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Irradiated Graphite Waste: Analysis and Modelling of Radionuclide Production with a View to Long Term Disposal

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Irradiated Graphite Waste: Analysis and Modelling of Radionuclide Production with a View to Long Term Disposal IRRADIATED GRAPHITE WASTE: ANALYSIS AND MODELLING OF RADIONUCLIDE PRODUCTION WITH A VIEW TO LONG TERM DISPOSAL A thesis submitted to the University of Manchester for the degree of Doctor of Engineering in the Faculty of Engineering and Physical Sciences 2014 Greg Black School of Mechanical, Aerospace and Civil Engineering The University of Manchester Table of Contents Table of Contents ................................................................................................................ 2 List of Figures ....................................................................................................................... 6 List of Tables ...................................................................................................................... 11 Abstract ................................................................................................................................ 14 Declaration .......................................................................................................................... 15 Copyright Statement .......................................................................................................... 16 Acknowledgements ............................................................................................................ 17 1. Introduction ............................................................................................................. 18 1.1 The use of Graphite in Nuclear Reactors ...................................................... 18 1.1.1 Nuclear Fission ............................................................................................. 18 1.1.2 Nuclear Grade Graphite ............................................................................. 20 1.1.3 Graphite Moderated Reactors in the UK................................................. 22 1.2 Origin of Radioactivity in Graphite Wastes ................................................... 23 1.2.1 Elemental Composition of Graphite ........................................................ 23 1.2.2 Production Pathways ................................................................................... 24 1.2.3 Contamination in the Reactor Circuit....................................................... 24 1.2.4 Radiolytic Oxidation .................................................................................... 25 1.3 Predicting the Radiological Inventory of Graphite Wastes......................... 25 1.4 Graphite Wastes Arising in the UK ................................................................ 29 1.5 Summary of Issues ............................................................................................. 31 1.6 Funding of Research .......................................................................................... 32 1.7 Research Objectives ........................................................................................... 32 1.8 Summary of Chapter 1....................................................................................... 33 2. Literature Review .................................................................................................... 34 2.1 Graphite Inventory Studies............................................................................... 34 2.1.1 Summary of Graphite Inventory Studies ................................................. 42 University of Manchester Greg Black 2 2.2 Operational Conditions in UK Graphite Moderated Reactors .................. 43 2.2.1 British Experimental Pile-Zero (BEPO) .................................................. 43 2.2.2 Magnox Reactors .......................................................................................... 46 2.2.3 Advanced Gas-cooled Reactors (AGRs) .................................................. 54 2.3 Impurity Concentrations in UK Nuclear Graphite Grades ........................ 57 2.3.1 Graphite used in BEPO .............................................................................. 57 2.3.2 Graphite used in the Magnox Reactors .................................................... 58 2.3.3 Graphite used in the AGRs ........................................................................ 61 2.4 Summary of Chapter 2....................................................................................... 63 3. Context of Research ............................................................................................... 65 3.1 The Office for Nuclear Regulation (ONR) ................................................... 65 3.1.1 The Operating Environment of ONR ..................................................... 66 3.2 Structure of Nuclear Industry in the UK ....................................................... 68 3.3 Nuclear Waste Management in the UK.......................................................... 69 3.3.1 Graphite Waste Management ..................................................................... 71 3.4 Graphite Waste Management Research .......................................................... 72 3.5 Summary of Chapter 3....................................................................................... 75 4. Experimental Characterisation ............................................................................. 76 4.1 Introduction ........................................................................................................ 76 4.2 Irradiated Graphite Samples ............................................................................. 76 4.2.1 British Experimental Pile Zero Samples .................................................. 76 4.2.2 Oldbury Magnox Reactor Samples ........................................................... 78 4.2.1 Wylfa Magnox Reactor Samples ................................................................ 79 4.2.2 Hinkley Point-B AGR Samples ................................................................. 80 4.2.3 Sample Preparation ...................................................................................... 81 4.3 Autoradiography Methodology ........................................................................ 81 4.4 Beta Isotope Characterisation Methodology ................................................. 82 4.5 Gamma Spectroscopy Methodology ............................................................... 82 University of Manchester Greg Black 3 4.5.1 Gamma-ray Interaction and Detection Principles .................................. 83 4.5.2 Gamma Spectroscopy Equipment ............................................................ 89 4.5.3 Equipment Calibration ................................................................................ 89 4.5.4 Spectrum analysis ......................................................................................... 91 4.6 Autoradiography Results and Discussion ...................................................... 93 4.7 Beta Characterisation Results and Discussion ............................................... 95 4.8 Gamma Spectroscopy Results and Discussion ............................................. 97 4.8.1 Round Robin Test (RRT) Validation ........................................................ 97 4.8.2 Gamma analysis of BEPO samples .......................................................... 98 4.8.3 Gamma analysis of Wylfa samples .......................................................... 100 4.8.4 Gamma analysis of Oldbury samples ..................................................... 105 4.8.5 Gamma analysis of Hinkley Point-B samples ....................................... 112 4.9 Summary of Chapter 4..................................................................................... 114 5. Activation Calculations ........................................................................................ 116 5.1 Introduction ...................................................................................................... 116 5.2 Computational Methods.................................................................................. 117 5.2.1 Neutron Flux Calculations........................................................................ 117 5.2.2 Activation Calculation ............................................................................... 120 5.3 Neutronic Modelling ........................................................................................ 122 5.3.1 Wylfa Reactor Calculations ....................................................................... 123 5.3.2 Oldbury Reactor Calculations .................................................................. 138 5.3.3 BEPO Reactor Calculations ..................................................................... 140 5.3.4 Hinkley Point-B Reactor Calculations .................................................... 141 5.4 Activation calculations ..................................................................................... 142 5.5 Development of Calculation Methodology ................................................. 144 5.5.1 Stage 1 .......................................................................................................... 144 5.5.2 Stage 2 .......................................................................................................... 145 5.5.3 Stage 3 .......................................................................................................... 146 University of Manchester Greg Black 4 5.6 Stage 1- Results and Discussion ..................................................................... 147 5.6.1 Wylfa Stage
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