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WP4: Project 3
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Radiation Damage Simulations
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Investigators: Professor R. Grimmes
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Nuclear materials are constantly subject to displacement processes that result in the formation of atomic scale defects. These strongly influence transport of fission products through in pile fuels and waste forms although, clearly, there is an enormous flux difference. The aim is to develop the ability to predict the dynamical evolution of fission products in fuel and waste forms subject to displacement damage. We will employ conventional molecular dynamics and a new multi-time scale simulation approach (developed in collaboration with Los Alamos). This will result in underpinning mechanistic principals, parameters and data for reactor safety case models for the release of volatile fission products (in particular gas atoms) from fuel. At the present time there is no reliable mechanistic model that will predict the release of Xe at local burn-up in excess of 55 GWd/t of uranium. This is major obstacle to establishing the safety case for taking fuels to higher burn-up. Equivalent issues are emerging for advanced fuels, for example, the migration of Ag through carbide layers of PBMR reactor fuels. The models will be developed so that they are applicable to these emerging fuels. Long time scale simulations, in particular, are required to develop our understanding of fundamental release/transport processes in waste forms (either reprocessed from fuel or not). For waste, the radiation tolerance behavior is determined not only by the number and nature of the residual defects associated with a cascade event, but also by the evolution of those defects over longer timescales with residual defects both annihilating and aggregating. For the first time, we can now predict, without any prior assumptions about the dynamics, the fate of defects generated under ballistic radiation damage conditions out to timescales approaching those which can be probed experimentally (i.e. order of seconds).
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