TRR用過燃料鈽含量非破壞性檢測研究

Determination of Plutonium Content in TRR Spent Fuel by Nondestructive Neutron Counting

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/博士(2011年)

摘要

台灣研究用反應器(TRR)用過燃料含有武器等級鈽元素，燃料安定化作業將把金屬TRR用過燃料經由熱室燒製處理成氧化物粉末。為了核子保防，本研究將於燃料安定化前後，分別以非破壞性檢測方法測定鈽元素含量。
我們建立兩套中子偵測系統，即Spent Fuel Neutron Counter (SFNC)系統和Neutron Coincidence Counter (NCC)系統，分別用於量測TRR 用過燃料棒和燒製成氧化物粉末中Pu-240含量。鈽元素總量則依MCNPX計算分析TRR用過燃料之鈽元素各同位素含量，求出Pu/240Pu重量比率加以轉換。SFNC 系統偵檢效率校正係以一全新的TRR燃料棒置於一乾淨的水槽中測量為之，並經MCNPX 程式模擬計算驗證。七根TRR 用過燃料棒之測量則在鄰近用過燃料貯存池之相連水槽中進行。除了已氧化和/或斷裂的用過燃料棒外，測得鈽元素含量與根據燃耗資料之MCNPX計算值相當吻合。而NCC 系統的偵檢效率，包含總計數和雙重計數效率之校正係以U3O8 粉末測量搭配MCNPX 程式計算獲得。三根TRR 用過燃料棒經熱室燒製成之氧化物粉末，以NCC 系統在熱室測得之鈽元素含量，與安定化前測定結果，差異皆在18%以內。
總結而論，本論文之非破壞性檢測技術可準確測定TRR用過燃料的鈽元素含量，透過安定化前後的兩次測量，更證明TRR用過燃料的鈽元素含量並無明顯的自然或人為流失。

關鍵字

用過燃料 ； 核子保防 ； 鈽元素分析 ； 中子計數

並列摘要

Taiwan Research Reactor (TRR) spent fuel rods contain weapons-grade plutonium. For the nuclear safeguard purpose, this work aims to determine the plutonium content in the TRR spent fuel rods by using the nondestructive neutron measurement before and after the fuel stabilization process, by which the metallic spent fuel rods will be transformed to oxide power for interim storage.
We established two neutron detection systems, namely, the SPent-fuel Neutron Counter (SPNC) system and the Neutron Coincidence Counter (NCC) system for determining the Pu-240 content in the TRR spent fuel rod and in the transformed oxide powder, respectively. The measured Pu-240 contents in the TRR spent fuel were then converted into total plutonium contents by using the MCNPX-calculated Pu-to-240Pu mass ratio. The detection efficiency of the SPNC system was calibrated by the measurement of a TRR fresh fuel in a water trench filled with clean water and verified by the MCNPX simulation calculation. Seven TRR spent fuel rods were measured in the nearby water trench connected to the spent fuel storage pool. The measured plutonium contents agree well with the MCNPX-calculated values based on the burnup history of each spent fuel rod, except for the broken rods with fuel oxidation. The detection efficiencies consisting of singles rate and doubles rate efficiencies of the NCC system were determined by using measurements using U3O8 powder in couple with MCNPX calculations. Canisters filled with oxide powder converted from three TRR spent fuel rods were measured by the NCC system in the hot cell. The measured plutonium contents of the oxide powder from the spent fuel rods agree well (<18%) with the measured value before the fuel stabilization process.
In conclusion, our nondestructive neutron detection systems can accurately determine the plutonium content in TRR spent fuel. Furthermore, the two measurements for each TRR spent fuel prove that there is no obvious process and artificial loss of plutonium contents during the fuel stabilization process.

並列關鍵字

Spent Fuel ； Nuclear Safeguard ； Plutonium Assay ； Neutron Counting

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