NUSIMEP-7: Uranium isotope amount ratios in uranium particles

The Additional Protocol (AP) authorizes safeguards authorities to verify the absence of undeclared nuclear activities in all parts of a state’s nuclear fuel cycle as well as any other location where nuclear material is or may be present. As part of the Additional Protocol, environmental sampling has become an important tool for the detection of non-declared nuclear activities. In environmental sampling micrometer-sized uranium particles with an isotopic composition characteristic for the processes at the inspected facility need to be collected, identified and analysed. Considering the potential consequences of the analyses, these measurements need to be subjected to a rigorous quality management system. NUSIMEP-7 focused on measurements of uranium isotope amount ratios in uranium particles aiming to support laboratories involved in uranium particle analysis. It was the second NUSIMEP on particle analysis coordinated by IRMM. NUSIMEP-7 was open for participation to all laboratories in the field of particle analysis, particularly also to the IAEA network of analytical laboratories for environmental sampling (NWAL). The NUSIMEP test samples were prepared by controlled hydrolysis of well certified uranium hexafluoride. Participating laboratories in NUSIMEP-7 received the test samples of uranium particles on two graphite disks with undisclosed isotope amount ratio values n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U). The uranium isotope amount ratios had to be measured using their routine analytical procedures. Measurement of the major ratio n(235U)/n(238U) was obligatory; measurement of the minor ratios n(234U)/n(238U) and n(236U)/n(238U) were optional. 24 institutes registered for NUSIMEP-7, whereof 17 have reported measurement results using different analytical methods, among those were 7 NWAL laboratories. The participants’ measurement results have been evaluated against the certified reference values in compliance with ISO 13528:2005. The results of NUSIMEP-7 confirm the capability of laboratories in measuring n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U) in uranium particles of <1 µm. Furthermore they underpin the recent advances in instrumental techniques in the field of particle analysis. In addition feedback from the measurement communities from nuclear safeguards, nuclear security and earth sciences was collected in view of identifying future needs for NUSIMEP interlaboratory comparisons.JRC.D.2-Reference material

Can medio-lateral baseplate position and load sharing induce asymptomatic local bone resorption of the proximal tibia? A finite element study

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Certification of the uranium hexafluoride (UF6) isotopic composition: The IRMM-019 to IRMM-029 series

This report describes the re-determination and certification of the IRMM-019 to IRMM-029 series of uranium hexafluoride (UF6) reference materials certified for the uranium isotopic composition. The values were assigned following ISO Guide 34:2009. The IRMM-019 to IRMM-029 series was originally produced and certified in the 1980's-1990's. Since, the materials are stored in monel ampoules. Upon customer request, UF6 gas is distilled from a mother ampoule into a daughter ampoule, the isotopic composition is verified by Gas Source Mass Spectrometry (GSMS) and the daughter ampoule is sent to the customer. For the purpose of this project, the UF6 materials were converted into uranium nitrate solutions to perform the homogeneity and characterisation studies. Between-unit homogeneity was quantified and stability during dispatch and storage were assessed in accordance with ISO Guide 35:2006. The materials were characterised by Thermal Ionisation Mass Spectrometry (TIMS) using newly established measurement procedures such as the Modified Total Evaporation (MTE) and Double Spike (DS) methods, and with a new set of certified uranium isotope reference materials, which were prepared by gravimetrical mixing of highly enriched 233U, 235U, 236U and 238U oxides or solutions. The results of the characterisation measurements were also confirmed by GSMS measurements using the original UF6 gases. Uncertainties of the certified values were estimated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM) and include uncertainties related to the characterisation measurements and the homogeneity study. The materials are intended for the calibration of methods, quality control purposes, and the assessment of method performance for isotope mass spectrometry. As with any certified reference material, they can also be used for validation studies. The CRMs are available in monel ampoules. Based on physical reasons, there is no minimum sample intake to be taken into account.JRC.D.2-Standards for Innovation and sustainable Developmen

Development of Uranium Reference Particles to Support Nuclear Safeguards

Controlled hydrolysis of certified uranium hexafluoride, carried out in a specifically constructed aerosol chamber, leads to the production of uranyl fluoride particulates which ¿deposited on a graphite planchet support ¿ may be used as a quality control reference material. The particle size and surface distribution depends on several parameters, such as relative humidity inside the aerosol chamber and the concentration of gaseous uranium hexafluoride, determined by the distillation conditions. The best quality samples were obtained a RH ranging from 55 to 70% and low gas amount. These improvements for a single deposition were used to prepare a reference sample with two different uranium enrichments. Preliminary SIMS measurements proved good results with respect to both type of particles. It was also revealed that ¿ in some case ¿ the micrometer size uranium particles are accompanied by a large medium background.JRC.DG.D.2-Reference material

