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, com ponents, and structures in a boiling water reactor (BWR) primary cooli ng system have been directed toward avoiding intergranular stress corr osion cracking (IGSCC). Application of hydrogen water chemistry (HWC) to moderate corrosive circumstances is a promising approach to preserv e the structural integrity during extended lifetimes of BWRs. The bene fits of HWC application are (a) avoiding the occurrence of IGSCC on st ructural materials around the bottom of the reactor pressure vessel (R PV) and (b) moderating the crack growth rate, even if microcracks are present on the structural materials. Several disadvantages caused by H WC (e.g., turbine dose rate increase, Co-60 radioactivity buildup, and effects on fuel cladding) are evaluated to develop suitable counterme asures prior to HWC application. The advantages and disadvantages of H WC are quantitatively evaluated based on both BWR plant data and labor atory data shown in unclassified publications. Their trade-offs are di scussed, and suitable applications of HWC are described. It is conclud ed that an optimal amount of hydrogen injected into the feedwater can moderate corrosive circumstances, in the region to be preserved, witho ut 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 crac k growth rate at the RPV bottom - are planned that would collect data to support the theoretical considerations.