Alteration of synthetic basaltic glass in silica saturated conditions: Analogy with nuclear glass

International audienceThis study investigates the analogy between basaltic and borosilicate glasses of nuclear interest, by focusing onmechanisms controlling glass dissolution under silica saturation conditions. These conditions are representativeof a non- or slowly renewed contacting solution, favouring the formation of a potentially passivating silica richgel layer and secondary phases. Laboratory batch experiments were performed with synthetic basaltic glassaltered at 90 °C, at pH 7 in a saturated 29Si-doped aqueous solution for more than 600 days. Using elemental andisotopic solution analysis and solid characterizations by SEM, TEM and ToF-SIMS, we show that basaltic glasscorrodes at an unexpectedly high and constant dissolution rate of 4×10−3gm−2 d−1 associated with theabsence of passivating gel. Our results highlight the fact that the dissolution rate is controlled by the hydrolysisof the glassy network, sustained by the precipitation of clay-type minerals and amorphous silica. When tested insimilar conditions, the International Simple Glass (ISG), a six oxide borosilicate glasses of nuclear interest displaysa much lower rate limited by water diffusion through a passivating layer. The different behavior of the twoglasses is explained by their ability to form secondary crystalline phases at the expense of an amorphous passivatingfilm