JP2021135263A - Core reactivity control device, core reactivity control method and nuclear reactor - Google Patents

Abstract

To solve various problems that a LEM is hard to handle since liquid lithium is chemically active and is expensive since concentration lithium is used, and use thereof generates tritium.SOLUTION: A reactor core reactivity control device 16 comprises: a liquid neutron absorber 20 formed of alloy containing indium or indium as a main component; a reservoir 21 storing the neutron absorber 20; and an introduction pipe 22 which extends from the reservoir 21 to the inside of a reactor core 10 and in which the neutron absorber 20 advances to the inside when the neutron absorber 20 thermally expands. Thus, an easy-to-handle reactor core reactivity control technique can be provided since the neutron absorber is chemically inactivate.SELECTED DRAWING: Figure 5

Description

Embodiments of the present invention relate to core reactivity control techniques.

The inventors are developing an ultra-small nuclear reactor and envision using a passive device as its core reactivity control device. As a passive core reactivity control device, LEM (Lithium Expansion Module) using liquid lithium as a neutron absorber has been proposed. This LEM utilizes the fact that liquid lithium expands due to the heat of the core. When the core output increases, the liquid lithium thermally expands and is inserted into the core to control the output. Therefore, autonomous core reactivity control is possible.

Japanese Patent No. 3113028

M. Kambe, et. Al., “Startup Sequence of RAPID-L Fast Reactor for Lunar Base Power System”, Proc. Space Nuclear Conference 2007, Boston, USA (2017) T. B. Massalski, et. Al., Binary Alloy Phase Diagrams, ASM International (1986)

LEM is cumbersome because liquid lithium is chemically active. Since concentrated lithium is used, it becomes expensive. There are various problems such as the generation of tritium due to use.

An embodiment of the present invention has been made in consideration of such circumstances, and an object of the present invention is to provide a core reactivity control technique in which the neutron absorber is chemically inert and easy to handle.

The core reactivity control device according to the embodiment of the present invention includes a liquid neutron absorber composed of indium or an alloy containing the indium as a main component, a reservoir accommodating the neutron absorber, and a reservoir to the core. It includes an introduction tube that extends to the inside and allows the neutron absorber to advance inside when the neutron absorber thermally expands.

Embodiments of the present invention provide a core reactivity control technique in which the neutron absorber is chemically inert and easy to handle.

Longitudinal side view showing the nuclear power generation system of this embodiment. Longitudinal side view showing a nuclear reactor. Cross-sectional plan view showing a nuclear reactor. Enlarged cross-sectional plan showing the reactor. The longitudinal side view which shows the core reactivity control apparatus of 1st Embodiment. A graph showing the neutron capture cross section of a nuclide. The graph which shows the binary phase diagram of the indium-gadolinium alloy. A graph showing the control rod value in each case. A graph showing the weight ratio dependence of gadolinium for control rod values. The flowchart which shows the core reactivity control method. Longitudinal side view showing the core reactivity control device of the second embodiment. 11A is a cross-sectional view taken along the line AA showing the introduction pipe of the second embodiment. Longitudinal side view showing the core reactivity control device of the third embodiment. FIG. 13 is a cross-sectional view taken along the line BB showing the introduction pipe of the third embodiment. The longitudinal side view which shows the core reactivity control apparatus of 4th Embodiment. FIG. 15 is a cross-sectional view taken along the line CC showing the introduction pipe of the fourth embodiment. The longitudinal side view which shows the core reactivity control apparatus of 5th Embodiment. Longitudinal side view showing the core reactivity control device of the sixth embodiment.

(First Embodiment)
Hereinafter, the core reactivity control device, the core reactivity control method, and the embodiment of the nuclear reactor will be described in detail with reference to the drawings. First, the core reactivity control device, the core reactivity control method, and the nuclear reactor of the first embodiment will be described with reference to FIGS. 1 to 10.

Reference numeral 1 in FIG. 1 is the nuclear power generation system of the present embodiment. The nuclear power generation system 1 includes a small nuclear reactor 2.

