A synchrotron X-ray study on the wigner effect of the irradiated nuclear-grade graphite

We simulate the Wigner Effect of the nuclear-grade graphite for the High Temperature Gas-cooled Reactor (HTGR) operation environment. The graphite was artificially irradiated with 3MeV C²⁺ ion to mimic the fast neutron-radiation damage of the HTGR core environment. In a high vacuum environment of 10^-7 torr, the irradiation temperatures were controlled in the range of 600°C to 900°C. Due to the high-dosages radiation, enormous amounts of Frenkel pairs are created, and these defects induce the swelling of lattice spacing. Those vacancies and interstitials form new strain fields and store energy in the distorted crystalline structure. We quantify the structural integrity of the graphite with/without irradiation via synchrotron X-ray diffraction experiments. The synchrotron X-ray diffraction experimental results, gauged from bulk specimens, reveal the texture reorientation and microstructure development subjected to the combination of the irradiation and high temperature effects. A correlation between lattice strain and irradiation effect is developed. The deformation mechanisms are revealed.