Alteration scenario for bentonite under hyperalkaline conditions with regard to mineral paragenetic uncertainty

Oda, Chie  ; Sasaki, Ryoichi; Arthur, R. C,*; Savage, D.*; Honda, Akira

Bentonite materials are expected to be used as the main hydraulic barrier and cementitious materials are expected to be used for structure support in low level radioactive waste disposal systems. Interaction between bentonite and hyperalkaline fluids arising from cementitious materials has been recognized as a concern due to the close proximity of these materials in repository designs. The interaction could cause the alteration of mineralogy and associated hydraulic property of bentonite and have a deleterious influence on the function of bentonite as a hydraulic barrier, and may lead to adverse impact on the long-term safety of the repository. Many researches on such interaction have been performed to establish the bentonite alteration scheme, however, uncertainty in our understanding of the precise alteration scheme, especially mineral paragenetic sequences during the alteration, still remains. Therefore, it is important to take such uncertainty into account in estimating how the mineralogy and the hydraulic property of bentonite evolves subject to alteration by hyperalkaline fluids. In this work, multiple scenarios for mineralogical alteration of bentonite was investigated to limit the mineral paragenetic uncertainty and to identify appropriate assumption for numerical simulation of chemical and mineralogical evolution of bentonite under hyperalkaline conditions over the long-term.