Uranyl Nitrate Research Articles

Tough strippable hydrogel films based on acrylic acid/acrylamide/zirconyl chloride for surface radioactive decontamination at low temperatures

Strippable films are extensively utilised for the decontamination of radioactive surfaces because of their cost-effectiveness, ease of operation, and minimal liquid waste. However, traditional strippable detergents are formulated for use at normal ambient temperatures and typically lose their efficacy at low temperatures because of poor performance or excessively long film-forming time. In this study, we have developed an anti-freezing and sprayable AMZW detergent based on acrylic acid (AA), acrylamide (AM), zirconyl chloride octahydrate (ZrOCl2·8H2O), and water (H2O), which possesses a freezing point of approximately −34 ℃ due to the solvation interaction between Zr4+ and H2O. Even at temperatures as low as −25 ℃, the AMZW detergent can be easily sprayed using a conventional apparatus and rapidly cured into a strippable hydrogel film under irradiation by 365 nm UV LED light (LED@365 nm), household LED panel light, or sunlight. The coordination bond formed between Zr4+ and the carboxyl group of the polymer chain imparts excellent mechanical properties to the hydrogel while the carboxyl group can complex with uranyl nitrate hexahydrate (UO2(NO3)2·6H2O)—a radioactive simulant. As a result, the strippable hydrogel film demonstrates high tensile strength (6.1 ∼ 19.3 MPa), excellent flexibility (elongation of 90 ∼ 855 %), moderate peel strength (0.05 ∼ 3 N/cm, room temperature (RT)), and high decontamination efficiency (>91.6 % on stainless steel and glass; >81.3 % on concrete) over a wide range of temperatures (−25 ∼ 25 ℃). This work presents a novel approach for producing anti-freezing, fast-forming, flexible, and high-strength strippable hydrogel films for surface radioactive decontamination at low temperatures.

Chiral discrimination during photoinduced electron transfer from L/D-tryptophan to electron-excited uranyl ion as a part of UO22+ ⊂ α–CD inclusion complex

Spectral-luminescent research indicates the formation of inclusion complexes during the interaction of uranyl nitrate and α–cyclodextrin (α–CD) in aqueous solutions. The chiral α–CD matrix imparts optical activity to the electronically excited uranyl ion *UO22+aq in the clathrate, which manifests itself in the chiral discrimination of the quenching of *UO22+aq by tryptophan enantiomers. It was found that the Stern-Volmer constant for D–Trp is 1.8 ± 0.2 times higher than that for L–Trp. A mechanistic explanation for the observed effect is proposed by DFT calculations.

Soybean Extract Ameliorates Lung Injury induced by Uranium Inhalation: An integrated strategy of network pharmacology, metabolomics, and transcriptomics

AimThis study aimed to evaluate the protective effect of soybean extract (SE) against uranium-induced lung injury in rats. Materials and methodsA rat lung injury model was established through nebulized inhalation of uranyl nitrate. Pretreatment with SE or sterile water (control group) by gavage for seven days before uranium exposure and until the experiment endpoints. The levels of uranium in lung tissues were detected by ICP-MS. Paraffin embedding-based hematoxylin & eosin staining and Masson’s staining for the lung tissue were performed to observe the histopathological imaging features. A public database was utilized to analyze the network pharmacological association between SE and lung injury. The expression levels of proteins indicating fibrosis were measured by enzyme-linked immunosorbent assay. RNA-seq transcriptomic and LC-MS/MS targeted metabolomics were conducted in lung tissues. ResultsUranium levels in the lung tissues were lower in SE-pretreated rats than in the uranium-treated group. Inflammatory cell infiltration and the deposition of extracellular matrix were attenuated, and the levels of alpha-smooth muscle actin, transforming growth factor beta1, and hydroxyproline decreased in SE-pretreated rats compared to the uranium-treated group. Active ingredients of SE were related to inflammation, oxidative stress, and drug metabolism. A total of 67 differentially expressed genes and 39 differential metabolites were identified in the SE-pretreated group compared to the uranium-treated group, focusing on the drug metabolism-cytochrome P450, glutathione metabolism, IL-17 signaling pathway, complement, and coagulation cascades. ConclusionsThese findings suggest that SE may ameliorate uranium-induced pulmonary inflammation and fibrosis by regulating glutathione metabolism, chronic inflammation, and immune regulation.

