The materials of interest include some nuclear graphite used in the core of current operating UK reactors and also some new designs for next generation of reactors worldwide. In both cases, these graphite components are located in the core of a reactor as a structure component, to moderate the fast neutrons and provide channel for the control rods during shutting down procedure. They cannot be replaced therefore limiting the lifetime of nuclear power plants. Our study using neutron diffraction is to obtain the lattice deformation of these graphite when working at high temperature, for example, 650C for the current UK reactors. The lattice deformation will then be correlated to the bulk deformation and fracture to gain understanding on the evaluation of the integrity of the component.