The nuclear power generation system 1 includes an above-ground container 3 installed on the ground and an underground container 4 installed underground. These can be loaded on a vehicle such as a trailer and transported to the installation site. That is, the reactor 2 has portability. The nuclear power generation system 1 of the present embodiment is an example of the embodiment of the nuclear reactor 2. The shape or size of the reactor 2 is not limited to this embodiment.

The ground container 3 houses a generator 5, a gas turbine 6, a regenerative heat exchanger 7, a radiator 8, and a compressor 9. The underground container 4 houses the reactor 2. The nuclear reactor 2 includes a core 10, a heat exchanger 11, a heat pipe 12, a core container 13, nuclear fuel 14, moderator 15, and a core reactivity control device 16. The core container 13 is a metal container that houses the core 10, the heat exchanger 11, and the heat pipe 12.

The core 10 and the heat exchanger 11 are connected by a plurality of heat pipes 12. The heat generated in the core 10 is conducted to the heat exchanger 11 via the heat pipe 12. The working gas (refrigerant) expands due to this heat and is sent to the gas turbine 6. This gas rotates the gas turbine 6. The gas turbine 6 is connected to the generator 5 via a rotating shaft, and power is generated by the generator 5 by the rotational force of the gas turbine 6.

The working gas that has passed through the gas turbine 6 is sent to the radiator 8 through the regenerative heat exchanger 7. The heat of the gas is released into the air by the radiator 8. The compressor 9 is connected to the gas turbine 6 by a rotating shaft, and the working gas is compressed by the rotational force of the gas turbine 6. Here, the working gas is compressed into a high-temperature and high-pressure semi-liquid state. This working gas passes through the regenerative heat exchanger 7 and is returned to the heat exchanger 11 of the reactor 2 again. By such a cycle, power is generated in the nuclear power generation system 1.

As shown in FIG. 2, a core 10 including a nuclear fuel 14 and a moderator 15 is provided inside the core container 13 of the reactor 2. The nuclear fuel 14 and the moderator 15 form a rod shape extending in the vertical direction. In the present embodiment, the plurality of nuclear fuels 14 and the plurality of moderators 15 are alternately arranged in the horizontal direction.

In FIG. 2, the configuration of the core 10 is simplified and shown in order to aid understanding. For example, the number of nuclear fuel 14 and moderator 15 is omitted.

The nuclear fuel 14 is a member that causes a fission chain reaction to generate energy. The nuclear fuel 14 contains uranium as a main nuclear fuel material. Nuclear fuel 14, for example, by concentrating the natural uranium, are enhanced as the content of U ²³⁵ is about 4% from 3%. Further, the nuclear fuel 14 may contain ^{Pu 239.} The nuclear fuel 14 may contain at least a sufficient amount of nuclear fuel material for operating the reactor 2.

The moderator 15 is a member that decelerates neutrons. The nuclear fuel 14 and the moderator 15 have a hexagonal shape in cross-sectional view (see FIG. 4).

The core 10 forms a columnar shape in which a plurality of nuclear fuels 14 and moderators 15 are bundled. The shape of the core 10 may be a rectangular parallelepiped (cube) or a cone.

As shown in FIG. 2, a plurality of heat pipes 12 (heat removing portions) are provided between the nuclear fuel 14 and the moderator 15, respectively, and extend from the core 10 to the heat exchanger 11.

The heat pipe 12 is a device that transfers heat using a working fluid (working fluid). The heat pipe 12 includes, for example, a pipe case made of a material having high thermal conductivity, a volatile working fluid enclosed in the pipe case, a cavity for moving the vaporized working fluid, and a pipe case. It is provided with a wick that is provided on the inner wall of the sill and forms a capillary structure.

Aluminum or copper is used for the pipe case and the wick. Further, as the working fluid, for example, liquid sodium is used. Further, an alternative CFC may be used as the working fluid. Further, other working fluids may be used.

When one end of this heat pipe is a high temperature part and the other end is a low temperature part, the high temperature part is heated and the low temperature part is cooled to evaporate the working fluid (absorb latent heat) and condense the working fluid (latent heat). Cycle) occurs to transfer heat.

For example, the working fluid of a liquid in a high temperature portion evaporates when heated, becomes a gas, passes through a cavity, and is moved to a low temperature portion. Then, the heat of the working fluid is taken away in the low temperature part, and it condenses and returns to the liquid. Further, the liquid of this working fluid is moved to the high temperature part through the wick by the capillary phenomenon. By repeating this phenomenon, heat is transferred from the high temperature part to the low temperature part.

