A tomographic method for verification of the integrity of spent nuclear fuel assemblies - II: Experimental investigation

A tomographic method for verification of the integrity of used light water reactor fuel has been experimentally investigated. The method utilizes emit ted gamma rays from fission products in the fuel rods. The radiation field is recorded in a large number of positions relative to the assembly, whereb y the source distribution is reconstructed using a special-purpose reconstr uction code. An 8 X 8 boiling water reactor fuel assembly has been measured at the Swedi sh interim storage (CLAB), using installed gamma-scanning equipment modifie d for the purpose of tomography. The equipment allows the mapping of the ra diation field around a fuel assembly with the aid of a germanium detector f itted with a collimator with a vertical slit. Two gamma-ray energies were r ecorded: 662 keV (Cs-137) and 1274 keV(Eu-154). The intensities measured in 2520 detector positions were used as input for the tomographic reconstruct ion code. The results agreed very well with simulations and significantly r evealed a position containing a water channel in the central part of the as sembly.