Fire is a typical scenario for nuclear accidents, in which uranium-containing materials will release uranium aerosols. Limited by many aspects, uranium aerosols cannot be used directly to carry out nuclear emergency training and equipment development research under real conditions. Therefore, it is necessary to filter and evaluate available surrogate materials through experiments. In this paper, metallic zinc is used to study the source term and particle size distribution of zinc aerosols under fire conditions, and the feasibility of zinc as a surrogate material for uranium aerosol research is evaluated based on the data of uranium aerosols in the literature. The experimental results show that the mass median aerodynamic diameter obtained by fitting with lognormal distribution is between 0.36 and 0.59 µm. The cumulative mass fraction distribution data are consistent with those given in the literature, indicating that the zinc aerosols generated under fire have a nice simulation effect on uranium aerosols in terms of particle size distribution. As for air release fraction (ARF) and respirable fraction (RF), the experiment of zinc aerosols is greater than that of uranium aerosols, which means the simulation in ARF and RF is not so good.

U(VI) was found to form intrinsic colloids in the natural groundwater. Fluorescence spectra, TEM, SEM techniques and thermodynamic calculation were used to identify the species of U(VI) and characterize the intrinsic uranium colloidal particles in the groundwater. The effect of pH on the formation of U(VI) colloidal particles was studied. It was found that under near-neutral and strong alkaline conditions, several elements, mainly Ca, Na and Si were responsible for the formation of intrinsic U(VI) colloid, and under weak alkaline conditions, U(VI) colloidal particles were not formed due to the formation of calcium uranyl carbonate complex.

在偶发事故导致的高温环境下,含铀材料会释放铀气溶胶,危害环境及周边人员.本文从典型场景、研究材料、研究方法、源项表征及研究结果等方面综述了国内外对高温条件下铀气溶胶生成规律的相关研究.

In this study, the basic physicochemical properties (composition, morphology and surface charge) of the colloids obtained from Gaomiaozi (GMZ) bentonite were analyzed and photon correlation spectroscopy (PCS) tests were conducted for looking into the effects of ionic strength and pH on the stability. The results showed that the bentonite colloids were composed primarily of montmorillonite and cristobalite, and remained stable up to at least 8 months in pure water system, and its self-coagulation was negligible. The titration curves of the bentonite colloids showed a typical titration shape of montmorillonite clay, while a common intersection at the point of zero charge (PZC) around 9.5 and a slightly higher net proton sorption capacity compared with bulk form of GMZ bentonite reported in the literature were observed. The stability was strongly PZC dependent, around which the critical coagulation concentration (CCC) value rose rapidly with increasing pH stemming from the transition of different aggregation mechanisms. Further, a more important effect of the edge charge in strongly alkaline conditions was found to exist. This work can be helpful for better understanding the stability characterization of layered clay colloids and provides a valuable reference for safety assessments of the deep geological disposal repository for high-level radioactive wastes.

Plutonium is one of the key radionuclides in nuclear decommission. In this study, a rapid method was developed to analyze Pu for concrete samples using total digestion, CaF2/LaF3 coprecipitation, extraction chromatography using TEVA and DGA resins, and ICP-MS measurement. The whole analytical process can be achieved within 2 days, with sufficiently high decontamination factors of interfering elements and high Pu chemical recovery (57–93%). The high throughput (22 samples/2 days) and low LODs (0.008 mBq g−1 for 239Pu and 0.02 mBq g−1 for 240Pu) allow this method to effectively detect low level Pu contamination in concrete samples.

Clay minerals are widely used as backfill and buffer materials, and it is known that clay colloids derived from an engineered barrier system may affect the migration behaviors of radionuclides. Based on a study of the stability of attapulgite colloids and the sorption behavior of uranium on attapulgite, the effect of attapulgite colloids on U(VI) migration was investigated in a quartz column. The results show that attapulgite colloids are stable without disturbance, but changes on pH or addition of an electrolyte can reduce their stability. Quartz column experiments in the presence of attapulgite indicated U(VI) adsorption to the colloid that retarded U(VI) migration. In a system consisting of U-colloid-chloride at pH 6.0, U(VI) migration showed almost no change compared to when only uranium was present. However, U(VI) migration was accelerated significantly in the U- colloid-phosphate system because of the formation of U(VI)-phosphate complexes rather than U(VI) adsorbing on the attapulgite colloid.

