The Diffusion of Tc-99 in Beishan Granite-Temperature Effect

C Li,L H Wang,Z Zheng,C L Wang,W Y Tian,X Y Liu,C L Liu,T Chen

doi:10.4236/wjnst.2013.31006

C Li, L H Wang + Show 6 more

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https://doi.org/10.4236/wjnst.2013.31006

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Abstract

In the safety assessment of a potential site for high-level radioactive wastes (HLW) disposal, the investigation on the geochemical behaviors of key radionuclides with the possibility for releasing from the potential repository is an important aspect. Due to the high mobility of technetium under most repository conditions, lots of research works were performed to investigate the diffusion of technetium in different potential rocks. In spite of these studies, there remains a lack of data addressing temperature effects. In this paper, the diffusion of 99Tc in Beishan granite at temperatures from 25℃ to 55℃ was studied with laboratory small scale diffusion devices. The experimental data were fitted with a finite difference scheme to get the effective diffusion coefficient (De) of . The results indicated that the relationship of De with temperatures could be described as the modified Stokes-Einstein equation, and the formation factor of Beishan granite was constant in the temperature range of 25℃ - 55℃ with the value of (3.91 ± 1.77) × 10-4.

Highlights

Safety disposal of high-level radioactive wastes (HLW) is a worldwide challenge of nuclear industry
The results indicated that the relationship of diffusion coefficient (De) with temperatures could be described as the modified Stokes-Einstein equation, and the formation factor of Beishan granite was constant in the temperature range of 25 ̊C - 55 ̊C with the value of (3.91 ± 1.77) × 10−4
The diffusion of 125I− as a surrogate for 129I− in Beishan granite obtained at 300-m depth by laboratory diffusion experiments, and the results showed that the effective diffusion coefficient ranged from 2.44 × 10−12 to 2.72 × 10−12 m2/s [15]

Summary

Introduction

Safety disposal of high-level radioactive wastes (HLW) is a worldwide challenge of nuclear industry. To demonstrate that the wastes can be safely isolated from the biosphere in a long time scale which is needed for the HLW radioactivity decays to natural level, the safety assessment of the geologic repository is an essential task. In the safety assessment of a potential site for HLW disposal, investigation on the geochemical behaviors of key radionuclides with the possibility for releasing from the potential repository is an important aspect. Chen et al investigated the influence of temperature on 125I− diffusion in 600-m deep Beishan granite, and found that the relationship between the effective diffusion coefficient and temperature could be described by the modified Nernst equation at 27 ̊C - 50 ̊C [16]. Its diffusion and migration data are important to the data base for performance assessment of the potential geologic repository, while the temperature effect on the diffusion of 99Tc in host rocks has not yet been reported. The temperature effect on its diffusion in Beishan granite was investigated by through-diffusion method

Materials

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Results and Discussions

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