Fuel breeding unit, nuclear fusion reactor, and heat pipe

Abstract

In order to realize a fuel breeding unit that does not require the introduction of tritium recovery piping, a fuel breeding unit (1) converts kinetic energy of neutrons generated by nuclear fusion in plasma into thermal energy and generates tritium using neutrons. The fuel breeding unit (1) discharges the generated tritium directly into the reactor.

Description

Fuel breeder unit, fusion reactor, and heat pipe

[0001] The present invention relates to a fuel breeder unit that converts the kinetic energy of neutrons generated by nuclear fusion in a plasma into thermal energy, and also generates tritium using those neutrons. The present invention also relates to a nuclear fusion reactor equipped with such a fuel breeder unit.

[0002] One nuclear fusion reaction expected to be put into practical use in the near future is the DT reaction. The DT reaction is a nuclear reaction in which one deuterium atom and one tritium atom (hereinafter referred to as "tritium") fuse to produce one helium atom and one neutron. One of the fuels, deuterium, is easily extracted from the environment (mainly seawater), while the other fuel, tritium, is difficult to extract from the environment. Therefore, securing tritium is one of the technical challenges in nuclear fusion reactors that use the DT reaction.

[0003] The fuel breeder unit (sometimes called a "tritium breeder unit") is one of the key devices in a fusion reactor. The fuel breeder unit is positioned to surround the plasma formed inside the reactor, slowing down neutrons produced by DT reactions in the plasma, and using those neutrons to perform nuclear transmutation reactions that generate tritium from lithium.

[0004] Furthermore, it is difficult to utilize all the neutrons generated in the DT reaction to produce the same number of tritium atoms in the fuel breeder unit as those consumed in the DT reaction. Therefore, in order to produce the same number (or more) of tritium atoms in the fuel breeder unit as those consumed in the DT reaction, a configuration is adopted in which beryllium, which has a neutron multiplier effect, is sealed in the fuel breeder unit together with lithium.

[0005] For example, Patent Document 1 is a document that discloses a conventional fuel breeder unit.

[0006] Japanese Patent Publication No. 2018-124178

[0007] The main components of the fusion reactor 100' being considered in the ITER project will be explained with reference to Figure 11. Figure 11 is a block diagram showing the main components of the fusion reactor 100'. The components shown in Figure 11 are those components of the fusion reactor 100' that are directly or indirectly related to the fuel breeder unit 1'. The fusion reactor 100' may include components other than those shown in Figure 11.

[0008] The fusion reactor 100' includes a fuel breeder unit 1', a cooling system 100A', and a fuel recovery system 100B'.

[0009] Fuel breeder unit 1' has a "neutron deceleration function," a "neutron multiplication function," and a "tritium breeding function." Here, the "neutron deceleration function" refers to the function of decelerating neutrons produced by nuclear fusion in the plasma, that is, the function of converting the kinetic energy of neutrons produced by nuclear fusion in the plasma into thermal energy. The "neutron deceleration function" is sometimes also called the "neutron shielding function." The "neutron multiplication function" refers to the function of multiplying neutrons produced by nuclear fusion in the plasma, for example, by using neutrons produced by nuclear fusion in the plasma to split one beryllium atom into two helium atoms and two neutrons, thereby multiplying the neutrons. The "tritium breeding function" refers to the function of producing tritium by using neutrons produced by nuclear fusion in the plasma, or neutrons produced by the splitting of beryllium atoms, to split one lithium atom into one tritium atom and one helium atom.

[0010] The cooling system 100A' is a system for transporting the energy generated by nuclear fusion in the plasma to the outside of the reactor. The main energy generated by nuclear fusion in the plasma is the thermal energy generated by nuclear fusion in the plasma and the kinetic energy of neutrons produced by nuclear fusion in the plasma. The cooling system 100A' includes a primary cooler 101 and a secondary cooler 102.

[0011] The fuel breeder unit 1' transfers the heat generated by slowing down neutrons produced by nuclear fusion in the plasma, along with the heat generated by nuclear fusion in the plasma, to the low-temperature primary coolant supplied by the primary coolant 101. The high-temperature primary coolant heated by the fuel breeder unit 1' is returned to the primary coolant 101. The primary coolant 101 transfers the heat from the high-temperature primary coolant to the low-temperature secondary coolant supplied by the secondary coolant 102. The high-temperature secondary coolant heated by the primary coolant 101 is returned to the secondary coolant 102. The thermal energy of the secondary coolant is used, for example, to drive a power generation turbine.

[0012] The fuel recovery system 100B' is a system for recovering fuel (deuterium and tritium) from plasma exhaust gas generated by nuclear fusion in a plasma. The fuel recovery system 100B' includes an discharge device 103, a plasma exhaust gas treatment system (TEP) 104, a hydrogen isotope separation system (ISS) 105, a storage and delivery system (SDS) 106, a fuel input device 107, a tritium atmosphere treatment system (ADS) 108, and a tritium water treatment system (WDS) 109.

[0013] The discharge device 103 discharges plasma exhaust gas from inside the reactor. The plasma exhaust gas treatment system 104 separates the plasma exhaust gas into hydrogen isotope gas (containing light hydrogen, deuterium, and tritium) and impurity gas that does not contain hydrogen isotopes. The hydrogen isotope separation system 105 separates the hydrogen isotope gas into light hydrogen gas and fuel gas (heavy water gas and tritium gas), and concentrates the fuel gas. The storage and supply system 106 contacts the concentrated fuel gas with hydrogen-absorbing metals in the storage bed and stores it as a metal hydride. The deuterium and tritium in the metal hydride generated by the storage and supply system 106 are introduced into the reactor using the input device 107.

[0014] The tritium atmosphere treatment system 108 extracts tritium from the exhaust gas of various devices (for example, the plasma exhaust gas treatment system 104 and the storage and supply system 106). The tritium extracted by the tritium atmosphere treatment system 108 is supplied to the tritium water treatment system 109 as high-concentration tritiated water. The tritium water treatment system 109 concentrates the high-concentration tritiated water supplied from the tritium atmosphere treatment system 108, as well as high-concentration tritiated water discharged from various devices (for example, the hydrogen isotope separation system 105), and then converts it into tritium gas. The tritium gas obtained in the tritium water treatment system 109 is concentrated in the hydrogen isotope separation system 105 and stored as a metal hydride in the storage and supply system 106.

[0015] The fuel breeder unit 1' is included in the tritium recovery loop LY together with the hydrogen isotope separation system 105. The tritium generated in the fuel breeder unit 1' is transported to the hydrogen isotope separation system 105 by light hydrogen gas circulating in the tritium recovery loop LY. The tritium transported from the fuel breeder unit 1' to the hydrogen isotope separation system 105 is concentrated in the hydrogen isotope separation system 105 and stored as a metal hydride by the storage and supply system 106 described above. For this reason, a piping Y for tritium recovery, which is part of the fuel recovery loop LY, is drawn into the fuel breeder unit 1'.

[0016] If a pipe Y for tritium recovery is connected to the fuel breeder unit 1', the following problems may arise. Specifically, each time one of the numerous fuel breeder units 1', which are arranged to surround the plasma formed inside the reactor, is replaced, it becomes necessary to cut, weld, and inspect the pipe Y for tritium recovery. The cost of cutting, welding, and inspecting the pipe Y for tritium recovery will increase the maintenance costs of the fusion reactor 100', and the time required for cutting, welding, and inspecting the pipe Y for tritium recovery will reduce the operating rate of the fusion reactor 100'. In other words, the structure of the conventional fuel breeder unit 1', which requires the connection and disconnection of the pipe Y for tritium recovery, will increase the power generation costs of the fusion reactor 100'.

[0017] Furthermore, the fuel breeding unit 1' is included in the primary cooling loop LX together with the primary cooling device 101. The heat generated in the fuel breeding unit 1' is transported to the primary cooling device 101 by primary cooling water circulating in the primary cooling loop LX. For this reason, cooling pipes X, which are part of the primary cooling loop LX, are drawn into the fuel breeding unit 1'.

[0018] If cooling pipe X is connected to fuel breeder unit 1', the same problems as those that occur when tritium recovery pipe Y is connected to fuel breeder unit 1' will arise. In addition, if fuel breeder unit 1' is damaged by plasma contact caused by plasma disruption, primary coolant flowing through cooling pipe X may be released into the reactor. If primary coolant is released into the reactor, it may reduce the safety of the fusion reactor 100'.

[0019] One aspect of the present invention has been made in view of the above-mentioned problems, and its objective is to realize a fuel breeder unit that does not require the installation of piping for tritium recovery. Another objective is to realize a fusion reactor with low power generation costs using a fuel breeder unit that does not require the installation of piping for tritium recovery.

[0020] To solve the above problems, a fuel breeder unit according to one aspect of the present invention is a fuel breeder unit that converts the kinetic energy of neutrons generated by nuclear fusion in a plasma into thermal energy and generates tritium using the neutrons, and releases the generated tritium directly into the reactor.

[0021] To solve the above problems, a fusion reactor according to one aspect of the present invention is equipped with the fuel breeding unit described above.

[0022] To solve the above problems, a heat pipe according to one aspect of the present invention comprises a lithium encapsulant having a cylindrical portion, a lid portion that closes one opening, and a bottom portion that closes the other opening, with liquid metallic lithium sealed in a cavity surrounded by the cylindrical portion, the lid portion, and the bottom portion, and a transport channel for transporting the liquid metallic lithium from the low temperature side to the high temperature side provided on the inner surface of the cylindrical portion or in the center of the cavity.

