Uranium Matrix Research Articles

Collaborative Study for Certification of Trace Elements in Uranium Ore Concentrate CRMs UCLO-1, UCHI-1, and UPER-1

Trace impurity patterns are important nuclear forensic signatures in uranium ore concentrates (UOCs) and Certified Reference Materials (CRMs) are used to validate the analysis methods employed by end users. Herein, we discuss the certification campaign for three new UOC CRMs from the National Research Council Canada: UCLO-1 (https://doi.org/10.4224/crm.2020.uclo-1), UCHI-1 (https://doi.org/10.4224/crm.2020.uchi-1), and UPER-1 (https://doi.org/10.4224/crm.2020.uper-1). This study involved 15 laboratories from 10 countries, using sector-field and (triple) quadrupole inductively-coupled plasma mass spectrometry to analyze 64 trace element impurities. We discuss the importance of the acids used for sample digestion, difficulties analyzing in a high uranium matrix, and data combination and uncertainty evaluation for this large dataset.

A phase-field study on the hydrogen-induced pitting corrosion with solid–solid phase transformation in [formula omitted]-Uranium

Hydrogen-induced pitting corrosion of uranium is a common phenomenon, which damages the integrity and durability of this widely and expensive nuclear material. Its numerical simulation is still a challenge due to many complex mechanisms, especially solid–solid phase transformation and mechanical interaction, leading to the anisotropic growth of hydride and inducing some bulges on the surface of the uranium matrix. We apply a phase-field model to simulate hydrogen-induced pitting corrosion in α-uranium (α-U) at 673 K. In the model, the elastic strain energy is introduced to approximate the mechanical interaction between the matrix and hydride, and the free boundary condition based on the finite element method is adopted to describe the surface bulges. In our simulation, the elliptical pit morphology and its kinetics are consistent with experiment results. An analysis of displacements and stresses inside the materials reveals that the surface bulge is caused by the compression of the matrix and the dilation of the hydride. Moreover, the compressive and tensile stress concentrations are observed around the edge and top of surface bulge respectively. This phenomenon is due to the dilation and growth of hydride on the matrix. Our study provides important simulating evidence and physical interpretations for the growth of pit morphology and failure of α-U materials. This work also shows the potential of the phase-field model in the simulation of hydrogen-induced pitting corrosion.

Cloud point extraction assisted spectrophotometric quantification of trace boron impurity in uranium-based nuclear fuels

The separation of boron in nuclear fuels by cloud point extraction (CPE) has been a challenge due to high acidity of digested sample solutions. High acidity hampers the coacervation of micelles. As a result, the cloud point temperature increases and thus could cause the inevitable loss of boron as volatile species. Herein we have proposed a novel CPE-assisted colorimetric method for the quantification of traces of boron (B) in uranium-based fuels. A 1:1 mixture of 2-ethyl hexane-1,3-diol (EHD) and curcumin dispersed in Triton X-114 surfactant was used in the proposed CPE process. We had investigated several compounds to act as micelle surface modifiers. Among them, only bromine water (Br2) was found not only to lower the cloud point temperature (CPT, from 80 °C to 42 ± 2 °C) but also resulted in the quantitative recovery of boron (≥95%). The CPE of boron from uranium matrix in a 2.0 mol L−1 HCl medium was suitable for direct chemical quality assurance of routine uranium-based fuels. The molar extinction coefficient of the boron-EHD-curcumin complex was found to be 4.75 × 105 L mol−1 cm−1 (λmax at 458 nm) in N,N-dimethyl formamide medium. The linear dynamic range and detection limit of the proposed analytical procedure were calculated to be 10–150 ng mL−1 and 0.8 ng mL−1 respectively. The proposed analytical methodology was validated by analysis of three in-house working reference materials of uranium. Determination of traces of boron in two uranium dioxide and two metallic uranium samples were found to demonstrate the applicability of the method. The relative standard deviation of the proposed method was found to be of 3–5%.

