NUSIMEP-6, uranium isotope amount ratios in uranium particles : interlaboratory comparison report

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-6 focused on measurements of Uranium isotope amount ratios in uranium particles aiming to support laboratories involved in uranium particle analysis. It was the first NUSIMEP on particle analysis coordinated by IRMM and was also intended as a pilot interlaboratory comparison in this field to gather feedback towards future optimisation and improvements. NUSIMEP-6 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 close to natural uranium isotopic composition. Participating laboratories in NUSIMEP-6 received a test sample of uranium particles on a graphite planchet with undisclosed isotope amount ratio values n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U). The uranium isotope amount ratios were to be measured using their routine analytical procedures. Measurement of the major ratio n(235U)/n(238U) was obligatory; measurements of the minor ratios n(234U)/n(238U) and n(236U)/n(238U) were optional. 15 institutes reported measurement results using different analytical methods, among those 7 NWAL laboratories. The participants' measurement results were evaluated against the certified reference values. In addition, zeta scores were calculated. The results of NUSIMEP-6 confirm the capability of laboratories in measuring the ratio n(235U)/n(238U) and n(234U)/n(238U) in uranium particles. Difficulties were particularly observed for the ratio n(236U)/n(238U). In addition feedback from the participants was collected in view of improvements and optimisation of future NUSIMEP interlaboratory comparisons for uranium isotope amount ratios in uranium particles.