NANOSCALE STRUCTURE DAMAGE IN IRRADIATED W-TA ALLOYS FOR NUCLEAR FUSION REACTORS A thesis submitted to the University of Manchester for the degree of Doctor of Philosophy in the Faculty of Science and Engineering 2018 Iuliia Ipatova School of Materials TABLE OF CONTENTS List of figures .............................................................................................................................. 4 List of tables .............................................................................................................................. 12 Abstract ..................................................................................................................................... 14 Declaration ................................................................................................................................ 15 Copyright Statement ................................................................................................................. 16 Acknowledgements ................................................................................................................... 17 1 Introduction ........................................................................................................................ 18 1.1 Nuclear fusion reactors ....................................................................................................... 18 1.1.1 Plasma facing materials (PFM) .................................................................................. 26 1.2 Challenges of current material selection for fusion ............................................................ 32 1.3 Material degradation during reactor operation ................................................................... 35 1.4 References ........................................................................................................................... 40 2 Material properties and degradation mechanisms of W, Ta and their alloys ...................... 44 2.1 Fundamental properties ....................................................................................................... 44 2.1.1 Crystallography ........................................................................................................ 44 2.1.2 Phase diagram ......................................................................................................... 47 2.1.3 Diffusion .................................................................................................................. 48 2.1.4 Physical properties ................................................................................................... 54 2.2 Microstructure ..................................................................................................................... 57 2.2.1 Recovery, recrystallization and grain growth .......................................................... 57 2.2.2 Dislocation structures ............................................................................................... 60 2.3 Mechanical properties ......................................................................................................... 66 2.4 Radiation damage ................................................................................................................ 69 2.4.1 Radiation-matter interaction ..................................................................................... 69 2.4.2 Quantification of cascade damage ........................................................................... 72 2.4.3 Correlating neutron and ion irradiation damage ...................................................... 74 2.4.4 Radiation-induced hardening and embrittlement ..................................................... 78 2.4.5 Radiation-induced void swelling .............................................................................. 82 2.4.6 Nuclear transmutation reactions ............................................................................... 88 2.5 Main research tasks, limitations found in literature and objectives of the project ............. 91 2.5.1 Current status of the work in the literature ............................................................... 91 2.5.2 Limitations ............................................................................................................... 92 2 2.5.3 Thesis objectives ...................................................................................................... 93 2.6 References ........................................................................................................................... 94 3 Experimental methods ...................................................................................................... 102 3.1 Sample preparation ........................................................................................................... 102 3.2 Ion irradiation experiments ............................................................................................... 106 3.3 Characterisation methods .................................................................................................. 110 3.3.1 Optical microscopy ................................................................................................ 110 3.3.2 Electron-matter interaction ..................................................................................... 111 3.3.3 Scanning electron microscopy ............................................................................... 113 3.3.4 Transmission electron microscopy ......................................................................... 117 3.3.4.1 Diffraction contrast mechanisms ................................................................ 119 3.3.4.2 Contrast of dislocation loops and voids ...................................................... 123 3.3.4.3 Burgers vector analysis ............................................................................... 124 3.3.4.4 Convergent beam electron diffraction technique (CBED) ........................ 126 3.3.5 Hardness measurements ......................................................................................... 129 3.4 References ......................................................................................................................... 132 4 Structural defect accumulation in tungsten and tungsten-5wt.% tantalum under incremental proton damage ............................................................................................... 134 5 Thermal evolution of the proton-irradiated structure in tungsten-5wt.% tantalum ................ ........................................................................................................................................... 152 6 Lattice damage formation in irradiated tantalum at variable temperatures ...................... 163 7 Radiation-induced void formation and ordering in Ta–W alloys ..................................... 181 8 Overall discussion ............................................................................................................. 200 9 Conclusions ....................................................................................................................... 206 10 Future work ....................................................................................................................... 208 3 List of Figures 1.1 Binding energy per nucleon as a function of the mass number ........................................ 19 1.2 Design of an inertial fusion confinement (IFC) reactor .................................................... 21 1.3 Diagram of a beamline at NIF .......................................................................................... 22 1.4 Simplified diagram for one LMJ beam line showing the main equipment involved during the alignment phase prior to the shot ................................................................................ 22 1.5 Schematic of fast ignition fusion ...................................................................................... 23 1.6 Two concepts of toroidal MCF ......................................................................................... 23 1.7 The main ITER superconducting magnet system view .................................................... 24 1.8 Power path to the commercial fusion reactor ................................................................... 25 1.9 Schematic representation of ITER with key parts highlighted ......................................... 25 1.10 View of the vacuum vessel with selected positions of blanket and divertor ................... 26 1.11 Cross-sectional view of the fusion nuclear components in tokamak wall ....................... 27 1.12 Overview of the operating temperatures and radiation damage levels expected after 60 years of operation for different fission and fusion nuclear reactors ................................. 27 1.13 Plasma-facing components corresponding to the ITER cross-section; and view of the divertor assembly .............................................................................................................. 28 1.14 Operating temperature windows of candidate fusion materials based on radiation damage and thermal creep considerations ........................................................................ 30 1.15 SEM images of cracks formed on the tungsten surface after different numbers of plasma pulses at 0.45 MJ m−2 ......................................................................................................