Accelerated chemical aging of crystalline nuclear waste forms: A density functional theory study of 109Cdx109Ag1-xS

Recently, a combined experimental-theoretical approach to assess the effect of daughter product formation on the stability of crystalline compounds comprised of radioisotopes has been developed. This methodology was motivated by the potential impact on crystalline nuclear waste form stability of a significant fraction of the constituent atoms undergoing transmutation. What is particularly novel about this approach is the experimental use of very short-lived isotopes to accelerate the chemical evolution that occurs during decay. In this paper, we present results of density functional theory (DFT) calculations that have been performed in support of corresponding experiments on the 109Cdx109Ag1-xS material system. 109Cd has been selected in order to simulate the decay of important “short-lived” fission products 137Cs or 90Sr (which decay via β- to 137Ba and 90Zr respectively with ≈30-year half-lives). By comparison, 109Cd decays by electron capture with a half-life of 109 days to 109Ag. DFT results predict the formation of heretofore unobserved CdxAg1-xS structures, which support corresponding experiments and ultimately may have implications for waste form stability.