Preparation and structure of uranium-incorporated Gd2Zr2O7 compounds and their thermodynamic stabilities under oxidizing and reducing conditions.

Gd2Zr2O7 is being contemplated as a futuristic matrix for the incorporation of high-level radioactive nuclear waste. This compound has the unique ability to incorporate several fission products and heavy metal ions like uranium and thorium into its lattice sites without undergoing structural changes. X-ray diffraction analyses of Gd2-xUxZr2O7+δ samples indicate that the parent compound can incorporate a substantial amount of uranium, both under oxidizing and reducing conditions. The oxidation state of these samples was investigated by X-ray photoelectron spectroscopy. The thermodynamic stability of uranium-substituted Gd2Zr2O7 is an important parameter that will govern the long-term storage of uranium and minor actinides in this matrix. High-temperature calorimetry has been used to investigate the stability of the Gd2-xUxZr2O7+δ (0.00 ≤ x ≤ 0.15) compositions. The standard molar free energy of the formation of Gd2-xUxZr2O7+δ (0.00 ≤ x ≤ 0.15) compositions has been estimated. From the free energy of formation data, the sample corresponding to x = 0.15 was found to be most stable in the Gd2-xUxZr2O7+δ (0.00 ≤ x ≤ 0.15) series. The relative stabilities of U(4+) and U(6+) substituted gadolinium zirconate have been discussed on the basis of the charge on the uranium ion and the incorporation of corresponding extra oxygen atoms into the lattice for charge compensation.

Development of a Simple Electroless Method for Depositing Metallic Pt-Pd Nanoparticles over Wire Gauge Support for Removal of Hydrogen in a Nuclear Reactor.

Electroless noble metal deposition on the conducting substrate is widely used to obtain the desired film or coating on the substrate of interest. Wire-gauge-based Pt/Pd/Pt-Pd (individually, sequentially, and simultaneously deposited) catalysts have been developed using formaldehyde and sodium formate as reducing agents. Various surface pretreatment methods like SnCl2 + PdCl2 seeding, oxalic acid etching, and HCl activation (etching) have been employed to obtain the desired noble metal coating. Minimum time duration was observed for simultaneously deposited catalysts using formaldehyde as a reducing agent. Prepared catalysts were characterized for noble metal deposition, coating kinetics, surface morphology, and binding energy. The catalyst was found to be active for H2 and O2 recombination reactions for hydrogen mitigation applications in nuclear reactors.