FBR type reactors

Purpose: To attain a reactor core structure with a flattened reactor core power distribution in LMFBR type reactors. Constitution: In a conventional reactor core, inner blanket fuels are disposed in a disc-like shape near the axial center of the reactor core central portion and the reactor core power distribution is flattened by properly selecting the radial extension and the thickness thereof. However, the power is actually reduced substantially at the periphery of the inner blanket. In this invention, the axial length of the reactor core fuels disposed above and below then periphery of the inner blanket fuels is made longer than the axial length of the reactor core fuels situated above and below the blanket fuels. As a result, the power of the fuel assembly with the longer axial length is increased to flatten the power distribution more. Then, not only the reactor core power density is increased but also the flow rate control mechanism can be simplified and the reactor power efficiency is improved, whereby the reactor economy and safety can be improved. (Kamimura, M.)