[en] The subject of this paper are fluid-structure interactions which are characterized by large pressure loadings on shell structures and significant pressure changes in the fluid due to high wall accelerations. Such interactions have to be taken into account in the analysis of blowdown loadings on vessel internals in pressurized water reactors under postulated accident conditions. Several groups have undertaken the development of computer models for analysis of such situations. An important mile-stone are comparisons with the large-scale experiments presently being conducted in the HDR experimental facility. At the Institut fur Reaktorentwicklung the computer code FLUX2 has been developed for analysis of this problem. The code uses a three-dimensional compressible potential flow model. An implicit and stable integration scheme is employed. The large systems of linear equations, which are to be solved at each time step, are solved efficiently by use of the influence matrix technique and fast elliptic solvers. First comparisons between measured and precomputed HDR results are not yet fully satisfying but show the importance of fluid-structure interaction effects