JP5717091B2 - Equipment equipped with a nuclear reactor - Google Patents

Description

The present invention relates to a facility including a nuclear reactor .

  Nuclear reactors are used in power generation facilities. The nuclear reactor includes a fast neutron reactor. A fast neutron reactor is a nuclear reactor that generates power by fissioning fissionable nuclides mainly with fast neutrons, and the core is cooled by heavy metals such as sodium and lead bismuth alloys, or gas. In conventional nuclear reactors, fission occurs and power is generated throughout the core.

  The maintenance of the criticality of the reactor core and the adjustment of the power are performed by, for example, control rods. The control rod is made of a material that easily absorbs neutrons. At the beginning of the operation cycle, the control rod is inserted into the reactor core, and as the combustion proceeds, the control rod is gradually pulled out to maintain the critical state while maintaining the output. Thus, in the operation of the nuclear reactor, control for maintaining the criticality of the nuclear reactor is necessary. From the beginning of the operation cycle to the end of the operation cycle, the control for continuously maintaining the criticality is performed.

  Japanese Patent No. 3463100 discloses a nuclear reactor that does not require control for maintaining criticality in an operation cycle. This nuclear reactor adopts a combustion method called CANDLE (Constant Axial Shape of Neutron Flux, Nuclide Densities and Power Shape During Life of Energy Production) combustion method. In the CANDLE combustion method, the core can be roughly divided into a new fuel part, a combustion part, and a part where combustion has progressed. The combustion section moves toward the new fuel section at a speed proportional to the output with combustion. In CANDLE combustion, after one operation cycle is completed, the fuel is changed to perform the next operation cycle. When the fuel is exchanged, the fuel which has been burned in the direction of the core axis can be taken out, and new fuel can be loaded on the end opposite to the taken-out end.

  In the CANDLE combustion method, it is not necessary to adjust the criticality, and the output distribution is kept almost constant without adjusting the output distribution. For this reason, it has the characteristic that the reactivity control of the core, such as the operation of the control rod, does not have to be performed from the beginning to the end of the operation cycle. In addition, the reactivity coefficient does not change, and the operation method does not have to be changed with combustion.

Japanese Patent No. 3463100

  By adopting the CANDLE combustion method as the fuel combustion method for the nuclear reactor, the reactor core characteristics can be made almost constant even when combustion progresses, operation control is simplified, and a nuclear reactor with a low probability of accidents. Can be provided. Further, since there is no need to arrange the control rod in the core, there is no possibility of an accident that the control rod is accidentally pulled out during the operation period. In addition, the amount of waste can be reduced because of the high burnup when fuel is taken out.

  In the CANDLE combustion method, operation can be performed using only natural uranium or degraded uranium as a new fuel after the second cycle. Since these fuels are subcritical, they can be easily transported and stored. Moreover, since about 40% of uranium can be used as energy without enrichment or reprocessing, resources can be used effectively. In addition, the new fuel after the second cycle has characteristics such as high proliferation resistance because it does not require enrichment or reprocessing.

  The nuclear reactor is arranged in a power generation facility or a ship. The reactor may change its output depending on the amount of heat required during the operation period. For example, in a power generation facility, the output of the core is changed corresponding to the generated power. In a conventional nuclear reactor, the output of the core is controlled by inserting or withdrawing a control rod into the core, for example.

  Even in a nuclear reactor including a core adopting the CANDL combustion method, the output of the core can be adjusted by arranging control rods to be inserted into the core. However, in the CANDLE combustion method, if a flow path (channel) for inserting a control rod is formed in the core, it may be difficult to achieve criticality. In the core of the prior art, criticality could be easily achieved by increasing the concentration of fissile uranium or plutonium or increasing the number of fuel assemblies of new fuel. In the CANDLE combustion method, enriched uranium or the like can be included in the new fuel, but it is preferable to use only natural uranium or degraded uranium as the new fuel without using enriched uranium or the like.

  In order to burn the fuel uniformly, it is preferable that the radial power distribution is substantially constant. However, when the flow path for inserting the control rod is formed in the core, a space in which no fuel is loaded is formed in the core. In this space, there is a problem that the output density becomes small and the radial output distribution becomes non-uniform.

An object of the present invention is to provide a facility including a nuclear reactor that includes a core in which a combustion section moves toward a new fuel section as fuel is burned, and that can perform power adjustment without using control rods. .

  A first nuclear reactor of the present invention includes a new fuel part loaded with a new fuel, and a combustion part disposed on one side of the new fuel part and generating neutrons to burn the fuel. Contains at least one of natural uranium and depleted uranium. Plutonium produced by uranium absorbing neutrons generates fission and generates an output. The combustion part is almost constant from the beginning to the end of the operation cycle. A core that moves in the direction toward the new fuel section while maintaining its shape is provided. The nuclear reactor is equipped with a reactivity application mechanism that applies a reactivity that can change the output of the core when the temperature of the coolant flowing in the core changes, and changes the temperature of the coolant flowing into the core. The output of the core is adjusted by performing the coolant temperature adjustment control.

  In the above invention, the reactivity application mechanism is arranged in a fuel body including a fuel rod or a fuel assembly and a region included in the combustion portion at an early stage of the operation cycle, and supports the plurality of fuel bodies to each other, An interval adjusting member that defines an interval between them, and the interval adjusting member is formed of a material that expands when the temperature rises. When the temperature of the coolant in the core rises, the interval adjusting member expands, It is preferable that the space | interval between bodies becomes large.

  In the above invention, the coolant is preferably composed mainly of lead 208 of lead isotopes.

  In the above invention, when the flow rate of the coolant flowing into the core changes, the temperature of the coolant flowing in the core changes, and the reactivity capable of changing the output of the core is applied. The output of the core is preferably adjusted by performing coolant flow rate adjustment control for changing the flow rate of the coolant flowing into the core.

  A first power generation facility according to the present invention includes the first nuclear reactor, a steam generator that generates steam by heat generated by the core, a turbine that rotates by being supplied with steam generated by the steam generator, And a generator connected to the turbine.

