PNNL

Abstract

To ensure that a robust safety case for the long-term disposal of vitrified radioactive wastes can be developed, it is essential that the degradation processes, durability and dissolution kinetics of the glass are understood. Alkali-borosilicate glass is the favoured waste form for the immobilisation of high activity waste arising from nuclear material reprocessing in many countries, and vitrification is being increasingly considered for other materials classified as low and intermediate activity waste. Around the world, a wide range of subsurface disposal environments, ranging from shallow to deep surface, are being proposed for radioactive waste glasses. Standard methods to assess the durability of these materials within disposal environments were first developed in the 1980’s and, over the last several decades, the methods have evolved to yield a range of different responses, depending on experimental conditions and glass composition. Scientific understanding of glass dissolution mechanisms has progressed in parallel, enhancing our interpretation of the data acquired using these standard methods. In this review, the response of the International Simple Glass (ISG) to each standard method is used to demonstrate their respective contribution to understanding glass durability. With the implementation of subsurface disposal for vitrified radioactive waste drawing closer, it is timely to review the available standard durability methodologies, and reflect upon their relative advantages, limitations, and how the data obtained can be interpreted to support the development of the post-closure safety case for their disposal.