Abstract
In France, borosilicate glass, known as R7T7, is used to contain the long-lived high-level radioactive waste remaining after reprocessing of spent nuclear fuel. The objective of the R&D studies is to predict their long-term behavior to ensure the safety of the disposal solution: the physical and chemical stability of the glass on a geological time scale must therefore be demonstrated, which requires studying the response of the glass to the radiation emitted by the nuclear waste as well as its behavior when subjected to alteration by water.This work focuses on the leaching behavior of a chemically simplified borosilicate glass, chosen by the international community, called ISG (International Simple Glass). Pristine glass pellets were subjected to several external irradiation scenarios (electrons, Au ions, electrons followed by Au ions) in order to simulate the different irradiation sources of a real radioactive glass, inducing electronic and/or nuclear interactions. The irradiation dose values were chosen to induce significant changes in the structure and properties of the glass and they also correspond to the dose level expected in storage conditions when water will come in contact with the glass. The effects of the irradiations on the structure and properties of the glass were studied by various techniques.Pristine and irradiated glass pellets were then altered for several months in pure water at 90 °C and high surface-to-volume ratio (SA/V = 200 cm-1) to rapidly reach the residual alteration rate regime expected in long-term storage conditions. The thickness of the gel layer was measured by ToF-SIMS to calculate the glass alteration rate and TEM characterizations with cryogenic sample holder were performed to describe the nanostructure of the gel layer.The results show that electron irradiation induces only small changes in the structure and properties of the glass, including its weathering behavior. However, irradiation with Au ions induces changes in the structure and properties of ISG glass, as well as an increase in the glass alteration rate. The results obtained for the sequentially irradiated glass (electrons followed by Au ions) are close to those obtained on the glass irradiated with Au ions only. This suggests that long-term glass leaching is sensitive to structural changes induced by nuclear damage, simulated here by external irradiation with Au ions.