Modelling Porosity in Quasi-Brittle Reactor Core Graphite

Abstract

Some designs of nuclear reactors involve a graphite moderator within their core. Different forms of graphite have been adopted in the UK gas-cooled reactors but all have a complex structure of filler particles, matrix and pores. Changes occur in the graphite during service and in particular, porosity increases from that found in the virgin material. As part of a structural assessment, it is important to analyse the effects of this change in porosity. Software has been developed to represent the microstructure of pile grade A (PGA) and Gilsocarbon graphite with a range of porosities, to support finite element determination of material properties. The models are three dimensional geometric and voxel models based on the observed microstructures of these different graphites. Creating a sequence of model specimens with increasing porosities while holding other parameters constant, provides a representative microstructure to test the effect of increasing porosity on mechanical and physical properties.