核反應器運轉參數對於燃耗信用之耦合相依性研究

Investigation of coupling dependence of operating parameters on burnup credit of spent fuel for nuclear reactors

吳尚謙(Shang-Chien Wu)

指導教授 ： 梁正宏

國立清華大學/原子科學院/核子工程與科學研究所/博士(2019年)

摘要

本論文致力於研究耦合運轉參數對燃耗信用（burnup credit，簡稱 BUC）之臨界安全計算的影響。BUC 可改善用過核子燃料貯存設施的單位容量，具有提升經濟價值、減少風險的優點。擬針對三種反應器類型進行研析：沸水式（Boiling Water Reactor，簡稱 BWR）、壓水式（Pressurized Water Reactor，簡稱 PWR），以及高溫氣冷式（High Temperature Gas-cooled Reactor，HTGR）。在計算上，使用 SCALE6.1.3 與 MCNP6.1 程式，並搭配使用 ENDF/B-VII 的中子截面資料庫。各反應器分別建立兩種模型，以用於進行燃耗與臨界安全計算。基本上，隨著運轉參數的相異，造成易裂材料（fissile material）的消耗速率與中子毒物（如分裂產物或部分錒系元素）的產生速率改變，進而使中子增殖因數（effective multiplication factor，簡稱 keff）也將隨之改變，導致反應度偏移（reactivity deviation，簡稱 ∆k）。在此，茲將單項運轉參數與同時考量多項運轉參數對 keff 的影響，分別稱為單一效應（single effect）與複合效應（compound effect），藉以探討各運轉參數之間的耦合關係（coupling dependence）。又複合效應 ∆k 常非單一效應 ∆k 的線性相加，將直接影響臨界安全評估的準確度。因此，本論文擬將各反應器中最重要的運轉參數，進行複合效應的深入探討，並以各效應對中子能譜之影響，瞭解造成效應背後的因由與機制。最後，將總結各複合效應的機制與重要性，以利未來相關研究亦或核能工業參考及使用。

關鍵字

用過核子燃料 ； 臨界安全分析 ； 燃耗信用 ； 運轉參數 ； 耦合相依性

並列摘要

This study aims to investigate the influence of coupling dependence between operating parameters on the burnup credit criticality safety analysis for PWR, BWR, and HTGR spent nuclear fuels. Burnup credit is of vital importance in the criticality safety analysis due to the fact that it can improve the capacity of storage system and subsequently reduce the cost and the risk of storage system. All the calculations were carried out using SCALE6.1.3 and MCNP6.1 Monte-Carlo simulation codes associated with ENDF/B-VII neutron cross section data libraries. In each type of reactors, two geometrical models were established in order to implement the depletion calculations and criticality calculations. In general, the change of operating parameters will induce a reactivity deviation (∆k) due to the variations in the depletion rates of fissile materials as well as the production rates of plutonium, fission products, or other actinides. In convenience, this study defined the effects of simultaneous variations in one and multiple operating parameters on the effective multiplication factor (keff) as the so-called single and compound effects, respectively. Notably, ∆k resulting from compound effects is not always a simple summation of ∆k’s resulting from the associated single effects. This phenomenon may influence the precise assessment of burnup credit to some extent. Furthermore, this study investigated the influences not only on the magnitudes of ∆k’s but also the neutron energy spectrum due to either single or compound effects. The mechanisms causing each single and compound effect were studied in depth as well. Finally, this study concluded the importance of the compound effects in nuclear spent fuel storage for future research or nuclear industrial applications.

並列關鍵字

spent nuclear fuel ； criticality safety analysis ； burnup credit ； operating parameter ； coupling dependence

參考文獻

[1] Code of Federal Regulations, Title 10, “Energy” (2011).

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[5] J.C. Wagner, M.D. DeHart, “Review of Axial Burnup Distribution Considerations for Burnup Credit Calculations”, ORNL/TM-1999/246, Oak Ridge National Laboratory (2000).