Corrosion of Carbon and Low-Alloy Steels In Out-of-Pile Boiling-Water-Reactor Environment

Abstract

Abstract Results are reported of extensive corrosion testing of carbon and low-alloy steels in a dynamic test loop simulating the various environments found in a nuclear boiling-water-reactor system. Quantitative data and metallographic and visual observations of specimens tested in saturated steam, saturated water and a steam-water mixture, all at 545 F and 1000 psi are presented. Water and steam conditions are based on 10 to 20 ppm oxygen in the steam with a 1:8 stoichiometric ratio of hydrogen to oxygen, a condition representative of the hydrogen and oxygen formed in a boiling-water reactor from radiolytic water decomposition. The water is maintained at pH 7, high purity with no other additives. A description of the boiling-water dynamic-test facilities and operating procedures is included. Total corrosion and corrosion product released into the system is measured. No appreciable difference was noted among corrosion rates of carbon steels, high-strength low-alloy steels and alloy steels studied, although all showed higher rates than the AISI Type 300 series stainless steels tested. Comparisons also were made with other stainless steels. No selective attack was noted on welded specimens. Corrosion rates obtained on the carbon and low-alloy steels are lower than those obtained by other investigators on similar materials in test loops simulating pressurized water-reactor systems operated at high pH (> 10) with only hydrogen gas in the water. The iron-to-system rates in the present tests were appreciably lower than those in similar tests in high pH and neutral pH systems with a hydrogen environment. 8.4.5, 6.2.3, 6.2.4