Fast elliptic solvers and three-dimensional fluid-structure interactions in a pressurized water reactor

Abstract

A numerical method is described for analysis of the response of internal structures in the vessel of a pressurized water reactor to a sudden depressurization (“blowdown”). The three-dimensional geometry and fluid-structure interactions are taken into account. Potential flow is assumed for a compressible fluid with constant speed of sound which is appropriate for subcooled water. Any linear-elastic dynamic model in terms of a finite number of degrees of freedom can be employed for the internal structure, in particular the core barrel; here the model “CYLDY2” is implemented. An implicit and stable time-differencing scheme is used. Spatially, finite differences or spectral approximations are introduced. The resultant set of linear equations is solved efficiently by means of fast elliptic solvers and the capacitance, or influence, matrix technique. The resultant code, FLUX2, is applied to predict the dynamics in case of the planned HDR experiment. A sensitivity analysis shows that truncation errors can be kept sufficiently small. By comparison of results with and without fluid-structure interactions it is found that the coupling has an essential effect on the resultant maximum stress.