Self-diffusion of 22Na and 137Cs in simulated nuclear waste glass

Abstract

The knowledge of self-diffusion of various elements is important for understanding and elucidating the long-term dissolution of the nuclear waste glass. The self-diffusion coefficients of Na and Cs in P0798 simulated nuclear waste glass have been measured by an ion beam sputter-sectioning technique using the radioactive isotopes 22Na and 137Cs. The temperature dependence of the diffusion coefficients in each temperature range in P0798 glass below the glass transition temperature Tg can be expressed by the following equations: (428-574 K) : DNa-belowTg = 2.7 × 10-6 exp(-113±4 kJ·mol-1 / RT)m2·s-1 (713-758 K) : DCs-belowTg = 7.1 × 10-5 exp(-241±10 kJ·mol-1 / RT)m2·s-1 The diffusion coefficient of 22Na was about ten orders of magnitude larger than that of 137Cs at 573 K. The large difference in the diffusion coefficients is explained in terms of the ion size effect, the mixed-alkali effect and lower concentration of Cs compared with Na in P0798 glass.