Molten salt reactor moderator and molten salt reactor

Abstract

To provide a molten salt reactor moderator and molten salt reactor, capable of obtaining a sufficient length of a wetted perimeter for obtaining the occurrence prevention of stress and a large negative temperature reactivity coefficient, improving flexibility related to the selection of arrangement, etc., of a control rod and improving workability, such as coating.SOLUTION: A plurality of molten salt reactor moderator (moderators 222) provided at a core in the reactor vessel of a molten salt reactor are formed in a pillar shape having a main body side part 222a1 including a plurality of side surfaces 222a3 and a plurality of corner parts 222a2 around a moderator axis CL extended along the core axis. Each of the plurality of side surfaces 222a3 is formed in a curved surface shape so as to be convex on the side close to the moderator axis CL2 (so as to depress the main body side part 222a1).SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a molten salt reactor moderator and a molten salt reactor. [Background technology]

[0002] Molten salt reactors (sometimes simply referred to as reactors) have been known in the past, such as that shown in Patent Document 1. Molten salt reactors generally have a moderator (molten salt reactor moderator) in the reactor core, and when liquid nuclear fuel (molten salt fuel; hereinafter simply referred to as fuel salt or molten salt) flows through the moderator, a nuclear fission reaction occurs to generate energy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-91178 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional techniques including the technique described in the above-mentioned Patent Document 1, it was necessary to obtain a large negative temperature reactivity coefficient in order to suppress an abnormal temperature rise of the molten salt, improve the effectiveness of the brake for reactor shutdown, and lower the upper limit temperature of the molten salt in the core. However, the moderator was not able to secure a sufficient wetted edge length due to its shape. In addition, in the prior art, when adjacent moderators are arranged in contact with each other, there is a risk that the contact will cause stress such as friction, which may lead to, for example, breakage. Also, in the prior art, there are holes inside the moderator through which the fuel salt flows, and the presence of these holes inside makes it difficult to perform coating processing.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a molten salt reactor moderator and a molten salt reactor capable of ensuring a sufficient wetted edge length to obtain a large negative temperature reactivity coefficient, and also to provide a molten salt reactor moderator and a molten salt reactor capable of preventing damage by avoiding contact between adjacent moderators and facilitating coating processing. [Means for solving the problem]

[0006] In order to achieve the above object, a moderator for a molten salt reactor according to one embodiment of the present invention comprises: A molten-salt reactor moderator is provided in a reactor core in a reactor vessel of a molten-salt reactor, the moderator axis extends along the reactor core axis, and the molten-salt reactor moderator is formed in a columnar shape having a main body side portion with a plurality of side surfaces and a plurality of corners around an axis centered on the moderator axis, The side surfaces are each formed in a curved shape that is convex (so that the side portions of the main body are concave) toward the moderator shaft. In addition, a molten salt reactor according to one embodiment of the present invention comprises: A plurality of the above-described molten-salt reactor moderators are provided in the reactor core within the reactor vessel. Effect of the Invention

[0007] According to the present invention, a sufficient wet edge length can be ensured to ensure a large negative temperature reactivity coefficient. Also, according to the present invention, contact between adjacent elements can be avoided to prevent damage, and further, coating processing can be facilitated. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a building in which a molten salt reactor according to an embodiment of the present invention is located. [Diagram 2] 1 is an external perspective view of a molten salt reactor according to an embodiment of the present invention; [Diagram 3] 2 is a vertical cross-sectional view of the molten salt reactor according to the present embodiment (cross-sectional view taken along line AA in FIG. 2). [Figure 4] 1 is a perspective view including a horizontal cross-sectional view of a molten salt reactor according to an embodiment of the present invention. [Diagram 5] 5 is a horizontal cross-sectional view of the molten salt reactor according to the present embodiment, taken from the direction of arrow B in FIG. 4. [Figure 6] FIG. 2 is an explanatory diagram showing a cross-sectional shape of a molten-salt reactor moderator according to the present embodiment. [Figure 7] FIG. 2 is an explanatory diagram (plan view) relating to the arrangement of a molten-salt reactor moderator according to the present embodiment. [Figure 8] FIG. 2 is an explanatory diagram (perspective view) regarding the arrangement of a molten-salt reactor moderator according to the present embodiment. [Figure 9] 1A to 1C are explanatory views relating to the shape of a molten-salt reactor moderator according to an embodiment of the present invention, where (a) is a perspective view, (b) is a front view, and (c) is a vertical cross-sectional view. [Figure 10] FIG. 2 is an explanatory diagram regarding a consideration of a core region of a reactor core when a molten-salt reactor moderator according to the present embodiment is adopted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that what is described below is merely an example, and the technical scope of the present invention is not limited to this example. FIG. 1 is a cross-sectional view of a building in which a molten-salt reactor according to this embodiment is located.

[0010] <About Building 1> A building 1 of a molten salt reactor plant is a structure in which a molten salt reactor is located. The building 1 may be constructed as a single story as shown in FIG. 1, or may be constructed in a multi-story stacked structure (not shown). Here, for the sake of simplicity of explanation and, for example, to reduce construction costs, a building 1 constructed as a single story is used. At a designated position in the building 1, there is a molten salt reactor 2 (sometimes simply called a reactor; details will be described later).

[0011] There are multiple rooms and areas in the building 1. In the cross-sectional view of the building 1 in Fig. 1, only representative rooms and areas are labeled. The building 1 is provided with a reactor room 11, an instrumentation room 12, a fuel tank room 13, a reprocessing tank storage area 14, and a helium gas heating area 15.

[0012] The reactor room 11 is formed so that the ceiling is higher than other rooms (rooms) or areas. The molten salt reactor 2 is installed in the reactor room 11. An exhaust stack 16 is provided next to the reactor room 11. A plurality of equipment storage rooms 17 are provided in the basement of the reactor room 11. The equipment storage room 17 is formed as a deep room (room) capable of storing the decommissioned molten salt reactor and the drain tank. When the decommissioned molten salt reactor and the drain tank are stored in the equipment storage room 17, the upper part (the part opened for storage) of the equipment storage room 17 is covered with a lid. In this embodiment, it is assumed that the decommissioned reactor and high-level nuclear waste are buried and sealed underground for final disposal. The instrumentation room 12 is a room for instrumentation, and is provided to the left of the reactor room 11 in the case of FIG. 1. The fuel tank room 13 next to the instrumentation room 12 is where the fuel tank is placed. Reprocessed tanks are placed in a reprocessed tank storage area 14 adjacent to the fuel tank room 13. Meanwhile, a helium gas heating area 15 to the right of the reactor room 11 is where a helium gas heater and the like are installed.