Correlative morphological, elemental and chemical phase analyses at the micrometric scale of powdered materials: Application to nuclear forensics

To characterize a mixture of powders using several analytical techniques, it is necessary that successive analyses be carried out on well-identified and localized particles, so that each characterization corresponds to a given powder. In this publication, powdered nuclear materials are characterized at the morphological and elemental levels with a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and at the chemical level with a micro-Raman spectrometer (MRS). However, to avoid a time-consuming and insufficiently accurate microparticle relocation process between SEM/EDS and MRS, micro-Raman analyses are carried out inside the SEM using a coupling device. In this way, all three pieces of information are obtained for exactly the same micrometric spot, without moving the sample or relocating the microparticles analyzed. The information can therefore be combined to characterize each component of the mixture. In this article, we describe in detail the methodology we have developed and optimized for morphological, elemental and chemical analysis of microparticles using a combined SEM/EDS and SRM. This methodology has been applied to powdered nuclear materials in two international nuclear forensics exercises. In the first exercise, named CMX-6, the combined use of the two instruments identified the presence of PuO2 microparticles and several uranium compounds (UO2, U3O8, UO2F2) in both materials. In the second exercise, called CMX-7, the methodology developed enabled us to distinguish two chemical phases of uranium, a uranyl oxy-hydroxide and a uranyl nitrate, each characterized by specific morphologies and the detection or non-detection of a minor elemental constituent (calcium).

Behavior of uranium(VI) in the presence of a geomaterial: an aquifer sediment

Sediments from aquatic environments can be contaminated with uranium from natural and anthropogenic sources; the behavior of U(VI) was investigated in two natural (SPT and DS) and gamma-irradiated (SPT-I) aquifer sediments in batch systems. Sediments were characterized, and quartz, albite, and kaolinite were mainly found in both sediments by X-ray diffraction. The points of zero charge were 5.4, 5.3, and 5.5, and the organic matter percentages were 48.0, 46.0, and 4.7% for SPT, SPT-I, and DS, respectively. Uranyl nitrate solutions were put in contact with each sediment considering different parameters (pH, contact time, initial concentration of uranium, and temperature). DS sediment did not adsorb any quantity of uranium at different pH values; SPT and SPT-I, attained the highest q e values at pH 3.5–4. The results show chemisorption on homogenous materials and endothermic processes. Desorption behavior of U(VI)/SPT showed a hundred percent desorption with nitric acid and humic acid solutions; in the last case, it is due to the high stability constant of the complex of uranium with the humic acids. The results help to understand the contamination and decontamination processes of sediments with uranium, the bioavailability of uranium, the ecological risk of U-contaminated sediments, and remediation. Doses of 1 MGy of Co-60 gamma radiation did not affect the uranyl ions behavior in the aquifer sediment.

The Cytotoxic Effects of Human Mesenchymal Stem Cells Induced by Uranium.

Bone is a major tissue for uranium deposition in human body. Considering mesenchymal stem cells (MSCs) play a vital role in bone formation and injury recovery, studying the mechanism of MSCs responding to uranium poisoning can benefit the understanding of bone damage and repair after uranium exposure. Cellular structural alterations were analyzed via transmission electron microscopy (TEM). Changes in cellular behaviors were assessed through cellular viability, apoptosis, and the production of DNA double-strand breaks (DSBs). In addition, the influence of gap junctional intercellular communication (GJIC) on uranium toxicity was assessed. The disruption of MSCs was elevated with the increase in uranyl nitrate concentration, as shown by TEM micrograph. This was verified by the results of cellular viability and DSB production. Interestingly, the results of apoptosis assay indicated significant apoptosis occurred, which was accompanied with an obvious disruption of cellular membranes. Furthermore, closely contacted cell confluence groups exhibited resistant to uranium poisoning in contrast to sparse growth groups, which can be eliminated with the pretreatment of a GJIC inhibitor in the close connection group. To verify the association between GJIC and cytotoxic effects of uranyl nitrate, GJIC function was evaluated by wound healing and cellular migration. The results showed an inhibition of the healing ratio and migration ability induced by the exposure of uranyl nitrate. The low transfer efficiency of the dye coupling experiment and depressed expression of gap functional protein connexins confirmed the impairment of GJIC function. These results suggest that uranium toxicity is involved with GJIC dysfunction.

