Analysis of the PWR core support columns under blowdown loading

A failure of the primary coolant system in a pressurized water reactor has been assessed to be very unlikely. Nevertheless a sudden and very large break of the primary coolant circuit at an outlet nozzle of the reactor pressure vessel is postulated in this paper. It causes a fast blowdown of the primary system accompanied with strong transient bending loadings of the core support columns. These loadings must not result in major plastic deformations or breaks of several columns. In order to investigate the transient bending loading and the resulting stresses during the initial phase of the blowdown, the accelerating flow in the upper plenum is calculated. The closely spaced core support columns located in this plenum are treated as circular obstacles. For solution of this problem having a very unfavourable geometry a boundary integral method (computer program SING1) is used which has been developed recently for highly transient internal flow problems. In this method the unknowns describing the problem are distributed over the outer fluid boundary and along the axes of the columns only. In this way the computational effort has been considerably reduced in comparison with usual methods, where the unknowns are distributed over the whole three-dimensional flow field. (orig./GL)