Effects of H2 Additions on Stress Corrosion Cracking in a Boiling Water Reactor

Abstract

Abstract Controlled amounts of hydrogen were injected into the Dresden-2 boiling water reactor (BWR) during a five week period. The effect of the hydrogen modifed water chemistry on major structural alloys used in the BWR system was studied. The studies were conducted in a test facility consisting of two 1 L vessels which were piped to receive reactor water from the discharge side of the main recirculation pump. One of the vessels was used to measure electrochemical potentials. The second vessel was used to perform slow strain rate stress corrosion cracking tests. Electrochemical measurements were conducted continuously during normal BWR operation and during periods of hydrogen injection. The hydrogen injection caused the quantity of dissolved oxygen to decrease, which resulted in a substantial drop in corrosion potentials. At the highest injection rate, the corrosion potential of AISI 304 stainless steel dropped below the potential at which intergranular stress corrosion cracking (IGSCC) could be expected. Stress corrosion tests were conducted on severely sensitized AISI 304 stainless steel and pressure vessel steel. During normal operation, the stainless steel failed primarily by IGSCC. During H2 injection when the water contained <20 ppm O2, both IGSCC of the stainless steel and transgranular SCC of pressure vessel steel were eliminated.