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- Claisse, Antoine, 1988-
(författare)
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Multiscale modeling of nitride fuels
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nitride fuels have always been considered a good candidate for GENIV reactors, as well as space reactors, due to their high fissile density, highthermal conductivity and high melting point. In these concepts, not beingcompatible with water is not a significant problem. However, in recent years,nitride fuels started to raise an interest for application in thermal reactors,as accident tolerant or high performance fuels. However, oxide fuels havebenefited from decades of intensive research, and thousands of reactor-years.As such, a large effort has to be made on qualifying the fuel and developingtools to help assess their performances.In this thesis, the modeling side of this task is chosen. The effort istwo-fold: determining fundamental properties using atomistic models andputting together all the properties to predict the performances under irradi-ation using a fuel performance code. The first part is done combining manyframeworks. The density functional theory is the basis to compute the elec-tronic structure of the materials, to which a Hubbard correction is added tohandle the strong correlation effects. Negative side effects of the Hubbardcorrection are tackled using the so-called occupation matrix control method.This combined framework is first tested, and then used to find electronic andmechanic properties of the bulk material as well as the thermomechanicalbehavior of foreign atoms. Then, another method, the self-consistent meanfield (SCMF) one, is used to reach the dynamics properties of these foreignatoms. In the SCMF theory, the data that were obtained performing the abinitio simulations are treated to provide diffusion and kinetic flux couplingproperties.In the second step of the work, the fuel performance code TRANSURA-NUS is used to model complete fuel pins. An athermal fission gas releasemodel based on the open porosity is developed and tested on oxide fuels.A model for nitride fuels is introduced, and some correlations are bench-marked. Major issues remaining are pointed out and recommendations asto how to solve them are made.
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| 2. |
- Claisse, Antoine, 1988-
(författare)
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Open porosity fission gas release model applied to nuclear fuels
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nitride fuels have gained a new interest in the last few years as both a candidate for GEN IV reactors and as accident tolerant fuels for current light water reactors. They however are decades behind oxide fuels when it comes to qualication and development of tools to assess their performances. In this thesis, such a tool is developed. The fuel performance codeTRANSURANUS, which has very good results with oxide fuels, is extended to handle nitride fuels. The relevant thermo-mechanical properties are implemented and fuel type dependent modules are updated. Their limitations and discrepancies are discussed. A particular attention is brought to the athermal ssion gas release, and a new model based on the open fabrication porosity is developed and added to the code, as a starting point toward a mechanistic model. It works well on oxide fuels, but its eciency is harder to evaluate for nitride fuels, due to large uncertainties on many key correlations such as the thermal conductivity and the eective diusion coecient of gas atoms. Recommendations are made to solve the most important problems.
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