Investigation of microscopic radiation damage in waste forms using ODNMR and AEM techniques. 1998 annual progress report

Abstract

'This project seeks to understand the microscopic effects of radiation damage in nuclear waste forms. The authors approach to this challenge encompasses studies of crystals and glass containing short-lived alpha- and beta-emitting actinides with electron microscopy, laser spectroscopy, and computational modeling and simulation. Much of the initial effort has focused on alpha-decay induced microscopic damage in 17-year old samples of crystalline yttrium and lutetium orthophosphates and thorium dioxide that initially contained {approximately}1% of the alpha-emitting isotope Cm-244 (18.1 y half life) or the beta-emitting isotope Bk-249 (0.88 y half life). Studies will also be conducted on borosilicate glasses that contain Cm-244 or Am-241, respectively. The goal is to gain clear insight into accumulated radiation damage and the influence of aging on such damage, which are critical factors in the long-term performance of high-level nuclear waste forms. Amorphization previously has been thought to be the most important effect of radiation damage in crystalline and ceramic materials. The studies show that for alpha-emitting actinide ions in certain crystalline phosphates, amorphization is not a significant effect of radiation damage. Instead, formation of microscopic cavities (bubbles) is an important consequence of alpha-decay events. This amorphization-resistant property makes orthophosphates a very attractive high level nuclear waste form. However, aggregation and mobilization of cavities (bubbles) might increase the leach rate of radionuclides and influence the long-term stability of the waste forms. Further research is needed before the authors can draw a final conclusion on the long-term effects of radiation damage in high level waste forms.'