[0023] According to one aspect of the present invention, a fuel breeder unit can be realized that does not require the installation of piping for tritium recovery. Furthermore, according to one aspect of the present invention, a fusion reactor can be realized that does not require the installation of a tritium recovery loop for recovering tritium from the fuel breeder unit.

[0024] This is a block diagram showing the main components of a fusion reactor according to one embodiment of the present invention. This is an exploded perspective view showing the configuration of a fuel breeder unit according to one embodiment of the present invention. This is a cross-sectional view showing the configuration of a fuel breeder unit according to one embodiment of the present invention. This is a cross-sectional view showing a first specific example of a lithium encapsulant provided in the fuel breeder unit shown in Figures 2 and 3. This is a cross-sectional view showing a modified example of the lithium encapsulant shown in Figure 4. This is a cross-sectional view showing a second specific example of a lithium encapsulant provided in the fuel breeder unit shown in Figures 2 and 3. This is a cross-sectional view showing a modified example of the lithium encapsulant shown in Figure 6. This is a cross-sectional view showing a third specific example of a lithium encapsulant provided in the fuel breeder unit shown in Figures 2 and 3. This is a perspective view showing the configuration of a water-cooled back wall according to one embodiment of the present invention. This is a perspective view showing the configuration of a helium-cooled back wall according to one embodiment of the present invention. This is a block diagram showing the main components of a fusion reactor being considered in the ITER project.

[0025] [Fusion Reactor] The main components of the fusion reactor 100 according to this embodiment will be described with reference to Figure 1. Figure 1 is a block diagram showing the main components of the fusion reactor 100.

[0026] The fusion reactor 100 includes a fuel breeder unit 1, a back wall 2, a cooling system 100A, and a fuel recovery system 100B. The components shown in Figure 1 are those components of the fusion reactor 100 that are directly or indirectly related to the fuel breeder unit 1. The fusion reactor 100 may include components other than those shown in Figure 1.

[0027] (1) Cooling System The cooling system 100A in the fusion reactor 100 includes a primary cooler 101 and a secondary cooler 102, similar to the cooling system 100A' in the fusion reactor 100' described above. The operation of the cooling system 100A in the fusion reactor 100 is the same as the operation of the cooling system 100A' in the fusion reactor 100' described above. However, while the primary cooler 101 of the fusion reactor 100' described above is configured to cool the fuel breeder unit 1', the primary cooler 101 of the fusion reactor 100 according to this embodiment is configured to cool the back wall 2.

[0028] The back wall 2 is a device for cooling the fuel breeding unit 1 and is located on the side of the fuel breeding unit 1 opposite the plasma side. The fuel breeding unit 1 can be easily attached to and removed from the back wall 2. By attaching the fuel breeding unit 1 to the back wall 2, the fuel breeding unit 1 and the back wall 2 come into thermal contact. The structure of the fuel breeding unit 1 and the back wall 2 will be described later with reference to different drawings.

[0029] (2) Fuel Recovery System The fuel recovery system 100B in the fusion reactor 100 is similar to the fuel recovery system 100B' in the fusion reactor 100' described above and includes an exhaust device 103, a plasma exhaust gas treatment system 104, a hydrogen isotope separation system 105, a storage and supply system 106, an input device 107, a tritium atmosphere treatment system 108, and a tritium water treatment system 109. The operation of the fuel recovery system 100B in the fusion reactor 100 is the same as the operation of the fuel recovery system 100B' in the fusion reactor 100' described above.

[0030] (3) Characteristics of the fusion reactor The fuel breeder unit 1 according to this embodiment has a neutron doubling function and a tritium breeding function, similar to the fuel breeder unit 1 of the fusion reactor 100' described above. However, while the fuel breeder unit 1' of the fusion reactor 100' described above releases the generated tritium into a piping Y for tritium recovery, the fuel breeder unit 1 according to this embodiment releases the generated tritium directly into the reactor.

[0031] Therefore, in the fusion reactor 100' described above, tritium generated in the fuel breeder unit 1' is transported using the tritium recovery loop LY and recovered using the fuel recovery system 100B'. On the other hand, in the fusion reactor 100 according to this embodiment, tritium generated in the fuel breeder unit 1 is returned to the reactor and recovered together with the tritium contained in the plasma exhaust gas inside the reactor using the fuel recovery system 100B. Therefore, in the fusion reactor 100 according to this embodiment, the tritium recovery loop LY is omitted. This makes it possible to reduce the construction cost (time and cost required for construction) of the fusion reactor 100. In addition, it is possible to miniaturize the fusion reactor 100 and reduce the tritium inventory (improve safety). In other words, it is possible to improve the performance (including miniaturization) of the fusion reactor 100.

[0032] Furthermore, in the fuel breeder unit 1 according to this embodiment, the piping Y for tritium recovery is omitted. This eliminates the need to cut, weld, and inspect the piping Y each time the fuel breeder unit 1 is replaced. As a result, the maintenance costs of the fusion reactor 100 can be reduced, and the operating rate of the fusion reactor 100 can be increased. Consequently, for example, the power generation costs of the fusion reactor 100 can be reduced.

[0033] Furthermore, the fuel breeder unit 1 according to this embodiment has a neutron moderation function, similar to the fusion reactor 100' described above. However, while the fuel breeder unit 1' of the fusion reactor 100' described above transfers the heat generated by neutron moderation to the primary coolant along with radiant heat from the plasma, the fuel breeder unit 1 according to this embodiment transfers the heat generated by neutron moderation to the back wall 2 along with radiant heat from the plasma.

[0034] Therefore, the fuel breeder unit 1 according to this embodiment is equipped with a function (hereinafter also referred to as the "heat transport function") that transports the heat generated by the neutron deceleration from the plasma side to the opposite side, along with the radiant heat from the plasma.

[0035] Furthermore, in the fuel breeder unit 1 according to this embodiment, the cooling piping X is omitted. This eliminates the need to cut, weld, and inspect the cooling piping X each time the fuel breeder unit 1 is replaced. As a result, the maintenance costs of the fusion reactor 100 can be reduced, and the operating rate of the fusion reactor 100 can be increased. Consequently, for example, the power generation cost of the fusion reactor 100 can be reduced. In addition, even if the fuel breeder unit 1 is destroyed by plasma contact or escape electron beam irradiation caused by plasma disruption, primary cooling water will not be released into the reactor. As a result, the safety of the fusion reactor 100 can be improved.

[0036] Furthermore, the cooling pipe X is routed to the back wall 2 instead of being routed to the fuel breeding unit 1. However, the back wall 2 is located on the side of the fuel breeding unit 1 opposite the plasma side. Therefore, the possibility of plasma contact with the back wall 2 in the fusion reactor 100 according to this embodiment is lower than the possibility of plasma contact with the fuel breeding unit 1' in the fusion reactor 100' described above. Consequently, the possibility of primary coolant being released into the reactor due to the destruction of the back wall 2 in the fusion reactor 100 according to this embodiment is lower than the possibility of primary coolant being released into the reactor due to the destruction of the fuel breeding unit 1' in the fusion reactor 100' described above.

[0037] Furthermore, it is not realistic, given the heat output of the plasma, for the plasma to completely melt the fuel breeder unit 1 and come into contact with the back wall. Also, even if the fuel breeder unit 1 were to detach and the back wall 2 were exposed, the plasma would come into contact with the detached fuel breeder unit 1 and dissipate before it could come into contact with the back wall 2. For this reason, in practice, the plasma will not come into contact with the back wall 2, and therefore, primary coolant will not be released into the reactor due to the destruction of the back wall 2.

[0038] (4) Modified Forms of the Fusion Reactor In this embodiment, the fusion reactor 100 is assumed to be a fusion reactor using a DT reaction in plasma. Here, a DT reaction refers to a nuclear reaction in which one deuterium atom and one tritium atom fuse to produce one helium atom and one neutron. In this case, the "neutron produced by nuclear fusion" in the above explanation refers to the neutron produced by this DT reaction.

[0039] Incidentally, the fuel breeding unit 1 has a neutron moderation function and a heat transport function in addition to the tritium breeding function. Although the tritium breeding function can be effectively utilized in a fusion reactor using a DT reaction that uses tritium as fuel, the neutron moderation function and the heat transport function can also be effectively utilized in a fusion reactor using a nuclear reaction other than the DT reaction. For this reason, the fuel breeding unit 1 can be applied not only to a fusion reactor using the DT reaction but also to a fusion reactor using any nuclear reaction as a heat removal device that can withstand a high heat load.

[0040] 〔Fuel Breeding Unit〕 (Configuration of Fuel Breeding Unit) The configuration of the fuel breeding unit 1 will be described with reference to FIGS. 2 and 3. FIG. 2 is an exploded perspective view of the fuel breeding unit 1. FIG. 3 is a cross-sectional view of the fuel breeding unit 1.

[0041] The fuel breeding unit 1 includes a lithium seal 11, a beryllium block 12, and a sleeve 13. The lithium seal 11 mainly bears the neutron moderation function, the heat transport function, and the tritium breeding function among the four functions of the fuel breeding unit 1 described above. Also, the beryllium block 12 mainly bears the heat transport function, the neutron moderation function, and the neutron multiplication function among the four functions of the fuel breeding unit 1 described above. Further, the sleeve 13 bears the function of integrating the lithium seal 11 and the beryllium block 12.

