Transversal mapping of Gd concentration in UO2-Gd2O3 nuclear fuel pellets

DINA TOBIA; ELIN WINKLER; JULIÁN MILANO; ALEJANDRO BUTERA; RODOLFO KEMPF; LAURA BIANCHI; FEDERICO KAUFMANN

Barcelona

Conferencia; 20th International Conference on Magnetism; 2015

One of the major challenges of the nuclear industry is the research and development of new materials in order to extend the fuel lifetime, increase the burn-up and optimize the power density distribution. With this aim Gd is usually incorporated into the UO2 nuclear fuel as a burnable poison, due to its high cross section for neutron absorption. However, the fabrication process of the solid solution (U, Gd)O2 and the amount of Gd incorporated could affect some physical and chemical properties, that can eventually alter the proper and safe performance of this fuel in reactors, as well as the stability in storage and disposal conditions. Within this frame, it is crucial the search of new and more precise analysis techniques that allow a better characterization of Gd content and distribution in the fuel pellets. Due to its high sensitivity, electron paramagnetic resonance spectroscopy (EPR) emerges as an excellent candidate to carry out this goal. In this work we present a method to measure with a very high precision the transversal mapping of the Gd concentration in UO2?Gd2O3 nuclear fuel pellets by EPR.The quantification of Gd3+ ions in the UO2 matrix was made from the direct comparison with a Gd2O3 reference sample. The simple protocol employed allows to determine the relative concentration of Gd in UO2 with an error smaller than 5%. The nominal concentration in the pellets is UO2: 7.5% Gd2O3. However, a concentration gradient was found, which indicates that the Gd2O3 amount diminishes towards the edges of the pellets. The concentration varies from (9.3 ± 0.5)% in the center to (5.8 ± 0.3)% in one of the edges.