The Leaching Behavior of Zircaloy Cladding and Its Impact on the Conditioning of Waste for Final Disposal

The leaching behavior of real Zircaloy cladding hulls, originating from the pressurized water reactor nuclear power station at Obrigheim, Federal Republic of Germany, was investigated using distilled water; nitric acid; sodium hydroxide solution; Portland, alumina, and Sorel cement lye solutions; and a potassium pyrosulfate melt as leachants. The leached fraction was determined for six gamma-emitting isotopes and two actinides. The distributions of the radionuclides in the hulls were determined using a potassium pyrosulfate melt. The results indicated that actinides (plutonium and curium) were concentrated on the surface; the diffusing species (ruthenium and cesium) had high concentrations at the surface but also appeared in the inner portions of the hulls. The distribution of activation products (cobalt and antimony) was very nearly homogeneous throughout the hulls. It is recommended that, prior to reprocessing, the Zircaloy-clad fuel rods be separated from the fuel assembly to facilitate handling of the alpha-contaminated waste stream. The results of this study show that decontamination with nitric acid should be sufficient for further conditioning prior to disposal if conditioning is required.