NUSIMEP-7: uranium isotope amount ratios in uranium particles

The Institute for Reference Materials and Measurements (IRMM) has extensive experience in the development of isotopic reference materials and the organization of interlaboratory comparisons (ILC) for nuclear measurements in compliance with the respective international guidelines (ISO Guide 34:2009 and ISO/IEC 17043:2010). The IRMM Nuclear Signatures Interlaboratory Measurement Evaluation Program (NUSIMEP) is an external quality control program with the objective of providing materials for measurements of trace amounts of nuclear materials in environmental matrices. Measurements of the isotopic ratios of the elements uranium and plutonium in small amounts, typical of those found in environmental samples, are required for nuclear safeguards and security, for the control of environmental contamination and for the detection of nuclear proliferation. The measurement results of participants in NUSIMEP are evaluated according to international guidelines in comparison to independent external certified reference values with demonstrated metrological traceability and uncertainty. NUSIMEP-7 focused on measurements of uranium isotope amount ratios in uranium particles aiming to support European Safeguards Directorate General for Energy (DG ENER), the International Atomic Energy Agency’s (IAEA) network of analytical laboratories for environmental sampling (NWAL) and laboratories in the field of particle analysis. Each participant was provided two certified test samples: one with single and one with double isotopic enrichment. These NUSIMEP test samples were prepared by controlled hydrolysis of certified uranium hexafluoride in a specially designed aerosol deposition chamber at IRMM. Laboratories participating in NUSIMEP-7 received the test samples of uranium particles on two graphite disks with undisclosed isotopic ratio values n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U). The uranium isotope ratios had to be measured using their routine analytical procedures. Measurement of the major ratio n(235U)/n(238U) was obligatory; measurement of the minor ratios n(234U)/n(238U) and n(236U)/n(238U) was optional. Of the twenty-four institutes that registered for NUSIMEP-7, 17 have reported their results achieved by different analytical methods. The results of NUSIMEP-7 confirm the capability of laboratories in measuring n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U) in uranium particles of the size below 1 mm diameter. Furthermore, they underpin the recent advances in instrumental techniques in the field of particle analysis. In addition, feedback from the measurement communities from nuclear safeguards, nuclear security and earth sciences was collected in view of identifying future needs for NUSIMEP interlaboratory comparisons.JRC.D.2-Standards for Innovation and sustainable Developmen

Standards for uranium hexafluoride (UF6) mass spectrometry

For UF6 mass spectrometry two types of "standards" are equally important: firstly "documentary standards" which describe specific measurement techniques and associated calculations, and secondly "material standards" which are preferentially SItraceable certified isotopic reference materials, as e.g. provided by the European Commission's Institute for Reference Materials and Measurements (IRMM). Recently the IRMM has upgraded its facilities for uranium isotopic measurements using uranium hexafluoride (UF6) gas by the acquisition of a new gas source mass spectrometer (GSMS), the "URANUS" from Thermo Fisher. By that IRMM has expanded its UF6 mass spectrometry capability from measurements of only the "major" isotope ratio n(235U)/n(238U) towards the so-called "minor" isotope ratios n(234U)/n(238U) and n(236U)/n(238U). The minor ratios contain increasingly valuable information about the source of the original ("feed") material used for the commercial or possibly clandestine isotopic enrichment of UF6 and have therefore reached a high level of attention for safeguards authorities. "Documentary standards": within the recent few years new measurement techniques for UF6-GSMS have been developed at IRMM, e.g. the "memory corrected double standard" (MCDS) technique which shows an improved measurement performance for both the "major" n(235U)/n(238U) isotope ratio as well as the "minor" isotope ratios n(234U)/n(238U) and n(236U)/n(238U). A careful revision of some of the documentary standards for UF6 GSMS measurements (e.g. ASTM C1429-99) is now strongly suggested by IRMM. This will be an important contribution to improve the overall performance of UF6 GSMS measurements. It is a good example of the JRC’s expertise contributing to standardization and innovation by further developing material standards and reference methods but also documentary standards to the benefit of the safeguards community and industry. "Material standards": IRMM has just started a comprehensive project for a new certification of the worldwide most widely used and well-known IRMM-019 to IRMM-029 series of 12 UF6 reference materials. Special emphasis will be given on achieving lower uncertainties particularly for the "minor" isotope ratios using previously established high performance TIMS instrumentation and techniques. This new certification is a prerequisite for achieving accurate results for UF6 GSMS measurements also for the minor ratios to be used for nuclear safeguards investigations.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Uranium hexafluoride (UF6) gas source mass spectrometry for certification of reference materials and nuclear safeguard measurements at IRMM

