Study of Steel Corrosion Cracking Mechanisms for VVER RPV Internals Based on Simulation Tests

Abstract

Different hypotheses of irradiation assisted stress corrosion cracking for materials of internals in the light water reactor environment were analyzed. Irradiation-induced grain boundary chromium depletion, localized deformation, and material hardening were considered. Heat treatment and cold working of 18Cr–10Ni–Ti steel were made to simulate the influence of neutron irradiation. Autoclave tests in the light water reactor environment at a temperature 290°C and at a strain rate of 3 × 10^–7 s^–1 were carried out. 18Cr–10Ni–Ti steel specimens in the initial state, after heat treatment, and after heat treatment followed by cold working were used. Fracture surfaces and lateral surfaces of specimens were examined by scanning electron microscopy. The microstructure of the material was also examined using transmission electron microscopy. It was shown that the grain boundary chromium depletion and the material hardening are not the main causes of corrosion cracking of 18Cr–10Ni–Ti steel in the primary coolant deoxygenated environment. The localization of deformation has a profound effect on corrosion cracking in the absence of the grain boundary sliding. The conditions determining the crack propagation by the corrosion cracking mechanism are defined.