Nuclear heat propulsion reactor core structure based on TPMS microstructure

Abstract

The invention discloses a nuclear heat propulsion reactor core structure based on a TPMS microstructure, which belongs to the technical field of high-temperature gas cooled reactors, comprises a fuel element, a graphite moderator, a cooling channel, a control rod and a reflecting layer, and is characterized in that a TPMS structure with a height adjustable topological form is introduced into the fuel element of the high-temperature gas cooled reactor; a cooling channel with a high specific surface area is formed in the fuel element, and the contact area of a coolant and a fuel reactor core is increased, so that the heat exchange capacity is improved; the periodically arranged holes or reinforcement phases of the TPMS structure can effectively disperse external loads, reduce local stress concentration and have adjustable mechanical properties, and the structure can be customized by adjusting the aperture, porosity, wall thickness and arrangement mode (such as orthogonality, hexagon and the like) so as to meet the working condition requirements of different high-temperature gas cooled reactors.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature gas-cooled reactors, and particularly relates to a core structure of a nuclear thermal propulsion reactor based on a TPMS microstructure. Background Art

[0002] Nuclear Thermal Propulsion (NTP) is an efficient deep-space propulsion technology. Its core principle is to use the high temperature generated by nuclear fission reactions to heat a coolant (usually hydrogen or helium), and then eject it at high speed through a nozzle to generate thrust. Compared with traditional chemical propulsion systems, NTP has a higher specific impulse (Isp), which can significantly improve the mission capabilities and long-range capabilities of spacecraft. Therefore, NTP technology is regarded as an important propulsion method for future manned Mars missions and deep-space exploration.

[0003] A High-Temperature Gas-Cooled Reactor (HTGR) is an advanced nuclear reactor technology that uses helium as a coolant and graphite as a moderator. Its core characteristics are high operating temperature (up to 1000 °C, significantly higher than the 300 - 350 °C of conventional pressurized water reactors), strong inherent safety, and high fuel utilization rate. It is suitable for fields such as efficient power generation, nuclear hydrogen production, industrial heating, and space nuclear power, and is considered one of the ideal reactor types for nuclear thermal propulsion systems.

[0004] The fuel form of HTGR adopts coated particle fuel, that is, the fuel is wrapped by multiple layers of high-temperature resistant materials (such as silicon carbide) to prevent the leakage of radioactive substances; the fuel utilization rate of HTGR can reach more than 90%, far exceeding that of traditional light water reactors (about 1%). Usually, helium is used as a coolant, which is high-temperature resistant and chemically stable, and directly transfers heat to the secondary loop system. Graphite is used as a moderator to slow down the neutron speed to achieve a controllable chain reaction. At high temperatures, the graphite moderator is prone to oxidation (an inert gas environment is required), and the silicon carbide fuel coating layer needs to resist radiation and thermal shock.

[0005] Therefore, the design of the fuel core in the HTGR reactor core is crucial for heat transfer efficiency, core stability, and overall system performance. Traditional fuel core structures mostly adopt a pebble bed structure or a prismatic graphite block structure, and their cooling channels are usually designed as straight-through or grid-shaped, which to a certain extent limits the heat transfer efficiency and may cause problems such as local temperature non-uniformity and large pressure loss.

[0006] The current fuel core design of nuclear thermal propulsion systems mainly has the following problems:

[0007] 1. Limited heat transfer capacity: The straight-through cooling channels of traditional fuel cores have a small heat transfer area, resulting in a low heat exchange efficiency between the coolant and the fuel core, affecting the effective utilization rate of the fuel;

[0008] 2. High flow resistance: In the core of a high-temperature gas-cooled reactor, an unreasonable design of the flow path of helium or hydrogen may lead to a high pressure loss, reducing the overall efficiency of the propulsion system.

[0009] 3. Limited room for structural performance optimization: Traditional fuel cores adopt regular geometric shapes with limited mechanical strength, making it difficult to balance high-temperature stability, thermal expansion adaptability, and radiation resistance. Summary of the Invention

[0010] In view of the problems existing in the existing fuel core of high-temperature gas-cooled reactors, such as limited heat transfer capacity, large flow resistance, and uneven cooling, the present invention proposes a core structure of a nuclear thermal propulsion reactor based on the TPMS microstructure.

