JP7374844B2 - Nuclear reactors and reactor heat removal methods - Google Patents

Description

Embodiments of the present invention relate to heat removal technology for a nuclear reactor.

The inventors are developing a small nuclear reactor that uses heat pipes as elements to cool the reactor core. Such nuclear reactors use heat pipes for heat removal, so the temperature of the nuclear fuel and moderator is low near the surface of the heat pipe, and the temperature increases as they move away from the surface of the heat pipe. Furthermore, when a metal hydride moderator is used, the temperature of the moderator becomes a constraint on the core temperature, making efficient operation impossible. Therefore, there is a known technique for suppressing the temperature of the entire reactor core by creating a peak output around the heat pipes. Furthermore, a technology is known in which nuclear fuel and moderator are thermally separated using a heat pipe. However, in such a technique, the nuclear fuel and the moderator must be arranged alternately in the radial direction of the reactor core, which creates constraints on the layout of the reactor core. Furthermore, when a heat pipe is disposed in the fuel region without using a moderator, a gap is created between the heat pipe and the nuclear fuel, which becomes a factor in increasing contact thermal resistance.

Patent No. 6633471

Rei Kimura, Tetu Suzuki, Kazuhito Asano, Chikako Iwaki, Hideki Horie, “The conceptual design of heat-pipe cooled and calcium-hydride moderated vSMR”, 013, ICAPP2019, Juan-les-pins, France, May 2019 (2019) David I. Poston, Marc Gibson and Patrick McClure, “KILOPOWER reactors for potential space exploration missions”, Nuclear Emerging Technologies for Space, Richland, WA, Feb 2019 (2019) Rei Kimura, Satoshi Wada, “Temperature Reactivity Control of Calcium-Hydride-Moderated Small Reactor Core with Poison Nuclides”, Nucl. Sci. Eng., 193 (9), 1013-1022, (2019)

In a reactor core equipped with heat pipes as cooling elements, it is desirable to place nuclear fuel and moderators in a highly independent manner for each heat pipe, while also easing restrictions on core temperature in order to reduce constraints on the core layout. There is. In particular, there is a need to increase core output by suppressing uneven temperature increases within the core.

The embodiments of the present invention have been made in consideration of such circumstances, and the purpose is to provide a heat removal technology for a nuclear reactor that can improve the heat removal efficiency by heat pipes and improve the output of the reactor core. do.

A nuclear reactor according to an embodiment of the present invention includes: a rod-shaped main heat pipe that transfers heat within the reactor core to the outside of the reactor core; and a nuclear fuel unit that is arranged around the main heat pipe and generates heat through a nuclear fission reaction. a moderator unit arranged around the main heat pipe and arranged adjacent to the nuclear fuel unit along the axial direction of the main heat pipe and moderating neutrons; and between the nuclear fuel unit and the moderator unit. a heat diffusion layer that is provided in the nuclear fuel unit and moves heat of the nuclear fuel unit toward the main heat pipe.

Embodiments of the present invention provide a heat removal technique for a nuclear reactor that can improve the heat removal efficiency by heat pipes and improve the output of the reactor core.

FIG. 1 is a sectional view showing a nuclear power generation system of this embodiment. A cross-sectional view showing the reactor core. FIG. 2 is an exploded perspective view showing a nuclear fuel unit and a moderator unit. FIG. 3 is a perspective view showing a nuclear fuel unit and a moderator unit. An exploded sectional view showing a nuclear fuel unit and a moderator unit. A sectional view showing a nuclear fuel unit and a moderator unit. Conceptual diagram showing a nuclear fuel unit and a heat diffusion layer. A conceptual diagram showing a graphite sheet. FIG. 3 is a perspective view showing a heat diffusion layer of Modification Example 1; FIG. 7 is a side view showing a heat diffusion layer of Modification Example 1. FIG. 7 is a conceptual diagram showing a heat insulating section of Modification 2. FIG. 7 is a conceptual diagram showing a metal foil of Modification 3. FIG. 7 is a sectional view showing a nuclear fuel unit and a moderator unit of Modification 4. A graph showing the relationship between operating temperature and temperature reactivity coefficient. Flowchart showing a method for removing heat from a nuclear reactor.

Hereinafter, embodiments of a nuclear reactor and a method for removing heat from a nuclear reactor will be described in detail with reference to the drawings.

