Rod bundle fuel assembly testing device

Abstract

The invention belongs to the technical field of nuclear reactor engineering tests, and particularly relates to a rod bundle fuel assembly testing device. The device comprises a pressure channel, a simulation rod bundle arranged in the pressure channel, and a neutron imaging system arranged outside the pressure channel. The cross section of the pressure channel is in a regular hexagon shape, a lengthened pipe assembly is designed on the upper portion of the pressure channel, the simulation rod bundle is composed of a plurality of electric heating rods, and an outlet pipeline and an inlet pipeline are arranged at the upper end and the lower end of the pressure channel respectively and used for being connected with an external liquid metal loop. According to the invention, high-heat-flux heating of the reactor core can be simulated under the condition of liquid metal cooling, so that the thermal hydraulic phenomenon in the reactor core channel can be accurately simulated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear reactor engineering test, and particularly relates to a rod bundle fuel assembly test device. BACKGROUND

[0002] In the design and safety analysis of advanced nuclear reactors, especially liquid metal cooled fast reactors, it is crucial to accurately grasp the flow and heat transfer characteristics, critical heat flux (CHF) and dryout phenomena in the rod bundle fuel assembly. However, there are great challenges in carrying out related experiments:

[0003] Heat source simulation: it is necessary to simulate nuclear fission heat at high power density stably and uniformly.

[0004] Measurement difficulty: traditional optical measurement methods (such as PIV, LIF) are ineffective for opaque liquid metals (such as sodium, lead-bismuth eutectic), and the durability and reliability of invasive temperature measurement probes are extremely high in high temperature and high pressure environment.

[0005] System integration: integrating high heat flux heating, accurate temperature measurement and flow field visualization technology in a compact pressure boundary that can withstand severe operating conditions is complex.

[0006] The existing electric heating test device adopts single-end lead or lower heat flux density design, which is difficult to meet the high power level requirement of fast reactor. The temperature measurement point is mostly an external wall thermocouple, which cannot obtain the continuous temperature field inside the coolant channel or the axial temperature field of the heating rod. Flow field measurement is mostly limited to transparent working medium (water, air), and cannot be directly applied to liquid metal.

[0007] Therefore, there is an urgent need for an integrated rod bundle fuel assembly test body that can overcome the above technical bottlenecks and realize high heat flux heating, accurate internal temperature field measurement and non-invasive visualization of opaque medium flow field. SUMMARY

[0008] The technical problem solved by the present application: in view of the deficiencies of the prior art, the present application provides a rod bundle fuel assembly test device integrating distributed temperature measurement and non-invasive neutron radiography measurement, which can simulate high heat flux heating in the reactor core under liquid metal cooling conditions, and further realize accurate simulation of thermal hydraulic phenomena in the core channel.

[0009] The technical scheme adopted by the present application:

[0010] A kind of rod bundle fuel assembly test device, comprising: pressure channel, simulation rod bundle being arranged in the pressure channel and neutron imaging system being arranged outside the pressure channel;The cross section of the pressure channel is regular hexagon, the upper portion of the pressure channel is designed with lengthening tube assembly, the simulation rod bundle is composed of several electric heating rods, the upper and lower ends of the pressure channel are respectively equipped with outlet pipe and inlet pipe, for being connected with external liquid metal loop.

[0011] The wall surface of the pressure channel is equipped with neutron imaging window for penetrating neutron beam, the position of the neutron imaging window corresponds with the area to be measured of the simulation rod bundle, the neutron imaging system includes neutron emitter and neutron imaging screen, neutron emitter is arranged at one side of pressure channel, neutron imaging screen is arranged at the other side of pressure channel according to the irradiation angle of neutron emitter and the orientation of the area to be measured.

[0012] The electric heating rod includes metal cladding tube, resistance heating wire arranged in the metal cladding tube, magnesium oxide insulation layer filled in the gap between the resistance heating wire and the metal cladding tube;The two ends of the electric heating rod are equipped with electrode connecting column, the resistance heating wire is wound on the central ceramic column, and the two ends are connected with the electrode connecting column;Double-end lead structure with one end wire-in and one end wire-out is adopted.

