CONTROL OF HYDROGEN PEROXIDE CONCENTRATION IN HIGH TEMPERATURE WATER AND DETERMINATION OF ITS EFFECTS ON STRESS CORROSION CRACKING OF STAINLESS STEEL

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Stress corrosion cracking (SCC) of BWR reactor internals are determined mainly by hydrogen peroxide (H_2O_2), an unsteady radiolytic specie in high temperature water. Major purposes of the studies are to construct high temperature high pressure H_2O_2 water loop which can control H_2O_2 concentration with minimal O_2 co-existence, to determine the effects of H_2O_2 on SCC crack growth rate and then to propose an index for corrosive condition to determine residual lifetime of reactor internals.1. Development of a flow cell type hydrogen peroxide detector based on luminol chemiluminescence.2. Design and construction of high temperature high pressure H_2O_2 water loop.3. Determination of relationship of electrochemical corrosion potential (ECP) and crack growth rate (CGR).(1) The relationship between ECP and CGR as a function of H_2O_2 and O_2 concentrations was determined.(2) High resistant hematite rich oxide film was confirmed under H_2O_2 condition.(3) The effects of surface properties on the relationship of oxidant concentration, ECP and CGR were evaluated.4. Justification of the measured result based on comparison of theoretical estimation and measurement.(1) ECP and CGR were evaluated theoretically based on H_2O_2 concentration obtained water radiolysis analysis.(2) ECP and CGR were measured for simulated corrosive conditions shown in (1).(3) Evaluation procedures was justified by comparing the results (1) and (2).(4) Future subject for application of ECP and CGR evaluation procedures to power plants were discussed.5. Derivation of newly defined corrosion index for reactor internals.(1) Proposal of newly defined corrosion index for reactor internals.(2) Positive application of the corrosion index and weak alkali control to mitigate SOC of reactor internals in Japanese BWRs and their improvement for residual lifetime evaluation.