Theoretical study of actinide oxides

Abstract

The development of nuclear power brings much attention to the actinides, as they are the most important part of nuclear power production. The first generation of nuclear fuel is uranium dioxide (UO2), and it remains the most used fuel, so there are many research works studying UO2, to gain better understanding and hence safe handling. However, the burning of UO2 accumulates considerable amounts of highly-radioactive nuclear wastes, including used U and plutonium (Pu). Reprocessing of spent fuel in the UK over the last few decades has led to the country having the largest civil stockpile of separated Pu (currently stored as plutonium dioxide: PuO2). Minor actinides, include neptunium (Np), americium (Am), and curium (Cm), also accumulate during the reprocessing of spent UO2 fuel. There are two acknowledged ways to deal with these highly-radioactive nuclear wastes, reusing as mixed oxides (MOX) nuclear fuel or deep geological long-term storage. A closed fuel cycle is fulfilled by reusing highly-radioactive actinides from spent fuel, to decrease highly-radioactive wastes. Therefore, actinide MOX are important for the future development of nuclear power. Regarding deep geological disposal of highly-radioactive nuclear wastes, what happens in the stockpile, especially chemical processes, are important for the safe long-term storage; thus, understanding possible chemical reactions on PuO2 surfaces is crucial. In this thesis, uranium and other actinides (Np, Pu, Am, and Cm) MOX have been extensively studied computationally using periodic boundary condition density functional theory, and the influence of other actinides on UO2 has been investigated, mainly focusing on surface properties and water adsorption behaviour. However, for a better discussion of MOX, sufficient knowledge of pure actinide oxides is essential for the comparison, so the study of minor actinide dioxides (NpO2, AmO2, and CmO2) are presented before MOX; bulk and surface properties are simulated. Then, turning to civil stockpiles of separated Pu, the influence of Am, which has been found in the PuO2 stockpiles, and the residual molecule hydrogen chloride (HCl) have been investigated respectively.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Francis Livens (Supervisor) & Nikolas Kaltsoyannis (Supervisor)