@article{JRC125513,
	number = {KJ-NA-30-740-EN-N (online)},
	address = {Luxembourg (Luxembourg)},
	issn = {1831-9424 (online)},
	year = {2021},
	author = {Richter S and Hennessy C and Venchiarutti C and Aregbe Y and Hexel C},
	isbn = {978-92-76-38745-9 (online)},
	publisher = {Publications Office of the European Union},
	abstract = {This report describes the certification of the IRMM-3000 series of uranium nitrate solution reference materials, certified for the uranium isotopic composition. The certified values and their uncertainties were assigned following ISO 17034 [ ], ISO Guide 35 [ ] and the Guide to the Expression of Uncertainty in Measurement [ ].
		This certification project was a collaboration between the International Atomic Energy Agency (IAEA-SGAS, Austria), the Oak Ridge National Laboratory (ORNL, U.S. DOE), Lawrence Livermore National Laboratory (LLNL, U.S.DOE) and the Joint Research Centre (JRC-Geel, Unit G.2 in Geel/Belgium and Unit G.II.6 in Karlsruhe/Germany).
		The IRMM-3000-series consists of a set of five uranium nitrate solution reference materials named IRMM-3020, IRMM-3035, IRMM-3050, IRMM-3075 and IRMM-3090 with the isotopic ratio n(235U)/n(238U) varying from about 0.25 to 6.6, and the 235U enrichment n(235U)/n(U) varying from 20% to 90%. The solutions were prepared by dissolving uranium oxide (U3O8) materials, which were prepared by gravimetrically mixing oxides which were highly enriched in 235U and 238U, in a similar way as performed for the preparation of the IRMM-074, IRMM-075 and IRMM-3636a,b series of isotope reference materials [ , , ].
		The isotopically enriched starting materials were purified using identical methods involving separation on anion and cation columns followed by a precipitation as peroxide. Both starting materials were treated in separate clean glove-boxes to eliminate cross-contamination. The oxides were calcined to convert them into U3O8 in parallel, in an oven installed in a glove-box that provided a controlled low-humidity environment. For each of the mixtures, the oxides of 235U and 238U were weighed and dissolved to form a solution with a concentration of about 5 mg /·g. The final solutions were dispensed into individual quartz ampoules containing 0.5  mL, 1 mL or 5 mL of a 1 M nitric acid solution and subsequently flame-sealed. 
		The isotope ratios of the IRMM-3000-series were calculated based on the weighings of the two starting materials enriched in 235U and 238U and the measured impurities for both of them. The uncertainties contributing to the final uncertainties of the isotopic ratios are originating from the weighing uncertainties, the uncertainties of the measured isotope ratios and impurities in the two starting materials, and the uncertainties of the stoichiometry of the oxides. 
		The methods for the preparation and certification of the IRMM-3000 series will be described, including verification measurements for the isotope ratios by several methods of mass spectrometry, such as TIMS/MTE, TIMS/DS and MC-ICPMS. As explained in detail in the report, in case of IRMM-3035, the isotope ratios were only certified using mass spectrometry by TIMS/MTE and TIMS/DS at JRC-Geel, with subsequent verification by IAEA and ORNL.
		The isotopic reference materials IRMM-3020 (20% 235U), IRMM-3035 (35% 235U), IRMM-3050 (50% 235U), IRMM-3075 (75% 235U) and IRMM-3090 (90% 235U) are part of a systematic program of JRC-G.2 to supply isotope reference materials to the safeguards community. The materials are intended for the calibration of instruments and methods, quality control purposes. As with any certified reference material, they can also be used for validation studies.
		},
	title = {Preparation and Certification of Highly Enriched Uranium Nitrate Solutions, IRMM-3000 Series},
	url = {},
	doi = {10.2760/141638 (online)}
}