  A second nuclear reactor according to the present invention includes a new fuel part loaded with a new fuel, and a combustion part disposed on one side of the new fuel part and generating neutrons to burn the fuel. Contains at least one of natural uranium and depleted uranium. Plutonium produced by uranium absorbing neutrons generates fission and generates an output. The combustion part is almost constant from the beginning to the end of the operation cycle. A core that moves in the direction toward the new fuel section while maintaining its shape is provided. The nuclear reactor is equipped with a reactivity application mechanism that applies a reactivity that can change the output of the core when the temperature of the coolant flowing in the core changes, and the flow rate of the coolant flowing into the core changes. The coolant flow rate that changes the flow rate of coolant flowing into the core is configured so that the temperature of the coolant flowing in the core changes and the reactivity that can change the output of the core is applied. By performing adjustment control, the output of the core is adjusted.

  A second power generation facility according to the present invention includes the above-described second nuclear reactor, a steam generator that generates steam by heat generated by the core, a turbine that is rotated by being supplied with the steam generated by the steam generator, And a generator connected to the turbine.

ADVANTAGE OF THE INVENTION According to this invention, an equipment provided with the nuclear reactor which equips the core which a combustion part moves toward a new fuel part with combustion of a fuel, and can perform output adjustment without using a control rod can be provided. .

1 is a schematic diagram of a power generation facility in Embodiment 1. FIG. 2 is a schematic plan view of a quarter of the core in the first embodiment. FIG. 2 is a schematic perspective view of a fuel assembly according to Embodiment 1. FIG. 2 is a schematic perspective view of a fuel rod in Embodiment 1. FIG. FIG. 3 is a schematic diagram for explaining a combustion state of core fuel in the first embodiment. 6 is a graph illustrating a change in infinite neutron multiplication factor with respect to a neutron fluence of fuel in the first embodiment. It is a graph explaining the relationship between a core height and an infinite neutron multiplication factor of fuel. FIG. 3 is a diagram for explaining a change in core power density and fuel replacement in the first embodiment. 1 is a schematic partial cross-sectional view of a core in a first embodiment. FIG. 3 is an enlarged schematic plan view of a distance adjusting member in the first embodiment. FIG. 5 is another schematic partial cross-sectional view of the core in the first embodiment. 3 is a time chart of coolant temperature adjustment control in the first embodiment. It is a graph of the inelastic scattering cross section of a lead isotope. 6 is a time chart of coolant flow rate adjustment control in the second embodiment.

(Embodiment 1)
With reference to FIG. 1 to FIG. 13, a nuclear reactor and power generation equipment in the first embodiment will be described. The core of the reactor in this embodiment is a fast neutron reactor that generates plutonium fission mainly by fast neutrons. The nuclear reactor in the present embodiment is arranged in a power generation facility, and generates power using the heat of the coolant flowing out from the nuclear reactor.

  FIG. 1 is a schematic diagram of power generation equipment in the present embodiment. The power generation facility in the present embodiment includes a nuclear reactor 1. The nuclear reactor 1 includes a nuclear reactor vessel 9 and a reactor core 10 disposed inside the nuclear reactor vessel 9. The core 10 is loaded with fuel. In the core 10 in the present embodiment, the vertical direction corresponds to the axial direction of the core. A coolant is supplied to the inside of the nuclear reactor 1, and the coolant flows through the core 10, whereby the heat of the core 10 is transmitted to the coolant.

  As the coolant in this embodiment, a material having a small neutron moderating ability and a small neutron absorption ability can be used. In the present embodiment, liquid sodium 51 is used as the coolant. As the coolant for the reactor, in addition to the sodium coolant, a lead-based coolant such as a lead-bismuth coolant, a gas coolant such as helium, or the like can be used. In the present embodiment, liquid sodium 52 is also used as a heat medium for transferring heat from the intermediate heat exchanger 2 to the steam generator 3.

  The power generation facility includes an intermediate heat exchanger 2 and a steam generator 3 for generating steam for rotating the turbine 4 using heat of the coolant flowing through the core 10. The heat of the coolant is transferred to the steam generator 3 through the intermediate heat exchanger 2.

  By driving the pump 41, the primary sodium 51 that functions as a coolant flows into the reactor vessel 9 as indicated by an arrow 112. The coolant rises in temperature as it flows through the core 10. The coolant whose temperature has risen is sent to the intermediate heat exchanger 2 as indicated by an arrow 111. The coolant is supplied into the reactor vessel 9 by the pump 41 after performing heat exchange in the intermediate heat exchanger 2.

  The secondary sodium 52 that transfers heat from the intermediate heat exchanger 2 to the steam generator 3 is supplied to the intermediate heat exchanger 2 as indicated by an arrow 114 when the pump 42 is driven. The secondary sodium 52 undergoes heat exchange with the coolant and the temperature rises. The secondary sodium 52 whose temperature has risen is supplied to the steam generator 3 as indicated by an arrow 113.

  Steam generator 3 in the present embodiment heats water 53 with the heat of secondary sodium 52. When the pump 43 is driven, water is supplied to the steam generator 3 as indicated by an arrow 116. In the steam generator 3, steam is generated by heat exchange between the secondary sodium 52 and water. The secondary sodium 52 that has exchanged heat in the steam generator 3 is supplied to the intermediate heat exchanger 2 by a pump 42.

  The power generation facility in the present embodiment includes a turbine 4 and a generator 5. The steam generated by the steam generator 3 is supplied to the turbine 4 through the flow rate adjustment valve 44 as indicated by an arrow 115. By adjusting the opening degree of the flow rate adjusting valve 44, the flow rate of steam supplied to the turbine can be adjusted. The steam rotates the turbine 4. When the rotational force of the turbine 4 is transmitted to the generator 5, the generator 5 generates power.

  Water vapor and condensed water flowing out from the turbine 4 flows into the condenser 6. The condenser 6 includes a heat exchanger 6a. Cooling water such as seawater is supplied to the heat exchanger 6a as indicated by an arrow 118. The steam is returned to the water 53 in the condenser 6. The water 53 flowing out from the condenser 6 is supplied to the steam generator 3 by the pump 43.

  FIG. 2 shows a schematic plan view of the reactor core in the present embodiment. FIG. 2 shows a quarter of the core. The core 10 in the present embodiment is formed in a substantially hexagonal shape in plan view. The core of the nuclear reactor is not limited to this form, and can be formed in an arbitrary shape or a circle that is substantially circular when viewed in plan.

  The core 10 in the present embodiment includes a fuel assembly 21 as a fuel body. In the present embodiment, a plurality of fuel assemblies 21 are regularly arranged. The plurality of fuel assemblies 21 in the present embodiment are loaded with the same new fuel. In the present embodiment, depleted uranium is loaded as a new fuel. Although no reflector is disposed around the core 10 in the present embodiment, the present invention is not limited to this configuration, and a reflector may be disposed around the core 10.

