Tentative re-embrittlement analysis for WWER-440 welds after annealing

Re-irradiation data available in RRC-KI and in Fortum Engineering /VTT is analysed in order to identify dependencies of re-irradiation shifts on re-irradiation fluence and flux, Charpy-V specimen size and phosphorus content. The data is considered as a whole and it is well identified that the data is of multi-parameter nature i.e. initial irradiation condition before annealing, re-irradiation condition after annealing, CH-V specimen size, neutron fluence rate, neutron fluence and phosphorus content of welds vary within relatively wide limits. Hence only systematic dependencies on the above mentioned parameters were aimed to be identified. No clear bias in the data based on CH-V specimen size or fluence rate was noticed. When modelling the shift as a function of fluence and phosphorus content, the conservative shift is found to be conservative. The best fit average re-embrittlement rate was found to be less than the upper limit lateral shift model, which is described in the paper.