[0042] (1) Lithium Seal The lithium seal 11 includes a cylindrical portion 111, a lid portion 112, a bottom portion 113, a flange portion 114, and a coating 115. Inside the lithium seal 11, a cavity 11a surrounded by the cylindrical portion 111, the lid portion 112, and the bottom portion 113 is formed. In the present embodiment, lithium is enclosed in this cavity 11a.

[0043] Note that the lithium enclosed in the cavity 11a may be metallic lithium or a lithium compound. For the configuration in which metallic lithium is enclosed in the cavity 11a, refer to the first specific example (FIG. 4) and its modification (FIG. 5) described later, as well as the second specific example (FIG. 6) and its modification (FIG. 7) described later. On the other hand, for the configuration in which a lithium compound is enclosed in the cavity 11a, refer to the third specific example (FIG. 8) described later.

[0044] The cylindrical portion 111 is a cylindrical structure. The cylindrical portion 111 is arranged such that one of the openings at both ends faces the plasma side and the other opening faces the side opposite to the plasma side. Hereinafter, the opening at one end of the cylindrical portion 111 that faces the plasma side will also be referred to as the "plasma-side opening". Also, the opening at one end of the cylindrical portion 111 that faces the side opposite to the plasma side will also be referred to as the "anti-plasma-side opening". In the present embodiment, the shape of the cylindrical portion 111 is a cylindrical shape in which the inner diameter and the outer diameter gradually increase as it approaches the plasma-side opening in the vicinity of the plasma-side opening. Further, in the present embodiment, the material of the cylindrical portion 111 is a SiC / SiC composite material designed so as not to effectively transmit tritium atoms.

[0045] Note that the SiC / SiC composite material has the following merits: (1) good heat resistance, (2) good radiation resistance at 800°C or higher and 1100°C or lower, and (3) rapid decay of induced radioactivity. By using the SiC / SiC composite material, these merits can be enjoyed.

[0046] The lid portion 112 is a plate-like structure that closes the plasma-side opening of the cylindrical portion 111, and the bottom portion 113 is a plate-like structure that closes the anti-plasma-side opening of the cylindrical portion 111. In the present embodiment, the shape of the lid portion 112 is a dome shape (the central portion protrudes toward the plasma side more than the peripheral portion) with a circular shape in plan view, and the shape of the bottom portion 113 is a flat plate shape with a circular shape in plan view. Further, in the present embodiment, the material of the lid portion 112 is a SiC / SiC composite material designed so as to effectively transmit tritium atoms. On the other hand, the material of the bottom portion 113 is a SiC / SiC composite material designed so as not to effectively transmit tritium atoms.

[0047] The flange portion 114 is a plate-like structure that extends outward from the plasma-side end of the cylindrical portion 111. In this embodiment, the shape of the flange portion 114 is a flat plate with a regular hexagonal shape in plan view. In this embodiment, the material of the flange portion 114 is a SiC / SiC composite material designed to effectively permeate tritium (tritium atoms, tritium ions, or molecules containing tritium atoms). In order to prevent wear of the lithium encapsulant 11 due to sputtering, the plasma-side surface of the flange portion 114 is covered with a coating 115. In this embodiment, the material of the coating 115 is tungsten. Choosing tungsten as the material of the coating 115 has the advantage of not inhibiting tritium permeability, as well as making it less likely for the coating 115 to peel off due to thermal fatigue. This is because the thermal expansion coefficient of tungsten is roughly the same as that of SiC.

[0048] The coating 115 does not necessarily cover the lid 112, nor does it necessarily cover the lid 112. For configurations in which the coating 115 does not cover the lid 112, please refer to the first specific example (Figure 4), the second specific example (Figure 6), and the third specific example (Figure 8) described later. On the other hand, for configurations in which the coating 115 covers the lid 112, please refer to the modified example of the first specific example (Figure 5) and the modified example of the second specific example (Figure 7) described later.

[0049] In this embodiment, the cylindrical portion 111 and the bottom portion 113 are integrally molded to form a first component, and the lid portion 112 and the flange portion 114 are integrally molded to form a second component. Furthermore, a screw thread 111a is formed on the plasma-side end of the outer surface of the cylindrical portion 111, and a screw thread 114a is formed on the inner surface of a recess provided in the center of the surface of the flange portion 114 opposite to the plasma side. By screwing the screw threads 111a and 114a together with an auxiliary material, integration (mechanical coupling) of the first component and the second component is achieved. High-melting-point materials such as tungsten and yttria are envisioned as auxiliary materials. In this embodiment, a configuration is adopted in which the first component, in which the cylindrical portion 111 and the bottom portion 113 are integrally molded, and the second component, in which the lid portion 112 and the flange portion 114 are integrally molded, are mechanically coupled, but the embodiment is not limited to this. For example, a configuration may be adopted in which a first part, in which a cylindrical portion 111, a lid portion 112, and a flange portion 114 are integrally molded, is mechanically joined to a second part, which consists of a bottom portion 113. The mechanical joining of the first part and the second part may be achieved not by screwing, but by interlocking joints (such as wooden joinery, connections, or joinery).

[0050] Furthermore, in order to prevent corrosion of the SiC / SiC material by lithium, it is preferable that the inner surface of the cylindrical portion 111 and the plasma-side surface of the bottom portion 113 are coated with a corrosion-resistant coating. Examples of materials for the corrosion-resistant coating include oxides or vanadium (V). In this embodiment, erbium (III) oxide (Erbium) is used as the material for the corrosion-resistant coating. ２ O ３ ) is used. Furthermore, from the viewpoint of preventing corrosion of the SiC / SiC material by lithium, it is desirable that the surface of the lid 112 opposite to the plasma side also be coated with a corrosion-resistant coating. However, the lid 112 needs to be able to effectively pass tritium atoms through. Therefore, for the surface of the lid 112 opposite to the plasma side, it is preferable to improve corrosion resistance by methods other than corrosion-resistant coating, such as reducing impurities in the SiC matrix that constitutes the SiC / SiC material, or covering the surface of the SiC / SiC composite material with SiC fibers that are more corrosion-resistant than the SiC matrix.

[0051] (2) Beryllium Block The beryllium block 12 is a columnar structure made of metallic beryllium or a beryllium compound such as beryllide (beryllium intermetallic compound). The beryllium block 12 is arranged such that one of its two bottom surfaces faces the plasma side and the other bottom surface faces away from the plasma side. Hereinafter, the bottom surface of the beryllium block 12 that faces the plasma side will also be referred to as the "plasma-side bottom surface". The bottom surface of the beryllium block 12 that faces away from the plasma side will also be referred to as the "anti-plasma-side bottom surface". In this embodiment, the shape of the beryllium block 12 is a hexagonal prism. In this embodiment, the material of the beryllium block 12 is beryllide (for example, Be １２ V or Be １２ Use Ti).

[0052] The beryllium block 12 has a plasma-side insertion hole 12a extending from the plasma-side bottom surface to the anti-plasma-side bottom surface. The plasma-side insertion hole 12a is an insertion hole for inserting the cylindrical portion 111 of the lithium encapsulant 11, and the depth of the plasma-side insertion hole 12a is the same as or approximately the same as the height of the cylindrical portion 111. The beryllium block 12 also has an anti-plasma-side insertion hole 12b extending from the anti-plasma-side bottom surface to the plasma-side bottom surface. The anti-plasma-side insertion hole 12b is an insertion hole for inserting the cooling head 22 of the back wall 2, and the depth of the anti-plasma-side insertion hole 12b is the same as or approximately the same as the height of the cooling head 22.

[0053] The beryllium block 12 is divided by a plane perpendicular to the central axis of the beryllium block 12 into a plasma-side block positioned on the plasma side and an anti-plasma-side block positioned on the opposite side of the plasma side. Furthermore, the plasma-side block is divided into a plurality of plasma-side subblocks 121 by a plane that includes the central axis of the beryllium block 12 and the edges of the side surface of the beryllium block 12. The anti-plasma-side block is divided into a plurality of anti-plasma-side subblocks 122 by a plane that includes the central axis of the beryllium block 12 and the edges of the side surface of the beryllium block 12.

[0054] In this embodiment, the hexagonal prism-shaped plasma-side block is divided into six congruent plasma-side sub-blocks 121. Each plasma-side sub-block 121 is triangular prism-shaped. However, each plasma-side sub-block 121 has a notch 121a formed therein that constitutes the plasma-side insertion hole 12a when the six plasma-side sub-blocks 121 are combined. Furthermore, a recess 121b is formed at the lower end of the notch 121a that engages with a convex portion 111b that protrudes outward from the end of the cylindrical portion 111 opposite to the plasma side.

[0055] In this embodiment, the plasma-side block is divided into six plasma-side subblocks 121, but the present invention is not limited thereto. The plasma-side block can be divided into any number of plasma-side subblocks 121. Furthermore, instead of providing a protrusion 111b at the lower end of the cylindrical portion 111, a protrusion 111b may be provided in the middle of the cylindrical portion 111, and instead of providing a recess 121b at the lower end of the notch 121a, a recess 121b may be provided in the middle of the notch 121a.

