(A) study on the annealing mechanism of the neutron-irradiated reactor pressure vessel weld

Abstract

In order to investigate annealing mechanism of neutron-irradiated Lined 80 reactor pressure vessel weld, the recovery activation energy and order of reaction were determined through isochronal and isothermal annealing experiments. Specimens were prepared from a broken half of a Charpy impact surveillance sample(Fluence : $1.21×10^19n/㎠$, Cu:0.29 wt%) and the Vickers microhardness tests were performed to trace recovery after heat treatment. It was found that recovery occurred through two annealing stages (stage I : 400℃-480℃, stage II : 480℃-550℃) and recovery activation energies, which were determined by the Meedchan and Brinkman method, were 2.68 eV and 2.83 eV for stage I and II, respectively. The recovery activation energies determined in this study are approximately equal to that activation energy for copper diffusion in α -iron in the presence of vacancies, suggesting that recovery occur through the diffusion of copper element. The order of reactions for both annealing stages were 2, which also agrees with the vacancy mechanism for the diffusion of copper element. The present results suggest that recovery of neutron-irradiated Linde 80 weld seems to occur by the coalescence of fine copper-rich precipitates.