Large grain Y-Ba-Cu-O (YBCO) superconductors doped with various amounts of depleted uranium oxide have been fabricated by top seeded melt growth (TSMG). The effect of depleted UO2 on the large grain microstructure has been studied systematically in samples with and without added Pt. Addition of uranium oxide results in the formation of U-phase particles of dimensions of a few hundred nanometers with an approximately spherical morphology in the superconducting YBa2Cu3O7-δ(Y-123) phase matrix. Addition of Y2O3 to the uranium doped precursor powder, rather than Y-211, yields a significantly finer distribution of second phase particles. The chemical composition of the U-phase particles, found in samples with no Pt addition, has been identified as Y2Ba4CuUOy, which exhibits paramagnetic behaviour. It has been confirmed experimentally that this phase forms during the peritectic solidification process. Magnetic measurements show that U-doped melt processed YBCO exhibits improved critical current densities and Large grain Y-Ba-Cu-O (YBCO) superconductors doped with various amounts of depleted uranium oxide have been fabricated by top seeded melt growth (TSMG). The effect of depleted UO2 on the large grain microstructure has been studied systematically in samples with Addition of uranium oxide results in the formation of U-phase particles of dimensions of a few hundred nanometers with an approximate spherical morphology in the superconducting YBa2Cu3O7-δ (Y-123) phase matrix. Addition of Y2O3 to the uranium The chemical composition of the U-phase particles, found in samples with no Pt addition, has been identified as Y2Ba4CuUOy, which exhibits paramagnetic behavior. It has been confirmed experimentally that this phase forms during the peritectic solidification process. Magnetic measurements show that U-doped melt processed YBCO exhibits improved critical cur rent densities and