Atomistic Simulation Group (Posts about Robin)

New Paper - "Fission Gas in Thoria"

N. Kuganathan — Wed, 04 Jan 2017 14:34:37 GMT

Our recent computational work using density functional theory on “Fission gas in thoria” has been accepted and is now available from the Journal of Nuclear Materials.

Navaratnarajah Kuganathan, Partha S. Ghosh, Conor OT. Galvin, Ashok K. Arya, Bijon K. Dutta, Gautam K. Dey, Robin W. Grimes, “Fission gas in thoria”, J. Nucl. Mater., 485 (2017) 47–55. doi:10.1016/j.jnucmat.2016.12.011

This study uses first-principles density functional theory together with a dispersion correction (DFT+D) to calculate the energetics of neutral and charged point defects and defect cluster geometries in ThO₂. It also investigates their interaction with Xe and Kr. ThO₂ has been identified as a possible alternative nuclear fuel, partly because spent ThO₂ fuels give rise to considerably smaller inventories of minor actinides, especially Pu. Furthermore, ThO₂ is a highly stable oxide, and exhibits higher thermal conductivity, higher melting temperature, higher corrosion resistance and lower thermal expansion compared to UO₂. At high fuel temperatures, fission gas atoms migrate and are accommodated at point defect sites in the fuel matrix. Over time some of these aggregate into bubbles. Formation of bubbles is important as it leads to swelling and degrades mechanical properties of the material. In order to understand fuel performance, it is necessary to understand the interaction of gas atoms with point defects.

New Paper - "Thermophysical properties and oxygen transport in (Thx,Pu1−x)O2"

C.O.T. Galvin — Mon, 31 Oct 2016 12:23:49 GMT

Our latest paper exploring properties and oxygen transport in the superionic region of (Th_x,Pu_1−x)O₂ is now available:

C.O.T.Galvin, M.W.D. Cooper, M.J.D. Rushton and R.W.Grimes, “Thermophysical properties and oxygen transport in (Th_x,Pu_1−x)O₂”, Scientific Reports 6 (2016) 36024. doi:10.1038/srep36024 Open Access PDF

Using Molecular Dynamics, this paper investigates the thermophysical properties and oxygen transport in (Th_x,Pu_1−x)O₂ (0<x<1) between 300–3500K. In particular, the superionic transition is investigated and viewed via the thermal dependence of lattice parameter, linear thermal expansion coefficient, enthalpy and specific heat at constant pressure. Oxygen diffusivity and activation enthalpy are also investigated.

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New Paper and CRG Potential Update - Addition of Xe and Kr parameters for use with the actinide potential model

M.W.D. Cooper — Mon, 31 Oct 2016 11:52:29 GMT

Potential parameters have been derived for Xe and Kr in CeO₂, ThO₂, UO₂ and PuO₂.

The CRG model for actinide oxides has been effective at reproducing a wide range of properties for actinide oxides and CeO₂. Many problems relating to fuel performance revolve around the behaviour of the fission gases Xe and Kr in nuclear fuel. We have, thus, used a new approach, which combines DFT with MD at 300K, 1500K, 3000K and 5000K, to develop interactions for Xe and Kr in CeO₂, ThO₂, UO₂, PuO₂, and mixed oxides.

The fission-product model is described in our new paper:

M.W.D. Cooper, N. Kuganathan, P.A. Burr, M.J.D. Rushton, R.W. Grimes, C.R. Stanek and D.A. Andersson, “Development of Xe and Kr empirical potentials for CeO₂, ThO₂, UO₂ and PuO₂, combining DFT with high temperature MD”, Journal of Physics: Condensed Matter, 28 (2016) 405401. doi:10.1088/0953–8984/28/40/405401

The website has been updated to include the new parameter set. Additionally, the support files for LAMMPS have also been updated.

New Paper - "Simulations of Threshold Displacement in Beryllium"

M.L. Jackson — Fri, 01 Jul 2016 15:18:21 GMT

Our new paper on the radiation damage of beryllium is now available:

M.L. Jackson, P.C.M. Fossati and R.W. Grimes, “Simulations of threshold displacement in beryllium”, Journal of Applied Physics, 120 (2016) 045903 doi:10.1063/1.4958974.

