Modelling of nuclear graphite behaviour under irradiation conditions

The graphite components in gas-cooled reactors provide channels for the fuel and control rods. During operation the dimensions and material properties of these graphite components are modified by fast neutron irradiation and, in the case of carbon dioxide cooled reactors, by radiolytic oxidation. Due to local gradients in the fast flux and temperature these dimensional and property changes result in the build up of component internal stresses. This paper describes a constitutive material model for the assessment of stresses and deformations in nuclear graphite components. Examples are given for typical stress analysis of nuclear graphite components under irradiation and radiolytic oxidation. The influence that the different irradiation induced strains have on resulting stress profile is discussed. These analyses provide an insight into the effect of irradiation in nuclear graphite components.