PWR的開放式燃料循環為目前最普遍採用的策略，然而開放式循環這種一次性的燃料，燃耗結束的用過核燃料內仍有高達95%以上的核種仍可作為燃料使用，因此使用封閉式燃料循環的採用能增進燃料的使用效率。用過核燃料中包含的次要錒系元素(MA)屬於長半衰期放射性元素，對於環境的影響可長達數十萬年以上，因此MA減量相當重要。MA可藉由中子源將其分裂成半衰期較短的分裂產物，也因此封閉式燃料循環的使用可以將MA回收重新置入反應器內利用反應器內的中子以達到消滅MA的目的。
本研究首先比較PWR開放式及封閉式燃料循環在燃料使用率、MA產量上的差異。接著選擇以PWR代表熱中子反應器及SFR代表快中子反應器，再考慮對三種易裂元素對應的三種燃料系統(233U/232Th, ThU3、235U/238U, UOX、239Pu/238U, MOX)，形成6組假想封閉式燃料循環(PWR-UOX、PWR-MOX、PWR-ThU3、SFR-UOX、SFR-MOX、SFR-ThU3)做比較。本研究設定在總燃耗熱能為1080 GWd的情境下，比較燃料使用效率以及MA的產量。
在總燃耗熱能達1080 GWd下，理論上所需消耗的重金屬(Z≧89)為1.13公噸，在PWR開放式循環的用過核燃料棄置不回收再利用，所以需要使用約30公噸的濃縮鈾(1.65公噸的235U與28.35公噸的238U)；而封閉式循環因持續回收可用核種僅需使用1.32公噸的235U及238U(0.81公噸的235U與0.51公噸的238U)，兩者在資源使用效率上有極大的差異。封閉式循環中6組循環消耗的重金屬總量差異並不大，均在1.17~1.32公噸左右。PWR-UOX消耗0.81公噸的235U與0.51公噸的238U；PWR-MOX消耗0.63公噸的239Pu與0.58公噸的238U；PWR-ThU3消耗0.73公噸的233U與0.51公噸的232Th；SFR-UOX滋生3.67公斤的235U但消耗1.20公噸的238U；SFR-MOX滋生43.04公斤的239Pu但消耗1.21公噸的238U；SFR-ThU3消耗2.15公斤的233U與1.21公噸的232Th。PWR的燃料循環均需補充易裂元素維持反應器臨界，而SFR搭載UOX及MOX不僅可以在只添加238U下即能維持臨界，還能滋生易裂元素；儘管ThU3在SFR中無法滋生出更多的233U，但仍然可以只添加232Th達到燃料永續循環。
MA產量的部分，開放式循環累積的MA約為29.44公斤而封閉式循環累積的MA約為23.64公斤，封閉式循環大約可比開放式循環減少約20%的MA累積量。封閉式燃料循環中SFR-UOX及SFR-MOX累積的MA分別為8.04公斤與8.12公斤；PWR-UOX與PWR-MOX分別為23.64公斤與26.36公斤，SFR的使用大約可再比PWR減少約70% MA的累積量。ThU3燃料累積的MA則遠小於UOX或MOX，在PWR與SFR中分別為1.02公斤與0.59公斤，充分顯現其核反應物理上的優勢。
綜觀上述結果，封閉式循環可以大幅增加燃料使用效率、抑制MA產生；快反應器可以達到燃料永續、減少MA產量；釷燃料因核物理上的優勢可以僅累積微量的MA。然而封閉式循環現階段在經濟上與政治上的可行性均有不小的阻礙；SFR仍處於研究階段，商轉還有很長的一段距離；釷燃料亦有許多缺點包含燃料本身轉換效率沒鈾燃料好、製造與再處理過程會產生高放射性的核種等，對於燃料循環的選擇仍須多方面考量與比較。

