高溫純水中不同溫度下鉑金被覆於304不鏽鋼之電化學行為研究

The Electrochemical Behavior of Platinum Treatment on Type 304 SS with Different Coating Temperature in High Temperature Water

苑主用(Yuan, Chu Yung)

指導教授 ： 葉宗洸

國立清華大學/原子科學院/工程與系統科學系/碩士(2017年)

摘要

沸水式反應器在運轉多年後，應力腐蝕裂縫被發現在爐心組件上產生，為了減緩裂縫的成長，及抑制新裂縫的起始以延長電廠使用壽命及運作安全，加氫水化學被廣泛地運用在多個沸水式反應器中，其利用氫氣與氧氣的再結合作用，降低水中的氧化性，以達到抑制腐蝕的效果。由於過多的氫氣會造成輻射人員劑量過高等副作用，貴重金屬被覆配合氫氣使用的技術開始被使用，利用貴重金屬催化氫與氧再結合的效果，在相同的腐蝕電位下，能有效的降低注氫量。一般在電廠的啟動過程中，會由於上一個工作循環殘留大量的氧化劑在爐心環境中，且當時氫氣尚不能注入爐心，因此對於貴重金屬是否會加速氧化劑的反應，造成啟動過程裂縫的啟始產生疑慮。
本研究利用三個被覆溫度(90℃、150℃、288℃)，被覆鉑金至304不鏽鋼表面，並在三個不同的工作溫度(200℃、250℃、288℃)中，測量不同水環境，鉑金被覆試片以及304不鏽鋼試片的電化學差異。結果顯示在氧化性的水環境中，鉑金被覆試片的腐蝕電位及腐蝕速率皆高於未被覆的304不鏽鋼試片；但在還原性環境裡，鉑金則能有效的催化氫氣的反應，使得腐蝕電位及腐蝕速率都低於未被覆的不鏽鋼試片。

關鍵字

沸水式反應器 ； 應力腐蝕龜裂 ； 加氫水化學 ； 貴重金屬添加 ； 腐蝕電位

並列摘要

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.

並列關鍵字

Boiling Water Reactor ； stress corrosion cracking ； hydrogen water chemistry ； noble metal chemical addition ； electrochemical corrosion potential

參考文獻

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