Radiological characterization of spent control rod assemblies

Three different spent control rods were obtained for direct-assay measurements and empirical sampling and analysis. They were: 1) a BWR cruciform control rod, 2) a PWR rod-cluster control assembly, and 3) a burnable poison-rod assembly. The dominant activity of the BWR cruciform control rod and the PWR burnable poison-rod assembly is⁶⁰Co, whereas the PWR rod-cluster control assembly is dominated not only by⁶⁰Co, but also by^108mAg and^110mAg, which are found in the Ag–In–Cd alloy of the absorber rods. The radionuclide inventories calculated for the three spent control rods from the empirical sampling data agree very well with data determined from the two direct assay methodologies. The concentration of^108mAg in the rod-cluster control assembly will have to be considered when these types of spent control rods are prepared for waste disposal.