[0056] In this embodiment, the hexagonal prism-shaped anti-plasma side block is divided into six congruent anti-plasma side sub-blocks 122. Each anti-plasma side sub-block 122 has a triangular prism shape. However, each anti-plasma side sub-block 122 has a notch 122a formed therein that constitutes the anti-plasma side insertion hole 12b when the six anti-plasma side sub-blocks 122 are combined. Furthermore, a recess 122b is formed in the middle of the notch 122a, which engages with a convex portion 22a that protrudes outward from the middle portion of the cooling head 22.

[0057] In this embodiment, the anti-plasma side block is divided into six anti-plasma side sub-blocks 122, but the present invention is not limited thereto. The anti-plasma side block can be divided into any number of anti-plasma side sub-blocks 122. Also, instead of providing a protrusion 22a in the middle of the cooling head 22, a protrusion 22a may be provided at the lower end of the cooling head 22, and instead of providing a recess 122b in the middle of the notch 122a, a recess 122b may be provided at the lower end of the notch 122a.

[0058] In this embodiment, both the plasma-side block and the anti-plasma-side block are made of veriride, but this is not the only option. For example, the plasma-side block may be made of veriride, and the anti-plasma-side block may be made of a material that reflects neutrons and has high thermal conductivity. Examples of materials that reflect neutrons and have high thermal conductivity include copper alloys.

[0059] Furthermore, in this embodiment, the beryllium block 12 is divided into a plasma-side block and an anti-plasma-side block, but the embodiment is not limited to this. For example, a beryllium block 12 that is not divided into a plasma-side block and an anti-plasma-side block may be divided into a plurality of small blocks by a plane that includes the central axis of the beryllium block 12 and the edges of the side surface of the beryllium block 12.

[0060] (3) Sleeve The sleeve 13 is a cylindrical structure that covers the side surface of the beryllium block 12. The sleeve 13 has a slit 13a that extends from the plasma side end to the opposite side of the plasma, and a slit 13b that extends from the plasma side end to the middle. In this embodiment, a slit 13a is formed along one of the six ridges of the sleeve 13, and slits 13b are formed along each of the remaining five ridges. Therefore, the side of the sleeve 13 opposite to the plasma side functions as a C-ring that elastically embraces and binds each of the anti-plasma side small blocks 122 from the outside. In addition, each portion of the sleeve 13 divided by the slit 13b on the plasma side functions as a leaf spring that elastically presses the plasma side small blocks 121 that are in contact with that portion inward. In this embodiment, the material of the sleeve 13 is a SiC / SiC composite material.

[0061] The sleeve 13 is sized so that its inner surface contacts the side surface of the beryllium block 12, which expands due to thermal activity during fusion reactor operation. Therefore, at room temperature, a gap is created between the side surface of the beryllium block 12 and the outer surface of the sleeve 13. This allows the beryllium block 12 to be easily inserted into the sleeve 13 at room temperature.

[0062] Using the sleeve 13, the fuel breeding unit 1 can be assembled to the back wall 2 described later by following the steps 1 to 4 below. Note that the steps 1 to 4 below may be performed in the order of step 1, step 2, step 3, step 4, or in the order of step 3, step 4, step 1, step 2.

[0063] Procedure 1: Arrange the six plasma-side small blocks 121 around the cylindrical portion 111 of the lithium encapsulant 11. At this time, determine the orientation of each plasma-side small block 121 so that the notch 121a faces the cylindrical portion 111.

[0064] Step 2: Insert the six plasma-side small blocks 121 into the sleeve 13 while they are assembled and pressed against the cylindrical portion 111.

[0065] Furthermore, when the six plasma-side small blocks 121 are assembled by pressing them against the cylindrical portion 111, the protrusions 111b provided on the cylindrical portion 111 engage with the recesses 121b provided on each plasma-side small block 121. Therefore, when the six plasma-side small blocks 121 are bound together by the sleeve 13, it is possible to prevent the cylindrical portion 111 from coming out of the plasma-side insertion hole 12a of the beryllium block 12.

[0066] Step 3: Place the six anti-plasma side small blocks 122 around the cooling head 22 of the back wall 2. At this time, determine the orientation of each anti-plasma side small block 122 so that the notch 122a faces the cooling head 22.

[0067] Step 4: Insert the six anti-plasma side small blocks 122 into the sleeve 13, with the blocks assembled so as to be pressed against the cooling head 22.

[0068] Furthermore, when the six anti-plasma side small blocks 122 are assembled by pressing them against the cooling head 22, the protrusions 22a on the cooling head 22 engage with the recesses 122b on each anti-plasma side small block 122. Therefore, when the six anti-plasma side small blocks 122 are bound together by the sleeve 13, it is possible to prevent the cooling head 22 from coming out of the anti-plasma side insertion hole 12b of the beryllium block 12.

[0069] Here, we have described a method in which the six plasma-side small blocks 121 are assembled by pressing them against the cylindrical portion 111 and then inserted into the sleeve 13 for binding, but the method is not limited to this. Conversely, a method may be adopted in which the six plasma-side small blocks 121 are inserted into the sleeve 13 for binding, and then the cylindrical portion 111 is inserted into the plasma-side insertion hole 12a. This is because, at room temperature, a gap exists between the plasma-side small blocks 121 and the inner surface of the sleeve 13. Even if the height of the protrusions 111b provided on the cylindrical portion 111 is greater than this gap, the six plasma-side small blocks 121 are only elastically bound together by the sleeve 13, so it is possible to push the cylindrical portion 111 into the plasma-side insertion hole 12a while expanding the plasma-side insertion hole 12a. In this case, it is preferable to make the shape of the protrusions 111b and recesses 121b smooth and without corners. This makes it easier for the convex portion 111b to slide into the concave portion 121b when the cylindrical portion 111 is inserted into the plasma-side insertion hole 12a.

[0070] Similarly, although a method of assembling the six anti-plasma side small blocks 122 by pressing them against the cooling head 22 and then inserting and binding them into the sleeve 13 has been described here, the method is not limited to this. Conversely, a method of inserting and binding the six anti-plasma side small blocks 122 into the sleeve 13 and then inserting the cooling head 22 into the anti-plasma side insertion hole 12b may also be adopted. This is because, at room temperature, a gap exists between the anti-plasma side small blocks 122 and the inner surface of the sleeve 13. Even if the height of the protrusion 22a provided on the cooling head 22 is greater than this gap, the six anti-plasma side small blocks 122 are only elastically bound together by the sleeve 13, so it is possible to push the cooling head 22 into the anti-plasma side insertion hole 12b while expanding the anti-plasma side insertion hole 12b. In this case, it is preferable to make the shape of the protrusion 22a and recess 122b smooth and without corners. This makes it easier for the protrusion 22a to slide into the recess 122b when the cooling head 22 is inserted into the insertion hole 12b on the opposite side of the plasma.

[0071] (Specific Example 1 of Lithium Encapsulation) A first specific example of the lithium encapsulation 11 will be described with reference to Figure 4. Figure 4 is a cross-sectional view of the lithium encapsulation 11 according to this specific example.

[0072] In the lithium encapsulant 11 according to this specific example, metallic lithium is sealed within a cavity 11a. The pressure inside the cavity 11a is set to a pressure lower than atmospheric pressure (approximately 5.4 kPa in this specific example) so that the boiling point of the liquid metallic lithium falls within the target operating temperature range of the fusion reactor (for example, 800°C to 1100°C). Furthermore, the heat transport function of the lithium encapsulant 11 according to this specific example is realized by the lithium encapsulant 11 operating as a heat pipe with liquid metallic lithium as the working fluid. In this specific example, capillary action is used as the driving force for transporting liquid metallic lithium from the anti-plasma side to the plasma side. In addition, a transport path provided on the inner surface of the cylindrical portion 111 is used as a transport path for transporting liquid metallic lithium from the anti-plasma side to the plasma side. In the lithium encapsulant 11 according to this specific example, a capillary structure 111c is provided as this transport path.

[0073] The operation of the lithium encapsulant 11 in this specific example will be described below, divided into (1) operation for realizing the neutron moderation function, (2) operation for realizing the heat transport function, and (3) operation for realizing the tritium breeding function. In addition, (4) notable features of the lithium encapsulant 11 in this specific example and (5) modified examples of the lithium encapsulant 11 in this specific example will be described.

[0074] (1) Operation to realize the neutron deceleration function Neutrons generated by nuclear fusion are incident on the lid portion 112 and flange portion 114 of the lithium encapsulant 11 from the plasma side. The lid portion 112 and flange portion 114 decelerate these neutrons, thereby converting their kinetic energy into thermal energy. In addition, the lithium sealed in the cavity 11a also decelerates these neutrons, thereby converting their kinetic energy into thermal energy. This realizes the neutron deceleration function of the lithium encapsulant 11.

[0075] The lithium sealed in the lid portion 112, flange portion 114, and cavity 11a generates a temperature gradient in the lithium encapsulant 11, with the lid portion 112 being the higher temperature side and the bottom portion 113 being the lower temperature side, due to the heat generated by (1) slowing down neutrons produced by nuclear fusion, or (2) undergoing a nuclear transmutation reaction using neutrons multiplied in the beryllium block 12. In this case, the temperature of the region including at least the lid portion 112 becomes above the boiling point of metallic lithium, and the temperature of the region including at least the bottom portion 113 becomes below the boiling point of metallic lithium. For example, if the atmospheric pressure of gaseous metallic lithium in cavity 11a is 5.4 kPa, the boiling point of liquid metallic lithium in cavity 11a is 1000°C. In this case, the temperature of the region including at least the lid portion 112 becomes 1000°C or higher, and the temperature of the region including at least the bottom portion 113 becomes less than 1000°C.

