Quantum-mechanical study of the electronic properties of UxPuyOz compounds formed during the recovery of spent nuclear fuel

A promising way to recover spent nuclear fuel (SNF) is the method of extracting transuranium compounds from molten salt, which makes it possible to obtain a partial separation between transuranium compounds and lanthanides. This work is devoted to the quantum mechanical study of changes in the structure, energy and electronic properties of the main SNF component, uranium dioxide, upon the removal of oxygen from the system. The influence on the considered properties of the system of the substitution of uranium by plutonium is also studied at a ratio of the number of plutonium atoms to uranium atoms of 1:7 and 1:3. The removal of oxygen leads to a narrowing of the band gap up to the transition to a conductive state at a ratio of uranium to oxygen of 2:3. The band gap narrows and metallization sets in even when uranium is replaced by plutonium. A two-stage UO2 metallization scheme based on lithium reduction and direct (electronic) reduction is proposed.