[0011] A core structure of a nuclear thermal propulsion reactor based on the TPMS microstructure includes fuel elements, graphite moderators, cooling channels, control rods, and reflectors. By introducing the TPMS structure with adjustable topological morphology into the fuel elements of high-temperature gas-cooled reactors, cooling channels with a high specific surface area are formed inside the fuel elements, increasing the contact area between the coolant and the fuel core, thereby enhancing the heat transfer capacity.

[0012] Furthermore, the TPMS structure adopts a Diamond structure, a Gyroid structure, or a Schwarz-D structure, preferably a TPMS structure that forms continuous and non-through cooling channels inside the fuel core.

[0013] Furthermore, the fuel element is of a TPMS structure, columnar as a whole, and contains several channels inside. All inner walls are composed of the core in the middle and the cladding outside. Among them, the graphite moderator also acts as an independent annular moderator layer to wrap the fuel core.

[0014] Furthermore, an upper reflector and a lower reflector are respectively arranged above and below the fuel assembly. The upper and lower reflectors have the same TPMS structure as the fuel assembly, forming connected channels.

[0015] Furthermore, an upper gas cavity and a lower gas cavity are respectively arranged above the upper reflector and below the lower reflector, and a reversing valve for controlling the flow direction of the coolant is arranged at the corresponding channel openings. Some of the several channels are for lower intake and upper exhaust, and some are for upper intake and lower exhaust; after the coolant is introduced from the lower gas cavity, it enters the upper gas cavity from bottom to top along some channels and then flows out of the core from top to bottom along the other channels.

[0016] Furthermore, through local optimization of the TPMS structure, cylindrical control rod insertion holes are reasonably arranged inside the fuel element, making the coolant flow around the control rods more evenly and reducing local overheating phenomena.

[0017] Furthermore, the TPMS structure adopts a Diamond structure, a Gyroid structure or a Schwarz-D structure. Preferably, a TPMS structure that forms continuous and non-direct cooling channels inside the fuel core is adopted. For example, a Diamond structure or a modified Gyroid structure is adopted. The modified Gyroid structure means that control terms containing a control factor α are introduced into the three additive terms of the standard Gyroid function to form a modified Gyroid function. By adjusting the size of the control factor α, the size of the straight-through holes and the tortuosity of the surface structure in the Gyroid structure can be regulated. At the same time, the control terms of the additive terms in the xy plane contain the associated variable z, the control terms of the additive terms in the yz plane are associated with the variable x, and the control terms of the additive terms in the zx plane contain the associated variable y.

[0018] The present invention introduces a TPMS structure with a highly adjustable topological morphology into the fuel element of a high-temperature gas-cooled reactor, enabling the formation of cooling channels with a high specific surface area inside the fuel element, increasing the contact area between the coolant and the fuel core, and thus enhancing the heat transfer capacity.

[0019] The periodically arranged holes or reinforcing phases in the TPMS structure can effectively disperse external loads, reduce local stress concentration, and have adjustable mechanical properties. By adjusting the pore diameter, porosity, wall thickness, arrangement pattern (such as orthogonal, hexagonal, etc.), the structure can be customized to meet the working conditions of different high-temperature gas-cooled reactors.

[0020] By eliminating the straight-through holes, the fluid guiding characteristics can be optimized, the straight-through high-flow-rate paths can be reduced, the flow pressure drop can be lowered. At the same time, by strengthening the local turbulence effect, the secondary flow disturbance ability can be improved, the heat transfer effect can be enhanced, and the temperature distribution of the entire core can be made more uniform. During the coolant flow process, the disturbance effect is enhanced, promoting efficient secondary flow and vortex effect, enhancing the turbulent heat transfer ability, reducing the risk of local hot spots, and thus improving the overall heat transfer performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the TRISO-coated fuel particle structure;

[0022] Figure 2 It is a schematic diagram of the Diamond unit structure;

[0023] Figure 3 It is the hierarchical structure of the inner wall of the fuel element proposed in Embodiment 1;

