Igneous Activity at Yucca Mountain: Technical Basis for Decision Making

Igneous Activity at Yucca Mountain: Technical Basis for Decision Making

Igneous Activity at Yucca Mountain: Technical Basis for Decisionmaking A Report Prepared by the Advisory Committee on Nuclear Waste and Materials U.S. Nuclear Regulatory Commission Looking south along the crest of Yucca Mountain, Nevada, towards Amargosa Valley and the extinct Lathrop Wells volcano. June 2007 CONTENTS Contents……………...................................................................................................................... ii Executive Summary ..................................................................................................................... xi Acknowledgements................................................................................................................... xxv 1. Introduction…………………………………………………………………………… ...............2 1.1. Igneous Activity and the Proposed Yucca Mountain Repository...........................2 1.2. Objective and Rationale of Report.........................................................................4 1.3. Scope of Report ....................................................................................................6 1.4. Content and Organization of Report......................................................................6 1.5. Report Preparation Process ................................................................................10 1.6. Constraints on the Report ...................................................................................11 1.7. Previous Reviews of Igneous Activity Technical Bases ......................................13 2. Brief Geologic History of the Yucca Mountain Region ....................................................15 3. Overview of Igneous Activity Processes .........................................................................23 3.1. Introduction..........................................................................................................23 3.2. Origin and Nature of Igneous Activity..................................................................23 3.2.1. Magma Generation ..............................................................................................23 3.2.2. Magma Composition ............................................................................................24 3.2.3. Volcanos and Their Products...............................................................................25 3.3. Magma/Repository Interaction ............................................................................27 3.3.1. Nature of Magma Ascent .....................................................................................27 3.3.2. Key Features of Magmatic Dikes.........................................................................27 3.3.3. Basic Nature of Eruptive Event............................................................................28 3.3.4. Magma Interaction with Repository and Waste Packages ..................................28 3.4. Dispersal of Contaminated Ash...........................................................................33 3.4.1. How is Ash Dispersed?........................................................................................34 3.4.2. How does Ash become Contaminated? ..............................................................34 3.5. Remobilization and Resuspension of Contaminated Ash....................................35 4. Nature of Potential Igneous Events in the Yucca Mountain Region................................38 4.1. Introduction..........................................................................................................38 4.2. Volcanic Analogs.................................................................................................38 4.3. NRC and DOE Perspectives ...............................................................................42 4.3.1. NRC/DOE KTI Agreement on the Likely Range of Tephra Volumes...................42 4.3.2. DOE Approach to Event Definition.......................................................................43 4.3.3. NRC Approach to Event Definition.......................................................................46 4.3.4. EPRI Approach to Event Definition......................................................................47 4.3.5. Comments on Hydromagmatic (Maar) Volcanism...............................................48 4.4. Summary .............................................................................................................49 5. Probability of Potential Igneous Activity ..........................................................................54 5.1. Introduction..........................................................................................................54 ii 5.2. Spatial and Temporal Distribution of Igneous Events..........................................55 5.2.1. Introduction ..........................................................................................................55 5.2.2. Surface Exposures...............................................................................................55 5.2.3. Known Occurrences of Buried Basalts ................................................................58 5.2.4. Undetected Igneous Activity ................................................................................62 5.2.5. Change in Basaltic Volcanism with Time.............................................................63 5.3. Time Period Used in Extrapolation of Igneous Activity........................................67 5.4. Controls on Occurrence of Igneous Activity ........................................................67 5.5. Calculation Methods............................................................................................70 5.5.1. Physical Precursors .............................................................................................70 5.5.2. Proposed Linkages to Other Volcanic Zones ......................................................71 5.5.3. Expert Elicitation ..................................................................................................72 5.5.4. Mathematical and Statistical Techniques ............................................................75 5.5.4.1. Data-Based Approach ......................................................................75 5.5.4.2. Locally Homogeneous Spatial and Temporal Models......................76 5.5.4.3. Nonhomogeneous Spatial Models ...................................................76 5.5.4.3.1. Parametric Spatial Density Function................................76 5.5.4.3.2. Nonparametric Spatial Density Function..........................77 5.5.4.4. Nonhomogeneous Temporal Models ...............................................77 5.6. Treatment of Probability in Performance Assessments.......................................77 5.6.1. DOE Analysis..........................................................................................................78 5.6.2. EPRI Analysis .........................................................................................................78 5.6.3. NRC Analysis..........................................................................................................78 5.7. Perspectives on Igneous Activity Probability.......................................................79 5.7.1. NRC Analysis.......................................................................................................84 5.7.2. DOE Analysis.......................................................................................................85 5.7.3. Probabilistic Volcanic Hazard Analysis (PVHA)...................................................86 5.7.4. DOE Igneous Consequence Peer Review Panel (ICPR) ....................................86 5.7.5. Electric Power Research Institute (EPRI) ............................................................87 5.7.6. State of Nevada Contractors................................................................................88 5.7.7. Nuclear Energy Institute (NEI) .............................................................................90 5.7.8. Other Estimates of Probability .............................................................................90 5.7.9. ACNW&M Observations of PVHA-U....................................................................91 5.8 Summary (Igneous Event Probability).......................................................................91 6. Consequences of Igneous Activity Intersecting the Repository ......................................94 6.1. Introduction..........................................................................................................94 6.2. Effects from an Intrusive Event (Magma/Drift/Waste Interaction)........................94 6.2.1. Critical Magmatic Aspects....................................................................................94 6.2.1.1. Magma Composition.........................................................................94 6.2.1.2. Magma Viscosity ..............................................................................95 6.2.1.3. Perspectives on Magma Viscosity..................................................100 6.2.1.3.1. DOE Perspective............................................................100 6.2.1.3.2. EPRI Perspective ..........................................................101 6.2.1.3.3. Additional Comments on Magma Viscosity....................102 6.2.2. DOE, EPRI, and NRC Perspectives on the Magma/Waste Package Interaction ..........................................................................................................105

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