Environmental Swipe Samples Research Articles

A new era of plutonium assay and isotope ratio measurements at ultra-low levels in IAEA safeguards environmental swipe samples by isotope dilution MC-ICP-MS using a 244Pu spike

A new era of plutonium assay and isotope ratio measurements at ultra-low levels in IAEA safeguards environmental swipe samples by isotope dilution MC-ICP-MS using a 244Pu spike

Shelf-life of uranium oxide microparticle reference materials and possible implications for the identification of optimal storage conditions

During their inspections of nuclear facilities, inspectors of the International Atomic Energy Agency (IAEA) collect environmental swipe samples containing uranium dust particles. As reference materials, well-characterized uranium microparticles are required that are suitable for quality control, analytical refinement and method development tasks. At Forschungszentrum Jülich (FZJ), uranium oxide reference microparticles are produced using an aerosol-based process. A core requirement for distribution of a potential reference material is to guarantee a practical shelf-life. Previous studies of structure and shape of uranium oxide microparticles demonstrated possible alteration leading to the formation of uranium hydroxides such as schoepite. A systematic shelf-life study exploring storage under different environmental conditions was launched in late 2021. Uranium microparticles were stored in three environments simulating potential long-term storage conditions, whereas a fourth experiment used an unrealistically harsh environment to assess the effects of accelerated alteration. At the time of writing, only the uranium microparticles intentionally stored under these extreme conditions have shown significant signs of alteration. This implies that synthetic uranium oxide microparticles under common storage conditions have minimal shelf-lives of at least 1 year, and likely much longer.Graphical abstract

Assessing high fidelity multi-component models to facilitate safeguards at Gas Centrifuge Enrichment Plants

• Comparison of 1D vs 2D centrifuge performance calculations on cascade analysis. • Development of cascades enriching 235 U to 5% vs 19.75% • Details of isotopic signatures for cases of intentional misuse and machine failures. • Discussion on safeguards implications of developing HALEU. The International Atomic Energy Agency (IAEA) inspectors routinely carry out environmental sampling (ES) as a verification method. Collection of environmental swipe samples at various locations in Gas Centrifuge Enrichment Plants (GCEPs) is an important process in detecting misuse of a declared facility and possibly the existence of undeclared nuclear material. These samples are measured for isotopic composition in uranium containing particles by Thermal Ionization Mass Spectrometry (TIMS) or Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Even though ES is highly effective in detecting the absolute value of enrichments and their deviations from the declared values, it cannot explain the cause of those changes. Several potential explanations can serve as possibilities for particles detected above or other than the declared enrichment. These include normal and non-malicious events such as the design of the enrichment cascades, unintentional failures of the machines, or overshoot during startup of a cascade. It can also be the result of deliberate misuse by the facility operators. The primary objective of this work is to understand how these factors affect the enrichments produced by a cascade and quantify anticipated multi-isotopic concentrations for each case. The following methodology is employed to determine signatures at a particular facility. 1) Utilize a new two-dimensional multi-component diffusion code to obtain centrifuge performance data and use that information to design and perform cascade analysis. Compare and contrast the results with previous 1-D radially averaged solutions from the Pancake code. 2) Design a GCEP cascade with the production goal of 19.75% 235 U for each set of machine data above. Investigate two cascade scenarios that include enrichment of natural uranium (NU) feed to 19.75% 235 U in a single cascade compared to a two-step process of NU to 5% and then 5% to 19.75%. 3) Simulate the intentional vs unintentional off-normal scenarios in the cascades to assess the differences in isotopic concentrations. A non-ideal squared-off cascade model developed at the University of Virginia is used to calculate flow rates and isotopic concentrations of the process gas. The analysis is performed using the Rome machine model operated at 600 m/s rotor speed. The upper and lower bounds of normal and abnormal enrichments in a typical facility are used in conjunction with ES results to understand the root causes of such observations.