  FIG. 3 shows a schematic perspective view of the fuel assembly in the present embodiment. The fuel assembly 21 includes a plurality of fuel rods 22. The end of the fuel rod 22 in the longitudinal direction is supported by the nozzle 27. Alternatively, the fuel rod 22 is disposed inside the fuel assembly 21 and is supported by a fixing member fixed to the nozzle 27. The fuel rod 22 is supported by a plurality of support grids 25a and 25b. The support grids 25a and 25b support the fuel rods 22 apart from each other. The coolant flows between the fuel rods 22 to cool the fuel rods 22. In this embodiment, the distance between the fuel rods is maintained by the support grid. However, the present invention is not limited to this configuration, and a wire spacer or the like can be used instead of the support grid.

  FIG. 4 shows a schematic perspective view of the fuel rod in the present embodiment. FIG. 4 shows a fuel rod in which the combustion of fuel moves from the upper side to the lower side. In addition, a part of the covering material is shown broken. The fuel rod 22 in the present embodiment includes a covering material 23. The covering material 23 is formed in a cylindrical shape. The covering material 23 is made of stainless steel, for example. The fuel rod 22 includes fuel pellets 24a, 24b, and 24c. The fuel pellets 24a, 24b, and 24c are disposed inside the covering material 23. The fuel rod 22 is sealed with a stopper 29. The fuel pellets 24a, 24b, and 24c are pressed by the coil spring 28.

  The fuel rod shown in FIG. 4 shows the initial state of the operation cycle. The plurality of fuel pellets 24a, 24b, 24c are arranged in the order of a fuel pellet 24a containing new fuel, a fuel pellet 24b in the middle of combustion, and a fuel pellet 24c in which combustion has sufficiently progressed. The portion of the fuel pellet 24a containing the new fuel defines the new fuel portion of the core. The burning part of the core is defined by the part of the fuel pellet 24b in the middle of combustion. The portion of the fuel pellet 24c where the combustion has progressed defines the portion where the combustion of the core has progressed.

  As described above, the fuel rods 22 in the present embodiment are arranged with the fuel pellets 24a, 24b, and 24c having different burnups. After the completion of one operation cycle, for example, the covering material 23 is peeled off, and the fuel pellets in the burned portion and the other fuel pellets are separated. Next, fuel rods for the next operation cycle can be formed by arranging fuel pellets containing new fuel, recovered fuel pellets, and the like inside the new coating material.

  Alternatively, as a method for collecting fuel pellets, the covering material 23 may be peeled off after the fuel rod is cut for each portion. Also by this method, the fuel pellets arranged in the combustion part and the part where the combustion has progressed can be recovered.

  2 to 4, the fuel pellets arranged in the new fuel portion of the fuel assembly 21 in the present embodiment include deteriorated uranium. The fuel in the present embodiment is a metal fuel, but is not limited to this form, and for example, a nitride fuel or the like can be used.

  Next, the output operation of the core in the present embodiment will be described. In the present embodiment, an example will be described in which the output is kept substantially constant during the output operation.

  FIG. 5 is a schematic diagram for explaining the progress of the combustion of the core in the present embodiment. FIG. 5 is a schematic cross-sectional view when the core is cut along the axial direction. FIG. 5 shows an initial (BOC) core of the nth cycle after a plurality of operation cycles and an end (EOC) core of the nth cycle. Also shown is a core that has been operated for multiple cycles with the same cycle length and the same fuel replacement method. The axis where the radial position r is zero is the core axis.

  In the reactor core 10 in the present embodiment, the combustion section 12 moves toward the new fuel section 11 from the beginning to the end of the operation cycle. That is, the core in the present embodiment performs CANDLE combustion. The moving speed of the combustion unit 12 is roughly proportional to the power density and inversely proportional to the fuel atom number density.

  The power density of the core in the present embodiment is high at the center of the core. At the outer periphery of the core, neutron leakage increases, so the power density decreases toward the outside in the radial direction. For this reason, the position of the combustion part in the axial direction is arranged at a position that is delayed toward the outside in the radial direction.

  The core 10 in the present embodiment includes a new fuel part 11, a combustion part 12, and a part 13 where combustion has progressed. The new fuel portion 11 is a portion where new fuel is disposed. The combustion part 12 is a part where neutrons are spontaneously generated and fuel combustion occurs. In the combustion part 12, the output is actually generated by the occurrence of fission. The portion 13 where combustion has progressed is a portion where combustion has progressed and almost no output is generated.

  In the initial core of the nth cycle, the new fuel unit 11 is disposed below the core 10. The combustion unit 12 is disposed on the upper side of the new fuel unit 11. In the combustion section 12, fuel that has already started combustion in the previous cycle is arranged.

  In the present embodiment, the combustion section 12 arranged at the initial stage of the operation cycle is a part for starting combustion. Combustion of fuel is started from the combustion unit 12, and combustion proceeds in a direction toward the new fuel unit 11 as indicated by an arrow 101. When the combustion in the nth cycle proceeds and the end of the operation cycle is reached, the combustion unit 12 proceeds to the lower end of the core 10. In the present embodiment, the combustion is continued until the new fuel part 11 is almost exhausted. At the end of the operation cycle, the new fuel part 11 may remain.

FIG. 6 shows a graph for explaining the relationship between the neutron fluence of the fuel and the infinite neutron multiplication factor in the present embodiment. The horizontal axis represents the neutron fluence obtained by integrating the neutron flux with time, and the vertical axis represents the infinite neutron multiplication factor kinf. The neutron fluence is an amount corresponding to the burnup of the fuel, for example. In this embodiment, deteriorated uranium is used as fuel. Depleted uranium includes, for example, about 99.8% uranium 238 and about 0.2% uranium 235. Uranium 238 transmutates as shown in the following equation 1 by absorbing neutrons. Uranium 238 is converted to plutonium 239.

  In the vicinity of zero neutron fluence, uranium 238 absorbs neutrons to generate plutonium 239, thereby increasing the infinite neutron multiplication factor. When a predetermined neutron fluence is reached, the ratio of the abundance of plutonium 239 and the like to the abundance of uranium 238 approaches a constant value, and fission products (FP) accumulate, and the infinite neutron multiplication factor gradually decreases. As described above, the fuel in the present embodiment has a characteristic that the infinite neutron multiplication factor increases at the initial stage of combustion, and then the infinite neutron multiplication factor gradually decreases.

