Heat pipe fuel elements, reactor cores and methods of operating the same and applications thereof

Abstract

The application discloses a heat pipe type fuel element, a reactor core and a method for operating the same and application thereof. The heat pipe type fuel element comprises coaxially fixed first and second substrates from bottom to top, both of which are hollow tubular structures and are in communication with each other; the inner side walls of the tubular structures of the first and second substrates are respectively provided with axially distributed first and second grooves, and the connecting part of the two is continuous without fault; the first substrate is made of metal or a moderator material, and fuel particles are dispersedly distributed in the interior of the first substrate, and the fuel particles have a coating layer; and the second substrate is a metal substrate without fuel particles. The heat pipe type fuel element of the application adopts an integrated design to avoid the heat efficiency problem and safety problem caused by gap thermal resistance, and ensures the close contact of the fuel particles and the heat transfer working medium. The reactor core of the application has simple and compact structure, high heat transfer efficiency, stable and reliable performance, and can meet the energy supply of multiple scenes and multiple purposes.

Description

TECHNICAL FIELD

[0001] The present application relates to a heat pipe type fuel element, a reactor core and a method for operating the same and applications thereof. BACKGROUND

[0002] A heat pipe is a passive heat transfer component that relies on the phase change and continuous circulation of the internal working medium to achieve heat transfer. It has the advantages of high heat transfer efficiency, reversible heat flow direction, compact structure, and effective isolation of primary and secondary fluids. Since the 1990s, many heat pipe reactor schemes have been developed. In recent years, with the success of the Kilopower ground prototype reactor KRUSTY in the United States, heat pipe reactors have become a research hotspot for new reactors. In the design of heat pipe reactors, heat pipes are directly inserted into the reactor core to extract nuclear heat. The system is simplified, the volume is moderate, and it has good controllability and optimal thermal transient feedback performance. At the same time, it has high reliability and the lowest maintenance requirements, and can be flexibly applied to deep sea, deep space, land-based nuclear power plants and other application scenarios, which has a profound significance for the development of China's science and technology and energy.

[0003] In the prior art, the heat pipe is mostly inserted into the reactor core. For example, the following three forms of core fuel and heat pipe design: (1) The fuel rod and the heat pipe form a fuel module, and the metal block enhances the heat conduction between the fuel and the heat pipe in the module, and multiple modules are inserted into the core, such as HOMER Mars / Moon exploration reactor, HP-STMCs space reactor; (2) Metal matrix: the fuel rod or fuel block and the heat pipe are placed in the channel of the metal matrix, such as Magepower, eVinciTM. Part of the liquid sodium is filled to reduce the gap thermal resistance, but the filling amount needs to consider thermal expansion and cold contraction, especially when the core inclination changes, the gap position changes, and it is difficult to ensure the uniformity of heat transfer; (3) Fuel matrix: the heat pipe is inserted into the fuel matrix channel, such as 1-10kWe Kilopower, 1kWe FSP, which is only suitable for small power reactors with fewer heat pipes, and cannot be applied to large power reactors. However, the fuel rod or fuel block is directly in contact with the working medium, which can easily cause the working medium to be activated, and the fission gas can enter the heat pipe, which may cause radioactive leakage when a single heat pipe is damaged.

[0004] In addition, there is a primary loop heat pipe in the prior art, which is not convenient to assemble with the fuel block to form a core, and the 1-3mm gap between the heat pipe and the fuel block also causes a large gap thermal resistance when it is applied in a vacuum environment (such as space), which may cause hot spots and even safety problems.

[0005] In the above scheme, the heat pipe insertion channel or the heat pipe and fuel rod connecting metal block method is adopted, and the heat transfer thereof depends on the solid heat conduction. Due to the long time high temperature operation, the uneven power and temperature, there is a large stress between the fuel and the heat pipe, combined with the swelling problem caused by fuel irradiation, which will cause the connection between the fuel rod and the heat pipe to be damaged and a gap to appear, especially in a vacuum environment, the gap thermal resistance makes the heat transfer performance decrease sharply, and the fuel operating temperature rises significantly, which even endangers the safety of the reactor. When the core of the heat pipe reactor using liquid metal to fill the gap tilts or changes position, the liquid metal may not fill the upper gap, which may cause hot spots. In addition, in most core schemes using fuel rods, the core temperature is too high, which will face the problem of safety accidents such as core meltdown of nuclear power plants.

