A heat pipe stack

Abstract

This invention relates to the field of nuclear reactor technology and discloses a heat pipe reactor, comprising a pressure vessel and a reactor core disposed within the pressure vessel. The pressure vessel is connected to a pressure system to maintain the pressure within the pressure vessel within a preset low-pressure range. Multiple heat pipes are uniformly arranged within the reactor core. Each heat pipe includes an evaporation section, a transition section, and a condensation section connected in sequence. The evaporation section is located inside the reactor core, the condensation section is located outside the reactor core, and the transition section is sealed to the pressure vessel. The wall thickness of the evaporation section is less than that of the condensation section, and the inner diameters of the evaporation section, transition section, and condensation section are the same. This invention provides a heat pipe reactor that can improve heat transfer efficiency while ensuring reactor safety.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor technology, and in particular to a heat pipe reactor. Background Technology

[0002] A heat pipe reactor is an advanced reactor that uses heat pipes as the core heat removal element. Its core working principle is as follows: the evaporation end of the heat pipe is inserted into the reactor core to absorb the heat generated by fuel fission, while the adiabatic and condensation ends extend outside the core. The condensation end is connected to a heat exchanger, and efficient heat transfer and utilization are achieved through the phase change cycle of the working fluid within the heat pipe. Heat pipe reactors offer advantages such as high passive safety characteristics, compact structure, and no need for external power to drive coolant circulation, making them promising for applications in small modular reactors, space reactors, and remote area power supply.

[0003] Existing heat pipe reactors employ a unified design with equal diameter and wall thickness for the evaporation and condensation sections, meaning the heat pipe maintains the same inner diameter and wall thickness from the evaporation to the condensation section. Under this design, after the evaporation section is inserted into the core, its outer diameter (the sum of its inner diameter and wall thickness) determines the space occupied by the heat pipe within the core. Since the fuel load within the core directly affects reactivity (i.e., the core's ability to maintain a self-sustaining fission chain reaction), there is an upper limit constraint on the outer diameter of the evaporation section—when the space occupied by the heat pipe is too large, causing the fuel percentage to fall below a critical value, the core will be unable to maintain a critical state and will shut down.

[0004] The aforementioned upper limit constraint on the outer diameter of the evaporation section has led to multiple technical bottlenecks: 1. Limited heat transfer efficiency The heat transfer efficiency of a heat pipe is positively correlated with its internal flow cross-sectional area (i.e., a function of its inner diameter). Given an upper limit on the outer diameter of the evaporation section, the sum of the inner diameter and wall thickness is also limited by a fixed upper limit, creating a competitive relationship between the two. Increasing the inner diameter to improve heat transfer efficiency requires thinning the wall thickness; conversely, increasing the wall thickness to ensure structural strength requires decreasing the inner diameter. Regardless of the trade-off, the heat transfer efficiency cannot exceed the theoretical extreme value under this upper limit constraint. Therefore, low heat transfer efficiency is one of the direct consequences of the upper limit constraint on the outer diameter of the evaporation section.

[0005] 2. Insufficient structural safety of the condensation section. The condenser section, located outside the reactor core, functions to transfer heat to the secondary loop heat exchanger. Since the working fluid circulation channels inside the heat pipes are connected to the reactor core, a rupture in the condenser section could allow radioactive materials inside the core to leak out along these channels, causing radioactive contamination. Therefore, the condenser section's wall thickness should theoretically be as large as possible to improve its resistance to damage. However, under a design with equal diameter and wall thickness, the condenser section's wall thickness is forced to match that of the evaporator section, and is similarly constrained by the upper limit of the evaporator section's outer diameter, preventing independent thickening. This insufficient damage resistance of the condenser section is a structural defect that is transmitted from the upper limit constraint of the evaporator section's outer diameter to the outside of the reactor core.