Atomic scale molecular dynamics simulations of radiation damage have been performed on beryllium to calculate the threshold displacement energy. A geodesic projection of displacement directions was used to investigate the orientation dependence of the threshold displacement energy with respect to crystallographic direction with unprecedented spatial resolution. It was found that the directionally averaged probability of displacement increases from 0 at 35 eV, with the energy at which there is a 50 % chance of a displacement occurring is 70 eV and asymptotically approaching 1 for higher energies. This is however strongly directionally dependent with a 50% probability of displacement varying from 35 – 120 eV, with low energy directions corresponding to nearest neighbour directions. A new kinetic energy dependent expression for the average maximum displacement of an atom as a function of energy is derived which closely matches the simulated data.

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New Paper - "Resolving the structure of TiBe₁₂"

M.L. Jackson — Fri, 01 Apr 2016 15:06:51 GMT

We are pleased to announce the publication of our new paper looking titanium beryllide a promising material for application in nuclear fusion applications:

M.L. Jackson, P.A. Burr and R.W. Grimes, “Resolving the structure of TiBe₁₂”, Acta Crystallographica Section B, 72 (2016) 277. doi:10.1107/S205252061600322X.

A new family of intermetallics, Be₁₂X (X = Ti,V,W,Mo) have been proposed to replace Be in nuclear fusion applications due to improved radiation tolerance and operating temperatures, the most promising of which is Be₁₂Ti. In order to further investigate this material, we have first clarified the structure. There has previously been considerable controversy regarding the structure of TiBe₁₂, which is variously reported as hexagonal and tetragonal. Lattice dynamics simulations based on density functional theory show the tetragonal phase space group I4/mmm to be more stable over all temperatures, while the hexagonal phase exhibits an imaginary phonon mode, which, if followed, would lead to the cell adopting the tetragonal structure. We then report the ground state elastic constants and temperature dependence of the bulk modulus and thermal expansion for the tetragonal phase.

New Paper - "Effects of Gallium Doping in Garnet-Type Li₇La₃Zr₂O₁₂ Solid Electrolytes"

M.J.D. Rushton — Mon, 20 Apr 2015 14:15:39 GMT

The accepted manuscript of our new paper on gallium doping in LLZrO battery materials is now available online:

R. Jalem, M.J.D. Rushton, W. Manalastas Jr, M. Nakayama, T. Kasuga, J.A. Kilner, and Robin W. Grimes, "Effects of Gallium Doping in Garnet-Type Li₇La₃Zr2O₁₂ Solid Electrolytes ", Chemistry of Materials (2015). doi:10.1021/cm5045122

![Percolation Pathways in LLZrO][image]

The paper is the result of an ongoing collaboration between the group and Dr. Randy Jalem. Randy originally spent several months with us at Imperial whilst visiting us as a PhD student from Nagoya Institute of Technology (Japan) and we would like to thank him and the other authors for all their hard work in bringing this to completion.

Research highlights:

LLZrO is a candidate for use as solid electrolytes in battery applications.
The effects of Ga doping on the structure are considered.
Ga is found to stabilise the cubic phase.
The connectivity of Li percolation networks in LLZrO are visualised.

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Preprint of New Paper Now available: "From solid solution to cluster formation of Fe and Cr in α-Zr"

M.J.D. Rushton — Wed, 04 Feb 2015 10:12:17 GMT

![](2Cr3t.png)

Our latest paper on alloying additions in Zr is now available as a pre-print on arXiv:

P.A. Burr, M.R. Wenman, B. Gault, M.P. Moody, M.Ivermark, M.J.D. Rushton, M. Preuss, L. Edwards and R.W. Grimes, “From solid solution to cluster formation of Fe and Cr in α-Zr”, arXiv preprint (2015). PDF

By combining ab-initio simulations with advanced experimental techniques we investigate the microstructural change of Zr alloys under irradiation Zr alloys are used as nuclear fuel cladding, and their integrity is crucial for the safe production of nuclear power. Of particular concern is the increase in corrosion that is observed when Fe and Cr particles (alloys additions) are dissolved. Dissolution of these particles is related to neutron irradiation, but the mechanisms by which this occurs is still unknown.