Reference numeral 1 in FIG. 1 is a nuclear power generation system of this embodiment. Note that in the drawings, the vertical direction is defined to facilitate understanding. However, this nuclear power generation system 1 does not need to distinguish between the upper and lower directions (vertical direction), and can be used, for example, in outer space. In other words, this nuclear power generation system 1 is a device that is not affected by gravity. Note that the nuclear power generation system 1 can be used not only in outer space but also on the moon, Mars, the polar regions of the earth, and the like. Further, to aid understanding, hatching indicating a cross section may be omitted.

The nuclear power generation system 1 includes a nuclear reactor 2, a power generation device 3, and a radiator 4. In this embodiment, a power generation device 3 and a radiator 4 are provided in the upper part of the nuclear reactor 2. A power generation device 3 generates power using the heat generated in the nuclear reactor 2. Then, the radiator 4 releases the heat used for power generation by the power generation device 3 to the outside.

The nuclear reactor 2 includes a reactor core 5, a neutron reflecting section 6, and a shielding section 7. Nuclear fuel is arranged in the reactor core 5. The overall shape of this core 5 is, for example, a cylindrical shape. Note that the overall shape of the core 5 may be a rectangular parallelepiped or a cone. In this embodiment, the cylindrical axis of the core 5 extends in the vertical direction.

The reactor core 5 is covered with a neutron reflecting section 6. The neutron reflecting section 6 is made of a material that reflects neutrons emitted from nuclear fuel. The neutrons are reflected by the neutron reflector 6 and return to the inside of the reactor core 5 to promote nuclear fission reaction. Note that the neutron reflecting section 6 also serves as a container that houses the reactor core 5.

The neutron reflecting section 6 is covered by a shielding section 7. The shielding part 7 shields the radiation generated in the reactor core 5 and prevents the radiation from leaking to the outside of the nuclear reactor 2. The shielding section 7 also serves as a container that houses the neutron reflecting section 6.

An insertion space is provided in the center of the core 5 into which one safety rod 8 as a neutron absorber can be inserted. The safety rod 8 is a member inserted before the nuclear reactor 2 is started to prevent nuclear fission reactions from occurring in the nuclear fuel. For example, when transporting the nuclear reactor 2 to an installation location, the safety rod 8 is inserted into the reactor core 5. Moreover, when starting up the nuclear reactor 2, the safety rod 8 is pulled out from the reactor core 5.

Although not particularly illustrated, the nuclear reactor 2 includes a plurality of control rods as neutron absorbers that control nuclear fission reactions. Inserting these control rods into the reactor core 5 suppresses the nuclear fission reaction, and withdrawing the control rods from the reactor core 5 activates the nuclear fission reaction.

The reactor core 5 is provided with a plurality of main heat pipes 9. The main heat pipe 9 is a rod-shaped device that extends in the vertical direction. The main heat pipes 9 are arranged parallel to each other. Further, the main heat pipes 9 are arranged in the radial direction and the circumferential direction of the reactor core 5. Note that the rows of main heat pipes 9 arranged in the circumferential direction are arranged concentrically.

These main heat pipes 9 extend upward from the core 5 in a straight line and are connected to the power generation device 3. These main heat pipes 9 transfer heat generated by the nuclear fuel in the reactor core 5 to the power generation device 3.

The power generation device 3 generates power based on the heat of the reactor core 5 carried by the main heat pipe 9. This power generation device 3 includes, for example, a thermoelectric conversion element. The power generation device 3 generates power using the temperature difference between the heat of the reactor core 5 and the outside. Note that the power generation device 3 may generate power in other ways. For example, a predetermined liquid may be vaporized using the heat of the reactor core 5, and the vapor may drive a turbine to generate electricity. Alternatively, the heat of the reactor core 5 may be used to drive a Stirling engine to generate electricity.

The main heat pipe 9 is a device that transfers heat using a working fluid. The main heat pipe 9 includes, for example, a pipe case made of a material with high thermal conductivity, a volatile working fluid sealed in the pipe case, a cavity for moving the vaporized working fluid, and a pipe case. The wick is provided on the inner wall of the wick and has a capillary structure.

Note that aluminum, copper, or the like is used for the pipe case and the wick. Furthermore, liquid sodium, for example, is used as the working fluid. Further, alternative CFCs may be used as the working fluid. Furthermore, other substances may also be used as the working fluid.

When one end of the main heat pipe 9 is a high temperature section and the other end is a low temperature section, by heating the high temperature section and cooling the low temperature section, evaporation of the working fluid (absorption of latent heat) and condensation of the working fluid (absorption of latent heat) can be achieved. A cycle of latent heat release) occurs to transfer heat.

