Density Functional and Dislocation Theory of Graphite Related to Nuclear Materials

This thesis concerns the physicochemical understanding of radiation damage in graphite. It is structured in two parts, the first being a foundation of elastic and bonding properties in graphite and its intercalation compound with Bromine. The second builds on this with dislocation theory to analyse dimensional change and stored elastic energy. Part 1: Density functional theory (DFT) in the local density approximation (LDA) has been used to study the elastic properties of hexagonal graphite and of Bromine intercalated graphite. The second and third order elastic constants of graphite have been calculated ab initio. The internal strain has been considered and the results include partial and total elastic constant results. The nature of the interlayer binding energy has been studied using DFT with LDA. The London dispersion forces have been applied to the DFT results using a simple Lennard-Jones type model. The results of this study are in good agreement with other theoretical and experimental studies. The zero point energy has also been calculated and its effects applied to the interlayer energy and the related elastic constant C33 . This constant has also been calculated for stage-1 and stage-2 Bromine-intercalated graphite in order to aid interpretation of intercalation experiments which try to emulate with Br intercalation, the c-axis dimensional change that occurs from radiation damage. Part 2: A two dimensional dislocation model has been written based on both basal and prismatic dislocations. The model elucidates the stress fields arising from irradiation damage in graphite in either the standard damage model based on prismatic loops or the newly proposed model based on basal dislocations. It illustrates the different physical processes underlying dimensional change and should enable it to be quantified. The energy of the stress fields is calculated and found to be comparable to stored energies measured for graphite irradiated below 250C.