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

Experimental results obtained with high-level radioactive glass specimens t ypically containing 10(9) to 10(10) Bq g(-1) of beta gamma -emitters confir m the behavior observed on simulated non-radioactive glass, Most of the cur rent knowledge of the alteration mechanisms of nuclear glass in water and t he kinetic laws of glass alteration developed to model their longterm behav ior is based on studies of inactive material. No difference was found betwe en the initial alteration rates measured on active and inactive glass speci mens, nor in the long-term alteration rates at advanced stages of reaction progress (typically three or four orders of magnitude lower than the initia l 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. T his behavior would suggest that the alteration films are slightly less prot ective under high beta gamma dose rates (> 100 rad h(-1)). The alteration l ayer has strong retention capacities for the actinides. The key processes, and the corresponding retention models, are highlighted. (C) 2001 Elsevier Science B.V. All rights reserved.