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APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTFigure 11. Schematic illustration of the fundamental processes used as a framework fordefinition of the source term for spent nuclear fuel waste form (after Bruno and Ewing 2006).The fuel assembly represents one used in a typical light water nuclear reactor.At Yucca Mountain, for example, the waste form is one of a series of barriers, engineered andgeologic, to the release of radionuclides. The effectiveness of these barriers varies over time, asdoes the inventory of radioactive elements, the temperature, and the radiation field. Immediatelyafter emplacement in a geologic repository, the waste forms are protected from contact withwater by the waste package. During this time (hundreds to thousands of years), the waste formsexperience the highest temperatures and most intense radiation fields, but the waste forms are notin chemical contact with the surrounding geologic medium. The waste forms are only exposed tooutside water after the waste package has been breached. At intermediate times (thousands totens of thousands of years), some fraction of the waste packages is assumed to have failed, andthe waste forms will be in contact with water (or water vapor) and air. This represents the firstpossibility for release of radionuclides from the waste forms. At the longest time periods (tens ofthousands to hundreds of thousands of years), most of the waste forms will be exposed to theambient, geochemical/hydrological conditions. At this stage, one may expect extensive alterationof the waste form and hydrochemical interactions with corroded waste packages and thesurrounding geology (Allan and Nuttall 1997).By focusing on the changing conditions over time, identifying the processes within each timeinterval, and with attention to the radionuclides that are the major contributors to dose, newresearch will be able to improve fundamental understanding of source term processes. Theresearch addresses the need to understand the physical and chemical processes as a function oftime (see Figure 11 for a portrayal of potential processes). The research needs presented here areAppendix 1 • 36Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems
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
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TABLE OF CONTENTSBasic Science Chal
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TABLE OF CONTENTSTechnology Impacts
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EXECUTIVE SUMMARYpurpose of linking
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INTRODUCTIONINTRODUCTIONWorldwide e
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INTRODUCTIONway into the rock forma
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PANEL REPORTSMULTIPHASE FLUID TRANS
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PANEL REPORT: MULTIPHASE FLUID TRAN
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PANEL REPORT: MODELING AND SIMULATI
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GRAND CHALLENGE: COMPUTATIONAL THER
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GRAND CHALLENGE:INTEGRATED CHARACTE
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GRAND CHALLENGE: SIMULATION OF MULT
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PRIORITY RESEARCH DIRECTION:MINERAL
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PRIORITY RESEARCH DIRECTION:NANOPAR
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PRIORITY RESEARCH DIRECTION:DYNAMIC
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PRIORITY RESEARCH DIRECTION: TRANSP
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PRIORITY RESEARCH DIRECTION:FLUID-I
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PRIORITY RESEARCH DIRECTION:BIOGEOC
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CROSSCUTTING ISSUE:THE MICROSOPIC B
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CROSSCUTTING ISSUE:THE MICROSOPIC B
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CROSSCUTTING ISSUE:HIGHLY REACTIVE
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CROSSCUTTING ISSUE:THERMODYNAMICS O
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REFERENCESBenner, S.G., Hansel, C.M
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REFERENCESChen, J., Hubbard, S., Pe
Page 188 and 189: REFERENCESEnnis-King, J., Preston,
Page 190 and 191: REFERENCESHolman, H.-Y., Perry, D.L
Page 192 and 193: REFERENCESLi, L., and Tchelepi, H.A
Page 194 and 195: REFERENCESNeal, A.L., Techkarnjanar
Page 196 and 197: REFERENCESReeves, P.C., and Celia,
Page 198 and 199: REFERENCESSteefel, C.I., DePaolo, D
Page 200 and 201: REFERENCESZachara, J.M., Ainsworth,
Page 202 and 203: AppendicesBasic Research Needs for
Page 204 and 205: APPENDIX 1: TECHNICAL PERSPECTIVES
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