Characterisation of heterogeneities and evaluation of properties of nuclear grade graphite

Abstract

Graphite is one of the promising candidates to be used in the next-generation first breeder reactors as a moderator against first moving neutron effluence. During interaction with the neutron, substantial change in microstructure and mechanical and thermal properties occur for graphite. This affects its in-reactor performance. The changes depend on the characteristics of as received virgin material. Therefore, it is necessary to characterize as-received graphite accurately. This paper reports the microstructural characterisation of different nuclear graphite. Four different nuclear graphites were obtained from open source through end-user and were examined in the optical microscope. Quantification of microstructural features was carried out by Analysis Five software. A considerable number of pores with cracks were seen within the matrix. The pores and crack size distribution were found in the range of 0-10 µm2 to a 400-1000 µm2 for the investigated samples. The majority of the pores and cracks were seen within the range of 10-100 µm2 area. The total porosity was to the tune of 9.25 - 5.78%. Pores and cracks of a broad variety of the size were found, and which were uniformly distributed. The theoretical density was calculated from the obtained pores and cracks percentage data. There was no correlation found between the pores and the cracks density (no of pores and cracks per mm2) and the theoretical density of the graphite samples. Density was found to be independent of sizes of pores and cracks of nuclear graphite.