In the present embodiment, the high temperature portions of the plurality of heat pipes 12 are arranged in the core 10, and the low temperature portions of the heat pipes 12 extending linearly from the core 10 are arranged in the heat exchanger 11. Then, the heat generated in the core 10 is transferred to the heat exchanger 11 by the heat pipe 12, and the working gas (refrigerant) is heated based on this heat.

The core 10 is provided with a plurality of core reactivity control devices 16 for controlling the fission reaction. These core reactivity control devices 16 are provided in close proximity to the nuclear fuel 14. The core reactivity control device 16 is a self-acting device that passively controls the reactivity according to the output of the core 10.

A safety rod 17 as a neutron absorber can be inserted into the central portion of the core 10. The safety rod 17 is a member inserted so that the nuclear fuel 14 does not cause a fission reaction before the start of the reactor 2. For example, when the reactor 2 is transported to the installation location, the safety rod 17 is inserted into the core 10. Further, when starting the reactor 2, the safety rod 17 is pulled out from the core 10.

An insertion portion 18 (hole) into which the safety rod 17 can be inserted into the core 10 is opened in the upper part of the core container 13. After the safety rod 17 is pulled out, the insertion portion 18 is closed with a predetermined lid.

Next, the structure of the core 10 will be described with reference to FIGS. 3 and 4. Although these figures are cross-sectional views, hatching showing the cross-sections is omitted for the sake of understanding.

An insertion space 19 into which the safety rod 17 is inserted is provided in the central portion of the core 10. Nuclear fuel 14 is arranged in a ring so as to surround the insertion space 19. Moderators 15 are arranged in a ring so as to surround these nuclear fuels 14. Further, the nuclear fuels 14 are arranged in a ring so as to surround the moderators 15. In this way, the annular row of the nuclear fuel 14 and the annular row of the moderator 15 are arranged alternately in the radial direction of the core 10. That is, the annular row of the nuclear fuel 14 and the annular row of the moderator 15 are arranged concentrically.

The heat pipe 12 has a flat plate shape in cross-sectional view. The side surface of the nuclear fuel 14 is cut out, and each heat pipe 12 is arranged in the vicinity of the nuclear fuel 14.

Next, the core reactivity control device 16 of the first embodiment will be described with reference to FIG. Note that FIG. 5 is shown as a conceptual diagram of the core reactivity control device 16 in order to aid understanding.

The core reactivity control device 16 includes a liquid neutron absorber 20 composed of indium or an alloy containing indium as a main component, a reservoir 21 containing the neutron absorber, and neutrons extending from the reservoir 21 to the inside of the core. The neutron absorber 20 includes an introduction tube 22 that advances inside when the absorber 20 thermally expands.

The lower end of the introduction pipe 22 is connected to the upper end of the reservoir 21. Then, the inside of the reservoir 21 and the inside of the introduction pipe 22 are communicated with each other. That is, the liquid neutron absorber 20 contained in the reservoir 21 can enter and exit the introduction pipe 22. The neutron absorber 20 is guided by the introduction pipe 22 and advances to the inside of the core 10 or recedes from the inside of the core 10.

The reservoir 21 is provided at a position below the core 10. The introduction pipe 22 extends upward from the reservoir 21. The introduction pipe 22 is inserted inside the core 10 and extends above the core 10. The introduction pipe 22 is provided close to the nuclear fuel 14 (see FIG. 4).

For example, one core 10 is provided with 24 core reactivity control devices 16. The introduction pipes 22 provided inside the core 10 may be arranged in a circular shape along the circumferential direction of the core 10. Further, the introduction pipe 22 may be arranged between the annular row of the nuclear fuel 14 and the annular row of the moderator 15. Further, the rows of the introduction pipes 22 may be arranged concentrically.

The introduction pipe 22 may be provided between the nuclear fuel 14s, between the nuclear fuel 14 and the moderator 15, or between the nuclear fuel 14 and the heat pipe 12. It may be provided between the moderator 15 and the heat pipe 12.