[0006] 3. Risk of radioactive leakage from the reactor core Existing heat pipe reactors are all designed for atmospheric pressure. The fundamental reason for this design choice is that the wall thickness of the evaporation section is limited by an upper limit, resulting in a limited overall pressure-bearing capacity of the heat pipes, which cannot withstand higher internal working fluid pressures. Under atmospheric pressure operating conditions, if a heat pipe or fuel rod ruptures within the reactor core, radioactive gas or liquid will diffuse unimpeded within the core's free space and may leak to the outside along the channels through which the heat pipes penetrate the core, triggering a radioactive release accident. The atmospheric pressure design and the resulting risk of radioactive leakage are essentially an extension of the upper limit constraint on the outer diameter of the evaporation section at the system safety level—because the wall thickness cannot exceed the upper limit, the system loses its ability to use internal positive pressure to suppress the diffusion of radioactive materials, and can only resort to a passively sealed atmospheric pressure solution as a second-best option. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a heat pipe stack that can improve heat transfer efficiency while ensuring reactor safety.

[0008] This invention provides a heat pipe stack, comprising a pressure vessel and a core disposed within the pressure vessel. The pressure vessel is connected to a pressure system to maintain the pressure within the pressure vessel within a preset low-pressure range. Multiple heat pipes are uniformly arranged within the core. Each heat pipe includes an evaporation section, a transition section, and a condensation section connected sequentially. The evaporation section is located within the core, the condensation section is located outside the core, and the transition section is sealed to the pressure vessel. The wall thickness of the evaporation section is less than that of the condensation section, and the inner diameters of the evaporation section, transition section, and condensation section are the same.

[0009] Optionally, the wall thickness of the condensation section is 1.5 to 2 times that of the evaporation section.

[0010] Optionally, the wall thickness of the transition section gradually increases from the end near the evaporation section to the end near the condensation section, and the outer wall of the transition section is connected to the pressure vessel by a threaded seal.

[0011] Optionally, the reactor core includes a matrix and multiple fuel rods. The matrix is ​​a hexagonal prism metal matrix with multiple through holes uniformly opened along its axial direction. The fuel rods and heat pipes are alternately arranged in the through holes.

[0012] Optionally, the reactor core is composed of multiple fuel rods stacked together. The fuel rods are hexagonal prisms with heat pipe channels opened along their axial direction, and the heat pipes are inserted into the heat pipe channels.

[0013] Optionally, the outer wall of the condensation section is provided with threaded fins.

[0014] Optionally, the outer wall of the evaporation section is coated with a boron carbide coating, and the outer wall of the condensation section is coated with a silver or copper coating.

[0015] Optionally, the pressure vessel is equipped with a pressure probe and a safety relief port. The pressure probe is used to monitor the pressure inside the pressure vessel, and the safety relief port is connected to a purification system to purify the gas discharged from the pressure vessel.

[0016] Optionally, both the evaporation section and the fuel rods have tapered ends, and a positioning blind hole is provided at the corresponding position of the pressure vessel, with the tapered end engaging with the positioning blind hole.

[0017] Optionally, a spring is provided inside the positioning blind hole.

