Kunimine Industries Company’s Tsukinuno bentonite mine (NW Japan) is a source of Miocene age sodium bentonite (at depth in the mine) and calcium-bentonite (nearer-surface). The site is ideal for studying processes of direct relevance to safety cases for radioactive waste disposal concepts that utilise bentonite as part of their engineered barrier systems. The International Bentonite Longevity (IBL) project (www.iblproject.com, see also Reijonen & Alexander 2021) focusses on studying long-term, safety-relevant topics, including:
Saturation state – natural saturation states of bentonite in differing environments (on the surface and at varying depths underground, under dry and wet host rock conditions) for comparison with current safety case assumptions (based on short-term, laboratory and underground rock laboratory tests)
Bentonite density changes (swelling and heave) - due to exposure to groundwaters
Bentonite water interaction processes with fresh and deeper groundwater chemistries – for both surface and deep groundwater chemistries, including changes in cation exchange capacity and exchangeable cation composition across thin and thick bentonite beds
Bentonite erosion – both under repository-relevant conditions at depth in the tunnels where water conducting features contact the bentonite and under extreme conditions such as erosion from surface-water processes
Bentonite response to fracturing/faulting – assessment of the true impact on bentonite properties when a fracture propagates/fault movement occurs from the surrounding host rock into/through the bentonite
Bentonite reaction - with mudstone and siltstone host rocks
Microbial activity – microbial analysis on natural bentonites
Bentonite sampling/analytical development – novel sampling/analytical approaches are explored
Stakeholder communications – use of ‘real’ examples to explain repository safety concepts.
The results of the project to date are presented in Alexander et al. (in this conference) and Kremer et al. (in this conference). Here, we present an overview of the planned project work and its safety case relevance.
References
Reijonen, H.M. & Alexander, W.R. (2021). International Bentonite Longevity (IBL) project report - Phase A. Jacobs Report to NWS. NWS Ltd., Harwell, UK (in press).