Transmission electron microscopy analysis of the hydrothermal alteration products of R7T7 nuclear waste glass at 250 deg C

Alteration experiments of R7T7 nuclear waste glass in distilled water at 250 deg C have been performed during 1, 7 and 30 days. Ultramicrotomic thin sections were made in the alteration layers and studied under the transmission electron microscope. The samples altered 1 and 7 days are covered by an alteration layer rich in sheeted crystals with respective basal spacing of 7 and 10 A. Chemical microanalyses coupled with electron microdiffraction data suggest that the crystals formed after 1 and 7 days could be respectively classified as septechlorites and smectites. The sample altered for 30 days, contains a smectite (10 A), analcime and calcium silicate hydrate: gyrolite. (author). 8 figs., 3 tabs., 8 refs