  Moreover, since the subcriticality of depleted uranium is large, in order to make a part of the core more than critical, it is necessary to absorb many neutrons in the uranium 238. In the present embodiment, the size of the core is selected so as to satisfy such conditions, and the fuel assemblies and fuel rods are designed.

  CANDLE combustion can be performed by adopting the core configuration as described above. That is, it is possible to form a core in which power is generated over the entire radial direction of the core and a combustion part is generated in a partial region in the axial direction of the core.

  FIG. 7 shows a graph of the infinite neutron multiplication factor when burning at an infinite core height. The horizontal axis represents the core height, and the vertical axis represents the infinite neutron multiplication factor of the fuel. In the present embodiment, as indicated by an arrow 101, the combustion section moves toward the new fuel section. The combustion part includes a region where the infinite neutron multiplication factor exceeds 1. The actual reactor core height is finite, and in this case, the infinite neutron multiplication factor at the end of the reactor core may slightly deviate from the graph shown in FIG.

  FIG. 8 shows a graph for explaining the state in which the combustion of the core proceeds and the fuel replacement in the present embodiment. FIG. 8 shows an initial and final graph of the nth cycle core and an initial and final graph of the (n + 1) th cycle core. In each graph, the power density at the core axis, the number density of uranium 238, and the number density of fission products are shown.

  Referring to FIGS. 7 and 8, the maximum point of the power density moves toward the lower part of the core where the new fuel part 11 is arranged as indicated by an arrow 101. Combustion in the present embodiment moves in a direction from the upper end to the lower end of the core. The speed at which the combustion section moves, that is, the speed at which the maximum point of the power density moves is, for example, several centimeters per year. Thus, the combustion part moves slowly. The number density of uranium 238 becomes smaller on the downstream side of the combustion section by transmutation. In addition, the number density of fission products increases on the downstream side of the combustion section due to the occurrence of fission. In the present embodiment, the combustion ends when the combustion part reaches almost the lower end of the core.

  When the n-th cycle ends, a part of the fuel where combustion has progressed is taken out. In the core at the initial stage of the (n + 1) th cycle, as indicated by an arrow 117, the combustion part arranged at the lower part of the core in the nth cycle is arranged at the upper part of the core and used as a part for starting combustion. In the core of the (n + 1) th cycle, a new new fuel part 11 is disposed at the lower part of the core. By performing such fuel exchange, combustion in the (n + 1) th cycle core can be performed in the same manner as in the nth cycle core.

  FIG. 9 shows a schematic partial cross-sectional view of the core in the present embodiment. The core 10 in the present embodiment is disposed inside the baffle plate 34. The fuel assembly 21 is arranged so that the longitudinal direction is substantially parallel to the axial direction of the core 10. Reactor 1 in the present embodiment includes a reactivity application mechanism to which a reactivity capable of changing the output of core 10 is applied when the temperature of the coolant flowing in the core changes.

  An assembly lower end support member 32 is disposed at the lower end portion of the core 10. The lower end of the fuel assembly 21 is fixed to the assembly lower end support member 32. Since the assembly lower end support member 32 only needs to fix the fuel assembly 21, an excellent material can be used as a structural material. An assembly upper end support member 33 is disposed at the upper end portion of the core 10. The assembly upper end support member 33 is formed so as to movably support the upper end of the fuel assembly 21. The upper end of the fuel assembly 21 is supported by the assembly upper end support member 33 so as to be movable outward.

  The core 10 in the present embodiment includes a gap adjusting plate 31 as a gap adjusting member that supports the plurality of fuel assemblies 21 to each other. The interval adjusting plate 31 is disposed in the portion of the support lattice 25a among the plurality of support lattices 25a and 25b (see FIG. 3). In a portion where the interval adjusting plate 31 is not disposed, a gap is formed between the support lattices 25b of the fuel assemblies 21 adjacent to each other.

  In FIG. 10, the schematic plan view of the space | interval adjustment board in this Embodiment is shown. Referring to FIGS. 9 and 10, the interval adjusting plate 31 has a hole 31 a into which the fuel assembly 21 is inserted. The hole 31 a of the interval adjusting plate 31 is formed so as to fit into the support grid 25 a of the fuel assembly 21. The interval adjusting plate 31 in the present embodiment is formed so as to support all the fuel assemblies 21 included in the core 10. By arranging the support grid 25a of the fuel assembly 21 in the hole 31a, the adjacent fuel assemblies 21 can be restrained from each other. An interval between the plurality of fuel assemblies 21 is determined.

  The interval adjusting plate 31 in the present embodiment is formed of a material that expands when the temperature rises. The interval adjusting plate 31 is made of a material having a large coefficient of thermal expansion. Further, the interval adjusting plate 31 in the present embodiment is formed of a material having a larger coefficient of thermal expansion than the aggregate lower end support member 32. As a material having a large coefficient of thermal expansion, stainless steel can be exemplified. For example, SUS304 or SUS316 (based on Japanese Industrial Standard (JIS)) can be adopted among stainless steels.

  FIG. 9 shows the power density in the axial direction of the core and the coolant temperature in addition to the schematic diagram of the core. The solid line indicates the initial (BOC) state of the operating cycle, and the broken line indicates the end (EOC) state of the operating cycle. The distribution of the power density and the distribution of the coolant temperature move toward the lower end of the core as indicated by an arrow 101 from the beginning to the end of the operation cycle. The temperature of the coolant rises from the lower end of the core 10 toward the upper end.

  The interval adjusting plate 31 in the present embodiment is arranged in the region of the combustion part at the initial stage of the operation cycle. In particular, in the present embodiment, it is arranged in the region of the combustion part throughout the operation cycle. In other words, the interval adjusting plate 31 is disposed inside the region of the combustion section both in the initial and final stages of the operation cycle. The interval adjusting plate 31 is arranged in a region where the temperature of the coolant increases during the operation cycle.

  Further, the interval adjusting plate 31 in the present embodiment is disposed at a position where the power density is substantially maximized at the initial stage of the operation cycle in the axial direction of the core. Alternatively, the interval adjusting plate 31 in the present embodiment is disposed at a position where the temperature rise of the coolant in the direction from the core inlet to the core outlet becomes moderate at the initial stage of the operation cycle.

