Nations using borosilicate glass as an immobilization material for radioactive waste have reinforced the importance of scientific collaboration to obtain a consensus on the mechanisms controlling the long-term dissolution rate of glass. This goal is deemed to be crucial for the development of reliable performance assessment models for geological disposal. The collaborating laboratories all conduct fundamental and/or applied research using modern materials science techniques. This paper briefly reviews the radioactive waste vitrification programs of the six participant nations and summarizes the current state of glass corrosion science, emphasizing the common scientific needs and justifications for on-going initiatives

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Understanding the long-term release of radionuclides from nuclear waste to the environment is critical for public acceptance and sustainability of nuclear energy. Iodoapatite, a synthetic material similar to mineral vanadinite proposed for radioactive iodine-129 immobilization, is employed in this study as a model system for iodine waste forms and ceramic waste forms in general to understand its long-term chemical durability. Semidynamic leaching experiments were performed in cap-sealed Teflon vessels to evaluate the chemical durability at temperatures from 20 to 90 °C and pH values from 4 to 9 using deionized water and pH buffer solutions. The leachates were analyzed using inductively coupled plasma-mass spectrometry. The leached surfaces were examined by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Effects of test variables including surface-to-volume ratio, leachant replacement interval, and environmental variables including temperature and pH on the dissolution rate were systematically investigated. The activation energy of the dissolution was 16.9 ± 1.5 kJ/mol for the matrix elements and 34.4 ± 3.9 kJ/mol for the diffusive iodine release. The order of the pH effect on the dissolution rate as a power law exponent was 0.87 ± 0.08. The effect of the surface-to-volume ratio and replacement interval was approximated by a single exponential function rise to maximum. Fully parametrized models were then combined to predict iodine release rate under various conditions. The result suggests that the long-term iodine release is controlled by iodide diffusion when the matrix dissolution rate is very low in near neutral pH solutions and by matrix dissolution when the dissolution rate is high at low pH. The present study demonstrates a mechanistic approach to parametrize models that can be used to evaluate the performance of nuclear waste forms under various disposal environments.