Mechanism of Change In VVER-440, -1000 Vessel Material Properties in Irradiation–Recovery Annealing–Irradiation Cycle

The efficacy of recovery annealing of weld-seam metal for VVER vessel service life extension is examined. A comparative complex assessment of the degradation of VVER-440, -1000 weld-seam metal, as most subjected to radiation embrittlement due to operational factors, is presented. The main difference of the recovery annealing regimes associated with differences of their chemical composition and structural-phase state as well as the mechanisms of the degradation of the structure and properties during operation is substantiated. Comparative studies of the recovery of the structural state and mechanical properties of weld-seam metal after annealing in the chosen regimes as well as radiation embrittlement during re-irradiation were performed.