Kinetics study on the temperature-dependent reduction of aqueous U(VI) by natural pyrite

Previous studies have indicated that acid-washed pyrite is inert toward aqueous U(VI) under most pH conditions at ambient temperature, even though insoluble UO2 is the thermodynamically predicted product for the reduction of U(VI) by pyrite. Considering the exothermic nature of nuclear waste, the interaction between uranyl nitrate/acetate and natural pyrite was studied at temperatures ranging from 25 °C to 85 °C and at pH values between ∼4.0 and ∼9.5, to simulate the scenarios encountered in a high-level radioactive waste repository. The results revealed that the reactivity of pyrite toward aqueous U(VI) significantly increased with rising temperature, and the reaction could be described by a pseudo-first-order kinetic equation. Activation energies were calculated to be 79.4 ± 10.6 and 45.7 ± 3.8 kJ⋅mol−1 for the reduction of uranyl nitrate, and 78.2 ± 5.2 and 42.2 ± 5.8 kJ⋅mol−1 for the reduction of uranyl acetate, at pH values of ∼4.5 and ∼5.0, respectively. These values indicate that the reaction is controlled by the surface chemical processes. In addition, the complete reduction of aqueous U(VI) to UO2 product was first observed for the reactions at pH ∼4.0 to ∼5.5 when the temperature was ≥75 °C. Conversely, non-stoichiometric UO2+x(s) (0 < x ≤ 0.67) was found at lower temperatures within the same pH range, and also at 85 °C with a reaction pH of ∼9.5. Moreover, the ratio of reduced U(IV/V) on pyrite surfaces increased gradually over time, indicating that reaction time played a significant role in the reduction products. The findings are essential not only for the safety assessment of the high-level radioactive waste repository, but also for understanding the metallogenic mechanism of U(IV)-bearing ore deposits under the relevant anaerobic and hydrothermal conditions.

Study on Novel SCR Catalysts for Denitration of High Concentrated Nitrogen Oxides and Their Reaction Mechanisms

With the rapid development of industrialization, the emission of nitrogen oxides (NOx) has become a global environmental issue. Uranium is the primary fuel used in nuclear power generation. However, the production of uranium, typically based on the uranyl nitrate method, usually generates large amounts of nitrogen oxides, particularly NO2, with concentrations in the exhaust gas exceeding 10,000 ppm. High concentrations of nitrogen dioxide are also produced during silver electrolysis processing and the treatment of waste electrolyte solutions. Traditional V-W/TiO2 NH3-SCR catalysts typically exhibit high catalytic activity at temperatures ranging from 300 to 400 °C, under conditions of low NOx concentrations and high gas hourly space velocity. However, their performance is not satisfying when reducing high concentrations of NO2. This study aims to optimize the traditional V-W/TiO2 catalysts to enhance their catalytic activity under conditions of high NO2 concentrations (10,000 ppm) and a wide temperature range (200–400 °C). On the basis of 3 wt% Mo/TiO2, various loadings of V2O5 were selected, and their catalytic activities were tested. Subsequently, the optimal ratios of active component vanadium and additive molybdenum were explored. Simultaneously, doping with WO3 for modification was selected in the V-Mo/TiO2 catalyst, followed by activity testing under the same conditions. The results show that: the NOx conversion rates of all five catalysts increase with temperature at range of 200–400 °C. Excessive loading of MoO3 decreased the catalytic performance, with 5 wt% being the optimal loading. The addition of WO3 significantly enhanced the low-temperature activity of the catalysts. When the loadings of WO3 and MoO3 were both 3 wt%, the catalyst exhibited the best denitrification performance, achieving a NOx conversion rate of 98.8% at 250 °C. This catalyst demonstrates excellent catalytic activity in reducing very high concentration (10,000 ppm) NO2, at a wider temperature range, expanding the temperature range by 50% compared to conventional SCR catalysts. Characterization techniques including BET, XRD, XPS, H2-TPR, and NH3-TPD were employed to further study the evolution of the catalyst, and the promotional mechanisms are explored. The results revealed that the proportion of chemisorbed oxygen (Oα) increased in the WO3-modified catalyst, exhibiting lower V reduction temperatures, which are favorable for low-temperature denitrification activity. NH3-TPD experiments showed that compared to MoOx species, surface WOx species could provide more acidic sites, resulting in stronger surface acidity of the catalyst.

