Analysis Methods and Performance of an Automated System for Measureing Both Consentration and Enrichment of Uranium in Solutions

For the 1992INNM meeting, we reported on the general characteristics of an automated system—then under development—for measuring both the concentration and enrichment of uranium in solutions.1 That paper emphasized the automated control capability, the measurement sequences, and safety features of the system. In this paper, we report in detail on the measurement methods, the analysis algorithms, and the performance of the delivered system. The uranium concentration is measured by a transmission- corrected x-ray fluorescence method. Cobalt-57 is the fluorescing source and a combined 153Gd and 57Co source is used for the transmission measurements. Corrections are made for both the absorption of the exciting ^7Co gamma rays and the excited uranium x-rays. The 235IJ concentration is measured by a transmission-corrected method, which employs the 185.7-keV gamma ray of 235U and a transmission source of 75Se to make corrections for the self-absorption of the 235U gamma rays in the solution samples. Both measurements employ highresolution gamma-ray spectrometry and use the same 50- ml sample contained in a custom-molded, flat-bottomed, polypropylene bottle. Both measurements are intended for uranium solutions with concentrations >0.1 g U/t, although at higher enrichments the passive measurement will be even more sensitive.