Development and verification of an axially heterogeneous core for large fast breeder reactors

Taking up a demonstration fast breeder reactor with 1000 MWe output, especially a tank type reactor, as the object, the conceptual design of an axially heterogeneous core was carried out, aiming at the increase of economical efficiency, the improvement of safety, the extension of operation period and so on. This core is that the internal blanket with depleted uranium as the main composition is installed at the axial mid point of the core with plutonium fuel. By optimizing the arrangement of this internal blanket, the core volume can be reduced by about 5 % as compared with a homogeneous two-region core of the same type as that of the prototype fast breeder reactor ''Monju'', and the fuel life can be extended by about 20 %. Besides, the criticality experiment simulating the nuclear characteristics of the axially heterogeneous core was carried out by using the FCA cooperating with Japan Atomic Energy Research Institute in the research entrusted by Power Reactor and Nuclear Fuel Development Corp., to verify the basic nuclear characteristics such as the flattening of output distribution, and to confirm the propriety of applying the existing design techniques to the design of an axially heterogeneous core. (Kako, I.)