Dynamic response of a fluid filled test loop under FCI loading

For in-pile experiments with a LMFBR fuel pin bundle a special test loop will be used allowing for appropriate changes of the local cooling conditions. As a consequence of such experiments an energetic fuel coolant interaction (FCI) generating a high pressure peak in the loop cannot be ruled out under very pessimistic assumptions. Therefore, the walls of the loop must be able to withstand this pressure peak without major damage. In order to show this, the pressure propagations along the channels of the loop will be investigated in this paper. The geometry of the loop is very complex with several parallel coolant channels and sudden variations of the channel cross-sections. The smallest channel width is less than one centimeter, the outer diameter is about one decimeter and the loop length is several meters. Furthermore, in case of a pressure peak loading, fluid-structure interaction at thin walled parts of the loop must be considered. As computational tool for this complex problem the computer program SING-S has been used. It is based on a boundary integral method developed recently and allows for an adequate modelling of the problem without any artificial damping. In other methods such damping could cause considerable errors. The circular cross-sections of the loop are approximated by rectangular cross-sections having the same area. Then the boundaries of the resulting channels can be easily described by plane rectangular dipole panels. (orig./GL)