THE USE OF SELF-INDUCED XRF TO QUANTIFY THE PU CONTENT IN MOX SPENT NUCLEAR FUEL

A number of nondestructive analysis (NDA) techniques are being evaluated and developed to characterize spent nuclear fuel (SNF), its burnup, and fissile material content and detect of material diversion. Oak Ridge National Laboratory and Texas A&M University are jointly investigating measurements of self-induced x-ray fluorescence (XRF) of uranium and plutonium for quantification of fissile content in SNF. Because of the radioactive nature of SNF, decay energy is being deposited in the rod material at a relatively constant rate. That decay energy leads to self-induced XRF of the uranium and plutonium atoms in the fuel. These resulting x-rays are then emitted by the fuel rod and can be measured in an appropriately designed and implemented instrument. A previous study demonstrated measurability of the plutonium x-rays for pressurized water reactor spent fuel with burnups ranging from 35 to 70 GWd/MTU and the potential application of this technique as a quantitative assay tool. This paper describes measurements and analyses that were performed on spent mixed oxide lead test assembly rods irradiated at the Catawba Nuclear Power Plant. These rods received burnup up to 45 GWd/MT. Fuel rods were measured using two high-purity germanium detectors (coaxial and planar) for characterization of fission product ratios and x-rays induced in uranium and plutonium. Results of data analyses were compared to burnup code simulations. In the future, there are plans to perform destructive analysis on measured sections of fuel to determine the accuracy of the NDA measurements.