Closing repository void spaces using bentonite: does heat make a difference?

Bentonites are commonly proposed for use in the geological disposal of high heat generating radioactive wastes. Repository designs include bentonite as a buffer to occupy void space around waste canisters because favourable properties it can exhibit that enhance isolation and containment functionality repository. Many repository concepts introduce small voids within is incorporated individual bricks stacked canisters. These must be closed prevent persistence permeability pathways fluids. As hydrates, expands exert considerable swelling pressure on surrounding host rock. The also fill engineering cavities inherently present repository, but non-uniform development total stress pore could cause persistent material heterogeneities occur. This likely exacerbated by thermal gradients existing between hot temperature rock early stages post-closure. Whilst this an area ongoing research, final extent homogenisation how long property variations persist, not well understood. In study, four tests were conducted pre-compacted, sodium-activated MX80 samples placed next water-filled void, examine effect elevated function sample size. lengths chosen give bentonite-to-void ratios, represent extremities behaviour, such acceptable upper limit size might established. results demonstrated even under extreme was able swell completely space, exerting measurable pressure. Under conditions have shown larger end-of-test pressures higher dry densities along their entire length than equivalent at ambient temperature. addition, showed rapid initial increase then decrease start testing, approaching asymptote more quickly, whilst uptaking less water case. implied heating reduced test duration about 60%, which most explained reduction viscosity permeant temperatures.