[0006] The prior art discloses a boiling water reactor which utilizes the phase change heat transfer of water, fuel rods are inserted into the core, water flows through the fuel rods to become a mixture of steam and water, passes through a steam-water separator and a steam dryer, and uses the separated high-temperature steam to drive a steam turbine generator. However, the reactor contains many pumps, valves and circuits, and the structure is complex, and the pressure is high, and the circuit circulation is easy to cause radioactive leakage, which has safety hazards. SUMMARY

[0007] In order to overcome the defects of low heat transfer efficiency and low safety performance caused by the gap thermal resistance of the heat pipe reactor in the prior art, a heat pipe type fuel element, a core and a method for operating the same and applications thereof are provided. The heat pipe type fuel element of the present application adopts an integrated design to avoid the heat efficiency problem and safety problem caused by the gap thermal resistance, ensures the close contact of the fuel particles and the heat transfer working medium, and avoids radioactive leakage. The core structure of the present application is simple and compact, easy to assemble and maintain, and has high heat transfer efficiency, stable and reliable performance, and can meet the energy supply of multiple scenes and multiple purposes.

[0008] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0009] The present application provides a heat pipe type fuel element, which comprises a first base body and a second base body coaxially connected from bottom to top, both of which are hollow tubular structures and are in communication with each other; the structures of the first base body and the second base body are in mode one or mode two:

[0010] Mode one: the inner side walls of the tubular structure of the first base body and the tubular structure of the second base body are respectively provided with first grooves and second grooves which are axially distributed, and the connection parts of the first grooves and the second grooves are continuous without faults; wherein the first base body is made of metal or moderator material, and the inside of the first base body is dispersedly distributed with fuel particles, and the fuel particles have a coating layer; the second base body is a metal base body without fuel particles;

[0011] The inner side wall of the tubular structure of the first base body and the inner side wall of the tubular structure of the second base body are respectively attached with the first wire screen and the second wire screen which are distributed in the axial direction, and the connection part of the first wire screen and the second wire screen is continuous and has no fault; wherein the first base body is metal material or moderator material, and the inside of the first base body is dispersedly distributed with fuel particles, and the fuel particles have a coating layer; the second base body is metal material without fuel particles.

[0012] In the application, the continuous and faultless design of the connection part of the first wire screen and the second wire screen between the first groove and the second groove facilitates the return flow of the working medium.

[0013] In the application, the inner diameter of the tubular structure of the first base body is the same as the inner diameter of the tubular structure of the second base body.

[0014] In the application, the first groove and the second groove are the same in shape.

[0015] In the application, preferably, the first groove or the second groove is uniformly arranged on the inner side wall of the tubular structure.

[0016] In the application, preferably, the first groove or the second groove is one or more of a square groove, a rectangular groove, a circular groove and a special-shaped groove, more preferably an omega-shaped groove, forming a wick structure, which can better improve the fuel volume fraction and meet the use requirements.

[0017] In the application, preferably, the first groove or the second groove is independently attached with at least one layer of wire screen at the edge closest to the axis of the heat pipe type fuel element, and the first groove or the second groove and the wire screen form a composite wick structure, in which the large pores can reduce the flow resistance to help the liquid return flow, and the small pores can provide large capillary force.

[0018] In the application, preferably, the first wire screen or the second wire screen is a single-layer wire screen or a composite wire screen, more preferably a composite wire screen; further more preferably, the composite wire screen is a double-layer wire screen with different pore sizes; the double-layer wire screen can facilitate the return flow and increase the capillary force at the same time.

[0019] In the application, preferably, the first base body is cylindrical or polygonal; more preferably, when the first base body is metal material, the first base body is cylindrical; more preferably, when the first base body is moderator material, the first base body is a regular hexagonal prism.

[0020] In the application, the length of the first base body is the same as the length of the second base body.

[0021] In the present application, preferably, the outer diameter of the first base body is greater than or equal to the outer diameter of the second base body.

[0022] In the present application, preferably, the second base body is cylindrical or polygonal, more preferably cylindrical.

[0023] In the present application, the first base body and the second base body can have a sealing effect, so that the heat transfer working medium is in the heat pipe type fuel element, thereby more greatly increasing the share of the fuel volume of the reactor core and reducing the size of the reactor core.

[0024] In the present application, preferably, the metal material is a material without neutron absorption ability, high-temperature resistant and radiation resistant, more preferably 316ss stainless steel.

[0025] In the present application, preferably, the moderator material is one or more of silicon carbide, graphite and yttrium hydride, more preferably yttrium hydride or silicon carbide.

[0026] In the present application, preferably, the periphery of the first base body is further coated with a tube shell.

[0027] Preferably, the thickness of the tube shell is 1-3 mm.

