現有的輕水型核反應爐 (Light Water Reactor, LWR)所使用冷卻管道為功能複合材料 (Functionally Graded Composite Material, FGC)。該複合材料結構為表面鍍層約30um~100um之Fe-Cr-Si固溶體結構；基材為T91肥粒鐵-麻田散鐵合金結構或是化學氣象沉積碳化矽 (Chemical Vapor Deposited – Silicon Carbide, CVD-SiC)構成。此類核反應爐冷卻管道所使用的冷卻液常為鉛铋共晶體(Lead-Bismuth Eutectoid, LBE)，該液體在通過管道內部時會產生對內壁的腐蝕與損傷可能性。管道表面與LBE接觸之Fe-Cr-Si固溶體結構抗腐蝕性為藉由1.25wt%矽濃度與氧化層成長率作為判斷依據，Fe-Cr-Si固溶體結構當中的Cr與Si含量可與LBE液體反應形成氧化層達到保護基材損傷的功能。
　　本研究為了減緩應力集中且提升熱衝擊阻力以及矽濃度達到高耐腐蝕性之能力採用二相與三相功能性材料(Functionally Graded Material, FGM)比對傳統表面鍍層結構之FGC應用於圓管模型在靜態升溫與動態熱疲勞邊界條件中進行評估；材料強度部分會以安全裕度(Margin of Safety)做為評估標準。本文採用方法與技術以核反應爐管道高過於1200。C可能產生嚴重冷卻液外洩的事故發生的情況(Large-Break Loss-of-Coolant Accident, LBLOCA)進行強度比對。
　　本研究之結果表明在Fe-Cr-Si固溶體結構與CVD-SiC二相功能性材料以及Fe-Cr-Si固溶體結構、TiO2與CVD-SiC三相功能性材料所構成的冷卻管道模型在安全裕度、熱衝擊阻力以及表面氧化層厚度之生成與品質相較於傳統Fe12Cr2Si-T91的功能複合材料結構皆有所提升。相較於傳統冷卻管道最高安全裕度為0.98情況下能提升至0.99~3.17之範圍；熱衝擊阻力值相較於Fe12Cr2Si-T91的FGC結構提升7.64%；氧化層厚度在第10000小時時候能成長至相較於FGC結構提升25%。

The existing light water nuclear reactors utilize functionally graded composite materials for their cooling pipes. The composite material structure consists of Fe-Cr-Si solid solution structure with a surface coating of approximately 30um to 100um. The substrate is composed of either a T91 ferritic-martensitic alloy structure or a chemical vapor deposition silicon carbide (CVD-SiC) structure. The cooling liquid commonly used in such nuclear reactor cooling pipes is lead-bismuth eutectic (LBE), which can cause corrosion and damage to the inner walls of the pipes. The Cr and Si content in the Fe-Cr-Si solid solution structure can react with the LBE liquid to form an oxide layer, which protects the substrate from damage.
In this study, a two-phase and three-phase functionally graded material (FGM) is used to mitigate stress concentration, improve thermal shock resistance, and achieve high corrosion resistance with a high silicon concentration. A comparison is made between FGM and the traditional surface coating structure of FGC in evaluating the performance of circular tube models under static heating and dynamic thermal fatigue boundary conditions. Material strength will be evaluated based on the margin of safety. The methodology and techniques used in this paper are applied to assess the strength comparison in the event of a Large-Break Loss-of-Coolant Accident (LBLOCA) with temperatures exceeding 1200°C in nuclear reactor pipes.
The research results show that the cooling pipe models composed of the Fe-Cr-Si solid solution structure and CVD-SiC two-phase functionally graded materials, as well as the Fe-Cr-Si solid solution structure、TiO2 and CVD-SiC three-phase functionally graded materials, have improved safety margins、thermal shock resistance and surface oxide layer thickness compared to the traditional Fe12Cr2Si-T91 functionally graded composite material structure. Compared with the maximum safety margin of 0.98 for traditional coolant pipes, the results of this study can be improved to a range of 0.99-3.17. The thermal shock resistance value is improved by 7.64% compared to the FGC structure of Fe12Cr2Si-T91. The oxide layer thickness can grow by 25% compared to the FGC structure at 10,000 hours.

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