Aqueous wastes from the reprocessing of nuclear fuels at the Idaho Chemical Processing Plant are solidified in the Waste Calcination Facility. The calcined wastes are then stored in stainless steel bins contained in concrete vaults. It has been determined that the radionuclides of cesium and strontium leach readily on contact with aqueous solutions from the particulate fresh product calcine. Thus, the calcine may require further treatment for final disposal Calcine that is stored up to 12 years has remained particulate and its chemical and other physical properties are similar to those of the original product calcine.