Practical use of atomic-scale simulations for MYRRHA/XT-ADS evolutionary and innovative nuclear fuels

The driver fuels today considered forMYRRHA, namely enriched UO2 and MOX, can be considered as evolutionary fuels in view of their wide use, but with much lower enrichments, in conventional nuclear power plants. However, the foreseen operating conditions in MYRRHA will go much beyond the validation range of empirical correlations still used in some of parts of fuel performance codes, and will therefore require evolving towards mechanistic models, based on a true description of the physical processes at play. This is particularly true for the fission gas release process which, in view of the high temperatures expected, and the high He production, could be one of the most penalizing phenomena in terms of fuel performance. In this paper, we will discuss the possible practical contribution of atomic-scale computer simulations in order to better understand and model different phenomena at play during the fission gas release process. We will show the progress made at SCK CEN in terms of atomic-scale fuel modelling, by covering both atomic scale diffusion and irradiation effects (enhanced diffusion, trapping, re-solution of intragranular bubbles, . . .). In addition to modelling the driver fuel, the work performed also open the road for studying other compounds such as the IMF targets (MgO, ZrO2, Mo) which suffer from limited data in terms of in-pile behaviour. These studies are conducted in the framework of the fuel R and D programme for Gen-IV and ADS systems at SCK CEN. (author)