[en] Measurements have been undertaken at the Bettis Atomic Power Laboratory to determine the potential of the delayed neutron assay method for precision end-of-life fuel rod assay. A pre-pilot system has been built using a ²⁵²Cf spontaneous fission neutron source to provide two different interrogating neutron spectra for assay of unirradiated ²³³UO₂--ThO₂ fuel rods. A thermal neutron interrogating spectrum produced the largest number of delayed neutron counts per single rod assay. Neutron self-shielding in the fuel can be taken into account using a flux dip technique. An epithermal system using an indium cadmium liner exhibited a linear system response as a function of fuel rod loading