[0013] In addition to the above, Building 1 also houses a control room, a fuel salt loading / dehydration reduction room, a fuel salt storage room, an office, a conference room, toilets, a substation, a backup power supply, a heat removal area, an off-gas treatment area, a turbine / generator, a cooling salt drain tank area, an unloading yard, firefighting equipment, etc. Large trucks (symbol omitted) can enter and exit the unloading yard, for example.

[0014] In this embodiment, the building 1 is designed to have a service life of approximately 100 years, since the molten salt reactor 2 is replaced twice during use.

[0015] The molten salt reactor 2 installed in the reactor room 11 is housed (contained) in a containment vessel 4 together with a drain tank 3. Various pipes and tanks (reference numbers omitted) are also installed below the drain tank 3. The containment vessel 4 is installed above ground and underground. Although a detailed explanation of the entire system is omitted, the building 1 is equipped with a power generation system in which a nuclear fission reaction occurs when fuel salt flows through the core of the molten salt reactor 2 installed in the reactor room 11, and the thermal energy generated by this nuclear fission reaction is extracted via a primary heat exchanger unit, etc., and then this extracted thermal energy is converted into rotational energy, which is then converted into electrical energy by a generator to generate electricity. The molten salt reactor 2 will now be described.

[0016] FIG. 2 is an external perspective view of the molten salt reactor according to this embodiment.

[0017] <Configuration of Molten Salt Reactor 2> 2, the molten salt reactor 2 is configured to include a reactor vessel 21, a reactor core 22 provided in the reactor vessel 21, a primary heat exchanger unit 23 disposed on the upper part of the reactor core 22, two control rods 24, and piping 25 (this configuration is considered to be one example). In this embodiment, the molten salt reactor 2 has a thermal output of 56 MWt and an electrical output of approximately 25 MWe.

[0018] 2 is defined as the "upper" in the vertical direction, and the lower side of the paper is defined as the "lower" in the vertical direction for the remainder of the description. A drain tank 3 is disposed at a predetermined distance below the molten salt reactor 2. As can be seen from FIG. 2 and will also be understood from the following description, the molten salt reactor 2 employs an integrated reactor in which a primary heat exchanger 231 (described later) in a primary heat exchanger unit 23 is housed within the reactor vessel 21 (the arrangement of the primary heat exchanger 231 is an example, and is not limited to the arrangement in FIG. 2).

[0019] 3 is a vertical cross-sectional view (cross-sectional view taken along line AA in FIG. 2) of the molten salt reactor according to this embodiment. Hereinafter, a description will be given with reference to FIGS.

[0020] <About Reactor Vessel 21> The reactor vessel 21 has an upper wall 211 and a lower wall 212 (ceiling and bottom), and a side wall 213 is formed into a cylindrical sealed vessel. Hastelloy (registered trademark) N is used as the material of the reactor vessel 21. It should be noted that Hastelloy (registered trademark) N is only an example, and the material is not particularly limited as long as it is such a high nickel alloy. Specifically, in addition to Hastelloy (registered trademark) N and high nickel alloys, the material is not particularly limited as long as it is molybdenum alloy TZM (titanium-zirconium-molybdenum alloy). The reactor vessel 21 made of Hastelloy (registered trademark) N is formed to have a thickness of, for example, 20 mm (the dimensions are only an example).

[0021] The lower wall 212 (bottom) of the reactor vessel 21 has a circular periphery, the inside of which is flat or slightly inclined. A lower fuel salt plenum 214 is provided in the center of the lower wall 212 and has a cup shape that is convex downward. Pipes 25, which will be described later, are connected to the lower fuel salt plenum 214. The lower fuel salt plenum 214 is formed smaller than the upper fuel salt plenum 215, which will be described later. The lower fuel salt plenum 214 is formed to have a height (length in the vertical direction) of, for example, 500 mm (these dimensions are an example). The lower wall 212 is formed to have a diameter of, for example, 3220 mm (these dimensions are an example). The periphery of the lower wall 212 is formed to smoothly connect the lower end of the side wall 213 with a curved surface.

[0022] The side wall 213 of the reactor vessel 21 is formed in a cylindrical shape centered on the core axis CL1 of the core 22 described later (see Figs. 4 and 5). The side wall 213 is formed to have a height of, for example, 4200 mm (these dimensions are merely an example). Of the 4200 mm, 3030 mm is set to a height corresponding to the core 22 (these dimensions are merely an example). The remaining 4200 mm is set to a height corresponding to the primary heat exchanger 231 described later (these dimensions are merely an example). The upper end of the side wall 213 is connected to the periphery of the upper wall 211 by a smooth curved surface.

[0023] The upper wall 211 (ceiling) of the reactor vessel 21 is arranged, for example, parallel to the lower wall 212. An upper fuel salt plenum 215 is provided on the upper wall 211. Four pumps 232 constituting the primary heat exchanger unit 23 are also provided on the upper wall 211. The upper fuel salt plenum 215 is arranged in the center of the upper wall 211. The upper fuel salt plenum 215 is formed in an inverted cup shape that is convex upward. The upper fuel salt plenum 215 is formed to have a height (length in the vertical direction) of, for example, 800 mm (the dimensions are taken as an example). The upper part of the upper fuel salt plenum 215 is formed to be circular and flat.

[0024] Two guide tubes 216 are provided at the top of the upper fuel salt plenum 215. These two guide tubes 216 are provided so as to penetrate the top of the upper fuel salt plenum 215. The two guide tubes 216 are formed so as to be able to guide the control rods 24 in the vertical direction, respectively. Four pumps 232 are arranged around the upper fuel salt plenum 215. The four pumps 232 are arranged at 90 degree intervals around the core axis CL1. The piping extending from the upper fuel salt plenum 215 indicates an overflow path 253 (described later).