The once-through fuel cycle is currently the most preferred choice for light water reactor operation because of its simplicity. Used fuel roughly have 1% U-235, 95% U-238, 1% plutonium and around 3% fission products and minor actinides (MA). The use of closed fuel cycle can increase resource utilization and potentially reduce radioactive waste. Focusing on fuel utilization and MA reduction, this study compares the performance of open and closed fuel cycles in PWR operation. Furthermore, considering the combinations of two reactors (PWR as thermal reactor and SFR as fast reactor) and three fissile fuel materials (ThU3:233U/232Th, UOX:235U/238U, MOX:239Pu/238U), this study also investigated the characteristics of six hypothetical closed fuel cycles, that is, PWR-UOX、PWR-MOX、PWR-ThU3、SFR-UOX、SFR-MOX、SFR-ThU3.
Theoretically, 1.13 metric tons of heavy metal (Z≧89) is required to produce 1080 GWd reactor thermal energy. The spent nuclear fuel of once-through cycle is considered as nuclear waste, and it takes 30 metric tons of enrichment uranium (1.65 metric tons of 235U and 28.35 metric tons of 238U) to generate thermal energy. In closed fuel cycle, however, only 1.32 metric tons of 235U and 238U (0.81 metric tons of 235U and 0.51 metric tons of 238U) is needed due to fuel recycling.
The difference of heavy metal consumption between 6 groups of closed fuel cycle is not obvious, which are about 1.17 to 1.32 metric tons. PWR-UOX consumes 0.81 metric tons of 235U and 0.51 metric tons of 238U；PWR-MOX consumes 0.63 metric tons of 239Pu and 0.58 metric tons of 238U；PWR-ThU3 consumes 0.73 metric tons of 233U and 0.51 metric tons of 232Th；SFR-UOX breeds 3.67 kg of 235U but consumes 1.20 metric tons of 238U；SFR-MOX breeds 43.04 kg of 239Pu and consumes 1.21 metric tons of 238U；SFR-ThU3 consumes 2.15 kg of 233U and 1.21 metric tons of 232Th。All PWR fuel cycles should add fissile to maintain the criticality of the reactor, by contrast, SFR with UOX and MOX not only can add 238U that maintain the criticality of the reactor but also breed more fissile. Although SFR-ThU3 can’t breed more fissile, it can still achieve fuel self-sustain by only adding thorium.
The accumulations of MA production in once-through cycle and closed fuel cycle are, respectively, 29.44kg and 23.64kg, where a roughly 20% MA is reduced in closed fuel cycle compared to open fuel cycle. In closed fuel cycle, the MA productions of SFR-UOX, SFR-MOX, PWR-UOX and PWR-MOX are 8.04kg, 8.12kg, 23.64kg and 26.36kg, respectively. The MA accumulation in the SFR is approximately 70% lower than in the PWR. In comparison with UOX or MOX, the MA accumulation is extremely lower by using ThU3.
To summarize, by using closed fuel cycle not only the efficiency of fuel utilization is significantly increased but also the production of MA is inhibited. Fuel self-sustain and MA production reducing can be achieved by utilizing fast reactor. Only a few amount of MA will be accumulated while using thorium according to its physical properties. From the economic and political points of view, however, there are still a lot of obstacles for using closed fuel cycle. Meanwhile, more research and developments are required for SFR to become a commercial reactor. Regarding thorium fuel there are also some disadvantages, e.g., insufficient conversion efficiency and the production of high radioactivity during reprocessing. Therefore, considerations of different aspects should be taken in account while choosing the fuel cycle.

摘要 i
Abstract iii
致謝 v
目錄 vi
表目錄 ix
圖目錄 xi
縮寫表 xiii
第一章 序論 1
1.1 前言 1
1.2 燃料種類及燃料循環 2
1.3 次要錒系元素及放射毒性 2
1.4 文獻回顧 3
第二章 計算工具程式介紹 9
2.1 SCALE/TRITON/T-DEPL 9
2.1.1 SCALE 9
2.1.2 TRITON/T-DEPL 10
2.2 CARL 14
第三章 錒系元素及燃料循環 15
3.1 錒系元素 15
3.1.1錒系元素分類及特性 15
3.1.2核轉換 16
3.1.3放射毒性與CARL驗證 17
3.2 易裂元素、可裂元素及UOX、MOX、ThU3燃料特性 23
3.3燃料循環及再處理技術現況 29
3.3.1開放式與封閉式燃料循環 29
3.3.2再處理技術現況 32
第四章 反應器燃料束燃耗模型與驗證 34
4.1 壓水式反應器(PWR) 34
4.2 鈉冷式快反應器(SFR) 36
4.3 模型計算驗證 37
4.3.1驗證文獻1 37
4.3.2驗證文獻2 40
4.4 k值計算比較與驗證 43
4.4.1計算公式與TRITON比較 43
4.4.2六種封閉式燃料循環k值比較 44
第五章 燃料循環模擬結果與討論 50
5.1 開放式燃料循環與封閉式燃料循環的比較 50
5.1.1燃耗過程累積與消耗錒系元素數量 50
5.1.2次要錒系元素產量的比較 53
5.1.3次要錒系元素放射毒性的比較 57
5.2六種封閉式燃料循環的比較 59
5.2.1燃耗過程累積與消耗錒系元素數量 59
5.2.2 次要錒系元素產量的比較 63
5.2.3 次要錒系元素放射毒性的比較 68
第六章 結論及未來工作 70
6.1 結論 70
6.2 未來工作 73
參考文獻 74
附錄A 錒系元素捕獲及分裂截面圖 76
A-I 易裂、可裂元素及轉換鏈中的核種 76
A-II 次要錒系元素 81
附錄B 開放式與六組封閉式燃料循環錒系元素累積數量表 89
附錄C SCALE案例的輸入檔 103
C-I PWR-OTC輸入檔 103
C-II PWR-UOX輸入檔 107
C-III PWR-MOX輸入檔 110
C-IV PWR-ThU3輸入檔 113
C-V SFR-UOX輸入檔 116
C-VI SFR-MOX輸入檔 121
C-VII SFR-ThU3輸入檔 124

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