低放射性廢棄物最終處置場採用「多重障壁」概念，係利用多重防護設施將低放射性廢棄物與人類生活圈隔絕；由於障壁需長期提供阻絕功能，因此需探討障壁材料長期於最終處置場環境下可能造成劣化現象與其劣化速率情形。目前最終處置場候選場址可能建造於濱海區域且可能為淺地層處置，此環境易於造成鋼筋腐蝕現象之發生，影響混凝土長期耐久性。 本研究將延續以鋼纖維混凝土為處置場工程障壁材料，根據最終處置盛裝容器可能採用之混凝土配比，探討其抵抗氯離子入侵之能力，依據ASTM C1556標準方法製作試體並進行實驗，求取預定使用混凝土配比之氯離子擴散係數及時間因子。此外，為進一步提升盛裝容器混凝土之品質，採用高溫養治方式，以改善混凝土微結構，並提升其性能。針對常溫與高溫養治之混凝土，進行其工程特性及耐久性成效比較，以評估預定混凝土配比高溫養治的效能。此外，由於預定採用配比添加鋼纖維以增強混凝土抗彎強度，故針對混凝土中鋼纖維分布情形，建立方法進行統計分析，評估其分布之均勻性。 研究成果將用於評估障壁用混凝土配比之抗氯離子入侵能力能否滿足最終處置場服務年限之需求及推算其劣化速率，以提供國內興建低放射性廢棄物最終處置場之指標參考，提升低放射性廢棄物最終處置設施之安全性。 ;The final disposal of low-level radioactive wastes will be using concrete barriers. Due to the long service duration for the intended applications, it is likely that the barrier concrete will encounter adverse environments and thus the service life of the concrete barrier needs to be investigated. In this study, two concrete mixes possibly used for fabricating highly integrated containers, namely mixes C and M, will be tested by ASTM C1556 standard procedures to determine their diffusion coefficient under the attack of chloride irons. The profile of chloride concentration at various depths will be determined for concrete specimens at 28, 90, 183, and 365 days of age after immersing in NaCl solution for over 35 days. Then, Fick’s second law can be used to obtain chloride diffusion coefficient and surface chloride content using non-linear regression technique. And the experimental data will be used to estimate the change in diffusion coefficient with time for the two concrete mixes. Also, the shrinkage of the concrete after high-temperature curing will be tested. In addition, the porosity of concrete mixes after curing at elevated temperature is to be examined, along with the pore size distribution of the testing mixes. The resistivity of barrier concrete will be determined for use of quality control purposes. Finally, a computation scheme will be developed to calculate the time required for chloride irons to penetrate 35 mm of the concrete barrier and reac1uhing a concentration level of 0.05% by weight of concrete. The calculated results can be compared and verified with those derived from Program Life-365 to validate the effectiveness of the program. By using the computation scheme, the service life, in terms of resistance to chloride attack, of the two concrete mixes can be found.
