目前役期屆滿的核一廠進入除役階段，用過核燃料的貯存安全問題實為重要，在用過燃料池存放5-10年的用過核燃料，將移至乾式貯存設施進行中期貯存，此為適宜且安全的暫時貯存方法。目前核一廠第一期乾貯設施使用INER-HUP系統，內部密封鋼筒的材料為304L沃斯田鐵系不銹鋼，然而沃斯田鐵系不銹鋼在在富含氯離子及水氣的環境中，可能會發生孔蝕及應力腐蝕龜裂等腐蝕行為，為了確保乾貯系統的結構完整性，本研究著力於探討304、304L、316L不銹鋼於沿海環境中的腐蝕行為。
本實驗中使用固溶熱處理及敏化熱處理之304、304L、316L不銹鋼Ｕ-bend試片，以週期性噴灑氯化鎂、合成海鹽及混合氯鹽水溶液，來模擬沿海環境中氯鹽沉積的情形，並於40、60、80oC，固定相對濕度40%的環境中進行加速腐蝕試驗。根據裂縫形貌及並量分析的結果，在40oC及60oC下，304及304L不銹鋼表面的腐蝕型態主要為裂縫的生成，316L不銹鋼以孔蝕的生成居多；在80oC下，只有在316L不銹鋼表面觀察到裂縫生成，從橫截面觀察中可以發現裂縫有分支的情形，為應力腐蝕龜裂的特性。304及304L不銹鋼表面的腐蝕型態則以均勻腐蝕為主。此外，在40oC、相對濕度40%下進行合成鹽類及混合氯鹽的沉積，所有不銹鋼試片都沒有發現應力腐蝕龜裂的現象。

　　Austenitic stainless steel is the general material used in the canister of dry storage system, including Type 304, 304L, 316L stainless steels. When the spent fuel storage installations located nearby a coastal site, these types of austenitic stainless steel are prone to chloride induced stress corrosion cracking (CISCC) in aggressive environment. Therefore, the purpose of this work is to evaluate the susceptibility to chloride induced stress corrosion cracking of candidate canister materials by using U-bend tests in simulated coastal atmospheric environments. The U-bend specimens were under periodic spraying with magnesium chloride solution (MgCl2), mixed chloride solution (NaCl and MgCl2) and synthetic sea-salt solution at different temperatures but constant relative humidity of 40% for 1500 hours. Prior to the U-bend tests, specimens were prepared and underwent various pretreatments, including solution annealing and thermal sensitization.
After the tests, specimens were examined with the scanning electron microscope (SEM) in order to observe the morphology and measure the length of cracks. According to the results of 40oC, except for sensitized 304 and 304L specimens, no cracks longer than 500μm were observed in the other U-bend specimens. The difference of resistance to CISCC between solution annealed and sensitized specimens are significant at low temperature. The number of cracks on the sensitized specimens was more than solution-annealed ones, mainly from the increasing of the micro-cracks and pits. The cracks observed on the sensitized specimens were longer than the solution annealed specimens because of the intergranular corrosion cracking. There are more cracks and pits observed at 60oC under magnesium chloride periodic spraying than 40oC. At higher temperature 80oC, pitting coalescence is the major corrosion behavior instead of stress corrosion cracking. The results of mixed chloride and synthetic sea-salt showed that there was no SCC observed on all specimens.

目錄
第1章 前言 1
1.1 研究背景 1
1.2 研究動機 2
第2章 文獻回顧 4
2.1 乾式貯存筒的介紹 4
2.2 我國乾貯設施介紹 5
2.3 沃斯田鐵系不銹鋼的腐蝕行為之一－氯離子誘發應力腐蝕龜裂 8
2.3.1 敏感性材料對應力腐蝕龜裂的影響 10
2.3.2 應力對應力腐蝕龜裂的影響 11
2.3.3 腐蝕性環境對應力腐蝕龜裂的影響 12
2.4 沃斯田鐵系不銹鋼的腐蝕行為之二－孔蝕 14
2.4.1 孔蝕的起始－氯離子去鈍化、破壞鈍態層 15
2.4.2 孔蝕的起始－MnS的溶解 16
2.4.3 孔蝕的電化學反應 19
2.5 沃斯田鐵系不銹鋼的腐蝕行為之三－大氣腐蝕 21
2.6 台灣氯鹽沉積量 23
2.7 乾貯筒環境 25
2.7.1 密封鋼筒表面溫度 25
2.7.2 密封鋼筒表面濕度 26
2.8 探討環境因子的相關文獻彙整 28
2.8.1 溫度的影響 29
2.8.2 相對濕度的影響 31
2.8.3 氯鹽種類的影響 34
2.8.4 氯鹽沉積量的影響 38
2.8.5 實驗時間的影響 41
第3章 實驗設備及步驟 44
3.1 實驗方法與流程 44
3.2 實驗試片設計及備製 45
3.3 氯鹽沉積與模擬沿海環境設置 48
3.3.1 實驗設置圖 48
3.3.2 模擬沿海環境 49
3.4 分析方法 50
3.4.1 敏化程度分析 50
3.4.2 表面分析 52
3.4.3 深度分析 54
3.4.4 EDS / GDS 成分分析 55
第4章 結果與討論 56
4.1 氯鹽沉積量記錄 56
4.2 敏化程度分析 57
4.3 氯化鎂水溶液的實驗結果 58
4.3.1 尚未進行加速腐蝕實驗的U-bend試片表面觀察 58
4.3.2 不銹鋼形貌觀察 61
4.3.3 時間的影響 66
4.3.4 氯化鎂溶液濃度的影響 72
4.3.5 熱處理的影響 80
4.3.6 實驗溫度的影響 91
4.3.7 孔蝕深度量測與不銹鋼試片的橫截面觀察 103
4.4 混合鹽類溶液的實驗結果 111
4.4.1 合成海鹽的實驗結果 111
4.4.2 混和氯鹽的實驗結果 114
4.4.3 橫截面觀察結果 117
4.4.4 不同鹽類溶液的結果比較 119
第5章 結論 120
第6章 未來建議方向 122
參考文獻 123

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