Speaker
Description
Ensuring a safe long-term disposal of radioactive waste is essential for several reasons – environment and public safety, meeting requirements related to nuclear safeguards and non-proliferation, but also to support the continued development of nuclear applications in research, medicine and industry. In Sweden, a large inventory of radioactive waste, so called legacy waste, was produced during early years of nuclear research, including defense-related research and long-lived radionuclides from the industry and healthcare sectors. Before such waste is separated into the relevant categories, it has to be characterised with respect to current waste acceptance criteria. There are special challenges associated with the Swedish legacy waste that require careful non-destructive assay (NDA) of waste drums before they are opened for waste processing. For example, the legacy waste often contains mixed or heterogeneous materials including liquids with significant radiochemical hazards. To address these issues, a novel multi-modality tomographic scanning system has been developed for NDA of legacy waste drums in collaboration with the company charged with managing such waste in Sweden, AB Svafo. This Advanced Radwaste Characterisation (ARC) system integrates three different imaging techniques within a unified scanning platform, featuring a neutron-gamma emission tomography (NGET) detection system coupled with 3D gamma-ray densitometry (CT) and a spectrometric gamma-ray emission tomography (SPECT) system.
The NGET technique was invented at KTH and uses fast organic scintillator detectors to measure correlated fast neutrons and gamma rays emitted in the spontaneous or induced fission of actinide materials. By analyzing these time and energy correlations, the system enables three-dimensional localization of neutron-emitting sources [1-4]. The gamma-ray transmission CT system provides structural and attenuation information, which can be used for attenuation correction and material differentiation. The SPECT subsystem, based on a collimated high-purity germanium (HPGe) detector, maps gamma-emitting radionuclides within the drum and supports isotope identification.
Monte Carlo simulations and experimental measurements have been carried out as part of the ARC system’s testing and commissioning phase to evaluate and optimize its performance. The results from simulated and measured datasets show that the system can accurately localize neutron- and gamma-emitting sources in typical shielded waste matrix geometries. The integrated design enables multi-modal localization of both radioactive and non-radioactive components, providing a comprehensive three-dimensional characterization capability.
This work represents a significant step toward automated NDA of legacy waste drums and demonstrates the potential of combining these techiniques for enhanced localization, identification, and quantification of actinides and other radionuclides. We present the initial measurements and images obtained using the different systems, which are compared with Geant4 simulations of the complete setup.
[1] Jana Petrović, Alf Göök, and Bo Cederwall, Rapid imaging of special nuclear materials for nuclear nonproliferation and terrorism prevention, Sci. Adv. 7, 1 (2021). https://doi.org/10.1126/sciadv.abg3032
[2] B. Cederwall, A novel 3D-imaging and characterisation technique for special nuclear materials in radioactive waste,
EPJ Nuclear Sci. Technol., 9, 8 (2023) https://doi.org/10.1051/epjn/2022037
[3] Jana Vasiljević, Vivian Peters, Anders Puranen & Bo Cederwall,
Sensitive imaging of actinide materials in shielded radioactive waste,
Nature Scientific Reports, 14, 26798 (2024) https://doi.org/10.1038/s41598-024-78027-9
[4] Rafael Escudeiro, Ihor Tavrovskyi, Vivian Peters, Jana Vasiljević, Anders Puranen and Bo Cederwall, Spatial resolution of an organic scintillator-based Neutron-Gamma Emission Tomography system with different detector cell sizes, Nucl. Instrum.Methods Phys.Res. A, 1080, 170788 (2025) https://doi.org/10.1016/j.nima.2025.170788
