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Molecular dynamics simulations in graphite and carbon materials

Christie, HJ 2014, Molecular dynamics simulations in graphite and carbon materials , PhD thesis, The University of Salford.

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Despite having significant applications in the nuclear industry, there have been virtually no molecular dynamics (MD) simulations of radiation damage in graphite. The difficulties in developing an accurate yet computationally inexpensive description of carbon have limited the number of detailed investigations. Although previous work has reported point defect energies and estimates of threshold displacement energies, very little is known about the cascade behaviour and the evolution of damage at the atomic level. Gaining an understanding of the processes caused by irradiation in graphite is central to extending the life span of the current advanced gas-cooled nuclear reactors in the UK. In addition, this will provide crucial information to aid next-generation nuclear technology such as the high-temperature graphitemoderated reactors, which were recently selected for development in the USA. The Environment Dependent Interaction Potential (EDIP) has been employed along with the Zeigler-Biersack-Littmark potential to model radiation damage in graphite. Statistical sampling of 20 initial directions and over a range of energies has revealed that nuclear graphite behaves in a manner distinct from metals and oxides, with damage primarily in the form of isolated point defects as apposed to connected regions of transient damage. Simulations have given evidence of channelling occurring along the <10¯12> channel which has previously not been observed in graphite simulations. Graphite cascades have exhibited a fractal-like branching structure and binary-collision-type behaviour. Results produced agree with historical defect prediction models. Important quantities such as the range of the primary knock-on atom and the average energy loss per collision have been calculated. Results indicate that graphite cascades are not dependent on the initial cell temperature. EDIP has been further employed to simulate the effects of radiation damage in carbon allotropes. Results reveal how a material’s structure affects the collision cascade and have highlighted the unique radiation response of graphite.

Item Type: Thesis (PhD)
Themes: Energy
Schools: Schools > School of Computing, Science and Engineering > Salford Innovation Research Centre (SIRC)
Funders: Engineering and Physical Sciences Research Council (EPSRC)
Depositing User: HJ Christie
Date Deposited: 09 Apr 2015 10:21
Last Modified: 29 Oct 2015 00:10

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