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  • Author or Editor: W. Dai x
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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  

With the low permeability and high swelling property, Gaomiaozi (GMZ) bentonite is regarded as the favorable candidate backfilling material for a potential repository. The diffusion behaviors of HTO in GMZ bentonite were studied to obtain effective diffusion coefficient (De) and accessible porosity (ε) by through- and out-diffusion experiments. A computer code named Fitting for diffusion coefficient (FDP) was used for the experimental data processing and theoretical modeling. The De and ε values were (5.2–11.2) × 10−11 m2/s and 0.35–0.50 at dry density from 1,800 to 2,000 kg/m3, respectively. The De values at 1,800 kg/m3 was a little higher than that of at 2,000 kg/m3, whereas the De value at 1,600 kg/m3 was significantly higher (approximately twice) than that of at 1,800 and 2,000 kg/m3. It may be explained that the diffusion of HTO mainly occurred in the interlayer space for the highly compacted clay (dry density exceeding 1,300 kg/m3). 1,800 and 2,000 kg/m3 probably had similar interlayer space, whereas 1,600 kg/m3 had more. Both De and ε values decreased with increasing dry density. For compacted bentonite, the relationship of De and ε could be described by Archie’s law with exponent n = 4.5 ± 1.0.

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Two fundamental test systems were used to evaluate the visco-elastic properties of doughs from wheat samples of three varieties grown at four distinct sites. For comparison, tests were also performed with traditional equipment, namely the Mixograph, an extension tester and a Farinograph-type small-scale recording mixer. Uniaxial dough elongation (with an Instron) produced results similar to the conventional extension tester, except that results were provided in fundamental units (Pascals), the critical value recorded being the elongational stress at maximum strain. Stress relaxation measurements were performed following a small initial shear strain. With this method, it was possible to distinguish between the viscosity and the elastic components of dough visco-elasticity. In all the tests the extra dough-strength properties were evident for the variety (Guardian) that had the 5 + 10 glutenin subunits, in contrast to the other two with the 2 + 12 combination of subunits.

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To determine the prevalence of wheat sensitivity in a randomly selected Australian population, a study was carried out on sera samples of the Geelong Osteoporosis Study (GOS) age-stratified cohorts of men and women who were randomly selected from electoral rolls for the Barwon Statistical Division (n = 1145). The human sera were analysed by ELISA-based method using the ImmunoCAP 100 instrument (Phadia, Sweden). IgE from human sera were bound to the wheat (f4) and milk (f2) allergens that have been previously coated on the ImmunoCAPs. The number of IgE wheat and milk RAST positive individuals was determined. In order to relate the increased IgE immuno-reactivity to allergen symptoms, a questionnaire was established and sent to the blood donors and 974 individuals responded. Of these (n = 974) 147 individuals (15.1%) reported symptoms caused by wheat consumption, 179 (15.6%) and 112 (9.8%) sera showed RAST positive results (IgE > 60 response units) in wheat and milk RAST tests, respectively. However, only 2.5% of those participants with symptoms related to wheat had positive IgE values indicating that the relationship is complex: a large proportion (12.7%) of the investigated population might suffer from other wheat related disorders (i.e. not IgE mediated), such as celiac disease, non-celiac reaction to gluten, reaction to fructans for those with irritable bowel syndrome as well as other factors. For the 13.2% who showed raised IgE antibody levels without symptoms we postulate that these individuals have latent wheat sensitivity with the potential of developing symptoms sooner or later.A comparative study to investigate the immune reactivity of human IgE against wheat and spelt antigens was carried out using the sera of 73 patients found to be RAST positive for wheat. Of these 63% (n = 50) showed a higher IgE immune reactivity against wheat, while 30% (n = 24) showed higher IgE response against spelt antigens, the remaining 7% have indifferent responses against both antigens. Since the provided Phadia wheat and spelt antigens used in this study originated from Europe, Australian wheat and spelt varieties were also used to prepare antigens in order to investigate the response of Australian sera to local wheats. It was found that the immune reactivity of IgE wheat positive sera from a normal Australian population is lower for spelts compared to wheats regardless of their origin but much lower against an Australian spelt containing a mutation in its expansin gene. Aclinical feeding trial would be necessary to confirm if this difference in immune reactivity between spelt and wheat is consistent with a difference in allergenicity.

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