Core mechanical dynamics in the phenix reactor
Résumé
ASTRID is a project for an industrial prototype of a 600 MWesodium cooled Fast Reacrtor, in which CEA is involved, in the frameof the GEN IV Forum. An important program is in progress for thedevelopment and the validation of numerical tools for the simulationof the dynamic mechanical behavior of the Fast Reactor cores, withboth experimental and numerical parts. The cores are constituted ofFuel Assemblies (of FA) and Neutronic Shields (or NS) immersed inthe primary coolant (sodium), which circulates inside the FluidAssemblies. The FA and the NS are slender structures, which may beconsidered as beams, form a mechanical point of view.The dynamic behavior of this system has to be understood, for designand safety studies. Two main movements have to be consideredglobal horizontal movements under a seismic excitation, and openingof the core. The fluid leads to complex interactions between thestructures in the whole core. The dynamic behavior of the core isstrongly influenced by contacts between the beams and by thesodium, which limit the relative displacements. Numerical methodsand models are built to describe and simulate this dynamic behavior.The validation of the numerical tools is based on the results ofdifferent experimental programs, already performed or in progress.The paper presents the interpretation of tests performed in 2013 in thePhenix reactor. The French Phenix reactor was definitively shutdownin 2009 and is now under decommissioning preparatory phase.Before unloading the core, it has been decided to perform one lastexperimental campaign with an opening of the core.The interpretation of the tests highly contributes to the validation ofthe simulation methods. Relatively good comparisons have beenobtained between the theoretical and experimental results, for thestatic excitation (stiffness of the bundle) and for the dynamic release(characteristic times). The tests confirm that the fluid leads to animportant decrease of the frequencies. Uncertainties remains on theimportant damping which seems to be present, and may be due to thefluid or to the structures