An instrument has been developed which can nondestructively determine the U235 and boron content of highly enriched, unirradiated fuel assemblies in five to fifteen minutes per element. Two nuclear measurement methods are used: counting of the natural radioactivity of U235 and neutron attenuation measurements. For MTR and ETR fuel elements, the instrument appears to be accurate to 0.3% and 4.0% in terms of the respective U235 and boron contents.