Arrangement form of solid moderator material for miniaturized design of liquid metal cooled reactor

Abstract

The present invention discloses an arrangement form of a solid moderator material for the miniaturization design of a liquid metal cooled reactor. The core of the liquid metal cooled reactor is composed of regular hexagonal assemblies. The assembly includes a fuel assembly, a control rod assembly and a reflector. The fuel assembly consists of a solid moderator and 19 fuel rods. The material of the solid moderator is 11 B4C, which is arranged on the outermost layer of the 19 fuel rods. The present invention can reduce the fuel loading of the liquid metal cooled reactor and reduce the core size, improve the economy, maneuverability and transportation convenience of the reactor device, so as to provide stable, reliable and concealed mobile accompanying energy guarantee; it can effectively utilize the 10 B remaining after enrichment in boric acid, and 11 B, and follow the mature processing and manufacturing technology of the neutron absorption material 10 B4C, which has high engineering application feasibility and can reduce the manufacturing difficulty and cost of the solid moderator.

Description

Technical Field

[0001] The present invention relates to the technical fields of nuclear materials and nuclear reactors, and particularly to an arrangement form of a solid moderator material for miniaturized design of a liquid metal cooled reactor. Background Art

[0002] Benefiting from the good neutronics characteristics and excellent heat-carrying performance of liquid metal materials, nuclear reactors using liquid metal as a coolant can achieve an extremely long refueling cycle, safe operation at atmospheric pressure, and simplified system design, and have advantages in the comprehensive utilization of nuclear energy. Aiming at the energy supply demands in environments such as the deep sea, polar regions, and remote islands, small metal cooled reactors have broad development prospects and have received extensive attention from the world's major nuclear powers, and a variety of small liquid metal cooled reactors have been proposed, such as the Russian small modular lead-based fast reactor SVBR-100, the Korean small natural circulation lead-based fast reactor URANUS, the multi-functional small modular natural circulation lead-cooled fast reactor SNCLFR-100 designed by the University of Science and Technology of China, etc. However, due to the weak neutron moderation ability of liquid metal and the small fuel fission cross-section under fast spectrum conditions, the criticality of liquid metal reactors usually requires loading several tons of fuel or high-enrichment fuel, making the existing liquid metal cooled reactors heavy in mass and high in cost, resulting in poor reactor economy and flexibility. And softening the neutron energy spectrum of the reactor core by adding a solid moderator and increasing the fuel fission rate is one of the effective methods to reduce the fuel loading and the core size of liquid metal reactors.

[0003] Among the materials of moderators commonly used in current reactors, hydrogen-containing materials such as ZrH have good moderation ability, but there is a phenomenon of hydrogen release at high temperatures. For pool-type metal cooled reactors, the impact of hydrogen release on safety is less than that of pressurized water reactors, but as the hydrogen content decreases, the moderation ability of ZrH will also decrease accordingly, which is not conducive to increasing the fuel burnup depth; Be and BeO are highly toxic to the human body. Therefore, if a suitable moderator can be selected, the economy and inherent safety of small liquid metal cooled reactors will be improved. Scattering is the main nuclear reaction process that slows down neutrons, and it has two types: inelastic scattering and elastic scattering. In a thermal neutron reactor, elastic scattering plays a major role in the process of slowing down neutrons from high energy to low energy. Moderators generally select elements with a small atomic number. For example, pressurized water reactors generally use water as a moderator. Boron is one of the better alternative solid moderators. Boron carbide is a solid moderator with high temperature resistance, and its melting point can reach 2450 °C. It has the advantages of low density, stable chemical properties, high hardness, no strong γ-ray secondary radiation after neutron absorption, and no generation of radioactive isotopes. At the same time 11B has a high abundance in natural boron and a small thermal neutron absorption cross-section. It is an excellent solid moderator material that can improve the reactivity of the reactor and achieve neutron economy in the core. Finally, B4C, as a reflector or neutron absorber material, has practical applications in existing reactors, and its physical properties are proven. Therefore, exploring a 11 miniaturized liquid metal cooled reactor based on B4C as a solid moderator is necessary for reducing the core fuel loading or core size, enhancing the economy of small liquid metal cooled reactors, or further miniaturizing the core. Summary of the Invention

[0004] The object of the present invention is to address the problems of heavy core mass and large volume in the current small and lightweight design of liquid metal cooled reactors, overcome the deficiencies of the prior art, and provide a 11 miniaturized design method and core arrangement of a B4C moderated metal cooled reactor to improve the economy, maneuverability, and transportation convenience of the reactor device.

