Physical and Numerical Methods for the Dynamic Behavior of the Fast Reactor Cores

Abstract

In the frame of the GEN IV Forum and of the ASTRID Project, a program is in progress in the CEA (France) for the development and the validation of numerical tools for the simulation of the dynamic mechanical behavior of the Fast Reactor cores, with both experimental and numerical parts. The cores are constituted of Fuel Assemblies (of FA) and Neutronic Shields (or NS) immersed in the primary coolant (sodium), which circulates inside the Fluid Assemblies. The FA and the NS are slender structures, which may be considered as beams, form a mechanical point of view. The dynamic behavior of this system has to be understood, for design and safety studies. Two main movements have to be considered: global horizontal movements under a seismic excitation, and opening of the core. The dynamic behavior of the core is strongly influenced by contacts between the beams and by the sodium. The contacts between the beams limit the relative displacements. The fluid leads to complex interactions between the structures in the whole core. The paper presents the physical and numerical methods and tools used to describe and simulate the phenomena. A key point is the Fluid Structure Interaction (or FSI): the interactions between the beams and the liquid sodium. The fluid movement is assumed to be described by the equations of a perfect fluid. Simple and efficient homogenization methods may be used to reduce the size of the problem. These methods are integrated in a general computer code, CAST3M developed at the CEA Saclay. This computer code allows to take into account the impacts between the beams. Some applications are presented.

Numerical strategy for dynamic simulation of impacts on SFR fuel pins and experimental validation

“…The accuracy of the calculation methodology has to be approved by analytical and experimental reference. This work differs from the other ones on the dynamic of fuel assemblies (Broc et al, 2014;Moussallam et al, 2011) because the study is focused on the pins bundle without fluid.…”

Implementation and Comparison of Contact Models Within PIRAT for Nuclear Reactivity Control Systems

“…To convert this spectrum into a time history for the LS, a separate code is used. This code (called BASILIQ CAST 3M [22]) takes into account the whole-core system to derive the motion of the LS. The time history produced from this code is shown in Fig.…”