Published online by Cambridge University Press: 03 September 2012
Vitrification is the most developed method for the immobilisation of highly radioactive waste obtained from reprocessing irradiated nuclear fuel. Highly active wastes continue to be vitrified at Sellafield in the Waste Vitrification Plant (WVP) and the product glass has previously been subjected to rigorous characterisation in order to ensure waste form integrity and stability during interim storage. However, the vitrified waste may eventually be placed in an underground repository and so further studies may be needed to confirm the chemical stability of vitrified wastes in different disposal scenarios. One area of uncertainty is in knowing how the alteration products and surface layers on a corroded glass effect the dissolution process and the solution concentrations of long-lived radionuclides. This study shows how the technique of laser microprobe inductively coupled plasma mass spectrometry (LM-ICP-MS) can be used to provide a direct chemical analysis of vitrified samples, both in their as-cast state and after leach testing. LM-ICP-MS, solutions' nebulisation ICP-MS (to provide chemical analyses of the leachants), light microscopy, scanning electron microscopy and confocal laser microscopy were used to examine the effect of leaching on the surfaces of vitrified samples. Data were obtained for a number of simulated WVP-type product glasses that were subjected to soxhlet leach testing for varying lengths of time. The LM-ICP-MS data clearly show that the technique offers a rapid and relatively accurate method for detecting and monitoring minute changes in the surface layers of glass and in the build-up of alteration products. Hence, LM-ICP-MS could be used to obtain valuable mechanistic information on the degradation of glass by examining radionuclide behaviour in the surface layers of glass as it corrodes over extended time periods.