Analyses of the dynamic behavior of nuclear power reactor components containing fluid

This paper presents the application of a finite element method for the analysis of the dynamic behaviour of nuclear power reactor components containing fluids. If the acoustic assumption is made for the fluid a numerical solution of fluid solid interaction problem is easily obtainable. In the formulation it is assumed that the fluid velocity is negligible and Eulerian coordinate are used, the solid structure is described by a classical Lagrangian Formulation. In the case of incompressible fluid the pressure equations can be eliminated and the structure mass matrix is augmented by an added mass matrix. At the free surface the pressure can be stated as zero and in this case the surface wave is not described. To introduce the wave the vertical displacement of the horizontal free surface is simulated by a solid Lagrangian line and a boundary condition on pressure must be introduced in the fluid Eulerian mesh. Neigleting the inertia non linear terms, the pressure is proportional to the wave height. The same result is achieved using solid boundary element of vertical stiffness. This formulation has been implemented in the finite element program NOVAX specialised for the calculation of the response of axisymmetric structures by the technique of Fourier series decomposition. To check the assumption made a comparison has been made with three test problems. Problems 1 and 2 are the free vibration in the vertical and horizontal direction of a rigid cylindrical tank filled with liquid. Problem 3 is the sloshing mode of a fluid in a partially filled rigid spherical tank. Comparison is made with experiments involving several fluids. Application to a typical fast reactor of the pool type is shown, effect of the free surface boundary condition is discussed. (orig.)