[0005] The technical solution adopted by the present invention is as follows: A form of arranging solid moderator materials for the miniaturized design of a liquid metal cooled reactor. The core is composed of a regular hexagonal fuel assembly 1, a control rod assembly 2, and a reflector 3. The reflector 3 is arranged on the outermost layer of the core to cover the active zone composed of the fuel assembly 1 and the control rod assembly 2. The fuel assembly 1 and the control rod assembly 2 in the active zone are arranged evenly and alternately. The fuel assembly 1 consists of several fuel rods 4 and a hexagonal solid moderator 5, and the material of the 11 solid moderator 5 is B4C, which is arranged on the outermost layer of several fuel rods 4.

[0006] Specifically, a form of arranging solid moderator materials for the miniaturized design of a liquid metal cooled reactor. The core is composed of a regular hexagonal fuel assembly 1, a control rod assembly 2, and a reflector 3. The reflector 3 is arranged on the outermost layer of the core to cover the active zone composed of the fuel assembly 2 and the control rod assembly 2. 30 fuel assemblies 1 and 7 control rod assemblies 2 are arranged evenly and alternately in the active zone; the fuel assembly 3 consists of 19 fuel rods 4 and a solid moderator 5, and the material of the 11 solid moderator 5 is B4C, which is arranged on the outermost layer of 19 fuel rods 4; the fuel rod 4 is composed of a fuel pellet 9, an upper end plug 6, a lower end plug 14, a gas gap 10, an upper thermal insulation layer 8, a lower thermal insulation layer 12, an upper gas cavity 7, a lower gas cavity 13, and a cladding 11. Currently, boron is usually enriched after being made into boric acid and then used to manufacture neutron absorption materials 10 B, and then used to manufacture the neutron absorption material 10 B4C. The present invention uses the remaining 10 B after enriching 11 B and follows the 10 mature production process of B4C to make a solid moderator material11 B4C

[0007] Furthermore, the 11 B4C of the hollow regular hexagonal prism structure does not affect the internal structure of the fuel assembly and can be replaced separately. At the same time, high-energy fast neutrons have inelastic scattering with the fuel rod cladding 11 before reaching 11 the B4C solid moderator 5 and thus reduce their energy. Fast neutrons in the lower energy region have elastic scattering with the solid moderator and become thermal neutrons.

[0008] In the present invention, 11 the B4C solid moderator 5 enhances the moderation ability of the reactor core for fast neutrons, improves the neutron reflection ability, reduces the neutron leakage rate of the reactor core, increases the neutron flux density of the reactor core, and can reduce the fuel enrichment / fuel loading or reduce the geometric size of the reactor core, which is beneficial to the miniaturization and light weight of the liquid metal cooled reactor.

[0009] Furthermore, 11 B is derived from a neutron absorption material 10 and is the remaining product after boron acid solution is enriched during the manufacturing process of B4C. It is inexpensive and easily available, has good chemical stability and good corrosion resistance. 10 11 The production of B4C can follow the mature 10 B4C manufacturing technology, and the manufacturing cost and difficulty are low.

[0010] Furthermore, the reactor core is composed of 30 regular hexagonal fuel assemblies 1, 7 control rod assemblies 2 and a reflector 3.

[0011] Furthermore, the fuel assembly 1 includes 19 fuel rods 4 and a layer of 11 B4C solid moderator 5 with a hollow regular hexagonal prism structure.

[0012] Furthermore, the center distance between two adjacent fuel assemblies 1 is 91 mm.

[0013] Furthermore, 11 the inner opposite side distance of the B4C solid moderator 5 is 69.8 mm, the outer opposite side distance is 86 mm, the height is 1900 mm, and the center distance between adjacent fuel rods 4 is 15.12 mm.

[0014] Furthermore, the fuel rod 4 is composed of a fuel pellet 9, an upper end plug 6, a lower end plug 14, a gas gap 10, an upper thermal insulation layer 8, a lower thermal insulation layer 12, an upper gas cavity 7, a lower gas cavity 13 and a cladding 11, wherein the fuel pellet 9, the upper end plug 6 and the lower end plug 14 are all cylinders.

