Modelling the short term, near field performance of an in-room emplacement configuration

This paper presents a numerical investigation of the hydraulic performance of an in-room emplacement scenario. In this concept, two tubular shaped waste canisters are contained within a composite engineered shield of sand, sand/bentonite buffer, light backfill and dense backfill, all seated on a layer of high performance concrete. Because of anticipated excavation damage the elliptical shaped room has a 1.4m thick layer of fissured rock around its perimeter. A numerical study was employed to determine the extent of the granite 'near field' affected by the presence of the open excavation. A zone extending for 7m from the perimeter of the excavation was thus established. The time taken for the repository to fully saturate under isothermal conditions was initially predicted to be 12 years. Coupling the effects of temperature on to the flow of moisture increased the predicted time for saturation to 13 years. A sensitivity study showed that the time to achieve saturation is critically dependent on the assumed value for the coefficient of water storage capacity of the light backfill. Depending on the assumed magnitude of this parameter, it is shown that the repository may take over 250 years to attain a saturated condition. (author)