New Paper - "Prediction and Characterisation of Radiation Damage in Fluorapatite"

M.J.D. Rushton — Sat, 22 Nov 2014 14:12:39 GMT

![](phosphates.png "Phosphate polyhedra weaving their way through calcium metaprisms following radiation damage in fluorapatite")

Our latest paper is now available from the Journal of Materials Chemistry A site:

E.E. Jay, P.M. Fossati, M.J.D. Rushton and R.W. Grimes, “Prediction and Characterisation of Radiation Damage in Fluorapatite”, Journal of Materials Chemistry A, (2014) doi:10.1039/C4TA01707B

In this paper we performed threshold displacement energy calculations and full damage cascades for the fluorapatite structure using molecular dynamics in conjunction with effective pair potentials. Fluorapatite is being considered as a host for the long term immobilisation of halide bearing nuclear wastes. As a result it is important to understand how the apatite structure withstands and recovers from radiation damage. Of particular interest were the structural changes noted in our damaged structures: phosphate polyhedra were found to form polymer chains, typical of phosphate glasses, that were interwoven with the calcium metaprisms forming the backbone of the apatite structure. The coincidence of these amorphous and crystalline features should help in our further understanding of the long term durability of this material.

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New Paper - "Genetics of superionic conductivity in lithium lanthanum titanates"

M.J.D. Rushton — Sat, 22 Nov 2014 11:40:34 GMT

We are pleased to announce the publication of our new paper on lithium diffusion within lithium lanthanum titanate:

E.E. Jay, M.J.D Rushton, A. Chroneos, R.W. Grimes and J.A. Kilner, “Genetics of superionic conductivity in lithium lanthanum titanates”, Physical Chemistry Chemical Physics, (2014). doi:10.1039/C4CP04834B

Lithium lanthanum titanate (LLTO) is a material that shows high lithium diffusivity even at room temperature, this makes it of considerable interest for battery applications. In the present paper we set out to try and understand how the arrangement of lanthanum atoms within this material leads to LLTO’s beneficial properties. This was achieved by using a genetic algorithm to search for configurations with particularly high diffusivities. These were then examined to see what could be gleaned from their structure in order to unlock the key to LLTO’s beneficial properties. The paper can be found here.

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New Paper - "Thermal conductivity and energetic recoils in UO₂ using a many-body potential model"

M.W.D. Cooper — Tue, 18 Nov 2014 11:22:02 GMT

We are please to announce a new publication in collaboration with ANSTO on the effect of radiation damage on the thermal conductivity of UO₂ using our recently developed many-body actinide oxide potential.

A comparison of the damage profile predicted by the many-body potential is made against previous potential models. A significant degradation in thermal conductivity is then predicted as a consequence. The conductivity of amorphous UO₂ is also calculated.

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

Atomistic Simulation Group (Posts about Robin)

New Paper - "Fission Gas in Thoria"

New Paper - "Thermophysical properties and oxygen transport in (Thx,Pu1−x)O2"

New Paper and CRG Potential Update - Addition of Xe and Kr parameters for use with the actinide potential model

New Paper - "Simulations of Threshold Displacement in Beryllium"

New Paper - "Resolving the structure of TiBe12"

New Paper - "Effects of Gallium Doping in Garnet-Type Li₇La₃Zr₂O₁₂ Solid Electrolytes"

Preprint of New Paper Now available: "From solid solution to cluster formation of Fe and Cr in α-Zr"

New Paper - "Prediction and Characterisation of Radiation Damage in Fluorapatite"

New Paper - "Genetics of superionic conductivity in lithium lanthanum titanates"

New Paper - "Thermal conductivity and energetic recoils in UO₂ using a many-body potential model"

New Paper - "Resolving the structure of TiBe₁₂"