PNL-6333 UC-70 Completion of the data base will help provide the data to demonstrate the composition/durability relationships needed to develop durable waste glasses •

Reprint of hbtwical &xumeN HWVP-87-VllOU)2F PRMC -ZloaoD1s). dated Sepumkr 1987. Dam. fWmaning. and 0th eonventions reflect rtandardr I thc original dale of priaing. Technical peer reviews and editorial miewr may mt have b x n p e r f d .

Laboratory tests were conducted to validate a radionuclide mass transfer model. During the experiments, cesium and uranium releases from a simulated waste form embedded in an isotropic medium of quartz sand were measured. A 0.01 M NaH2PO4 buffer solution flowed past the waste form. Downstream concentrations obtained from computer simulations were compared with experimentally measured concentrations of cesium and uranium. Uranium release was found to be controlled by solubility-limited mass transfer, while cesium release was controlled by waste form dissolution kinetics. It was also found that the effects of dissolution on groundwater chemistry must be coupled with solubility-limited mass transfer models to defensibly predict radionuclide release rates under realistic repository conditions.