[0015] ​Further, the fuel pellet 9 is composed of Pu, Tu, and N, with the mass fractions of each nuclide being 19.3%, 75%, and 5.7% respectively, and the fuel density being 10.91 g / cm 3 , the radius of the fuel pellet 9 is 6 mm, and the height is 1600 mm.

[0016] Further, the upper thermal insulation layer 8 and the lower thermal insulation layer 12 have a radius of 6.1 mm, and the thicknesses of the upper and lower end thermal insulation layers are the same, both being 10 mm.

[0017] Further, helium is filled between the fuel pellet 9 and the cladding 11, with an inner radius of 6 mm, an outer radius of 6.1 mm, and the thickness of the gas gap 10 being 0.1 mm; helium is filled between the upper and lower end thermal insulation layers and the end plugs and the cladding 11. The radius of the helium is 6.1 mm, and the heights of the upper / lower gas cavities are different. The height of the upper gas cavity 7 is 40 mm, and the height of the lower gas cavity 13 is 180 mm.

[0018] Further, the rest consists of the fuel rod cladding 11, the upper end plug 6, and the lower end plug 14. The thickness of the cladding 11 is 2 mm, and the thicknesses of the upper / lower end plugs are 30 mm, and the material is HT-9.

[0019] The above core design method makes full use of 11 the inherent characteristics of the B4C material. Under the conditions of ensuring the core power, refueling cycle, etc., it can significantly reduce the core size and fuel loading, which is beneficial to the miniaturization and lightweight of the liquid metal cooled reactor.

[0020] Compared with the existing technology, the advantages of the present invention are as follows:

[0021] (1), in the present invention, the use of 11 B4C as a solid moderator can effectively improve the neutron utilization rate and core power, significantly improve the core reactivity, and can reduce the fuel enrichment degree, reduce the fuel loading, and reduce the core size under the same core power and refueling cycle, making the reactor device have a smaller critical size and fuel loading.

[0022] (2), in the present invention, the 11 B in B4C 11 comes from the product remaining after the enrichment of boric acid solution in the manufacturing process of the neutron absorber 10 B4C. It is low-cost and easily available, has good chemical stability, has good corrosion resistance, and at the same time 10 the absorption cross-section of B for thermal neutrons is extremely small, only 0.005 barn. 11 (3), the isotope material of B4C described in the present invention

[0023] (3), the 11 isotope material of B4C 10B4C is widely used in reactors. Its physical and chemical properties can meet the requirements for long-term use in reactors with harsh environments and it is non-toxic to humans. Description of the Drawings

[0024] Figure 1 is a schematic diagram of the arrangement of the reactor core components of the present invention;

[0025] Figure 2 is a radial schematic diagram of the fuel assembly of the present invention;

[0026] Figure 3 is a schematic diagram of the structure of the fuel rod of the present invention;

[0027] In the figure, 1 is the fuel assembly, 2 is the control rod assembly, 3 is the reflector, 4 is the fuel rod, 5 is the solid moderator, 6 is the upper end plug, 7 is the upper gas cavity, 8 is the upper adiabatic layer, 9 is the fuel pellet, 10 is the gas gap, 11 is the cladding, 12 is the lower adiabatic layer, 13 is the lower gas cavity, and 14 is the lower end plug. Detailed Embodiments

[0028] The present invention provides a solid moderator material and an arrangement form for the miniaturization design of a liquid metal cooled reactor. The following will elaborate on the detailed embodiments of the present invention in conjunction with the drawings:

