Nuclear reactor

A nuclear reactor provided with a core which includes a new fuel part at which new fuel is loaded and a burning part which is arranged at one side of the new fuel part and which generates neutrons to enable fuel to burn, the new fuel including at least one type of uranium from among natural uranium and depleted uranium, the uranium absorbing neutrons to generate plutonium which fissions to generate output, and the burning part moving in a direction toward the new fuel part from the beginning to end of the burning cycle, wherein

• during the period of power operation, a plurality of fuel assemblies are arranged at the core,
• the plurality of fuel assemblies include fuel assemblies which are fastened to the core and fuel assemblies which can move in the axial direction of the core,
• the reactor is further provided with a movement apparatus for making the movable fuel assemblies move,
• the movable fuel assemblies are pulled out from the core so that the nuclear reactor stops,
• the movable fuel assemblies are inserted into the core from a pulled out state so that the nuclear reactor starts, further, the movable fuel assemblies as a whole are inserted into the core so that burnup of the fuel becomes continuous at a boundary between the movable fuel assemblies and the fuel assemblies which are fastened to the core and the core becomes a predetermined power, and,
• when maintaining the predetermined power, a state where the movable fuel assemblies as a whole are inserted into the core is maintained.