  FIG. 11 shows another schematic partial cross-sectional view of the core in the present embodiment. In the core 10, the coolant contacts the interval adjusting plate 31. For this reason, the temperature of the space | interval adjustment board 31 also rises with the temperature rise of a coolant. When the temperature rises, the gap adjusting plate 31 expands outward in the radial direction as indicated by an arrow 120.

  The fuel assembly 21 is restrained by the interval adjusting plate 31. In the core 10 of the present embodiment, the lower end of the fuel assembly 21 is fixed to the assembly lower end support member 32. When the interval adjusting plate 31 expands, as shown by an arrow 121, the upper end of the fuel assembly 21 is directed outward in the radial direction. The moving distance of the upper end of each fuel assembly 21 gradually increases from the core axis (r = 0) toward the outside in the radial direction.

  As described above, when the temperature of the coolant rises, the interval between the fuel assemblies 21 increases, and neutron leakage increases. The effective neutron multiplication factor of the core 10 can be made less than 1, and the reactivity applied to the core 10 can be made negative. That is, in the core 10 in the present embodiment, a negative reactivity is applied when the temperature of the coolant rises.

  Further, when the temperature of the coolant is lowered, the interval between the fuel assemblies 21 is reduced, so that neutron leakage is reduced. A positive reactivity is applied to the core 10. Thus, the core 10 in this Embodiment can make the temperature coefficient regarding a coolant negative.

  The temperature coefficient of the fuel easily becomes negative due to the Doppler effect or the like, but its absolute value is small. The temperature coefficient related to the coolant in the present embodiment can be a negative value having a large absolute value. The temperature coefficient related to the coolant of the present embodiment can be a negative value much larger than the temperature coefficient of the fuel. For this reason, even if the temperature coefficient of other structural materials or the like is positive, the temperature coefficient of the entire core can be easily made negative.

  In addition, since the core in the present embodiment changes the shape of the core to reduce the temperature coefficient related to the coolant, the temperature coefficient related to the coolant is negative even in a large core having a large number of fuel assemblies. Can be.

  Referring to FIG. 9, interval adjusting plate 31 in the present embodiment is arranged in a region included in the combustion section at the initial stage of the operation cycle. With this configuration, when the output, coolant flow rate, or the like changes to change the coolant temperature, the interval adjusting plate 31 can be arranged in a region where the temperature change range of the coolant is large. The amount of expansion can be increased. The space | interval of the fuel assemblies 21 when the space | interval adjustment plate 31 expand | swells can be enlarged, and the temperature coefficient regarding a coolant can be made into a more negative value.

  For example, when the interval adjusting plate 31 is disposed in the vicinity of the lower end of the core 10, the interval adjusting plate 31 is disposed outside the combustion portion at the initial stage of the operation cycle. In the vicinity of the lower end of the core 10, since the heat generated by nuclear fission is not transferred to the coolant, the temperature change width of the coolant is reduced. For this reason, the space | interval adjustment board 31 cannot fully be expanded. As in the present embodiment, by arranging the interval adjusting plate 31 in the region of the combustion part, the interval adjusting plate 31 can be arranged in an area where the temperature of the coolant is relatively high. In this region, since the temperature change width of the coolant is increased, the interval adjusting plate 31 can be greatly expanded. The temperature coefficient for the coolant can be made more negative.

  Further, by arranging the interval adjusting plate 31 in the region of the combustion part, the temperature change width of the coolant is increased, and thus the speed at which the volume of the interval adjusting plate 31 changes is increased. By following the temperature change of the coolant with good responsiveness, the interval between the fuel assemblies 21 can be increased or decreased. That is, the response speed of the reactivity with respect to the temperature change of the coolant can be improved.

  Further, the interval adjusting plate 31 in the present embodiment is arranged at a position in the axial direction of the core where the coolant temperature becomes a value close to the coolant temperature at the core outlet at the initial stage of the operation cycle. The coolant temperature rises greatly from the core inlet toward the core outlet mainly in the region where the power density of the combustion section is high. Referring to FIG. 9, the core includes a high increase rate region 131 in which the temperature of the coolant rises from the core inlet toward the core exit, and a low increase rate region in which the rate of temperature increase is smaller than that in the high increase rate region 131. 132. The low increase rate region 132 is disposed downstream of the high increase rate region 131. FIG. 9 shows a high increase rate region 131 and a low increase rate region 132 in the initial stage of the operation cycle.

  The interval adjusting plate 31 in the present embodiment is disposed in the low increase rate region 132 where the temperature rise of the coolant is moderate at the beginning of the operation cycle. By adopting this configuration, the interval adjusting plate 31 can be disposed in the low increase rate region 132 from the beginning to the end of the operation cycle. Even if the combustion section moves during the operation cycle, the coolant temperature in the interval adjusting plate 31 does not change so much and the expansion amount does not change. For this reason, the change of the effective neutron multiplication factor accompanying fuel combustion can be suppressed, and ideal CANDLE combustion can be implement | achieved. Moreover, the change of the temperature coefficient regarding the coolant accompanying fuel combustion can be reduced.

  Further, the interval adjusting plate 31 is disposed at a position close to the assembly lower end support member 32 in which the interval between the fuel assemblies 21 remains unchanged in a range where the coolant temperature is close to the coolant temperature at the core outlet. Is preferred. In the present embodiment, it is preferable to arrange at a position close to the core inlet. For example, the interval adjusting plate 31 is preferably disposed at the end of the low increase rate region 132 on the core inlet side at the beginning of the operation cycle. With this configuration, when the interval adjusting plate 31 expands, the interval between the fuel assemblies can be increased, and the temperature coefficient related to the coolant can be set to a more negative value. In addition, the position of the space | interval adjustment plate 31 is not restricted to this form, For example, you may arrange | position at the core exit.

  In the core in the present embodiment, the lower end of the fuel assembly is fixed by the assembly lower end support member, but the present invention is not limited to this configuration, and the lower end of the fuel assembly has a diameter similar to the upper end of the fuel assembly. It may be supported so as to be movable in the direction. For example, the assembly lower end support member may be formed so as to thermally expand in accordance with the temperature of the coolant. The assembly lower end support member disposed at the lower end of the fuel assembly may be formed of the same material as the interval adjustment member.