For example, the liquid working fluid in the hot section is heated, evaporates, and moves through the cavity to the cold section as a gas. Then, heat is removed from the working fluid in the low-temperature section and it condenses back to liquid. Furthermore, this liquid working fluid is moved through the wick to the hot section by capillary action. By repeating this phenomenon, heat is transferred from the high temperature area to the low temperature area.

In this embodiment, the high-temperature parts of the plurality of main heat pipes 9 are arranged in the reactor core 5, and the low-temperature parts of the main heat pipes 9 are arranged in the power generation device 3. Then, the heat generated in the reactor core 5 is transferred to the power generation device 3 by the main heat pipe 9, and the working gas (refrigerant) is heated based on this heat.

As shown in FIG. 2, a plurality of main heat pipes 9 are provided in the reactor core 5. Note that, in this drawing, illustration of the neutron reflecting section 6 provided around the reactor core 5 is omitted to facilitate understanding.

The reactor core 5 is provided with a nuclear fuel unit 10, a moderator unit 11, and a thermal diffusion layer 12. In this embodiment, the nuclear fuel units 10 and the moderator units 11 are arranged alternately along the axial direction of the main heat pipe 9. Note that the heat diffusion layer 12 has a flat plate shape and is provided between the nuclear fuel unit 10 and the moderator unit 11. In this way, it becomes possible to have a flexible core layout while relaxing the core temperature constraints. In other words, design constraints are relaxed.

The nuclear fuel unit 10 provided in one main heat pipe 9 is adjacent to the nuclear fuel unit 10 provided in the other adjacent main heat pipe 9. Furthermore, the moderator unit 11 provided in one main heat pipe 9 is adjacent to the moderator unit 11 provided in the other adjacent main heat pipe 9.

In the reactor core 5, a layer in which nuclear fuel units 10 are arranged and a layer in which moderator units 11 are arranged are stacked in the vertical direction. Note that the nuclear fuel units 10 and the moderator units 11 may be arranged alternately between the main heat pipes 9 on one side and the main heat pipes 9 on the other side.

As shown in FIGS. 3 to 4, a nuclear fuel unit 10 and a moderator unit 11 are arranged so as to surround a main heat pipe 9 having a predetermined circular tube shape.

The nuclear fuel unit 10 and the moderator unit 11 of this embodiment have a hexagonal prism shape with a hole for passing the main heat pipe 9 along the central axis. That is, in the nuclear fuel unit 10 and the moderator unit, the shape of the cross section (planar view) perpendicular to the axis of the main heat pipe 9 is a regular hexagon. A reactor core 5 is formed by arranging a plurality of nuclear fuel units 10 or a plurality of moderator units 11 in a honeycomb shape (planar filling) in a plan view. Note that the cross-sectional shapes of the nuclear fuel unit 10 and the moderator unit may have other shapes as long as they can make the reactor core 5 critical. For example, it may be a triangle, a square, or a circle.

The nuclear fuel unit 10 generates heat through a nuclear fission reaction. The moderator unit 11 is arranged adjacent to the nuclear fuel unit 10 along the axial direction of the main heat pipe 9 and serves to moderate neutrons. The heat diffusion layer 12 moves the heat of the nuclear fuel unit 10 toward the main heat pipe 9.

The nuclear fuel unit 10 contains uranium as the main nuclear fuel material. The nuclear fuel unit 10 has, for example, enriched natural uranium to increase the ²³⁵ U content to about 3% to 4%. Further, the nuclear fuel unit 10 may include ²³⁹ Pu, ²⁴¹ Pu, ²⁴² Am, ²⁴³ Cm, ²⁴⁵ Cm, and the like. The nuclear fuel unit 10 may contain at least enough nuclear fuel material to operate the nuclear reactor 2. Further, various materials such as oxides of uranium or plutonium, silicides, carbides, nitrides, chlorides, fluorides, metals, alloys, etc. can be used as the material constituting the nuclear fuel unit 10.

One nuclear fuel unit 10 includes an HPPF 13 as a heat pipe peripheral fuel provided so as to surround the main heat pipe 9, and a main fuel section 14 provided so as to surround the HPPF 13.

The HPPF 13 has a cylindrical shape. The inner peripheral surface of this HPPF 13 contacts the outer peripheral surface of the main heat pipe 9. The main fuel part 14 occupies most of the volume and mass of the nuclear fuel unit 10, and has a regular hexagonal shape in plan view. Note that the volume ratio between the HPPF 13 and the main fuel section 14 can be various depending on the design conditions, so the volume ratio is not limited to this embodiment.

