Release of boron and cesium or uranium from simulated borosilicate waste glasses through a compacted Ca-bentonite layer

The long-term release behavior of some elements from simulated borosilicate waste glasses (S-, K- and A-glass) in contact with a domestic compacted Ca -bentonite block and synthetic granitic groundwater at 80 degreesC under ar gon atmosphere has been studied by dynamic leach tests since 1997 at KAERI. S- and K-glass differ mainly in their aluminum content. and A-glass contai ns 19.35 wt% UO2 instead of fission product elements. Up to the present. th e mass loss is almost the same as the normalized boron loss. This means tha t boron is an indicator on the dissolution of borosilicate waste glass. The leach rates of boron from K- and S-glasses after 861 days were approximate ly 3.1 x 10(-2) and 3.0 x 10(-2) g/m(2) day, respectively. However, the rel ease rates of cesium through the bentonite block from K- and S-glasses were about 1/10th of the release rate of boron. which were almost the same arou nd 2.5 x 10(-3) g/m(2) day. This may be due to their adsorption on the bent onite. The leach rate of boron from the A-glass was about 5.4 x 10-2, but t he leach rate of uranium from the A-glass specimen was quite low. below 4 x 10(-7) g/m2 day. The low concentration of uranium in the leachates suggest s that it hardly moves in a compacted bentonite block. By the EPMA, a yello wish uranium compound was deposited on the surface of the bentonite in cont act with the A-glass specimen. The species of this phase should be identifi ed to understand the release mechanism of uranium. (C) 2001 Elsevier Scienc e B.V. All rights reserved.