Influence of temperature and relative humidity on vapor hydration of an AVM nuclear waste glass

Abstract

The safety assessment of the geological disposal of nuclear waste glasses requires a thorough understanding of the vapor hydration mechanisms of these glasses. In this context, the effect of temperature and relative humidity on vapor hydration of the AVM6 glass, which is the most reactive among the studied French AVM glasses, was investigated in the present study. Polished glass monoliths were vapor hydrated for 1 year (i) at 97% relative humidity (RH), at temperatures 70°C and 90°C to study the effect of temperature and (ii) at 50°C and 50% RH, 76% RH, 88% RH and 97% RH to study the effect of RH. The altered glass samples were characterized by SEM, XRD and ToF-SIMS. The results were compared with published results of AVM6 glass vapor hydrated at 50°C and 95% RH. The nature of the secondary phases that precipitate varied with both temperature and relative humidity, leading to variation in the behavior of elements in the altered layer (gel) but the altered layer morphology is similar at all temperatures studied. The Arrhenius law for temperature dependence is respected between the temperature range 50–90°C and the activation energy suggests that network-hydrolysis is the predominant rate controlling mechanism at these temperatures and duration. The secondary phases that incorporate transition metals and rare-earth elements are identified by XRD only in experiments conducted at lower RH values.