Loop type FBR reactors

Purpose: To reduce the thermal shocks to the overflow pipeways in a reactor vessel. Concentration: In a nuclear reactor vessel, there occurs a thermal laminar flow phenomenon in which high temperature sodium stagnates in the upper layer portion due to the reduction in the recycling amount caused by the interruption of the main recycling pump and the sodium temperature in the upper layer portion is maintained at the same extent of high temperature as that in the reactor power operation. However, in this invention, high temperature sodium in the reactor upper layer portion A overflown from overflow pipes is caused to flow through a heat exchanger and introduced into an overflow return pipeway. In this way, since the sodium temperature in the low temperature sodium layer B is as low as the sodium temperature at the exit of the reactor, overflown sodium at high temperature passed through the heat exchanger is lowered with the temperature and then introduced to the overflow return pipeway. This can reduce the thermal shocks resulted to the overflow return pipeway. (Seki, T.)