[0025] <About the primary heat exchanger unit 23> The primary heat exchanger unit 23 is provided to transfer thermal energy (heat) generated by the above-mentioned nuclear fission reaction to the cooling salt of the secondary loop in the reactor vessel 21. In this embodiment, the primary heat exchanger unit 23 is configured to include four primary heat exchangers 231 and the above-mentioned four pumps 232. The four pumps 232 are each provided with a pump shaft 232a and a pump fin 232b. The four pumps 232 are provided in accordance with the arrangement of the four primary heat exchangers 231. The four pumps 232 are provided to forcibly convect the fuel salt described below. In this embodiment, the four primary heat exchangers 231 are arranged on the reactor core 22 described below. The four primary heat exchangers 231 are provided with the fuel salt that moves by driving the pump shaft 232a and the pump fin 232b of the four pumps 232. Although not particularly shown, the four primary heat exchangers 231 are connected to a piping of the secondary loop through which the cooling salt flows.

[0026] <About piping 25> The piping 25 includes piping of a primary loop (the primary loop is a system in which fuel salt circulates). As one of the piping of the primary loop, a fuel salt return path 251 is connected to each of the four primary heat exchangers 231. The upper ends of the four fuel salt return paths 251 are connected to the lower sides of the four primary heat exchangers 231, respectively. The lower ends of the four fuel salt return paths 251 are connected to the lower fuel salt plenum 214. The four fuel salt return paths 251 are formed such that the portion that fits the side wall 213 of the reactor vessel 21 has a semicircular cross-sectional shape or a crescent-like cross-sectional shape, for example. The four fuel salt return paths 251 are formed such that the portion that is arranged on the side of the lower wall 212 of the reactor vessel 21 has a circular cross-sectional shape.

[0027] The piping 25 also includes a discharge pipe 252 connecting the lower fuel salt plenum 214 and the drain tank 3, and an overflow path 253 connected to the drain tank 3. The overflow path 253 here connects to the above-mentioned upper fuel salt plenum 215. Other piping 25 also includes a pipe 254 connecting from the lower fuel salt plenum 214 to a fuel salt storage tank (not shown).

[0028] <About the core 22 and graphite reflector 221> In Fig. 3, the core 22 is provided inside the reactor vessel 21. The core 22 is a so-called core where nuclear fission takes place, and is surrounded by a graphite reflector 221 made of graphite. The graphite reflector 221 is configured to have an upper graphite reflector 221a, a lower graphite reflector 221b, and a side graphite reflector 221c. The graphite reflector 221 is formed into a vessel shape by the upper graphite reflector 221a, the lower graphite reflector 221b, and the side graphite reflector 221c. The graphite reflector 221 is provided to protect the reactor vessel 21 from neutron irradiation.

[0029] The upper graphite reflector 221a is formed to have a thickness of, for example, 250 mm (these dimensions are merely an example). The lower graphite reflector 221b is also formed to have a thickness of, for example, 250 mm (these dimensions are merely an example). The side graphite reflector 221c is formed to have a thickness of, for example, 250 mm or more (these dimensions are merely an example). The thickness of the graphite reflector 221 is one of the important factors in considering the shape of the reactor core 22 (core).

[0030] In this embodiment, the inner circumferential surface of the side graphite reflector 221c is formed to have projections and recesses due to the presence, arrangement and shape of the moderator 222 described later (see Figs. 4 and 5 for the shape of the projections and recesses).

[0031] Fig. 4 is a perspective view including a horizontal cross-sectional view of the molten salt reactor according to this embodiment. Fig. 5 is a horizontal cross-sectional view of the molten salt reactor according to this embodiment, which is a cross-sectional view seen from the direction of the arrow B in Fig. 4. Fig. 3 should also be referred to.

[0032] <About the core 22, moderator 222, and fuel salt> In Fig. 3 to Fig. 5, the core 22 is configured to include a plurality of moderators 222 in addition to the graphite reflector 221 described above. In other words, the core 22 is configured to include a plurality of moderators 222 arranged inside the graphite reflector 221 so as to be surrounded by the graphite reflector. The core 22 is formed so that fuel salt flows between the plurality of moderators 222. The core 22 is also formed so that fuel salt flows between the inner circumferential surface of the graphite reflector 221 and the plurality of moderators 222. That is, a fuel salt passage 223 through which the fuel salt passes is formed between adjacent ones of the plurality of moderators 222. The fuel salt passage 223 is formed so as to exist around the moderator 222. The fuel salt passage 223 is formed as a gap between adjacent moderators 222. Details of the moderator 222 will be described later.

[0033] The fuel salt may be liquid nuclear fuel or molten salt fuel, which is made by mixing uranium, a fission material, and thorium, a fertile material, in a molten salt free base (for example, LiF-BeF2-ThF4-UF4) (not particularly limited). The fuel salt flows between the multiple moderators 222, and then flows further upward through the opening of the upper graphite reflector 221a (the fuel salt moves upward by driving the pump shaft 232a and pump fins 232b of the pump 232. When the pump 232 is stopped, the fuel salt moves upward by natural convection). After heat exchange in the primary heat exchanger 231, the fuel salt that moves upward returns to the core 22 from the bottom of the primary heat exchanger 231 through the fuel salt return path 251, the lower fuel salt plenum 214, and the opening of the lower graphite reflector 221b.

[0034] In this embodiment, the primary heat exchanger 231 and the pump 232 are arranged so that the fuel salt naturally circulates by convection when the pump 232 is stopped.

[0035] <Types and arrangement of moderator 222> The moderator 222 is made of graphite and is used to slow down the speed of neutrons (fast neutrons) emitted by nuclear fission and cause nuclear fission with the slowed-down neutrons. As can be seen from Fig. 5, several tens of moderators 222 are used. The multiple moderators 222 are arranged in the core 22 in an assembly as shown in the figure.

[0036] In this embodiment, a plurality of types of moderators 222 are adopted. The types are classified according to the fuel salt volume fraction (classification according to the fuel volume fraction will be described later with reference to FIG. 10). Here, the types are classified according to the direction of hatching showing the cross section (see FIG. 5. In FIG. 5, the hatching indicates that there are a plurality of types, and the number of types is not limited to the figure. As will be described with reference to FIG. 10, two regions with two types have been found to be a preferable result). In this embodiment, the plurality of moderators 222 are arranged in a ring shape and in a plurality of layers around the core axis CL1 of the core 22. The two holes 224 shown in FIG. 5 are formed as holes for the two control rods 24.

