RELEASE AND DIFFUSION OF SR-90 FROM SPENT UO2 FUEL IN BENTONITE CLAY

Ten diffusion cells were loaded in 1985 with slices of spent UO2-fuel embedded in compacted bentonite clay. In some of the cells, additives (metallic iron, metallic copper or the mineral vivianite) were mixed w ith the bentonite clay to study their influence on the leaching and di ffusion behaviour. The diffusion cells were contacted with synthetic g roundwater for certain times, whereafter the clay was sliced into thin samples to be analyzed by radiometric methods. The release of the fis sion product Sr-90 from spent nuclear fuel into bentonite clay has bee n mesaured after contact times of 101, 197, 386 and 2213 days. The app arent diffusivity of strontium in bentonite clay was determined using two clay compactations and is in good agreement with literature data. The release of Sr-90 was approximately five to ten times lower after s ix years compared to fuel-leaching experiments.