Power transient irradiation device suitable for fuel rod bundle

Abstract

The invention discloses a power transient irradiation device suitable for a fuel rod bundle, and relates to the technical field of reactor irradiation, the power transient irradiation device comprises an outer tube, the lower end of the outer tube is open, and an inner cavity of the outer tube is axially provided with a helium outlet tube; the spiral tube helium screen is coaxially wound on the outer side of the outer tube, an inlet in the upper end of the spiral tube helium screen is communicated with a helium inlet tube, an outlet in the lower end of the spiral tube helium screen is communicated with the lower end of the helium outlet tube, and the upper end of the helium outlet tube is communicated with external equipment; an annular area between the outer wall of the helium outlet pipe and the inner wall of the outer pipe is a middle flow channel for cooling water to pass through, and a plurality of rod-shaped fuel elements are annularly and evenly distributed in the middle flow channel at equal intervals. By adopting the scheme, a plurality of fuel rods can simultaneously realize large-amplitude power jump, the power difference of the fuel rods at different positions is greatly reduced, and the test parameters of different fuel rods in the test process are basically consistent, so that a plurality of rod-shaped fuel elements can be used for simultaneously carrying out a power transient test.

Description

Technical Field

[0001] The invention relates to the technical field of stack irradiation, and in particular to a power transient irradiation device suitable for a fuel rod bundle. Background Art

[0002] The performance of pressurized water reactor fuel elements is directly related to the safety and economy of the reactor. Carrying out in-pile irradiation tests on fuel elements is a key link in the research and development and design of fuel elements. Power transient irradiation tests on fuel elements are generally carried out in research reactors using special power transient irradiation test equipment; by changing the power of the fuel elements in a short period of time, the performance parameters and safety margins of the fuel elements are verified. In order to conduct power transient irradiation tests on pressurized water reactor fuel elements in research reactors, some foreign research reactors, such as the HBWR reactor in Norway, the BR2 reactor in Belgium, the R2 reactor in Sweden and the JMTR reactor in Japan, use helium-3 gas loops as power regulating devices for fuel elements. By changing the gaseous neutron poison ( 3 He gas) to effectively regulate the irradiation power of the test fuel element.

[0003] The helium shield of the helium-3 gas circuit and some of the helium pipelines connected to it are located in the active area of ​​the research reactor core; 3 He gas absorbs thermal neutrons in the reactor, producing tritium ( 3 H). Tritium is an isotope of hydrogen. Tritium in gaseous state has strong permeability. Tritium at higher temperatures can easily penetrate containers made of metal materials and leak into the environment. The permeability of tritium increases sharply as its temperature rises.

[0004] Since the gas pressure adjustment range provided by the helium-3 gas circuit is limited, generally 0.1 to 4.5 MPa; at the same time, the traditional helium screen structure adopts an annular gas cavity design and is far away from the test fuel rods. These two factors limit the power variation range of the test fuel element. On the other hand, in order to increase the number of fuel rods in a single power transient test, fuel bundles are generally used for testing; due to the differences in neutron injection rate distribution in the research reactor and the "mutual screen" effect of the fuel rod bundle, the power of the fuel rods at different positions in the bundle varies greatly, which does not meet the requirement that the fuel rod power and its changes are as similar as possible in a single test. Therefore, it is necessary to develop a power transient irradiation device that can achieve large power changes and flatten the power of fuel rods at different positions for the power transient test of the fuel rod bundle. Summary of the invention

[0005] The present invention aims to solve the deficiencies of the prior art and to provide a power transient irradiation device suitable for a fuel rod bundle. By adopting this scheme, a plurality of fuel rods can simultaneously achieve a large power jump and greatly reduce the power difference of fuel rods at different positions. During the test, the test parameters of different fuel rods are basically the same, so that a power transient test can be carried out simultaneously with a plurality of rod-shaped fuel elements.

[0006] The present invention is achieved through the following technical solutions:

[0007] A power transient irradiation device suitable for a fuel rod bundle, comprising:

[0008] An outer tube, wherein the upper and lower ends of the outer tube are open, and the inner cavity of the outer tube is axially provided with a helium outlet pipe;

[0009] A spiral tube helium shield, wherein the spiral tube helium shield is coaxially wound around the outer side of the outer tube, the upper inlet of the spiral tube helium shield is connected to the helium inlet pipe, the lower outlet of the spiral tube helium shield is connected to the lower end of the helium outlet pipe, and the upper end of the helium outlet pipe is connected to an external device;

[0010] The annular area between the outer wall of the helium outlet pipe and the inner wall of the outer pipe is an intermediate flow channel for cooling water to pass through, and a plurality of rod-shaped fuel elements are evenly distributed in an annular direction and at equal intervals in the intermediate flow channel; the spacing between adjacent rod-shaped fuel elements is consistent with the spacing between fuel rods in the prototype fuel assembly; both ends of the fuel segment of the rod-shaped fuel element are located between the two ends of the spiral tube helium shield.

