Salt Disposal of Heat-Generating Nuclear Waste

CONTENTS
1 Introduction ............................................................................................................................... 1
1.1 Background and Regulatory Framework ......................................................................... 2
1.2 Salt Formations in the United States ................................................................................ 5
1.3 History of Salt Disposal Research for Heat-Generating Nuclear Waste ......................... 8
1.4 Analogues for Salt Disposal........................................................................................... 10
2 Technical Basis And Characterization .................................................................................... 15
2.1 Nuclear Waste Characteristics ....................................................................................... 15
2.2 Salt Repository Design .................................................................................................. 18
2.2.1 Concept of Disposal for HLW in Salt .............................................................. 19
2.3 Seals ............................................................................................................................... 20
2.4 Thermal-Hydrologic-Mechanical Conditions in the Host Rock .................................... 24
2.4.1 Excavation/Construction Effects ...................................................................... 24
2.4.2 Thermal Effects ................................................................................................ 34
2.4.3 Coupled Thermal-Hydrologic-Mechanical Effects .......................................... 37
2.5 Chemical Conditions in the Host Rock .......................................................................... 42
2.5.1 The Thermal Period .......................................................................................... 42
2.5.2 After the Thermal Period .................................................................................. 44
2.5.3 State-of-the-Art Geochemical Modeling .......................................................... 47
2.5.4 Coupled Reactive Transport Modeling ............................................................ 49
2.5.5 Radionuclide Transport .................................................................................... 49
2.5.6 International Collaboration on Salt Repository Chemistry .............................. 49
3 Performance Analysis for HLW Disposal In Salt ................................................................... 51
3.1 Identification of Relevant Features, Events, and Processes ........................................... 52
3.1.1 Catalogs of FEPs .............................................................................................. 53
3.2 Scenario Selection .......................................................................................................... 54
3.2.1 Scenario for an Isothermal “Cool” Salt Repository ......................................... 54
3.2.2 Scenario for a Thermal “Hot” Salt Repository ................................................. 54
3.2.3 Important FEPs for a “Hot” Salt Repository .................................................... 56
4 A Performance-Based Directed Research Program ................................................................ 57
4.1 Thermal-Hydrologic-Mechanical Response of Salt....................................................... 58
4.2 DRZ Evolution and Healing .......................................................................................... 58
4.3 Consolidation of Backfill Materials at Elevated Temperature ...................................... 59
4.4 Availability and Movement of Brine and Vapor Phases ............................................... 60
4.5 Geochemical Environment............................................................................................. 60
4.6 Radionuclide Solubility Controls and Transport Mechanisms ...................................... 61
4.7 Findings of the U.S./German Workshop on Salt Repository Research, Design and
Operation........................................................................................................................ 61
4.7.1 Description of the Work ................................................................................... 62
4.7.2 Future Direction ............................................................................................... 64
5 Summary and Recommendations ........................................................................................... 67
5.1 Summary of Findings ..................................................................................................... 67
5.2 Recommendations for Continued Research ................................................................... 69
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