Models of coefficient of thermal expansion (CTE) for Gilsocarbon graphites irradiated in inert and oxidising environments

This paper presents the development and validation of an empirical model of radiation effects on coefficient of thermal expansion (CTE) for the Gilsocarbon graphites used in Advanced Gas-cooled Reactors (AGRs). The combined irradiation and oxidation model is based in part on a new model of fast neutron damage in inert environment. The new inert model shows an increase to an “upper shelf” irradiated CTE value at very low dose, then CTE values decrease with increasing dose following a hyperbolic tangent function. The effect of the actual exposure in AGRs is modelled by shifting the inert model in both dose and CTE directions to agree with the CTE measurements on material trepanned from moderator bricks in operating AGRs. The shift in the inert model that is needed to match the trepanned data varies significantly by reactor. The new model predicts randomly-selected validation data that were not used in model fitting as well as it fits the calibration data.