Diffusion characteristics of HTO and 99TcO4 − in compacted Gaomiaozi (GMZ) bentonite
The characteristics of diffusion are essential to the transport of radionuclides through buffer/backfill materials, such as bentonite, which are commonly found in waste repositories. This study used through-diffusion techniques to investigate the diffusion behavior of HTO and 99TcO4 − on GMZ bentonite of various densities. Diffusion rates were calculated by measuring the diffusion coefficients (D e, D a), plotting breakthrough curves and interpreting experiment data. The apparent and effective diffusion coefficients of HTO ranged from (1.68 ± 0.40) × 10−11 to (2.80 ± 0.62) × 10−11 m2/s and from (4.61 ± 1.28) × 10−12 to (16.2 ± 2.50) × 10−12 m2/s, respectively. The apparent and effective diffusion coefficients of 99TcO4 − ranged from (5.26 ± 0.16) × 10−12 to (7.78 ± 0.43) × 10−12 m2/s and from (1.49 ± 0.002) × 10−12 to (4.16 ± 0.07) × 10−12 m2/s, respectively. The distribution coefficients of HTO and 99TcO4 − ranged from (0.70 ± 0.12) × 10−2 to (1.36 ± 0.53) × 10−2 mL/g and from (1.12 ± 0.06) × 10−2 to (5.79 ± 2.22) × 10−2 mL/g, respectively. The D e and K d values were shown to decrease with an increase in the bulk dry density of compacted bentonite. Our results show that HTO and 99Tc could be considered non-sorbent radionuclides. The data obtained in this study provide a valuable reference for the safety assessment of waste repositories.
KeywordsDistribution coefficient Apparent diffusion coefficient Effective diffusion coefficient Compacted bentonite Through-diffusion
The authors would like to thank the Nuclear Backend Management Department at Taiwan Power Company for financially supporting this research.
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