Development of a Method of Neutron Radiography of Mixed Oxide Fuels Using Radiographic Analogs

A high-resolution neutron radiographic system has been developed at the University of Washington Nuclear Reactor to radiograph mixed oxide particle fuels. The method was tested without fuel using TiO₂, Eu₂O₃, and RhO₂ mixtures as analogs for the oxides of U, ²³⁹Pu, and ²⁴⁰Pu, respectively. These analogs have microscopic cross sections similar to the fuel isotopes. Two weight percent PuO₂-UO₂ fuel rod radiographic analogs were built containing PuO₂ analog particle diameter distributions from 0 to 800 μm. These radiographic analogs were radiographed with resonant energy neutrons using the activation transfer neutron detection technique to examine both the homogeneity of the mixed oxide and the imaging of the various diameter PuO₂ analog particles. A divergent neutron collimator was designed to successfully complete this study. Also, an experiment was performed to determine the contrast sensitivity of neutron radiography for the radiographic discrimination between the analog for ²³⁹PuO₂ and the analog for ²⁴⁰PuO₂.