Radiation damage in crystalline nuclear-waste solids

Radiation damage in nuclear wastes is shown to be linked to decay of the actinide elements, particularly Cm and Am. Both alpha-recoil damage in actinide-containing phases and alpha bombardment of all phases must be considered. Phases either remain crystalline, with small volume changes (<2%), or become amorphous, often with large volume changes, when subjected to alpha-recoil or ion bombardment. Ionic compounds appear to fall mainly in the stable category and the stability can be estimated from the ionicity. Both alpha-recoil and alpha bombardment induced changes follow an exponential function of the dose to some saturation value. It is possible to establish some limits of general application in terms of total dose received and relate these to the corresponding nuclear waste storage times. A figure schematically summarizes this information showing lattice constant changes plotted against dose. The waste storage times required to achieve these doses are given for both defense and commercial HLW waste solids, assuming a 30% waste loading. This comparison shows that existing defense wastes can be converted to crystalline solids without concern for radiation-induced changes. If commercial nuclear fuels are reprocessed and wastes solidified, there is a real potential for large radiation-induced changes, even within the first hundred years