Comparison of Surface Layers Formed on Synthetic Basaltic Glass, French R7T7 and HMI Borosilicate Nuclear Waste form Gla
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COMPARISON OF SURFACE LAYERS FORMED ON SYNTHETIC BASALTIC GLASS, FRENCH R7T7 AND HMI BOROSILICATE NUCLEAR WASTE FORM GLASSES MATERIALS INTERFACE INTERACTIONS TESTS, WASTE ISOLATION PILOT PLANT
MICHAEL J. JERCINOVIC*, STACY A. KASER*, RODNEY C. EWING*, and WERNER LUTZE** ,*Department of Geology, University of New Mexico, Albuquerque, NM 87131 Hahn Meitner Institut, Berlin GmbH, Glienicker StraBe, 1000 Berlin 39, F.R. Germany. ABSTRACT Materials Interface Interaction Test results for up to 2 years indicate that surface layers formed on synthetic basaltic glass in brine are predominantly Mg-chloride or oxychloride. Layers formed on HMI and R7T7 borosilicate glass are Mg-silicates. Layer thickness increases from I year to 2 years for basaltic glass and HMI borosilicate glass. Mg-silicate contains Ni and Zr in amounts that are generally related to the composition of associated glass, but layers formed on basaltic glass also contain Ni and Zr, elements not present in the glass. Ni and Zr are, in part externally derived, however, Ti appears to be completely immobile, and is not found in layers formed on Ti-free glass (R7T7). Some chemical components of the surface layers are derived, in part, from alteration of glass but major components of the layers are from the brine. INTRODUCTION The in situ Materials Interface Interactions Tests (MIIT) were initiated in 1986 in order to evaluate nuclear waste form behavior in a repository environment 1 . The MIIT experiments were carried out in instrumented boreholes in the salt deposits of the WIPP site in southeastern New Mexico. WIPP Brine A, a concentrated Na, Mg, K, Cl, SO 4 brine, was used as a leachant at 90,C 2. Samples were removed for analysis after 6 months, I year, and 2 years. Various waste glasses were included in the MIIT experiments, which were placed in contact with brine, salt, metal canister materials and overpack components. This study involves the microanalytical characterization of surfaces of three MIIT glasses, one basaltic and two borosilicate. Specific objectives include: I) defining the mineralogic characteristics of surface layers formed on the glasses; and 2) assessing whether the surface layers are alteration products (components derived, at least in part, from the glass) or are brine deposits which have not involved glass alteration. Basaltic glasses have been suggested to be analogous to borosilicate glasses in terms of alteration processes and rates, thus, offering a possible means to evaluate modelsP, 4,S Owhich have been developed to predict the long term corrosion of waste form glass 7, 8. Natural analogues may also be useful in constraining possible long term corrosion rates7. The inclusion of basaltic glass along with borosilicate glass in the MIIT program is significant in the evaluation of whether or not the glasses perform analogously in relatively short term repository corrosion tests. SAMPLES Borosilicate glass samples included in this study include the HMI glass (Germany) and the R7T7 glass (France). The basaltic glass was synthesized at t
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