  In the present embodiment, the fuel body whose interval is adjusted by the interval adjusting member includes a fuel assembly, but is not limited to this form, and a fuel rod may be employed as the fuel body. The fuel assembly in which the fuel rods are bundled may not be configured, and the fuel rods may be directly supported by the interval adjusting member so as to ensure a coolant flow path. Further, the interval adjusting member in the present embodiment is formed so as to support all the fuel bodies among the plurality of fuel bodies included in the reactor core, but is not limited to this embodiment, and some fuel bodies are used. You may form so that it may support.

  Although the space | interval adjustment member in this Embodiment contains the space | interval adjustment plate currently formed in plate shape, it is not restricted to this form, A space | interval adjustment member adjusts the distance of mutually adjacent fuel bodies according to temperature. It does not matter as long as it is formed as described above. For example, the interval adjusting member may include a member such as a wire formed in a linear shape. Alternatively, the gap adjusting member may be a massive member that is thermally expanded and attached to the fuel assembly. For example, the interval adjusting member includes a rectangular parallelepiped member attached to the outer surface of the support grid so that the rectangular parallelepiped members of adjacent fuel assemblies come into contact with each other when the fuel assemblies are loaded on the core. Can be formed.

  Further, in the present embodiment, the interval adjusting plate is disposed at one position in the axial direction of the core, but the present invention is not limited to this configuration, and interval adjusting members may be disposed at a plurality of positions. .

  Reactor 1 in the present embodiment can apply a reactivity having a large absolute value when the temperature of the coolant flowing in core 10 changes. Reactor 1 in the present embodiment adjusts the output of the core by performing coolant temperature adjustment control that changes the temperature of the coolant flowing into core 10. In the core 10 of the present embodiment, the temperature coefficient related to the coolant has a negative value with a large absolute value. For this reason, by raising the temperature of the coolant flowing into the core 10, a negative reactivity having a large absolute value can be applied to the core 10, and the output of the core 10 can be reduced. Alternatively, by reducing the temperature of the coolant flowing into the core 10, a large positive reactivity can be applied to the core 10, and the output of the core 10 can be increased. In particular, in the present embodiment, not only fine adjustment for changing the core power by about several percent, but rough adjustment for changing the core power by several tens of percent, for example, can be performed.

  In the present embodiment, in order to change the temperature of the coolant flowing into the core 10, control is performed to change the load of the apparatus connected to the nuclear reactor. Referring to FIG. 1, the power generation facility in the present embodiment performs control to change the generated power.

  For example, when the temperature of the coolant flowing into the core 10 is increased, the generated power is reduced to reduce the load. By reducing the opening degree of the flow rate adjusting valve 44, the flow rate of steam supplied to the turbine 4 is reduced, and the generated power is reduced. The amount of heat exchanged in the steam generator 3 is reduced. The temperature of the secondary sodium 52 circulating through the intermediate heat exchanger 2 and the steam generator 3 rises. As the temperature of the secondary sodium 52 rises, the temperature of the primary sodium 51 (coolant) flowing out from the intermediate heat exchanger 2 also rises. The temperature of the coolant flowing into the core 10 rises, and the temperature of the coolant flowing inside the core 10 rises. Alternatively, the temperature of the coolant is higher at the core outlet than at the core inlet, but the average temperature of the coolant in the core increases. The average coolant temperature can be exemplified by the average coolant temperature in the direction of the core axis. Since the core 10 has a negative temperature coefficient related to the coolant, a negative reactivity is applied to the core 10 when the temperature of the coolant rises. As a result, the output of the core 10 can be reduced.

  Further, when the temperature of the coolant flowing into the core 10 is lowered, the generated power is increased in order to increase the load. By increasing the opening degree of the flow rate adjustment valve 44, the flow rate of steam supplied to the turbine 4 increases, and the generated power increases. The amount of heat for heat exchange in the steam generator 3 increases. For this reason, the temperature of the secondary sodium 52 and the primary sodium 51 (coolant) decreases. The temperature of the coolant flowing into the core 10 is lowered, and a positive reactivity is applied to the core 10. As a result, the output of the core 10 can be increased.

  Thus, in the present embodiment, by reducing the amount of heat consumed by the device connected to the nuclear reactor 1, the temperature of the coolant flowing into the core 10 can be increased, and the output of the core 10 can be increased. Can be reduced. Further, by increasing the amount of heat consumed by the device connected to the nuclear reactor 1, the temperature of the coolant flowing into the core 10 can be reduced, and the output of the core 10 can be increased.

  Thus, the reactor in the present embodiment can change the output of the core without using control rods. In addition, as a nuclear reactor, it is not restricted to this form, You may use the reactivity adjustment by a control rod together.

  In this embodiment, the temperature of the coolant flowing into the reactor core is changed by adjusting the flow rate of the steam supplied to the turbine. Any device that can be adjusted can be employed. For example, referring to FIG. 1, at least one of a circulation channel for primary sodium 51, a circulation channel for secondary sodium 52, and a circulation channel for water and water vapor is used as a heat exchanger. Etc. may be arranged to adjust the temperature of the heat medium.

  FIG. 12 shows a time chart of the coolant temperature adjustment control in the present embodiment. FIG. 12 illustrates control for reducing the output of the core. The nuclear reactor in the present embodiment is operated so that the output of the core is substantially constant in normal operation control.

  FIG. 12 shows a case where the coolant temperature at the core inlet is increased stepwise by a solid line. Until time t1, steady operation is performed. Further, the flow rate of the coolant flowing into the core is kept substantially constant during the period of changing the power output of the core.

  At time t1, control is performed to reduce the generated power. The coolant temperature at the core inlet rises stepwise. The fuel temperature and the coolant temperature at the core outlet increase as the coolant temperature at the core inlet increases. The fuel temperature gradually rises from the core inlet toward the core outlet as the coolant temperature rises. The fuel temperature shown in FIG. 12 indicates the average temperature in the core 10. As the average temperature of the fuel, a value obtained by averaging the fuel temperature in the direction of the core axis can be exemplified as in the average temperature of the coolant.

  As the coolant temperature at the core inlet increases, the average temperature of the coolant in the core also increases. In the core in the present embodiment, since the temperature coefficient related to the coolant has a negative value having a large absolute value, a negative reactivity is applied to the core. For this reason, the state where the criticality is maintained is changed to the subcritical state, and the output of the core is lowered.

