Re-embrittlement behaviour of VVER-440 reactor pressure vessel weld material after annealing

摘要

The radiation embrittlement behaviour of Cr-Mo-V alloyed weld metal (VVER-440 RPV weld) after post-irradiation thermal annealing treatment is described in this paper. The experimental program includes two weld materials, two irradiation conditions, three different annealing temperatures and two subsequent annealing and re-irradiation cycles. The effects of these parameters on the embrittlement behaviour are determined by impact and fracture toughness testing.The results of the work show that the thermal annealing treatment can effectively restore the mechanical properties of Cr-Mo-V alloyed weld materials that was embrittled by neutron radiation. Repeated annealing treatment after re-irradiation show similar recovery of toughness properties as the first annealing. The phosphorus content has a clear influence on the embrittlement behaviour of the studied welds. The results indicate that the post-annealing embrittlement rate may be lower than the pre-annealing embrittlement rate and that an increase of the annealing temperature tends to reduce total post-annealing embrittlement.Based on the results of this work, a new approach for predicting the post-annealing re-embrittlement rate of Cr-Mo-V alloyed weld metals is proposed. The approach is based on the hypothesis that the post-annealing re-embrittlement is mainly governed by radiation induced precipitation of phosphorus-rich features. The proposed approach seems to describe the experimental findings of the work with relatively good accuracy.