Some thoughts on MCC-14: recommended practice for experimentally evaluating waste form leaching in a geologic repository

Although knowledge of comparative chemical durabilities and the mechanism of water attack on waste form surfaces is important, this knowledge does not enable prediction of the long-term behavior of a specific waste form in a repository setting. This is a much more complex undertaking, which requires an understanding of the effects of the other waste package components and of the repository setting. Tests that can include all of these effects have come to be called interactions tests. The goal of interactions testing is to produce data that, when used in conjunction with mathematical modes, will yield predictions of long-term waste package behavior in a repository. The MCC-14 is a test method that will qualify a waste form for disposal in a given repository. In contrast to MCC-1 through 5, which are test methods with strictly defined limits, it is anticipated that MCC-14 will be rather more a carefully peer-reviewed test methodology. This methodology will include many separate tests in order to adequately define site-specific materials interaction. Tests that will probably become part of the MCC-14 methodology are already in use by the geologic repository R and D programs. The Materials Characterization Center (MCC) plans to work with the repository projects to integrate these existing tests into a comprehensive MCC-14 methodology for peer review by the Materials Review Board (MRB). Three separate methodologies, one for each major candidate geologic medium, basalt, tuff and salt, may be submitted to the MRB. The following criteria for MCC-14 methodology were proposed by the MCC: (1) output data is to be used in extrapolatable mathematical models; (2) emphasize times beyond 1000 years, but be amenable to shorter time repository conditions; (3) output data must be treated statistically. 4 figures