Bituminised waste re-treatment: Replacement of the bitumen matrix by a glass matrix

The vitrification of nuclear waste salts similar to the salts present in Eurobitum produced by the former Eurochemic reprocessing plant, Mol-Dessel, Belgium, is investigated. In order to approach the composition of the high-level waste reference glass SON68, mixtures with different ratios of glass frit to waste salts have been prepared and vitrified. The concentration of the waste salts varied between 17 and 25% by weight. To compare the short term corrosion behaviour with reference waste glass, leach tests have been performed. During 8 weeks, the glass samples were submitted to leach tests at 363 K using Milli Q water as leachant, at a glass exposed area over leachant volume ratio equal to 100 m-1. During this short period, scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) showed no gel layer formation. This technique did not detect changes in the chemical composition. However, X-ray photoelectron spectroscopy (XPS) showed that the binding energy of the Zr 3d and Si 2p electrons decreased as a function of leaching time, indicating an increasing covalent character of the glass surface. Inductively coupled plasma-mass spectrometry (ICP-MS) of the leachate as a function of time shows that ionic species such as Na and K leach faster than e.g. Si and B. These results together with the XPS data suggest the onset of a gel layer formation. The effect of waste content in the glass on the leaching rate is also studied. The results are compared with similar leaching tests on R7T7 type SON68 glass. Most elements arc better retained in the simulated Eurobitum glass than in the SON68 glass.