Thermal and radiation effects in the range of the glass transition temperature Tg

Licencing procedures for the disposal of vitrified HLW require that there should be no unforeseen changes in the product properties prior to and after emplacement of the waste. Such changes could occur upon deliberate or accidental self-heating of the glass up to or even beyond the glass transformation temperature, Tg, over extended periods of time. Hence, an evaluation of the consequences or excessively high temperatures in the waste form is necessary. This paper reviews data on liquid-liquid phase separation and crystallization. Diffusion data are applied in a simple model to calculate crystal sizes in simulated borosilicate nuclear waste glasses especially in the range of the glass transition temperature. The effect of thermodiffusion on the homogeneity of ion concentrations as well as the effects of radiation on alkali and helium diffusion are discussed