Tank type FBR reactor

The breeder of the present invention employs a reactor wall cooling system and has a thin walled structure so as to reduce an amount of materials and improve earthquake proofness. That is, most of primary coolants discharged from a primary circulation pump flow into a high pressure plenum and then into a reactor core. The coolants heated in the reactor core flow to an intermediate heat exchanger and exchange heat with secondary coolants. On the other hand, a portion of the primary coolants discharged from the high pressure plenum passes through a bybassing pipeline and flows into a gap between a reactor container and a low temperature coolant flow channel forming walls, and cool the inner wall surface of the reactor container to keep low temperature state of the reactor container. Then, thermal stresses of the reactor container are moderated. Further, if the bypassing pipeline is used, the amount of existent flow channel forming plates, etc. can be remarkably saved. Further, if high temperature coolant containing vessel is supported from a roof slub, the earthquake proofness of the reactor container is improved since the vibration weight of the high temperature coolants is supported by the containing vessel. (I.S.)