Wet and dry cycle leaching: aspects of releases in the unsaturated zone

The NRC criteria of containment and controlled release for a HLW repository have in the past been addressed by leaching and radionuclide release experiments that correspond to repository flooding or temporally independent saturation. Both high-level waste repository and low-level waste burial sites can be expected to experience unsaturated conditions, as determined by the nature, frequency, and length of the wetting fronts. An important aspect of radionuclide release in the unsaturated zone is the effect of cyclic wet/dry leaching conditions. In this paper we have considered aspects of radionuclide release from low-level waste form subjected to wet/dry cycles, simulating burial in the unsaturated zone. Some preliminary results of cesium and strontium release are presented, showing that the processes occurring during the unsaturated period of the wet/dry cycle can have a profound effect on the overall release of radionuclides