[0037] Fig. 6 is an explanatory diagram of the cross-sectional shape of the molten salt reactor moderator according to this embodiment. Fig. 7 is an explanatory diagram (plan view) of the arrangement of the molten salt reactor moderator according to this embodiment. Fig. 8 is an explanatory diagram (perspective view) of the arrangement of the molten salt reactor moderator according to this embodiment. Fig. 9 is an explanatory diagram of the shape of the molten salt reactor moderator according to this embodiment, where (a) is a perspective view, (b) is a front view, and (c) is a vertical cross-sectional view.

[0038] <Specific shape of moderator 222> As can be seen from Figures 3 and 9, each of the moderators 222 is formed into a columnar shape. As mentioned above, there are multiple types of moderators 222 (classified according to the fuel salt volume fraction), and as can be seen from Figure 3, some have slightly different lengths. However, for simplicity of explanation, the symbols will be unified to one type for explanation. In addition, since the external shapes of the main parts of the moderators 222 are the same, the shapes will also be unified to one type for explanation.

[0039] The columnar moderator 222 is characterized by a shape as shown in the cross section of Fig. 6. The moderators 222 having this characteristic shape are arranged in a group as shown in Fig. 7 and Fig. 8, and fuel salt flows through a fuel salt passage 223 between adjacent moderators 222. As shown in Fig. 9, the moderator 222 has a moderator body 222a and moderator ends 222b that are continuous with the upper and lower ends of the moderator body 222a, respectively, and is formed in a columnar shape extending long along the moderator axis CL2. Note that the moderator axis CL2 is parallel to the core axis CL1 when the moderator 222 is arranged in the core 22.

[0040] 6 and 9, the moderator body 222a has a body side portion 222a1 as an outer periphery around an axis centered on the moderator axis CL2. Note that the moderator axis CL2 in FIG. 6 is an axis extending in a direction perpendicular to the paper at the position of an imaginary point in the center of the figure. The body side portion 222a1 has n corners 222a2 and n side surfaces 222a3 in the cross-sectional shape of FIG. 6, where n is defined as an integer of 3 or more. Also, the outer shape shown in FIG. 9 has n corners 222a2 and n side surfaces 222a3. In FIG. 6 and FIG. 9, n is shown as 6, but this is not limited to this.

[0041] 6, in order to virtually show the arrangement region of the moderator 222 (moderator body 222a) and the boundary between adjacent moderators 222 (moderator bodies 222a), if a regular hexagon 222a4 is drawn with the moderator axis CL2 as the center, the main body side portion 222a1 is formed so as to be surrounded by this regular hexagon 222a4. Specifically, the main body side portion 222a1 is formed so that the corners 222a2 are located inside the six corners 222a5 of the regular hexagon 222a4. In addition, the main body side portion 222a1 is formed so that the side surface 222a3 is located inside the six sides 222a6 of the regular hexagon 222a4.

[0042] The main body side portion 222a1 is formed with a curved shape such that the corners 222a2 are convex toward the side away from the moderator shaft CL2. In other words, the corners 222a2 are formed with a curved shape such that they are convex toward the outside of the main body side portion 222a1. The main body side portion 222a1 is also formed with a curved shape such that the side surface 222a3 is convex toward the side approaching the moderator shaft CL2. In other words, the side surface 222a3 is formed with a curved shape that concaves the side surface 222a3. The curved shape shown in the figure is formed in a state that describes an arc of a perfect circle, but is not limited to this. That is, it may be formed into a curved surface that describes an arc of an ellipse, for example.

[0043] In the case shown in FIG. 6, the main body side portion 222a1 is formed in a curved shape such that the corner portion 222a2 is not inscribed in the corner 222a5 of the regular hexagon 222a4 and the side 222a6 sandwiching the corner. In the case shown in FIG. 9, the corner portion 222a2 is formed in a curved shape such that the corner portion 222a2 is not inscribed in a hexagonal prism frame (not shown). In addition, in the case shown in FIG. 6, the main body side portion 222a1 is formed in a curved shape such that the side surface 222a3 is not inscribed in the side 222a6 of the regular hexagon 222a4. In the case shown in FIG. 9, the side surface 222a3 is formed in a curved shape such that the side surface 222a3 is not inscribed in a hexagonal prism frame (not shown). Note that the arc that forms the curved shape of the corner portion 222a2 is an arc with a smaller radius of curvature than the arc of the side surface 222a3.

[0044] Since the corners 222a2 of the main body side portion 222a1 are formed in a curved shape (arc), and since the shape does not cause inscription as described above, it goes without saying that there is no contact between adjacent moderators 222. Therefore, it is possible to prevent the generation of stress such as friction caused by contact between adjacent moderators 222, and thereby prevent damage.

[0045] In the case shown in FIG. 6, the corners 222a5 and sides 222a6 of the regular hexagon 222a4 and the corners 222a2 and side surfaces 222a3 of the main body side 222a1 are spaced apart, and this space becomes the fuel salt passage 223 through which the fuel salt flows. In the case shown in FIG. 9, the corners 222a2 and side surfaces 222a3 of the main body side 222a1 are spaced apart, and this space becomes the fuel salt passage 223 through which the fuel salt flows. The curved side surface 222a3 of course has a larger contact area with the fuel salt than, for example, a straight line (vertical surface in FIG. 9). Therefore, as a result of the larger contact area with the fuel salt, an effect can be obtained in terms of shape that the wet edge length can be sufficiently secured. The purpose of increasing the wetted edge length is to obtain a large negative temperature reactivity coefficient, suppress abnormal temperature rise of the molten salt, improve the braking effect for reactor shutdown, and lower the upper limit temperature of the molten salt in the core. The wetted edge length is the circumferential length around the moderator axis CL2, and can also be said to be the length of contact with the fuel salt.

[0046] In Fig. 5, Fig. 6, and Fig. 9, the moderator body 222a is formed in a shape in which the entire range along the direction in which the moderator axis CL2 extends is solid and does not have a hollow. In other words, the moderator body 222a is formed in a shape that extends in the direction of the moderator axis CL2 and does not have, for example, a through hole. In this specification, "hollow" refers to a structure in which holes (pores) or spaces exist inside. Also, "solid" refers to a structure in which the above-mentioned holes (pores) or spaces do not exist (are filled). The moderator body 222a has a simple structure because of its solid shape as described above. In addition, because it has a solid shape, it is not only easier to manufacture, but also has an increased strength.