Assessment of matrix tolerance for the direct trace elemental analysis in uranium by X-Ray Fluorescence technique using micro focussed beam

Determination of trace elemental concentrations in presence of heavy Z matrix like uranium using X-Ray Fluorescence (XRF) based technique requires separation of major matrix from the sample matrix. This separation process is laborious and also produces large amount of organic waste. To counter this problem we have developed a Micro-XRF based technique for the trace elemental analysis in uranium matrix without applying any matrix separation steps. The main challenge of trace elemental analysis in presence of heavy matrix like uranium is severe matrix effect which deteriorates the detection limit as well as the analytical result. In order to assess the matrix tolerance for the direct trace elemental analysis in uranium by X-Ray Fluorescence technique, a detailed study has been conducted to observe the effect of uranium matrix on the analytical results like detection limits or recovery rate etc in the present paper. Based on the detail studies, a limiting concentration for uranium as major matrix has been optimized, up to which matrix effect can be tolerable for trace elemental analysis without further matrix separation. However if the matrix concentration goes beyond that limit, the sample has to be diluted to maintain the uranium matrix concentration below that limit. The presently developed methodology has been validated by determining trace elemental concentration in real natural uranium samples down to few hundred ng/mL concentration level. The methodology reported in this work is simple, cost-effective and less time consuming, with detection limits comparable to other well established trace analytical methods. Moreover it is having an added advantage of avoiding the complex matrix separation steps up to a certain level of matrix concentration.

Rapid and automated separation of uranium ore concentrates for trace element analysis by inductively coupled plasma – optical emission spectroscopy/triple quadrupole mass spectrometry

The present study documents an automated approach to performing elemental analysis on a large group uranium ore concentrate (UOC) samples. Here, 17 UOC samples, 2 quality control samples, and 26 process blanks were purified sequentially through a single 500 μL Uranium and TEtra Valent Actinides (UTEVA®) column. For each sample, the trace elemental impurities were separated from its dissolved uranium matrix on the UTEVA column and collected for analysis by inductively coupled plasma – optical emission spectroscopy / triple quadrupole mass spectrometry (ICP-OES/TQMS). The UTEVA column was subsequently regenerated prior to separation of the following sample. The column was efficiently regenerated, for each UOC, even after processing ~50 mg of uranium, cumulatively. The validity of the method was established by determining the trace impurities of two quality control uranium reference samples (CRM 124–1 and CUP-2). The current trace element measurements from the 17 UOC samples were compared to previously reported values from an interlaboratory comparison exercise, when available. The methodology employed here produces trace elemental analysis with excellent correlation to the previously reported data for many of the elements / samples, particularly when viewed through the context of existing geochemical comparisons tools (e.g. chondrite normalized variation plots).

Determination of Zirconium, Niobium, Iron, Nickel, Copper and Manganese in Uranium Alloys-Emission Spectrometry

This method established an inductively coupled plasma emission spectrometry method to determine the contents of zirconium, niobium, iron, nickel, copper and manganese in uranium and uranium alloy through the sample pretreatment, sample weighing, dissolution method, uranium separation method, interference test between coexisting elements, precision and recovery test. This method separated the uranium matrix, and avoided the influence of uranium matrix on zirconium, niobium, iron, nickel and manganese.

Determination of rare earth elements in uranium materials by ICP-MS and ICP-OES after matrix separation by solvent extraction with TEHP

A simple analytical procedure has been developed for the determination of trace rare earth elements (REEs) in uranium materials by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES), after selective extraction of uranium matrix using tri(2-ethylhexyl)phosphate (TEHP). The separation method reduces uranium concentration in the raffinate to less than 10 mg L−1 (from initial value of ~40,000 mg L−1), thus, eliminating severe matrix interferences from uranium, such as isobaric and polyatomic interferences in ICP-MS, and spectral interferences in ICP-OES. The raffinate is directly used for the analysis of REEs, without any pretreatment. The proposed method was validated by applying it to the ICP-MS determination of REEs in uranium dioxide (UO2) samples, by spiking with standard reference REE solutions and performing the recovery tests. The recoveries ranged from 94.0 to 105.5%. The validation was also performed similarly for ICP-OES measurements on U3O8 as well as UO2 samples, which provided recoveries in the ranges of 96–105.8% and 99.2–101.6%, respectively. The method offers a fast, simple and effective method with low detection limit, and is suggested for the determination of REEs in uranium-based nuclear grade materials such as uranyl nitrate hexahydrate, uranium hexafluoride and uranium trioxide.

Interactions and immobilization of lanthanides with dopants in uranium-based metallic fuels

In uranium-based fuels, production and migration of lanthanide fission products and subsequent chemical interactions with cladding constituents lead to fuel–cladding chemical interaction (FCCI), limiting fuel performance. In general, dopant addition to the fuel matrix to arrest lanthanides within the fuel by forming intermetallics is found to be effective in mitigating FCCI. Recently, we proposed ab-initio based alloy-design principles, which can be useful in identifying dopant(s) that can bind a lanthanide (Nd) inside the fuel matrix. Here, we demonstrate the robustness of such principles by performing a systematic study to choose dopants to form compounds with a range of experimentally-observed lanthanide fission products. Results reveal that for a given dopant, lanthanide Ce and La exhibit similar behavior in their compound-forming tendencies compared to Nd and Pr, which is linked to lanthanide intrinsic characteristics such as the electronic configurations. Our predicted lanthanide-dopant intermetallic formation is verified experimentally in selective cases. Finally, we showed alloy design principles that accurately identify previously known dopants like Pd, and also predict new dopants As and Se, that can be effective in binding all lanthanides within the uranium matrix. Overall, this research helps to develop generic alloy-design principles for complex multi-component systems based on lanthanide and dopant intrinsic characteristics.

