| Summary: | 碩士 === 國立清華大學 === 工程與系統科學系 === 105 === After many decades of operation, stress corrosion cracking (SCC) have been found in many boiling water reactors (BWR). To mitigate SCC, hydrogen water chemistry (HWC) has been widely adopted in BWRs around the world. HWC is a technology injecting H2 into feedwater to recombine H2 with O2 or hydrogen peroxide (H2O2) under radiative environment. The recombination can decrease the concentration of O2 and H2O2, accompanying lower electrochemical corrosion potential (ECP), in coolant system. ECP is a driving force of SCC initiation, which alters with the variation of dissolved O2, H2O2 and H2 concentration. By lowering the ECP, the susceptibility to SCC is reduced and the crack initiation and growth rate are effectively slowed down.
There are some side effects have been reported by using HWC. Noble metal chemical application (NMCA) or On-line NobleChemTM (OLNC) have been developed to solve the problems. The concept of these technologies are coating noble metal on structure components to catalyst the recombination of H2 and O2 or H2O2. HWC combines with NMCA or OLNC can achieve the same level as HWC only of ECP by injecting lower H2. ECP decreases by lacking of oxidant, so structural components can be well protected. However, if noble metal existed on the structural components without injecting H2, it might catalyst the reaction of oxidant, which will enhance the corrosion rate.
Both HWC and noble metal coating technology needed to inject H2 to mitigate SCC. During the startup process, coolant dissolved massive remaining O2 and H2O2 from the last operation cycle, SCC might grow faster. When O2 and H2O2 are catalyzed by coated noble metal, the redox reaction on the components will be enhanced. The corrosion behaviors on the components get stronger.
In this study, we used three coating temperature (90℃、150℃、288℃) to coat Pt particle on surfaces of stainless steel. Then used three working temperature (200℃、250℃、288℃) to detect the electrochemistry differences. The results show that the ECP and corrosion current density of Pt coated specimens are both higher than the untreated specimens’ under oxidizing environment. However, in the reducing environment, Pt particles which can also catalyze the reaction of hydrogen cause the ECP and corrosion current density of Pt coated specimens smaller than the untreated ones.
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