Comparison of the Layer Structure of Vapor Phase and Leached SRL Glass by Use of AEN
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COMPARISON OF THE LAYER STRUCTURE OF VAPOR PHASE AND LEACHED SRL GLASS BY USE OF AEN
BRUCE M. BIWER,* JOHN K. BATES,* TEOFILO A. ABRAJANO, Jr., * AND JOHN P. BRADLEY** Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 • Argonne McCrone National Environmental Services, Inc., 850 Pasquinelll Drive, Westmont, IL 60559 ABSTRACT Test samples of 131 type glass that have been reacted for extended time periods in water vapor atmospheres of different relative humidities and in static leaching solution have been examined to characterize the reaction products. Analytical electron microscopy (AEM) was used to characterize the leached samples, and a complicated layer structure was revealed, consisting of phases that precipitate from solution and also form within the residual glass layer. The precipitated phases include birnessite, saponite, and an iron species, while the intralayer phases include the U-TI containing phase brannerite distributed within a matrix consisting of bands of an Fe rich montmorillonite clay. Comparison Is made between samples leached at 40*C for 4 years with those leached at 90C for 3-1/2 years. The samples reacted in water vapor were examined with scanning electron microscopy and show increasing reaction as both the relative humidity and time of reaction increases. These samples also contain a layered structure with reaction products on the glass surface. INTRODUCTION The ability to understand and model the reaction of nuclear waste glasses under conditions relevant to those expected at the proposed Yucca Mountain repository site requires a complete description of the reacted glass. The identification of stable secondary phases, whether formed on the surface of the glass or as an in-situ rearrangement of products of the reacted glass layer, is essential because it is these secondary phases that set the solution saturation levels of all elements, and in essence are the driving force of continued glass reaction [1]. In the unsaturated environment expected at the tuff repository, glass will be exposed to water vapor and subsequently may be contacted by small amounts of standing water. To study the behavior of glasses under both conditions, long-term tests have been performed by Westinghouse Savannah River Company (WSRC) and by Tests of long duration are of interest the Yucca Mountain Project (YMP). because they allow for the greatest degree of alteration. In this report we examine the reaction of 131 type glass with water vapor and liquid water. This glass was chosen because samples from longterm vapor hydration and static leach tests are available, and because the results from the leach tests have been used in developing models [1,2] to predict glass performance. While the composition of the 131 glass samples examined is not expected to be used for glasses produced in the Defense Waste Processing Facility (DWPF), It is possible that glasses of similar durability may be manufactured. Thus, experience gained in studying the alteration processes of this glass is likely to be transferable to the study of
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