Atomic Scale Simulation of Irradiated Nuclear Fuel

Dr. Cooper’s Google Scholar Profile

Support for the potential model developed during the project

Abstract

Atomic scale simulations have been performed investigating various phenomena governing nuclear fuel performance during reactor operation and during post irradiation storage or disposal.

Following a review of some of the key features of irradiated nuclear fuel, such as fission product distribution, two key factors were identified as the focus for this investigation: i) the role of uranium dioxide non-stoichiometry and ii) the effect of temperature. The former has been carried out using a previous pair potential model, whilst a new many-body potential was developed to enable temperature effects to be studied over the full range of temperatures of interest.

Secondary oxide precipitates are known to exist in irradiated nuclear fuel with Ba, Sr and Zr precipitating to form the perovskite (Ba,Sr)ZrO₃ grey phase. The binary BaO, SrO and ZrO₂ may also be formed. The precipitation enthalpies of these oxides were predicted as a function of hyper-stoichiometry. Additionally, CrUO₄ can also precipitate from Cr-doped UO_2+x. The possibility of fission product segregation to the phases from UO₂ or UO_2+x was also investigated with a broad range of species preferring segregation from stoichiometric UO₂.

The role of defect cluster configuration on vacancy mediated uranium migration was investigated for UO₂ and UO_2+x. In both cases the lowest enthalpy migration pathway involved reconfiguration of the cluster to a metastable configuration. Furthermore, there were a very large number of alternative pathways that had similar migration enthalpies, especially for UO_2+x.

A new potential model was developed that uses a novel approach to include many-body interactions in the description of the actinide oxide series. This represents a significant improvement on previous models in the ability to describe the thermal expansion, specific heat capacity and elastic properties of CeO₂, ThO₂, UO₂, NpO₂, PuO₂, AmO₂ and CmO₂ from 300 to 3000 K.

Using the new model the thermal expansion, specific heat capacity, oxygen diffusivity and thermal conductivity of the mixed oxides (U_xTh_1-x)O₂ and (U_xPu_1-x)O₂ were predicted. Enhanced oxygen diffusion and a degradation in thermal conductivity were predicted in terms of the non-uniform cation sublattice.

Full Text

• Atomic Scale Simulation of Irradiated Nuclear Fuel (PDF)
• Available at Imperial’s Spiral Digital Document Repository

Journal Articles Resulting from this Thesis

• M.W.D.Cooper, S.T. Murphy, M.J.D. Rushton and R.W. Grimes, “Thermophysical properties and oxygen transport in the (U_x,Pu_1-x)O₂ lattice”, Journal of Nuclear Materials, 461 (2015) 206–214. http://dx.doi.org/10.1016/j.jnucmat.2015.03.024
• M.J. Qin, M.W.D. Cooper, E.Y. Kuo, M.J.D. Rushton, R.W. Grimes, G.R. Lumpkin and S.C. Middleburgh, “Thermal conductivity and energetic recoils in UO₂ using a many-body potential model”, Journal of Physics: Condensed Matter 26 (2014) 495401. doi:10.1088/0953–8984/26/49/495401
• S.T. Murphy, M.W.D. Cooper and R.W. Grimes, “Point defects and non-stoichiometry in thoria”, Solid State Ionics 267 (2014) 80–87. doi:10.1016/j.ssi.2014.09.017
• M.W.D. Cooper, S.T. Murphy, P.C.M Fossati, M.J.D. Rushton and R.W. Grimes, “Thermophysical and anion diffusion properties of (U_x,Th_1-x)O₂”, Proceedings of the Royal Society A 470 (2014) 20140427. doi:10.1098/rspa.2014.0427
• M.W.D. Cooper, S.C. Middleburgh and R.W. Grimes, “Vacancy mediated cation migration in uranium dioxide: The influence of cluster configuration”, Solid State Ionics 266 (2014) 68–72. doi:10.1016/j.ssi.2014.08.010
• M.W.D. Cooper, S.C. Middleburgh and R.W. Grimes, “Swelling due to the partition of soluble fission products between the grey phase and uranium dioxide”, Progress in Nuclear Energy 72 (2014) 33–37. doi:10.1016/j.pnucene.2013.09.006
• M.W.D. Cooper, M.J.D. Rushton and R.W. Grimes, “A many-body potential approach to modelling the thermomechanical properties of actinide oxides” Journal of Physics: Condensed Matter, 26 (2014) 105401. doi:10.1088/0953–8984/26/10/105401
• M.W.D. Cooper, D.J. Gregg, Y. Zhang, G.J. Thorogood, G.R. Lumpkin, R.W. Grimes, S.C. Middleburgh, “Formation of (Cr, Al) UO₄ from doped UO₂ and its influence on partition of soluble fission products”, Journal of Nuclear Materials, 443 (2013) 236. doi:10.1016/j.jnucmat.2013.07.038
• M.W.D. Cooper, S.C. Middleburgh and R.W. Grimes, “Partition of soluble fission products between the grey phase, ZrO₂ and uranium dioxide”, Journal of Nuclear Materials, 438 238–245 (2013). doi:10.1016/j.jnucmat.2013.02.082