(A) study on the radiation damage and recovery characteristics of reactor structural steels

Abstract

The recovery activation energy, the order of reaction and the characteristic recovery rate constant were determined by isochronal(573 K ~ 823 K) and isothermal(723 K and 775 K) annealing experiments on specimens made from a broken half of a RPV surveillance welds specimen (fluence: $1.21×10^19n/㎠$, E≥1 MeV, Cu : 0.29 wt%) to investigate the recovery characteristics of a neutron-irradiated reactor pressure vessel (RPV) high copper weld. The Vickers microhardness test was conducted to trace the recovery behavior after heat treatments. The results were analyzed in terms of recovery stages and trends, behavior of responsible defects and recovery kinetics. It was shown that recovery occurred through two annealing stages (stage I : 673K~753K, stage II : 753K~823K) with recovery activation energies of 2.68 eV and 2. 83eV for stage I and II, respectively. The isothermal hardness recovery at 723 K and 775 K coincided with the ratio of the characteristic recovery rate constant for each recovery stage. The order of recovery 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 elements. The present results strongly support the copper precipitates coarsening annealing model. Damage depth profile and thermal recovery characteristics of 16 MeV proton irradiated 12Cr-1MoV steel ($~2×10^18 p/㎠$, Irr.temp.<~398K) were investigated by Vickers microhardness measurement, thermal annealing experiments and TRIM 90 computer calculation. A damage depth profile estimated by Vickers microhardness in depth showed a relatively similar profile trend to the result of calculation but hardness peak appeared nearer to the surface and the half-value width was broader in hardness profile than calculation. The isochronal anneal showed two recovery stages. The recovery activation energies were 1.4eV ...