Long-term alteration mechanisms in water for SON68 radioactive borosilicate glass

Experimental results obtained with high-level radioactive glass specimens typically containing 109 to 1010 Bq g−1 of βγ-emitters confirm the behavior observed on simulated non-radioactive glass. Most of the current knowledge of the alteration mechanisms of nuclear glass in water and the kinetic laws of glass alteration developed to model their long-term behavior is based on studies of inactive material. No difference was found between the initial alteration rates measured on active and inactive glass specimens, nor in the long-term alteration rates at advanced stages of reaction progress (typically three or four orders of magnitude lower than the initial rates). At high reaction progress under conditions with very low solution renewal, however, the time necessary for the highly radioactive specimens to reach the low final rate is longer than for the non-radioactive glass. This behavior would suggest that the alteration films are slightly less protective under high βγ dose rates (>100 rad h−1). The alteration layer has strong retention capacities for the actinides. The key processes, and the corresponding retention models, are highlighted.