Determining P, S, Br, and I content in uranium by triple quadrupole inductively coupled plasma mass spectrometry

The trace impurities of a uranium ore concentrate (UOC) can be examined to determine mine source, methods of production, and quality. This study presents a method to determine the concentration of halides and main group elements, specifically P, S, Br and I, utilizing triple quadrupole inductively coupled plasma–mass spectrometry. These analytes were measured in a uranium matrix to simulate a UOC sample. The concentrations determined with this method showed agreement with known values. Solutions with and without uranium were compared. A UOC certified reference material, CUP-2, was analyzed to further demonstrate the effectiveness of the method.

Rare Earth Element Determination in Uranium Ore Concentrates Using Online and Offline Chromatography Coupled to ICP-MS

The determination of trace elements, particularly rare earth elements, in uranium ore concentrates (UOCs) is important as the pattern can be indictive ore characteristics. Presented here is a methodology for accurately quantifying rare earth elements (REE) in UOCs. To improve the measurement uncertainty, isotope dilution mass spectrometry (IDMS) was utilized over other quantification techniques such as external calibration or standard addition. The isotopic determinations were measured by inductively coupled plasma-mass spectrometry (ICP-MS). To obtain high-fidelity isotopic measurements, separation of the REE from the uranium matrix was achieved by high-performance ion chromatography (HPIC), reducing the isobaric interferences. After separation, the target analytes were analyzed in two different modalities. For high precision analysis, the separated analytes were collected and measured by ICP-MS in an “offline” fashion. For a rapid approach, the separated analytes were sent directly into an ICP-MS for “online” analysis. These methods have been demonstrated to accurately quantify the REE content in a well-characterized UOC sample.

Leaching behavior of gamma-emitting fission products, calcium, and uranium from simulated MCCI debris in water

ABSTRACT Gamma-ray radionuclides (Cs-137, Ba-140, I-131, Ru-103, and Zr-95) were produced by neutron irradiation of simulated molten core–concrete interaction (MCCI) debris, which was synthesized by the heat treatment of a mixture of UO2 with concrete components at a relatively low temperature of 1473 K under reducing and oxidizing conditions. The major uranium solid phases were unreacted UO2 and calcium uranate. The leaching ratio of the radionuclides in the powdered sample of the simulated MCCI debris was investigated under atmospheric conditions at 298 K in 0.1 mol/dm3 NaClO4 after filtration of the leachate through a 0.45-µm pore membrane. The uranium molar concentration in the filtrate was affected by the oxidation state in the solids. In the present study, however, the effect of various solid phase conditions on the leaching ratio normalized to that of uranium matrix could not be clarified. It was found that the leaching ratio of various fission products (R M) was proportional to that of Cs (R Cs), and this trend did not depend on the oxidation state of uranium, the type of uranium complex (including a colloidal species), or the presence of Ca, Si, cement, or Zr.

Trace element determinations in uranium by energy dispersive X-ray fluorescence spectrometry using thin film specimens

Thin film specimens on scotch tape base with analyte amounts in ng level have been used for trace element determinations in Certified Reference Materials (CRMs) of uranium oxides. The samples were prepared by dissolving the CRMs in nitric acid and separating the major matrix uranium by solvent extraction. Small volume aliquots of the aqueous phases, obtained after uranium matrix separation from sample solutions, were mixed with gallium internal standard and deposited on scotch tape supports. These specimens were presented for Energy Dispersive X-Ray Fluorescence measurements. The trace elements present in the specimens were determined after processing the spectra and consideration of the relative sensitivity values of the elemental X-ray lines. The results obtained were found to be in good agreement with the Total reflection X-Ray Fluorescence (TXRF) determined and certified values. The methodology has all the advantageous features of TXRF for nuclear material elemental characterization e.g. small sample amount requirement, multi-elemental analytical capability etc. along with simple instrumentation. In addition, such specimens can be isolated using scotch tape sealing and spread of radioactive materials during their analysis can be avoided.

