3 D Seismic analysis of pool type LMFBR vessel and internals

The vessel and the different internal baffles of a pool type LMFBR are thin axisymmetric shells separated by narrow sodium sheets. Unfortunately important internal components like intermediate heat exchangers and primary pumps, are located unsymmetrically and coupled to the shells both mechanically and though the fluid-structure interaction effect due to the sodium of the hot and cold collectors. Generally axisymmetric models are used to performe the seismic analysis of the reactor. The strong 3 D features of the internals makes this axisymmetric modelisation difficult and uncertain. A more exact calculation is therefore necessary to put into evidence the 3 D effects and to adjust the 2 D models. The great complexity of the problem don't allow a complete 3 D finite element computation. Therefore we have chosen a substructure procedure using the TRISTANA computer code. The 3 D structure is divided into axisymmetric substructures characterized by their natural modes and then connected one to another (the variables of the connected problem are the modal components and the connection forces). This paper presents the specific method used to calculate the coupling effects of the natural modes of the different substructures due to the 3 D fluid volumes, and the first results of the seismic analysis of the internals: actually the calculation of the assembled structure is not yet achieved. However some intermediate results are given: natural modes of the substructures, coupling coefficients due to the fluid