High conversion type light water cooled reactor

Purpose: To ensure the fuel rod integrity without complicating the fuel design. Constitution: In a high conversion type light water cooled reactor having, arranged therein, a plurality of fuel assemblies each comprising a channel box of a hexagonal cross section in which a plurality of fuel rods are disposed in a trigonal lattice-like configuration, the fuel assemblies are so arranged that a trigonal cross sectional scope is defined between each of adjacent fuel assemblies. It is possible to control the size of the trigonal space and also change the cross section of the control rod by adjusting the length of the side of the adjacent hexagonal shape. In this way, the control rod and the power monitoring device can be disposed to the outside of the fuel assemblies, by which the problem in the reduction of the integrity accompanying the displacement of the fuel rod can be avoided and the fuel rods in the fuel assembly can be made into a uniform constitution to render the power distribution more uniform. Accordingly, the power peaking coefficient is lowered and the operation margin to the linear power density limit can be increased. (Kamimura, M.)