Abstract: A core of a boiling water reactor as a burner type core of the boiling water reactor having a ratio of 3 or more of number of fuel assemblies loaded in the core to number of control rods installed in the nuclear reactor and using an oxide of low enriched uranium having a mean enrichment of the fuel assemblies of 3 wt % to 8 wt % or a mixed oxide having a mean fissile plutonium enrichment of the fuel assemblies of 2 wt % to less than 7 wt %, wherein a mean weight of at least one of uranium and plutonium included in a unit volume of a core region is 2.25 to 3.4 kg/l when load of the fuel assemblies having a burnup of 0 into the core is finished, and a mean thickness of the channel box of the fuel assemblies is 2.10 to 3.55 mm.

Abstract: An method for operating a nuclear power generation plant, comprising the steps of: forming a plurality of control rod patterns by operating a plurality of control rods during a first period of one operation cycle of a reactor including said first period before a point of time when all control rods are completely withdrawn from a core of said reactor and a core flow rate reaches firstly a set core flow rate, and a second period after said point of time, controlling stepwise at least once a temperature of feed water supplied to said reactor based on a different set feed water temperature during a period included in said first period for operating said reactor with a formed same control rod pattern, and continuing feed water temperature control based on said set feed water temperature until said core flow rate reaches a set core flow rate set based on said set feed water temperature.

Abstract: A reactor core, comprising: an outermost region; a core region surrounded by said outermost region; a plurality of fuel support members, each of which is disposed at a lower end portion of said outermost region and said core region; and a plurality of fuel assemblies loaded in said outermost region and said core region and supported by said fuel support members, wherein a plurality of fuel assemblies disposed in said core region include a plurality of first fuel assemblies, each of which is inserted into a first coolant passage which is formed in said fuel support member and has a first resistor having an opening, and a plurality of second fuel assemblies, each of which is individually inserted into each of second coolant passage which is formed in said fuel support member and has a second resistor having an opening and a larger pressure loss than that of said first resistor; and, four fuel assemblies, each of which is adjacent to each of four lateral sides of each of a plurality of first fuel assemblies, inc