The introduction pipe 22 is a member having a circular shape in a cross-sectional view. The core 10 is provided with a through hole into which the introduction pipe 22 is inserted. The introduction pipe 22 may have an elliptical shape or a quadrangular shape in cross-sectional view.

Further, the introduction pipe 22 is a member that extends linearly from the reservoir 21. The introduction pipe 22 may have a shape that allows the liquid neutron absorber 20 to flow inside, and may be bent or curved in the middle. That is, the shape of the introduction pipe 22 is not particularly limited because various shapes can be considered. The portion of the introduction pipe 22 in which the neutron absorber 20 does not enter may be filled with a predetermined gas or may be in a vacuum.

When the output of the core 10 increases and the amount of heat generated increases, the heat is transferred to the liquid neutron absorber 20 inside the reservoir 21 or the introduction pipe 22. This heat raises the temperature of the neutron absorber 20. Then, the neutron absorber 20 is thermally expanded. Here, as the volume of the neutron absorber 20 increases, the neutron absorber 20 travels inside the introduction pipe 22.

When the neutron absorber 20 advances along the introduction pipe 22 and its liquid level rises, the neutrons radiated from the core 10 are absorbed by the neutron absorber 20. Then, the output of the core 10 is reduced, and the amount of heat generated is also reduced. Therefore, the temperature of the neutron absorber 20 drops. Then, the neutron absorber 20 is shrunk. Here, when the volume of the neutron absorber 20 is reduced, the neutron absorber 20 retracts inside the introduction pipe 22.

When the neutron absorber 20 recedes along the introduction pipe 22 and its liquid level drops, the neutron absorber 20 also reduces the neutron absorption rate, so that the output of the core 10 is increased again.

That is, the fission reaction is reduced when the neutron absorber 20 advances to the inside of the core 10 due to thermal expansion, and the fission reaction becomes active when the neutron absorber 20 recedes from the inside of the core 10 due to contraction. .. By repeating such an action, the reactivity is passively controlled according to the output of the core 10.

Various modes are conceivable in which the heat of the core 10 is conducted to the neutron absorber 20. For example, the heat of the core 10 may be conducted to the neutron absorber 20 via the introduction pipe 22. Further, the neutron absorber 20 may be heated by the radiant heat of the core 10.

Further, the core reactivity control device 16 may include a heat transport unit that transports heat from the core 10 to the reservoir 21. In this way, the heat of the core 10 can be transported to the neutron absorber 20 inside the reservoir 21 for heating.

Various forms of the heat transport unit can be considered. For example, the core container 23 accommodating the core 10 may be in contact with the reservoir 21, and heat may be conducted to the reservoir 21 through the core container 23 to heat the neutron absorber 20 inside the reservoir 21. That is, the core container 23 accommodating the core 10 may form the heat transport unit. Further, members other than the core container 23 may form the heat transport unit.

In the core reactivity control device 16, the neutron absorber 20 used is chemically inert, does not require isotope concentration, does not generate tritium, and has an appropriate melting point at a relatively low temperature. Therefore, characteristics such as a sufficiently large neutron absorption cross section are desired.

In the prior art, lithium with isotope enrichment was used as the liquid neutron absorber, but in the present embodiment, only indium or an indium-gadolinium alloy is used as the liquid neutron absorber 20. ing. In this way, the core reactivity control device 16 is chemically stable as compared with lithium and hardly generates tritium.

Further, the indium or an alloy containing indium as a main component used as the neutron absorber 20 has a melting point of 400 ° C. or lower. In addition, it has a high neutron absorption cross section.

The neutron absorber 20 is preferably an indium-gadolinium alloy. In this way, the neutron absorption rate can be improved. In the present embodiment, the weight ratio of gadolinium contained in the neutron absorber 20 is within the range of 0.1% or more and 1.0% or less. When the weight ratio of gadolinium is 0.1% or more, the neutron absorption rate can be sufficiently improved. Further, even if the weight ratio of gadolinium is 1% or less, neutrons can be sufficiently absorbed, so that the amount of gadolinium used can be reduced.

