Applicability Assessment of Spectroscopic Assay Tool for Monitoring Lanthanide and Uranium Stream in Pyroprocessing

Pyroprocessing for recycling used nuclear fuel has been developed vigorously in Korea as a new potential back-end fuel cycle technology. In order to achieve desirable process efficiency, recovered uranium and TRU should not contain any substances harmful to the usage of re-manufactured actinide metallic fuel. Moreover, from a proliferation point of view, uranium and TRU should be sustained in the facility and fully recovered during the process without any loss or leakage. In an effort to monitor material stream in pyrochemical process, laser spectroscopy has been selected as one of the promising candidates because of its simplicity, non-destructiveness, and continuousness. In this research, UV/Vis absorption and fluorescence spectroscopy are utilized to analyze lanthanide impurities in pyrochemical operation condition (773 K, no H2O or O2). The assay tool deconvolutes measured absorption and fluorescence spectra for the elemental identification and quantitative analysis on lanthanides included in samples. At this moment, the tool successfully works well for four lanthanide inputs (Nd, Pr, Sm, Dy) and has been still in the course of expansion step to other lanthanides and uranium as representative actinide element. Absorption and fluorescence spectra of uranium chlorides in molten LiCl-KCl eutectic at 773 K are measured. Uranium has an extremely large and broad absorption band from the UV region to 700 nm (834 ± 31 M-1cm-1 at 463 nm and 791 ± 23 M-1cm-1 at 550 nm)) for the f-d energy transition and one relatively small peak at the NIR region with a molar absorptivity of 41 ± 3 M-1cm-1. Because of its larger molar absorptivity in the UV/Vis region than those of other lanthanides, a simultaneous monitoring of lanthanide and uranium streams should be carried out at the region over 700 nm. On the other hand, no fluorescence of uranium indicates that the fluorescence spectroscopy can identify lanthanides no matter how much uranium is included. Therefore, the fluorescence spectroscopy can be a more appropriate and feasible candidate for monitoring lanthanide impurities in pyroprocessing.