Uranium hexafluoride gas source mass spectrometry at IRMM is based on two foundations, firstly the operation of a UF6 gas source mass spectrometer (GSMS) and secondly the preparation of primary UF6 reference materials, which were converted from gravimetrically prepared mixtures of highly enriched oxides of 235U and 238U. Recently a new GSMS for uranium isotopic measurements using UF6 gas, the "URANUS" from Thermo Fisher, was installed at IRMM, which also allows measurements of the so-called "minor" isotope ratios n(234U)/n(238U) and n(236U)/n(238U). In this paper the design and the implementation of measurement techniques for the new URANUS GSMS are described. This includes the "single standard" and the "double standard" (DS) method as well as the newly developed "memory corrected double standard" method (MCDS). This required a detailed investigation of memory effects within the GSMS instrument, in particular regarding the dependence of memory effects on the isotope ratios of samples and standards. The results of this study led to new recommendations for the selection of the standards for a given sample and for suitable measurement procedures. The measurement performance for the "major" isotope ratio n(235U)/n(238U) as well as the “minor” isotope ratios n(234U)/n(238U) and n(236U)/n(238U) is presented and compared with other mass spectrometric techniques. With the installation and validation of the new URANUS GSMS instrument IRMM has established two new complementary techniques for measuring the full isotopic composition of uranium samples. UF6 GSMS in combination with the MCDS method is considered the preferred technique for samples in the UF6 form and for smaller uncertainties for measurements of the major ratio n(235U)/n(238U), while thermal ionization mass spectrometry (TIMS), in combination with the "modified total evaporation" (MTE) method as well as ion counting and high abundance sensitivity for the detection of 236U, provides a superior measurement performance for the minor isotope ratios n(234U)/n(238U) and n(236U)/n(238U).JRC.D.2-Standards for Innovation and sustainable Developmen

In-SEM Raman microspectroscopy coupled with EDX – a case study of uranium reference particles

Information about the molecular composition of airborne uranium-bearing particles may be useful as an additional tool for nuclear safeguards. In order to combine the detection of micrometer-sized particles with the analysis of their molecular forms, we used a hybrid system enabling Raman microanalysis in high vacuum inside a SEM chamber (SEM-SCA system). The first step involved an automatic scan of a sample to detect and save coordinates of uranium particles, along with X-ray microanalysis. In the second phase, the detected particles were relocated in a white light image and subjected to Raman microanalysis. The consecutive measurements by the two beams showed exceptional fragility of uranium particles, leading to their ultimate damage and change of uranium oxidation state. We used uranium reference particles prepared by hydrolysis of uranium hexafluoride to test the reliability of the Raman measurements inside the high vacuum. The results achieved by the hybrid system were verified by using a standalone Raman microspectrometer. When deposited on exceptionally smooth substrates, uranyl fluoride particles smaller than 1000 nm could successfully be analyzed with the SEM-SCA system.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Analysis of Single Micro-Sized Uranium Particles by Thermal Ionization Mass Spectrometry

In this work, a method is described that allows measuring the U enrichment in small uranium oxides particles (less than 1 µm in diameter) by the use of Thermal Ionization Mass Spectrometry (TIMS). This project is driven by the need of improving IRMM's capabilities in the area of low-level isotopic analysis for the support in "Environmental Sampling" for nuclear safeguards. The particle manipulation and analysis techniques presented here enable the examination of a single particle of interest by a combination of analytical techniques, thus yielding surface morphological, elemental and isotopic information. Individual particles of NUSIMEP-6 and NBS-200 samples containing pg-size amounts or uranium were analyzed. First experimental data showed the technique used in this work was an accurate method for the determination of the U isotope ratios, including the minor isotopes, which were derived with good precision.JRC.DG.D.2-Reference material

Certification of the uranium hexafluoride reference materials for isotopic composition

The IRMM-019 to IRMM-029 series of uranium hexafluoride materials is certified for the isotopic composition. After conversion into uranyl nitrate solution, certification and homogeneity measurements were performed by Thermal Ionization Mass Spectrometry. Analyses were performed by Modified Total Evaporation and for some materials the major isotope amount ratio n(235U)/n(238U) was measured using a n(233U)/n(236U) double spike. Measurements were confirmed by UF6 Gas Source Mass Spectrometry. Major isotope amount ratios were certified with relative expanded uncertainties (k=2) from 0.015 % to 0.030 %, minor isotope amount ratios n(234U)/n(238U) and n(236U)/n(238U) with relative expanded uncertainties ranging from 0.02 % to 3 %.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard