Pertechnetate diffusion in GMZ bentonite

摘要

~(99)Tc is an important radionuclides related to repository safety assessment. The mobility pertechnetate (TcO_4~-) can be reduced to immobility technetium(IV) hydrous oxides (TcO_2·nH_2O) 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 ~(99)Tc was investigated in GMZ bentonite by through- and out-diffusion methods. The effective diffusion coefficient (D_e), the accessible porosity (e_(acc)), apparent diffusion coefficient (D_a) and distribution coefficient (K_d) were decreased with the increasing of dry density. The D_e values were (2.8 ± 0.2) 9 10~(-11) m~2/s and (3.5 ± 0.2) 9 10~(-12) m2/s at dry density of 1,600 and 1,800 kg/m~3, respectively. It was indicated that the dominating species was TcO_4~- during the diffusion processing. While, outdiffusion results showed that part of TcO_4~- may be reduced by Fe(II). The relationship of D~e and e_(acc) could be described by Archie’s law with exponent n = 2.4 for ~(99)Tc diffusion in GMZ bentonite. Furthermore, the relationship between D_a and dry density (q) was exponential.