Uranium-tolerant soil bacteria protect Arabidopsis thaliana seedling growth from uranium toxicity

Uranium (U) is a naturally occurring radioelement that is chemically toxic to all living organisms. We investigated the effect of U on Arabidopsis thaliana seed germination and the early stages of seedling development. We showed that U had very little effect on Arabidopsis seed germination, with germination rates above 90 % at 500 µM uranyl nitrate. However, U had a drastic effect on the Arabidopsis seedling development and the root was the most U-sensitive organ, with severe growth inhibition (>75 %) starting at 20 µM uranyl nitrate. We showed that the two soil bacterial strains Microbacterium sp. ViU2A and Stenotrophomonas bentonitica BII-R7, which are able to tolerate high concentrations of U, strongly reduced the toxic effects of U on seedling development. Thus, in the presence of both strains, root growth inhibition was prevented up to 100 µM uranyl nitrate. This protection was specific to U-tolerant soil bacteria, as Escherichia coli was unable to protect seedlings. The analysis of U distribution between Arabidopsis seedlings and soil bacteria showed that the protective effect of bacteria was due to their ability to sequester U, either by biosorption at the cell surface and/or by intracellular or extracellular biomineralization. Also, the ability of both soil bacterial strains to prevent U toxicity was much less efficient when dead bacteria were used, suggesting the involvement of metabolism-dependent biological processes in seedling protection. Accordingly, we showed that the Uranium-induced protein A (UipA) contributes to the protection of Arabidopsis seedlings by Microbacterium sp. ViU2A. This study suggests that U-tolerant soil bacteria may be useful for phytostabilization strategies of U-contaminated soils and for limiting the entry of this toxic element into crops.

Kinetic evaluation of the uranyl peroxide synthetic route on morphology

Abstract An important challenge in utilizing particle morphology in nuclear forensic or fuel fabrication applications is understanding why differences in morphologies are observed following varying processing conditions. This is often due to competition and interplay between thermodynamic and kinetic influences. To that end, some of the kinetic influences in the uranyl peroxide precipitation reaction were evaluated and compared to thermodynamic influences studied previously. Metastudtite (UO2O2·2H2O) was synthesized from solutions of uranyl nitrate or chloride, and the reaction time was varied from 100 s to 230 min enabling an evaluation of kinetic and thermodynamic influences. The metastudtite was then calcined to U3O8, and all materials were analyzed by powder X-ray diffraction (p-XRD) and scanning electron microscopy (SEM). Analysis by p-XRD confirmed the sample purity of metastudtite and U3O8. SEM images were analyzed using the Morphological Analysis for Materials (MAMA) software to measure the size and shape of the nanoparticles for a statistical comparison between materials. Metastudtite produced at shorter reaction times exhibited a kinetically controlled shape by forming smaller and rounder particles than metastudtite produced at longer reaction times. Metastudtite produced at the longer reaction times exhibited differences between the uranyl nitrate and uranyl chloride routes with the nitrate exhibiting a more angular and faceted morphology than the chloride. Overall, the control of the supersaturation ratio (S) played a significant role in determining the morphology of the metastudtite. Morphological differences between the U3O8 confirmed the role of nanoparticle agglomeration in forming larger sintered particles. The results help demonstrate the importance of understanding particle formation mechanisms in the long-term development of morphology in nuclear forensics or in developing advanced fuels with specific characteristics.

Semiconductive Behavior and Photoconductivity of Uranyl Dithiophosphinate Single Crystal.