  As the output of the core decreases, the temperature of the fuel that has risen temporarily decreases, and becomes substantially constant at a predetermined temperature. Further, as the output of the core decreases, the temperature of the coolant at the core outlet that has temporarily increased also decreases and becomes substantially constant at a predetermined temperature. The reactivity applied to the core temporarily decreases, but returns to almost zero as the coolant outlet temperature decreases and the fuel temperature decreases. That is, the core returns from the subcritical state to the critical state. When the power of the core is reduced, the critical state is entered again. As described above, by increasing the coolant temperature at the core inlet, the output of the core can be decreased.

  FIG. 12 shows a case where the coolant temperature at the core inlet is gradually increased by a broken line. In order to gradually increase the coolant temperature at the core inlet, for example, the generated power can be gradually decreased. When the coolant temperature at the core inlet is gradually increased, the output of the core can be gradually decreased. The reactivity applied to the core continues to be almost constant at zero. That is, the power of the core can be changed while the core is maintained in a substantially critical state. The fuel temperature and the coolant temperature at the core outlet also change gradually without changing rapidly.

  As described above, as the coolant temperature adjustment control for changing the coolant temperature flowing into the core, the coolant temperature flowing into the core can be changed stepwise or gradually. When increasing the output of the core, the coolant temperature at the core inlet can be lowered stepwise or gradually, contrary to the above control example.

The reactivity application mechanism of the present embodiment is formed such that the temperature adjustment factor for the coolant becomes a negative value having a large absolute value when the interval adjusting member expands or contracts due to the temperature change of the coolant. ing. The reactivity application mechanism is not limited to this form, and any mechanism to which reactivity capable of changing the output of the core can be applied. For example, the reactivity application mechanism preferably employs a coolant mainly composed of ²⁰⁸ Pb of lead isotopes in order to make the temperature coefficient related to the coolant a negative value having a larger absolute value.

  Lead is suitable as a coolant for fast reactors because of its large scattering cross section of fast neutrons and small capture cross section. Lead has four isotopes of lead 204, lead 206, lead 207, and lead 208. Among these isotopes, lead 208 has a smaller neutron capture cross section than other lead isotopes, and is therefore suitable as a coolant. Furthermore, lead 208 can have a more negative temperature coefficient for the coolant than other lead isotopes.

FIG. 13 shows a graph of the inelastic scattering cross section of the lead isotope. The horizontal axis and the vertical axis are shown on a logarithmic scale. The inelastic scattering cross section of each lead isotope has a predetermined threshold. For example, lead 204 and lead 206 have a threshold when the neutron energy is about 10 ⁶ eV. If it is larger than this threshold, the neutron is inelastically scattered and decelerated.

The neutron spectrum of the fast reactor has a peak at a neutron energy slightly lower than 10 ⁶ eV. For example, when lead 204 and lead 206 are used as the coolant, many neutrons are inelastically scattered by the coolant and decelerated. For this reason, when the coolant temperature rises and the coolant density decreases, the effect of slowing down the inelastic neutron scattering becomes very small. The neutron spectrum hardens and the reactivity changes to the positive side.

  On the other hand, when lead 208 is used as the coolant, the effect of inelastically scattering neutrons is smaller than that of lead 204 and the like because the neutron energy threshold of the inelastic scattering cross section is large. For this reason, even if the temperature of the coolant rises and the density of the coolant decreases, the effect of hardening the neutron spectrum can be made smaller than that of lead 204 or the like. The action of the reactivity shifting to the positive side can be made smaller than that of lead 204 or the like. For this reason, when lead 208 is used as the coolant, the temperature coefficient related to the coolant can be set to a more negative value than when other lead 204 or the like is used as the coolant.

  For this reason, it is preferable to employ a coolant mainly composed of lead 208 in which the content of lead 208 is increased by isotopic separation of lead or the like. Furthermore, it is preferable that almost all of the lead contained in the coolant is lead 208. With this configuration, the temperature coefficient related to the coolant can be set to a negative value having a larger absolute value. Further, the output of the core can be easily changed.

  The fuel in the present embodiment has been described by taking deteriorated uranium as an example of new fuel loaded in the core, but is not limited to this form, and at least one of natural uranium and deteriorated uranium is used to achieve CANDLE combustion be able to. Alternatively, the present invention can be applied to any fast neutron reactor capable of performing CANDLE combustion.

  In the present embodiment, the combustion part of the previous cycle is arranged above the new fuel part at the beginning of the operation cycle, but the present invention is not limited to this form, and the new fuel part is one of the combustion parts in the axial direction of the core. It can be arranged at either end. Furthermore, new fuel portions may be disposed on both sides of the combustion portion.

  Further, in the present embodiment, the portion that starts the initial combustion of the operation cycle uses the fuel disposed in the lower part of the core at the end of the operation cycle of the previous cycle. However, the portion that starts combustion at the early stage of the operation cycle may be formed so as to spontaneously generate neutrons. For example, a fuel containing a predetermined concentration of plutonium, enriched uranium, or the like may be disposed. Furthermore, combustion may be started by supplying neutrons from the outside.

  In the core in the present embodiment, the axial direction of the core is parallel to the vertical direction, but the present invention is not limited to this, and the axial direction of the core may be parallel to the horizontal direction. That is, the core in the present embodiment may be placed horizontally.

  In the present embodiment, the core of a nuclear reactor used for power generation equipment has been described as an example. However, the present invention is not limited to this embodiment, and the present invention can be applied to a nuclear reactor of any equipment. For example, the nuclear reactor of the present invention can be used as a power source for ships and the like.

(Embodiment 2)
Referring to FIG. 14, the reactor and power generation equipment in the second embodiment will be described. The structures of the nuclear reactor and power generation equipment in the present embodiment are the same as those in the first embodiment. In the present embodiment, the coolant flow rate adjustment control for changing the flow rate of the coolant flowing into the core is performed, thereby changing the reactivity applied to the core and changing the output of the core.

  With reference to FIG. 1, when the temperature of the coolant flowing into the core 10 is constant, the temperature of the coolant at the core outlet can be changed by changing the flow rate of the coolant flowing into the core 10. . In this case, the average temperature of the coolant in the core 10 changes. For example, the average value of the coolant temperature changes in the axial direction of the core from the core inlet to the core outlet. As a result, a positive or negative reactivity can be applied to the core 10.

