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Title: Microstructural characterisation and quantitative evaluation of nuclear graphite grades candidate for Generation-IV nuclear reactors
Author: Alnairi, Marzoqa Mabrok H.
ISNI:       0000 0004 8509 0630
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2019
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Nuclear Graphite is a complex material, and its microstructure depends strongly upon the starting materials, manufacturing processes, and operating conditions (Aitkaliyeva, 2017; Heijna et al., 2017; Marsden et al., 2017; Zhou et al., 2017a). Nuclear graphite plays a critical role as a moderator, a neutron reflector, and a core structural component in the operation of old generation reactors, still it is the potential candidates for very high-temperature reactors ((V)HTRs), (Generation-IV reactor). The understanding of nuclear graphite behaviour under irradiation is critical in helping select nuclear graphite grades that offer an enhancement in the safe and economical operation of (V)HTR, and as a basis for core design and safety evaluation. Hence, the experimental work described in this Thesis was designed to quantitatively study the changes in the crystallinity and porosity of virgin and neutron-irradiated nuclear graphite. After neutron irradiation, highly damaged regions (defects) were observed in which the thicknesses reached a few hundred nanometres. Various material characterisation techniques were used to characterise the nuclear graphite samples at various length scales (macroscale, microscale, and nanoscale), including X-ray diffraction (XRD), Raman spectroscopy, polarised light microscopy (PLM), Scanning Electron Microscopy (SEM), and Focussed Ion Beam–Scanning Electron Microscopy (FIB-SEM). PLM and SEM were used to study the changes in the shape and size of the filler particles and porosity in the whole structure, while PLM image analysis facilitated a qualitative and quantitative analysis of domains in different grades of virgin nuclear graphite (PGA, Gilsocarbon, PCEA, and PCIB). For the first time, FIB-SEM was also adopted to study the porosity in 3D of two different virgin nuclear graphite grades (PCEA and PCIB), which are possible candidate materials for (V)HTRs. The data was then compared to the results obtained from PLM and used to build up a 3D view after progressive polishing. As for XRD, it was used to investigate the deformation of the crystal lattice and quantify the build-up of the lattice micro-strains. Raman spectroscopy was performed to evaluate the change in crystallite coherence lengths of virgin and neutron-irradiated graphite, which gave information on the accumulation of defects within the basal plane and the introduction of basal plane fragmentation. The findings of this Thesis enhance current understanding of how the structure of nuclear graphite changes under neutron irradiation using a novel combination of techniques and by improving the use of existing techniques to study the changes in the porosity of nuclear graphite.
Supervisor: Drummond-Brydson, Richard ; Scott, Andrew ; Westwood, Aidan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available