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 significantly depleted, while more `inert' elements (e.g., Al, Zr, Cr) remained essentially preserved in the residual network of the `gel'.