To non-destructively determine the burnup of a spent nuclear fuel assembly, it is essential to analyze the nuclear isotopes present in the assembly and detect the neutrons and gamma rays emitted from these isotopes. Specifically, gamma-ray measurement methods can utilize a single radiation measurement value of 137Cs or measure based on the energy peak ratio of Cs isotopes such as 134Cs/137Cs and 154Eu/137Cs. In this study, we validated the extent to which the results of gamma-ray measurements using cadmium zinc telluride (CZT) sensors based on 137Cs could be accurately simulated by implementing identical conditions on MCNP. To simulate measurement scenarios using a lead collimator, we propose equations that represent radiation behavior that reaches the detector by assuming “Direct hit” and “Penetration with attenuation” situations. The results obtained from MCNP confirmed an increase in measurement efficiency by 0.47 times when using the CZT detector, demonstrating the efficacy of the measurement system.

The burnup of spent fuel is one of the important management items that must be managed before storing the fuel in dry storage facilities, as well as for transportation and disposal in the future. Currently, the burnup of spent fuel is managed by calculating the design burnup at the time of design and measuring the real burnup using in-reactor measurement devices. Furthermore, to ensure the reliability of such data, the burnup of spent fuel can be measured using burnup measurement equipment to compare and analyze the data. In fact, KHNP is measuring the burnup of spent fuel using the burnup measurement equipment (SICOM-NG-FA) developed by ENUSA in Spain. The burnup measurement equipment analyzes the axial burnup profile of spent fuel using gamma and neutron detectors. Burnup measurement is performed by moving the spent fuel up and down inside the measurement equipment and measuring the burnup of the fuel surface facing the gamma and neutron detectors. This paper aims to compare the results of measuring the burnup of spent fuel on two sides versus four sides using the burnup measurement equipment.