[0018] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: The heat pipe stack provided in this invention, through the coordinated design of a heat pipe structure with variable diameter and unequal wall thickness and active pressure control of a pressure vessel, fundamentally overcomes multiple bottlenecks constrained by the upper limit of the outer diameter of the evaporation section. Specifically, the heat pipe adopts an integrated structure with a wall thickness of less than that of the evaporation section and the same inner diameter for the evaporation section, transition section, and condensation section. This allows the outer diameter of the evaporation section to be reduced, thereby releasing space for increased wall thickness in the condensation section while meeting reactivity requirements. The independent thickening of the condensation section wall significantly improves its resistance to breakage and pressure bearing capacity. At the same time, maintaining a consistent inner diameter ensures the smooth flow of the working fluid phase change circulation channel, and the transition section achieves a smooth structural transition and mechanical transfer between the evaporation section and the condensation section. Crucially, this invention elevates the safety boundary of the heat pipe stack from the wall of a single heat pipe to the entire pressure vessel. By maintaining the pressure vessel within a preset low-pressure range through a pressure system, it utilizes the controllable low-pressure environment inside the vessel to form a self-suppressing barrier against radioactive material leakage, replacing the passive defense mode of traditional atmospheric pressure designs that rely on external seals. This shift in system-level safety architecture reduces the requirements for rupture prevention of the evaporation section wall. Unlike existing designs where the heat pipe wall thickness must independently bear the full responsibility for preventing rupture and leakage under long-term high temperatures, the evaporation section wall thickness of this invention can be further reduced under the overall protection of the pressure vessel. This allows for greater inner diameter space while maintaining the upper limit of the evaporation section's outer diameter, resulting in higher heat exchange efficiency. Meanwhile, the condensation section can effectively increase its wall thickness without being limited by this upper limit, thus enhancing its rupture prevention performance. Therefore, this invention takes the dual improvement of decoupling the wall thickness of the evaporation section and the upward shift of the safety boundary as the fulcrum, and simultaneously achieves the improvement of heat transfer efficiency (thinning the wall thickness of the evaporation section to obtain a larger inner diameter), the enhancement of the structural safety of the condensation section (independent thickening of the wall thickness), and the reduction of the risk of core radioactive leakage (low-pressure environment suppresses radioactive escape), thus systematically solving the triple technical problems derived from the upper limit constraint of the outer diameter of the evaporation section. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a heat pipe provided in an embodiment of the present invention; Figure 2A three-dimensional structural schematic diagram of a heat pipe stack provided in an embodiment of the present invention; Figure 3 A cross-sectional view of a heat pipe stack provided in an embodiment of the present invention; Figure 4 This is a partial cross-sectional schematic diagram of the first type of heat pipe stack provided in an embodiment of the present invention; Figure 5 This is a partial cross-sectional schematic diagram of the second type of heat pipe stack provided in an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures: 1. Evaporation section; 2. Condensation section; 3. Transition section; 4. External system; 5. Pressure vessel; 6. Heat pipe; 7. Substrate; 8. Fuel rod; 9. Pressure probe; 10. Safety relief port. Detailed Implementation

[0021] The following detailed description of a specific embodiment of the present invention is provided in conjunction with the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiment.

[0022] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the technical solution of this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0023] First, an embodiment of the present invention provides a heat pipe stack, specifically as follows: Figure 1 , Figure 2 and Figure 3As shown, the reactor includes a pressure vessel 5 and a reactor core located within the pressure vessel 5. The pressure vessel 5 is connected to a pressure system to maintain the pressure within the pressure vessel 5 within a preset low-pressure range. Multiple heat pipes 6 are uniformly arranged within the reactor core. By using the pressure vessel 5, if a heat pipe 6 or fuel rod 8 within the reactor core ruptures, the pressure vessel 5 can confine radioactive gas or liquid within itself, preventing leakage. The heat pipe 6 includes an evaporation section 1, a transition section 3, and a condensation section 2 connected in sequence. The evaporation section 1 is located inside the reactor core, the condensation section 2 is located outside the reactor core, and the transition section 3 is sealed to the pressure vessel 5. The wall thickness of the evaporation section 1 is less than that of the condensation section 2. Simultaneously, the neutron characteristics of the tube wall material of the evaporation section 1 must also meet the requirements of the neutron energy spectrum, such as a smaller neutron absorption cross-section. By setting the wall thickness of the heat pipe evaporation section 1 to be less than that of the condensation section 2, the cross-sectional area of ​​the channel is increased, improving heat exchange efficiency and performance. The evaporation section 1, transition section 3, and condensation section 2 have the same inner diameter, ensuring smooth two-phase fluid heat transfer and axial heat transport. Evaporation section 1 and condensation section 2 have the same inner diameter but different wall thicknesses. This difference in wall thickness ensures the sealing of condensation section 2 outside the reactor core. Evaporation section 1 has a thinner wall thickness inside the reactor core, and its sealing is achieved by the pressure vessel 5 outside the entire reactor core. This approach of using different methods to solve the sealing problem on the same heat pipe 6 allows for a reduction in the wall thickness of evaporation section 1 inside the reactor core to increase fuel loading and thus enhance core reactivity, without concern for heat pipe sealing issues.

