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APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTTECHNOLOGY AND APPLIED RESEARCH AND DESIGN PERSPECTIVES ANDNEEDSThe grand technical challenge for nuclear waste disposal is the need to understand and predictwith sufficient confidence flow and transport processes and performance of materials(engineered and geologic) over geological time scales (at least to a million years), with long-termclimate changes and the impact of extreme events taken into account. It is important to enhancethe interaction of engineered barriers with natural systems, to maintain retrievability andmonitoring, and to prioritize/address the performance in a regulatory framework. The longevityof engineered barrier components depends on the quantity and chemistry of fluids in thesurrounding natural system. Finally, there is a need to establish a sound foundation for modelabstraction and stochastic approaches used for performance assessment (e.g., Helton et al. 1999).The following subsections address technology and applied research and development needs forgeologic disposal, focusing on the engineered and natural systems, cross-cutting areas, andquestions primarily addressed by geosciences. The research needs are derived from technologicaland scientific challenges associated with each element of the repository system.Engineered systems1. Engineered materials performanceA major component of the long-term strategy for safe disposal of nuclear waste is, first, tocompletely isolate the radionuclides in waste packages for long times, and then, to greatly retardthe egress and transport of radionuclides from breached packages. The materials used forisolating waste in the repository are an important component of the overall approach to thedesign of the repository system.Corrosion is a primary determinant of waste package performance in any storage or disposalenvironment and will control the delay time for radionuclide release and transport from the wastepackage. Intact waste packages fully contain and isolate radionuclides. Corrosion is the mostlikely degradation process that will determine when waste packages will be penetrated and theshape, size, and distribution of those penetrations. Thus, corrosion resistance is important to thelong-term performance of waste packages. The waste packages are manufactured from highlycorrosion-resistant metals, and the surface of these metals is protected by the formation of a selfhealing,passive layer. Based upon previous measurements of corrosion rates of passive metals, ifthe passive film remains stable, the waste packages can remain intact with no penetrationsresulting from corrosion for durations of tens of thousands and even hundreds of thousands ofyears (DOE 2002a; DOE 2002b).Materials optimization must be realized through a coordinated program of targeted, appliedresearch. Areas of materials research needed are:• Long-term behavior of protective, passive films• Composition and properties of moisture in contact with metal surfaces• Rate of penetration and extent of corrosion damage over extremely long times2. Radioactive waste form (which is the source for radionuclide releases)There are two important reasons for understanding radioactive waste form and near-fieldbehavior. First, almost all of the radioactive elements are initially within the waste forms, mainlyAppendix 1 • 34Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems
APPENDIX 1: TECHNICAL PERSPECTIVES RESOURCE DOCUMENTin the spent nuclear fuel and vitrified waste. Therefore, the waste form character itself placesboth initial as well as long-term limits on radionuclide release. Possible interactions of the wasteforms with the near-field environment, such as the corroded waste packages, place additionalconstraints on the long-term behavior and mobility of radionuclides (see Grambow et al. 2000and references therein; Poinssot et al. 2001 and references therein). An enhanced understandingand realistic estimates of the extent to which radionuclides will be retained in the waste form ornear-field environment reduce the demands on the performance of subsequent, far-field barriers.Realistic estimates of radionuclide release will also reduce the uncertainty in the total systemperformance assessment. Second, over long periods, after the engineered barriers have degraded,the waste form is a primary control on the release of radioactivity. Thus, it is essential to knowthe physical and chemical state of the waste form after hundreds of thousands of years.The goal of source term research is to enhance the understanding of the performance andevolution of nuclear waste forms (mainly spent nuclear fuel and nuclear waste glass) and toquantify the release of radionuclides in the evolving near-field environment expected in therepository. A basic understanding of the fundamental mechanisms of radionuclide release and aquantification of the release as repository conditions evolve over time, particularly at longertimes (>10 5 years), must be developed. Radionuclide release will be sensitive to variations intemperature, the radiation field, redox conditions, pH, P CO2 , surface area-to-solution volume, andthe presence of near-field materials. Among the important processes that can controlradionuclide release are:1. The kinetics of waste form corrosion2. The formation of secondary, alteration phases3. The reduction and sorption onto the surfaces of near-field materials (see Figure 11)In addition, biogeochemical processes and microbial activity may influence the geochemicalenvironment and promote colloid formation with resultant impacts on waste form stability andradionuclide transport.The prediction of the long-term behavior of nuclear waste forms cannot be based entirely onmodels of laboratory results that are extrapolated to long periods; hence, integration of multiplelines of evidence (e.g., results from natural analogue studies) is required to clarify the scientificbasis for waste form degradation mechanisms in relation to source term models (see Lutze andEwing 1988 and references therein).The nuclear waste forms, spent nuclear fuel and nuclear waste glass, may serve differentfunctions at different times in the multi-barrier system of a geologic repository (see Grambow etal. 2000 and references therein; Shoesmith et al. 2003 and references therein; Lutze and Ewing1988 and references therein; National Research Council 1996; Van Iseghem 2001 and referencestherein). The waste form may be:1. the sole barrier to release of radionuclides to the biosphere2. an effective, but not the primary, barrier to radionuclide release3. a solid-medium for transportation and temporary storage (National Research Council 1996.)Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems Appendix 1 • 35
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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: CHEMICAL MIGRATION PR
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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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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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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
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APPENDIX 4: ACRONYMS AND ABBREVIATI
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