Heavy ion radiation ageing impact on long-term glass alteration behavior

Abstract The major contribution of the alpha decay of minor actinides to the long-term radiation component of nuclear glasses under disposal conditions has been recently highlighted, and its impact needs to be assessed in terms of the leaching behavior. Thus, in this study, simple borosilicate glasses were externally irradiated by heavy ions to assess their effect on alteration processes at high reaction progress. Multiple-energy gold ion irradiation was performed on monoliths of two simple borosilicate glasses, at low energy (0.5–3.5 MeV) and with nuclear doses of up to 214 MGy. The samples were then altered in pure water at 90 °C for up to 3 months, with a S/V = 200 cm −1 . Elemental depth profiles were acquired by ToF-SIMS, and the morphology of the altered layer was characterized by SEM and TEM. The results showed that the irradiated glass was more altered—by a factor of about 4.5 at a given time—than the reference material, indicating that the initial structure of the glass has an impact on the long-term alteration process. This evolution of the leaching rate with the irradiation dose is attributed to nuclear collisions, and follows the same tendency with nuclear dose as other structural and mechanical properties of the solids modified by such an irradiation. Therefore, the authors suggest that the effect of irradiation on the alteration mechanism in the residual rate regime is linked to changes in either the glass structure or its properties, inducing an increase in water migration through the growing alteration layer or an increase in the glass reactivity. Lastly, as the level of alpha decay sustained by a nuclear glass before water arrival will exceed the dose needed to significantly damage the glass, leaching studies should take into account glass damage to predict its long-term behavior as accurately as possible.