DETERMINATION OF TRACE LANTHANIDE IMPURITIES IN NUCLEAR GRADE URANIUM BY COUPLED-COLUMN LIQUID-CHROMATOGRAPHY

Impurities such as Sm, Gd, Eu, and Dy will degrade the neutron economy of a nuclear reactor when present even at sub-parts-per-million levels, as a result of their high neutron absorption cross sections. Conventional determinations of lanthanide impurities in uranium require 0.5-100 g of uranium. A coupled-column chromatographic procedure has been developed which dramatically reduces the quantity of uranium required. The first column, a semipreparative reversed-phase column, removes the uranium matrix, while the second column, an analytical-scale cation exchange column, concentrates and separates the lanthanides prior to their postcolumn reaction detection with arsenazo III. The maximum loading of uranium onto the reversed-phase column is determined by the volume overload of the lanthanides rather than the concentration overload of the uranium. Using 20 mg of uranium, a detection limit of 0.02 mug/g of U is achieved for Sm, Gd, Eu, and Dy with no interference from transition or alkaline earth metals present in the uranium.