[0076] Hereinafter, the region in the lithium encapsulant 11 where the temperature during fusion reactor operation is above the boiling point of metallic lithium will be referred to as the evaporation region Zg. The evaporation region Zg may include the entire area of ​​the lid portion 112, as well as the area of ​​the cylindrical portion 111 adjacent to the lid portion 112. Furthermore, the region in the lithium encapsulant 11 where the temperature during fusion reactor operation is below the boiling point of metallic lithium will be referred to as the condensation region Zl. The condensation region Zl may include the entire area of ​​the bottom portion 113, as well as the area of ​​the cylindrical portion 111 adjacent to the bottom portion 113.

[0077] (2) The metallic lithium sealed in the operating cavity 11a circulates within the cavity 11a while repeatedly evaporating and condensing as follows. Specifically, the liquid metallic lithium present in the condensation region Zl is transported through the capillary structure 111c toward the lid 112. This is because the surface tension of the liquid metallic lithium causes capillary action. The liquid metallic lithium that reaches the evaporation region Zg absorbs heat and evaporates, changing into gaseous metallic lithium. On the other hand, the gaseous metallic lithium present in the evaporation region Zg is transported outside the capillary structure 111c toward the bottom 113. The gaseous metallic lithium that reaches the condensation region Zl releases heat and condenses, changing into liquid metallic lithium.

[0078] The metallic lithium sealed within the cavity 11a circulates within the cavity 11a, repeatedly undergoing evaporation and condensation as described above. This circulates the lithium present in the lid portion 112, the flange portion 114, and the evaporation region Zg, which slows down neutrons, and the heat generated from this process is transported as latent heat from the plasma side to the opposite side. Furthermore, the metallic lithium sealed within the cavity 11a also transports radiant heat from the plasma as latent heat from the plasma side to the opposite side. This realizes the heat transport function of the lithium encapsulant 11.

[0079] The SiC / SiC composite material is composed of a knitted structure made of SiC fibers and a SiC matrix that fills the gaps in the knitted structure. Therefore, for example, if the knitted structure is exposed on the inner surface of the cylindrical portion 111 without filling the gaps with the SiC matrix, this knitted structure functions as the capillary structure 111c described above. However, the capillary structure 111c may be a porous structure and is not limited to a knitted structure. In other words, any SiC / SiC composite material containing any structure that can generate capillary action due to the surface tension of liquid metallic lithium can be used as the material for the cylindrical portion 111.

[0080] (3) Operation to realize the tritium breeding function Neutrons slowed down by the lid portion 112 pass through the lid portion 112 and enter the cavity 11a. Neutrons slowed down by the flange portion 114 pass through the flange portion 114 and enter the beryllium block 12. The beryllium block 12 multiplies these neutrons. The neutrons multiplied by the beryllium block 12 pass through the cylindrical portion 111 and enter the cavity 11a. The neutrons that enter the cavity 11a in this way split the lithium atoms in the metallic lithium (gaseous metallic lithium or liquid metallic lithium) sealed in the cavity 11a into tritium atoms and helium atoms.

[0081] When the atmospheric pressure of gaseous metallic lithium in cavity 11a is 5.4 kPa, the boiling point of lithium (1000°C) is higher than the decomposition temperature of lithium hydride (LiT) (720°C). Therefore, the tritium produced in the evaporation region Zg exists as tritium atoms in the gaseous metallic lithium. On the other hand, tritium produced in the region of the aggregation region Zl where the temperature is below the decomposition temperature of lithium hydride exists as more stable lithium hydride (LiT) in the liquid metallic lithium. However, the liquid metallic lithium is transported from the aggregation region Zl to the evaporation region Zg by capillary action. Therefore, the lithium hydride in the liquid metallic lithium decomposes into lithium atoms and tritium atoms when the liquid metallic lithium evaporates in the evaporation region Zg. Consequently, in the evaporation region Zg, in addition to the tritium atoms produced in the evaporation region Zg, the tritium produced in the aggregation region Zl accumulates as tritium atoms. The tritium atoms accumulated in the evaporation region Zg in this way diffuse into the lid portion 112. Then, tritium atoms that reach the plasma-side surface of the lid 112 react with electrons from the plasma and are released into the furnace. This realizes the tritium breeding function of the lithium encapsulant 11.

[0082] Here, we have described the mode in which the generated tritium permeates the lid 112 as tritium atoms, but we are not limited to this. That is, there may be modes in which the generated tritium permeates the lid 112 as tritium ions, or modes in which the generated tritium permeates the lid 112 as tritium molecules (molecules containing tritium), and these modes are also included in the scope of the present invention.

[0083] (4) Notable features of the lithium encapsulant The first notable feature of the lithium encapsulant 11 in this specific example is that it releases the generated tritium into the reactor. This eliminates the need to draw tritium recovery piping into or out of the fuel breeder unit 1.

[0084] Furthermore, a second noteworthy point regarding the lithium encapsulant 11 in this specific example is that it operates as a heat pipe using liquid metallic lithium as the working fluid, transporting the heat generated by slowing down neutrons and the radiant heat from the plasma as latent heat. This eliminates the need to draw primary cooling piping into or out of the fuel breeding unit 1.

[0085] (5) Modified Lithium Encapsulation In the lithium encapsulant 11 shown in Figure 4, the lid portion 112 is not covered with a tungsten coating 115. Therefore, when used in a fuel breeding unit 1 that is positioned around the divertor or limiter, i.e., in close proximity to the plasma, the lid portion 112 is prone to wear due to physical sputtering. In such cases, it is preferable to adopt a configuration in which the lid portion 112 is covered with a tungsten coating 115 in order to suppress wear of the lid portion 112. Figure 5 is a cross-sectional view of a lithium encapsulant 11 that adopts a configuration in which the lid portion 112 is covered with a tungsten coating 115.

[0086] Furthermore, in fuel breeding units 1 positioned around the divertor or limiter, the heat input is greater compared to fuel breeding units 1 positioned elsewhere. For this reason, it is preferable to also employ configurations to improve heat removal performance, such as increasing the length of the cylindrical portion 111 of the lithium encapsulant 11 to bring the bottom portion 113 of the lithium encapsulant 11 closer to the cooling head 22 of the back wall 2, or increasing the diameter of the cylindrical portion 111 of the lithium encapsulant 11 to increase the amount of liquid metallic lithium that functions as the working fluid for the heat pipe.

[0087] (Specific Example 2 of Lithium Encapsulation) Figure 6 shows the structure of the lithium encapsulation 11 according to the second specific example. Figure 6 is a cross-sectional view of the lithium encapsulation 11 according to this specific example.

[0088] In the lithium encapsulant 11 according to this specific example, metallic lithium is sealed within a cavity 11a. The pressure inside the cavity 11a is set to a pressure lower than atmospheric pressure (approximately 5.4 kPa in this specific example) so that the boiling point of the liquid metallic lithium falls within the target operating temperature range of the nuclear fusion reactor (for example, 800°C to 1100°C). Furthermore, the heat transport function of the lithium encapsulant 11 according to this specific example is realized by the lithium encapsulant 11 operating as a heat pipe with liquid metallic lithium as the working fluid. In this specific example, the pressure difference due to the phase change of metallic lithium is used as the driving force for transporting liquid metallic lithium from the anti-plasma side to the plasma side. In addition, a transport path provided in the center of the cavity 11a is used as the transport path for transporting liquid metallic lithium from the anti-plasma side to the plasma side. In the lithium encapsulant 11 according to this specific example, a capillary tube 116 is provided as this transport path, with one end open in the evaporation region Zg and the other end open in the condensation region Zl. In this embodiment, the capillary tube 116 is made of a SiC / SiC composite material. The definitions of the evaporation region Zg and the aggregation region Zl are as described above.

[0089] The operations of the lithium encapsulant 11 in this specific example, specifically the operations for realizing the neutron moderation function and the operations for realizing the tritium breeding function, are the same as those of the lithium encapsulant 11 in the first specific example described above. Therefore, the operation of the lithium encapsulant 11 in this specific example will be explained below, focusing on (1) the operations for realizing the heat transport function. In addition, (2) the notable features of the lithium encapsulant 11 in this specific example and (3) modifications of the lithium encapsulant 11 in this specific example will be explained.

[0090] (1) The metallic lithium sealed in the operating cavity 11a, which is necessary for realizing the heat transport function, circulates within the cavity 11a while repeatedly evaporating and condensing as follows. That is, of the metallic lithium sealed in the cavity 11a, the liquid metallic lithium present in the condensation region Zl is transported through the capillary tube 116 toward the lid portion 112. This is because the gaseous metallic lithium, whose pressure has increased in the evaporation region Zg, pushes the liquid metallic lithium present outside the capillary tube 116 in the condensation region Zl toward the bottom portion 113. The liquid metallic lithium that reaches the evaporation region Zg absorbs heat and evaporates, changing into gaseous metallic lithium. On the other hand, of the metallic lithium sealed in the cavity 11a, the gaseous metallic lithium present in the evaporation region Zg is transported outside the capillary tube 116 toward the bottom portion 113. The gaseous metallic lithium that reaches the condensation region Zl releases heat and condenses, changing into liquid metallic lithium.