[0013] The two ends of the electric heating rod are sealed with insulating end plug, the center of the end plug is embedded with nickel-based alloy electrode connecting column, the inside is welded with heating wire, and the outside forms standard power supply interface;The magnesium oxide insulation layer can be sealed in the metal cladding tube after the insulating end plug is pressed.

[0014] One end of the metal cladding tube is welded with corrugated pipe sealing element, and the other end of the corrugated pipe sealing element is welded with metal cladding extension.

[0015] The outer diameter of the extension is greater than the maximum outer diameter of the corrugated pipe sealing element.

[0016] Liquid metal heat conduction is adopted between the metal cladding tube, the corrugated pipe sealing element and the magnesium oxide insulation layer.

[0017] The material of the metal cladding tube is stainless steel, inconel or zirconium alloy same as real fuel cladding;The material of the corrugated pipe sealing element is stainless steel;The magnesium oxide insulation layer is high-purity, high-thermal-conductivity magnesium oxide powder filled in the annular space between the heating wire and the cladding tube after being vibrated and dried.

[0018] Spiral ribs are designed on the outer wall surface of the metal cladding tube of the electric heating rod;Optical fiber temperature measurement unit is embedded in the metal cladding tube of the electric heating rod along the axial direction of the metal cladding tube.

[0019] The fiber optic temperature measurement unit is a distributed fiber optic sensor that can continuously measure the wall temperature distribution of the electric heating rod along the axial direction.

[0020] The simulated rod bundle consists of 7 electric heating rods arranged in an equilateral triangle.

[0021] The upper metal cladding tubes of the seven electric heating rods pass through the corresponding holes in the upper end cap of the pressure channel and enter the extension component channel. Laser sealing is used between the top of the extension component and the metal cladding extension of the heating rod to form a permanent and absolutely reliable pressure boundary seal. Distributed optical fibers exit through the inner wall of the upper metal cladding tubes. The lower metal cladding tubes of the electric heating rods pass through the corresponding holes in the lower end cap of the pressure channel, and the cladding tube of each heating rod is connected to and sealed to the lower end cap.

[0022] The beneficial effects of this invention are:

[0023] (1) The present invention provides a test device for a rod bundle fuel assembly with high heat flux density simulation capability: the armored electric heating rod with double-ended lead design solves the problem of local overheating of single-ended lead and can achieve a surface heat flux density far exceeding that of conventional designs, and more realistically simulate the working conditions of fast reactor core.

[0024] (2) The present invention provides a test device for a rod bundle fuel assembly, which can accurately acquire the internal temperature field: the embedded distributed optical fiber temperature measurement technology provides unprecedented high-resolution, all-axial temperature data, providing key data support for the verification of thermal-hydraulic models.

[0025] (3) The present invention provides a test device for rod bundle fuel assembly with revolutionary flow field visualization function: integrating neutron radiography technology, it realizes for the first time non-invasive, full-field, quantitative measurement of the flow and heat transfer process of opaque liquid metal in the rod bundle channel, solving the measurement bottleneck that has long existed in this field.

[0026] (4) The test device for rod bundle fuel assembly provided by the present invention has high reliability in design: the connection method of welding at one end and dynamically sealing at the other end ensures the integrity of the pressure boundary and the long-term operational reliability of the equipment under thermal cycling.

[0027] (5) The rod bundle fuel assembly test device provided by the present invention has a high degree of system integration: the three major functional modules of heating, temperature measurement and visualization are highly integrated into one test body, which is powerful, saves space and reduces the overall experimental cost.

[0028] (6) The present invention provides a test device for a rod bundle fuel assembly, which integrates a neutron imaging window, allowing the neutron beam emitted by the neutron imaging system to penetrate the channel and be received by the imaging system, thereby realizing non-invasive measurement of the internal flow field and temperature field of the opaque liquid metal coolant.

[0029] (7) The present invention provides a test device for a rod bundle fuel assembly, wherein the built-in distributed optical fiber can acquire the axial temperature distribution of the heating rod in real time.

