In situ testing of the chemical durability of vitrified high-level waste in a Boom Clay formation in Belgium: discussion of recent data and concept of a new test

SCK·CEN has been conducting in situ experimental programmes on candidate high-level waste (HLW) glasses, as part of a global approach to evaluate the long-term chemical durability of the HLW glasses. The in situ tests are conducted in the underground research facility high activity disposal experimental site (HADES), located in the Boom Clay at 223 m below the SCK·CEN site. We briefly present the test concepts for three in situ tests: a first type of corrosion test, tests as part of the Control Experiment with Radiation of the BElgian Repository for Underground Storage (CERBERUS) test (involving γ-radiation sources), and the CORrosion of Active gLass in Underground Storage condition (CORALUS) test, that involves both γ-sources and glass samples doped with α-radionuclides (Np, Pu, Am). The glasses are corroded slightly less compared with the first in situ tests (where no γ-radiation was present). By using mass loss data and an extensive analysis of the reaction layer formed on top of the glasses, we managed to identify the main interaction processes: matrix dissolution and selective leaching. The four glasses studied reveal significant differences in dissolution behaviour. We further discuss the status of the CORALUS in situ corrosion test, which is in its first phase. An inactive CORALUS tube has been prepared and is presently in operation.