[0024] The heat pipe stack provided in this invention, through the coordinated design of a heat pipe structure with variable diameter and unequal wall thickness and active pressure control of a pressure vessel, fundamentally overcomes multiple bottlenecks constrained by the upper limit of the outer diameter of the evaporation section. Specifically, the heat pipe adopts an integrated structure with a wall thickness of less than that of the evaporation section and the same inner diameter for the evaporation section, transition section, and condensation section. This allows the outer diameter of the evaporation section to be reduced, thereby releasing space for increased wall thickness in the condensation section while meeting reactivity requirements. The independent thickening of the condensation section wall significantly improves its resistance to breakage and pressure bearing capacity. At the same time, maintaining a consistent inner diameter ensures the smooth flow of the working fluid phase change circulation channel, and the transition section achieves a smooth structural transition and mechanical transfer between the evaporation section and the condensation section. Crucially, this invention elevates the safety boundary of the heat pipe stack from the wall of a single heat pipe to the entire pressure vessel. By maintaining the pressure vessel within a preset low-pressure range through a pressure system, it utilizes the controllable low-pressure environment inside the vessel to form a self-suppressing barrier against radioactive material leakage, replacing the passive defense mode of traditional atmospheric pressure designs that rely on external seals. This shift in system-level safety architecture reduces the requirements for rupture prevention of the evaporation section wall. Unlike existing designs where the heat pipe wall thickness must independently bear the full responsibility for preventing rupture and leakage under long-term high temperatures, the evaporation section wall thickness of this invention can be further reduced under the overall protection of the pressure vessel. This allows for greater inner diameter space while maintaining the upper limit of the evaporation section's outer diameter, resulting in higher heat exchange efficiency. Meanwhile, the condensation section can effectively increase its wall thickness without being limited by this upper limit, thus enhancing its rupture prevention performance. Therefore, this invention takes the dual improvement of decoupling the wall thickness of the evaporation section and the upward shift of the safety boundary as the fulcrum, and simultaneously achieves the improvement of heat transfer efficiency (thinning the wall thickness of the evaporation section to obtain a larger inner diameter), the enhancement of the structural safety of the condensation section (independent thickening of the wall thickness), and the reduction of the risk of core radioactive leakage (low-pressure environment suppresses radioactive escape), thus systematically solving the triple technical problems derived from the upper limit constraint of the outer diameter of the evaporation section.

[0025] Refer again Figure 1In this embodiment of the invention, the wall thickness of the condensing section 2 is 1.5 to 2 times that of the evaporating section 1. This ratio range has been optimized to ensure a significant improvement in the structural strength and damage resistance of the condensing section 2, while avoiding the problems of increased material costs and increased thermal resistance caused by excessive wall thickness. On the one hand, the wall thickness increment of more than 1.5 times provides sufficient mechanical strength reserve for the condensing section, enabling it to withstand the structural integrity requirements of external accidental impacts, thermal stress cycles, and long-term corrosive environments, reducing the probability of damage to an extremely low level. On the other hand, the upper limit constraint of less than 2 times controls the excessive increase in thermal resistance of the condensing section 2, ensuring that the efficient transfer of heat from the heat pipe working fluid to the heat exchanger is not excessively inhibited, maintaining the balance between the thermal performance and economy of the entire heat pipe stack. Thus, this invention, with the triple innovation of decoupling the wall thickness of the evaporating section and the condensing section, moving the safety boundary upward, and optimizing the wall thickness ratio of the condensing section as its fulcrum, simultaneously achieves improved heat transfer efficiency, significantly enhanced structural safety of the condensing section, and effective reduction of the risk of core radioactive leakage, thereby systematically solving the triple technical problems derived from the upper limit constraint of the outer diameter of the evaporating section.

[0026] Optionally, the wall thickness of the transition section 3 gradually increases from the end near the evaporation section 1 to the end near the condensation section 2. The outer wall of the transition section 3 is connected to the pressure vessel 5 by a threaded seal. Through the thread and thermal expansion, the core portion of each heat pipe 6, i.e., the evaporation section 1, can be sealed inside the pressure vessel 5. This ensures that radioactive materials inside the reactor will not escape axially to the outside of the reactor along the gap between the heat pipe 6 and the pressure vessel 5, thereby improving safety performance.