FIG. 6 is a graph showing the neutron capture cross sections of lithium (Li), gadolinium (Gd), and indium (In). The horizontal axis shows the neutron capture cross section, and the vertical axis shows the incident energy. Graph G1 shows the neutron capture cross section of Li-6. Graph G2 shows the neutron capture cross section of Gd-155. Graph G3 shows the neutron capture cross section of Gd-157. Graph G4 shows the neutron capture cross section of In-115. Graph G5 shows the neutron capture cross section of In-113.

Focusing on the region H having a high fission reaction rate, it can be seen that the neutron capture cross sections of Gd-155 and Gd-157 are about two orders of magnitude larger than that of Li-6. Therefore, sufficient control rod value can be expected if a small amount of gadolinium is present.

It can also be seen that the neutron capture cross sections of Gd-155 and Gd-157 have higher neutron capture cross sections than In-115 and In-113. Since 95% of the isotope ratio of natural indium is In-115, the neutron absorption effect of indium itself can be expected.

FIG. 7 is a graph showing a binary phase diagram of an indium-gadolinium alloy (see Non-Patent Document 2). The horizontal axis shows the atomic concentration ratio (upper row) and weight ratio (lower row) of gadolinium. The vertical axis indicates the temperature at which the melting point is reached. It is shown that the region L in the graph is the liquid phase.

Focusing on the point Q in the graph, it can be seen that when the weight ratio of gadolinium is 1% or less, the melting point is 400 ° C. or less. Many of the design proposals for next-generation nuclear reactors have an operating temperature of 500 ° C. or higher, and if the melting point is 400 ° C. or lower, they can be sufficiently applied as the core reactivity control device 16.

FIG. 8 is a graph showing control rod values. The vertical axis shows the control rod value. A graph of lithium, a graph of indium alone, a graph of an In-Gd alloy with a weight ratio of gadolinium of 0.5%, a graph of an In-Gd alloy with a weight ratio of gadolinium of 1.0%, and a graph of gadolinium. The graph of the In-Gd alloy of 1.5% is shown.

FIG. 9 is a graph showing the weight ratio dependence of the control rod value of gadolinium. The vertical axis shows the control rod value. The control rod values when the weight ratio of gadolinium is 0%, 0.5%, 1.0%, and 1.5% are shown.

With reference to these graphs, it can be seen that the use of the indium-gadolinium alloy as the neutron absorber 20 has more than double the control rod value as compared with the case of using lithium. Further, it can be seen that the value of the control rod is increased even with indium alone as compared with the case where lithium is used.

Furthermore, it can be seen that when the gadolinium weight ratio exceeds 1%, there is almost no effect of increasing the control rod value. It is considered that this is because gadolinium has a high neutron absorption cross section and therefore has a high shielding effect (spatial self-shielding effect) of gadolinium itself.

As shown in the graph of FIG. 7 above, the melting point of the indium-gadolinium alloy increases sharply with the weight ratio of gadolinium. When it is assumed that the gadolinium is used at a melting point as low as possible, even if the weight ratio of gadolinium is higher than 1%, the melting point is only increased and the control rod value is not increased. Therefore, when used in the neutron absorber 20, the weight ratio of gadolinium is preferably 1% or less.

Next, the core reactivity control method executed by the core reactivity control device 16 will be described with reference to the flowchart of FIG. The action and effect passively generated by the operation of the core reactivity control device 16 will be described. The above drawings will be referred to as appropriate.

First, in step S11, the temperature of the core 10 rises as the output of the core 10 rises. The heat of the core 10 is transferred to the neutron absorber 20 of the core reactivity control device 16.

In the next step S12, the temperature of the neutron absorber 20 is increased by the heat of the core 10. Here, the neutron absorber 20 is thermally expanded.

In the next step S13, the volume of the neutron absorber 20 increases due to thermal expansion, and the neutron absorber 20 advances inside the introduction pipe 22.

In the next step S14, when the liquid level of the neutron absorber 20 is raised, the neutrons emitted from the core 10 are absorbed by the neutron absorber 20. That is, the neutron absorber 20 is inserted into the core 10 and applies a negative reactivity to the core 10.

In the next step S15, the neutrons are absorbed by the neutron absorber 20, so that the output of the core 10 decreases, and the temperature of the core 10 decreases accordingly.

