An advanced multidimensional method for structural and hydrodynamic analysis of piping systems of liquid-metal fast breeder reactors under various accident loads is described. The method couples a two-dimensional finite difference hydrodynamic technique with a three-dimensional finite element structural dynamics program. In the analysis, an elbow hydrodynamic model has been developed to account for the effect of global elbow motion. Treatment is provided for calculating fluid motion in the vicinity of the isolated flow region, rigid obstacle, and baffle plates, which commonly occurs in the in-line components. Also, an implicit time-integration scheme has been developed for structural analysis under long-duration accident loads. Three sample problems are given, dealing with analyses of (a) multidimensional fluid-structure interaction, (b) hydrodynamics in the in-line components, and (c) seismic response of a pipe-elbow loop.