Flux effect analysis in WWER-440 reactor pressure vessel steels

The results of long term research programme concerning the determination of irradiation embrittlement dependence on fast neutron flux for WWER-440 reactor pressure vessel steels before and after annealing are presented in this paper. The study of flux effect was carried out on commercial WWER-440 steels which differ significantly in phosphorous (0.013–0.036 wt%) and copper (0.08–0.20 wt%) contents. All specimens were irradiated in surveillance channel positions under similar conditions at high ∼4 × 1012 cm−2 s−1 and low ∼6 × 1011 cm−2 s−1 fluxes (E > 0.5 MeV) at a temperature of 270 °S. The radiation embrittlement was evaluated by transition temperature shift on the basis of Charpy specimens test results. In case of low flux, the measured Tk shifts could be 25–50 °C bigger than the Tk shifts obtained from high flux data. A significant flux effect is observed in WWER-440 reactor pressure vessel steels with higher copper content (>0.13 wt%). Microstructural studies show that copper content decreases in the ferrite matrix and that there is formation of copper-enriched clusters and precipitates under irradiation and subsequent thermal annealing. Due to this fact the radiation damage does not depend on copper re-irradiation after annealing. Dependence of transition temperature shift on neutron flux is not expected for WWER-440 steels under re-irradiation after annealing