A gauge for nondestructive assay of irradiated fuel rods

The light water breeder reactor (LWBR) was developed by the Bettis Atomic Power Laboratory under the technical direction of the Office of Naval Reactors, U.S. Department of Energy. The LWBR operated successfully in the Shippingport Atomic Power Station from 1977 to 1982, producing more than 29,000 equivalent full-power hours. Because of the small breeding gain (1.35%) predicted for this self-sustaining breeder, proof of breeding required accurate nondestructive assay of expended fuel from the LWBR. The fact that breeding has been proven in the LWBR means that this reactor provides a vast alternative energy resource using plentiful thorium fuel. A gauge, called the production irradiated fuel assay gauge (PIFAG), was developed to nondestructively assay whole irradiated fuel rods from the LWBR. The gauge uses the method of active interrogation with /sup 252/Cf source neutrons and delayed neutron counting. A description is given of the PIFAG, its calibration, and its application to the assay of irradiated LWBR fuel rods. A comparison of the PIFAG results with destructive assay results for 17 irradiated LWBR fuel rods show that the two methods are in excellent agreement, differing by 0.069 and 0.162% for the low- and high-energy PIFAG interrogation spectra, respectively