In the present study, graphene (rGO) hydrogel was fabricated by reducing graphene oxide (GO) with ascorbic acid to remove U(VI) from aqueous solution. The resulting rGO hydrogel shows a 3D porous network structure and good mechanical stability. The effect of contact time, pH, and initial U(VI) concentration on U(VI) adsorption, as well as the reusability of the material were estimated with batch experiments. The results illustrate that U(VI) adsorption on rGO hydrogel agreed well with pseudo-second order kinetic model, indicating a chemical adsorption. According to correlation coefficients, Freundlich model is the most suitable isothermal model to describe the U(VI) adsorption process of rGO hydrogel, with a maximum adsorption capacity of 134.23 mg/g (pH 4.0). The solution pH posed significant influence on U(VI) adsorption: the adsorption amount rises sharply from pH 2.0 to 4.6, reaches a plateau at 4.6-6.5, and then declines slightly at pH levels above 6.5. The rGO hydrogel shows good reusability, with maintaining 94.76% adsorption ability after ten adsorption/desorption cycles, demonstrating that rGO hydrogel is a promising adsorbent for U(VI) removal from aqueous solution, providing a new insight for the developing of U(VI) adsorbents.

为了解铀在北山地下水的存在种态和吸附行为,利用CHEMSPEC软件计算了铀在北山地下水的种态分布及其在石英和水合氧化铁两种材料上的吸附,并考察了pH、Eh和不同离子浓度的变化对铀种态分布的影响.结果显示:在酸性条件下,铀主要以U(OH)4(aq)形式存在;在中性和弱碱性条件下,主要以UO2(CO3)2?2和UO2(CO3)4?3形式存在;在强碱性条件下,主要以UO2(OH)?3形式存在.U的价态受电位影响较大,在还原条件下,U(Ⅳ)较稳定,在氧化条件下,U(Ⅵ)较稳定.不同离子的引入会影响U的种态分布,其影响大小顺序为HCO?3>F?>SO2?4>Cl?.U(Ⅵ)在石英上的吸附随pH同步增大,并在pH=4.3处达到最大值,U(Ⅵ)在水合氧化铁的吸附随pH增大而先增大后减小,pH在5.7～8.2内达到最大值.

Contamination of soil with Americium (241Am) at nuclear sites in China poses a serious problem. We screened six plants, from five families, for their 241Am-enrichment potential. Europium (Eu), which is morphologically and chemically similar to the highly toxic 241Am, was used in its place. Moreover, the effects of sylvite, citric acid (CA), malic acid (MA), and humic acid (HA) on the absorption of 241Am by the plants, and its transport within them, were evaluated along with their effect on plant biomass and 241Am extraction volume. Barley and cabbage showed relatively stronger Eu accumulation capacities. Citric acid promoted the absorption of 241Am by barley roots and its transport within the plants. The effects of sylvite were not obvious and those of HA were the weakest in case of sunflower; HA, however, maximally increased the biomass of the plants. Our results could provide the basis for future radionuclide phytoremediation of contaminated soils.

The microbial reduction of U(VI) by Bacillus sp. dwc-2, isolated from soil in Southwest China, was explored using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). Our studies indicated that approximately 16.0% of U(VI) at an initial concentration of 100mg/L uranium nitrate could be reduced by Bacillus sp. dwc-2 at pH8.2 under anaerobic conditions at room temperature. Additionally, natural organic matter (NOM) played an important role in enhancing the bioreduction of U(VI) by Bacillus sp. dwc-2. XPS results demonstrated that the uranium presented mixed valence states (U(VI) and U(IV)) after bioreduction, which was subsequently confirmed by XANES. Furthermore, the TEM and high resolution transmission electron microscopy (HRTEM) analysis suggested that the reduced uranium was bioaccumulated mainly within the cell and as a crystalline structure on the cell wall. These observations implied that the reduction of uranium may have a significant effect on its fate in the soil environment in which these bacterial strains occur.

Natural groundwater colloids are significantly important since they are closely related with toxic substances migration in subsurface systems. In this paper, a cross-flow ultrafiltration (CFUF) system equipped with 100 kDa cartridges was developed to enrich groundwater colloids and multiple analytical techniques were used to characterize colloid properties. Analytical techniques included scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM) with energy dispersive X-ray spectra (EDS), excitation-emission matrix (EEM) fluorescence spectra, inverted fluorescence microscopy (IFM), and 16S rDNA sequencing. SEM and AFM results indicated that the mean diameter and height of colloids were 322 +/- 90 nm and 10.4 +/- 2.1 nm respectively and two different morphologies of colloids existed which seem to be hollow and platy structure. XRD analysis showed that the mineralogical composition of inorganic colloids consisted of albite (NaAlSi3O8), orthoclase (KAlSi3O8), clinochlore ((Mg,Fe)(6)(Si,Al)(4)O-10(OH)(8), lepidocrocite ((FeO)-O-III(OH)), muscovite (KAl2(Si3Al)O-10(OH,F)(2)), calcite (CaCO3) and quartz (SiO2), most of which was confirmed by TEM-EDS information. Different types of dissolved organic matter (DOM) were characterized by EEM fluorescence spectra, while a larger fraction of 'protein-like' fluorescent DOM was found. Bacteria was observed under 488 nm laser excitation by IFM and 16S rDNA sequencing revealed that Thermomonas was the most likely genus the bacteria may belong to.

