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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 (D e), the accessible porosity (εacc), 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) × 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 D e and εacc could be described by Archie’s law with exponent n = 2.4 for 99Tc diffusion in GMZ bentonite. Furthermore, the relationship between D a and dry density (ρ) was exponential.

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Abstract  

Distribution coefficients (K d), apparent diffusion coefficients (D a) and retardation factor (Rf) in this work obtained by batch and through-diffusion experiments have been performed, respectively. The accumulative concentration method developed by Crank (The mathematics of diffusion, <cite>12</cite>) was applied to realize apparent and effective diffusion coefficient (D a and D e) of Se. Besides, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (K d) obtained by batch tests in 14 days under aerobic and anaerobic systems were 6.98 ± 0.35 and 5.21 ± 0.25 mL/g. Moreover, Rfcal and K d cal of Se obtained from accumulative concentration’s method in through-diffusion test showed an obvious discrepancy with the increase of length/diameter (L/D) ratio. However, it presented an agreement of RfH/Se and K d H/Se in a various L/D ratio by comparison of apparent diffusion coefficient’s (D a) between HTO and Se. It appears that the RfH/Se and K d H/Se obtained from the through-diffusion experiments are lower than those derived from the batch experiments. Therefore, it demonstrates that reliable Rf and K d of Se by through-diffusion experiments could be achieved at a non-reactive radiotracer (HTO) prior to tests and will be more confident in long-term performance assessment of disposal repository.

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Abstract  

Developing a better understanding of xenon transport through porous systems is critical to predicting how this gas will enter the atmosphere after a below ground nuclear weapons test. Radioxenon monitoring is a vital part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System. This work details the development of prompt gamma activation analysis for measuring the diffusion rates of xenon and argon gases through a porous medium. The University of Texas at Austin maintains a prompt gamma activation analysis facility with a peak neutron flux of ~1.5 × 107 cm−2 s−1 and a beam diameter of 1 cm. Due to the relatively large prompt gamma cross sections of many stable xenon isotopes at thermal and sub-thermal neutron energies, prompt gamma activation analysis is a suitable technique for in situ non-destructive analysis of natural xenon. A test chamber has been designed and constructed to utilize prompt gamma activation analysis to measure xenon and argon diffusion through geological materials (e.g., sand, soil, etc.). Initial experiments have been conducted to determine the detection limits for stable gas measurements. The results from these experiments will be utilized to benchmark parts of a xenon transport model that is being used to determine diffusion coefficients for xenon and argon.

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Abstract  

Repositories for radioactive wastes are sited in the environment with very low permeability. One of the most important processes leading to the release of radionuclides to the environment is therefore diffusion of radionuclides in both natural and engineered barriers. Data for its description are crucial for the results of safety assessment of these repositories. They are obtained usually by comparison of the results of laboratory diffusion experiments with analytical and/or numerical solution of the diffusion equation with specified initial and boundary conditions. Results of the through-diffusion experiments are obviously evaluated by the “time-lag” method that needs for most of sorbing species unfortunately very long time of the experiment duration. In this paper a modified approach is proposed for the evaluation of diffusion data for safety assessment, which decreases the influence of propagation uncertainties using incorrect data and reduces time for acquiring data for safety assessment. This approach consist in the following steps: (i) experimental measurement of material diffusion parameters under various conditions using non-sorbing tritiated water or chlorine for which it is easy to reach conditions under which the “time-lag” method of evaluation of the result of the through-diffusion experiment is applicable—this step provides well established diffusion characteristics of materials for neutral species and anions, then (ii) to evaluate sorption isotherms for sorbing radionuclides from batch experiments under conditions corresponding to composition of material pore water, (iii) to assess the values of effective and apparent diffusion coefficients for sorbing radionuclides from well-defined diffusion coefficients of species in free water and (iv) to verify the obtained results using relatively short-term diffusion experiments with sorbing radionuclides, which will be evaluated using the time dependent decrease of the concentration in the input reservoir of the diffusion cell. A numerical model of the diffusion cell can model the decrease of concentration of species. The code, which we used for this type of evaluation of diffusion experiment, is based on the same approach to modelling that we use for modelling of the diffusion transport in performance assessment studies. The advantage of this approach consists in the compatibility of the approaches used for both evaluation and verification of the laboratory diffusion experiments and performance assessments and in considerable less time needed for experiments.

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Abstract  

Kinetics of N-methyl pyrrolidone evaporation from swollen photo-crosslinked polyacrylate was monitored thermogravimetrically at temperatures ranging from 323 to 398 K. Crosslink density dependence of evaporation kinetics was investigated in photo-crosslinked polyacrylates with crosslinked density ranging from ≈1.2 × 102 to ≈1.7 × 104 mol m−3 and number of main chain atoms between crosslinks ranging from ≈70 atoms to ≈6 atoms, respectively. As was shown, evaporation kinetics was controlled by the solvent diffusion in polymer. Activation energies of evaporation (diffusion) were deduced from the rate measurements at different temperatures. Apparent activation energy of evaporation decreased from 48.7 to 31.1 kJ mol−1 with crosslink density increase. Activation energy of pure N-methyl pyrrolidone evaporation was 50.6 kJ mol−1. Decrease of the rate of solvent diffusion and unexpected decrease of diffusion activation energy with increase of crosslink density of swollen polymer matrix was explained by decrease in polymer chain segments mobility, as indicated by Eyring’s approach to diffusion in polymers.

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Abstract  

In terms of pre-safety assessment of a potential site for high-level radioactive wastes disposal in China, the geochemical behavior of key radionuclides which tend to be released from the repository must be thoroughly investigated. 99Tc is a long-lived fission product with appreciable productivity in nuclear fuel, and Tc (+7) has unlimited solubility in near-field geochemical environments. In this study, the effects of ionic strength and humic acid on 99TcO4 sorption and diffusion in Beishan granite were investigated with through-diffusion and batch sorption experiments. Results indicated that the effective diffusion coefficients (D e) of 99TcO4 in Beishan granite varied from 1.07 × 10−12 to 1.28 × 10−12 m2/s without change with ionic strength, while the distribution coefficients (K d) negatively correlated with ionic strength of the rock/water system. This study also indicates that there is no evident influence of humic acid concentration on the diffusion behavior of 99TcO4 in Beishan granite, due to the limited interaction between humic acid and 99TcO4 .

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Abstract  

Through theoretical analysis and empirical demonstration, this paper attempts to model the behavior of science and technology by investigating the self-propagating behavior of their diffusion for South Korea, Malaysia and Japan. The dynamics of the self-propagating behavior were examined using the logistic growth function within a dynamic carrying capacity, while allowing for different effectiveness of potential influence of science and technology producers on potential adopters. Evidence suggests that the self-propagating growth function is particularly relevant for countries with advanced science and technology, like Japan. While self-propagating growth was also found for South Korea, the diffusion process remained fairly static for Malaysia.

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), ASIS , 2000 , pp. 405 – 432 . 2. Crane , D. 1972 Invisible Colleges: Diffusion of Knowledge in Scientific Communities University of Chicago Press

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Introduction Knowledge diffusion is the adaptation of knowledge in a broad range of scientific and engineering research and development. It can be defined as the adaptations and applications of knowledge documented in

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. (1966): Medical Innovation: A Diffusion Study . Indianapolis: Bobbs-Merill. Katz E. Medical Innovation: A Diffusion Study

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