[0047] The moderator body 222a is formed in a shape that matches the above-mentioned regular hexagon or hexagonal prism frame. To explain in more detail, the cross section is formed in the above-mentioned "starfish" shape that does not have a hollow space. In the case of such a "starfish" cross-sectional shape, it is of course a simple design, but it is also possible to obtain a large negative temperature reactivity coefficient. In other words, the negative temperature reactivity coefficient is -4.0×10 -5 This negative temperature reactivity coefficient is -4.0×10 -5 This corresponds to a large value, about 5 times larger than that of the known thorium molten salt breeder reactor (MSBR), and about 1.5 times larger than that of the known FUJI. Note that this is the result of a calculation using the continuous energy Monte Carlo method MVP.

[0048] By making the cross-sectional shape into the above-mentioned "starfish type" (see FIG. 6) without a hollow, the multiple moderators 222 can be arranged in an annular shape and in multiple layers as shown in FIG. 5, FIG. 7, and FIG. 8. The above-mentioned arrangement of the multiple moderators 222 and the graphite reflector 221 of a predetermined thickness surrounding the multiple moderators 222 are effective in obtaining a large negative temperature reactivity coefficient. In addition, by making the cross-sectional shape into a "starfish type" (by making it into a hexagon or a shape surrounded by a hexagonal prism frame), it is effective in improving the flexibility in selecting the arrangement of the control rods 24, etc.

[0049] 9, the moderator end 222b is formed so as to be continuous with the upper and lower ends of the moderator body 222a, as described above. The moderator end 222b is formed in a protruding shape such that the moderator body 222a is made smaller in diameter and shorter. The moderator end 222b is shaped to be held by the upper graphite reflector 221a and the lower graphite reflector 221b of the graphite reflector 221. The tip of the moderator end 222b is formed in a shape that makes it easy to insert into the upper graphite reflector 221a and the lower graphite reflector 221b.

[0050] The moderator end 222b is formed in a simple shape because there is no hollow portion in the moderator body 222a (in the known FUJI, there is a hollow portion through which fuel salt flows, so terminal processing was required to drain the fuel salt. However, in the present embodiment, there is no hollow portion, so the moderator end 222b can be formed in an extremely simple shape).

[0051] FIG. 10 is an explanatory diagram relating to a consideration of the core region of the core when the molten-salt reactor moderator according to this embodiment is adopted. In FIG. 10, the configuration of the molten salt reactor moderator (moderator) based on the fuel salt volume fraction Fr is called the "core configuration," and the region of the core divided into regions by the core configuration is called the core region. For example, if the core configuration has one type of fuel salt volume fraction Fr, the core configuration is single, and the core is divided into regions with this single core configuration, so the core region is a single region. Also, for example, if the core configuration has two types of fuel salt volume fraction Fr, the core configuration is two, and the core is divided into regions with these two core configurations, so the core region is two regions. Also, for example, if the core configuration has three types of fuel salt volume fraction Fr, the core configuration is three, and the core is divided into regions with these three core configurations, so the core region is three regions.

[0052] In FIG. 10, the optimal core region of the core was considered based on the neutron fluence (>53 KeV) distribution for each core region as described above.

[0053] The reason why we decided to consider the core region of the core by the neutron fluence (>53KeV) distribution for each core region is that when we calculated the fluence distribution of a single-region core (for fuel salt volume fraction Fr=36%, 30 years of continuous operation), we found that the fluence distribution was biased toward the center of the core. This means that the fluence to the moderator in the center of the core is high, which affects the life of the entire core. Therefore, we concluded that we should devise a core configuration to homogenize the fluence distribution. When considering the core region, we analyzed each of the regions by dividing the core configuration into (1) single region, (2) two regions, and (3) three regions as described above. Through the analysis, we can pursue the optimal region and moderator cross section. The analysis results are shown in Figure 10.

[0054] In Fig. 10, the core configurations are arranged vertically (top to bottom in the figure) in the table below the description of the fuel concentration effect (0.33 mol% Fuel). The fuel layer numbers are arranged in order horizontally (left to right in the figure) in the table, and the multiplication factors are also shown. The fuel layer numbers are defined as follows: the moderator 222 in the center of Fig. 5 is fuel layer number 1 (the moderator 222 arranged at the position of the core axis CL1 in Fig. 4 is fuel layer number 1), and the layers of moderator 222 on the outer sides are fuel layer numbers 2, 3, 4, etc. The fuel layer numbers correspond to the number of "layers" in which the moderator 222 is arranged. Specific numerical values ​​are shown below.

[0055] If the core configuration is "single region (fuel salt volume fraction Fr=39%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.772 × 10 22 (In FIG. 10, it is shown as 2.772E+22.) The core configuration here corresponds to graph a in the graph described later (the fluence here is plotted in graph a). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.903 × 10 22 (In Figure 10, it is shown as 2.903E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 3.033 × 1022 (In Figure 10, it is shown as 3.033E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.916 × 10 22 (In Figure 10, it is shown as 2.916E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm 2 ) is 2.585 × 10 22 (In Figure 10, it is shown as 2.585E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.147 × 10 22 (In Figure 10, it is shown as 2.147E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 1.552 × 10 22 (In Figure 10, it is shown as 1.552E+22).

[0056] If the core configuration is "single region (fuel salt volume fraction Fr=40%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.782 × 10 22 (In FIG. 10, it is shown as 2.782E+22.) The core configuration here corresponds to graph b of the graph described later (the fluence here is plotted in graph b). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.878 × 10 22 (In Figure 10, it is shown as 2.878E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 2.991 × 10 22 (In Figure 10, it is shown as 2.991E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.868 × 10 22 (In Figure 10, it is shown as 2.868E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm2 ) is 2.534 × 10 22 (In Figure 10, it is shown as 2.534E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.141 × 10 22 (In Figure 10, it is shown as 2.141E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 1.54 × 10 22 (In Figure 10, it is written as 1,54E+22). The multiplication factor is 0.9405.