[0028] Preferably, the tube shell is of metal material or moderator material.

[0029] In the present application, preferably, the filling rate of the fuel particles in the interior of the first base body is 10-64%, more preferably 40-60%.

[0030] In the present application, preferably, the material of the coating layer is metal, carbide or carbide-refractory metal, more preferably carbide, and further more preferably silicon carbide.

[0031] In the present application, preferably, the core of the fuel particle is one or more of uranium nitride, uranium oxide and uranium oxycarbide, more preferably uranium nitride. Uranium nitride has large density, and compared with uranium oxide or uranium oxycarbide, uranium nitride can increase the heavy metal loading by 40%.

[0032] In the present application, preferably, the fuel particle is one or more of TRISO particle, FCM and MOX, more preferably TRISO particle. The TRISO particle comprises, from the core of the fuel particle outward, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a silicon carbide layer and an outer dense pyrolytic carbon layer; the TRISO particle can still maintain integrity at 2100℃.

[0033] In the present application, preferably, the diameter of the fuel particle is 0.5-1 mm. In the range of the particle, the filling rate in the heat pipe type fuel element is more facilitated to be increased, thereby facilitating to reduce the volume of the heat pipe type fuel element and thereby the size of the reactor core.

[0034] In the present application, the heat pipe type fuel element can be processed by traditional processing method or by additive manufacturing technology (such as 3D printing).

[0035] The present application also provides a reactor core, which comprises a reactor core container and a plurality of heat pipe type fuel elements as described above filled in the reactor core container and arranged in parallel with the axis of the reactor core container.

[0036] In the present application, preferably, the reactor core further comprises a reflecting layer and a plurality of control drums arranged in the reflecting layer; more preferably, when the number of control drums is more than two, each of the control drums is arranged in the reflecting layer symmetrically with respect to the central axis of the reactor core container.

[0037] In the present application, preferably, the reactor core further comprises a shutdown control rod; more preferably, the shutdown control rod is arranged at the center of the reactor core.

[0038] In the present application, preferably, the reflecting layer is arranged at the periphery of the reactor core container.

[0039] In the present application, preferably, when the first base body is made of moderator material, the fuel particles account for 10-30% of the volume of the reactor core container.

[0040] In the present application, preferably, when the first base body is made of metal material, the fuel particles account for 30-50% of the volume of the reactor core container.

[0041] In a preferred embodiment, when the first base body is made of metal material, the bottom of the reactor core container is provided with a plurality of moderator channels; and the heat pipe type fuel elements are connected to the moderator channels one by one in parallel with the axis of the reactor core container.

[0042] In a preferred embodiment, when the first base body is made of moderator material, the plurality of heat pipe type fuel elements are uniformly distributed in the reactor core container in parallel with the axis of the reactor core container.

[0043] The present application also provides a method for operating the reactor core as described above, which comprises the following steps: placing the heat pipe type fuel element filled with heat transfer working medium into the reactor core and operating the reactor core.

[0044] In the present application, the heat transfer working medium is generally added according to the filling process of high-temperature heat pipe; preferably, the heat pipe type fuel element filled with heat transfer working medium is in vacuum state in the tubular structure.

[0045] In the present application, the working temperature of the heat transfer working medium can be in the range of 400-1800℃, and the heat transfer working medium is preferably operable in the range of below 500℃ and above 1600℃.

[0046] In the application, preferably, the heat transfer working medium comprises one or more of Li, Na, K, NaK alloy or nanofluid, more preferably Li or NaK alloy. When the heat transfer working medium is Na, its latent heat of vaporization is 4090 kilojoules per kilogram, which is twice that of water (2260 kilojoules per kilogram), and can carry more heat; when the heat pipe type fuel element can operate at high temperature, the utilization efficiency of high temperature output heat is high, and the application mode is also various, such as hydrogen production, energy storage, etc.

[0047] In the application, preferably, the filling rate of the heat transfer working medium in the inner cavity of the tubular structure of the heat pipe type fuel element is 15-35%.

[0048] In the application, preferably, the operating temperature of the reactor core is 500℃ and above, more preferably 500-1600℃, to ensure effective heat discharge of the system.

[0049] In a preferred embodiment, when the operating temperature of the reactor core is 650-1100℃, the heat transfer working medium can be NaK alloy, and when the weight ratio of K to Na of the NaK alloy is 77.2:22.8, the melting point is -12.3℃, which is in liquid state at room temperature and easy to start.

[0050] In a preferred embodiment, when the operating temperature of the reactor core is above 1000℃, the heat transfer working medium can be Li.

