以迭代解析解法推估放射性核種於膨潤土之傳輸係數研究

Estimating Transport Parameters of Radionuclide in Bentonite by Iterative Analytical Method

汪柏岑(B. T. Wang) ； 李傳斌(C. P. Lee) ； 蔡翠玲(T. L. Tsai) ； 蔡世欽(S. C. Tsai) ； 李奕賢(I. H. Lee) ； 徐國錦(K. C. Hsu)

《鑛冶：中國鑛冶工程學會會刊》 63卷4期 (2019/12) Pp. 7-19

https://doi.org/10.30069/MM.201912_63(4).01

摘要

2025年「非核家園」是目前政府極力推動的重要政策，無論未來我國能源政策如何改變或調整，過去近40年核能電廠運轉所產生的放射性廢棄物是我們必須共同面對的課題，目前國內外研究將深層地質處置視為最可行之處理策略，緩衝材料（膨潤土）用以將放射性廢棄物進行隔離，主要為防止及減緩廢棄物從處置罐中洩漏至生物圈。緩衝材料的物理特性對於吸收放射性核種洩漏及延緩放射性廢棄物的遷移至關重要，其中孔隙率、擴散係數和遲滯因子為主要傳輸參數。Crank於1975年所提出繪圖法係利用管柱擴散實驗數據進行參數推估，其擬合過程僅考慮累積濃度曲線之後段線性部分及固定孔隙率值，因此繪圖法之過程主觀性與結果精準度具有相當大的爭議。本研究提出一新穎方法（PIPIAM）透過迭代計算並結合解析解用以進行參數推估，擬合完整累積濃度曲線用以獲得主要參數，並透過正規化均方根誤差（NRMSE）比較PIPIAM及繪圖法之結果。研究結果顯示，將PIPIAM所求得之參數代回計算濃度後，其濃度誤差及參數不確定性方面優於圖解法，有顯著的效果提升，因此，本研究所提出之方法可用以提供核廢物處置庫安全評估的運輸參數的良好替代方案。

關鍵字

擴散係數 ； 解析解 ； 參數反推 ； 管柱實驗

並列摘要

Nuclear-free homeland in 2025 is an important policy of Taiwan government. No matter how energy policy changes or adjusts in the future, the radioactive waste generated by the operation of nuclear power plants in the past 40 years is a subject we must face together. Deep geological disposal is regarded as the most feasible treatment strategy. Nuclear waste deposit is commonly isolated by buffer material, such as bentonite, to prevent its leak from deposit cane. Buffer materials such as bentonite are vital for absorbing radionuclide leakage and retarding migration from radioactive waste canisters. The diffusion coefficient and the retardation factor are the predominant properties controlling the diffusion-reaction process in a buffer material. Diffusion experiments combined with Crank's graphical method are a well-established process for determining asymptotic diffusion coefficients. However, the inaccuracy of the diffusion coefficient that results from the subjective judgement of the late-time linear part of the cumulative concentration data and the fixed porosity in Crank's graphical method will deteriorate the estimate of the retardation factor. A novel parameter identification process based on an iterative and analytical method (PIPIAM) is proposed here to obtain the diffusion coefficients and porosity of bentonite using concentration data. The results of PIPIAM and the graphical method are compared through an error analysis of concentration. The results show that PIPIAM outperforms the graphical method in terms of the error reduction of the concentration and the uncertainty decrease of the estimated parameters. The proposed method is thus a good alternative for acquiring transport parameters for use in safety assessments of nuclear waste repositories.

並列關鍵字

Diffusion coefficients ； Analytical solution ； Parameter inversion ； Through-diffusion test