THERMAL TREATMENT OF OLDBURY MAGNOX REACTOR IRRADIATED GRAPHITE A thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Engineering and Physical Sciences 2015 Robert Numa Worth School of Mechanical, Aerospace and Civil Engineering The University of Manchester - 2 - Table of Contents Table of Contents ..................................................................................................................... 3 List of Figures ........................................................................................................................... 7 List of Tables .......................................................................................................................... 12 Abstract .................................................................................................................................. 13 Declaration ............................................................................................................................. 14 Copyright Statement .............................................................................................................. 15 Acknowledgments .................................................................................................................. 16 Thesis Structure ..................................................................................................................... 17 1. Introduction ....................................................................................................................... 19 1.1 Graphite: The Material ................................................................................................. 22 1.2 Neutron Moderators .................................................................................................... 24 1.3 Graphite as a UK Moderator Material ......................................................................... 27 1.4 Current Nuclear Graphite Waste in the UK.................................................................. 31 1.4.1 UK Classification of Radioactive Waste ................................................................. 31 1.4.2 UK Total Graphite Waste ...................................................................................... 32 1.5 Irradiated Graphite Waste Management in the UK ..................................................... 34 1.6 International Irradiated Graphite Waste Research ..................................................... 35 1.7 Summary of Section 1 .................................................................................................. 36 2. Literature Review ............................................................................................................... 38 2.1 The Manufacturing Process of Graphite ...................................................................... 38 2.1.1 The Process ........................................................................................................... 39 2.1.2 Summary of Section 2.1 ........................................................................................ 47 2.2 Production of Radioactivity in Graphite ....................................................................... 48 2.2.1 Activation .............................................................................................................. 48 2.2.2 Radioactivity in Graphite ....................................................................................... 49 2.2.4 Summary of Section 2.2 ........................................................................................ 56 2.3 Production and Location of Carbon-14 in Irradiated Graphite .................................... 57 - 3 - 2.3.1 Sensitivity to Nitrogen ........................................................................................... 59 2.3.2 Nitrogen Impurity Levels ....................................................................................... 60 2.3.3 Carbon-14 Production Pathway Analysis .............................................................. 63 2.3.4 Consequent Location of Produced Carbon-14 ...................................................... 65 2.3.5 Alternative Sources of Carbon-14 in Irradiated Graphite ..................................... 74 2.3.6 Summary of Section 2.3 ........................................................................................ 76 2.4 Thermal Oxidation ........................................................................................................ 78 2.4.1 Introduction to Thermal Oxidation ....................................................................... 78 2.4.2 Carbon Oxidation Reactions .................................................................................. 79 2.4.3 Oxidation Mechanisms and Influencing Factors ................................................... 82 2.4.4 Regimes of Oxidation ............................................................................................ 84 2.4.5 Effect of Pressure .................................................................................................. 88 2.4.6 Single Layer Oxidation ........................................................................................... 89 2.4.7 Oxidation of Irradiated Graphite ........................................................................... 92 2.4.8 Oxidation of Carbonaceous Deposits .................................................................... 96 2.4.9 Graphite Oxidation by Impurity Catalysis .............................................................. 96 2.4.10 Summary of Section 2.4 ...................................................................................... 98 2.5 Thermal Treatment .................................................................................................... 100 2.5.1 Inert Atmosphere Treatment .............................................................................. 100 2.5.2 Oxidising Atmosphere Treatment ....................................................................... 109 2.5.3 Thermal Treatment of Graphite: A Model .......................................................... 116 2.5.4 Summary of Section 2.5 ...................................................................................... 121 2.6 Major Conclusions of the Literature Review .............................................................. 123 2.7 Research Statement: Aims and Objectives ................................................................ 126 3. Experimental Methodology .............................................................................................. 127 3.1 Samples: Irradiated Graphite Samples and Provenance ............................................ 127 3.2 Methodology .............................................................................................................. 131 3.2.1 Thermal Treatment ............................................................................................. 131 - 4 - 3.2.1.1 Irradiated Graphite Sample Preparation ..................................................... 132 3.2.1.2 Liquid Scintillation Counting ........................................................................ 133 3.2.1.3 Thermal Treatment Apparatus and Method ............................................... 136 3.2.2 Characterisation Techniques............................................................................... 142 3.2.2.1 Germanium Gamma Spectrometry .............................................................. 142 3.2.2.2 Autoradiography .......................................................................................... 148 3.2.2.3 Metrology ..................................................................................................... 150 3.3 Data Validation........................................................................................................... 152 3.3.1 Thermal Treatment System Adaptations and Validation .................................... 152 3.3.1.1 Adaptations to Existing Process ................................................................... 152 3.3.1.2 Recovery Checks .......................................................................................... 153 3.3.1.3 Sample Temperature Profile Validation....................................................... 159 3.3.1.4 Gas Composition Determination ................................................................. 163 3.3.2 Data Validation for Other Characterisation Techniques ..................................... 165 3.3.2.1 Germanium Gamma Spectrometry .............................................................. 165 3.3.2.1.1 Energy Calibration ................................................................................. 165 3.3.2.1.2 Scan Time Determination ..................................................................... 167 3.3.2.2 Autoradiography .......................................................................................... 169 3.3.2.3 Metrology ..................................................................................................... 170 3.3.2.3.1 Validation of Mass Balances ................................................................. 170 3.3.2.3.2 Geometry Measurements ..................................................................... 173 3.3.2.4 Liquid Scintillation Counting ........................................................................ 174 3.3.3 Thermal Treatment Uncertainty Calculations ....................................................