The Oxidation of A3-3 Matrix Material in a CO₂ Atmosphere in Support of a Nuclear Battery Type Reactor Design

A significant attraction of a small-scale self-contained nuclear reactor that requires limited human intervention is a reduction in the required infrastructure costs through on-site generation. The option of CO₂ coolant rather than helium within a VHTR-type design has been considered, as the use of CO₂ results in a higher potential for convective cooling, and lower costs. Within a CO₂ coolant environment, graphite components are subject to oxidation, both through radiolysis and potentially thermally, and for modern nuclear graphites alongside the graphitic matrix A3-3, this behaviour must be considered as part of the design process. This research presents the results from irradiation experiments within pressurised sealed quartz ampoules, which have been conducted at The Technical University of Delft, alongside thermal oxidation experiments and material characterisation at The University of Manchester. Characterisation work has been undertaken to understand changes to the microstructure in terms of pre- and post-oxidation. The techniques applied include laser con-focal microscopy and helium pycnometry, with SEM and X-ray tomography planned for future work. The effects of oxidation on A3-3 matrix are compared to two grades of nuclear graphite: NBG-18 and Gilsocarbon with the effects of oxidation on TRISO coated particles also planned for investigation.