[0091] The metallic lithium sealed within the cavity 11a circulates within the cavity 11a, repeatedly undergoing evaporation and condensation as described above. This circulates the lithium present in the lid portion 112, the flange portion 114, and the evaporation region Zg, which slows down neutrons, and the heat generated from this process is transported as latent heat from the plasma side to the opposite side. Furthermore, the metallic lithium sealed within the cavity 11a also transports radiant heat from the plasma as latent heat from the plasma side to the opposite side. This realizes the heat transport function of the lithium encapsulant 11.

[0092] (2) Notable features of the lithium encapsulant The first notable feature of the lithium encapsulant 11 in this specific example is that, like the lithium encapsulant 11 in the example described above, it releases the generated tritium into the reactor. This eliminates the need to draw tritium recovery piping into or out of the fuel breeding unit 1.

[0093] Furthermore, a second noteworthy point regarding the lithium encapsulant 11 in this specific example is that, similar to the lithium encapsulant 11 in the example described above, it operates as a heat pipe using liquid metallic lithium as the working fluid, transporting the heat generated by slowing down neutrons and the radiant heat from the plasma as latent heat. This eliminates the need to draw primary cooling piping into or out of the fuel breeding unit 1.

[0094] (3) Modified Lithium Encapsulation In the lithium encapsulant 11 shown in Figure 6, the lid portion 112 is not covered with a tungsten coating 115. For this reason, it is placed around the divertor or limiter. In other words, when used in a fuel breeding unit 1 that is placed close to the plasma, the lid portion 112 is prone to wear due to physical sputtering. In such cases, it is preferable to adopt a configuration in which the lid portion 112 is covered with a tungsten coating 115 in order to suppress wear of the lid portion 112. Figure 7 is a cross-sectional view of a lithium encapsulant 11 that adopts a configuration in which the lid portion 112 is covered with a tungsten coating 115.

[0095] Furthermore, in fuel breeding units 1 located around the diverter or limiter, the amount of heat input is greater compared to fuel breeding units 1 located elsewhere. For this reason, it is preferable to also employ configurations to improve heat removal performance, such as increasing the length of the cylindrical portion 111 of the lithium encapsulant 11 to bring the bottom portion 113 of the lithium encapsulant 11 closer to the cooling head 22 of the back wall 2, or increasing the diameter of the cylindrical portion 111 of the lithium encapsulant 11 to increase the amount of liquid metallic lithium that functions as the working fluid for the boiling-driven heat pipe.

[0096] (Specific Example 3 of Lithium Encapsulation) A third specific example of the lithium encapsulation 11 will be described with reference to Figure 8. Figure 8 is a cross-sectional view of the lithium encapsulation 11 according to this specific example.

[0097] The heat transport function of the lithium encapsulant 11 in this specific example is realized by contact heat conduction. Therefore, the lithium sealed in the cavity 11a may be metallic lithium or a lithium compound. Suitable lithium compounds include, for example, lithium oxide (Li ２ O) and lithium titanate (Li ２ TiO ３ ) are examples. In this specific example, the lithium compound is assumed to be sealed in the cavity 11a as a pebble.

[0098] The operation of the lithium encapsulant 11 in this specific example, specifically for realizing the neutron moderation function, is the same as the operation of the lithium encapsulant 11 in the first specific example described above. Therefore, the operation of the lithium encapsulant 11 in this specific example will be explained below, focusing on (1) the operation for realizing the heat transport function and (2) the operation for realizing the tritium breeding function. In addition, (3) the notable features of the lithium encapsulant 11 in this specific example will be explained.

[0099] (1) Operation to realize the heat transport function Note that the heat transport function performed by the lithium encapsulant 11 in this specific example is limited because it depends on contact heat conduction. Therefore, the beryllium block 12 will be responsible for most of the heat transport function required of the fuel breeding unit 1.

[0100] (2) Operation to realize the tritium breeding function Neutrons slowed down by the lid portion 112 pass through the lid portion 112 and enter the cavity 11a. Neutrons slowed down by the flange portion 114 pass through the flange portion 114 and enter the beryllium block 12. The beryllium block 12 multiplies these neutrons. The neutrons multiplied by the beryllium block 12 pass through the cylindrical portion 111 and enter the cavity 11a. The neutrons that enter the cavity 11a in this way split the lithium atoms in the lithium compound sealed in the cavity 11a into tritium atoms and helium atoms. The tritium atoms produced by the splitting of lithium atoms exist in the cavity 11a as tritium atoms in the vicinity of the lid portion 112 where the temperature exceeds the decomposition temperature of lithium hydride (LiT), and as lithium hydride in other regions.

[0101] Tritium atoms or tritium hydride (hereinafter also simply referred to as "tritium") produced by the fission of lithium atoms diffuse within the cavity 11a. Of the tritium diffused within the cavity 11a, the tritium that reaches the surface of the lid 112 opposite to the plasma side diffuses within the lid 112. Of the tritium diffused within the lid 112, the tritium that reaches the surface of the lid 112 on the plasma side reacts with electrons and is released into the furnace. Meanwhile, of the tritium diffused within the cavity 11a, the tritium that reaches the inner surface of the cylindrical portion 111 diffuses within the cylindrical portion 111. Of the tritium diffused within the cylindrical portion 111, the tritium that reaches the inner surface of the beryllium block 12 diffuses within the beryllium block 12. Of the tritium diffused within the beryllium block 12, the tritium that reaches the surface of the flange 114 opposite to the plasma side diffuses within the flange 114. Then, of the tritium diffused within the flange portion 114, the tritium that reaches the surface of the coating 115 opposite to the plasma side diffuses within the coating 115. Of the tritium diffused within the coating 115, the tritium that reaches the plasma side surface of the coating 115 reacts with electrons and is released into the furnace.

[0102] (3) Notable features of the lithium encapsulant The notable feature of the lithium encapsulant 11 in this specific example is that, like the lithium encapsulant 11 in the example described above, it releases the generated tritium atoms into the reactor. This eliminates the need to draw tritium recovery piping into or out of the fuel breeder unit 1.

[0103] It should be noted that the heat transport function performed by the lithium encapsulant 11 in this specific example is limited because it relies on contact heat conduction. However, if the fusion reactor is used in a location with a low surface heat load, the heat transport function required for the fuel breeder unit 1 can be provided by the beryllium block 12. Therefore, there is no need to run primary cooling piping into or out of the fuel breeder unit 1.

[0104] [Backwall] A backwall 2 according to one embodiment of the present invention will be described with reference to Figures 9 and 10. Figure 9 is a perspective view of a water-cooled backwall 2. Figure 10 is a perspective view of a helium-cooled backwall 2. The backwall 2 is also called a cooling shield rear wall and is located on the side of the fuel breeding unit 1 opposite the plasma side. The structure including the fuel breeding unit 1 and the backwall 2, or the assembly thereof, is sometimes called a "blanket" or "lithium blanket".

[0105] (1) Water-cooled backwall The water-cooled backwall 2, as shown in Figure 9, comprises a cooling plate 21 and a plurality of cooling heads 22. The cooling plate 21 is a plate-shaped structure, and each cooling head 22 is a columnar structure provided on the plasma-side surface of the cooling plate 21. In this embodiment, low-activation ferrite steel is used as the material for the cooling plate 21 and the cooling heads 22. The material for the cooling plate 21 and the cooling heads 22 does not need to be ferromagnetic, as long as it can provide the backwall 2 with heat resistance and pressure resistance. The cooling heads 22 do not need to be structures that protrude from the plasma-side surface of the cooling plate 21, and their shape may be, for example, columnar, conical, or dome-shaped.

[0106] A network of coolant channels is laid out inside the back wall 2. In this embodiment, to enhance the neutron shielding function of the back wall 2, a mixture of water and iron in a ratio of 3:7 is used as the coolant. Control coils for ELM (Edge Localized Mode) control may be placed on the plasma-side surface of the back wall 2, or on the surface opposite the plasma side.

[0107] The fuel breeder unit 1 is installed by inserting the cooling head 22 of the back wall 2 into the anti-plasma side through hole 122a of the beryllium block 12. The position of each cooling head 22 on the cooling plate 21 is determined so that the coatings 115 of the fuel breeder unit 1 attached to each cooling head 22 are laid out in a single plane. When the fusion reactor is operating, the flange 114 and coating 115 of the fuel breeder unit 1 attached to each cooling head 22 expand due to thermal expansion. As a result, for two adjacent fuel breeder units 1, the gap between the coatings 115 of these two fuel breeder units 1 disappears along with the gap between the flanges 114 of these two fuel breeder units 1. Consequently, the coatings 115 of two adjacent fuel breeder units 1 become electrically conductive to each other. As a result, the coatings 115 of the fuel breeder unit 1 attached to each cooling head 22 function as an electrically integrated conductive shell.

[0108] (2) Helium-cooled backwall The helium-cooled backwall 2, as shown in Figure 10, comprises a helium cooling passage 23 and a neutron shielding plate 24. The helium cooling passage 23 is a plate-shaped structure with a helium gas flow path inside. Holes 23a leading to the helium gas flow path are drilled on the plasma-side surface of the helium cooling passage 23. In this embodiment, SiC / SiC material is used as the material for the helium cooling passage 23. The neutron shielding plate 24 is a plate-shaped structure laminated on the side of the helium cooling passage 23 opposite to the plasma side. In this embodiment, boron carbide (B) is used as the material for the neutron shielding plate 24. ４ C) is used. Tungsten carbide (WC), gadolinium oxysulfide (GOS), or tungsten boride (WB) may be used instead of boron carbide.

