Evaluation of bentonite alteration due to interactions with iron; Sensitivity analyses to identify the important factors for the bentonite alteration

Sasamoto, Hiroshi   ; Wilson, J.*; Sato, Tsutomu*

Performance assessment of geological disposal systems for high-level radioactive waste requires a consideration of long-term systems behaviour. In the present study, iron (as a candidate overpack material)-bentonite (I-B) interactions were evaluated as the main buffer alteration scenario. Existing knowledge on alteration of bentonite during I-B interactions was first reviewed, then the evaluation methodology was developed considering modeling techniques previously used overseas. A conceptual model for smectite alteration during I-B interactions was produced. The following reactions and processes were selected: (1) release of Fe due to overpack corrosion; (2) diffusion of Fe in compacted bentonite; (3) sorption of Fe on smectite edge and ion exchange in interlayers; (4) dissolution of primary phases and formation of alteration products. Sensitivity analyses were performed to identify the most important factors for the alteration of bentonite by I-B interactions.