APPLICATION OF HYDROGEN WATER CHEMISTRY TO MODERATE CORROSIVE CIRCUMSTANCES AROUND THE REACTOR PRESSURE-VESSEL BOTTOM OF BOILING WATER-REACTORS

Many efforts to preserve the structural integrity of major piping, components, and structures in a boiling water reactor (BWR) primary cooling system have been directed toward avoiding intergranular stress corrosion cracking (IGSCC). Application of hydrogen water chemistry (HWC) to moderate corrosive circumstances is a promising approach to preserve the structural integrity during extended lifetimes of BWRs. The benefits of HWC application are (a) avoiding the occurrence of IGSCC on structural materials around the bottom of the reactor pressure vessel (RPV) and (b) moderating the crack growth rate, even if microcracks are present on the structural materials. Several disadvantages caused by HWC (e.g., turbine dose rate increase, Co-60 radioactivity buildup, and effects on fuel cladding) are evaluated to develop suitable countermeasures prior to HWC application. The advantages and disadvantages of HWC are quantitatively evaluated based on both BWR plant data and laboratory data shown in unclassified publications. Their trade-offs are discussed, and suitable applications of HWC are described. It is concluded that an optimal amount of hydrogen injected into the feedwater can moderate corrosive circumstances, in the region to be preserved, without serious disadvantages. The conclusions have been drawn by combining experimental and theoretical results. Experiments in BWR plants - e.g., direct measurements of electrochemical corrosion potential and crack growth rate at the RPV bottom - are planned that would collect data to support the theoretical considerations.