[0109] The connection between the fuel breeding unit 1 and the two backwalls 2 is made, for example, by inserting one end of the cooling rod 25 into the hole 23a of the helium cooling channel 23 and inserting the other end of the cooling rod 25 into the through-hole 122a on the anti-plasma side of the beryllium block 12. The positions of the holes 23a in the helium cooling channel 23 are determined such that the coating 115 of the fuel breeding unit 1 attached to each hole 23a is laid flat in a single plane. Regarding the point that the coatings 115 of the fuel breeding units 1 attached to the holes 23a are electrically integrated during the operation of the fusion reactor, it is the same as that of the water-cooled backwall 2.

[0110] In addition, the fuel breeding unit 1 may be directly attached to the helium cooling channel 23 without passing through the cooling rod 25. In this case, in the beryllium block 12, a through-hole extending from the plasma-side bottom surface to the anti-plasma-side bottom surface is provided instead of the plasma-side insertion hole 12a and the anti-plasma-side insertion item 12b. Also, in the lithium sealing body 11, the length of the cylindrical portion 111 is extended to be longer than the height of the beryllium block 12 (the distance from the plasma-side bottom surface to the anti-plasma-side bottom surface). Then, the tip of the cylindrical portion 111 protruding from the anti-plasma-side bottom surface of the beryllium block 12 is inserted into the hole 23a of the helium cooling channel 23.

[0111] Here, the helium-cooled backwall 2, that is, the backwall 2 with the refrigerant being helium gas, has been described, but it is not limited to this. For example, instead of the helium-cooled backwall 2, a supercritical CO ２ cooled backwall 2 with the refrigerant being supercritical CO ２ or a liquid metal-cooled backwall 2 with the refrigerant being liquid metal may be used.

[0112] (3) In-core maintenance As described above, the fuel breeding unit 1 and the back wall 2 can be easily combined and easily separated. Therefore, if a malfunction occurs in any of the multiple fuel breeding units 1 attached to the back wall 2, only the malfunctioning fuel breeding unit 1 can be easily replaced. Each fuel breeding unit 1 is small and lightweight. For example, the size of the lithium encapsulant 11 can be such that the diameter of the cylindrical part 111 is about 10 cm and the length of the cylindrical part 111 is about 30 cm. The size of the beryllium block 12 can be such that the diameter is 20 cm or more and 30 cm or less (one side of the hexagonal base is 10 cm or more and 15 cm or less) and the length is about 50 cm. In this case, the weight of the fuel breeding unit 1 will be 40 kg or more and 70 kg or less. Of this, about 5 kg is the weight of the lithium encapsulant 11 and the remainder is the weight of the beryllium block 12. Therefore, the removal of the old fuel breeder unit 1 and the installation of the new fuel breeder unit 1 can be performed, for example, using a robotic arm that grips the workpiece using a vacuum suction method. Furthermore, the transport of the removed old fuel breeder unit 1 and the transport of the new fuel breeder unit 1 to be installed can be performed, for example, using a vacuum suction pipe. Note that instead of replacing the entire fuel breeder unit 1, only the lithium encapsulant 11 may be replaced (the beryllium block 12 and sleeve 13 do not need to be replaced). In this case, the removal of the old lithium encapsulant 11 and the installation of the new lithium encapsulant 11 are performed using a robotic arm. As a result of the above, the time and cost required for in-reactor maintenance work can be reduced. In addition, the amount of radioactive waste generated as a result of in-reactor maintenance work can be reduced. This makes it possible to increase the operating rate of the fusion reactor and lower the power generation cost of the fusion reactor.

[0113] Furthermore, the main material of the fuel breeder unit 1 and the back wall 2 (in the case of a water-cooled system) is a SiC / SiC composite material. SiC / SiC composite materials have the property that when the fusion reactor is shut down, the radiation dose decays relatively quickly and almost no decay heat is emitted. Therefore, not only the time required for in-reactor maintenance work but also the waiting time from the shutdown of the fusion reactor to the start of maintenance work can be reduced. This makes it possible to further increase the operating rate of the fusion reactor. This makes it possible to further increase the operating rate of the fusion reactor and further reduce the power generation cost of the fusion reactor.

[0114] [Summary] (Aspect 1) A fuel breeder unit that converts the kinetic energy of neutrons generated by nuclear fusion in a plasma into thermal energy and generates tritium using the neutrons, and releases the generated tritium directly into the reactor.

[0115] According to the above configuration, there is no need to run piping for tritium recovery to the fuel breeder unit. Therefore, it is possible to realize a fusion reactor with low power generation costs.

[0116] (Aspect 2) The fuel breeding unit according to aspect 1, comprising a cylindrical portion having one opening facing the plasma side and the other opening facing the opposite side from the plasma side, a lid portion that closes the one opening, and a bottom portion that closes the other opening, wherein lithium is sealed in a cavity surrounded by the cylindrical portion, the lid portion and the bottom portion, and the lid portion is permeable to tritium.

[0117] According to the above configuration, tritium generated within the cavity of the lithium encapsulant can be directly released into the reactor of the lithium encapsulant through the lid of the lithium encapsulant that faces the plasma inside the reactor.

[0118] (Aspect 3) The fuel breeding unit according to aspect 2, wherein liquid metallic lithium is sealed in the cavity, and a transport channel is provided on the inner surface of the cylindrical portion for transporting the liquid metallic lithium from the side opposite to the plasma side to the plasma side.

[0119] According to the above configuration, the lithium encapsulant functions as a heat pipe with liquid metallic lithium as the working fluid. Therefore, the heat generated by neutron deceleration, along with radiant heat from the plasma, can be efficiently transported from the plasma side of the lithium encapsulant to the opposite side. This allows the heat generated in the fuel breeding unit, along with radiant heat from the plasma, to be efficiently transferred to the back wall located on the opposite side of the fuel breeding unit from the plasma side. In other words, the heat load concentrated on the plasma side can be distributed throughout the entire fuel breeding unit, and further to the back wall. Therefore, there is no need to run cooling piping into the fuel breeding unit. Consequently, a fusion reactor with a reduced risk of cooling water flowing through cooling piping being released into the reactor can be realized.

[0120] (Aspect 4) The fuel breeder unit according to aspect 3, wherein the transport channel has a capillary structure.

[0121] According to the above configuration, the liquid metallic lithium can be transported from the side opposite the plasma (low temperature side) to the plasma side (high temperature side) by capillary action.

[0122] (Aspect 5) The fuel breeding unit according to aspect 2, wherein liquid metallic lithium is sealed in the cavity, and a transport channel is provided in the center of the cavity for transporting the liquid metallic lithium from the side opposite to the plasma side to the plasma side.

[0123] According to the above configuration, the lithium encapsulant functions as a heat pipe with liquid metallic lithium as the working fluid. Therefore, the heat generated by neutron deceleration, along with radiant heat from the plasma, can be efficiently transported from the plasma side of the lithium encapsulant to the opposite side. This allows the heat generated in the fuel breeding unit, along with radiant heat from the plasma, to be efficiently transferred to the back wall located on the opposite side of the fuel breeding unit from the plasma side. In other words, the heat load concentrated on the plasma side can be distributed throughout the entire fuel breeding unit, and further to the back wall. Therefore, there is no need to run cooling piping into the fuel breeding unit. Consequently, a fusion reactor with a reduced risk of cooling water flowing through cooling piping being released into the reactor can be realized.

[0124] (Aspect 6) The fuel breeding unit according to aspect 5, wherein the transport channel is a narrow tube with one end opening in the region including the lid and the other end opening in the region including the bottom.

[0125] According to the above configuration, the liquid metallic lithium can be transported from the side opposite the plasma (low temperature side) to the plasma side (high temperature side) by the pressure difference caused by the phase change of metallic lithium.

[0126] (Aspect 7) The fuel breeding unit according to aspect 2, wherein lithium compounds are sealed in the cavity as pebbles.

[0127] According to the above configuration, the heat generated by neutron deceleration can be transported, along with radiant heat from the plasma, from the plasma side of the lithium encapsulant to the opposite side by contact heat conduction. This allows the heat generated in the fuel breeding unit, along with radiant heat from the plasma, to be moved to the back wall located on the opposite side of the fuel breeding unit from the plasma side. If the heat transport function of the fuel breeding unit is insufficient, the beryllium block surrounding the fuel breeding unit can supplement the heat transport function. This allows the heat load concentrated on the plasma side to be distributed throughout the fuel breeding unit and further to the back wall. Therefore, there is no need to run cooling pipes to the fuel breeding unit. Consequently, a fusion reactor can be realized with a reduced risk of cooling water flowing through cooling pipes being released into the reactor.

[0128] (Aspect 8) A fuel breeding unit according to any one of aspects 2 to 7, wherein at least one of the cylindrical portion, the lid portion, and the bottom portion is made of a SiC / SiC composite material.

[0129] According to the above configuration, a fuel breeder unit with excellent heat resistance and irradiation resistance, and rapid decay of induced radioactivity can be realized.

[0130] (Aspect 9) A fuel breeding unit according to any one of aspects 2 to 8, further comprising a columnar beryllium block arranged such that one bottom surface faces the plasma side and the other bottom surface faces the opposite side of the plasma side, wherein the one bottom surface of the beryllium block is provided with a plasma-side insertion hole facing the other bottom surface, and the plasma-side insertion hole is an insertion hole for inserting the cylindrical portion of the lithium encapsulant.

