Parametric Effects of Glass Reaction Under Unsaturated Conditions
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PARAMETRIC EFFECTS OF GLASS REACTION UNDER UNSATURATED CONDITIONS JOHN K. BATES, THOMAS J. GERDING, AND ALAN B. WOODLAND, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439. ABSTRACT Eventual liquid water contact of high-level waste glass stored under the unsaturated conditions anticipated at the Yucca Mountain site will be by slow intrusion of water into a breached container/canister assembly. The water flow patterns under these unsaturated conditions will vary, and the Unsaturated Test method has been developed by the YMP to study glass reaction. The results from seven different sets of tests done to investigate the effect of systematically varying parameters such as composition and degree of sensitization of 304L stainless steel, water input volume, and the interval of water contact are discussed. Glass reaction has been monitored over a period of five years, and the parametric effects can result in up to a ten-fold variance in the degree of glass reaction. INTRODUCTION The Unsaturated Test method has been developed (1,2] as a procedure to monitor the reaction of high-level nuclear waste with water under conditions that are relevant to the proposed repository site at Yucca Mountain, Nevada. The repository horizon is located in welded tuff, and the anticipated hydrology is unsaturated. This unsaturated environment adds a new dimension to waste form testing in that the amount of water expected to contact the waste is minimal, and the sequence of water/waste interaction will be from humid air to small volumes of dripping water. The emphasis of the Unsaturated Test is to investigate interactive effects between waste package components, to identify processes that are accentuated due to the small water contact volume, and to provide a measurement of waste form reaction as a function of time. Data obtained from the Unsaturated Test may be used to validate models of glass reaction [3], that have been developed independently from site-specific considerations. BACKGROUND The Unsaturated Test method has been applied rigorously to study the behavior of glass waste. Three types of interactions that affect the reaction of glass are anticipated to occur under unsaturated conditions. These include (1)contact between the glass and moist air, followed by periodic rinsing of the glass surface with flowing water; (2) contact between the glass and standing water; and (3) contact between the glass and standing water in close contact with partially sensitized 304L stainless steel. The Unsaturated Test provides for the possibility that these interactions will occur, and specifies analyses be performed to judge the importance of each one. A schematic diagram of the test apparatus is shown in Fig. 1. The components are the test vessel, which provides for collection and containment of liquid and support of the waste package; the waste package assemblage (WPA), which consists of the waste form and presensitized metallic components representing the canister; and a solution feed system to inject test water. The WPA is con
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