[0057] If the core configuration is "2 regions (fuel salt volume fraction Fr=39% / 27%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.467 × 10 22 (In FIG. 10, it is shown as 2.467E+22.) The core configuration here corresponds to graph c of the graph described later (the fluence here is plotted in graph c). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.604 × 10 22 (In Figure 10, it is shown as 2.604E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 2.841 × 10 22 (In Figure 10, it is shown as 2.841E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.985 × 10 22 (In Figure 10, it is shown as 2.985E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm 2 ) is 2.701 × 10 22 (In Figure 10, it is shown as 2.701E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.361 × 10 22 (In Figure 10, it is shown as 2.361E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 1.65 × 10 22 (In Figure 10, it is shown as 1.65E+22).

[0058] When the core configuration is "2 regions (fuel salt volume fraction Fr=40% / 26%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.381 × 10 22 (In FIG. 10, it is shown as 2.381E+22.) The core configuration here corresponds to graph d in the graph described later (the fluence here is plotted in graph d). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.518 × 10 22 (In Figure 10, it is shown as 2.518E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 2.705 × 10 22 (In Figure 10, it is shown as 2.705E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.82 × 10 22 (In Figure 10, it is shown as 2.82E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm 2 ) is 2.65 × 10 22 (In Figure 10, it is shown as 2.65E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.329 × 10 22 (In Figure 10, it is shown as 2.329E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 1.643 × 10 22 (In Figure 10, it is shown as 1.643E+22). Also, if the fuel layer number is "8", the fluence (neutrons / cm 2 ) is 2.784 × 10 22(In Figure 10, it is shown as 2.784E+22). The multiplication factor is 1.0151.

[0059] If the core configuration is "3 regions (fuel salt volume fraction Fr=39% / 27% / 45%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.558 × 10 22 (In FIG. 10, it is shown as 2.558E+22.) The core configuration here corresponds to graph e of the graph described later (the fluence here is plotted in graph e). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.702 × 10 22 (In Figure 10, it is shown as 2.702E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 2.855 × 10 22 (In Figure 10, it is shown as 2.855E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.898 × ​​10 22 (In Figure 10, it is shown as 2.898E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm 2 ) is 2.673 × 10 22 (In Figure 10, it is shown as 2.673E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.252 × 10 22 (In Figure 10, it is shown as 2.252E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 1.661 × 10 22 (In Figure 10, it is shown as 1.661E+22).

[0060] If the core configuration is "3 regions (fuel salt volume fraction Fr=39% / 27% / 39%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.39 × 1022 (In FIG. 10, it is shown as 2.39E+22.) The core configuration here corresponds to graph f of the graph described later (the fluence here is plotted on graph f). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.522 × 10 22 (In Figure 10, it is shown as 2.522E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 2.752 × 10 22 (In Figure 10, it is shown as 2.752E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.892 × 10 22 (In Figure 10, it is shown as 2.892E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm 2 ) is 2.775 × 10 22 (In Figure 10, it is shown as 2.775E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.42 × 10 22 (In Figure 10, it is shown as 2.42E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 2.083 × 10 22 (In Figure 10, it is shown as 2.083E+22).

[0061] If the core configuration is "3 regions (fuel salt volume fraction Fr=40% / 26% / 45%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.517 × 10 22 (In FIG. 10, it is shown as 2.517E+22.) The core configuration here corresponds to graph g in the graph described later (the fluence here is plotted in graph g). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.637 × 10 22(In Figure 10, it is shown as 2.637E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 2.829 × 10 22 (In Figure 10, it is shown as 2.829E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.882 × 10 22 (In Figure 10, it is shown as 2.882E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm 2 ) is 2.583 × 10 22 (In Figure 10, it is shown as 2.583E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.169 × 10 22 (In Figure 10, it is shown as 2.169E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 1.674 × 10 22 (In Figure 10, it is shown as 1.674E+22). Also, if the fuel layer number is "8", the fluence (neutrons / cm 2 ) is 2.801 × 10 22 (In Figure 10, it is shown as 2.801E+22). The multiplication factor is 1.00142.

[0062] If the core configuration is "3 regions (fuel salt volume fraction Fr=40% / 26% / 40%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.528 × 10 22 (In FIG. 10, it is shown as 2.528E+22.) The core configuration here corresponds to graph h in the graph described later (the fluence here is plotted in graph h). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.64 × 10 22 (In Figure 10, it is shown as 2.64E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 2.796 × 10 22 (In Figure 10, it is shown as 2.796E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.86 × 10 22 (In Figure 10, it is shown as 2.86E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm 2 ) is 2.606 × 10 22 (In Figure 10, it is shown as 2.606E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.256 × 10 22 (In Figure 10, it is shown as 2.256E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 1.364 × 10 22 (In Figure 10, it is shown as 1.364E+22). Also, if the fuel layer number is "8", the fluence (neutrons / cm 2 ) is 2.857 × 10 22 (In Figure 10, it is shown as 2.857E+22). The multiplication factor is 1.0069.

[0063] If the core configuration is "3 regions (fuel salt volume fraction Fr=40% / 27% / 40%)" and the fuel layer number is "1", the fluence (neutrons / cm 2 ) is 2.436 × 10 22 (In FIG. 10, it is shown as 2.436E+22.) The core configuration here corresponds to graph i of the graphs described later (the fluence here is plotted in graph i). Also, if the fuel layer number is "2", the fluence (neutrons / cm 2 ) is 2.582 × 10 22 (In Figure 10, it is shown as 2.582E+22). Also, if the fuel layer number is "3", the fluence (neutrons / cm 2 ) is 2.785 × 1022 (In Figure 10, it is shown as 2.785E+22). Also, if the fuel layer number is "4", the fluence (neutrons / cm 2 ) is 2.863 × 10 22 (In Figure 10, it is shown as 2.863E+22). Also, if the fuel layer number is "5", the fluence (neutrons / cm 2 ) is 2.658 × 10 22 (In Figure 10, it is shown as 2.658E+22). Also, if the fuel layer number is "6", the fluence (neutrons / cm 2 ) is 2.298 × 10 22 (In Figure 10, it is shown as 2.298E+22). Also, if the fuel layer number is "7", the fluence (neutrons / cm 2 ) is 1.283 × 10 22 (In Figure 10, it is shown as 1.283E+22). Also, if the fuel layer number is "8", the fluence (neutrons / cm 2 ) is 2.717 × 10 22 (In Figure 10, it is shown as 2.717E+22). The multiplication factor is 1.0094.