An improved method for determination of isotope ratios in individual uranium particles by thermal ionization mass spectrometry

The determination of isotope ratios of individual uranium particles in environmental swipe samples is very important for nuclear safeguards. A new technique to measure isotope ratios for individual uranium particle was developed in this work, which was a combination of particle transfer by scanning electron microscope (SEM) and isotope ratios analysis by thermal ionization mass spectrometry (TIMS). The technique was verified by measuring isotope ratios in individual micrometer-size uranium particles of known isotopic abundance. The particles were identified by SEM combined with energy dispersive X-ray spectrometer (EDX) and transferred by micromanipulator, which could improve the efficiency of sample preparation and simplify the procedure. The experimental condition was optimized by using a new kind of thermal ion emitter to enhance the ionization efficiency of uranium. Several individual uranium particles from certified reference materials were successfully measured by SEM-TIMS. The results show that the measured isotope ratios were in good agreement with the reference values. The relative errors of 13 particles were within 2.7% for 234 U/ 238 U, 1.1% for 235 U/ 238 U and 4.5% for 236 U/ 238 U isotope ratios, respectively, and the relative standard deviation (RSD) were within 1.6% for 234 U/ 238 U, 0.5% for 235 U/ 238 U and 3.3% for 236 U/ 238 U, respectively. It is expected that this method will become a promising alternative technique for determining uranium isotope ratios in particle analysis. The particles used in this study had sizes between 1.3 and 4.7 μm. A new technique to measure isotope ratios for individual uranium particle was developed in this work. The particles were identified by SEM combined with energy dispersive X-ray spectrometer (EDX) and transferred by micromanipulator, which simplify the procedure of sample preparation. A new type of thermal ion emitter was used to enhance the ionization efficiency of uranium. Several micrometer-size (1–5 μm) individual uranium particles from certified reference materials (CRM U200 and U850) were measured by SEM-TIMS. The results show that the relative errors of 13 particles were within 2.7% for 234 U/ 238 U, 1.1% for 235 U/ 238 U and 4.5% for 236 U/ 238 U isotope ratios, respectively, and the relative standard deviation (RSD) were within 1.6% for 234 U/ 238 U, 0.5% for 235 U/ 238 U and 3.3% for 236 U/ 238 U, respectively. • The sample preparation was improved and simplified by using SEM. • The experimental condition was optimized by using a new kind of thermal ion emitter. • The relative errors and relative standard deviations of minor isotope ratios were within 5%.

Optimization of uranium and plutonium separations using TEVA and UTEVA cartridges for MC-ICP-MS analysis of environmental swipe samples

The analysis of environmental swipe samples for ultra-trace uranium (U) and plutonium (Pu) determinations is essential in the nuclear safeguards community. While mass spectrometry techniques for U and Pu detection continually improve, established separation methods are seldom reevaluated. Currently, actinide separations within the forensics community predominantly employ either Eichrom TEVA® or UTEVA® resins. The direct optimization of U and Pu separations utilizing both resins has not been widely reported. Here, several methods were explored with goals of increasing analyte recovery, acquiring cleaner blanks, and improving the separation efficiency of ultra-trace levels of U and Pu from environmental swipe samples. The optimized separation methodology of U and Pu was examined using certified reference materials and archived environmental swipe samples.

Automated Separation of Uranium and Plutonium from Environmental Swipe Samples for Multiple Collector Inductively Coupled Plasma Mass Spectrometry.

A fully automated method for the separation of low-concentration uranium from plutonium in environmental swipe samples has been developed. The offline chromatography system features renewable 1 mL Eichrom TEVA and UTEVA column generation from bulk resin slurry. Discrete fractions of the separated actinides are delivered into user defined vials for future analysis. Clean room background levels were achieved outside of a cleanroom environment with this method. Purification of uranium and plutonium from various sample matrixes and at various concentrations was successful. Major and minor isotope ratios for both elements were measured via multiple collector inductively coupled plasma mass spectrometry and were in good agreement with certified reference values. Validation of the separation method was conducted on archived environmental samples and agreed with values previously reported using standard column chemistry.