The nuclear fuel unit 10 includes a first nuclear fuel section containing fissile material at a first concentration, and a second nuclear fuel section disposed further from the main heat pipe 9 than the first nuclear fuel section and containing fissile material at a second concentration lower than the first concentration. 2 nuclear fuel sections. In this embodiment, the HPPF 13 serves as the first nuclear fuel section, and the main fuel section 14 serves as the second nuclear fuel section. When the concentration of fissile material contained in the nuclear fuel unit 10 is high, the density of heat generated by the nuclear fission reaction increases. In other words, the HPPF 13 has a higher heat generation density than the main fuel section 14.

As shown in FIGS. 5 and 6, the HPPF 13 serving as the first high-concentration nuclear fuel section is arranged to surround the main heat pipe 9. As shown in FIGS. Moreover, the main fuel part 14 as a low concentration second nuclear fuel part is arranged further away from the main heat pipe 9 than the HPPF 13 is. The main fuel part 14 is arranged to surround the HPPF 13. That is, the HPPF 13 is provided between the main fuel section 14 and the main heat pipe 9.

In this embodiment, the region where the HPPF 13 (first nuclear fuel section) is arranged constitutes a high reactivity fuel region, and the region where the main fuel section 14 (second nuclear fuel section) is arranged constitutes a low reactivity fuel region. . When the nuclear reactor 2 becomes critical and the fuel generates heat, the power density (calorific value) of the HPPF 13 becomes higher than the power density (calorific value) of the main fuel section 14 . This is due to the high concentration of fissile material. Since the HPPF 13 is closer to the main heat pipe 9 than the main fuel section 14, heat needs to pass through the HPPF 13 in order to transport heat from the main fuel section 14 to the main heat pipe 9.

In this embodiment, the concentration of fissile material in the main fuel part 14 is lower than that of the HPPF 13, and the output of the main fuel part 14 is made smaller than the output of the HPPF 13. Therefore, in the HPPF 13, even if the temperature difference between the surface in contact with the main heat pipe 9 and the surface in contact with the main fuel section 14 is reduced, a predetermined amount of heat can be transported to the main heat pipe 9.

If the output generated by the entire reactor 2 is the same, it is better to install the first nuclear fuel section with a higher concentration of fissile material than to provide the second nuclear fuel section with a lower concentration of fissile material near the main heat pipe 9. By providing it near the main heat pipe 9, the maximum temperature of the reactor core 5 can be suppressed. Therefore, uneven temperature rise inside the reactor core 5 can be suppressed, and the entire nuclear fuel can be sufficiently combusted. As a result, core power can be increased.

The moderator unit 11 is made of calcium hydride as a metal hydride. In this way, the neutrons can be efficiently slowed down, so the nuclear reactor 2 can be made smaller. Note that the moderator unit 11 may be formed only of metal hydride, or may contain a substance other than metal hydride. Moreover, the moderator unit 11 may be formed of ceramics that are difficult to thermally expand.

Note that the moderator unit 11 may be formed of a metal hydride other than calcium hydride. For example, the moderator unit 11 may be formed of a metal hydride such as yttrium hydride, lanthanum hydride, zirconium hydride, praseodymium hydride, or the like.

As shown in FIG. 3, the main fuel section 14 is divided into two members sandwiching the main heat pipe 9. Furthermore, the HPPF 13 is divided into two members sandwiching the main heat pipe 9. That is, the nuclear fuel unit 10, which has a regular hexagonal shape when viewed from above, is divided into parts with one diagonal line passing through the center as a boundary. In this way, the nuclear fuel unit 10 can be brought into close contact with the main heat pipe 9, making it easier for heat to be transferred from the nuclear fuel unit 10 to the main heat pipe.

For example, if the nuclear fuel unit 10 is not divided and only a hole is made for the main heat pipe 9 to pass through, the inner diameter of the hole needs to be larger than the diameter of the main heat pipe 9 in order to insert the main heat pipe 9. be. Therefore, there is a possibility that a gap may occur between the inner circumferential surface of the nuclear fuel unit 10 and the outer circumferential surface of the main heat pipe 9, resulting in an increase in contact thermal resistance. In contrast, in this embodiment, the nuclear fuel unit 10 is divided, so that the inner diameter of the hole can be made the same as the diameter of the main heat pipe 9. Therefore, the nuclear fuel unit 10 can be brought into close contact with the main heat pipe 9, and contact thermal resistance can be reduced.