[0051] In the application, preferably, the operating power of the reactor core is 1kW-10MW.

[0052] In the application, preferably, when the operating temperature of the reactor core is 650-1100℃, the heat transfer working medium is NaK alloy, and the weight ratio of K to Na of the NaK alloy is 77.2:22.8.

[0053] In the application, preferably, when the operating temperature of the reactor core is above 1000℃, the heat transfer working medium is Li.

[0054] In the application, preferably, during the operation of the reactor core, the heat pipe type fuel element comprises an evaporation section, an adiabatic section and a condensation section; the evaporation section is located in the reactor core container; the adiabatic section of the heat pipe type fuel element does not lose or generate heat; and the condensation section is a heat dissipation part for transferring heat to an energy conversion system.

[0055] In the application, the heat pipe type fuel element in the reactor core utilizes phase change of the working medium to guide the nuclear heat generated by the fuel particles in the evaporation section to the condensation section during operation, and then transfers the heat to the energy conversion system by the condensation section.

[0056] The application also provides an application of the reactor core in land-based mobile, deep-sea exploration or energy supply.

[0057] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred examples of the application.

[0058] The reagents and raw materials used in the application are commercially available.

[0059] The positive progress effect of the application is that:

[0060] (1) In the application, the fuel particles are dispersed in the metal matrix with good thermal conductivity, and the grooves formed by the metal matrix are directly in contact with the working medium flowing in the heat pipe. This integrated design avoids the thermal and safety problems caused by gap thermal resistance, and further reduces the volume of the pipe shell metal, increases the volume fraction of the fuel, and is beneficial to reducing the core structure.

[0061] (2) The fuel particles in the heat pipe type fuel element of the application have a coating layer, which can accommodate the fission gas generated during operation. It has high temperature resistance and containment, reduces radioactive contamination and thermal stress deformation, and ensures system safety even at high temperature.

[0062] (3) The heat pipe type fuel element of the application is in a vacuum state and in a negative pressure environment, and the pressure is also low during the operation of the reactor core, which will not cause safety problems. Moreover, the fuel element is a closed heat pipe, which can effectively isolate the reactor core and the subsequent loop, and avoid radioactive contamination and other problems.

[0063] (4) The reactor core of the application has no moving parts, and can realize efficient heat transfer and be safe and reliable. Due to the reversibility of heat pipe heat flux density and the integrated heat transfer of fuel and working medium, the environmental applicability of the reactor core of the application is strong, and it can stably operate in horizontal, vertical and swing conditions.

[0064] (5) The reactor core of the application has a simple and compact structure, and can be assembled by inserting the element into the reactor core, which is easy to assemble and maintain, and can be applied to land-based mobile, deep-sea exploration, deep space, star table or remote areas and other multi-scene and multi-purpose energy supply. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 It is a structure schematic view of the heat pipe type fuel element a of Example 1.

[0066] Figure 2 It is a sectional view of the second base body of the heat pipe type fuel element a of Example 1.

[0067] Figure 3 It is a sectional view of the first base body of the heat pipe type fuel element a of Example 1.

[0068] Figure 4Perspective view of the first base of the heat pipe type fuel element a of Example 1;

[0069] Figure 5 Structural view of the core containing the heat pipe type fuel element a of Example 1;

[0070] Figure 6 Schematic view of the distribution of the heat pipe type fuel element a of Example 1 in the core;

[0071] Figure 7 Structural schematic view of the heat pipe type fuel element b of Example 2;

[0072] Figure 8 Cross-sectional view of the second base of the heat pipe type fuel element b of Example 2;

[0073] Figure 9 Cross-sectional view of the first base of the heat pipe type fuel element b of Example 2;

[0074] Figure 10 Dimensional view of the first base of the heat pipe type fuel element b of Example 2;

[0075] Figure 11 Schematic view of the Ω-shaped groove of the heat pipe type fuel element b of Example 2;

[0076] Figure 12 Perspective view of the first base of the heat pipe type fuel element b of Example 2;

[0077] Figure 13 Schematic view of the division of the regions of the heat pipe type fuel element b of Example 2;

[0078] Figure 14 Schematic view of the arrangement of the heat pipe type fuel element b of Example 2.

