31:Nuclear engineering, earth resources engineering, energy engineering, and related fields
• Research Institution: Tohoku University
• Principal Investigator: Chida Taiji 東北大学, 工学研究科, 准教授 (30415880)
• Co-Investigator(Kenkyū-buntansha): 新堀 雄一 東北大学, 工学研究科, 教授 (90180562) ; 関 亜美 東北大学, 工学研究科, 助教 (80912328)
• Project Period (FY): 2021-07-09 – 2024-03-31
• Keywords: 放射性廃棄物 / 地層処分 / 核種移行 / 収着 / 拡散 / 雲母 / 花崗岩 / 固定化

Outline of Final Research Achievements

This study examined the interaction of cationic radionuclides with biotite flakes which is ubiquitous underground and revealed that the radionuclides not only sorb at the edge of the flakes by ion exchange but also diffuse into the interior of the flakes. Such incorporation of radionuclides into biotite flakes may also produce further immobilization effects within the flakes. On the other hand, apparent diffusion coefficients of cationic radionuclides in biotite flakes, which was estimated by applying a two-dimensional diffusion model to the experimental date, were smaller than that in a granite matrix contained biotite flakes. This suggests that the sorption of radionuclides onto biotite flakes in granite is restricted by the diffusion process in the flakes and apparent sorption rates on the flakes will be required to take the diffusion process into account in the assessment of the radionuclide migration.

Free Research Field

工学

Academic Significance and Societal Importance of the Research Achievements

放射性廃棄物処分において重要となる，地下の鉱物と放射性核種の相互作用に関して，従来の考え方は粉末試料で評価される収着および脱着のような化学平衡に基づいている．これに対し本研究では，薄片状黒雲母を用いた検討により，核種が鉱物内へ拡散浸入する過程を考慮した速度論的な扱いを加味する必要があることを提示した点に学術的意義がある．また，地下を移行する放射性核種の収着効果が大きい黒雲母について，本研究の成果はその収着効果が従来の評価手法では過剰に見積もられる場合があることを示唆しており，より現実的な核種移行評価に資するとともに，処分システムの信頼性向上に貢献するものである．