The isotopic composition of commercially available uranium chemical reagents

The uranium isotopic compositions of 12 commercially available uranium chem icals, obtained from various suppliers, were measured by high accuracy isot ope mass spectrometry. The goal was to establish the range of isotopic comp ositions in currently available commercial uranium chemicals, offered in di fferent chemical forms and used for different purposes (e.g., atomic absorp tion spectrometry or inductively coupled plasma mass spectrometry). The relative isotope abundances of U-234, U-235, U-236 and U-238 were deter mined by thermal ionisation mass spectrometry with high abundance sensitivi ty (Finnigan MAT262-RPQ-Plus), using the n(235U)ln(238U) amount ratio measu rements of a gravimetrically prepared Isotopic Reference Material (IRMM-183 ) for mass fractionation correction. All uncertainties were calculated acco rding to the ISO Guide to the Expression of Uncertainty in Measurement (Int ernational Standards Organization, Geneva, Switzerland), using a coverage f actor k = 2. For n(U-235)/n(U-238) relative uncertainties of 0.2-0.3% and f or n(U-234)/n(U-238) and n(U-236)/n(U-238) of 0.4-3.0%, depending on the re lative amounts of the U-234 and U-236 isotopes, were achieved. All samples were found to be depleted in U-235 by a factor of two compared with its natural molar abundance (0.72%). The non-natural isotope 236U was present in all samples analyzed. The range found for the molar abundances o f U-234 is 0.0022-0.00081%, for U-235 0.35-0.21%, for U-236 0.021-0.000011% and for U-238 99.788-99.634%.