EU Science Hub

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.