Thermal constraints on disposal of heat-emitting waste in argillaceous rocks

Although the post-closure thermal phase of a repository containing heat-emitting radioactive wastes is likely to be of comparatively short duration when judged against performance assessment time-scales, the effects of temperature increase and associated thermal gradients within an argillaceous host-rock are likely to be wide-ranging and include: (a) geomechanical effects on the rock-mass and engineered structures (linings, emplacement boreholes, etc.), (b) perturbation of groundwater pressures and flow by ‘aquathermal mechanisms’, (c) possible near-field effects on mass transport properties and mechanisms (e.g. coupled flow phenomena), and (d) effects on the chemical evolution of the near-field environment. Maximum allowable temperature in a repository is likely to be constrained by host-rock and/or clay buffer/backfill thermal behaviour. Given the diverse range of the thermal responses, the identification of a primary constraint on near-field temperature and the specification of a maximum allowable temperature remains problematic.