Effect of Chloride on the Oxides on Low-Alloyed Steel in Conditions of a Light Water Reactor Pressure Vessel Cladding Flaw

Abstract

Strain-induced corrosion cracking in low alloyed steels has been extensively investigated during the last decades. One finding from recent investigations is that small amounts of chlorides tend to increase the cracking susceptibility of such materials. The present paper investigates the effect of chloride addition on oxide films on low-alloyed steel in conditions simulating those in a cladding flaw of a light water reactor pressure vessel under oxygenated high-temperature water conditions. The films were studied by in-situ electrochemical impedance spectroscopy and mixed potential measurements, coupled to ex-situ characterization of the formed oxides by microscopic and surface analytical techniques. The impedance data were quantitatively interpreted by the mixed-conduction model for oxide films to yield estimates for the main kinetic and transport parameters of oxide growth and restructuring. On the basis of the experimental data and calculation results, it can be concluded that the effect of chloride on low-alloyed steel oxide is moderate, concerns mostly the processes at the inner layer/coolant interface and is to a major extent reversible.