Note that a fixing device (not shown) may be provided to fix the divided nuclear fuel units 10 to each other. Then, the nuclear fuel unit 10 is fixed with the main heat pipe 9 sandwiched therebetween. In this way, the nuclear fuel unit 10 can be brought into close contact with the main heat pipe 9 using the fixing device.

Further, the surface of the nuclear fuel unit 10 that comes into contact with the main heat pipe 9 has a shape that matches the outer surface of the main heat pipe 9. In this embodiment, the side surface of the main fuel part 14 that is in contact with the main heat pipe 9 is cut out in a semicircular shape, and a cylindrical HPPF 13 that is in contact with the outer surface of the main heat pipe 9 is provided in the cutout part. It is being In other words, the surface of the main fuel portion 14 that contacts the main heat pipe 9 has a shape that matches the outer surface of the main heat pipe 9. Furthermore, since the inner diameter of the HPPF 13 is the same as the outer diameter of the main heat pipe 9, the inner peripheral surface of the HPPF 13 has a shape that matches the outer peripheral surface of the main heat pipe 9. In this way, the contact thermal resistance between the nuclear fuel unit 10 and the main heat pipe 9 can be reduced.

Further, the moderator unit 11 is divided into two members sandwiching the main heat pipe 9. In other words, the moderator unit 11, which has a regular hexagonal shape in plan view, is divided into sections with one diagonal line passing through the center as a boundary. Furthermore, the surface of the moderator unit 11 that comes into contact with the main heat pipe 9 has a shape that matches the outer surface of the main heat pipe 9.

Note that a fixing device (not shown) may be provided to fix the divided moderator units 11 to each other. Then, the moderator unit 11 is fixed with the main heat pipe 9 sandwiched therebetween. In this way, the moderator unit 11 can be brought into close contact with the main heat pipe 9 using the fixing device.

Furthermore, the heat diffusion layer 12 is also divided into two members. Note that the heat diffusion layer 12 has the same area as the upper surface or lower surface of the nuclear fuel unit 10. That is, the heat diffusion layer 12 is in contact with both the HPPF 13 and the main fuel section 14. Further, the heat diffusion layer 12 has the same area as the upper surface or lower surface of the moderator unit 11. The heat diffusion layer 12 is in contact with the entire top or bottom surface of the moderator unit 11.

The thermal diffusion layer 12 is made of a material having significantly higher thermal conductivity than the nuclear fuel unit 10 or the moderator unit 11. For example, the heat diffusion layer 12 may be formed of a graphite sheet. In this way, the heat diffusion layer 12 can be formed thin while increasing the heat removal efficiency by the heat diffusion layer 12. Further, the heat diffusion layer 12 may be formed by a sub-heat pipe having a flat plate shape. Note that, like the main heat pipe 9, the sub heat pipe is a thin heat pipe that is a device that transfers heat using a working fluid. In this way, a large amount of heat can be transferred from the nuclear fuel unit 10 to the main heat pipe 9.

Note that a part of the heat diffusion layer 12 may be formed of a graphite sheet, and the other part may be formed of a sub-heat pipe. For example, a graphite sheet and a sub-heat pipe may be provided side by side, or a graphite sheet and a sub-heat pipe may be provided in a stacked manner. Further, since the heat diffusion layer 12 can be formed using a material other than a graphite sheet or a sub-heat pipe, the material of the heat diffusion layer 12 is not limited to that of this embodiment.

As shown in FIG. 7, a heat diffusion layer 12 is in contact with the upper and lower surfaces of the nuclear fuel unit 10.

In the nuclear fuel unit 10, heat 15 is basically transported to the main heat pipe 9 by solid state heat conduction, that is, by temperature differences within the solid state. Assuming the case of the heat diffusion layer 12, inside the nuclear fuel unit 10, the temperature is low near the main heat pipe 9, and the temperature increases as the distance from the main heat pipe 9 increases.

Therefore, in this embodiment, the heat diffusion layer 12 is provided, and the heat 15 is transported from the high temperature region at the outer edge of the nuclear fuel unit 10 to the low temperature region near the main heat pipe 9 of the nuclear fuel unit 10 through the heat diffusion layer 12. do. In this way, the temperature of the entire nuclear fuel unit 10 can be made uniform. Then, uneven temperature rise inside the nuclear fuel unit 10 can be suppressed, and the entire nuclear fuel unit 10 can be sufficiently combusted. As a result, core power can be increased.

The heat diffusion layer 12 is made of a material such as a graphite sheet or a sub-heat pipe, which has a high thermal conductivity in a certain direction, but has a high thermal conductivity in other directions, rather than a material such as copper, which has a uniformly high thermal conductivity. It is desirable to have a material that does not have such thermal conductivity.