  For example, the coolant temperature in the core 10 can be raised by reducing the flow rate of the coolant flowing into the core 10. Since the core of the nuclear reactor in the present embodiment has a temperature coefficient related to a negative coolant having a large absolute value, by increasing the coolant temperature in the core 10, negative reactivity with respect to the core 10 is increased. Can be applied. As a result, the output of the core 10 can be reduced. Further, by increasing the flow rate of the coolant flowing into the core 10, a positive reactivity can be applied to the core 10, and the output of the core 10 can be increased.

  In the present embodiment, the flow rate of the coolant flowing into the core 10 is changed by changing the output of the pump 41 that supplies the coolant to the core 10. In the present embodiment, even if the flow rate of the coolant flowing into the core 10 is changed, the load connected to the nuclear reactor is set so that the temperature of the coolant flowing into the core 10 becomes substantially constant. It is adjusted. That is, the generated power is adjusted.

  FIG. 14 shows a time chart of the coolant flow rate adjustment control in the present embodiment. FIG. 14 illustrates control for reducing the output of the core. FIG. 14 shows a case where the flow rate of the coolant flowing into the core is changed in a step shape by a solid line. Until time t1, steady operation is performed.

  At time t1, the flow rate of the coolant flowing into the core 10 is decreased stepwise. The coolant temperature at the core outlet temporarily rises because the flow rate of the coolant flowing through the core 10 decreases. The average temperature of the coolant in the core will also rise. The fuel temperature temporarily increases as the average temperature of the coolant increases. The fuel temperature shown in FIG. 14 indicates an average temperature in the core.

  In the core 10 according to the present embodiment, since the temperature coefficient related to the coolant is a negative value having a large absolute value, a negative reactivity is applied to the core 10 and the output of the core 10 is reduced. As the output of the core 10 decreases, the coolant temperature and fuel temperature at the core outlet decrease, and become substantially constant. The reactivity shifts to the positive side as the coolant temperature in the core decreases and the fuel temperature decreases, and returns to almost zero. That is, the core temporarily becomes subcritical and then returns to the critical state. The output of the core decreases from time t1 and becomes substantially constant at a predetermined output.

  As described above, the core of the nuclear reactor according to the present embodiment can reduce the output of the core by reducing the flow rate of the coolant supplied to the core.

  FIG. 14 shows a case where the flow rate of the coolant is gradually changed by a broken line. When the flow rate of the coolant is gradually changed, the reactivity of the core is kept at a substantially zero value. The power of the core can be reduced while the core is maintained in a substantially critical state. While gradually changing the coolant flow rate, the coolant temperature and fuel temperature at the core outlet also change gradually. Thus, even if the flow rate of the coolant flowing into the core is gradually changed, the output of the core can be changed.

  When increasing the output of the core, the flow rate of the coolant flowing into the core can be increased stepwise or gradually, contrary to the above control example.

  In this embodiment, the flow rate of the coolant flowing into the core is changed by changing the output of the pump that supplies the coolant to the core. The flow rate of the coolant flowing in can be changed. For example, a device for adjusting the flow rate of the coolant may be disposed inside the reactor vessel, or a device for adjusting the flow rate of the coolant may be disposed at the end of the fuel assembly.

  Other configurations, operations, effects, and the like are the same as those in the first embodiment, and thus description thereof will not be repeated here.

  The coolant temperature adjustment control of the first embodiment and the coolant flow rate adjustment control of the second embodiment can be performed in combination. For example, the coolant flow rate adjustment control can be performed as the auxiliary control during the period when the output of the core is changed using the coolant flow rate adjustment control as the main control.

  In the respective drawings described above, the same or corresponding parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. In the embodiment, the change shown in a claim is included.

DESCRIPTION OF SYMBOLS 1 Reactor 2 Intermediate heat exchanger 3 Steam generator 4 Turbine 5 Generator 6 Condenser 10 Core 11 New fuel part 12 Combustion part 13 The part which combustion advanced 21 Fuel assembly 22 Fuel rod 25a, 25b Support grid 31 Space | interval Adjustment plate 32 Assembly lower end support member 33 Assembly upper end support member 41 to 43 Pump 44 Flow rate adjustment valve 51, 52 Sodium

Claims (4)

A new fuel part of the new fuel is loaded, the is disposed on one side of the core in the axial direction of the new fuel part, and the reactor comprising the reactor core comprising a combustion unit for combusting the fuel to generate neutrons ,
An apparatus capable of adjusting a temperature of a coolant supplied to the nuclear reactor,
The new fuel includes at least one of natural uranium and degraded uranium,
The new fuel part absorbs neutrons generated in the combustion part by the new fuel and is transmuted to plutonium to change into the combustion part,
The combustion unit, the thermal output is produced the plutonium and fission, the by new fuel part is changed to the combustion section, toward the end of the initial operation cycle, the new fuel part while maintaining a substantially constant shape Move in the direction towards
The reactor, when the temperature of the coolant flowing through the reactor core is changed, includes the reaction of applying mechanism heat output can change reactivity of the reactor core is applied,
The reactivity application mechanism is arranged in a fuel body including a fuel rod or a fuel assembly and a region included in the combustion unit at an early stage of the operation cycle, and supports the plurality of fuel bodies to each other, and the fuel body An interval adjusting member for determining an interval between each other,
The spacing adjusting member is formed of a material that expands when the temperature rises,
In the nuclear reactor, when the temperature of the coolant in the core rises, the interval adjusting member expands, the interval between the fuel bodies is increased, and negative reactivity is applied,
By performing the coolant temperature adjustable the device coolant temperature adjustment control for changing the temperature of the coolant flowing into the core of a, characterized in that the thermal output of the reactor core is adjusted, Equipment equipped with a nuclear reactor . The facility including the nuclear reactor according to claim 1 , wherein the coolant is mainly composed of lead 208 of lead isotopes. With the flow rate adjustable pump of the coolant flowing into the core,
The reactor, when the flow rate of the coolant flowing into the core is changed, the temperature of the coolant flowing in the core is changed, the heat output can change reactivity of the reactor core is applied Is formed as
By performing the coolant flow adjustment control for changing the flow rate of the coolant flowing into the reactor core, characterized in that the thermal output of the reactor core is adjusted, installation comprising a nuclear reactor according to claim 1. A steam generator for generating steam by the heat generated in the reactor core,
A turbine steam generated in the steam generator is rotated is supplied,
The facility comprising the nuclear reactor according to claim 1, further comprising a generator connected to the turbine .

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