Speaker
Description
This study will describe how hyperspectral imaging (HSI) can be used as a tool to detect and quantify fission products in uranium dioxide (UO₂) nuclear fuel pellets. The rapid, non-contact capabilities of HSI offer a promising approach for spent nuclear fuel analysis in high-risk hot cell environments. An HSI system is used to analyse sintered UO₂ pellets and SIMFuel pellets (UO₂ doped with non-active fission product surrogates). We hypothesise that fission products alter the spectral response of UO₂ pellets, making these changes detectable through HSI and providing valuable information for nuclear fuel characterisation. Pellets are produced using both traditional and spark plasma sintering methods. In addition to SIMFuel pellets, pellets doped exclusively with lanthanides, grey-phase oxides, or epsilon particles are prepared to isolate the source of observed spectral differences. Imaging is performed with two cameras, covering the visible to near-infrared (VNIR) range of 399 to 1001 nm and the short-wave infrared (SWIR) range of 949 to 2472 nm. Reflectance spectra are then compared, focusing on how different dopant compositions affect the spectral response. Spectra are analysed by normalising data with quadratic detrending, which reduces intraclass variance and highlights differences among pellet sub-groups. Results show that pure UO₂ pellets exhibit consistent spectral features in the SWIR range, with distinct absorbance bands at 1116 nm, 1630 nm, and 2257 nm, and prominent peaks at 1862 nm and 1994 nm, while VNIR spectra contain no distinctive features. In contrast, SIMFuel pellets display a much flatter spectral response, significantly suppressing key absorbance features. Analysis of pellets doped with specific substances indicates that lanthanide-doped pellets similarly exhibit this flatter spectral response, while grey-phase and epsilon-particle-doped pellets retain a spectral response closer to pure UO₂. These findings confirm that fission products impact the SWIR spectral characteristics of UO₂, with lanthanides exerting the most significant effect. We propose an index based on spectral values at 1870 nm and 2257 nm as an empirical metric to differentiate between pellet types, demonstrating that this index shows significant differentiation between pure and doped pellets, supported by statistical analysis. Traditional spectral similarity metrics, including spectral angle mapper (SAM) and spectral information divergence (SID), further indicate that doped pellets are most similar to each other but distinctly different from pure pellets. Additionally, the spatial data from hyperspectral imaging reveal regions of spectral variation, with lanthanide-doped samples exhibiting localised “hot spots” where spectral peaks are more pronounced. These findings suggest hyperspectral imaging as an effective, non-contact technique for nuclear fuel characterisation, particularly in post-irradiation examination. The rapid acquisition time of HSI, combined with its spatial and spectral insights, positions it as a valuable tool for screening hazardous materials in hot cell environments, potentially streamlining the analysis of spent nuclear fuels. Future research will explore the physicochemical mechanisms underlying the spectral changes introduced by fission products, especially lanthanides, with a focus on quantifying lanthanide content using complementary techniques such as Raman spectroscopy and scanning electron microscopy. Additionally, SWIR-HSI imaging of spent reactor fuel samples will be needed to confirm the general applicability of the identified methods. Overall, this study demonstrates the significant potential of hyperspectral imaging for non-invasive nuclear fuel characterisation, offering a method to identify and quantify fission products and ultimately supporting improved post-irradiation examination and spent fuel storage decision-making.
