Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Neutron irradiation induced embrittlement of the reactor pressure vessel (RPV) reduces the operating lifetime of nuclear reactors and leads to an increase in the transition temperature T0. Fracture mechanics testing of RPV steels before and after neutron irradiation, which reveals the shift in T0, is often limited by the shortage of irradiated material. To solve this, we tested sub-sized 0.16T C(T) specimens manufactured from already tested SE(B) standard Charpy sized specimens using the Master Curve concept. The transferability of fracture mechanics data from small to standard sized specimens forms a key part of this study. To investigate the effect of chemical composition on neutron irradiation, four western RPV steels are chosen in this study, three base and one weld metal. Fractography is performed on broken mini-C(T) specimens using scanning electron microscopy in order to determine the location of the fracture initiating particles as well as the mode of fracture. In order to make the testing procedure simpler, based on large statistical data, we studied the impact of the slow stable crack growth censoring criterion on the determination of T0. We found that the results from the small specimens are comparable to the standard specimens. RPV steels containing higher amounts of Cu, Ni and P exhibit a higher increase in T0 after irradiation. The fracture initiating particles were located at greater distances from the crack front in irradiated specimens of the weld material as compared to the unirradiated specimens. The fracture toughness of all materials remained constant for similar test temperatures irrespective of their irradiation state. Furthermore, we found that the stable crack growth censoring criterion did not influence the T0 significantly. Our results demonstrate the validity of small specimen testing and confirms the role of the impurity elements Cu and P in neutron embrittlement.