IRMM-2030: certification of a uranium nitrate solution reference material with a 235U "enrichment" (i.e. n(235U)/n(U)) of 6 % : certified for isotope ratios

This report describes the certification of the IRMM-2030 uranium nitrate solution reference material, certified for the uranium isotopic composition. The certified values and their uncertainties were assigned following ISO 17034 [1], ISO Guide 35 [2] and the Guide to the Expression of Uncertainty in Measurement [3]. This certification project was a collaboration between the Joint Research Centre's Unit G.2 in Geel/Belgium, the Urenco facility in Gronau/Germany and the Analytical Services Laboratory of Unit JRC-G.II.8 of the Joint Research Centre in Karlsruhe/Germany. The IRMM-2030 reference material has been prepared in order to provide a uranium nitrate solution isotopic reference material with an isotope amount fraction n(235U)/n(U) of 6 %, commonly called a 235U enrichment of 6 %, in response to a need expressed by nuclear industry. This reference material is particularly needed at enrichment facilities such as Urenco/Germany that typically enrich 235U between 3 %and 5 % but are aiming to enrich uranium up to 6 %. The material was also requested by the International Atomic Energy Agency (IAEA) as a reference material for quality control (QC) purposes. For the preparation of IRMM-2030, two already characterized uranium base materials were mixed to achieve a 235U enrichment within limits specified by the requestor. The first material was a previously characterized UF6 material named UREU502648 with a 235U enrichment of about 4.9 %. The UF6 material was hydrolysed and converted to a uranyl nitrate solution. The second base material is a solution prepared from the certified reference material NBL U500 with a 235U enrichment of about 50 %. By the use of this highly enriched second base material, the lower 234U, 235U and 236U abundances of the first base material were increased to achieve the specified 234U, 235U and 236U abundances for IRMM-2030 simultaneously in one mixing step. The isotopic composition of the base solution IRMM-2030 was measured and certified using the TIMS/MTE method at JRC-G.2 in Geel. After dilution and dispensing into screw-cap quartz ampoules, the isotope ratios were verified for three randomly stratified chosen ampoules internally at JRC-G2 in Geel. The Analytical Service Laboratory at JRC-G.II.8 in Karlsruhe verified independently another set of three randomly stratified chosen ampoules. The isotopic reference material IRMM-2030 with an enrichment of 6 % for 235U is part of a systematic program of JRC-G.2 to supply isotope reference