[0131] According to the above configuration, neutrons multiplied by the beryllium block can be supplied to the lithium in the lithium encapsulant. Therefore, the amount of tritium produced per unit time can be increased. Furthermore, according to the above configuration, the beryllium block can assist or replace the function of the lithium encapsulant in transporting the heat generated by the neutron deceleration, along with the radiant heat from the plasma, from the plasma side to the opposite side.

[0132] (Aspect 10) The fuel breeding unit according to aspect 9, wherein the bottom surface of the other beryllium block is provided with an anti-plasma side insertion hole facing the one bottom surface, and the anti-plasma side insertion hole is an insertion hole for inserting a cooling head protruding from a back wall for cooling the fuel breeding unit, or a cooling rod for connecting the fuel breeding unit and the back wall.

[0133] The above configuration makes it easy to attach and detach the fuel breeding unit from the back wall. Furthermore, when the fuel breeding unit is attached to the back wall, the heat generated in the fuel breeding unit can be efficiently transferred to the back wall.

[0134] (Aspect 11) The fuel breeding unit according to aspect 9, wherein the plasma-side insertion hole is a through hole reaching the bottom surface of the other, the cylindrical portion of the lithium encapsulant is longer than the distance from one bottom surface to the other bottom surface of the beryllium block, and the tip of the cylindrical portion protrudes from the other end surface of the beryllium block so that it can be inserted into an insertion hole provided in the back wall for cooling the fuel breeding unit.

[0135] The above configuration makes it easy to attach and detach the fuel breeding unit from the back wall. Furthermore, when the fuel breeding unit is attached to the back wall, the heat generated in the fuel breeding unit can be efficiently transferred to the back wall.

[0136] (Aspect 12) A fuel breeding unit according to any one of aspects 9 to 11, further comprising a sleeve covering the side surface of the beryllium block, the sleeve having a slit formed therein from the plasma side end to the end opposite to the plasma side, the beryllium block being divided into a plurality of small blocks arranged around the cylindrical portion of the fuel breeding unit, and the plurality of small blocks being bound together by the sleeve.

[0137] The above configuration makes it even easier to attach the fuel breeding unit to and remove it from the back wall.

[0138] (Aspect 13) A fusion reactor comprising a fuel breeder unit as described in any one of aspects 1 to 12.

[0139] According to the above configuration, there is no need to run piping for tritium recovery to the fuel breeder unit. Therefore, it is possible to realize a fusion reactor with low power generation costs.

[0140] (Aspect 14) The fusion reactor according to aspect 13, further comprising a fuel recovery system for recovering fuel from plasma exhaust gas, wherein tritium generated in the fuel breeder unit is released directly into the reactor from the fuel breeder unit and recovered by the fuel recovery system.

[0141] According to the above configuration, there is no need to run piping for tritium recovery to the fuel breeder unit. Therefore, it is possible to realize a fusion reactor with low power generation costs.

[0142] (Aspect 15) The fusion reactor according to aspect 13 or 14, further comprising a back wall for cooling the fuel breeding unit and a cooling system for cooling the back wall, wherein the back wall is located on the opposite side of the fuel breeding unit from the plasma side, and the fuel breeding unit and the back wall are in thermal contact.

[0143] With the above configuration, there is no need to run cooling pipes to the fuel breeding unit. Therefore, it is possible to realize a fusion reactor with even lower power generation costs and higher safety.

[0144] (Aspect 16) A heat pipe comprising a lithium encapsulant having a cylindrical portion, a lid portion that closes one of the openings, and a bottom portion that closes the other opening, wherein liquid metallic lithium is sealed in a cavity surrounded by the cylindrical portion, the lid portion, and the bottom portion, and a transport channel for transporting the liquid metallic lithium from the low temperature side to the high temperature side is provided on the inner surface of the cylindrical portion or in the center of the cavity.

[0145] The above configuration makes it possible to realize a heat pipe that uses liquid metallic lithium as the working fluid, that is, a heat pipe that operates efficiently near the boiling point of liquid metallic lithium. Here, "boiling point of liquid metallic lithium" refers to the boiling point of liquid metallic lithium inside the cavity of the lithium encapsulant, not the boiling point of liquid metallic lithium at atmospheric pressure. Therefore, please note that when the cavity of the lithium encapsulant is depressurized or pressurized, the "boiling point of liquid metallic lithium" will differ from the boiling point of liquid metallic lithium at atmospheric pressure (1330°C to 1350°C).

[0146] [Additional Notes] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in each of the embodiments described above are also included in the technical scope of the present invention. For example, the lithium encapsulant can be used as a heat pipe that efficiently transports heat from the high-temperature side to the low-temperature side, in particular as a heat pipe that can withstand high thermal loads, and its scope of application is not limited to fuel breeding units.

[0147] 1 Fuel breeding unit 11 Lithium encapsulant 111 Cylinder 112 Lid 113 Bottom 114 Flange 115 Coating 12 Beryllium block 121 Plasma-side small block 122 Anti-plasma-side small block 13 Sleeve 13a Slit 2 Back wall 21 Cooling plate 22 Cooling head 23 Helium cooling passage 24 Neutron shielding plate 100 Fusion reactor 100A Cooling system 100B Fuel recovery system

Claims

1. A fuel breeder unit that converts the kinetic energy of neutrons generated by nuclear fusion in a plasma into thermal energy, and generates tritium using the neutrons, wherein the generated tritium is directly released into the reactor.

2. A fuel breeding unit according to claim 1, comprising a cylindrical portion having one opening facing the plasma side and the other opening facing the opposite side from the plasma side, a lid portion that closes the one opening, and a bottom portion that closes the other opening, wherein lithium is sealed in a cavity surrounded by the cylindrical portion, the lid portion, and the bottom portion, and the lid portion is permeable to tritium.

3. The fuel breeding unit according to claim 2, wherein liquid metallic lithium is sealed in the cavity, and a transport channel is provided on the inner surface of the cylindrical portion for transporting the liquid metallic lithium from the side opposite to the plasma side to the plasma side.

4. The fuel breeding unit according to claim 3, wherein the transport channel has a capillary structure.

5. The fuel breeding unit according to claim 2, wherein liquid metallic lithium is sealed in the cavity, and a transport channel is provided in the center of the cavity for transporting the liquid metallic lithium from the side opposite to the plasma side to the plasma side.

6. The fuel breeding unit according to claim 5, wherein the transport channel is a tubular tube with one end opening in the region including the lid and the other end opening in the region including the bottom.

7. The fuel breeding unit according to claim 2, wherein lithium compounds are sealed in the cavity as pebbles.

8. The fuel breeding unit according to any one of claims 2 to 7, wherein at least one of the cylindrical portion, the lid portion, and the bottom portion is made of a SiC / SiC composite material.

9. A fuel breeding unit according to any one of claims 2 to 8, further comprising a columnar beryllium block arranged such that one bottom surface faces the plasma side and the other bottom surface faces the opposite side of the plasma side, wherein the one bottom surface of the beryllium block is provided with a plasma-side insertion hole facing the other bottom surface, and the plasma-side insertion hole is an insertion hole for inserting the cylindrical portion of the lithium encapsulant.

10. The fuel breeding unit according to claim 9, wherein the bottom surface of the other beryllium block is provided with an anti-plasma side insertion hole facing the bottom surface of the one side, and the anti-plasma side insertion hole is an insertion hole for inserting a cooling head protruding from a back wall for cooling the fuel breeding unit, or a cooling rod for connecting the fuel breeding unit and the back wall.

11. The fuel breeding unit according to claim 9, wherein the plasma-side insertion hole is a through hole reaching the bottom surface of the other, the cylindrical portion of the lithium encapsulant is longer than the distance from one bottom surface to the other bottom surface of the beryllium block, and the tip of the cylindrical portion protrudes from the other end surface of the beryllium block so as to be inserted into an insertion hole provided in the back wall for cooling the fuel breeding unit.

12. A fuel breeding unit according to any one of claims 9 to 11, further comprising a sleeve covering the side surface of the beryllium block, the sleeve having a slit formed therein from the plasma side end to the end opposite the plasma side, wherein the beryllium block is divided into a plurality of small blocks arranged around the cylindrical portion of the fuel breeding unit, and the plurality of small blocks are bound together by the sleeve.

13. A fusion reactor comprising a fuel breeder unit according to any one of claims 1 to 12.

14. A fusion reactor according to claim 13, further comprising a fuel recovery system for recovering fuel from plasma exhaust gas, wherein tritium generated in the fuel breeder unit is released directly into the reactor from the fuel breeder unit and recovered by the fuel recovery system.

15. A fusion reactor according to claim 13 or 14, further comprising a back wall for cooling the fuel breeding unit and a cooling system for cooling the back wall, wherein the back wall is located on the side opposite to the plasma side of the fuel breeding unit and the fuel breeding unit and the back wall are in thermal contact.

16. A heat pipe comprising a lithium encapsulant having a cylindrical portion, a lid portion that closes one opening, and a bottom portion that closes the other opening, wherein liquid metallic lithium is sealed within a cavity surrounded by the cylindrical portion, the lid portion, and the bottom portion, and a transport channel for transporting the liquid metallic lithium from a low temperature side to a high temperature side is provided on the inner surface of the cylindrical portion or in the center of the cavity.

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