[0079] BRIEF DESCRIPTION OF THE DRAWINGS:

[0080] Heat pipe type fuel element 1

[0081] First base 2

[0082] Evaporation section 21

[0083] Second base 3

[0084] Thermal insulation section 31

[0085] Condensation section 32

[0086] First groove 5

[0087] Second groove 6

[0088] Tube 7

[0089] Core 8

[0090] core vessel 9

[0091] reflection layer 10

[0092] control drum 11

[0093] wire mesh 13

[0094] inner diameter d of the first base o

[0095] vapor cavity diameter d of the first base v

[0096] outer diameter di of the second base

[0097] Ω groove circle diameter d

[0098] fine groove width w

[0099] fine groove depth δ DETAILED DESCRIPTION

[0100] The present application will be further illustrated by the following examples, but the present application is not limited to the scope of the examples. The experimental methods in the following examples, for which no specific conditions are noted, were performed according to conventional methods and conditions, or according to the instructions of the commercial products.

[0101] Example 1

[0102] Figure 1 is a schematic view of the structure of the heat pipe type fuel element a of the present example; Figure 2 is a cross-sectional view of the second base 3 of the heat pipe type fuel element a of the present example; Figure 3 is a cross-sectional view of the first base 2 of the heat pipe type fuel element a of the present example; Figure 4 is a perspective view of the first base 2 of the heat pipe type fuel element a of the present example.

[0103] The heat pipe type fuel element 1 comprises a coaxially fixed first base body 2 and a second base body 3 from bottom to top, both of which are hollow tubular structures and are in communication with each other; the inner side walls of the tubular structures of the first base body 2 and the second base body 3 are respectively provided with axially distributed first grooves 5 and second grooves 6, and the connecting portions of the first grooves 5 and the second grooves 6 are continuous without faults; the first base body 2 is made of 316ss stainless steel, and the inside of the first base body 2 is dispersedly distributed with fuel particles with a diameter of 0.5mm, which are TRISO particles, and sequentially comprise a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a silicon carbide layer and an outer dense pyrolytic carbon layer from the core of the fuel particle outward; the filling rate of the fuel particles in the first base body 2 is 40%; the fuel particles have a silicon carbide coating layer; the second base body 3 is a fuel particle-free metal base body made of 316ss stainless steel; the inner diameter of the tubular structure of the first base body 2 is 2.2cm, which is the same as the inner diameter of the tubular structure of the second base body 3, and the shapes of the first grooves 5 and the second grooves 6 are the same. The first grooves 5 and the second grooves 6 are uniformly and annularly arranged on the inner side walls of the tubular structures, and are independently 60 rectangular grooves with a width of 0.8mm and a depth of 1mm, which are symmetrically distributed along the circumference of the inner wall of the first base body 2, and are independently provided with 4 layers of stainless steel wire meshes at the edges closest to the axis of the heat pipe type fuel element a, and the pore size of the wire meshes is 0.254mm. The first base body 2 is cylindrical; the length of the first base body 2 is 50cm, and the length of the second base body 3 is 50cm. The outer diameter of the first base body 2 is 4cm, and the outer diameter of the second base body 3 is 3.2cm. The second base body 3 is cylindrical. The periphery of the first base body 2 is further coated with a 316ss stainless steel shell with a thickness of 2mm.

[0104] The heat pipe type fuel element a of the embodiment is processed and manufactured by using additive manufacturing technology (such as 3D printing). After printing by the manufacturing method, vacuumizing and filling liquid, the end cover is sealed.

[0105] Figure 5 It is a structural diagram of the core 8 containing the heat pipe type fuel element a of the embodiment; Figure 6 It is a schematic diagram of the distribution of the heat pipe type fuel element a of the embodiment in the core 8. The core 8 comprises a core container 9, 37 heat pipe type fuel elements 1 distributed in parallel with the axis of the core container 9, a reflecting layer 10 and two control drums 11 symmetrically distributed in the reflecting layer 10 with the central axis of the core container 9. The filling amount of the fuel particles accounts for 30% of the volume of the core container 9. The core container 9 further comprises a moderator channel, the heat pipe type fuel element 1 is inserted into the moderator channel to realize core assembly. The fuel particles account for 18% of the volume of the core container 9. The tubular structure of the heat pipe type fuel element a is in a vacuum state, and 100g of heat transfer working medium sodium is filled into the inner cavity.

[0106] The operating power of the reactor is 50 kW, and the operating temperature of the core is 700 DEG C. The active zone of the core has a diameter of 36 cm and a height of 50 cm. The heat transfer required by a single heat pipe is 1.35 kW, and the heat pipe type fuel element 1 has a heat transfer limit of 3.6 kW in a non-gravity environment, which meets the heat transfer requirements of multiple scenarios.

