Interlaboratory comparison of UO{sub 2} dissolution rates

Direct disposal of spent nuclear fuel in deep underground geologic repositories (vaults) is being pursued by several countries. Isolation relies on multiple barriers consisting of the site geology, engineered barriers including containers to surround the fuel, and the spent fuel itself. These barriers are intended to inhibit dissolution and transport of radionuclides by groundwater, which is virtually the only mechanism available to release radionuclides from the repository. Performance assessment studies are needed to demonstrate the adequacy of the various repository designs. Essential to this performance assessment is an understanding of the dissolution behavior of the spent fuel. Since the dissolution behavior of spent fuel in an actual repository cannot be adequately approximated in a laboratory, laboratory tests and data must be used to develop a mechanistic model that can predict long-term behavior in a repository. Three different laboratories have performed flowthrough dissolution tests at room temperature on portions of the same batch of unirradiated UO{sub 2} powder, and good agreement was achieved between the different test results. Dissolution rates obtained from electrochemical studies conducted with UO{sub 2} electrodes at Whiteshell Laboratories are compared with the flowthrough test results.