[0064] Fluence (neutrons / cm) for the (1) single-region, (2) two-region, and (3) three-region core configurations described above. 2 ) is plotted as shown in Figure 10. The vertical axis of the graph is the fluence (neutrons / cm 2 ) and the horizontal axis is the fuel layer number. The allowable fluence level of graphite, which is the criterion, is 3×10 22 (In Figure 10, it is written as 3E+22), and the area where the peak of the graph (the top of the mountain-shaped graph) is furthest from this allowable fluence level is "Area 2 (Fuel salt volume fraction Fr = 40% / 26%)" shown in graph d. Since graph d has the furthest peak from the allowable fluence level, it can be said to have the lowest maximum fluence.

[0065] As a result of the study, it can be said that a two-region core configuration in which layers 1 to 5 have a fuel salt volume fraction Fr = 40% and layers 6 to 8 have a fuel salt volume fraction Fr = 26% is the optimal solution.

[0066] The study results showed that it is possible to divide the reactor core 22 into two regions based on the volume fraction of fuel salt, uniformly distributing the cumulative neutron flux and minimizing its maximum value, which makes it possible to achieve a core life of more than 30 years. Therefore, it can be said that there is no longer any need to replace the reactor core 22 until decommissioning.

[0067] Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within the scope that can achieve the object of the present invention are included in the present invention.

[0068] 1 to 10 are merely examples and are not intended to be limited in any way. That is, it is sufficient that the molten salt reactor 2 and the moderator 222 are provided with a part or all of the above-mentioned series of components, and while the optimal shape of the moderator 222 to realize this configuration has been described using, for example, a regular hexagon with n=6 and a hexagonal prism frame, the shape is not intended to be limited to this. That is, the shape may be a regular n-gon with n=3, 4, 5, 7, . . .

[0069] According to the above-mentioned embodiment of the present invention, the moderator 222 and the molten salt reactor 2 can prevent stress generation, ensure the wet edge length, improve the flexibility of selection of the arrangement of the control rods 24, and improve the workability. That is, adjacent moderators 222 do not contact each other, and the occurrence of stress such as friction between adjacent moderators 222 can be prevented, and thus damage can be prevented. In addition, the curved peripheral recess can ensure the wet edge length. In addition, in order to virtually indicate the arrangement area of ​​the moderator 222 (moderator body 222a) and the boundary between adjacent moderators 222 (moderator body 222a), the shape of a regular hexagon or hexagonal column frame is formed around the moderator axis CL2. With this shape, the position and number of the control rods 24 can be relatively flexibly selected. In addition, since there are no sharp corners or hollows in the core area, graphite coating can be advantageously performed. Moreover, by making the cross-sectional shape of the above-mentioned "starfish type", it is possible to provide the moderator 222 with two types of fuel salt volume fractions, and to realize a two-region core. Also, since the moderator 222 has no hollow, it is possible to eliminate the need for terminal processing for draining the fuel salt, and it is possible to make the shape extremely simple. In addition, the moderator 222 and the molten salt reactor 2 can realize a large negative temperature coefficient.

[0070] To summarise the above, the molten salt reactor 2 and the moderator 222 to which the present invention is applied need only have the following configuration, and can take on a variety of different embodiments.

[0071] That is, the moderator for a molten salt reactor to which the present invention is applied (for example, the moderator 222 in FIG. 9) is A molten salt reactor moderator is provided in a plurality of portions in a core (e.g., core 22 in FIG. 3) in a reactor vessel (e.g., reactor vessel 21 in FIG. 3) of a molten salt reactor (e.g., molten salt reactor 2 in FIG. 3), the moderator axis (e.g., moderator axis CL2 in FIG. 9) extending along the core axis (e.g., core axis CL1 in FIG. 3) of the core, and the molten salt reactor moderator is formed in a columnar shape having a main body side portion (e.g., main body side portion 222a1 in FIG. 9) having a plurality of side surfaces (e.g., side surface 222a3 in FIG. 9) and a plurality of corners (e.g., corner portion 222a2 in FIG. 9) around an axis centered on the moderator axis, The side surfaces are each formed in a curved shape that is convex (so that the side portions of the main body are concave) toward the moderator shaft.

[0072] According to the molten salt reactor moderator to which the present invention is applied, the side surfaces of the main body are each formed in a curved shape that is convex toward the moderator axis (so that the main body side is concave), so that a sufficient wetted edge length can be ensured compared to a case where the side surfaces are straight and flat. This ensures a large negative temperature reactivity coefficient, suppresses abnormal temperature rise of the molten salt, improves the braking effect for reactor shutdown, and lowers the upper limit temperature of the molten salt in the core. In other words, it is possible to provide a molten salt reactor moderator that ensures a sufficient wetted edge length in order to ensure a large negative temperature reactivity coefficient. Furthermore, according to the molten salt reactor moderator to which the present invention is applied, contact between adjacent main body sides can be avoided to prevent damage, and further, coating processing can be made easier.

[0073] Furthermore, according to the moderator for a molten salt reactor, each of the multiple corners is formed into a curved shape that is convex on the side away from the moderator axis (convex toward the outside of the main body side).

[0074] The molten-salt reactor moderator to which the present invention is applied has a plurality of corners each formed in a curved shape, which makes it difficult to break compared to when the corners are edges. The molten-salt reactor moderator has no sharp corners in the core area, which makes it advantageous for coating the graphite.

[0075] Furthermore, according to the moderator for molten salt reactors, the cross-sectional shape of the moderator when cut in a direction perpendicular to the moderator axis is formed into a shape that is surrounded by a regular n-polygon (n is an integer of 3 or more) drawn around the moderator axis to virtually indicate the placement area of ​​the main body side portions and the boundaries between adjacent main body sides, and has arcs that are not inscribed in the n corners and n sides of the regular n-polygon.