Rapid measurements of 235U fission product isotope ratios using an online, high-pressure ion chromatography inductively coupled plasma mass spectrometry protocol with comparison to isotopic depletion models

An automated online separation–direct analysis method, RAPID (rapid analysis of post-irradiation debris), has been developed for the measurement of the concentration and isotopic composition of over 40 elements down to the low-picogram level. Here we discuss the application of RAPID to irradiated highly-enriched uranium, demonstrating that it has the sensitivity required to achieve precise, low-level analyses of non-natural isotopes, even in the presence of a bulk uranium matrix. Isotopic ratios have been successfully measured at the low-picogram level, and the accuracy of these ratios was confirmed using an isotopic depletion and decay modeling software to within 1–2%.

Trace element determinations in uranium by Total reflection X-Ray Fluorescence spectrometry using a newly developed polymer resin for major matrix separation

Trace element determinations in uranium samples by Total reflection X-Ray Fluorescence (TXRF) spectrometry were carried out using a new polymer resin gel for uranium matrix elimination from the sample solutions. The resin was prepared by using the 1:1 mol proportion of monomers bis [2-(methacryloyloxy) ethyl] phosphate (bis-MEP) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS). This new poly (bis-MEP-AMPS) resin has exhibited superior features for the trace element determinations in uranium matrix compared to the solvent extraction based methods, which could be attributed to its remarkable selectivity towards uranium in 4 M HNO3 medium without sacrificing its uptake efficiency (94%) just by simple equilibration of the resin in the solutions. The separation procedure is very simple and the polymer resin gel can be regenerated by sonicating in a 0.5 wt% Na2CO3 solution for one hour. This resin was successfully used for the trace elemental analysis in a certified reference material (CRM-IV) of uranium oxide by TXRF after separation of uranium from the sample matrix with satisfactory analytical results. Photoluminescence and FTIR studies were performed to understand the coordination of uranyl species with this polymer resin.

Trace elemental analysis of bulk uranium materials using an inline automated sample preparation technique for ICP-OES

An automated inline method for the separation of trace element impurities from uranium matrices using a 200 µL column packed with UTEVA resin is presented here utilizing an Elemental Scientific, Inc. prepFAST IC in combination with a Perkin Elmer Avio 500 ICP-OES. This method reduces human exposure to highly concentrated acids and uranium-rich samples by automating the chemistry and introduction to the ICP. Calibration standards were prepared using inline dilutions requiring a single stock standard. The separation of trace elements from uranium matrices requires samples to be prepared in 8 M HNO3, which can be detrimental to the ICP, thus a post-column dilution step was employed to dilute the eluent matrix to 4 M HNO3. The method was optimized for a sample-to-sample time of < 9 min and monitored 21 elements in total. Proof of concept experiments for 1 µg mL−1 trace elements spiked into 0.1 vol%, 0.5 vol%, and 1.0 vol% uranium matrices resulted in < 5% relative difference and < 10% relative standard deviation for triplicate measurements of each uranium matrix analyzed. Inline dilutions (pre-column) of 2 vol% uranium + 20 µg mL−1 trace elements resulted in accurate and precise measurements using dilution factors of 2×, 4×, 5×, and 20×. Method detection limits for the 21 elements (Al, B, Ba, Be, Cd, Ca, Co, Cu, Fe, Li, Pb, Mg, Mn, Ni, K, Sr, Na, V, Zn, Zr, and U) analyzed for ranged from 7 to 326 ng mL−1 for 70 µL volume injections.

An automated micro-separation system for the chromatographic removal of uranium matrix for trace element analysis by ICP-OES

An automated, miniaturized, off-line separation technique is presented here using an Elemental Scientific Inc. microFAST MC system with UTEVA resin to extract the uranium matrix from its trace element impurities in aqueous media. The collected fractions were analyzed for ~ 30 trace elements using inductively coupled plasma – optical emission spectroscopy. Ten replicate samples were processed with a single column resulting in precision ranging from 3.3% to 6.2% relative standard deviation with regards to the trace element recoveries. Accuracy, with respect to trace element concentrations in the U3O8 Certified Reference Material 124-1, resulted in an average of 13.9% relative deviation while accuracy to the Canadian U3O8 reference material, CUP-2, resulted in an average relative deviation of 8.6%. The total separation time of this automated process was reduced to ~ 30 min per sample while employing a 0.5 mL UTEVA chromatographic resin bed and 2.5 mg of uranium.

Analysis of Rare Earth Elements in Uranium Using Handheld Laser-Induced Breakdown Spectroscopy (HH LIBS).