Herein, we detail the synthesis, structure, and photoconductivity of the uranyl dithiophosphinate single crystal UO2[S2P(C6H5)2]2(CH3OH)·CH3OH (denoted as U-DPDPP). The formation of bonds between uranyl ions and sulfur-based ligands endows U-DPDPP with a distinct electronic absorption property with a broadband spectrum spanning from 250 to 550 nm, giving rise to a unique semiconductive property. Under X-ray illumination, U-DPDPP displays a distinctive photoconductivity response, with a charge carrier mobility lifetime (μτ) of 2.78 × 10-4 cm2·V-1 achieved, which contradicts the electronic-silence behavior of uranyl nitrate crystal.

Inhibition of Skin Cancer using Human Epidermal Keratinocytes (HaCaT) Cells from Siam Weeds (Chromolaena odorata L.)

Cancer can usually develop due to exposure to sunlight. UV radiation from sunlight is known to damage DNA and is bad for the skin. Skin P stem cell carcinogenesis is caused by UV-A rays that penetrate deep into the dermis layer. UV-B damages cell DNA by being absorbed by proteins in the epidermis. Chromolaena odorata was extracted using methanol solvent, then partitioned into 5 solutions in the form of n-Hexane, Ethyl Acetate, Acetonitrate, n-Buthanol, and Ethanol. The five extracts obtained were tested with Human Epidermal Keratinocyte cells using the bioassay method. Results obtained from the microplate reader after incubation. Each extract was divided into three concentrations, it is 100, 50, 20(µg/mL). Then in the positive control (Etoposide), it was divided into four concentrations, 100, 50, 20, 10(µg/mL). After being analyzed with the results of the microplate reader, the IC50 of Chromolaena odorata was 48% in the ethyl acetate extract with a concentration of 100µg/mL. HaCaT cell proliferation was determined at indicated intervals using the MTT colorimetric assay. This assay was based on the ability of live cell succinate dehydrogenase to reduce the yellow salt MTT (3-(4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide)) (Sigma-Aldrich, St. Louis, MO, USA) to insoluble purple-blue formazan precipitate. Experiments were carried out on 96-well plates containing a final volume of 100µl of medium/well.

Enhance U(VI) reduction on natural pyrite surfaces by gamma irradiation

Pyrite with acid-washed surfaces is chemically inert toward aqueous U(VI) at routine conditions. Given that there is a strong radiation field in the nuclear waste repository, the impact of gamma irradiation on the interaction between aqueous U(VI) and natural pyrite was investigated. Three different natural pyrites, namely Si-, Pb-, and As-pyrites, were used for reactions with uranyl nitrate and uranyl acetate, and the focus was set on Si-pyrite. With an initial pH of ∼ 4.5 and ∼ 6.5, results showed that the solution pH increased mainly due to the reduction of nitrate or the decomposition of acetate caused by the gamma irradiation, while it decreased for the reaction with an initial pH of ∼ 9.0 after gamma irradiation due to the oxidation of aqueous Fe2+. Meanwhile, significant amounts of U(IV)/U(V) were formed on pyrite surfaces at these three pH conditions, demonstrating that gamma irradiation can greatly enhance the U(VI) reduction by pyrite. We proposed that the oxidizing ·OH radical generated by water radiolysis could react with pyrite, leaving the concomitant eaq− and ·H radicals to be effective reductants for aqueous U(VI) or the U(VI)-precipitate formed on pyrite surfaces. Conversely, the impact of gamma irradiation on the U(VI) reduction is insignificant at pH ∼ 3.0, mainly due to the quenching effect of eaq− by H+. Besides, carbonate has an inhibitive effect, because it is a quencher of eaq− and can form anionic complexes with U(VI). The presence of pyrite can also protect UO2 from γ-irradiation-induced oxidation.