[0107] During the operation of the core, the heat pipe type fuel element 1 is divided into an evaporation section 21, an adiabatic section 31 and a condensation section 32; the evaporation section 21 corresponds to the first base body 2, and the groove of the evaporation section 21 accounts for 46% of the total volume of the core 46; the adiabatic section 31 and the condensation section 32 correspond to the second base body 3; the evaporation section 21 is located in the core container 9; the adiabatic section 31 of the heat pipe type fuel element 1 is a part that does not exchange energy with the outside world, which is located in the reflector 10; the condensation section 32 is located outside the core, and is used to transfer heat to the energy conversion system.

[0108] Compared with the existing 600 DEG C single heat pipe heat transfer limit of 3.7 kW, the heat transfer limit of the single heat pipe type fuel element 1 in the embodiment is 11.5 kW when the core is vertically placed at a working temperature of 700 DEG C, and the heat transfer limit is 3.6 kW in a horizontal or non-gravity environment.

[0109] The core structure in the embodiment is simple and reliable, which can effectively improve the thermal efficiency of the molten salt reactor, reduce the hot spot and the safety problem, and has high heat transfer capacity when coping with vacuum, swing and other environments. The heat pipe reactor can be applied to land-based mobile, deep space, deep sea exploration or energy supply.

[0110] Embodiment 2

[0111] Figure 7 The structure diagram of the heat pipe type fuel element b of the embodiment is shown in the figure; Figure 8 The cross-sectional view of the second base body 3 of the heat pipe type fuel element b of the embodiment is shown in the figure; Figure 9 The cross-sectional view of the first base body 2 of the heat pipe type fuel element b of the embodiment is shown in the figure; Figure 10 The size diagram of the first base body 2 of the heat pipe type fuel element b of the embodiment is shown in the figure; Figure 11 The Ω type groove schematic diagram of the heat pipe type fuel element b of the embodiment is shown in the figure; Figure 12 The perspective view of the first base body 2 of the heat pipe type fuel element b of the embodiment is shown in the figure.

[0112] The heat pipe type fuel element 1 comprises a first base body 2 and a second base body 3 coaxially fixed from bottom to top, both of which are hollow tubular structures and are in communication with each other; the inner side walls of the tubular structures of the first base body 2 and the second base body 3 are respectively provided with first grooves 5 and second grooves 6 distributed in the axial direction, and the connecting parts of the first grooves 5 and the second grooves 6 are continuous without faults; the first base body 2 is made of a slow neutron moderator material of dense silicon carbide, and the inside of the first base body 2 is dispersedly distributed with fuel particles with a diameter of 0.5 mm, which are TRISO particles, and the fuel particles comprise, from the core outward, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a silicon carbide layer and an outer dense pyrolytic carbon layer; the filling rate of the fuel particles in the first base body 2 is 40%; the fuel particles have a silicon carbide coating layer; the second base body 3 is a metal base body of 316ss stainless steel without fuel particles; the inner diameter of the tubular structure of the first base body 2 is 2.4 cm, which is the same as the inner diameter of the tubular structure of the second base body 3, and the shapes of the first grooves 5 and the second grooves 6 are the same. The first base body 2 is a regular hexagonal prism; the length of the first base body 2 is 50 cm, and the length of the second base body 3 is 50 cm. The second base body 3 is a cylinder. The first grooves 5 and the second grooves 6 are uniformly and circularly arranged on the inner side walls of the tubular structures, and are independently Ω-shaped grooves with a circular diameter d of 1.4 mm, a fine groove width w of 0.3 mm, a fine groove depth δ of 0.72 mm, and 50 groove channels symmetrically distributed along the inner wall of the first base body 2.

[0113] The heat pipe type fuel element b of the embodiment is processed and manufactured by using an additive manufacturing technology (such as 3D printing). After printing by the manufacturing method, vacuumizing, liquid filling and end cover sealing are performed.

[0114] The outer diameter of the first base body 2 is 4 cm, the inscribed diameter d o of the first base body 2 is 3.86 cm, the outer diameter di of the second base body 3 is 3.2 cm, and the steam cavity diameter d v of the first base body is 2.4 cm.

[0115] The processing of the heat pipe type fuel element b can be performed by using an additive manufacturing method, that is, on the basis of a design model, using silicon carbide powder, TRISO particles, a binder and other materials, and constructing the fuel element by layer-by-layer printing. After printing, the fuel element b is processed by vacuumizing, liquid filling, sealing and other processes to complete the manufacturing and processing of the entire heat pipe type fuel element.