[0030] (8) The present invention provides a test device for rod bundle fuel assembly, which solves the problem of difficult to accurately measure the thermal and hydraulic parameters in the rod bundle channel under high temperature, high pressure and opaque medium conditions, and is especially suitable for the study of the safety characteristics of fuel assembly of liquid metal cooled fast reactor. Attached Figure Description

[0031] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in describing the embodiments of the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments recorded in the present invention. Those skilled in the art can derive other drawings from the following drawings without any creative effort.

[0032] Figure 1 This is a schematic diagram of a test device for a rod bundle fuel assembly provided by the present invention;

[0033] Figure 2 This is a schematic diagram of the electric heating rod structure provided by the present invention;

[0034] Figure 3 This is a schematic diagram of the electric heating rod structure provided by the present invention;

[0035] In the diagram: 1. Pressure channel; 2. Neutron imaging window; 3. Neutron emitter; 4. Extension tube assembly; 5. Electric heating rod; 6. Outlet pipe; 7. Neutron imaging screen; 8. Inlet pipe; 9. Electrode connection post; 10. Insulating end plug; 11. Central ceramic column; 12. Resistance heating wire; 13. Metal cladding tube; 14. Magnesium oxide insulation layer; 15. Bellows seal; 16. Metal cladding extension; 17. Distributed optical fiber; 18. Positioning wire or rib. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0037] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., refer to the orientation or positional relationship shown in the accompanying drawings, and are used only for the convenience of describing the 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, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or a connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] like Figure 1 As shown, the present invention provides a test apparatus for a rod bundle fuel assembly, comprising: a pressure channel 1, a simulated rod bundle disposed within the pressure channel 1, and a neutron imaging system disposed outside the pressure channel 1;

[0040] The pressure channel 1 is an irregularly shaped channel, its cross-sectional shape adapted to the outer contour of the simulated rod bundle; it is made of 316 stainless steel, possessing good high-temperature strength, corrosion resistance, and neutron performance (relatively low neutron absorption cross-section). Its design pressure is 2.0 MPa, and its design temperature is 600℃. The cross-section of the pressure channel 1 is a regular hexagon; this irregular design more accurately simulates the flow conditions within a real reactor assembly box. The total height of the channel is approximately 2500 mm, with a constant-diameter test section of 1500 mm. The pressure channel 1 has an outlet pipe 6 and an inlet pipe 8 at its upper and lower ends, respectively, for connection to an external liquid metal loop. An extension pipe assembly 4 is designed at the upper part of the pressure channel.

[0041] The simulated rod bundle consists of several electrically heated rods 5;

[0042] In this embodiment, the simulated rod bundle consists of 7 electric heating rods 5 arranged in an equilateral triangle;

[0043] like Figure 2As shown, the electric heating rod 5 includes a metal shell tube 13, a resistance heating wire 12 disposed inside the metal shell tube, and a magnesium oxide insulating layer 14 filling the gap between the resistance heating wire 12 and the metal shell tube 13; the electric heating rod 4 has electrode connecting posts 9 at both ends, and adopts a double-ended lead wire structure with one end for wire inlet and one end for wire outlet.

[0044] One end of the metal cladding tube is welded with a bellows seal 15, and the other end of the bellows seal 15 is welded to a metal cladding extension 16; the outer diameter of the extension 16 is greater than the maximum outer diameter of the bellows.

[0045] The metal cladding tube 13, the bellows seal 15, and the magnesium oxide insulation layer 14 are connected by liquid metal for heat conduction.

[0046] The resistance heating wire is made of nickel-chromium 80 / 20 (Cr20Ni80) alloy wire, which has high resistivity, high melting point, oxidation resistance and good long-term stability. The resistance heating wire 12 is wound on the central ceramic column 11; both ends are connected to the electrode connecting column 9.

[0047] The metal cladding tube is made of stainless steel, Inconel alloy, or zirconium alloy, the same as that used in the actual fuel cladding; its function is to isolate the coolant, bear pressure, and provide the same wall heat transfer characteristics as the actual component.

[0048] The bellows seal is made of stainless steel and its function is to absorb the thermal stress generated by the difference in axial thermal expansion between the electric heating rod 5 and the pressure channel 1 at high temperature.

