Uranium Isotope Fractionation Resulting from UF sub 6 Vapor Distillation from Containers

摘要

This empirical study for possible isotopic fractionation due to UF sub 6 vapor distillation from valved containers was performed to determine the effects of repeated vapor sampling. Four different experiments were performed, each of which varied by the method of measuring the isotopic contents and/or by the difference in temperature gradients as follows: The ratio of the parent UF sub 6 to the desublimed UF sub 6 collected at liquid nitrogen temperature and homogenized was measured by sampling the containers. The ratio of the parent UF sub 6 to the desublimed UF sub 6 collected at liquid nitrogen temperature and homogenized was measured by direct comparison to each other without subsampling. The ratio of the parent UF sub 6 to the desublimed UF sub 6 collected at liquid nitrogen and ice-water temperatures and homogenized was measured by indirect comparison to a common UF sub 6 reference material without subsampling. The ratio of the parent UF sub 6 to the desublimed UF sub 6 collected at liquid nitrogen temperature without homogenizing was measured by indirect comparison to a common UF sub 6 reference. Gas-phase, relative mass spectrometry was used for all isotopic measurements. Results of the study indicate that fractionation does occur. The U-235 isotope becomes more enriched in the parent container as the UF sub 6 is vaporized from it and desublimed into the receiving cylinder; i.e., the vaporized fraction is enriched in the U-238 isotope. The degree of fractionation indicates that the separation is due to the U-238 isotope of UF sub 6 having a higher vapor pressure than the U-235 isotope of UF sub 6 . 3 refs., 4 figs., 4 tabs. (ERA citation 10:043809)