[0116] Figure 13Schematic diagram of the region division of the heat pipe type fuel element b of the embodiment. During the operation of the reactor core, the heat pipe type fuel element b is divided into an evaporation section 21, an adiabatic section 31 and a condensation section 32; the evaporation section 21 corresponds to the first base body 2, the groove of the evaporation section 21 accounts for 46% of the total volume of the reactor core, and the adiabatic section 31 and the condensation section 32 correspond to the second base body 3; the evaporation section 21 is located in the reactor core container 9; the adiabatic section 31 of the heat pipe type fuel element b is a section that does not exchange energy with the outside, which is located in the reflector 10; and the condensation section 32 is located outside the reactor core and is used for transferring heat to the energy conversion system.

[0117] Figure 14 Schematic diagram of the arrangement of the heat pipe type fuel element b of the embodiment. In the reactor core container of a 50kW micro reactor, 37 heat pipe type fuel elements b are arranged in a hexagonal cross-section. When the heat pipe type fuel element b is vertically placed, it is mainly limited by the carrying limit, and the heat transfer limit is 6.7kW; when it is placed horizontally or operated in a deep space environment without gravity, it is affected by the capillary limit, and the heat transfer limit is 2.2kW.

[0118] The active region of the reactor core has a diameter of 28cm and a height of 50cm. The reactor core is filled with a slow neutron moderator to enhance the heat transfer between adjacent elements and avoid local hot spots caused by the failure of a single heat pipe. According to a particle silicon carbide matrix filling rate of 0.4, the fuel particles account for 18% of the volume in the reactor core, meeting the neutron physical requirements. The tubular structure of the heat pipe type fuel element b is in a vacuum state, and the inner cavity is filled with 100g of heat transfer working medium sodium. When operating at full power, a single heat pipe requires a heat transfer amount of 1.35kW, which is much lower than the heat pipe type fuel element heat transfer limit. Compared with the heat pipe type fuel element a, the heat pipe type fuel element b can more effectively simplify the structure of the reactor core and reduce the size of the reactor core because the fuel particles are directly dispersed in the slow neutron moderator matrix.

[0119] The reactor operates at a power of 50kW, and the operating temperature of the reactor core is 700℃. The active region of the reactor core has a diameter of 28cm and a height of 50cm. The heat transfer amount required by a single heat pipe is 1.35kW, and the heat pipe type fuel element b has a heat transfer limit of 3.6kW in a gravity-free environment, meeting the heat transfer requirements in multiple scenarios.

[0120] Effect embodiment 1

[0121] Table 1 is the hot spot temperature of the reactor core under different conditions. Because of the internal gap, the existing land reactor and space reactor have a relatively high hot spot temperature. In contrast, the land reactor and space reactor formed by embodiments 1 and 2 of the present application have relatively stable hot spot temperatures of 740℃ due to the integrated design avoiding gap thermal resistance.

[0122] Table 1

[0123]

[0124] For the heat pipe-fuel assembly with single heat transfer of 5 kW and evaporation section temperature of 700 DEG C, the design in the application does not have the problem of local hot spot caused by gap thermal resistance, compared with the design of inserting heat pipe into fuel channel, the overall core temperature distribution is more uniform, the hot spot difference in different application environment is more than 180 DEG C, which is extremely important for heat transfer stability, material service life and core safety.

Claims

1. A heat pipe fuel element characterized by, The heat pipe type fuel element comprises coaxially fixed first and second bases from bottom to top, both of which are hollow tubular structures and are in communication with each other; the first and second bases are in structure mode one or mode two: Mode one: the inner side walls of the tubular structures of the first and second bases are respectively provided with axially distributed first and second grooves, and the connecting parts of the first and second grooves are continuous and have no faults; wherein the first base is of metal material or moderator material, and fuel particles are dispersedly distributed in the interior of the first base, and the fuel particles have a coating layer; the second base is a metal base without fuel particles; Mode two: the inner side walls of the tubular structures of the first and second bases are respectively attached with axially distributed first and second wire meshes, and the connecting parts of the first and second wire meshes are continuous and have no faults; wherein the first base is of metal material or moderator material, and fuel particles are dispersedly distributed in the interior of the first base, and the fuel particles have a coating layer; the second base is of metal material without fuel particles.