Background: Very low level waste (VLLW) landfill antiseepage layer is a key engineering measure to prevent the radioactive nuclides from entry into the surrounding environment.Purpose:This study aims to give an example of quickly evaluating the retardation capability of a VLLW antiseepage.Methods:The landfill soil's distribution coefficient (Kd), saturated permeability coefficient (Ks) and dispersion coefficient (D) were got by batch test and column migration test, and the concentration of nuclides through antiseepage layer was calculated with the advection dispersion equation.Results:The results showed that theKd of Co and Ni were 140.92 mL·g?1 and 380.43mL·g?1, respectively, and retardation factors (Rd) of Co and Ni were 859 and 2317, respectively, which means this soil has a very strong retardation capacity for Co and Ni. In addition, the breakthrough concentrations of Co and Ni by calculation under the normal circumstance were very low.Conclusion: So the antiseepage layer using this site soil can effectively ensure the environment safety.

Humic acid (HA)1 is ubiquitous in the environment and is an important factor in the migration behavior of U(VI) in the geological medium. The present work investigated the effect of HA on the migration behavior of U(VI) using quartz column experiments at different pH values and in the presence of various anions. The U(VI) adsorption characteristics and speciation were also studied to illuminate' further the migration behavior of U(VI). Our results indicated that, at pH 6.0, HA slightly increased the migration velocity of U(VI) during the initial phase and reduced the quantity of eluted U(VI) because of the formation of HA-U(VI). The relative concentration (c/c(o)) of U(VI)was higher in the HA-U system at pH 8.0 than that at pH 5.0 because of the higher solubility of HA in basic solutions and the difference in charge of HA-U(VI). In the U-HA-anion system at pH 6.0, the breakthrough pore volumes (PVs(2)) of U(VI) in electrolytes containing Cl- and SO42- anions (PV = 8) are much higher than for solutions containing phosphate (PV = 3), while the HA migration behavior was not significantly affected by the type of anion. Thus, the fast migration of U(VI) under HA and phosphate was attributed to phosphate rather than HA. This result suggests that phosphate should be given more attention in predictions of U(VI) migration, especially in regions with high groundwater phosphate content. (C) 2017 Elsevier Ltd. All rights reserved.

In the present study, five plant species were screened for uranium uptake using a hydroponic experimental set-up. The effect of the U concentration, pH, as well as the presence of carbonates, phosphates, and organic acids (lactic acid, malic acid, citric acid) on the uptake of U by variant S. alfredii (V S. alfredii) and wild S. alfredii (W S. alfredii) were investigated. Results showed that V S. alfredii exhibited higher U content in the roots than the other four plants and with the increase of U concentration in the solution, the U uptake by V S. alfredii and W S. alfredii increased. The results also showed that different U speciation in different cultivation solution took an important role on the uptake of U in variant Sedum alfredii: at pH 6.5, U hydrolysis species (UO2)3(OH)5 +is predominant and the U concentrations in V S. alfredii roots reached a maximum value (3.7 × 104 mg/kg). U complexation with carbonates, phosphates, and some organic acids in the solution resulted in a decrease in the U content in the roots except for lactic acid. Our researches highlight the correlations between U speciation and the uptake on V S. Alfredii, which will be helpful for improved removal of U from the groundwater using phytoremediation method.

In this paper, TEM-EDX, FTIR, XPS, PIXE, and EPBS were employed to identify the uranium biosorption behavior and the potential mechanism on cells of Geotrichum sp. dwc-1, isolated from soils. These results displayed that the biosorption behavior was greatly dependent on pH and uranium was absorbed by bounding to amino, phosphate as well as carboxyl functional groups. Uranium biosorption behavior on Geotrichum sp. dwc-1 involves bioaccumulation, electrostatic interaction and ion exchange process. This work throws further light on potential fungal roles these mechanisms for elemental recovery and bioremediation.

Brassica juncea var. foliosa (B. juncea var. foliosa) is a promising species for thorium (Th) phytoextraction due to its large biomass, fast growth rate and high tolerance toward Th. To further understand the mechanisms of Th tolerance, the present study investigated the subcellular distribution and chemical forms of Th found in B. juncea var. foliosa Our results indicated that in both roots and leaves, Th contents in different parts of the cells follow the order of cell wall > membranes and soluble fraction > organelles. In particular, Transmission Electron Microscope (TEM) analysis showed that Th was abundantly located in cell walls of the roots. Additionally, when plants were exposed to different concentrations of Th, we have found that Th existed in B. juncea var. foliosa with different chemical forms. Much of the Th extracted by 2% acetic acid (HAc), 1 M NaCl and HCl in roots with the percentage distribution varied from 47.2% to 62.5%, while in leaves, most of the Th was in the form of residue and the subdominant amount of Th was extracted by HCl, followed by 2% HAc. This suggested that Th compartmentation in cytosol and integration with phosphate or proteins in cell wall might be responsible for the tolerance of B. juncea var. foliosa to the stress of Th.

Variant Sedum alfredii Hance (V S. alfredii) could simultaneously take up U and Th from water with the highest concentrations recorded as 1.84 × 104 and 6.72 × 103 mg/kg in the roots, respectively. Th stimulated U uptake by V S. alfredii roots at Th10 (10 μM of Th), however, the opposite was observed at Th100 (100 μM of Th). A similar result was found in the effect of U on the uptake of Th by V S. alfredii. Subcellular fractionation studies of V S. alfredii indicated that U and Th were mainly stored in cell wall fraction, and much less was found in organelle and soluble fractions. Chemical form examination results showed that water-soluble U and Th were the predominant chemical forms in this plant. Addition of the other radionuclide in aqueous solutions altered the concentration and percentage of U or Th in cell wall fraction and in water-soluble form, resulting in the change of the uptake capacity of U or Th by V S. alfredii roots. Comparing with single U or Th treatment, the plant cells revealed more swollen chloroplasts and enhanced thickening in cell walls under the U100 + Th100 treatment, as observed by TEM. Those results collectively displayed that V S. alfredii may be utilized as a potential plant to simultaneously remove U and Th from aqueous solutions (rhizofiltration).

In this study, we examined the sorption and desorption behavior of U(VI) on/from a Chinese bentonite in the solid–liquid system using batch experiments, and the influence of pH, ionic strength and humic acid (HA) on the sorption–desorption hysteresis in the solid–liquid system were quantitatively calculated. It was revealed that the hysteresis was enhanced with increasing pH and increasing ionic strength. HA promoted the sorption, but lower the sorption–desorption hysteresis. Meanwhile, hysteresis in ternary bentonite-HA-U system was found to be higher than that in bentonite-U-HA system, indicating different sorption structures formed because of different addition sequence.

The biosorption mechanisms of uranium on an aerobic bacterial strain Streptomyces sporoverrucosus dwc-3, isolated from a potential disposal site for (ultra-)low uraniferous radioactive waste in Southwest China, were evaluated by using transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), proton induced X-ray emission (PIXE) and enhanced proton backscattering spectrometry (EPBS). Approximately 60% of total uranium at an initial concentration of 10mg/L uranium nitrate solution could be absorbed on 100mg S. sporoverrucosus dwc-3 with an adsorption capacity of more than 3.0mg/g (wet weight) after 12hr at room temperature at pH3.0. The dynamic biosorption process of S. sporoverrucosus dwc-3 for uranyl ions was well described by a pseudo second-order model. S. sporoverrucosus dwc-3 could accumulate uranium on cell walls and within the cell, as revealed by SEM and TEM analysis as well as EDX spectra. XPS and FT-IR analysis further suggested that the absorbed uranium was bound to amino, phosphate and carboxyl groups of the cells. Additionally, PIXE and EPBS results confirmed that ion exchange also contributed to the adsorption process of uranium.

The adsorption mechanisms of NH4+ and Cs+ on phosphomolybdate ion were investigated in detail by density functional theory (DFT). The computational results indicate that [PMo12O40](3-) is a cage -like structure formed by the three -membered rings and four -membered rings constructed by the Mo-O bonds. Both NH4+ and Cs+ could be easily adsorbed at the bridge oxygen site of the four -membered ring on the surface of the [PMo12O40](3-) ion. The adsorption of Cs+ on [PMo12O40](3-) is more energetically favorable than that of NH4+, which likely accounts for the better Cs+ adsorption capability of ammonium phosphomolybdate. (C) 2016 Elsevier B.V. All rights reserved.