For example, as shown in FIG. 8, a case will be described in which a graphite sheet is used for the heat diffusion layer 12. Graphite sheets have a thermal conductivity of 1000 W/mK or more in the horizontal direction 16, which is the direction in which the sheet spreads, and a thermal conductivity of only about 30 to 100 W/mK in the vertical direction 17, which is the thickness direction. There are things you don't have. In this way, by using a graphite sheet oriented in the direction of heat transport for the heat diffusion layer 12, heat transfer from the nuclear fuel unit 10 to the moderator unit 11 can be inhibited. Heat can then be transported from the outer edge of the nuclear fuel unit 10 to the low temperature region near the main heat pipe 9.

As shown in FIGS. 9 and 10, the heat diffusion layer 12A of Modification 1 includes a contact portion 18, an extended portion 19, and a rib 20. As shown in FIGS.

The contact portion 18 is a portion that contacts the nuclear fuel unit 10 and the moderator unit 11. This contact portion 18 is sandwiched between the nuclear fuel unit 10 and the moderator unit 11.

The expanded portion 19 is a portion that extends between the main heat pipe 9 and the moderator unit 11. This expanded portion 19 is provided at the interface between the main heat pipe 9 and the moderator unit 11. That is, the extended portion 19 is sandwiched between the main heat pipe 9 and the moderator unit 11. In this way, the area where the heat diffusion layer 12A is in contact with the main heat pipe 9 can be expanded. Therefore, the efficiency of transferring heat from the heat diffusion layer 12A to the main heat pipe 9 can be improved.

The rib 20 is a portion that extends away from the nuclear fuel unit 10 and toward the main heat pipe 9 . This rib 20 is sandwiched between two members of the divided moderator unit 11. In this way, heat can be efficiently transferred toward the main heat pipe 9 via the ribs 20.

Since the moderator unit 11 does not generate heat, the ribs 20 sandwiched between the moderator unit 11 do not receive heat from the moderator unit 11. Therefore, when the heat that has entered the heat diffusion layer 12A from the nuclear fuel unit 10 is transported by the ribs 20, the heat can be transported more efficiently than when the heat is transported by the contact portion 18. In other words, a large amount of heat can be transported using the ribs 20 in a direction away from the nuclear fuel unit 10 that is generating heat.

Note that the shape or dimensions of the extended portion 19 or the rib 20 are not limited to this first modification, since various aspects can be considered. Furthermore, the ribs 20 may be extended outward and used as part of a fixing device for fixing the divided nuclear fuel unit 10 or moderator unit 11.

As shown in FIG. 11, in the second modification, a heat insulating section 21 is provided between the moderator unit 11 and the heat diffusion layer 12. This heat insulating section 21 makes it difficult for the heat of the nuclear fuel unit 10 to be transmitted to the moderator unit 11. In this way, it is possible to suppress the heat transmitted from the nuclear fuel unit 10 to the thermal diffusion layer 12 from being transmitted from the thermal diffusion layer 12 to the moderator unit 11. Therefore, heat can be efficiently transferred to the main heat pipe 9 using the heat diffusion layer 12.

The heat insulating portion 21 of the second modification is formed of a flat heat insulating material. For example, the heat insulating portion 21 may be formed using a heat insulating material such as glass wool. Alternatively, the heat insulating section 21 may be formed by forming a vacuum container whose inside is evacuated into a flat plate shape.

Note that the heat insulating section 21 may have other forms as long as it makes it difficult for the heat of the nuclear fuel unit 10 to be transmitted to the moderator unit 11. For example, a gap may be provided between the moderator unit 11 and the heat diffusion layer 12, and this gap may be used as the heat insulating section 21.

As shown in FIG. 12, in Modification 3, a metal foil 22 containing at least one of europium (Eu) and cadmium (Cd) is provided between the nuclear fuel unit 10 and the moderator unit 11. In this modification 3, two metal foils 22 are provided on the upper and lower surfaces of the heat diffusion layer 12 so as to sandwich the same. In this way, at least one of europium and cadmium can be placed in the reactor core without changing the configuration of the thermal diffusion layer 12. Since europium and cadmium have a large absorption cross section, the metal foil 22 may be formed thinner than the heat diffusion layer 12.

Note that the metal foil 22 may contain either europium or cadmium, or may contain both of these. Furthermore, the metal foil 22 may contain either europium oxide or cadmium oxide, or may contain both of these.

