為了解決日益關鍵的用過核燃料貯存問題，將已在濕式貯存燃料池冷卻多年的燃料棒移至乾式貯存將會是良好且安全的解決辦法。乾式貯存分為室內及室外兩種，本實驗之目的為探討此設施在使用上的安全性，是否會因應力腐蝕龜裂之裂痕貫穿密封筒導致輻射外洩。由美國核能管制委員會的報告[1]中得知，不鏽鋼乾貯桶上應力腐蝕龜裂的發生條件，包含其表面必須有氯鹽沉積、環境相對濕度的高低循環變化及張應力。
本實驗以模擬乾貯筒放置之沿海環境的U-bend試片進行實驗，材料為固溶熱處理及敏化熱處理之304、304L、316L不鏽鋼與GGG-40 球墨鑄鐵(Ductile Cast Iron, DCI)，以氯化鈉水溶液噴灑，使試片表面形成鹽類沈積之後，於不同溫度、固定相對濕度環境中進行長時間的測試。實驗完成後，以電子顯微鏡及光學顯微鏡觀測其試片表面是否有產生裂紋或孔蝕之現象，並加以分析，接著針對定面積進行裂縫數目及長度量測。根據不鏽鋼裂縫形貌及數量計算的結果，可得知時間並未明顯影響裂縫的成長，敏化熱處理則有讓不鏽鋼材料表面小裂縫數目增加的趨勢，實驗溫度的提高使的氧化情形加劇的效果，同時也觀察到孔蝕與裂縫成長間的關係。

The dry cask storage of spent nuclear fuel is more suitable as an interim safer solution than spent fuel pool storage. Most canisters used in dry storage system for spent fuel are fabricated from austenitic stainless steel. Austenitic stainless steels are susceptible to chloride-induced stress corrosion cracking (SCC), and the corrosion initiated by the deliquescence of sea salts coupled with susceptible materials and residual stress can lead to stress corrosion cracking. The purpose of this study is to evaluate the susceptibility to chloride induced stress corrosion cracking (CISCC) of candidate canister materials (304, 304L,316L stainless steels and GGG-40 ductile cask iron) by U-bend tests in a simulated marine atmospheric environment. A detailed characterization on the microstructure of the samples was analyzed by using the scanning electron microscope (SEM) and optical microscope (OM). The number and length of cracks in selected area were also measured. The influence of sensitization heat treatment and temperature was obvious. More cracks were found in sensitized specimens. The oxidation behavior is more serious with higher environment temperature. Besides, the phenomena that the cracks tended to grow between pits was also found.

摘要 ii
Abstract iii
致謝 iv
目錄 vi
表目錄 viii
圖目錄 ix
第1章 前言 12
1.1 研究動機 12
1.2 研究目標 13
第2章 文獻回顧 14
2.1 乾式貯存 14
2.1.1 乾式貯存筒分類 14
2.1.2 乾式貯存筒材料 14
2.1.3 乾式貯存筒材料腐蝕情形 16
2.1.4 台灣乾式貯存現況 20
2.2 應力腐蝕龜裂要素 21
2.2.1 敏感性材料-不鏽鋼 22
2.2.1.1 不鏽鋼的敏化現象 23
2.2.2 張應力-殘留應力 26
2.2.3 腐蝕性環境-含氯離子環境 28
2.3 氯離子誘發應力腐蝕龜裂 28
2.3.1 應力腐蝕龜裂的起始階段 29
2.3.2 應力腐蝕龜裂的成長階段 33
2.3.3 不同不鏽鋼對應力腐蝕龜裂的影響 35
2.3.4 氯鹽對應力腐蝕龜裂的影響 36
2.3.5 溫度對應力腐蝕龜裂的影響 45
第3章 實驗設備及步驟 48
3.1 實驗方法與流程 48
3.1 實驗試片設計及備製 50
3.2 實驗設備 53
3.2.1 U-bend 製具及夾具 53
3.2.2 鹽水噴灑設備 54
3.2.3 溼度控制環境 54
3.3 實驗分析方法與工具 56
3.3.1 敏化程度測試-雙環電位再活化法(DLEPR) 56
3.3.2 表面分析-掃描式電子顯微鏡(SEM)、光學顯微鏡(OM) 58
3.3.3 連圖影像之定量分析 58
3.3.4 成分分析-能量分散式光譜儀(EDS)、輝光放電分光儀(GDS)、碳硫分析儀 60
第4章 實驗結果與討論 61
4.1 敏化程度測試結果 61
4.2 氯鹽沉積量記錄 62
4.3 不同材料表面形貌分析 64
4.3.1 球墨鑄鐵表面形貌分析 64
4.3.2 不鏽鋼表面形貌分析 67
4.3.3 熱處理對表面形貌的影響 75
4.3.4 溫度對表面形貌的影響 77
4.3.5 時間對表面形貌的影響 80
4.4 裂縫的定量分析 82
4.4.1 熱處理對裂縫數目的影響 82
4.4.2 溫度對裂縫數目的影響 84
4.4.3 時間對裂縫數目的影響 86
4.5 孔蝕與裂縫關係 91
第5章 結論 94
參考資料 96

 

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