The Performance Of Actinide-Containing Srl 165 Type Glass In Unsaturated Conditions
Materials Research Society Symposium Proceedings
As part of the effort by the Nevada Nuclear Waste Storage Investigations (NNWSI) Project to evaluate the volcanic tuff beds of Yucca Mountain, Nevada, as a repository for the permanent storage of high-level nuclear waste, the interaction of actinide-doped Savannah River Laboratory (SRL) 165 type glass with the unsaturated repository environment has been studied. Me NNWSI Unsaturated Test method has been used, and the results from batch and continuous tests completed through 18 months
... 8 months demonstrate that several Interactions are important for controlling both the reaction of the glass and the release of radionuclides. These Interactions Include (1) the reaction between the glass and moist air with Interludes of liquid water contact, which results 1n the release of alkali metals from the glass; and (2) the reaction between standing water, glass, and presensitized 304 L type stainless steel which results 1n breakdown of the glass matrix and the release of radionuclides from the glass-metal assemblage. A comparison of the results of the Unsaturated Test with those of parametric experiments Illustrates the Importance of presensitized steel In enhancing the glass reaction, and demonstrates the applicability of the Unsaturated Test to those conditions anticipated to exist In the NNWSI repository horizon. CONP-871124-78 INTRODUCTION ^n nn DE88 006000 Investigation of the volcanic tuff beds of Yucca Mountain, Nevada, as a potential site for a high-level waste repository Is a function of the Nevada Nuclear Waste Storage Investigations (NNWSI) Project. As part of this study the NNWSI Unsaturated Test has been developed as a method to obtain data on the release of waste components from the waste package in the NNWSI repository environment under conditions currently envisioned after the 300/1000-year containment period has elapsed. Specifically, the test will provide Information to be used by the NNWSI project In licensing the NNWSI repository site. The test method will provide (1) data that describe the release of radionuclides from a specifically designed glass/ container assemblage under strictly controlled test conditions, and (2) Information concerning synergistic effects that may occur between waste package components. The test results can be used to determine Interactions that are Important when glass leaching occurs In an environment of air, water vapor, and liquid water. Previously [1,2] a glass based on Savannah River Laboratory (SRL) frit 165 had been reacted using the Unsaturated Test method (F series tests). These Initial results demonstrated that the test method was capable of producing repository-relevant results and that the extent of glass reaction depended strongly on Interactions that occurred between waste package components. The greatest degree of reaction occurred when glass, standing water, and weld-affected 304 L stainless steel were in contact. When there was a strong interaction In the weld-affected area, the glass reaction was greater than when there was a weak Interaction. The glass reaction was described as occurring via (1) a diffusional process that resulted in a fairly constant release of alkali metals from the entire glass surface, and by (2) matrix breakdown that resulted in the release of all glass components from the weld-affected area.