Effect of Calcium Silicate Hydrate Precipitates at Cementitious and Bentonite Material Interface on Long-Term Engineered
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Effect of Calcium Silicate Hydrate Precipitates at Cementitious and Bentonite Material Interface on Long-Term Engineered Barrier System Performance in TRU Waste Disposal Facilities Susumu KUROSAWA1, Hiroyuki SAKAMOTO2, Kiyofumi NITTA3, Chiya NUMAKO4, Kazuko HAGA5, Masahito SHIBATA2, Tsutomu SATO6, Toshiyuki NAKAZAWA7 and Hitoshi OWADA1 1 EBS Technology Research Project, Radioactive Waste Management Funding and Research Center (RWMC), 1-15-7, Tsukishima, Chuo-ku, Tokyo, 104-0052, Japan 2 Solution Department, Taiheiyo Consultant Co., Ltd., 2-4-2, Ohsaku, Sakura-shi, Chiba, 2858655, Japan 3 Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1, Oho, Tsukuba-shi, Ibaraki, 305-0801, Japan 4 Faculty of Integrated Arts and Sciences, The University of Tokushima, 1-1, Minami-josanjima, Tokushima, 770-8502, Japan 5 Solution Department, Taiheiyo Consultant Co., Ltd., 3-8-5, Misaki-cho, Chiyoda-ku, Tokyo, 101-0061, Japan 6 Laboratory of Enviromental Geology, Graduate School of Engineering, Hokkaido University, Kita 8 Nishi 5, Sapporo, Hokkaido, 060-8628, Japan 7 Naka Energy Research Laboratory, Mitsubishi Materials Corporation,1002-14, Mukohyama, Naka-shi, Ibaraki, 311-0102, Japan ABSTRACT Chemical conditions and mass transport properties of engineered barrier systems in TRU waste facilities would change with time due to the interaction of cement/bentonite materials. ('TRU waste' is one of categories of the radioactive wastes and contains a significant amount of alpha-emitting transuranic nuclides. In some countries, these wastes are classified into the Intermediate Level Waste (ILW).) Previous numerical model analyses to assess the long-term performance of engineered barrier systems in TRU waste repositories predicted to form Calcium Silicate Hydrate (C-S-H) species at the interface between the cementitious and bentonite materials. If C-S-H precipitates in the bentonite side of the boundary, mass transport in the bentonite buffer decreases and mineralogical alterations are expected to be restricted for a long period. The evidence of C-S-H precipitation in the bentonite side, however, still has not been identified in the former experimental studies. To improve the reliability of numerical analyses, immersion experiments were performed using contact samples of cementitious and bentonite materials, and X-ray absorption fine structure (XAFS) analysis was carried out to detect C-S-H precipitation at the contacting interface. Precipitation of C-S-H was confirmed from the obtained XAFS spectra. This result is one of the evidences to show the validity of the current numerical model analyses, which suggests that the bentonite buffer performance as an engineered barrier would be kept over a long period. INTRODUCTION Given the low heat generation of TRU waste, it is possible to dispose a large volume of waste in disposal facilities with large cavities. Since there is a great deal of variation in TRU
waste characteristics (activity of radioactive nuclides in the waste, physica
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