In the next step S16, as the temperature of the core 10 decreases, the amount of heat given from the core 10 to the neutron absorber 20 also decreases. Therefore, the temperature of the neutron absorber 20 decreases. Here, the neutron absorber 20 is shrunk.

In the next step S17, when the volume of the neutron absorber 20 is reduced, the neutron absorber 20 retracts inside the introduction pipe 22. When the liquid level of the neutron absorbing material 20 drops, the neutron absorbing material 20 also reduces the neutron absorption rate. That is, the neutron absorber 20 is pulled out from the core 10 and applies a positive reactivity to the core 10.

Then, the output of the core 10 will increase again. By repeating these steps, the reactivity of the core 10 can be maintained in a constant state by utilizing the thermal expansion of the neutron absorber 20.

(Second Embodiment)
Next, the core reactivity control device 16A, the core reactivity control method, and the nuclear reactor of the second embodiment will be described with reference to FIGS. 11 to 12. The same components as those shown in the above-described embodiment are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIGS. 11 and 12, the introduction pipe 22A of the second embodiment is provided with a traveling portion 24 in which the neutron absorbing material 20 advances along the inner peripheral edge, and neutron absorbing along the central axis. An exclusion unit 25 for removing the material 20 is provided.

The traveling portion 24 is a space in which the neutron absorber 20 can flow. The exclusion portion 25 is a rod-shaped member extending from the introduction pipe 22A to the reservoir 21. The exclusion unit 25 may be a solid member or a member having a hollow inside. The presence of the exclusion portion 25 can reduce the volume of the neutron absorber 20 inside the introduction pipe 22A. In this way, the neutron absorber 20 can be removed from the center of the introduction tube 22A that does not contribute to the absorption of neutrons, so that the amount of the neutron absorber 20 used can be reduced.

Further, the exclusion portion 25 is provided at a central portion away from the inner peripheral surface of the introduction pipe 22A. Further, a part of the exclusion portion 25 may be connected to the inner peripheral surface of the introduction pipe 22A.

When trying to secure the stroke amount (length) in which the neutron absorber 20 advances along the introduction pipe 22A, when the exclusion unit 25 is provided, it is compared with the case where the exclusion unit 25 is not provided. , The amount of expansion of the volume required for the neutron absorber 20 can be small. Therefore, the volume of the reservoir 21 can be reduced, or the stroke amount of the neutron absorber 20 at the same temperature change amount can be increased.

When the neutron absorber 20 enters the introduction pipe 22A, neutrons hardly reach the central portion away from the inner peripheral surface of the introduction pipe 22A due to the shielding effect (spatial self-shielding effect) of the neutron absorbing material 20. Therefore, even if the exclusion portion 25 is provided in the central portion of the introduction pipe 22A, there is almost no effect on the control rod value.

(Third Embodiment)
Next, the core reactivity control device 16B, the core reactivity control method, and the nuclear reactor of the third embodiment will be described with reference to FIGS. 13 to 14. The same components as those shown in the above-described embodiment are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIGS. 13 and 14, the introduction pipe 22B of the third embodiment has a flat oval shape in a cross-sectional view. The introduction pipe 22B may have a rectangular shape. In this way, the area where the neutrons hit the neutron absorber 20 that has entered the introduction tube 22B can be increased.

The introduction pipe 22B is provided with a traveling portion 24B in which the neutron absorbing material 20 advances along the inner peripheral edge, and an exclusion portion 25B for eliminating the neutron absorbing material 20 along the central portion. .. By doing so, the amount of the neutron absorber 20 used can be reduced. Further, the exclusion portion 25B also has a flat oval shape in cross-sectional view according to the shape of the introduction pipe 22B.

(Fourth Embodiment)
Next, the core reactivity control device 16C, the core reactivity control method, and the nuclear reactor of the fourth embodiment will be described with reference to FIGS. 15 to 16. The same components as those shown in the above-described embodiment are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIGS. 15 and 16, the introduction tube 22C of the fourth embodiment is formed by bundling a plurality of thin tubes 26. In this way, the surface tension of the neutron absorber can be utilized to facilitate penetration into the introduction pipe 22C. The plurality of thin tubes 26 are arranged side by side in the circumferential direction so as to form an annular shape in a cross-sectional view. A space portion 27 in which the neutron absorber 20 does not enter is provided in the central portion of the ring.