[0029] A solid moderator material and an arrangement form for the miniaturization design of a liquid metal cooled reactor. The core structure of the liquid metal cooled reactor is as Figure 1 shown. The core of the liquid metal cooled reactor mainly consists of a fuel assembly 1, a control rod assembly 2, and a reflector 3, and an active region composed of the fuel assembly 1 and the control rod assembly 2. The reflector 3 is arranged on the outermost layer of the core, and the reflector 3 covers the active region. The fuel assembly 1 and the control rod assembly 2 in the active region are arranged evenly and alternately. The fuel assembly 1 is composed of a plurality of fuel rods 4 and a layer of hexagonal solid moderator 5. The material of the solid moderator 5 is 11 B4C, which is arranged on the outermost layer of a plurality of fuel rods 4. The 11 B4C with a hollow regular hexagonal prism structure does not affect the internal structure of the fuel assembly and can be replaced separately. At the same time, high-energy fast neutrons have inelastic scattering with the fuel rod cladding 11 before reaching the 11 B4C solid moderator 5 and thus reduce their energy. Fast neutrons in the lower energy region have elastic scattering with the solid moderator and become thermal neutrons. 11 The B4C solid moderator 5 enhances the moderation ability of the core for fast neutrons, improves the neutron reflection ability at the same time, reduces the neutron leakage rate of the core, increases the neutron flux density of the core, and can reduce the fuel enrichment / fuel loading or reduce the core geometric size, which is beneficial to the miniaturization and lightweight of the liquid metal cooled reactor. 11 B is derived from neutron absorption materials 10Enrichment of Boric Acid Solution during B4C Manufacturing Process 10 The product remaining after B has good chemical stability, low cost and easy availability, and has good corrosion resistance. 11 The production of B4C can follow the mature 10 B4C manufacturing technology, with low manufacturing cost and difficulty. Specifically, 30 hexagonal fuel assemblies 1 and 7 control rod assemblies 2 are arranged in a hexagonal pattern on the cross-section of the reactor core in the active area of the reactor core. Specifically, one of the fuel assemblies 1 is located at the center of the active area of the reactor core, and the remaining fuel assemblies 1 are installed in a single-layer hexagonal arrangement from the inside to the outside around this fuel assembly 1 in the active area of the reactor core. The first layer has 6 fuel assemblies 1, the second layer has 6 fuel assemblies 1 and 6 control rod assemblies 2, and the fuel assemblies 1 and the control plate assemblies 2 are arranged alternately. The center distance between adjacent fuel assemblies 1 in the third layer is 91 mm. Among them, the control rod assemblies 2 are arranged at the center of the reactor core and at the midpoint of the center of the hexagon connection line. The inner diameter of its guide tube is 35 mm, the outer diameter is 37 mm, and the wall thickness is 2 mm; the reflector 3 is located on the outermost periphery of the reactor core to cover the active area, and is an overall circular ring structure, which plays a role in reflecting neutrons and has a certain neutron shielding function; further, the detailed structure of the fuel assembly 1 is as Figure 2 shown. The fuel assembly 1 is an overall regular prism structure, with an inner opposite side distance of 69.8 mm, an outer opposite side distance of 86 mm, and an outer thickness of 8.1 mm 11 B4C solid moderator 5. 19 fuel rods 4 with an outer diameter of 6.3 mm are arranged in an overall hexagonal structure on the cross-section inside the fuel assembly 1, and the center distance is 15.12 mm. The 11 B4C solid moderator 5 wrapped around it cooperates with the metal reflector 3 on the periphery of the reactor core, which can provide neutron moderation for the reactor core while having a certain reflection ability and reducing neutron leakage. At the same time, the metal cladding 11 outside the fuel rod 4 can undergo inelastic scattering with fast neutrons to quickly reduce the energy of the fast neutrons; further, the detailed structure of the fuel rods 4 arranged inside the fuel assembly 1 is as Figure 3 shown. The fuel rod 4 is sequentially sleeved with a fuel pellet 9, a gas gap 10 and a fuel rod cladding 11 from the inside to the outside. The outer diameter of the fuel rod 4 is 6.3 mm, the radius of the fuel pellet 9 is 6.0 mm, the thickness of the fuel cladding 11 is 0.2 mm, and the gas gap 10 between the fuel pellet 9 and the cladding 11 is 0.1 mm thick and filled with helium. The fuel pellet 9 is a PuN-ThN fuel, and the fuel cladding 11 and the guide tube in the control rod assembly 2 are both made of HT-9 material composed of Si, Cr, Mn, Ni, Fe, Mo alloy. The fuel pellet 9 is composed of Pu, Tu and N, and the mass fractions of each nuclide are 19.3%, 75% and 5.7% respectively. The fuel density is 10.91 g / cm 3 , the radius of the fuel pellet 9 is 6 mm, and the height is 1600 mm.

