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

The radiation embrittlement behaviour of Cr-Mo-V alloyed weld metal (VVER-4 40 RPV weld) after post-irradiation thermal annealing treatment is describe d in this paper. The experimental program includes two weld materials, two irradiation conditions, three different annealing temperatures and two subs equent annealing and re-irradiation cycles. The effects of these parameters on the embrittlement behaviour are determined by impact and fracture tough ness testing. The results of the work show that the thermal annealing treatment can effec tively restore the mechanical properties of Cr-Mo-V alloyed weld materials that was embrittled by neutron radiation. Repeated annealing treatment afte r re-irradiation show similar recovery of toughness properties as the first annealing. The phosphorus content has a clear influence on the embrittleme nt behaviour of the studied welds. The results indicate that the post-annea ling embrittlement rate may be lower than the pre-annealing embrittlement r ate 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-a nnealing re-embrittlement rate of Cr-Mo-V alloyed weld metals is proposed. The approach is based on the hypothesis that the post-annealing re-embrittl ement is mainly governed by radiation induced precipitation of phosphorus-r ich features. The proposed approach seems to describe the experimental find ings of the work with relatively good accuracy. (C) 2000 Published by Elsev ier Science Ltd.