[0027] In this embodiment of the invention, the gradual transition of the wall thickness of the transition section 3 eliminates the structural abrupt change and stress concentration between the thin wall of the evaporation section 1 and the thick wall of the condensation section 2. This allows the heat pipe 6 to smoothly distribute thermal stress along the axial direction when subjected to thermal cycling loads, avoiding the risk of fatigue crack initiation caused by abrupt stiffness changes in traditional stepped variable cross-section designs, and significantly improving the long-term operational reliability of the heat pipe 6. Simultaneously, the combination of the gradual wall thickness of the transition section 3 and the constant inner diameter creates a smooth flow channel expansion within the transition section 3. As the working fluid vapor flows from the evaporation section 1 to the condensation section 2, the flow velocity gradually decreases, reducing eddy current losses and flow noise caused by abrupt flow channel changes, and optimizing the thermodynamic efficiency of the phase change cycle. The threaded sealing connection between the outer wall of the transition section 3 and the pressure vessel 5 enables a detachable sealing fit between the heat pipe 6 and the pressure vessel 5. This ensures the boundary integrity of the low-pressure environment and facilitates independent replacement and maintenance of the heat pipe, avoiding the non-removability and thermal expansion mismatch stress caused by welding. Finally, the combination of the threaded sealing structure and the gradually changing wall thickness makes the transition section an integrated load-bearing area for both mechanical buffering and sealing functions. The radial stiffness gradient provided by the gradually changing wall thickness effectively absorbs the thermal expansion difference between the heat pipe 6 and the pressure vessel 5, reducing the risk of shear deformation of the threaded sealing surface, thereby extending the service life of the seal while ensuring sealing reliability. Thus, this invention, based on multiple innovations such as decoupling of the evaporation section and condensation section wall thickness, upward shift of the safety boundary, optimization of the condensation section wall thickness ratio, and integrated design of the gradually changing wall thickness and threaded seal in the transition section, simultaneously achieves improved heat transfer efficiency, significantly enhanced structural safety of the condensation section, improved operational reliability of the heat pipe, improved maintenance convenience, and effective reduction of the risk of core radioactive leakage, thereby systematically solving multiple technical problems arising from the upper limit constraint of the outer diameter of the evaporation section.

[0028] As an optional approach, in this embodiment of the invention, reference is made to... Figure 4 The reactor core includes a substrate 7 and multiple fuel rods 8. The substrate 7 is a hexagonal prism metal substrate with multiple through holes evenly distributed along its axial direction. The fuel rods 8 and heat pipes 6 are alternately arranged in the through holes. This substrate 7 is like a whole piece of stainless steel hexagonal prism with many through holes drilled on its hexagonal base. Fuel rods 8 (usually round rods) and heat pipes 6 are placed in the through holes at intervals.

[0029] As another alternative approach, in this embodiment of the invention, reference is made to... Figure 5 The reactor core is composed of multiple fuel rods 8 stacked together. Each fuel rod 8 is hexagonal prism in shape, and heat pipe channels are formed along its axial direction. Heat pipes 6 are inserted into these channels. This design eliminates the need for a stainless steel substrate; the fuel rods 8 themselves are hexagonal prisms, and these hexagonal prisms are stacked to form the reactor. The heat pipes 6 are directly inserted into each hollow hexagonal prism fuel rod. The heat pipe 6 structure in this invention is applicable to two different reactor core structures.

[0030] Since the wall thickness of the condensing section 2 in this invention is increased compared to the existing condensing section 2 wall thickness, and the installation or production of fins requires a thicker wall surface as a foundation, in this embodiment of the invention, the outer wall of the condensing section 2 is provided with threaded fins. The threaded fins can increase the heat exchange area and enhance the heat exchange effect.

[0031] This invention minimizes the heat pipe wall thickness in the evaporation section 1 and improves the heat pipe wall's radiation resistance by adding special coatings, such as boron carbide or B4C. In the condensation section 2, the pipe wall thickness is increased, and the outer wall of the condensation section 2 is coated with a high thermal conductivity coating such as a silver coating or a copper coating. This increases the heat pipe's resistance to breakage at the condensation end while ensuring or even improving heat transfer performance.