[0049] The magnesium oxide insulating layer is made of high-purity, high-thermal-conductivity magnesium oxide (MgO) powder, which is compacted, dried, and then filled into the annular space between the heating wire and the casing tube. Its function is to efficiently conduct the heat generated by the heating wire to the casing tube, while ensuring the electrical insulation strength (>1500VAC) between the heating wire and the casing tube.

[0050] The electric heating rod 5 is sealed at both ends with insulating end plugs 10. The center of the end plug is embedded with a nickel-based alloy electrode connecting post 9, which is welded to the heating wire inside and forms a standard power interface on the outside. After the insulating end plug is pressed, the magnesium oxide insulating layer 14 can be sealed inside the metal shell tube 13.

[0051] like Figure 3 As shown, the outer wall of the metal casing tube 13 of the electric heating rod 5 is designed with spiral ribs 18. The rib structure can be rectangular or circular, which is used to simulate the positioning between fuel elements.

[0052] In another embodiment, a 316L stainless steel wire with a diameter of 1.5mm is designed on a central electric heating rod 5 at a certain pitch (e.g., 200mm). The other 6 heating rods are arranged close to the wire and are separated and positioned by it. The two ends of the wire are fixed to the upper and lower end caps. This positioning method has a simple structure, causes little flow disturbance, and can produce a beneficial mixing effect.

[0053] The electric heating rod 5 has an embedded fiber optic temperature measuring unit 17 arranged along the axial direction of the metal cladding tube 13.

[0054] The fiber optic temperature measurement unit 17 is a distributed fiber optic sensor that can continuously measure the wall temperature distribution of the electric heating rod 5 along the axial direction.

[0055] The distributed fiber optic sensor, before being filled with magnesium oxide powder, uses a 150μm diameter high-temperature resistant fluoride glass distributed fiber (such as OFS's Ultima). TM The fiber (series) is pre-laid along the inner wall of the cladding tube, requiring it to be tightly attached to the inner wall; the fiber can withstand long-term high temperatures up to 700℃. The two ends of the fiber are led out from special micro-sealed holes in the end plugs at one end of the heating rod, one end is connected to a distributed temperature sensing demodulator (such as the DTSX series), and the other end is a terminal reflector; by measuring the Raman scattered light along the fiber length, the demodulator can calculate the axial temperature distribution of the entire heating rod's outer wall surface in real time with a spatial resolution of up to one point per centimeter, based on the radial heat conduction formula, with a measurement accuracy of ±1℃.

[0056] In this embodiment, the upper metal-clad tubes of the seven electric heating rods 5 pass through the corresponding holes in the upper end cap of the pressure channel 1 and enter the channel of the extension component 4. Laser welding is used between the top of the extension component 4 and the metal-clad extension 16 of the heating rods 5 to form a permanent and absolutely reliable pressure boundary seal. Distributed optical fibers exit through the inner wall of the upper metal-clad tubes.

[0057] The lower end of the electric heating rod 4 is encased in a metal tube that passes through the corresponding hole in the lower end cap of the pressure channel 1. The encasing tube of each heating rod is connected to and sealed to the lower end cap.

[0058] The pressure channel 1 has a neutron imaging window 2 on its wall for penetrating the neutron beam, and the position of the neutron imaging window 2 corresponds to the test area of ​​the simulated rod beam.

[0059] The neutron imaging window 2 is made of materials such as aluminum, zirconium, or aluminum alloy, which have high transparency to thermal neutrons and low absorption cross-section.

[0060] The neutron imaging system includes a neutron emitter 3 and a neutron imaging screen 6. The neutron emitter 3 is located on one side of the pressure channel 1, and the neutron imaging screen 6 is located on the other side of the pressure channel according to the illumination angle of the neutron emitter and the orientation of the area to be measured.

[0061] The neutron emitter 3 is a compact DC deuterium-tritium (DT) neutron emitter with a yield of up to 10^11 n / s. It is placed on one side about 2-3 meters away from the test body, with its emission port collimator aligned with the test area in the center of the test section. The fast neutrons (14.1 MeV) generated by the neutron imaging system are slowed down into thermal neutrons by a moderator (such as high-density polyethylene), and then collimated by the collimation system to form a well-collimated thermal neutron beam that penetrates the entire test body vertically.

