INDUSTRIAL MODEL FOR THE DYNAMIC BEHAVIOR OF LIQUID METAL FAST BREEDER REACTOR (LMFBR) CORE

摘要

Modeling the dynamic behavior of a Liquid Metal Fast Breeder Reactor (LMFBR) core is needed for seismic design purpose and more generally for the study of dynamic solicitations due to internal or external accidents. On LMFBR cores, special attention should be given to reactivity variation under such solicitations. The core of a LMFBR is generally constituted of long fuel assemblies with hexahedral sections immersed in liquid metal with relatively thin fluid layers between assemblies. The dynamic behavior of each fuel assembly taken alone is close to the one of a cantilever beam. Contact points between adjacent assemblies can appear under a dynamic loading, making the problem non linear. Most important of all, the thin fluid layers between assemblies imply a strong inertial coupling of each assemblies with potentially all the others. Despite the interesting capabilities of the finite element codes, such as the introduction of fluid elements coupled to structural ones, and the increasing performances of the computers, the modeling of the LMFBR core can not be addressed directly, while keeping the costs within reasonable bounds. This article first presents a way to simplify the problem and make it manageable by usual commercial computers. Then, the general dynamic behavior of the LMFBR core is described and illustrated. The influence of fluid-structure coupling is underlined.