The lower end of each capillary 26 is connected to the upper end of the reservoir 21. Then, the inside of the reservoir 21 and the inside of each thin tube 26 are communicated with each other. That is, the liquid neutron absorber 20 contained in the reservoir 21 can enter and exit the thin tube 26. The neutron absorber 20 is guided by each of the thin tubes 26 and proceeds to the inside of the core 10 or recedes from the inside of the core 10. In the fourth embodiment, each thin tube 26 constitutes a traveling portion, and a space portion 27 in the center thereof constitutes an exclusion portion.

The neutron absorber 20 proceeds in a state of being dispersed in each of the thin tubes 26. In this way, since the introduction tube 22C, which is the flow path of the neutron absorber 20, is composed of a plurality of thin tubes 26, even if a part of the thin tubes 26 breaks, the soundness of the other thin tubes 26 can be maintained. Can be kept.

(Fifth Embodiment)
Next, the core reactivity control device 16D, the core reactivity control method, and the nuclear reactor of the fifth embodiment will be described with reference to FIG. The same components as those shown in the above-described embodiment are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIG. 17, the core reactivity control device 16D of the fifth embodiment is provided in the reservoir 21 and causes a nuclear reaction with neutrons radiated from the core 10 to heat the neutron absorber 20. 28 is provided. In this way, the neutron absorber can be heated according to the output of the core 10.

In the fifth embodiment, when the output of the core 10 increases, the temperature of the reservoir 21 can be rapidly increased to increase the response speed to the output fluctuation of the core reactivity control device 16D.

For example, when the output of the core 10 increases, the number of neutrons leaking from the core 10 increases, and the neutrons cause a fission reaction in the heating nuclear fuel 28. Then, the neutron absorber 20 is heated by the heat generated from the heating nuclear fuel 28, and the temperature rises. Here, when the volume increases due to the thermal expansion of the neutron absorber 20, the neutron absorber 20 advances inside the introduction pipe 22.

When the output of the core 10 decreases, the number of neutrons emitted from the core 10 also decreases. Therefore, the fission reaction of the heating nuclear fuel 28 is suppressed, and the temperature of the neutron absorber 20 is lowered. Here, when the volume is reduced by the contraction of the neutron absorber 20, the neutron absorber 20 retracts inside the introduction pipe 22.

In this fifth embodiment, the core vessel 23 is made of a material that allows neutrons to pass through. Further, the core 10 and the reservoir 21 may be insulated.

The heating nuclear fuel 28 is provided in contact with the outer peripheral surface on the upper side of the reservoir 21. In this way, the neutrons emitted from the core 10 are not blocked by the neutron absorber 20 and hit the nuclear fuel 28 for heating. Therefore, a nuclear reaction can occur in the heating nuclear fuel 28 according to the output of the core 10.

(Sixth Embodiment)
Next, the core reactivity control device 16E, the core reactivity control method, and the nuclear reactor of the sixth embodiment will be described with reference to FIG. The same components as those shown in the above-described embodiment are designated by the same reference numerals, and duplicate description will be omitted.

The core reactivity control device 16E of the sixth embodiment includes a heating heat pipe 29 as a heat transport unit that transports heat from the core 10 to the reservoir 21. In this way, heat can be efficiently transported from the core 10 to the reservoir 21. The temperature of the reservoir 21 can be rapidly raised as the temperature of the core 10 rises.

The heating heat pipe 29 extends from the core 10 to the reservoir 21. The heating heat pipe 29 is in contact with the outer peripheral surface of the reservoir 21. The end of the heating heat pipe 29 may be inserted inside the reservoir 21.

The core reactivity control device 16E of the sixth embodiment may include the nuclear fuel 28 for heating of the fifth embodiment.

The core reactivity control device, the core reactivity control method, and the nuclear reactor according to the present embodiment have been described based on the first to sixth embodiments, but the configurations applied in any one embodiment may be used in other embodiments. It may be applied to embodiments, or the configurations applied in each embodiment may be combined.

Although the flowchart of the present embodiment illustrates a mode in which each step is executed in series, the context of each step is not necessarily fixed, and even if the context of some steps is exchanged. good. Also, some steps may be executed in parallel with other steps.