2. The hot channel fuel element of claim 1, wherein, The inner diameter of the tubular structure of the first base is the same as that of the tubular structure of the second base; And / or, the shapes of the first and second grooves are the same; And / or, the first or second groove is uniformly annularly arranged on the inner side wall of the tubular structure; And / or, the first or second groove is one or more of square groove, rectangular groove, circular groove and special-shaped groove, preferably Ω-shaped groove; And / or, the first or second groove is independently attached with at least one layer of wire mesh at the edge closest to the axis of the heat pipe type fuel element, and the first or second groove and the wire mesh form a composite wick structure; And / or, the first or second wire mesh is single-layer wire mesh or composite wire mesh, preferably composite wire mesh; more preferably, the composite wire mesh is double-layer wire mesh with different pore sizes.

3. The hot channel fuel element of claim 1, wherein, The first base is cylindrical or multi-prismatic; preferably, when the first base is of metal material, the first base is cylindrical; preferably, when the first base is of moderator material, the first base is regular hexagonal prism; And / or, the length of the first base is the same as that of the second base; And / or, the outer diameter of the first base is greater than or equal to that of the second base.

4. The hot channel fuel element of claim 1, wherein, The second base is cylindrical or multi-prismatic, preferably cylindrical; And / or, the metal material is a material without neutron absorption capacity, resistant to high temperature and radiation, preferably 316ss stainless steel; And / or, the moderator material is one or more of silicon carbide, graphite and yttrium hydride, preferably yttrium hydride or silicon carbide.

5. The hot channel fuel element of claim 1, wherein, The first base is further coated with a shell; preferably, the thickness of the shell is 1-3 mm; preferably, the shell is of metal material or moderator material.

6. The hot channel fuel element of claim 1, wherein, The filling rate of the fuel particles in the interior of the first base is 10-64%, preferably 40-60%; And / or, the material of the cladding layer is metal, carbide or carbide-refractory metal, preferably carbide, more preferably silicon carbide; And / or, the core of the fuel particle is one or more of uranium nitride, uranium oxide and uranium oxycarbide, preferably uranium nitride; And / or, the fuel particle is one or more of TRISO particle, FCM and MOX, preferably TRISO particle; And / or, the diameter of the fuel particle is 0.5-1mm.

7. A core, characterized by It comprises a reactor vessel, and a plurality of heat pipe type fuel elements as claimed in any one of claims 1-6 filled in the reactor vessel and distributed in parallel with the axis of the reactor vessel.

8. The core of claim 7, wherein, It further comprises a reflector and a plurality of control drums arranged in the reflector; preferably, when the number of control drums is more than two, each of the control drums is symmetrically arranged in the reflector with the central axis of the reactor vessel; And / or, the reactor further comprises a shutdown control rod; preferably, the shutdown control rod is arranged in the center of the reactor; And / or, the reflector is arranged at the periphery of the reactor vessel; And / or, when the first matrix is moderator material, the fuel particles account for 10-30% of the volume of the reactor vessel; And / or, when the first matrix is metal material, the fuel particles account for 30-50% of the volume of the reactor vessel; Preferably, when the first matrix is metal material, the bottom of the reactor vessel is provided with a plurality of moderator channels; the heat pipe type fuel elements are connected with the moderator channels in parallel with the axis of the reactor vessel; Preferably, when the first matrix is moderator material, a plurality of the heat pipe type fuel elements are uniformly distributed in the reactor vessel in parallel with the axis of the reactor vessel.

9. A method of operating a core as claimed in claim 7 or 8, characterized in that, It comprises the following steps: placing the heat pipe type fuel elements filled with heat transfer working medium into the reactor, and operating the reactor; Preferably, the tubular structure of the heat pipe type fuel elements filled with heat transfer working medium is in vacuum state; Preferably, the heat transfer working medium comprises one or more of Li, Na, K, NaK alloy or nanofluid, more preferably Li or NaK alloy; Preferably, the filling rate of the heat transfer working medium in the inner cavity of the tubular structure of the heat pipe type fuel elements is 15-35%; Preferably, the operating temperature of the reactor is 500℃ and above, more preferably 500-1600℃; Preferably, the operating power of the reactor is 1kW-10MW; Preferably, when the operating temperature of the reactor is 650-1100℃, the heat transfer working medium is NaK alloy, and the weight ratio of K to Na in the NaK alloy is 77.2:22.8; Preferably, when the operating temperature of the reactor is 1000℃ and above, the heat transfer working medium is Li; Preferably, during the operation of the reactor, the heat pipe type fuel elements comprise an evaporation section, an adiabatic section and a condensation section; the evaporation section is located in the reactor vessel; the adiabatic section of the heat pipe type fuel elements does not lose or generate heat; the condensation section is a heat dissipation part for transferring heat to an energy conversion system.

10. Use of the core of claim 7 or 8 in land-based mobile, deep-sea exploration or energy supply.

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