Pre-Experimental Assessment of Uranyl Nitrate Solution Irradiation in Kartini Reactor Facilities

Medical radioisotope production using neutron irradiation via fission reaction requires a sufficient neutron source. The Kartini reactor has been proposed and studied to become a neutron source for radioisotope production under the Subcritical Assembly for 99Mo Production (SAMOP) project, which uses uranyl nitrate solution as the irradiation target. A full-scale experiment involving a liquid fission product is difficult to conduct and requires facility rearrangement to reduce the risk of contamination. Although a small-batch experiment is safer to perform, a pre-experimental assessment is necessary to address the practicality of production and the accompanying problems. The goals of this assessment are (1) to characterize the Kartini reactor irradiation facilities’ flux through experiment and Monte Carlo benchmark simulation, (2) to predict the irradiation product inventory in relation to the variation of uranium concentration and the measured flux, and (3) to predict the irradiated sample gamma spectrum reading using high-purity germanium detector simulation. The irradiation simulation uses natural uranium as a control parameter, which caused the irradiation inventory dominated by actinides from transmutation. The simulation also presents the possibility of instant small-batch 99Mo production using the measured Lazy Susan facilities’ flux from a neutronic perspective. The qualitative assessment of the predicted irradiation inventory and its spectrum reading from different sample concentrations are discussed along with the recommendation and possible action to improve the experiment or future production process.

Elucidating the Composition and Structure of Uranium Oxide Powders Produced via NO2 Voloxidation.

Voloxidation is a potential alternative reprocessing scheme for spent nuclear fuel that uses gas-solid reactions to minimize aqueous wastes and to separate volatile fission products from the desired actinide phase. The process uses NO2(g) as an oxidant for uranium dioxide (UO2) fuel, ideally producing soluble uranium powders which can then be processed for full recycle. To continue development of the process flowsheet for voloxidation, ongoing examination of the process chemistry and associated process materials is required: discrepancies in the proposed chemical reactions that occur when spent nuclear fuel is exposed to NO2(g) atmospheres must be addressed. The objective of this work is to analyze the intermediate solid phases produced during voloxidation to support verification of the proposed NO2(g) voloxidation reaction mechanisms. This objective was achieved through using (1) powder X-ray diffraction and Raman spectroscopy to identify bulk uranium phases and (2) scanning electron microscopy to describe the morphology and microstructure of the powders at each reaction stage. The initial oxidation of UO2 under NO2(g) reactions produced ε-UO3. Further exposure to NO2(g) did not nitrate the solid to produce uranyl nitrate, as reported in some literature. However, after the powder was hydrated with steam and then further exposed to NO2(g), some traces of uranyl nitrate hexahydrate were found. The results of this study suggest that surface hydration of powders plays a vital role in uranyl nitrate formation under voloxidation conditions and raises questions about the kinetics of the oxide-to-nitrate voloxidation conversion process. Future chemical and engineering design decisions for the voloxidation process may benefit from an improved understanding of these chemical mechanisms.

In-situ quantification of dispersity and sphericity of uranyl nitrate sol droplets using holographic imaging

Uniform-sized and highly spherical nuclear fuel microspheres are pivotal components in high-temperature gas-cooled reactors. In the manufacturing process of microspheres through external gelation, monodispersed droplets with high sphericity at the dispersion stage establishes the fundamental basis for the subsequent production of superior-quality microspheres. Addressing the monitoring requirements for droplet size and sphericity in dispersion process, this study develops a measurement apparatus based on digital in-line holography. The apparatus records droplet holograms within distances ranging from 96 mm to 183 mm, achieving imaging resolutions between 64 lp/mm to 32 lp/mm. Droplet measurements are conducted for nine operational conditions encompassing varied excitation frequencies and liquid flow rates. Observation under various dispersion parameters reveals diverse droplet morphologies. Polydisperse conditions manifest an abundance of satellite droplets, agglomerated droplets, coalesced droplets, and deformed droplets. The statistical results indicate that at 100 Hz, monodisperse droplets with high sphericity are produced, exhibiting a standard deviation below 30 μm. Moreover, droplet sizes demonstrate a deviation from theoretical calculations within 2.5%. Additionally, preliminary measurements are conducted during the dispersion process of a six-nozzle head, confirming the accuracy on locating droplets of the holographic system within a depth range of more than 30 mm.

Research on the Formation Conditions and Preventive Measures of Uranium Precipitates during the Service Process of Medical Isotope Production Reactors.