A portable handheld laser-induced breakdown spectroscopy (HH LIBS) instrument was evaluated as a rapid method to qualitatively analyze rare earth elements in a uranium oxide matrix. This research is motivated by the need for development of a method to perform rapid, at-line chemical analysis in a nuclear facility, particularly to provide a rapid first pass analysis to determine if additional actions or measurements are warranted. This will result in the minimization of handling and transport of radiological and nuclear material and subsequent exposure to their associated hazards. In this work, rare earth elements (Eu, Nd, and Yb) were quantitatively spiked into a uranium oxide powder and analyzed by the HH LIBS instrumentation. This method demonstrates the ability to rapidly identify elemental constituents in sub-percent levels in a uranium matrix. Preliminary limits of detection (LODs) were determined with values on the order of hundredths of a percent. Validity of this methodology was explored by employing a National Institute of Standards and Technology (NIST) standard reference materials (SRM) 610 and 612 (Trace Elements in Glass). It was determined that the HH LIBS method was able to clearly discern the rare earths elements of interest in the glass or uranium matrices.

Characterization of un-irradiated MIMAS MOX fuel by Raman spectroscopy and EPMA

In this study, Raman spectroscopy technique was implemented to characterize un-irradiated MIMAS (MIcronized - MASter blend) MOX fuel samples with average 7 wt.% Pu content and different damage levels, 13 years after fabrication, one year after thermal recovery and soon after annealing, respectively. The impacts of local Pu content, deviation from stoichiometry and self-radiation damage on Raman spectrum of the studied MIMAS MOX samples were assessed. MIMAS MOX fuel has three different phases Pu-rich agglomerate, coating phase and uranium matrix. In order to distinguish these phases, Raman results were associated with Pu content measurements performed by Electron Microprobe Analysis. Raman results show that T2g frequency significantly shifts from 445 to 453 cm−1 for Pu contents increasing from 0.2 to 25 wt.%. These data are satisfactorily consistent with the calculations obtained with Gruneisen parameters. It was concluded that the position of the T2g band is mainly controlled by Pu content and self-radiation damage. Deviation from stoichiometry does not have a significant influence on T2g band position. Self-radiation damage leads to a shift of T2g band towards lower frequency (∼1–2 cm−1 for the UO2 matrix of damaged sample). However, this shift is difficult to quantify for the coating phase and Pu agglomerates given the dispersion of high Pu concentrations. In addition, 525 cm−1 band, which was attributed to sub-stoichiometric structural defects, is presented for the first time for the self-radiation damaged MOX sample. Thanks to the different oxidation resistance of each phase, it was shown that laser induced oxidation could be alternatively used to identify the phases. It is demonstrated that micro-Raman spectroscopy is an efficient technique for the characterization of heterogeneous MOX samples, due to its low spatial resolution.

Improved approach for the determination of low‐Z elements in uranium samples using a vacuum chamber TXRF spectrometer

Total reflection X‐ray fluorescence (TXRF) method for the determination of low atomic number (Z) elements Na (Z = 11) to Ca (Z = 20) using Cr Kα excitation, vacuum atmosphere sample chamber, and ultrathin window detector of a low Z–high Z TXRF spectrometer has been developed. The earlier reported problem in determination of Al, due to interference of U Mα escape peak with Al Kα, was taken care by more intense solvent extraction‐based separation of uranium matrix from the sample solutions. Any dissolved tri‐n‐butyl phosphate having traces of uranium left after solvent extraction was removed from the sample solutions by equilibrating with n‐dodecane. This approach resulted in the betterment of analytical results. The method developed was validated by analyzing three Certified Reference Materials for trace metals in uranium oxide, developed by Department of Atomic Energy, Government of India. The TXRF determined results were found to have an average precision of 8.0% (1σ, n = 3) and the average deviation of the TXRF determined values from the certified concentrations was 7.3%. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Separation and determination of trace thorium in uranium matrix using chelation ion chromatography

ABSTRACTA simple chromatographic method for the determination of trace thorium in uranium matrix has been reported after studying the retention behavior of U(VI) and Th(IV) as their 2,6-pyridine dicarboxylic acid (PDCA) complexes on a reversed phase column. The method does not require pre-separation of uranium matrix. A mobile phase consisting of PDCA, KNO3, and HNO3 in 5% methanol was used. A calibration plot was constructed in the presence of uranium matrix (r2 = 0.9978). The precision of the method is 5% at 1 ppm of Th and LOD was obtained at 0.1 ppm (S/N =3). The accuracy of the method was checked by comparing the results with neutron activation analysis.