[0024] Figure 4 It is a schematic diagram of the main structure of the fuel element based on the Diamond structure in Embodiment 1;

[0025] Figure 5 It is a schematic diagram of the Gyroid unit structure;

[0026] Figure 6 The three-dimensional view and the top view of the improved Gyroid unit structure disclosed in the core of Example 2 at different α values;

[0027] Figure 7 The three-dimensional view and top view of other improved Gyroid unit structures at a fixed α value given in Example 2 are shown. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for the purpose of illustration and description, and are not intended to be exhaustive or to limit the present invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0029] Example 1

[0030] The existing high temperature gas cooled reactor structure is mainly a pebble bed structure or a prismatic graphite block structure, but the fuel elements are mainly spherical coated fuel particles. The cylindrical cavity cylinder structure made of carbon bricks and graphite bricks provides a place for the spherical coated fuel particles. Of course, other supporting structures that meet the requirements can also be used. Among the spherical coated fuel particles, the TRISO type is the most common. Its structure can be found in Figure 1 The present invention breaks the inherent thinking of the existing high-temperature gas-cooled reactor structure that mainly uses spherical coated fuel particles as fuel elements. The fuel element adopts a TPMS structure with a highly adjustable topological morphology, so that a cooling channel with a high specific surface area is formed inside the fuel element, increasing the contact area between the coolant and the fuel core, thereby improving the heat exchange capacity.

[0031] The TPMS structure is a complex topological structure with periodicity, connectivity and minimal surface characteristics. Its unique geometric features can significantly optimize the thermal management and fluid dynamics performance of fuel assemblies. Diamond, Gyroid and Schwarz-D are three typical TPMS structures, all of which are applicable to the present invention. The following embodiment will first be described using the Diamond structure as an example. Figure 2 This is a schematic diagram of the Diamond unit structure. The inner walls of the structure are staggered to form several channels. As a fuel element, all the inner walls are composed of a core in the middle and a cladding layer on the outside, see Figure 3 The outer coating layer may refer to TRISO-type coated fuel particles, or other types of existing coated fuel particles, or even other types of coated fuel particles that may appear in the future, and the present invention is not limited to this.Figure 3 The number of cladding layers shown is only for illustration. The graphite moderator also serves as an independent annular moderator layer to wrap the fuel core. The fuel element and the moderator are tightly integrated through structural integration, which can reduce neutron leakage.

[0032] Figure 4 The schematic diagram of the main structure of the fuel element based on the Diamond structure is given. A number of channels inside the fuel element can be used as cooling channels, which greatly increases the contact area between the coolant (helium or hydrogen) and the fuel element, thereby enhancing the heat transfer capacity. Compared with the prior art where the fuel element mainly uses spherical coated fuel particles and the coolant can only flow in the channels arranged inside the support structure, and they cannot be in full contact with the fuel element. In the present invention, the cooling channels are directly arranged inside the fuel element, which can enable the fuel element to obtain a better cooling effect.

[0033] In addition, the periodically arranged holes or reinforcing phases of the TPMS structure can effectively disperse the external load, reduce local stress concentration, and have adjustable mechanical properties. The structure can be customized by adjusting the pore size, porosity, wall thickness, arrangement pattern (such as orthogonal, hexagonal, etc.) to meet the working conditions requirements of different high-temperature gas-cooled reactors.

[0034] Example 2

[0035] The main advantage of the Gyroid structure is that it has a complex three-dimensional curved surface, which gives it significant advantages in fluid flow, heat conduction performance, mechanical stability and adaptability. Especially in applications that require uniform heat flux distribution and high heat exchange efficiency, the Gyroid structure performs excellently. In addition, its high strength-to-mass ratio and low fluid resistance make it an ideal choice in many engineering applications. Compared with the Diamond structure, the Gyroid structure provides better versatility, more uniform performance, and stronger adaptability.