Note that when the heat diffusion layer 12 is constituted by a sub-heat pipe, the sub-heat pipe may be formed of a material containing at least one of europium and cadmium. In this way, at least one of europium and cadmium can be placed in the reactor core using the subheat pipe.

Further, when the heat diffusion layer 12 is made of a graphite sheet or other metal material, at least one of europium and cadmium may be added to the heat diffusion layer 12 itself.

As shown in FIG. 13, in Modification 4, metal structural members 23 and 24 containing at least one of europium and cadmium are provided. Note that the metal structural members 23 and 24 may contain at least one of europium oxide and cadmium oxide.

In this modification 4, it is provided on the side surface of the nuclear fuel unit 10 or the moderator unit 11. For example, a plate-shaped metal structural member 23 is provided to surround the side surface of the moderator unit 11.

Further, inside the reactor core 5, nuclear fuel units 10 are provided at the upper and lower ends of the main heat pipe 9 in the axial direction. A flat metal structural member 24 is provided on the upper surface of the uppermost nuclear fuel unit 10 and the lower surface of the lowermost nuclear fuel unit 10. That is, the metal structural member 24 is provided at a position close to the neutron reflecting section 6 (FIG. 1).

FIG. 14 is a graph in which the horizontal axis represents the operating temperature and the vertical axis represents the temperature reactivity coefficient. As shown in this graph, by providing at least one of europium (Eu) and cadmium (Cd) inside the core 5, the temperature reactivity of the core 5 can be improved to the negative side. In particular, it is possible to construct a core that has a negative temperature reactivity in a high temperature range above the operating temperature.

In the core 5 using calcium hydride as the moderator unit 11, the temperature reactivity coefficient C is shown when Eu is added to the thermal diffusion layer 12 and when Eu is not added. This temperature reactivity coefficient C is expressed by the following equation 1. Here, ρT1 and ρT2 are the reactivity of the core temperature T ₁ and the core temperature T ₂ .

As shown in FIG. 14, it can be seen that when Eu is added to the heat diffusion layer 12, the temperature reactivity coefficient C becomes more negative when the temperature is higher than 800K. In other words, it can be seen that when Eu is added, the controllability of the core 5 is improved in the operating temperature range, compared to when Eu is not added.

This effect is mainly caused by an increase in the amount of neutron absorption in resonances such as Eu due to changes in the spectrum of thermal neutrons in the moderator unit 11. Note that even when Cd is added to the thermal diffusion layer 12, the same results as the graph of FIG. 14 are obtained, so the same effect as Eu can be obtained.

Therefore, when Eu, Cd, or the like is provided in the reactor core 5, it is better to provide the Eu or Cd at a position closer to the moderator unit 11. For example, Eu or Cd may be provided on the heat diffusion layer 12 adjacent to the moderator unit 11, at a position close to the heat diffusion layer 12, or on the side surface of the moderator unit 11.

Furthermore, Eu Alternatively, by providing Cd, the reactivity value can be increased.

Next, a heat removal method for the nuclear reactor 2 will be explained using the flowchart of FIG. 15. A description will be given including the effects passively produced by the operation of the nuclear reactor 2. Note that the above-mentioned drawings will be referred to as appropriate.

First, in step S11, heat is generated by a fission reaction of the nuclear fuel material contained in the nuclear fuel unit 10.

In the next step S12, the neutrons generated by the nuclear fission reaction are moderated by the moderator unit 11. The decelerated neutrons cause a chain reaction of nuclear fission in the nuclear fuel unit 10.

In the next step S13, the heat of the nuclear fuel unit 10 is transferred to the heat diffusion layer 12. Furthermore, the heat of the nuclear fuel unit 10 is transferred toward the main heat pipe 9 by the heat diffusion layer 12 .

In the next step S14, the heat of the reactor core 5 is transferred to the power generation device 3 outside the reactor core 5 by the main heat pipe 9.

In the next step S15, the power generation device 3 generates power using the heat transferred by the main heat pipe 9.

In the next step S16, the heat used for power generation by the power generation device 3 is transferred to the radiator 4. The heat is then radiated by the radiator 4.

In this embodiment, the main heat pipe 9 filled with working fluid is exemplified as a device for transferring heat from the reactor core 5, but other types of heat pipes (heat removal sections) may be used. For example, a solid heat pipe with no internal cavity may be used. Furthermore, heat may be transferred from the core using a heat pump type heat removal device.

