Effects of Radiation Exposure on Glass Alteration in a Steam Environment
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EFFECTS OF RADIATION EXPOSURE ON GLASS ALTERATION INA STEAM ENVIRONMENT D. J. Wronkiewicz,* L. M. Wang,** J. K. Bates,* and B. S. Tani*
*Argonne National Laboratory, 9700 South Cass Ave., Argonne, IL 60439-4837. **Dept. of Geology, University of New Mexico, Albuquerque, NM 87131. ABSTRACT
Several Savannah River Plant (SRL) glass compositions were reacted in steam at temperatures of 150 to 2000C. Half of the tests utilized actinide-doped monoliths and were exposed to an external ionizing gamma source, while the remainder were doped only with U and reacted without gamma exposure. All glass samples readily reacted to form secondary mineral phases within the first week of testing. An in situ layer of smectite initially developed on nonirradiated SRL 202 glass test samples. After 21 days, a thin layer of illite was precipitated from solution onto the smectite layer. A number of alteration products including zeolite, Casilicate, and alkali or alkaline earth uranyl silicate phases were also distributed over most sample surfaces. In the irradiated SRL 202 glass tests, up to three layers enveloped rounded, and sometimes fractured, glass cores. After 35 to 56 days these remnant cores were replaced by a mottled or banded Fe- and Si-rich material. The formation of some secondary mineral phases also has been accelerated inthe irradiated tests, and in some instances, the irradiated environment may have led to the precipitation of a different suite of minerals. The alteration layer(s) developed at rates of 2.3 and 32 jim/day for the nonirradiated and irradiated SRL 202 glasses, respectively, indicating that layer development is accelerated by a factor of -10 to 15X due to radiation exposure under the test conditions. INTRODUCTION
Radiation may affect the long-term performance of waste glass in an unsaturated repository environment by inducing radiation damage to solid materials and by interacting with air, water vapor, or liquid water to produce a variety of radiolytic products, including nitrogen and carboxylic acids, hydrogen peroxide, and radical species such as H02. and 02- [1-4]. The radiolytic products may influence glass stability by altering the solution pH, Eh, or by complexing with radionuclides and glass components. A summary review of radiation tests conducted with glass samples completely immersed in liquid water indicates that radiolysis has a minimal impact on glass reactivity [5 and references cited therein]. A single study of glass alteration in an irradiated vapor environment has identified the formation of deposits enriched in Mo and Ba, but direct comparisons between reactions in irradiated and nonirradiated environments were not made [6]. The present set of experiments examines the effects of radiation on glass reactions ina geologically unsaturated environment, such as that expected to exist at the potential Yucca Mountain Site, Nevada. Inthis type of environment, radiolytic product concentrations may rapidly increase in the limited quantities of water contacting the glass. Previous studies have demonstra
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