In the present embodiment, the core 10 is cooled by using the heat pipe 12, but the cooling method of the core 10 is not limited to the heat pipe 12 because various cooling methods can be considered.

In the present embodiment, the heat pipe 12 in which the working fluid is sealed is illustrated as a device for transferring heat from the core 10, but a heat pipe 12 (heat removal unit) of another embodiment may be used. For example, a solid heat pipe having no internal cavity may be used. Further, heat may be transferred from the core by using a heat pump type heat removing device.

In the present embodiment, an indium-gadolinium alloy is used as an alloy containing indium as a main component constituting the liquid neutron absorber 20, but other embodiments may be used. For example, the neutron absorber 20 may be composed of an alloy in which a metal other than gadolinium such as cadmium, silver, gold, europium, and hafnium is added to indium. The neutron absorber 20 is not limited because various compositions can be considered.

In the present embodiment, the liquid neutron absorber 20 is made of indium or an alloy containing indium as a main component, but other embodiments may be used. For example, lithium may be used as the liquid neutron absorber 20.

According to at least one embodiment described above, the neutron absorber is chemically inert and easy to handle by providing the liquid neutron absorber composed of indium or an alloy containing indium as a main component. It can be a reactivity control technique.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

1 ... Nuclear power generation system, 2 ... Reactor, 3 ... Ground container, 4 ... Underground container, 5 ... Generator, 6 ... Gas turbine, 7 ... Regenerative heat exchanger, 8 ... Radiator, 9 ... Compressor, 10 ... Core, 11 ... Heat exchanger, 12 ... Heat pipe, 13 ... Core container, 14 ... Nuclear fuel, 15 ... Reducer, 16 (16A, 16B, 16C, 16D, 16E) ... Core reaction control device, 17 ... Safety rod, 18 ... Insertion part, 19 ... Insertion space, 20 ... Neutral absorber, 21 ... Reservoir, 22 (22A, 22B, 22C) ... Introduction tube, 23 ... Core vessel, 24 (24B) ... Progressive part, 25 (25B) ... Exclusion Part, 26 ... Thin tube, 27 ... Space part, 28 ... Nuclear fuel for heating, 29 ... Heat pipe for heating.

Claims (11)

A liquid neutron absorber composed of indium or an alloy containing indium as a main component,
A reservoir accommodating the neutron absorber and
An introduction pipe that extends from the reservoir to the inside of the core, and when the neutron absorber thermally expands, the neutron absorber advances inside.
To prepare
Core reactivity control device. The neutron absorber is an indium-gadolinium alloy.
The core reactivity control device according to claim 1. The weight ratio of gadolinium contained in the neutron absorber is 1% or less.
The core reactivity control device according to claim 2. The introduction pipe is provided with a traveling portion in which the neutron absorbing material advances along the inner peripheral edge, and is provided with an exclusion portion for eliminating the neutron absorbing material along the central axis.
The core reactivity control device according to any one of claims 1 to 3. The introduction tube has a flat shape in cross-sectional view.
The core reactivity control device according to any one of claims 1 to 4. The introduction tube is a bundle of a plurality of thin tubes.
The core reactivity control device according to any one of claims 1 to 5. The reservoir is provided with a nuclear fuel for heating, which is provided in the reservoir and causes a nuclear reaction with neutrons radiated from the core to heat the neutron absorber.
The core reactivity control device according to any one of claims 1 to 6. A heat transport unit for transporting heat from the core to the reservoir is provided.
The core reactivity control device according to any one of claims 1 to 7. The heat transport unit is a heat pipe.
The core reactivity control device according to claim 8. When the liquid neutron absorber contained in the reservoir or composed of the alloy containing the indium as a main component thermally expands, the neutron absorber extends inside the introduction pipe extending from the reservoir to the inside of the core. Including steps to proceed,
Core reactivity control method. A liquid neutron absorber composed of indium or an alloy containing indium as a main component,
A reservoir accommodating the neutron absorber and
An introduction pipe that extends from the reservoir to the inside of the core, and when the neutron absorber thermally expands, the neutron absorber advances inside.
A core reactivity control device is provided.
Reactor.

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