Search

For nuclear safeguards purposes, two new uranium oxide micro-particle isotope reference materials were certified, IRMM-2329P and IRMM-2331P, with 235U enrichments of 3% and 5%, and 236U abundances of 30 µg·g1and 60 µg·g1, respectively. The isotopic compositions of the base materials were measured by TIMS. The production of the uranium oxide particles was achieved using a vibrating orifice aerosol generator (VOAG) and the particles deposited on carbon planchets. Process control verification measurements on dissolved uranium oxide particles were performed by MC-ICPMS. For IRMM-2329P also the uranium amount per particle was certified by TIMS/IDMS and verified by MC-ICPMS/IDMS. [ABSTRACT FROM AUTHOR]

The history of uranium isotopic reference materials from JRC-Geel during the last 50 years is reviewed by presenting certification methods and relevant applications. The certified isotope ratios are traceable to the SI via gravimetrical preparation, either directly through gravimetrical mixing of highly enriched materials, or indirectly using existing gravimetrically prepared reference materials for calibration of mass spectrometers used for certification measurements. Due to developments of mass spectrometers and analytical methods, certification measurements have improved regarding precision, uncertainties and accuracy. This has led to a comprehensive set of uranium isotopic reference materials available for nuclear safety, security and the scientific community. [ABSTRACT FROM AUTHOR]

Abstract: 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 μm 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. [Copyright &y& Elsevier]

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). [ABSTRACT FROM AUTHOR]

Abstract: The REIMEP 18 (Regular European Inter-laboratory Measurement Evaluation Programme) campaign for the measurement isotopic ratios of uranium in nitric acid solution was completed in December 2006. The task for all participating laboratories was to measure the uranium isotopic composition of four uranium samples ranging from depleted to slightly enriched uranium. With 71 participating laboratories REIMEP 18 has become the largest nuclear isotopic measurement campaign organized by IRMM so far. Participation in this kind of measurement campaign is an integral part of the external quality control required for nuclear safeguards laboratories worldwide. For the first time also a significant number of academic laboratories, mainly from the geochemistry area was included. Certification measurements were carried out at IRMM using state-of-the-art mass spectrometric methodology. A MAT511 UF6-gas source mass spectrometer (GSMS) was used to determine the n(235U)/n(238U) ratios and a TRITON thermal-ionization mass-spectrometer (TIMS) for the minor isotope ratios n(234U)/n(238U) and n(236U)/n(238U). Verification measurements on ampouled samples were performed successfully prior to sample shipping and showed good agreement with the certified ratios. The results of the REIMEP 18 campaign confirm in general the excellent capability of nuclear safeguards and scientific laboratories in measuring isotopic abundances of uranium, although some problems were discovered for the measurements of the minor isotope ratios n(234U)/n(238U) and n(236U)/n(238U) and the calculation of measurement uncertainties for isotope ratios in general. This paper describes the outcome of the REIMEP 18 campaign. It includes a graphical evaluation and discussion of the results, an evaluation of the applied measurement and calibration techniques and a discussion of conclusions and actions to be taken. [Copyright &y& Elsevier]

The IRMM-2019-2029 series of uranium nitrate solutions was certified for the isotopic composition. The solutions were originally prepared for the certification of the IRMM-019-029 series of uranium hexafluoride (UF6) materials in 2014, for which certification measurements were performed by thermal ionization mass spectrometry after conversion of UF6 into uranyl nitrate solutions. Analyses were performed using the modified total evaporation method and for some materials with low 236U abundances, the n(235U)/n(238U) ratio was measured using a n(233U)/n(236U) double spike. The integrity of the certified values after dilution and ampouling of the original solutions was checked through process control measurements. [ABSTRACT FROM AUTHOR]

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(U)/ n(U) was measured using a n(U)/ n(U) double spike. Measurements were confirmed by UF gas source mass spectrometry. Major isotope amount ratios were certified with relative expanded uncertainties ( k = 2) of 0.015-0.030 % and the minor isotope amount ratios n(U)/ n(U) and n(U)/ n(U) were certified with relative expanded uncertainties of 0.02-3 %. [ABSTRACT FROM AUTHOR]