This study focuses on the Medical Isotope Production Reactor (MIPR), an aqueous homogeneous reactor utilized for synthesizing medical isotopes like 99Mo. A pivotal aspect of MIPR's functionality involves the fuel solution's complex chemical interactions, particularly during reactor operation. These interactions result in the formation of precipitates, notably water filamentous uranium ore and columnar uranium ore, which can impact reactor performance. The research presented here delves into the reactions between liquid fuel uranyl nitrate and key radiolytic products, employing simulation calculations complemented by experimental validation. This approach facilitates the identification of uranium precipitate types and their formation conditions under operational reactor settings. Additionally, the article explores strategies to mitigate the formation of specific uranium precipitates, thereby contributing to the efficient and stable operation of MIPR.

Effect of di-butyl phosphate on the distribution behavior of uranyl ions in PUREX solvent

ABSTRACT Di-butyl phosphoric acid (HDBP) is one of the major hydrolytic and radiolytic degradation product of tri-n-butyl phosphate (TBP) employed for the extraction of U(VI) and Pu (IV) from the spent nuclear fuel dissolver solution. The presence of HDBP in the solvent phase limits the recovery of actinides during stripping. In view of this, the extraction and stripping behavior of uranyl nitrate in 1.1 M TBP in n-dodecane (n-DD) was studied in presence of di-butyl phosphate (HDBP). The distribution ratio (D) of uranium (VI) in HDBP/n-DD was negligible and the D value increased gradually with an increase in HDBP content in the organic phase. An alternate method was developed for estimation of HDBP in TBP/n-DD system based on uranium metal retention in organic phase. Based on the results it was found that 1 M HDBP in 1.1 M TBP/n-DD retained about 0.63 M of uranium (VI) in the organic phase during stripping. The results were further validated using irradiated solvent. FT-IR spectroscopic investigation also revealed the retention of U(VI) in 1.1 M TBP/n-DD containing HDBP even after several stripping with 0.01 M HNO3.

Electronic structure and complexation behavior of methyl substituted phosphonate ligands with uranyl nitrate

Quantum chemical calculations were applied to investigate the electronic structures and complexation behaviour of methyl-substituted phosphonic acids with uranyl (VI) nitrate. The Natural Bond Orbital (NBO) analysis indicated that the methyl groups in substituted phosphonic acids exhibit electron-withdrawing properties. Additionally, the methyl groups directly bonded to the phosphoryl P atom prefer a gauche orientation relative to the P=O group in compounds such as MPn, DMMP and DMPn. Weak to moderate H-bonding interactions provided extra stability to Pn, MHPn, MPn and DMPn complexes with U(VI). The ν(P=O) values were red-shifted in all the complexes, implying a moderate weakening of the P=O bond upon complexation. Furthermore, the complexation energy values indicated an increasing complexation tendency in 1:2 complexes, particularly when the methyl groups were introduced. This trend was observed in the sequence Pn → MHPn → MPn and DMHP → DMMP → DMPn.

Mapping of uranium particles on J-type swipes with microextraction-ICP-MS.

A microextraction liquid sampling system coupled to a quadrupole inductively coupled plasma-mass spectrometer (ICP-MS) was utilized to spatially discern uranium particles, isotopically, on a cellulose-based swipe material (i.e., J-type swipe). These types of swipes are often used by the International Atomic Energy Agency (IAEA) as part of their environmental sampling program. A grid was created such that extraction locations covered the center circle (n = 34 without overlapping). Uranium (U) particulates (<20 μm) of varying U isotopic abundance and chemical form (i.e., uranyl fluoride and uranyl nitrate hexahydrate) were mechanically placed on the swipes in random locations and detected via the microextraction-ICP-MS methodology. Heat maps were subsequently generated to show the placement of the particulate with their respective intensity and isotopic determination. This detection of the uranium particulates, via isotopic determination, agreed with reference values for these materials. Additionally, depleted (235U/238U = 0.002) uranium particulates were placed directly within a clay matrix, on the swipe surface, and subjected to analysis by microextraction-ICP-MS. The mapping of the swipe demonstrated, for the first time, the employment of the microextraction-ICP-MS method for extracting sample from a complex matrix, and correctly identifying the uranium isotopic composition. This example ultimately demonstrates the utility of the methodology for detecting particles of interest in complex matrices.