[0062] Imaging principle: When a thermal neutron beam penetrates the test body, its intensity attenuates depending on the materials along the path. Cavities or tracer particles in the liquid metal fluid strongly absorb / dissipate neutrons, while the liquid metal, the heating rod's metal cladding, and the aluminum alloy window are almost transparent to neutrons. As the neutron beam passes through a flow field containing cavitation particles or tracer particles, the attenuation distribution of the neutron beam changes accordingly.

[0063] The neutron imaging screen 6 is a large-area, high-resolution 6LiF / ZnS(Ag) scintillator screen. When neutrons penetrating the test body strike this screen, they are absorbed by the 6Li nuclei and undergo nuclear reactions, releasing alpha particles and tritium nuclei. These charged particles then excite ZnS(Ag) to emit visible fluorescence.

[0064] The neutron imaging system is equipped with a high-sensitivity scientific-grade CCD camera, which is a back-illuminated, cooled CCD camera with a built-in f / 0.85 large aperture lens, aimed at the scintillator screen. It captures the faint fluorescence image emitted by the scintillator.

[0065] The neutron imaging system is also equipped with an image acquisition and processing system: a computer controls the camera exposure (ranging from milliseconds to several seconds) and acquires images. By first calibrating the "background image" (no flow heating state) and the "dark field image," and then processing the acquired "data image," a two-dimensional neutron attenuation coefficient map reflecting the flow field density (i.e., temperature / cavitation) distribution can be obtained.

[0066] The neutron imaging system also has a three-dimensional tomographic scanning function: by rotating the test body or using a multi-angle neutron beam, combined with advanced tomographic reconstruction algorithms (such as filtered back projection algorithms or iterative algorithms), the three-dimensional distribution of the liquid metal flow field in the rod bundle channel can be further reconstructed.

[0067] The pressure channel 1 is also equipped with a pressure measurement interface, a temperature measurement interface, and a safety relief port.

[0068] The experimental apparatus is used for thermal-hydraulic experiments using liquid metal as a coolant.

[0069] The working principle of this invention is as follows:

[0070] Taking the flow and heat transfer characteristics of LBE within the rod bundle channel as an example:

[0071] Start the external LBE loop so that the LBE flows through the test body at a set flow rate (e.g., 4 m / s).

[0072] Turn on the neutron imaging system, preheat and stabilize the neutron yield.

[0073] Turn on the distributed fiber optic temperature measurement system (DTS) and CCD camera to begin collecting baseline data.

[0074] The power is gradually applied to the electric heating rod, from low to high, gradually increasing the surface heat flux density.

[0075] After stabilization at each power level:

[0076] The DTS system records the outer wall temperature distribution of each heating rod along its entire length in real time.

[0077] The CCD camera acquires neutron images at a rate of several frames per second.

[0078] By processing neutron images, two-dimensional / three-dimensional flow field cloud maps of LBE coolant in the rod bundle sub-channels are obtained, which can clearly show high and low flow velocity regions as well as flow stagnation regions.

[0079] By combining the wall temperature measured by DTS and the coolant volume temperature obtained by inverting the flow field distribution obtained by CCD camera, along with the known heating power and flow rate, the local heat transfer coefficient can be accurately calculated, and its variation with heat flux density can be studied.

[0080] Throughout the experiment, the bellows sealing structure effectively compensated for the thermal expansion of the electric heating rod, ensuring the sealing reliability during long-term operation.

[0081] Through the above specific implementation, this invention successfully integrates three cutting-edge technologies: electric heating simulation, built-in distributed temperature measurement, and neutron radiographic visualization, providing an unprecedentedly powerful experimental tool for the research and development of key technologies for advanced nuclear energy systems.

[0082] While those skilled in the art will recognize that the present invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and therefore all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0083] Furthermore, it should be understood that although the present invention is described according to embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A test apparatus for a rod bundle fuel assembly, characterized in that, include: The pressure channel (1), the simulated rod bundle disposed within the pressure channel (1), and the neutron imaging system disposed outside the pressure channel (1) are provided with the following: the cross-section of the pressure channel (1) is a regular hexagon; the upper part of the pressure channel is designed with an extended tube assembly (4); the simulated rod bundle is composed of several electric heating rods (5); the upper and lower ends of the pressure channel (1) are respectively provided with an outlet pipe (6) and an inlet pipe (8) for connecting to an external liquid metal circuit.

