Trygubenko O. The effect of impact toughness decrease for WWER reactor pressure vessel steels under the long-term operation

The thesis describes the effect of impact toughness decrease for WWER-1000 reactor pressure vessel (RPV) steels and re-irradiated WWER-440 RPV steels under the long-term operation. The study was based on surveillance-specimens test results for WWER RPVs. The specimens were irradiated in power reactors to fast neutron fluences, corresponding to the period of more than 60 years RPV operation. The paper analyses decrease in ductile properties of RPV steels under the impact of neutron irradiation. Correlation of impact toughness with other parameters, such as lateral expansion and yield strength, is empirically shown for WWER-1000 RPV steels. For WWER-440 RPV materials, re-irradiated after recovery annealing, the change in upper shelf energy level of impact toughness temperature dependence showed a decrease in metal ductile properties. It is also shown the effect of phosphorus content in weld metal on the upper shelf energy. It is demonstrated that for materials with low upper shelf energy value there may be an artificial overestimation of critical temperature of brittleness and unjustified RPV life limitation.