REIMEP-18, Inter-laboratory comparison for the measurement of uranium isotopic ratios in nitric acid solution : report to participants

The REIMEP 18 (Regular European Inter-laboratory Measurement Evaluation Programme) campaign was started in October 2005. For this campaign 4 samples of depleted to low-enriched uranium were chosen. State of the art certification measurements were carried out using a Varian MAT511 UF6-gas source mass spectrometer (GSMS) for the n(235U)/n(238U) ratio and using 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 and showed good agreement with the certified ratios. REIMEP 18 has been the largest nuclear measurement campaign organized by IRMM so far. Samples were shipped in March 2006 to 85 registered participants. Most of the participating laboratories submitted their results before May 31st 2006. Due to problems with the sample containers and extended shipping times the submission deadline had to be postponed until September 30th 2006 for some of the participating laboratories. In the end IRMM received results from 71 laboratories. The results of the REIMEP 18 campaign confirm in general the excellent capability of laboratories in measuring isotopic abundances of uranium although some problems arose for the measurements of the minor isotope ratios n(234U)/n(238U) and n(236U)/n(238U). This report describes the outcome of the REIMEP 18 campaign, including the graphical evaluation and discussion of the results, the evaluation of the questionnaire and the discussion of conclusions and actions to be taken.