Study of alpha-decay damage in a glass-bonded, sodalite ceramic waste.

A glass-bonded, sodalite ceramic waste form that contains fission products, uranium, and plutonium is intended for disposition in a geologic repository. Over the many years the waste is expected to be in the repository, there is a potential for waste form degradation due to alpha decay damage. To investigate the effects of alpha-decay damage in glass-bonded, sodalite ceramic waste forms, several waste forms were produced with a {sup 238}Pu loading of 1.8 weight percent. This loading is roughly ten times greater than the plutonium loading for all isotopes in the waste form intended for the repository. Due to the higher specific activity of {sup 238}Pu as well as a higher fraction of total plutonium, the same number of alpha decays per gram of material has been achieved after four years as a waste form of nominal composition after ten thousand years. This paper describes the results of different tests near the completion of a four-year study. Trends of these {sup 238}Pu-doped waste forms include volume expansion of crystalline phases and possible increases in the release rates of several elements in the chemical durability tests. There have not yet been any indications of macroscopic swelling by density measurements, amorphization by x-ray diffraction, or microstructural changes by electron microscopy. Overall, the observed changes to the waste form due to alpha-decay are not of sufficient magnitude yet to cause concern over waste form degradation.