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  • 1 Department of Chemistry, Huzhou Teachers College, Huzhou, 313000 People’s Republic of China
  • 2 China Resources New Energy Group Co., Ltd., Hong Kong, People’s Republic of China
  • 3 China Institute of Atomic Energy, P.O. Box 275(88), Beijing, 102413 People’s Republic of China
  • 4 East China Institute of Technology, Fuzhou City, Jiangxi Province, People’s Republic of China
  • 5 School of Nuclear Science and Technology, Xi’an Jiaotong University, Xi’an, 710049 People’s Republic of China
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Abstract  

99Tc is an important radionuclides related to repository safety assessment. The mobility pertechnetate (TcO4) can be reduced to immobility technetium(IV) hydrous oxides (TcO2·nH2O) by Fe(II)-bearing minerals. In China, Gaomiaozi (GMZ) bentonite is regarded as the favorable candidate backfilling material for the HLW repository, which is contained some FeO. The diffusion behavior of 99Tc was investigated in GMZ bentonite by through- and out-diffusion methods. The effective diffusion coefficient (De), the accessible porosity (εacc), apparent diffusion coefficient (Da) and distribution coefficient (Kd) were decreased with the increasing of dry density. The De values were (2.8 ± 0.2) × 10−11 m2/s and (3.5 ± 0.2) × 10−12 m2/s at dry density of 1,600 and 1,800 kg/m3, respectively. It was indicated that the dominating species was TcO4 during the diffusion processing. While, out-diffusion results showed that part of TcO4 may be reduced by Fe(II). The relationship of De and εacc could be described by Archie’s law with exponent n = 2.4 for 99Tc diffusion in GMZ bentonite. Furthermore, the relationship between Da and dry density (ρ) was exponential.