Examining the thermal properties of unirradiated nuclear grade graphite between 750 and 2500 K

• Published in: Journal of nuclear materials 2020-09, Vol.538, p.152176, Article 152176
• Main Authors: Pavlov, T.R., Lestak, M., Wenman, M.R., Vlahovic, L., Robba, D., Cambriani, A., Staicu, D., Dahms, E., Ernstberger, M., Brown, M., Bradford, M.R., Konings, R.J.M., Grimes, R.W.
• Format: Article
• Language: English
• Subjects: Computed tomography; Conductivity; Emissivity; Fillers; Gas cooled reactors; Graphite; Graphitization; Heat conductivity; Heat transfer; High temperature; Manufacturing industry; Microstructure; Morphology; Nuclear fuels; Platelets (materials); Scanning electron microscopy; Specific heat; Spectral emissivity; Thermal conductivity; Thermal diffusivity; Thermal properties; Thermodynamic properties
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2020.152176

This study presents the first high temperature measurements (between 750 K and 2500 K) of thermal conductivity, thermal diffusivity, specific heat and spectral emissivity of virgin graphite samples (type IM1-24) from advanced gas-cooled reactor (AGR) fuel assembly bricks. Scanning electron microscope (SEM) and X-ray computed tomography (XRT) techniques were used to verify the presence of Gilsocarbon filler particles (a characteristic microstructural feature of IM1-24 graphite). All thermal properties were investigated in two orthogonal directions, which showed the effective macroscopic thermal conductivity to be the same (to within experimental error). This can be linked to the morphology of the filler particles that consist of concentrically aligned graphitic platelets. The resulting spherical symmetry allows for heat to flow in the same manner in both macroscopic directions. The current thermal conductivity results were compared to other isotropic grade graphite materials. The significant discrepancies between the thermal conductivities of the individual grades are likely the result of different manufacturing processes yielding variations in the microstructure of the final product. Differences were identified in the filler particle size and structure, and possibly the degree of graphitization compared to other reported nuclear graphites.