Corrosion of Carbon Steel in Simulated Boiling Water and Superheat Reactor Enviroments

Abstract

Abstract Results are reported for the continuation1 of extensive corrosion testing of carbon steel exposed in a dynamic test loop simulating the various environments found in a nuclear boiling-water-reactor system. Water and steam conditions were based on 20 ppm oxygen and 2.5 ppm hydrogen in the 546 F (285 C) saturated steam, a condition representative of the radiolytic water decomposition in boiling-water reactors. The pH of the high-purity water was neutral with no chemicals added to the water. Tests were conducted to study the total corrosion and corrosion product released into the system from isothermal and heat-transfer surfaces as a function of operating conditions. Results of the investigation show that: (a) the corrosion of carbon steel in such an environment is characterized by an initially rapid filming period governed by nonlinear kinetics followed by an essentially linear corrosion rate, (b) once the system has been properly brought to the oxygen and hydrogen contents typical of BWR conditions, essentially no iron is lost to the system in further exposure to such conditions. A theory describing the formation of the protective oxide is proposed. Additional test results are included for carbon steel exposed to superheated steam at temperatures up to 932 F (500 C).