2. The test apparatus for rod bundle fuel assembly according to claim 1, characterized in that, The pressure channel (1) has a neutron imaging window (2) for penetrating the neutron beam on its wall. The position of the neutron imaging window (2) corresponds to the area to be tested of the simulated rod beam. The neutron imaging system includes a neutron emitter (3) and a neutron imaging screen (6). The neutron emitter (3) is located on one side of the pressure channel (1), and the neutron imaging screen (6) is located on the other side of the pressure channel according to the irradiation angle of the neutron emitter and the orientation of the area to be tested.

3. The test apparatus for rod bundle fuel assembly according to claim 2, characterized in that, The electric heating rod (5) includes a metal shell tube (13), a resistance heating wire (12) disposed in the metal shell tube, and a magnesium oxide insulating layer (14) filling the gap between the resistance heating wire (12) and the metal shell tube (13); the electric heating rod (5) is provided with electrode connecting posts (9) at both ends, the resistance heating wire (12) is wound on the central ceramic post (11), and both ends are connected to the electrode connecting posts (9); a double-ended lead wire structure with one end in and one end out is adopted.

4. The test apparatus for rod bundle fuel assembly according to claim 3, characterized in that, The electric heating rod (5) is sealed at both ends with insulating end plugs (10). The center of the end plug is embedded with a nickel-based alloy electrode connecting post (9), which is welded to the heating wire inside and forms a standard power interface outside. After the insulating end plug is pressed, the magnesium oxide insulating layer (14) can be sealed inside the metal shell tube (13).

5. The test apparatus for rod bundle fuel assembly according to claim 4, characterized in that, One end of the metal cladding tube (13) is welded with a bellows seal (15), and the other end of the bellows seal (15) is welded to the metal cladding extension (16).

6. The test apparatus for rod bundle fuel assembly according to claim 5, characterized in that, The outer diameter of the extension (16) is greater than the maximum outer diameter of the bellows seal (15).

7. The test apparatus for rod bundle fuel assembly according to claim 6, characterized in that, Liquid metal is used for heat conduction between the metal cladding tube (13), the bellows seal (15), and the magnesium oxide insulation layer (14).

8. The test apparatus for rod bundle fuel assembly according to claim 7, characterized in that, The metal cladding tube (13) is made of stainless steel, Inconel alloy, or zirconium alloy, the same as that used for real fuel cladding; the bellows seal (15) is made of stainless steel; the magnesium oxide insulation layer is made of high-purity, high-thermal-conductivity magnesium oxide powder that is compacted, dried, and then filled into the annular space between the heating wire and the cladding tube.

9. The test apparatus for rod bundle fuel assembly according to claim 8, characterized in that, The outer wall of the metal cladding tube (13) of the electric heating rod (5) is designed with spiral ribs (18); the metal cladding tube (13) of the electric heating rod (5) is embedded with an optical fiber temperature measuring unit (17) arranged along the axial direction of the metal cladding tube (13).

10. The test apparatus for rod bundle fuel assembly according to claim 9, characterized in that, The fiber optic temperature measurement unit (17) is a distributed fiber optic sensor that can continuously measure the wall temperature distribution of the electric heating rod (5) along the axial direction.

11. The test apparatus for rod bundle fuel assembly according to claim 10, characterized in that, The simulated rod bundle consists of 7 electric heating rods (5) arranged in an equilateral triangle.

12. The test apparatus for rod bundle fuel assembly according to claim 11, characterized in that, The upper metal shell tubes of the seven electric heating rods (5) pass through the corresponding holes of the upper end cap of the pressure channel (1) and enter the channel of the extension component (4). Laser sealing is used between the top of the extension component (4) and the metal shell extension (16) of the heating rod (5) to form a permanent and absolutely reliable pressure boundary seal. Distributed optical fibers pass through the inner wall of the upper metal shell tube. The lower metal shell tube of the electric heating rod (4) passes through the corresponding holes of the lower end cap of the pressure channel (1). The shell tube of each heating rod is connected to and sealed with the lower end cap.

Images