Robin W. Grimes

Accommodation of tin in tetragonal ZrO2

Atomic scale computer simulations using density functional theory were used to investigate the behaviour of tin in the tetragonal phase oxide layer on Zr-based alloys. The SnZr× defect was shown to be dominant across most oxygen partial pressures, with SnZr″ charge compensated by VO•• occurring at partial pressures below 10−31u2009atm. Insertion of additional positive charge into the system was shown to significantly increase the critical partial pressure at which SnZr″ is stable. Recently developed low-Sn nuclear fuel cladding alloys have demonstrated an improved corrosion resistance and a delayed transition compared to Sn-containing alloys, such as Zircaloy-4. The interaction between the positive charge and the tin defect is discussed in the context of alloying additions, such as niobium and their influence on corrosion of cladding alloys.

Development of Xe and Kr empirical potentials for CeO2, ThO2, UO2 and PuO2, combining DFT with high temperature MD

The development of embedded atom method (EAM) many-body potentials for actinide oxides and associated mixed oxide (MOX) systems has motivated the development of a complementary parameter set for gas-actinide and gas-oxygen interactions. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO2, ThO2, UO2 and PuO2. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matching to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT trapping energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO2, ThO2, UO2 and PuO2, providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO2 as well as advanced MOX fuels.

Pipe and grain boundary diffusion of He in UO2

Molecular dynamics simulations have been conducted to study the effects of dislocations and grain boundaries on He diffusion in [Formula: see text]. Calculations were carried out for the {1u20090u20090}, {1u20091u20090} and {1u20091u20091} [Formula: see text] edge dislocations, the screw [Formula: see text] dislocation and Σ5, Σ13, Σ19 and Σ25 tilt grain boundaries. He diffusivity as a function of distance from the dislocation core and grain boundaries was investigated for the temperature range 2300-3000 K. An enhancement in diffusivity was predicted within 20 Å of the dislocations or grain boundaries. Further investigation showed that He diffusion in the edge dislocations follows anisotropic behaviour along the dislocation core, suggesting that pipe diffusion occurs. An Arrhenius plot of He diffusivity against the inverse of temperature was also presented and the activation energy calculated for each structure, as a function of distance from the dislocation or grain boundary.

Defect processes in Be12X (X = Ti, Mo, V, W)

The stability of intrinsic point defects in Be

Cation ordering and oxygen transport behaviour in Sr1−3x/2LaxTiO3 perovskites

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A computational study on the superionic behaviour of ThO2

X intermetallics (where X = Ti, V, Mo or W) are predicted using density functional theory simulations and discussed with respect to fusion energy applications. Schottky disorder is found to be the lowest energy complete disorder process, closely matched by Be Frenkel disorder in the cases of Be

Development of an iridium dissolution method for the evaluation of potential radiological device materials

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Thermophysical properties and oxygen transport in (Thx,Pu1-x)O2

V and Be

Resolving the structure of TiBe12

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High temperature measurements and condensed matter analysis of the thermo-physical properties of ThO2

Ti. Antitisite and X Frenkel disorder are of significantly higher energy. Small clusters of point defects including Be divacancies, Be di-interstitials and accommodation of the X species on two Be sites were considered. Some di-interstitial, divacancy and X