In-depth distributions of elements in leached layers on two HLW waste glasses after burial in clay; Step-scan by SIMS

Two glasses developed as potential radioactive high-level waste (HLW) forms were investigated with respect to long-term corrosion resistance in geological environment. Loaded with simulated reactor waste, including fission products, the SON68 and SM513 HLW glasses were leached for 5 years, buried in Boom Clay at 85°C. The results were evaluated by quantitative secondary ion mass spectrometry (SIMS), using a step-scan technique yielding the in-depth concentration profiles of more than 20 relevant elements in successive sub-surface transformed layers to depths of the order of 500 μm. The observed elemental kinetics provided experimentally convincing evidence of a predominantly selective-substitutional leaching mode in both glasses. The rate of corrosion and element depletion in SON68 (a Cogéma type glass) was found to be by ca 20-40% slower than in SM513 (Pamela-type). In the reacted layers of both glasses, 'mobile' elements (e.g., Li, Cs, B) were practically eliminated, but also Si was signi ficantly depleted, while more 'inert' elements (e.g., Al, Zr, Cr) remained essentially preserved in the residual network of the 'gel'.