[0036] Standard Gyroid function equation:

[0037]

[0038] However, it is found in the research that the standard Gyroid structure has "through holes" that seemingly penetrate the flow channels. As Figure 5 shown, such a structure will cause part of the fluid to directly pass through the "through holes" without participating in the lateral mixing and directly flow out of the heat exchanger, resulting in less heat absorption of this part of the fluid, not only reducing the overall heat transfer efficiency but also causing uneven temperature distribution in the heat exchanger; secondly, although the TPMS structure can provide continuous flow channels, the wall surface of the standard Gyroid structure bends slowly, and the three-dimensional spiral disturbance of the fluid flow is relatively small, making it difficult to form stronger turbulent mixing.

[0039] Therefore, in this embodiment, an improved Gyroid structure is adopted. Control terms containing a control factor α are introduced into the three additive terms of the standard Gyroid function respectively to form an improved Gyroid function. The size of the straight through holes in the Gyroid structure and the tortuosity of the surface structure are regulated by adjusting the size of the control factor α. At the same time, the control term of the additive term in the xy plane contains the associated variable z, the control term of the additive term in the yz plane is associated with the variable x, and the control term of the additive term in the zx plane contains the associated variable y.

[0040] The improved Gyroid function equation given in this embodiment is as follows:

[0041]

[0042] Among them, L represents the unit length of the TPMS structure, and C represents the offset of the original unit surface. These control terms are selected because they can accurately control the structure without damaging its inherent topological structure and connectivity.

[0043] Figure 6 The three-dimensional view and top view of the Gyroid unit structure under different α values are shown. It can be seen that by adjusting the size of the control factor α, the surface morphology of the Gyroid structure has changed significantly. When α is 0, the improved Gyroid unit structure is exactly the same as the standard Gyroid unit structure.

[0044] From the top view perspective, as the control factor α increases, the shape and size of the straight through holes in the Gyroid structure change significantly. The straight through holes gradually change from circular to approximately quadrilateral in shape, and the overall area of the straight through holes is continuously shrinking. When α reaches 0.45L, the straight through holes completely disappear. Combining the three-dimensional perspective, as the control factor α increases, the surface morphology in the Gyroid structure also becomes more tortuous, which is beneficial to increasing the contact area between the fluid and the solid surface and enhancing the formation of turbulence on the structure surface.

[0045] By regulating the size of α, not only can the size of the straight through holes be adjusted to effectively avoid the fluid flowing preferentially through the low flow resistance area, thereby improving the heat transfer efficiency between the fluid and the solid surface. At the same time, the improved Gyroid unit structure also forms surface structures with different degrees of tortuosity, enhancing the perturbation effect of the fluid and making it easier for the fluid to form efficient secondary flow and vortex effects during the flow process.

[0046] Of course, in addition to this, there can also be other improved Gyroid structures. Figure 7Given several possible forms and their corresponding three-dimensional views and top views, it can be seen that for these control items of deformation adjustment, the shape of the straight through hole can be changed by adjusting the value of the control factor, achieving the effect of eliminating the straight through hole. In practical applications, its shape and structure can be adjusted according to actual needs to meet the actual requirements.

[0047] By eliminating the straight through hole, the fluid guiding characteristics can be optimized, the straight through high flow velocity path can be reduced, the flow pressure drop can be lowered. At the same time, by strengthening the local turbulence effect, the ability of secondary flow perturbation can be improved, the heat transfer effect can be enhanced, and the temperature distribution of the whole core can be made more uniform; during the coolant flow process, the perturbation effect is enhanced, promoting efficient secondary flow and vortex effect, improving the turbulent heat transfer ability, reducing the risk of local hot spots, and thus improving the overall heat transfer performance.

[0048] Embodiment 3

[0049] Based on the two types of fuel elements with TPMS structures disclosed in Embodiments 1 and 2, those skilled in the art can design a matching coolant flow mode.

[0050] The specific method given in this embodiment is that an upper reflector and a lower reflector are respectively arranged above and below the fuel assembly. The upper and lower reflectors have the same TPMS structure as the fuel assembly, forming a connected channel.

