Effects of Radiation Exposure on Glass Alteration in a Steam Environment

Abstract

Several Savannah River Plant (SRL) glass compositions were reacted in steam at temperatures of 150 to 200°C. 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 in the 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 μm/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.

The effects of the glass surface area/solution volume ratio on glass corrosion: A critical review

“…The phases formed initially will likely be replaced by more stable phases through diagenetic reactions over long time periods. In fact, paragenetic sequences have been observed in vapor hydration tests conducted over extended time periods [113,114].…”

“…The phases formed initially will likely be replaced by more stable phases through diagenetic reactions over long time periods. In fact, paragenetic sequences have been observed in vapor hydration tests conducted over extended time periods [113,114].Corrosion in a vapor environment represents a high SA/V system dominated by the solution chemistry, since very little glass must dissolve to saturate the thin film of sorbed water. While the geometric surface area of the specimen is easily measured, the volume of water in contact with the glass specimen will vary as the corrosion' progresses.…”

Effects of radionuclide decay on waste glass behavior: A critical review

“…These values thus represent an upper bound for radiation exposure. In these tests, alteration layer development was observed to occur 10 to 15 times faster for SRL 202 glasses reacted at 200*C [20] and 4 times faster for SRL 131 glass reacted at 150*C [191] relative to corresponding tests run without radiation exposure. Both the diversity and total quantity of secondary alteration products on the glass surface also increased in high SAN tests conducted with radiation exposure [20,31,191,192].…”

“…Dissolved molecular nitrogen and carbon dioxide in the water may also undergo radiolytic decomposition involving a several step recombination of the dissociation products with oxygen, water, and other associated radiolytic products to form nitrogen and carboxylic acids, respectively [14][15][16][17][18][19][20]. Because the solubility of nitrogen in water is low, G values for nitric acid production in air-saturated water will also be small.…”

“…Radiolysis Effects in an Unsaturated Environment Radiation exposure of glasses under relatively high SAN conditions, such as those expected to exist in an unsaturated repository setting, will lead to rapid concentration of radiolytic products in the relatively limited amounts of water condensed on the glass surface [20,190]. In such an environment, the bicarbonate present in the small volume of condensate may be neutralized by nitric acid produced in radiolysis reactions.…”