In addition, in this embodiment, each of the nuclear fuel unit 10, the moderator unit 11, and the heat diffusion layer 12 is divided into at least two members sandwiching the main heat pipe 9, but other aspects may be used. For example, these may be divided into three or more members. Furthermore, the term "sandwiching the main heat pipe 9" in this embodiment includes the meaning of "surrounding the main heat pipe 9."

In this embodiment, the nuclear fuel unit 10 includes the HPPF 13 and the main fuel section 14, which have different concentrations of fissile material, but other embodiments may be used. For example, the configuration of the HPPF 13 may be omitted and the nuclear fuel unit 10 may be configured only with the main fuel section 14.

According to the embodiment described above, by providing the heat diffusion layer that is provided between the nuclear fuel unit and the moderator unit and moves the heat of the nuclear fuel unit toward the main heat pipe, the heat removal efficiency by the heat pipe is increased. It is possible to improve the output of the reactor core.

Although several embodiments of the invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

DESCRIPTION OF SYMBOLS 1...Nuclear power generation system, 2...Nuclear reactor, 3...Power generator, 4...Radiator, 5...Reactor core, 6...Neutron reflecting part, 7...Shielding part, 8...Safety rod, 9...Main heat pipe, 10...Nuclear fuel unit , 11... Moderator unit, 12 (12A)... Heat diffusion layer, 13... HPPF, 14... Main fuel part, 15... Heat, 16... Horizontal direction, 17... Vertical direction, 18... Contact part, 19... Expansion part, 20... Rib, 21... Heat insulation part, 22... Metal foil, 23, 24... Metal structural material.

Claims (15)

A rod-shaped main heat pipe that transfers heat within the reactor core to the outside of the reactor core;
a nuclear fuel unit disposed around the main heat pipe and generating heat through a nuclear fission reaction;
a moderator unit arranged around the main heat pipe and arranged adjacent to the nuclear fuel unit along the axial direction of the main heat pipe and moderating neutrons;
a heat diffusion layer that is provided between the nuclear fuel unit and the moderator unit and moves heat of the nuclear fuel unit toward the main heat pipe;
Equipped with
Reactor. At least a portion of the heat diffusion layer is a graphite sheet.
A nuclear reactor according to claim 1. At least a portion of the heat diffusion layer is a sub-heat pipe having a flat plate shape.
The nuclear reactor according to claim 1 or claim 2. The sub-heat pipe is made of a material containing at least one of europium and cadmium.
The nuclear reactor according to claim 3. The heat diffusion layer contains at least one of europium and cadmium.
The nuclear reactor according to any one of claims 1 to 4. A metal foil is provided between the nuclear fuel unit and the moderator unit and includes at least one of europium and cadmium.
The nuclear reactor according to any one of claims 1 to 5. A heat insulating section is provided between the moderator unit and the heat diffusion layer and makes it difficult for the heat of the nuclear fuel unit to be transmitted to the moderator unit.
A nuclear reactor according to any one of claims 1 to 6. The heat diffusion layer includes an extension part extending between the main heat pipe and the moderator unit.
The nuclear reactor according to any one of claims 1 to 7. The heat diffusion layer includes a rib extending away from the nuclear fuel unit and toward the main heat pipe.
The nuclear reactor according to any one of claims 1 to 8. the nuclear fuel unit is divided into at least two members sandwiching the main heat pipe;
The nuclear reactor according to any one of claims 1 to 9. A surface of the nuclear fuel unit that contacts the main heat pipe has a shape that matches the outer surface of the main heat pipe.
A nuclear reactor according to any one of claims 1 to 10. The nuclear fuel unit and the moderator unit are arranged alternately along the axial direction of the main heat pipe,
A nuclear reactor according to any one of claims 1 to 11. The nuclear fuel unit is
a first nuclear fuel section containing a first concentration of fissile material;
a second nuclear fuel section that is disposed further from the main heat pipe than the first nuclear fuel section and includes the fissile material at a second concentration lower than the first concentration;
Equipped with
A nuclear reactor according to any one of claims 1 to 12. the moderator unit includes a metal hydride;
A nuclear reactor according to any one of claims 1 to 13. generating heat through a nuclear fission reaction in a nuclear fuel unit disposed around a main heat pipe having a rod shape;
Moderating the neutrons by moderator units arranged around the main heat pipe and arranged adjacent to the nuclear fuel unit along the axial direction of the main heat pipe;
Transferring the heat of the nuclear fuel unit toward the main heat pipe by a heat diffusion layer provided between the nuclear fuel unit and the moderator unit;
Transferring heat within the reactor core to outside the reactor core by the main heat pipe;
including,
How to remove heat from a nuclear reactor.

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