Chemical durability is not a single material property that can be uniquely measured. Instead it is the response to a host of coupled material and environmental processes whose rates are estimated by a combination of theory, experiment, and modeling. High-level nuclear waste (HLW) glass is perhaps the most studied of any material yet there remain significant technical gaps regarding their chemical durability. The phenomena affecting the long-term performance of HLW glasses in their disposal environment include surface reactions, transport properties to and from the reacting glass surface, and ion exchange between the solid glass and the surrounding solution and alteration products. The rates of these processes are strongly influenced and are coupled through the solution chemistry, which is in turn influenced by the reacting glass and also by reaction with the near-field materials and precipitation of alteration products. Therefore, those processes must be understood sufficiently well to estimate or bound the performance of HLW glass in its disposal environment over geologic time-scales. This article summarizes the current state of understanding of surface reactions, transport properties, and ion exchange along with the near-field materials and alteration products influences on solution chemistry and glass reaction rates. Also summarized are the remaining technicalmore » gaps along with recommended approaches to fill those technical gaps.« less

Current Understanding and Remaining Challenges in Modeling Long‐Term Degradation of Borosilicate Nuclear Waste Glasses

https://digital.library.unt.edu/ark:/67531/metadc898741/m2/1/high_res_d/928560.pdf

Performance of a buried radioactive high level waste (HLW) glass after 24 years

Static leach tests have been performed at glass surface area/leachant volume (SA/V) ratios of 10, 340, 2,000, and 20,000 m[sup [minus]1] to assess the effects of the SA/V on the mechanism and rate of the glass reaction. Tests were performed using actinide-doped borosilicate waste glasses [Savannah River Laboratory (SRL) 131 and SRL 202] to monitor the distribution of released radionuclides in tests at different SA/V. Solution results show the major effect of the SA/V to be dilution of reaction of products. Differences in the pH and silicic acid concentrations attained in tests at different SA/V then affect the reaction rate. Tests at low SA/V maintain leachate pH values similar to the initial leachant, while tests at higher SA/V result in higher leachate pH values being attained due to ion-exchange reactions. Transuranics released as the glass corrodes may exist in the leachate in concentrations far above their solubility limits by sorbing onto colloids, although the colloids may eventually settle out of solution. Transuranics also sorb onto the steel reaction vessel. The glass reaction progress can be characterized by three stages: (a) an initial stage where the reaction rate depends on the leachant pH, (b) an intermediate stage where the reaction slowsmore » toward a minimum rate as the leachate solution approaches saturation,'' and (c) a long-term stage where the reaction rate may be affected by the formation of secondary phases that control the solution chemistry. Tests at different SA/V cannot always be compared directly because the dominant reaction step and the observed reaction stage (initial, intermediate, or long-term) may not be the same.« less

A comparison of glass reaction at high and low glass surface/solution volume

The main immobilization technologies that have been demonstrated for radioactive waste disposal are cementation, bituminization, and vitrification. Vitrification is currently the most widely used technology for the treatment of high level radioactive wastes (HLW) throughout the world. Nations that have generated HLW are immobilizing in either alkali borosilicate glass or alkali aluminophosphate glass. The compositions of nuclear waste glasses are tailored for easy preparation and melting, avoidance of glass-in-glass phase separation, avoidance of uncontrolled crystallization, and acceptable chemical durability. Future waste generation is driven by interest in sources of clean energy. The development of advanced waste forms is a necessary component of the new nuclear power plant (NPP) flowsheets. A brief summary is given of existing and advanced waste forms and processing technologies.

Radioactive waste (RAW) conditioning, immobilization, and encapsulation processes and technologies: overview and advances

This review covers the corrosion interactions between different materials that are relevant to the disposal of high-level nuclear waste, in particular the waste forms and containers. The materials of interest are borosilicate glass, crystalline ceramics, metal alloys, and any corrosion products that might form. The available data show that these interactions depend on the structure, chemistry, thermodynamic history, and proximity of the materials in contact, as well as the environmental attributes, such as temperature, solution chemistry, and radiation. Several key mechanisms that govern these interactions are highlighted. Scientific gaps and open questions are summarized and discussed.

/pdf/review-of-corrosion-interactions-between-different-materials-4pyksn2fup.pdf

Review of corrosion interactions between different materials relevant to disposal of high-level nuclear waste

Solution compositional effects on the dissolution kinetics of borosilicate glass

This report provides an overview of progress during FY 1991 for the Technical Support Program that is part of the ANL Technology Support Activity for DOE, Environmental Restoration and Waste Management (EM). The purpose is to evaluate, before hot start-up of the Defenses Waste Processing Facility (DWPF) and the West Valley Demonstration Project (WVDP), factors that are likely to affect glass reaction in an unsaturated environment typical of what may be expected for the candidate Yucca Mountain repository site. Specific goals for the testing program include the following: (1) to review and evaluate available information on parameters that will be important in establishing the long-term performance of glass in a repository environment; (2) to perform testing to further quantify the effects of important variables where there are deficiencies in the available data; and (3) to initiate long-term testing that will bound glass performance under a range of conditions applicable to repository disposal.

/pdf/anl-technical-support-program-for-doe-environmental-2pf9shh5ot.pdf

ANL Technical Support Program for DOE Environmental Restoration and Waste Management. Annual report, October 1990--September 1991

A program was established for DOE Environmental Restoration and Waste Management (EM) to evaluate factors that are anticipated to affect waste glass reaction during repository disposal, especially in an unsaturated environment typical of what may be expected for the proposed Yucca Mountain repository site. This report covers progress in FY 1992 on the following tasks: 1. A compendium of the characteristics of high-level nuclear waste borosilicate glass has been written. 2. A critical review of important parameters that affect the reactivity of glass in an unsaturated environment is being prepared. 3. A series of tests has been started to evaluate the reactivity of fully radioactive glasses in a high-level waste repository environment and compare it to the reactivity of synthetic, nonradioactive glasses of similar composition. 4. The effect of radiation upon the durability of waste glasses at a high glass surface area-to-liquid volume (SA/V) ratio and a high gas-to-liquid volume ratio will be assessed. These tests address both vapor and high SA/V liquid conditions. 5. A series of tests is being performed to compare the extent of reaction of nuclear waste glasses at various SAN ratios. Such differences in the SAN ratio may significantly affect glass durability. 6. A series of natural analogue tests is being analyzed to demonstrate a meaningful relationship between experimental and natural alteration conditions. 7. Analytical electron microscopy (AEM), infrared spectroscopys and nuclear resonant profiling are being used to assess the glass/water reaction pathway by identifying intermediate phases that appear on the reacting glass. Additionally, colloids from the leach solutions are being studied using AEM. 8. A technical review of AEM results is being provided. 9. A study of water diffusion involving nuclear waste glasses is being performed. 10. A mechanistically based model is being developed to predict the performance of glass over repository-relevant time periods.

/pdf/anl-technical-support-program-for-doe-environmental-t2isn2qs9v.pdf

ANL technical support program for DOE Environmental Restoration and Waste Management. Annual report, October 1991--September 1992

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Solution compositional effects on the dissolution kinetics of borosilicate glass

ANL Technical Support Program for DOE Environmental Restoration and Waste Management. Annual report, October 1990--September 1991

ANL technical support program for DOE Environmental Restoration and Waste Management. Annual report, October 1991--September 1992