Seismic test of the Top Entry System for LMFBR

A new type of the piping system entitled 'Top Entry System' is to be investigated for the Loop-type Fast Breeder Reactor in order to minimize the construction cost by reducing the length of piping systems. In the Top Entry System shown, the pipings connecting the reactor vessel (R/V) and the intermediate heat exchangers (IHX) or the pumps are designed to be flexible to reduce the thermal stress and to be as compact as possible. There were two items to be evaluated from the point of view of the seismic design. One of them was to evaluate whether the cyphon breaking phenomenon would occur or not at the bottom of the inverted U-shaped piping between R/V and IHX caused by sloshing at the free surfaces. The other point was to evaluate the stress of the inverted U-shaped piping subjected to the seismic load and the fluid force due to sloshing. We investigated these two points in this study. In the experiment, the one-third scale models of the reactor vessel, the inverted U-shaped piping and the intermediate heat exchanger, were made and were examined by using the large scale three dimensional (6 freedoms) shaking table. The natural frequencies of the sloshing and the piping were examined by sinusoidal excitation. Also the responses of the piping and descent of liquid level by the earthquake were obtained. The experimental results were compared with the analytical results and these results were reduced to the actual scale by using the similarity law. From these results, we verified the safety of the Top Entry System at the seismic event. (orig./GL)