[0030] As shown Figure 3 in the figure, the fuel rod 4 is composed of fuel pellets 9, upper end plug 6, lower end plug 14, gas gap 10, upper thermal insulation layer 8, lower thermal insulation layer 12, upper gas cavity 7, lower gas cavity 13, and cladding 11; among them, the fuel pellets 9, upper end plug 6, and lower end plug 14 are all cylinders. The fuel pellets 9, upper end plug 6, lower end plug 14, gas gap 10, upper thermal insulation layer 8, lower thermal insulation layer 12, upper gas cavity 7, and lower gas cavity 13 are all arranged inside the cladding 11. An upper thermal insulation layer 8 is arranged on the fuel pellets 9, an upper gas cavity 7 is arranged on the upper thermal insulation layer 8, and an upper end plug 6 is arranged on the upper gas cavity 7. A lower thermal insulation layer 12 is arranged at the bottom of the fuel pellets 9, a lower gas cavity 13 is arranged at the bottom of the lower thermal insulation layer 12, and a lower end plug 14 is arranged at the bottom of the lower gas cavity 13. Among them, the fuel pellets 9, upper end plug 6, and lower end plug 14 are all cylinders.

[0031] The fuel pellets 9 are composed of Pu, Tu, and N, and the mass fractions of each nuclide are 19.3%, 75%, and 5.7% respectively. The fuel density is 10.91 g / cm 3 , and the radius of the fuel pellets 9 is 6 mm and the height is 1600 mm.

[0032] The upper thermal insulation layer 8 and the lower thermal insulation layer 12 have a radius of 6.1 mm, and the thicknesses of the upper and lower end thermal insulation layers are the same, both being 10 mm.

[0033] Helium is filled between the fuel pellets 9 and the cladding 11, with an inner radius of 6 mm and an outer radius of 6.1 mm, and the thickness of the gas gap 10 is 0.1 mm; helium is filled between the upper and lower end thermal insulation layers and the end plugs and the cladding 11. The radius of the helium is 6.1 mm, and the heights of the upper / lower gas cavities are different. The height of the upper gas cavity 7 is 40 mm, and the height of the lower gas cavity 13 is 180 mm.

[0034] The remaining part is the fuel rod cladding 11, upper end plug 6, and lower end plug 14. The thickness of the cladding 11 is 2 mm, and the thicknesses of the upper / lower end plugs are 30 mm, and the material is HT-9.

[0035] The thermal power of the reactor core is 5 MW, using PuN-ThN fuel, with a volumetric power density of 48.48 MW / cm 3 , a linear power density of 54.82 W / cm, a burnup life of 17 years, the height of the active core area is only 160 cm, and the radial diameter of the core is only 93.5 cm. The main design parameters of the core are shown in Table 1.

[0036] Table 1 Main parameters of the core

[0037]

[0038] ,

[0039] The arrangement form and material type of the moderator significantly affect the physical characteristics of the reactor core. For moderators with different arrangement forms, there are differences in the moderator loading and reactor core size required to maintain the criticality of the reactor core under the same reactor core fuel loading. The solid moderator used in the present invention 11 The main arrangement methods of B4C include: in the fuel assembly box, around the fuel pellets, and at both ends of the fuel pellets. By controlling the loading of the solid moderator in different arrangement forms, the reactor core is made critical and the initial keff is close to 1.03. The reactor physics analysis program is used to analyze parameters such as the keff of the reactor core under three different arrangement methods. It can be clearly found through calculation and simulation that when arranged at both ends of the pellets, as the moderator height is adjusted from 2 cm to 240 cm, the initial keff of the lead-bismuth reactor is less than 0.8, and the reactor core cannot be made critical; while for the keff of the two cases where the moderator is arranged in the fuel assembly box and around the pellets, the changing trend of the keff with time is similar. In the case where the moderator is arranged around the pellets, the rate of decrease of the reactor keff with time is slightly less than that in the case where the moderator is arranged in the fuel assembly box. However, when the moderator is arranged around the pellets compared to being in the assembly box, the overall volume of the reactor core increases by 1.825838 times, the amount of moderator used increases by 2.136 times, and the discharge burnup depth only increases by 11.1114%. It is more beneficial for the miniaturization and lightweight of the reactor core to use the moderator as the assembly box. The specific calculation results are shown in Table 2

[0040] Table 2 Calculation results of the moderator arranged in the assembly box and around the pellets

[0041]

