Hiroaki Kasai

Development of SAFA, a seismic analysis program for FBR core components

A computer program, SAFA (seismic analysis program for fuel assemblies) has been developed to analyze core component vibration in fast breeder reactors (FBRs) during seismic excitation. Since an FBR core is composed of as many as 1000 core subassemblies (fuel assemblies, blanket assemblies, neutron shield assemblies, etc.), which are immersed in a coolant fluid, seismic analysis of FBR cores must consider the vibrations generated in a system with a large number of degrees of freedom with impacts under fluid-structure interactions. SAFA models subassemblies as finite beam elements. Fluid interaction forces are considered as added mass and time integration is done using mode superposition and the Nigam method. The load pad impact is modeled using a gap, a linear spring and a linear damper. The program also uses a new method to determine the nonlinear impact force, making it unnecessary to use convergence iteration. Comparison with experimental results confirms that the program can closely predict the seismic response of FBR cores.