核燃料循環次要錒系元素減量理論探討

Theorectical Investigation of Minor Actinides Reduction in Fully Closed Fuel Cycle

陳彥甫(Yen-Fu Chen)

指導教授 ： 江祥輝

國立清華大學/原子科學院/工程與系統科學系/碩士(2006年)

摘要

用過核燃料中的次要錒系元素是造成放射性廢料擁有長期危害的主要原因。本論文利用再循環次要錒系元素的核燃料循環，探討次要錒系元素的減量效果，並採用SCALE計算程式系統中的SAS2H控制模組，模擬燃料在燃燒和冷卻過程中核種隨時間的變化。本論文分別針對輕水式反應爐和液金快滋生反應爐的核燃料循環作計算，並參考文獻資料建立兩種反應爐的計算模型。
輕水式反應爐使用氧化鈾作燃料，235U的濃化度是 3.2%，燃耗設定在 33 GWD/tHM。液金快滋生反應爐使用混合耗乏鈾和鈽的氧化燃料， 其中鈽是由輕水式反應爐中的用過核燃料提煉製成，耗乏鈾和鈽重量各佔 87.6% 和 12.4%，設定燃耗為 100 GWD/tHM。在經歷完整燃燒和冷卻過程之後，用過核燃料中的次要錒系元素再加到新的燃料中，然後儲存一段時間再放進反應爐中燃燒。核燃料循環中的冷卻和儲存時間的總和，在輕水式反應爐中是五年；而在液金快滋生反應爐中是十年。
結果顯示輕水式反應爐封閉核燃料循環跟一次核燃料循環相比，在第十次循環時，次要錒系元素總量減少達到 20%。在液金快滋生反應爐核燃料循環中，經過二十次再循環次要錒系元素，可使次要錒系元素總量減量高達 90%。由於次要錒系元素為高放射性的元素，基於輻射安全的考量，針對再循環之新燃料的射源強度和等效劑量率作評估。在幾次循環後，新燃料的射源強度約維持在同一個水平，每根燃料的中子射源強度約為 3.3×108 neutrons/s，光子射源強度約為 2.3×1013 gamma-rays/s；而在距離射源1米處，中子和光子等效劑量率分別為 3.8×103 µSv/hr 和 8.4×104 µSv/hr 。因此，在新燃料製造、運輸和吊裝上的屏蔽問題必須額外加以考慮。

關鍵字

次要錒系元素 ； 核燃料循環 ； 放射毒性

並列摘要

The minor actinides in spent fuels dominate long-term hazard radioactive waste. In this study, we evaluated the minor actinides reduction in minor actinides multiple recycling fuel cycle compared with minor actinides non-recycling. SAS2H control module in SCALE 4.4a code system was used to calculate fuel depletion and actinide transmutation. The LWR and LMFBR fuel cycle were investigated respectively.
For the LWR fuel cycle it was assumed that the fresh fuel consists of uranium oxide with a 3.2% enrichment of 235U and the burnup is 33 GWd/tHM. For the LMFBR fuel cycle the fresh fuel was assumed to be the oxide fuel consisting of 12.4% of Pu, which is from thirteen of the LWR spent fuels, and 87.6% depleted uranium and a burnup of 100 GWd/tHM was adopted. After the completion of the burnup and cooling, the minor actinides in the spent fuel were added in the fresh fuel and stored a while for recycling. It was assumed that the sum of cooling time and storage time are 5 years for LWR and 10 years for LMFBR.
For LWR, the minor actinides reduction in multiple recycling fuel cycle at 10th recycling are 20% compared with LWR once-through fuel cycle. For LMFBR the minor actinides reduction in minor actinides multiple recycling fuel cycles at 20th recycling are 90% compared with minor actinides non-recycling fuel cycle. For radiation shielding safety issue, the source intensity and dose equivalent rate of fresh fuels in minor actinides recycling LMFBR fuel cycle were also evaluated. It was found that after a few recycling the neutron intensity of the fresh fuel is ~3.3×108 neutrons/s per assembly and the gamma-ray source intensity is ~2.3×1013 gamma-rays/s per assembly. Furthermore, the neutron and gamma dose equivalent rate at 1 m distance from the fresh fuels are ~3.8×103 µSv/hr and ~8.4×104 µSv/hr, respectively. Therefore, shielding problems must be taken into account for fuel fabrication, transportation, and handling.

並列關鍵字

Minor Actinides ； Fuel Cycle ； Radiotoxicity

參考文獻

GLOBAL 2005, Tsukuba, Japan, October 2005.

Transuranic Waste Recycled in Light Water Reactors. Nuclear Technology, 152:354–

366, 2005.

[4] E.L. Gluekler. U.S. Advanced Liquid Metal Reactor(ALMR). Progress in Nuclear

[5] N. Messaoudi and J. Tommasi. Fast Burner Reactore Devoted to Minor Actinide