[0042] At the same time, since scattering is the main nuclear reaction process in neutron moderation, including elastic scattering and inelastic scattering. Inelastic scattering plays a major role in fast neutron reactors. In thermal neutron reactors, elastic scattering plays a major role in the process of slowing down neutrons from high energy to low energy. The method to quickly slow down fast neutrons is to quickly reduce the neutron energy below the corresponding first excitation level energy through inelastic scattering, and then further reduce the neutron energy to the thermal energy region through elastic scattering. When the solid moderator is arranged as the assembly box, the fast neutrons generated by fission first undergo inelastic scattering with the metal cladding and liquid lead coolant, quickly reducing to a lower energy level, and then undergo elastic scattering with the light nuclear moderator to become thermal neutrons, with a better moderation effect. If the moderator is arranged around the pellets, since the threshold of inelastic scattering increases with the decrease of atomic mass, the inelastic scattering of fast neutrons with light nuclei will weaken. At the same time, neutrons are more easily absorbed by the moderator material, which instead has a negative impact on the k of the lead-bismuth reactor eff Therefore, this arrangement method is more beneficial for the design and operation of liquid metal reactors

[0043] The parts not elaborated in detail in the present invention belong to the well-known technologies in the art

[0044] Although the above description of the illustrative specific embodiments of the present invention is provided for those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious. All inventions and creations using the concept of the present invention are within the scope of protection.

Claims

1. A layout form of a solid moderator material for the miniaturization design of a liquid metal cooled reactor, characterized in that, The core is composed of a regular hexagonal fuel assembly (1), a control rod assembly (2) and a reflector layer (3); the reflector layer (3) is arranged at the outermost layer of the core and covers an active region composed of the fuel assembly (1) and the control rod assembly (2); the fuel assembly (1) and the control rod assembly (2) are evenly arranged alternately in the active region; the fuel assembly (1) is composed of a plurality of fuel rods (4) and a layer of hexagonal solid moderator (5); 11 The B4C solid moderator (5) is uniformly filled in the outer periphery of the fuel assembly (1) as a component box, does not affect the internal structure of the fuel assembly (1), and can be replaced separately. 11 The B4C solid moderator (5) has previously been subjected to inelastic scattering with the fuel rod cladding (11) to reduce its energy, and the fast neutrons in the lower energy region are elastically scattered with the solid moderator (5) to become thermal neutrons; 11 The B4C solid moderator (5) is a hollow regular hexagonal prism structure, and the fuel rod (4) is arranged inside the hollow regular hexagonal prism structure; the material of the solid moderator (5) is 11 B4C, using neutron absorbing materials 10 Boric acid solution enrichment during B4C manufacturing process 10 The remaining product after B 11 B is made into solid moderator material 11 B4C; In the internal cross section of the fuel assembly (1), the fuel rods (4) are arranged in a hexagonal structure as a whole. 11 B4C solid moderator (5); fuel pellets (9), air gaps (10) and fuel rod cladding (11) are arranged in an annular manner from the inside to the outside of the fuel rod (4), the fuel pellets (9) are PuN-ThN fuel, the air gaps (10) are filled with helium, and the fuel rod cladding (11) is made of HT-9 material made of Si, Cr, Mn, Ni, Fe, and Mo alloy; The fuel rod (4) is composed of fuel pellets (9), upper end plug (6), lower end plug (14), gas gap (10), upper thermal insulation layer (8), lower thermal insulation layer (12), upper gas cavity (7), lower gas cavity (13) and fuel rod cladding (11). The fuel pellets (9), upper end plug (6), lower end plug (14), gas gap (10), upper thermal insulation layer (8), lower thermal insulation layer (12), upper gas cavity (7) and lower gas cavity (13) are all arranged inside the fuel rod cladding (11); the upper thermal insulation layer (8) is arranged on the fuel pellets (9), the upper gas cavity (7) is arranged on the upper thermal insulation layer (8), and the upper end plug (6) is arranged on the upper gas cavity (7); the lower thermal insulation layer (12) is arranged at the bottom of the fuel pellets (9), the lower gas cavity (13) is arranged at the bottom of the lower thermal insulation layer (12), and the lower end plug (14) is arranged at the bottom of the lower gas cavity (13). The gap between the fuel rod cladding (11) and the fuel pellets (9) is the gas gap (10); among them, the fuel pellets (9), upper end plug (6) and lower end plug (14) are all cylinders.

2. The arrangement form of the solid moderator material for the miniaturization design of a liquid metal cooled reactor according to claim 1, characterized in that, The number of the described fuel assemblies (1) is 30, the number of the control rod assemblies (2) is 7; the number of the fuel rods (4) is 19.

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