[0051] An upper gas cavity and a lower gas cavity are respectively arranged above the upper reflector and below the lower reflector, and a reversing valve for controlling the coolant flow direction is arranged at the corresponding channel openings. In some of the several channels, the coolant enters from the bottom and exits from the top, while in the other part, the coolant enters from the top and exits from the bottom; after the coolant enters from the lower gas cavity, it enters the upper gas cavity from bottom to top along a part of the channels, and then flows out of the core from top to bottom along the other part of the channels. Through appropriate control of the reversing valve, the coolant can flow controllably in the cooling channels.

[0052] For the vertical structure given in this embodiment, of course, a horizontal structure can also be adopted. In this case, the reflectors are arranged on both sides of the fuel assembly, and the internal channels of the horizontal reflectors are horizontally connected to the internal channels of the fuel assembly, forming a connected cooling channel.

[0053] The TPMS structure can also be locally optimized. For example, by reasonably arranging columnar control rod insertion holes inside the fuel element and cooperating with the control of the reversing valve, the coolant can flow around the control rod more evenly, reducing the phenomenon of local overheating.

[0054] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art in this field and related fields without creative efforts based on the embodiments of the present invention should fall within the protection scope of the present invention.

Claims

1. A core structure of a nuclear thermal propulsion reactor based on the microstructure of TPMS, comprising fuel elements, graphite moderators, cooling channels, control rods and reflectors, characterized in that, Introduce a TPMS structure with a height-adjustable topological morphology into the high-temperature gas-cooled reactor fuel element, so that a cooling channel with a high specific surface area is formed inside the fuel element, increasing the contact area between the coolant and the fuel core, thereby enhancing the heat transfer capacity.

2. The core structure of the nuclear thermal propulsion reactor based on the TPMS microstructure according to claim 1, wherein The TPMS structure adopts a Diamond structure, a Gyroid structure or a Schwarz-D structure.

3. The core structure of the nuclear thermal propulsion reactor based on the TPMS microstructure according to claim 1, characterized in that, The adopted TPMS structure enables a continuous and non-through cooling channel to be formed inside the fuel core.

4. The core structure of the nuclear thermal propulsion reactor based on the TPMS microstructure according to any one of claims 1-3, characterized in that, The fuel element has a TPMS structure, is columnar as a whole, contains several channels inside, and all inner walls are composed of the core in the middle and the cladding outside, where the graphite moderator also serves as an independent annular moderator layer to wrap the fuel core.

5. The core structure of the nuclear thermal propulsion reactor based on the TPMS microstructure according to claim 4, characterized in that, Upper and lower reflector layers are respectively arranged on the upper and lower parts of the fuel assembly. The upper and lower reflector layers have the same TPMS structure as the fuel assembly, forming a connected channel.

6. The core structure of the nuclear thermal propulsion reactor based on the TPMS microstructure according to claim 5, characterized in that An upper gas cavity and a lower gas cavity are respectively arranged above the upper reflector layer and below the lower reflector layer, and a reversing valve for controlling the flow direction of the coolant is arranged at the corresponding channel opening. Some of the several channels are for lower intake and upper outlet, and some are for upper intake and lower outlet. After the coolant is introduced from the lower gas cavity, it enters the upper gas cavity from bottom to top along a part of the channels, and then flows out of the core from top to bottom along another part of the channels.

7. The core structure of the nuclear thermal propulsion reactor based on the TPMS microstructure according to claim 6, characterized in that, Through local optimization of the TPMS structure, columnar control rod insertion holes are reasonably arranged inside the fuel element, so that the coolant flows around the control rod more evenly, reducing the phenomenon of local overheating.

8. The core structure of the nuclear thermal propulsion reactor based on the TPMS microstructure according to claim 3, characterized in that, The TPMS structure adopts a Diamond structure.

9. The core structure of the nuclear thermal propulsion reactor based on the TPMS microstructure according to claim 3, wherein, The TPMS structure adopts a Gyroid structure. Control terms containing a control factor α are respectively introduced into the three additive terms of the standard Gyroid function to form an improved Gyroid function. The size of the straight through holes and the tortuosity of the surface structure in the Gyroid structure are regulated by adjusting the size of the control factor α. At the same time, the control term of the additive term in the xy plane contains the associated variable z, the control term of the additive term in the yz plane is associated with the variable x, and the control term of the additive term in the zx plane contains the associated variable y.

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