LMFBR type reactor

In a reactor vessel of a FBR type reactor, especially, a tank type FBR type reactor using liquid metals as coolants, a temperature stratification boundary is formed not only upon occurrence of earthquakes but also upon usual reactor scram to form wave movement having a wavelength substantially corresponding to the diameter of the reactor vessel. Then, net-like or porous plates are disposed horizontally just above the inlet hole of an intermediate heat exchanger as a portion of generating the temperature stratification boundary. The plates have an effect of stopping the wave movement rapidly since they effectively absorb the energy of the vertical movement of the temperature stratification boundary and cause fine swirls in the flow upon passage to thereby diffuse energy. Further, the fine swirls promote the mixing of high and low temperature sodium to moderate the abrupt temperature gradient at the temperature stratification boundary and to moderate thermal stresses gives to structures. In this way, the vertical vibrations of the temperature stratification boundary can be prevented upon reactor scram and thermal fatigues can be prevented without causing periodical thermal stresses to the structures in the vicinity of the temperature stratification boundary. (N.H.)