Preliminary results of a single photon emission computed tomography (SPECT) detector for inspection of spent fuel assembly

SPECT systems are being used by international safeguards organizations for the measurement for structural evaluation of spent fuel assemblies. However, the low sensitivity still limits the verification of spent fuel assemblies within a short measurement time (1–2 h per assembly). In this study, the SPECT detector was optimized and evaluated to identify the structure of spent fuel. The detector module consists of 64 one-dimensional (1-D) multi-slit collimators and 1-D pixelated scintillators coupled to SiPMs. We evaluated and optimized the light collection efficiency and energy resolution according to the shape of scintillator (Trapezoid, Rectangular), and reflector materials (Paint, Teflon tape, BaSO₄) by Geant4 Application for Tomographic Emission (GATE) simulation and experiment. As a result, the trapezoidal scintillator coated with BaSO₄ showed the highest light collection efficiency among the six models in GATE simulation and in experiments. The spent fuel rods were imaged using trapezoidal scintillator coated with BaSO₄, and 1-D projections and line profiles were obtained in order to distinguish the source location. In this study, the scintillator structure and reflector material variables were optimized using Monte Carlo simulation to measure 662 keV gamma-ray of ¹³⁷Cs for inspection of spent fuel assembly using the SPECT system. In order to confirm the imaging potential of the spent fuel assembly, the detector performance was evaluated using unused fuel rods for testing. The performance of the detector for fuel rod identification has been proven, and we expect that the optimized detector module will contribute to the rapid verification of the spent fuel assembly compared to conventional systems.