Leaching behaviour of a simulated nuclear waste glass in groundwater of 50-2400C

A simulated nuclear waste glass, was leached at 50, 75, 95, 110 160, 210 and 2400C in groundwater from a granitic terrain. Except at 160 and 2100C, soluble components were leached out readily. During 312 h leaching at 1100C, a leached surface layer, about 5 μm thick, formed, enriched in immobile metals, and in precipitated components. At 160 and 2100C, the secondary layer is composed of an inner leached layer and an outer K-Si-Al-rich layer. The 50-μm thick layer formed during 508 h of leaching at 2400C is composed of an inner leached layer, an outer precipitation layer and a middle layer of intermediate composition. The suppression in leaching rate at 160 and 2100C, is interpreted as a result of rapid formation of the precipitation layer on the glass surface slowing the diffusive migration of solution species responsible for glass dissolution through the surface layer. At 2400C, the leaching rate of soluble species except for silica, increased significantly after an initial stage of slow leaching. Coarse crystalline analcime precipitated, probably at the expense of the surface precipitate, thus preventing the formation of a surface precipitation layer as impermeable to solution species migration as that formed at 160 and 2100C. (author)