FUEL ASSEMBLY, REACTOR CORE AND WATER-COOLED NUCLEAR REACTOR
In order to implement breeding in a water-cooled fast reactor, it is required to reduce the volume ratio of cooling water to fuel. When supercritical pressure water is used to cool a nuclear reactor, it is required to prevent the inflow and outflow of the cooling water between flow paths between fuel rods (cross flow between sub-channels), prevent the temperature of a high-temperature sub-channel from being further increased, and decrease the maximum fuel cladding tube temperature. The volume ratio of the cooling water to the fuel can be significantly reduced by adjacent fuel rods being bundled while being in contact with each other to form a fuel assembly. The cross flow between the sub-channels can be eliminated by the adjacent fuel rods being bundled while being in contact with each other. By providing a cooling water mixing unit in the vertical direction of the fuel assembly, the maximum fuel cladding tube temperature of a supercritical pressure water-cooled nuclear reactor can be reduced.