Fractographic Evaluation of the Fracture Toughness Tests of PWR Materials after Neutron Irradiation

Abstract

The Reactor pressure vessel is a main component of a nuclear power plant's primary circuit. WWER 440 is one of the most widely used nuclear reactors of the second generation. The main structural material of the WWER 440 is the base metal, ferritic steel 15Kh2MFA. For the purpose of anti-corrosive protection, the pressure vessels’ inner surface is covered with austenitic cladding. The cladding is made from the stainless steels Sv 07Kh25N13 (first layer) and Sv 08Kh19N10G2B (second layer). In frame of pressure vessel materials properties surveillance, fractographic analysis was performed on specimens (both in the neutron-irradiated and non-irradiated state) subjected to static fracture toughness testing. Specimens were collected from the area of the interfaces of the base metal and the austenitic cladding layers. Detailed fractographic analysis of fractured specimens was undertaken. Based on fractographic findings, individual failure micromechanisms taking place during the crack propagation across the materials’ interfaces were determined and described. The obtained results were used to find the relationship between the failure micromechanism changes and fracture toughness values. The fractographic analysis also offered information about the influence of the neutron irradiation on the failure micromechanisms.