近岸山區為台灣低階核廢料處置設施的建議候選場址之一，透過坑道處置來封存核廢料以減少核種外釋可能，處置設施規劃設置於地表下五十至兩百公尺處，包含多條處置坑道以存放不同類型的低階核廢料，處置坑道由多重工程障壁構成，利用多重工程障壁及母岩達到良好的核種圍阻與遲滯功能，防止核種從處置坑道遷移至人類生活圈進而對人類健康造成危害。 本研究參考瑞典SR-PSU場址技術報告，將模擬分為遠場與近場之流場模擬及核種傳輸模擬，在考量有限運算資源與提高運算解析度雙重考量下，將模擬網格設計為遠場、近場(處置設施)與近場(處置坑道)的三層級網格，透過邊界條件設定來串接不同層級的模擬成果，以達到近遠場核種衰變鏈整合數值模擬之目的。模擬工作採用HYDROGEOCHEM 5.6數值模擬工具，將處置設施預計接收國內核電廠除役廢棄物、運轉廢棄物的核種總量做為近場(處置坑道)源項進行核種傳輸模擬，分析近、遠場之穩態地下水流流場特徵，穩態傳輸、暫態傳輸及11種關鍵核種及其衰變鏈之暫態核種傳輸於近岸環境之移棲特性。 ;Tunnel disposal at nearshore was tentatively selected as one of final disposal sites for low-level wastes in Taiwan. The potential disposal facilities was located at 50m~200m below ground surface and designed with several disposal tunnels. The safety function of disposal tunnels with multiple engineered barriers and host rock is to provide retardation and containment of radionuclide for preventing potential release of radionuclides from the repository into human living environment to threaten human health. Simulations of flow and radionuclide transport were sequentially performed for near-field and far-field setups as proposed in technical reports of SKB SR-PSU site. In this study, three levels of grids were designed with far-field, near-filed (all tunnels), and near-field (selected tunnel section) to reduce computation time without compromising spatial resolution. The HYDROGEOCHEM_5.6 model was used to perform each level of simulations. The linkages between different simulation levels were connected by boundary conditions retrieved from outputs of other simulation levels.. Total radioactive activities of source term were estimated as given in the report of Taiwan Power Company. Steady transport, transient transport, and 11 radionuclide decay chains were performed with steady flow for demonstrations.
