PhD Theses - Simon Middleburgh

Atomistic Scale Simulation of Materials for Future Nuclear Reactors


Atomic scale simulations have been carried out on three systems that are being considered for use in future nuclear energy applications, both fission and fusion based. Uranium dioxide and chromium doped fuel are considered in the early chapters in order to understand the processes important in high burnup nuclear fuel. The oxygen stoichiometry of the uranium dioxide lattice was found to have a large effect on both fission product solution and crystal swelling. Predictions were found to replicate experimental data well. Transport properties of cations via uranium vacancies in hyperstoichiometic UO2+x have been studied for the first time on the atomic scale. Understanding the arrangement of U5+ cations around a migrating species has proved important for identifying low energy migration process. Zirconium diboride and beryllium have also been studied. Zirconium diboride is of interest due to its use as a burnable poison for some advanced fuel types and also because of its ability to resist very high temperatures. The variation in stoichiometry of ZrB2 was found to accommodate excess boron but very little excess zirconium. The accommodation of the boron-10 transmutation products, lithium and helium, are also studied with helium being released from the lattice via a low energy process. Beryllium is of importance as a potential cladding for fission fuel and in fusion reactors. The intrinsic defect behaviour has been discussed for the first time in this thesis while extrinsic species present in beryllium alloys through alloying, manufacturing processes or environmental exposure have also been studied. Again, helium was found to be readily released from the lattice but only as an interstitial species and not as a substitutional defect.

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