Study on the peroformance of pre-Neogene sedimentary rocks as batural barrier of HLW disposal

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01855
• 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: The University of Tokyo
• Principal Investigator: Saito Takumi 東京大学, 大学院工学系研究科(工学部), 教授 (90436543)
• Co-Investigator(Kenkyū-buntansha): 青柳 登 国立研究開発法人日本原子力研究開発機構, 原子力科学研究部門 原子力科学研究所 先端基礎研究センター, 研究副主幹 (80446400)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 先新第三紀堆積岩 / 付加体 / 収着 / 拡散 / 亀裂 / バリア

Outline of Final Research Achievements

In this the performance of accretionary prism rocks of Preneogene sediments as a natural barrier of HLW disposal are demonstrated. The sorption of Cs and Eu was dominated by clay minerals and could be described by ion exchange and surface complexation reactions. The diffusion of Cs through the matrix of the rock was small but that through the parts with factures became large. In all cases, the diffusion of Cs was greater than that of water, suggesting a contribution from surface diffusion. I, on the other hand, did not sorb onto the rock, but did not diffuse, indicating that anion exclusion prevented it from entering the rock pores. These results suggest that the matrix of the accretionary rock has high performance as a barrier for nuclides migration, and that the mineral composition, its distribution, and fracture network control their migration.

Free Research Field

放射性廃棄物処分工学

Academic Significance and Societal Importance of the Research Achievements

これまで，我が国では，花崗岩のような結晶質な深成岩や軟岩である新第三紀堆積岩を対象にそのようなバリア性能の評価が行われてきた．しかし，我が国の深度1,000 mまでの地質環境の半分近くを占める重要な基盤岩であるより古い時代の堆積岩（先新第三紀堆積岩）の天然バリアとしての性能は研究されていない．特に，我が国の先新第三紀堆積岩の多くは付加体と呼ばれ，複雑な性状を示すが，そのような岩石自体の複雑さが然バリアとしての性能の優劣を決める訳ではない．本研究の意義は，我が国におけるそのような付加体岩石の天然バリア性能を核種に対する収着特性と拡散特性の点から明らかにした点になる．