Thermal recovery characteristics of neutron-irradiated high-copper weld (Linde 80)

Abstract

The recovery activation energy, the order of reaction and the characteristic recovery rate constant were determined by isochronal (573–823 K) and isothermal (723 K and 775 K) annealing experiments on specimens made from a broken half of a surveillance weld specimen (fluence: 1.21 × 10 23 n/m 2, E ≥ 1 MeV, Cu: 0.29 wt%) to investigate the recovery characteristics of a high copper weld of neutron-irradiated reactor pressure vessel (RPV). Vickers microhardness tests were conducted to trace the recovery behavior after heat treatments. The results were analyzed in terms of recovery stages, behavior of responsible defects and recovery kinetics. It was shown that recovery occurred through two annealing stages (stage I: 673–753 K, stage II: 753–823 K) with recovery activation energies of 2.68 eV and 2.83 eV for stage I and II, respectively. The isothermal hardness recovery at 723 K and 775 K coincided with the ratio of the characteristic rate constant for each recovery stage. The order of reaction was 2 for both recovery stages. The recovery activation energies of present specimens are approximately equal to that of copper diffusion in α-iron in the presence of vacancies, suggesting that recovery may occur through the diffusion of copper atoms. The present results strongly support the copper precipitate coarsening model.