Decay-Associated Fluorescence for Boron Determination in Uranium-Based Nuclear Fuels

Herein is reported a novel as well as simple, sensitive, and cost-effective method for determination of boron by time-resolved fluorescence spectrometry in uranium-based nuclear fuels. Boron is complexed with fluorescent ligand chromotropic acid, and the complex formed is a measure of boron. Since the steady-state fluorescence spectra of excess ligand and complex are overlapping, the developed method emphasizes the power of time resolution. The signatory fluorescence decay times of ligand and complex are employed to derive their decay-associated spectra (DAS) and, thereby, spectroscopically eliminate the high background of ligand fluorescence. The calibration plot has a wide linear dynamic range of 5-100 ppb with r² better than 0.998. Precision is better than 5% at the 10 ppb level and 4% at the 50 ppb level (n = 9). The detection limit is 1.5 ppb, and recovery of spiked boron (25 ppb) from the uranium samples was better than 94%. The developed method was validated by analyzing U₃O₈-based ILCE Standards and applied to enriched uranium fuel samples. The main advantage of the developed method is a reduction in sample size requirement due to better sensitivity and selectivity. This in turn reduces the load of uranium recovery from analytical waste, especially in the case of enriched uranium samples. Additionally, it eliminates the need of organic solvents/medium.