Improvement in the chemical separation and determination of uncertainties for bulk analysis of Pu isotopes at ultra-trace levels by using MC-ICP-MS

Improved bulk analysis based on extraction chromatography and systematic evaluations of uncertainties of plutonium isotopes at ultra-trace levels in environmental swipe samples are presented. In the modified method based on a single column system using UTEVA resin for MC-ICP-MS, hydrogen peroxide was introduced to obtain pure plutonium isotopes from chemical separation by removing excess organic-based reducing reagents. We confirmed that hydrogen peroxide effectively decomposed the reducing reagents characterized by UV–Vis absorption spectroscopy and the peak fluctuations were significantly reduced. To examine the reliability of analytical performance, we systematically evaluated the combined uncertainties during the overall chemical procedures using simulated samples containing Pu reference materials.

Rapid separation and purification of uranium and plutonium from dilute-matrix samples

This work describes a streamlined approach to the separation and purification of trace uranium and plutonium in environmental swipe samples that contain a small amount of collected bulk material. We describe key modifications to conventional techniques that result in a relatively rapid, safe, cost-effective, and efficient U and Pu separation process. Simulated samples were produced by loading appropriate 235U, 238U, and 240Pu onto high purity cotton swipes. Uranium concentration and isotopic composition were measured by multi-collector inductively coupled mass spectrometry. Corresponding plutonium measurements were conducted with a three stage thermal ionization mass spectrometer. Quantitative U and Pu recoveries were observed with this method.

Feasibility study of solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of particulate uranium in swipe samples from nuclear facilities

The feasibility of a solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for “the particle analysis of safeguards environmental swipe samples” was studied with polycarbonate (PC) film samples containing thallium (Tl), lead (Pb) and uranium (U) particles in single element and with their solution sample. The influences of instrumental operating conditions on analytical results, especially accuracy and precision in isotope ratio measurements, were investigated. Isotope ratios obtained for Tl and Pb solution samples containing a few picogram amounts of particles were in good agreement with the reference values obtained using pneumatic nebulizer ICP-MS. It is revealed that when vaporization temperature was set to be optimal, the pyrolysis temperatures in the temperature range of this study did not affect the magnitude of integrated signals. Isotope ratios obtained for PC film samples including a few picogram amounts of particles were comparable to those of solution samples, and good values of isotope ratio were obtained in the wide range of measurement parameters even though analyte losses occurred in inappropriate temperature conditions. The pyrolysis and vaporization temperature dependence of the integrated signal was different from those of the solution sample, which is ascribed to the difference of transport efficiency of the vaporized analyte in both samples. Absolute limit of detection for PC film sample was found to be about 2 fg, which corresponds to 2 pg/g for a typical sample mass of 1 mg.

Strengthening IAEA safeguards through environmental sampling and analysis

The IAEA conducts nuclear safeguards world-wide to verify countries' compliance with international agreements such as the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). For the past 25 years, the traditional safeguards tools of materials accountancy, containment and surveillance were focused on the declared nuclear materials in a country's fuel cycle. Following events in Iraq in 1991 and elsewhere, the IAEA initiated `Programme 93+2' with the goals of strengthening the safeguards system, making it more cost-efficient and providing an enhanced ability to detect undeclared nuclear activities in States subscribing to comprehensive IAEA safeguards agreements. Environmental sampling and analysis are one important new feature introduced to aid in the detection of undeclared nuclear activities. This paper will describe the rationale behind this programme, the sampling and analytical methodology used, and the relevant quality assurance measures. The IAEA's Class-100 Clean Laboratory in Seibersdorf will be described along with the highly sensitive analytical techniques which will be employed there to determine the uranium and plutonium content and isotopic composition in environmental swipe samples collected during routine safeguards inspections. The analytical contribution of a Network of Analytical Laboratories in the Member States will also be described.