Simulation study of gamma-ray spectroscopy on MYRRHA spent fuel located in lead–bismuth eutectic

A concept model of a measurement station for gamma-ray spectroscopy for safeguards verification of spent fuel from the future MYRRHA facility has been developed using MCNP6.2. The measurement station consists of a collimator and a lanthanum bromide detector which are placed adjacent to a cylindrical container with the fuel assembly submerged in lead–bismuth eutectic for cooling. The total count rate as well as the peak-area uncertainties for several gamma-ray peaks have been studied for a number of measurement geometries to determine the optimal collimator dimensions and assess how the performance depends on the lead–bismuth container geometry. Finally, the contribution from each fuel pin in the assembly to the detected signal has been determined as a function of gamma-ray energy to determine if the inner parts of the fuel assembly can be assayed with gamma-ray measurements. The results show that the dimensions of the lead–bismuth container will have a considerable effect on both the total count rate and the peak-area uncertainties, but that gamma-ray spectroscopy could be used for verification of spent fuel from MYRRHA