Isotopic and Chemical Tracing of Uranium Ores Through Processing to Nuclear Fuels

English Abstract:

Oxygen, Sr, Pb and U isotopic and chemical compositions of uranium ore concentrates (UOC) and resulting processed materials are examined where UOC is converted to UO₃ and subsequently to UF₆. There are significant variations in the U, Sr, Pb and O isotopic compositions of UOC samples, although each source tends to a distinct isotopic composition. Digestion of the UOC in nitric acid results in a significant increase in the ²⁰⁷Pb/²⁰⁶Pb ratio from 0.1538 to 0.4015 and a slight decrease in the ⁸⁷Sr/⁸⁶Sr ratio from 0.71314 to 0.71274 as a result of contamination. The resulting UO₃ product has lower Pb contents and much less radiogenic ²⁰⁷Pb/²⁰⁶Pb ratios than the UOC and much higher ²³⁸U/²³⁵U ratios because of loss of ²³⁵U during the boildown and oxygen isotopes are also affected because of the preferential loss of ¹⁶O . The contents of most elements are diminished in the UO₃ product, although B, Pb, Cr and Co levels are similar to those in the original UOC and thus behave “conservatively”. Reduction of the UO₃ to UO₂ does not appreciably affect Pb or U isotopic compositions, but does affaect the oxygen isotopes. Conversion to UF₆ results in a decrease of most element contents, but also a change in the isotopic composition of uranium whereby ²³⁵U is lost.