低放射性廢棄物處置場全系統安全評估程式耦合地下水流模式之可行性研究

Abstract

低放射性廢棄物在掩埋後，廢料桶內的核種，可能會因為環境因素而發生外洩， 經地質圈及各種傳輸路徑，回到人類的生活圈，而對環境產生衝擊。因此在設置處置 場址之前，需先進行處置場的安全評估。在模擬低放射性廢棄物於處置場址遷移問題 時，需先調查場址的水文地質資料，並依照場址及廢棄物特性，篩選合適的模式，進 行情境模擬與環境安全評估。國內、外發展的地下水模式種類繁多，各有其優缺點及 適用性，在九十七年度計畫「地下水及表面水程式篩選及國內資料之蒐集」中，我們 篩選出適合模擬放射性廢棄物的地下水模式。九十八年度計畫「低放射性廢棄物處置 場全系統安全評估程式及重要參數之分析研究」中，則採用全系統安全評估程式 GoldSim 的核種傳輸模組，以一維流場模擬核種外洩後，進入地質圈的傳輸情形。本 年度計畫擬延續前兩年的研究成果，選用GoldSim 機率程式做全系統安全評估，但期 望能更準確地模擬核種自處置場釋出、外洩後，在地層介質中的遷移與衰變。本研究 中，GoldSim 核種傳輸模組中的裂隙網路路徑將用來模擬核種在岩層裂隙中二維或三 維的傳輸情形；此外，我們將初步瞭解GoldSim 的動態連結功能，評估適合耦合的地 下水流與生物圈相關的模式，針對輸入參數提供給值建議。本計畫的研究成果，可供 原能會物管局未來作安全管制與環境評估的參考。

The radioactive nuclides may release from the waste tanks and migrate in the environment due to the damage of waste tanks by some environmental factors after a long-term disposal. Therefore, the safety assessment for every candidate site should be made before its installation. To predict the impacts of low-level radioactive waste migrating in a disposal site, one should first collect the hydrogeological data in the field, select an appropriate model based on the field and wastes properties to simulate the release situation, and finally perform the environmental safety assessment. Many commercial or academic groundwater flow models had been developed based on various assumptions and limitations. In year 2008, we examined the capability of several groundwater flow and transport models in simulating the radioactive waste transport in the project “Review on the surface water and groundwater models and collection for hydrogeological information.” In year 2009, we have another project named “Safety assessment and major parameters analyses for low level nuclear waste disposal site,” in which the RT (Radionuclide Transport) module in GoldSim program was adopted to simulate the one-dimensional transport of radioactive nuclides in an aquifer. This project is a continued study after pervious two studies. The GoldSim program is again selected to do the total system safety assessment; nevertheless, it is expected to do the simulation of the migration, transport, and decay of radioactive nuclides in a more complex aquifer system. In this work, we apply the network pathway of the RT module in GoldSim program to simulate the radioactive nuclides transport in a two- or three-dimensional fracture matrix. In addition, we will try to understand the dynamic link function in the GoldSim program, assess the capability of the candidate groundwater flow models and simulation models for biosphere for coupling with the GoldSim program, and give the suggested values for the input data. The results of this project can be provided as a reference for Atomic Energy Council (AEC) to examine or review the reports of the environmental safety assessment and site selection.