Cementitious materials are included in the design of many geological disposal facilities for radioactive wastes, including the Nirex Reference Vault Backfill (NRVB). As part of a larger programme of work for Radioactive Waste Management Limited (RWM) to assess NRVB performance, Quintessa produced reactive-transport models to simulate its reaction with different groundwater compositions. Variant cases were also produced to explore the effect of model assumptions on the predicted behaviour of the backfill.
The results of this work have been published in a paper authored by James Wilson, Steven Benbow and Richard Metcalfe. Depending on groundwater composition, potential cement alteration pathways included: carbonation; external sulphate attack; chloride attack; the formation of magnesium-rich solids; and the precipitation of secondary aluminosilicate minerals. In general, the models suggest that the pore space in backfill associated with radioactive waste disposal systems is likely to become clogged (to some degree) over time close to backfill-rock interfaces resulting in a reduction in capacity for solute transport and thus radionuclide release. The paper discussed the implications of the work and identifies potential areas for further research.