Basic Research Needs for Geosciences - Energetics Meetings and ...

APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTfocused on spent nuclear fuel; other waste forms (e.g., glasses, ceramics, metals) would havesimilar needs but some specifics would change (e.g., no role of cladding for other waste forms).A closed fuel cycle requires a geologic repository for disposal of long-lived fission products andpotentially very small amounts of actinides, the latter being from minor separations processlosses. Potential waste form materials—oxides, glasses, and/or metals—containing radionuclidesare key components of the repository system. The potentially significant doses from the encasedradionuclides require long-term isolation in durable waste forms. As part of efforts in the U.S.and worldwide to develop advanced nuclear fuel cycles, additional research is required toidentify potential advanced waste form materials (see Lutze and Ewing 1988 and referencestherein; Ewing et al. 2004). If candidate advanced waste form materials are further developed,focused work to increase understanding of waste form performance in complex geologic settingsis needed. Prediction of geologic repository performance to 10 4 years (and even 10 6 years), andthe role of the source term in long-term safety, represent unprecedented scientific challenges.To provide durable waste forms and demonstrate their long-term performance, the behavior ofmaterials must be understood at a level of fundamental knowledge and predictability that couldallow for reduction in the conservatism of engineered system designs, while still achieving therequired safety margins, and perhaps lowering repository costs. The waste form materials formcomplex multi-component dynamic systems that evolve in time over a wide range of conditionsincluding high radiation fields, high temperatures, and potentially corrosive chemicalenvironments (see Lutze and Ewing 1988 and references therein; Smith et al. 1992).Fundamental understanding of the properties of waste forms is essential to predicting their longtermbehavior and can only result from closely coupled theory, modeling, and experimentation.A fundamental and integrated experimental and modeling approach to source term processes, asdescribed above for spent nuclear fuel, can also be readily applied to development of advancedwaste forms as part of a closed nuclear fuel cycle. Specifically, a fundamental understanding ofthe stability of candidate advanced waste form materials in high temperature/high radiationenvironments and near-field geochemical/hydrologic processes could enable development ofwaste forms “tailored” to specific geologic settings (Lutze and Ewing 1988). Closing the fuelcycle will generate a new class of waste forms with a different chemical composition, differentthermal and radiation profiles and time evolutions, and different requirements for wastepackaging, interim storage, and long-term disposition. Technical challenges include:1. Immobilization of high-heat fission products (cesium, strontium) and long-lived fissionproducts (iodine, technetium) in tailored storage/waste forms2. Higher fission-product loadings for ceramic waste-form technologies3. Determination of thermodynamic and thermophysical properties of actinide-containing wasteforms, including radiation effects, transport, and interfacial interactions4. New geologic waste-form materials tailored for reduced actinides and increased fissionproductsSee DOE 2006a for detailed discussions.Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems Appendix 1 • 37