The role of a bentonite-based packing in limiting steady radionuclide release from an underground high-level waste repository

Steady fractional release rates are calculated for an isolated waste canister protected by bentonite-based and alternative packing materials in both basalt and tuff repositories. The bentonite-based packing is shown to be superior to either crushed basalt or crushed tuff packing in reducing nuclide release. Additional fractional release rates assessing the role of the packing permeability, Ksub(p), are also studied. Nuclide release is found to be insensitive to large changes in Ksub(p), reducing concern over possible alteration of the bentonite to nonsmectite minerals. (author)