Enhanced accuracy in nuclear fuel analysis: a novel standard addition method with LIBS for quantifying La and Nd in unknown Th-U MOX fuel

Impurity elements such as lanthanum (La) and neodymium (Nd) in nuclear fuel can adversely impact its efficiency and operational lifespan, making their accurate quantification essential. This study employed laser-induced breakdown spectroscopy (LIBS) to analyze La and Nd in unknown thorium (Th) uranium (U) mixed oxide (Th-U MOX) fuel materials. A novel difference method (DM) was integrated with the standard addition method (SAM) and compared with the conventional extrapolation method (EM). Following a rigorous comparison, three analytical lines for each element were selected: 442.99 nm, 465.55 nm and 545.51 nm for La, and 430.35 nm, 445.15 nm and 529.31 nm for Nd. At 465.55 nm, the SAM-DM approach predicted a La concentration of 530 ppm with a relative error of the mean (REM) of 5.2%, markedly lower than the EM result of 600 ppm (REM = 24.9%). For Nd at 529.31 nm, SAM-DM yielded 475 ppm with 4.5% REM, compared to 550 ppm and 10.6% REM by EM. These results confirm the superior accuracy of SAM-DM over EM, particularly at the selected analytical lines. The two lines were subsequently used to construct optimized calibration curves, yielding limits of detection (LODs) of 155.22 ppm for La and 355.97 ppm for Nd. Furthermore, leave-one-out cross-validation (LOO-CV) confirmed the robustness of the proposed strategy, with prediction errors generally below 9% except in low concentration cases. Overall, this work establishes a reliable analytical framework for nuclear fuel impurity quantification by pioneering the combination of SAM-DM with LIBS for Th-U MOX analysis, demonstrating strong potential for quality control and safeguards applications.