Hydrogen water chemistry - a proven method to inhibit intergranular stress corrosion cracking in boiling water reactors

Intergranular Stress Corrosion Cracking (IGSCC) of stainless steel has occurred in several BWR plants in recent years. In Swedish plants the extent of cracking has been limited and the consequences, in terms of operational disturbances, have been quite small. Some cracks have been detected recently in the Ringhals 1 plant, however. As a phenomenon related to ageing, the cracks and their causes must receive the greatest attention. ASEA-ATOM initiated experimental work in the laboratory and in the Oskarshamn 2 BWR plant in the late seventies. The method chosen for these experiments, the aim of which was crack prevention, was hydrogen addition to the feedwater. Full scale demonstration runs have shown that oxygen suppression by hydrogen addition to the reactor coolant is technically feasible. Materials tests carried out in reactor coolant in the Ringhals 1 plant have demonstrated that intergranular stress corrosion cracking is eliminated when the oxygen concentration is kept low. The paper presents the main results of the Hydrogen Water Chemistry program. The technique developed has led to the design of a hydrogen injection system which is now commercially available for IGSCC prevention. (orig.)