[0032] Optionally, the pressure vessel 5 is equipped with a pressure probe 9 and a safety relief port 10. The pressure probe 9 is used to monitor the pressure inside the pressure vessel 5, and the safety relief port 10 is connected to a purification system to purify the gas discharged from the pressure vessel 5. In this embodiment of the invention, the purification system and the pressure system form a... Figure 2 External system 4. When the pressure inside the pressure vessel 5 exceeds the set limit due to thermal expansion, radiation, and the generation of fission gases in the reactor core, gas can be released through the safety relief port on the sealing layer to bring the pressure inside the sealing layer down to below the preset low pressure range. The released gas is then discharged into a sealed purification system, treated and purified to meet safety emission standards, and then discharged as exhaust gas. At the same time, the pressure probe 9 also provides an online monitoring method for the pressure vessel 5. Since most pressure vessel 5 ruptures begin with leakage, pressure monitoring through the pressure probe 9 can effectively detect this phenomenon in its early stages, thereby enabling early maintenance and preventing the leakage from expanding into a rupture. This monitoring work is impossible to do on the small fuel liner or heat pipe walls. Due to the presence of the safety relief port, during core startup, gas can be pumped out through the safety relief port to bring the pressure inside the pressure vessel 5 to a state lower than the ambient pressure. Even if the pressure vessel 5 leaks or even ruptures early, only ambient gas flows into the reactor, and no radioactive fluid from the reactor is released to the outside, thereby effectively increasing the safety of the system.

[0033] Optionally, both the evaporation section 1 and the fuel rod 8 have tapered ends, and the pressure vessel 5 has a positioning blind hole at the corresponding position. The tapered ends are inserted into the positioning blind hole to ensure that the evaporation section 1 and the fuel rod 8 can be quickly positioned when installed with the pressure vessel 5.

[0034] Optionally, a spring is installed inside the positioning blind hole. Pressure vessel 5 is actually a sealed tank, welded to form an open tank body. Fuel rods 8 and heat pipes 6 are then installed through the opening, and the top and side plates are sealed together via flanges. During installation, the spring provides a certain degree of elasticity for tightening. During later operation, the fuel rods 8 will undergo thermal deformation, and the spring tightening will also have a deformation allowance.

[0035] The above inventions are merely a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A heat pipe stack, characterized in that, It includes a pressure vessel and a reactor core disposed within the pressure vessel. The pressure vessel is connected to a pressure system to maintain the pressure inside the pressure vessel within a preset low-pressure range. Multiple heat pipes are uniformly arranged inside the reactor core. The heat pipe includes an evaporation section, a transition section, and a condensation section connected in sequence. The evaporation section is located inside the reactor core, the condensation section is located outside the reactor core, the transition section is sealed to the pressure vessel, the wall thickness of the evaporation section is less than the wall thickness of the condensation section, and the inner diameters of the evaporation section, the transition section, and the condensation section are the same.

2. The heat pipe stack as described in claim 1, characterized in that, The wall thickness of the condensation section is 1.5 to 2 times that of the evaporation section.

3. The heat pipe stack as described in claim 1, characterized in that, The wall thickness of the transition section gradually increases from the end near the evaporation section to the end near the condensation section, and the outer wall of the transition section is connected to the pressure vessel by a threaded seal.

4. The heat pipe stack as described in claim 1, characterized in that, The reactor core includes a matrix and multiple fuel rods. The matrix is ​​a hexagonal prism metal matrix with multiple through holes uniformly opened along its axial direction. The fuel rods and heat pipes are alternately arranged in the through holes.

5. The heat pipe stack as described in claim 1, characterized in that, The reactor core is composed of multiple fuel rods stacked together. The fuel rods are hexagonal prisms, and heat pipe channels are opened along their axial direction. The heat pipes are inserted into the heat pipe channels.

6. The heat pipe stack as claimed in claim 1, characterized in that, The outer wall of the condensation section is provided with threaded fins.

7. The heat pipe stack as claimed in claim 1, characterized in that, The outer wall of the evaporation section is coated with a boron carbide coating, and the outer wall of the condensation section is coated with a silver or copper coating.

8. The heat pipe stack as claimed in claim 1, characterized in that, The pressure vessel is equipped with a pressure probe and a safety relief port. The pressure probe is used to monitor the pressure inside the pressure vessel, and the safety relief port is connected to a purification system to purify the gas discharged from the pressure vessel.

9. The heat pipe stack as described in claim 4 or 5, characterized in that, Both the evaporation section and the fuel rod have tapered ends, and a positioning blind hole is provided at the corresponding position of the pressure vessel. The tapered end is inserted into the positioning blind hole.

10. The heat pipe stack as claimed in claim 9, characterized in that, A spring is installed inside the positioning blind hole.

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