Patent Number: 
Section: claims

1. A nuclear reactor, comprising:a core including, along an axial direction of the core, new fuel and burning fuel,the burning fuel being arranged, in said axial direction, at only one side of the new fuel,the burning fuel generating 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 power, andthe burning fuel growing at one end in said axial direction toward the new fuel while diminishing into burned up fuel at an opposite end in order to maintain a substantially constant shape from a beginning to an end of an operation cycle; anda reactivity applying mechanism configured to apply reactivity to change the power of the core when a temperature of coolant which flows through an inside of the core changes,whereinthe power of the core is adjusted by performing control to change the temperature of the coolant which flows through the inside of the core,the reactivity applying mechanism includesfuel members which include fuel rods or fuel assemblies, anda gap adjusting member arranged in a region which is included in the burning fuel at the beginning of the operation cycle,the gap adjusting member supports the fuel members together, and determines a distance between the fuel members,the gap adjusting member is formed by a material which expands when the temperature rises,the gap adjusting member expands and the distance between the fuel members becomes larger when the temperature of the coolant in the core rises, andthe gap adjusting member includes a gap adjusting plate which has holes, and the fuel members are supported in the holes. 2. The nuclear reactor as set forth in claim 1, whereinthe core hasa high rise rate region where the temperature of the coolant rises from a core inlet toward a core outlet, anda low rise rate region which is arranged downstream from the high rise rate region and has a smaller rate of rise of temperature than the high rise rate region, andthe gap adjusting member is arranged in the low rise rate region at the beginning of the operation cycle. 3. The nuclear reactor as set forth in claim 1, wherein the reactor changes the temperature of the coolant which flows inside the core by performing a coolant temperature adjustment control which makes the temperature of the coolant which flows into the core change. 4. The nuclear reactor as set forth in claim 1, whereinthe reactor is formed so that when a flow rate of the coolant which flows into the core changes, the temperature of the coolant which flows through the inside of the core changes to apply the reactivity to change the power of the core, andthe reactor changes the temperature of the coolant which flows inside the core by performing a coolant flow rate adjustment control which makes the flow rate of the coolant which flows into the core change. 5. The nuclear reactor as set forth in claim 1, wherein the coolant is mainly comprised of lead 208 among isotopes of lead. 6. A power generating facility, comprising:a nuclear reactor, the nuclear reactor comprising a core and a reactivity applying mechanism,a steam generator which generates steam by heat which is generated by the core,a turbine which turns by supply of steam which is produced by the steam generator, anda generator which is connected to the turbine,the core including, along an axial direction of the core, new fuel and burning fuel,the burning fuel being arranged, in said axial direction, at only one side of the new fuel,the burning fuel generating 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 power,the burning fuel growing at one end in said axial direction toward the new fuel while diminishing into burned up fuel at an opposite end in order to maintain a substantially constant shape from a beginning to an end of an operation cycle,the reactivity applying mechanism configured to apply reactivity to change the power of the core when a temperature of coolant which flows through an inside of the core changes,whereinthe power of the core is adjusted by performing control to change the temperature of the coolant which flows through the inside of the core,the reactivity applying mechanism includesfuel members which include fuel rods or fuel assemblies, anda gap adjusting member arranged in a region which is included in the burning fuel at the beginning of the operation cycle,the gap adjusting member supports the fuel members together, and determines a distance between the fuel members,the gap adjusting member is formed by a material which expands when the temperature rises,the gap adjusting member expands and the distance between the fuel members becomes larger when the temperature of the coolant in the core rises, andthe gap adjusting member includes a gap adjusting plate which has holes, and the fuel members are supported in the holes.