[0076] According to the molten-salt reactor moderator to which the present invention is applied, the cross-sectional shape of the moderator is formed into a shape surrounded by a regular n-polygon (n is an integer of 3 or more) drawn imaginarily around the moderator axis, and into a shape having arcs that are not inscribed in n corners and n sides of the regular n-polygon, so that it is possible to prevent contact between adjacent moderators. In other words, if there is no contact between adjacent moderators, it is possible to prevent the generation of stress such as friction. According to the molten-salt reactor moderator, since it is formed into a shape surrounded by a regular n-polygon, it is possible to improve the flexibility in selecting the arrangement of control rods, etc., by appropriately selecting n.

[0077] Furthermore, according to the molten-salt reactor moderator, at least the range in which the main body side portion exists along the direction in which the moderator axis extends is formed into a structure in which there is no internal space.

[0078] According to the molten-salt reactor moderator to which the present invention is applied, at least the area where the main body side portion exists is formed in a structure without any internal space, so that the shape is simple and it is possible to improve workability, etc. Therefore, since the shape of the molten-salt reactor moderator is simple, it is possible to advantageously coat the graphite.

[0079] According to the molten-salt reactor to which the present invention is applied, a plurality of the above-mentioned molten-salt reactor moderators are provided in the reactor core within the reactor vessel.

[0080] According to the molten salt reactor to which the present invention is applied, a plurality of the above-mentioned molten salt reactor moderators are provided, so that a better molten salt reactor can be provided.

[0081] In addition, according to the molten salt reactor, the multiple molten salt reactor moderators are arranged in a ring shape and in multiple layers around the core axis of the core, and the core is divided into regions with different fuel salt volume fractions by the desired number of layers of the multiple molten salt reactor moderators arranged in the multiple layers.

[0082] According to the molten salt reactor to which the present invention is applied, it is possible to provide a molten salt reactor moderator with a plurality of types of fuel salt volume fractions, and to realize a multi-region core. This makes it possible to homogenize the distribution of the cumulative neutron flux amount and minimize its maximum value. In other words, it is possible to provide a molten salt reactor capable of realizing a longer core life.

[0083] The above summarizes the characteristics of the molten salt reactor moderator based on its external shape, but the characteristics may also be summarized based on the following shapes. That is, the moderator for a molten salt reactor (for example, the moderator 222 in FIG. 9) is A molten-salt reactor moderator is provided in a plurality of portions in a core (e.g., core 22 in FIG. 3) in a reactor vessel (e.g., reactor vessel 21 in FIG. 3) of a molten-salt reactor (e.g., molten-salt reactor 2 in FIG. 3), the moderator axis (e.g., moderator axis CL2 in FIG. 9) extending along the core axis (e.g., core axis CL1 in FIG. 3) of the core, and the moderator is columnar in shape and has a main body side portion (e.g., main body side portion 222a1 in FIG. 9) that is long in the direction in which the moderator axis extends, At least the area along the extension direction of the moderator shaft where the main body side portion exists is formed solid with no hollow space along the extension direction of the moderator shaft.

[0084] According to the molten-salt reactor moderator, at least the area where the main body side is present is formed solid, so there is no hollow space, and therefore the shape is simple, which can improve workability, etc. In other words, since the molten-salt reactor moderator has no hollow space and a simple shape, it is possible to advantageously coat the graphite.

[0085] Furthermore, according to the moderator for molten salt reactors, the main body side has a plurality of side surfaces (e.g., side surface 222a3 in Figure 9) and a plurality of corners (e.g., corner surface 222a2 in Figure 9) around an axis centered on the moderator axis, and each of the side surfaces is formed into a curved shape that is convex toward the moderator axis.

[0086] According to the molten-salt reactor moderator, the multiple side surfaces of the main body are each formed in a curved shape that is convex toward the moderator axis (as if the main body side is concave), so that a sufficient wetted edge length can be ensured compared to a case where the side surfaces are straight and flat. This ensures a large negative temperature reactivity coefficient, suppresses abnormal temperature rise of the molten salt, improves braking effect for reactor shutdown, and lowers the upper limit temperature of the molten salt in the core. In other words, it is possible to provide a molten-salt reactor moderator that ensures a sufficient wetted edge length in order to ensure a large negative temperature reactivity coefficient. [Explanation of symbols]

[0087] 1. Building 2. Molten Salt Reactor 21...Reactor vessel 22. Core 23 Primary heat exchanger unit 24...Control rod 221...Graphite reflective material 222...Moderator (moderator for molten salt reactors) 222a... Moderator body 222a1 Body side 222a2... corner 222a3...side

Claims

1. A molten-salt reactor moderator is provided in a reactor core in a reactor vessel of a molten-salt reactor, the moderator axis extends along the reactor core axis, and the molten-salt reactor moderator is formed in a columnar shape having a main body side portion with a plurality of side surfaces and a plurality of corners around an axis centered on the moderator axis, each of the side surfaces is formed in a curved shape that is convex toward the moderator shaft; A moderator for a molten salt reactor, wherein the entire side surface of each of the multiple side surfaces is formed into a curved shape that does not come into contact with the adjacent molten salt reactor moderator, and the side length of each of the multiple side surfaces in the circumferential direction centered on the moderator axis becomes the wetted edge length with respect to the fuel salt, and the moderator is formed into a curved shape that contributes to improving the negative temperature reactivity coefficient.

2. Each of the plurality of corners is formed into a curved shape that is convex toward a side away from the moderator shaft.

2. The molten salt reactor moderator according to claim 1.

3. A cross-sectional shape of the moderator when cut in a direction perpendicular to the moderator axis is formed into a shape surrounded by a regular n-gon (n is an integer of 3 or more) drawn around the moderator axis in order to virtually indicate the arrangement area of ​​the main body side portion and the boundary between adjacent main body side portions, and has arcs that are not inscribed in n corners and n sides of the regular n-gon.

3. A molten salt reactor moderator according to claim 2.

4. At least a region in which the main body side portion exists along the direction in which the moderator shaft extends is formed to have a structure in which no space exists therein. A molten salt reactor moderator according to any one of claims 1 to 3.

5. A molten-salt reactor comprising a plurality of molten-salt reactor moderators according to any one of claims 1 to 4 provided in a reactor core within a reactor vessel.

6. The plurality of molten-salt reactor moderators are arranged in a ring shape and in a plurality of layers around the core axis of the core, The core is divided into regions having different fuel salt volume fractions by a desired number of layers of the plurality of molten salt reactor moderators arranged in the plurality of layers.

6. The molten salt reactor of claim 5.

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