An engineering concept for the steam bubble collapse analysis in the licensing procedure

The main topic is to derive a structural dynamic engineering concept for the bubble-fluid-structure analysis by subdividing the complete system into subsystems which do not interact each other: for example the bubble-fluid and the fluid-structure system. The mechanical behaviour of each subsystem is seperated into the global behaviour and some additional localized effects. This seems to be necessary since the pool geometry especially for steel containments and also the analysis of the structural system which consists of different shells is too complicated. In this way also the sensitivity of the results is proved. Since the wall loads that means the sum of the fluid pressure and the inertia forces of the oscillating walls are not sensitive on small modifications in the geometry as well as in the structural behaviour of the walls it is possible to determine first the distribution of the maximum wall loads by a simple fluid-structure model and introduce then in a second step these loads into a refined static shell analysis for calculating finally the stresses. Analytical and experimental results are compared. Some rules are given how to transfer the pressure time histories from small test facilities to the containment in respect to the geometry and the structural behaviour. Further we have to discuss how the hoop and bending stiffnesses of the walls, the arrangement of the pipes within the containment, the angular distance of the pipes and the durance of the chug influence the pressure distribution at the elastic outer wall and at the stiff interior wall. Finally the different behaviour of a steel and a concrete pressure suppression system will be explained. (orig./HP)