[0011] Compared with the existing technology, tritium is an isotope of hydrogen, and tritium in gas state has strong permeability; tritium at a higher temperature can easily penetrate containers made of metal materials and leak into the environment; and because the gas pressure adjustment range provided by the helium-3 gas circuit is limited, generally 0.1 to 4.5 MPa; at the same time, the traditional helium shield structure adopts an annular gas cavity design and is far away from the test fuel rod. These two factors limit the power variation range of the test fuel element. On the other hand, in order to increase the number of fuel rods in a single power transient test, a fuel bundle is generally used to carry out the test; due to the difference in neutron injection rate distribution in the research reactor and the "mutual screen" effect of the fuel rod bundle, the power of the fuel rods at different positions in the bundle is quite different, which does not meet the requirement that the power of the fuel rods and its change conditions are as similar as possible in a single test. The present invention provides a power transient irradiation device suitable for a fuel rod bundle. By adopting this scheme, a plurality of fuel rods can achieve a large power jump at the same time, and the power difference of fuel rods at different positions is greatly reduced. During the test, the test parameters of different fuel rods are basically the same, so that a power transient test can be carried out simultaneously with a plurality of rod-shaped fuel elements.

[0012] In the specific scheme, it includes an outer tube, a spiral tube helium shield, a helium inlet tube and a helium outlet tube. The spiral tube helium shield is spiral-shaped and coaxially wound around the outer side of the outer tube, that is, the helium shield is formed by spirally winding the helium pipeline of the above structure around the outer tube. At this time, the upper end of the spiral tube helium shield is connected to the helium inlet tube, and the lower end of the spiral tube helium shield is bent and enters the inner part of the outer tube from the open part of the lower end of the outer tube, thereby forming a helium outlet tube. In this way, helium can be filled into the spiral tube helium shield and the helium outlet tube through the helium inlet tube ( 3 He gas), helium-3 gas enters from the helium inlet pipe, flows through the spiral tube helium screen, and finally flows out through the helium outlet pipe at the center; in addition, there is an annular area between the outer wall of the helium outlet pipe and the inner wall of the outer tube, that is, an intermediate flow channel for cooling water to pass through, and a number of rod-shaped fuel elements are arranged circumferentially in the annular area, that is, N fuel rods are arranged in a circle with equal circumferential spacing, and the position of each rod is kept fixed by a corresponding fixed structure, and the spacing between the fuel rods is consistent with the spacing of the fuel rods in the prototype fuel assembly where they are located. In this way, through a number of rod-shaped fuel elements uniformly spaced circumferentially, the spiral tube helium screen arranged in an external spiral, and the helium outlet pipe located in the center, while multiple fuel rods can simultaneously achieve a large power jump, the power difference of fuel rods at different positions is greatly reduced, so that the test parameters of different fuel rods during the test are basically consistent. The above rod-shaped fuel elements adopt a shortened fuel rod design, and generally overlap the fuel area of ​​the fuel rod with the flat area of ​​the axial distribution of the core thermal neutron injection rate. The axial position of the helical tube helium shield is substantially the same as the axis around which the fuel segments of the plurality of rod-shaped fuel elements are surrounded, that is, the axis around which the plurality of rod-shaped fuel elements are surrounded is coaxial with the helical tube helium shield, and the length of the helium shield is slightly greater than the length of the fuel segment, thereby accommodating the fuel segment therein.

[0013] The above scheme aims to achieve: by adopting a compact circular arrangement, multiple fuel rods can be carried at the same time; at the same time, the design of the spiral tube helium screen and the central helium pipeline can achieve a significant power jump and effectively reduce the power difference between different fuel rods. In addition, the spiral tube helium screen and the central helium pipeline are both located outside the middle flow channel for cooling the fuel rod bundle, which reduces the influence of the heat release of helium-3 gas and its helium screen structural materials on the measurement of fuel heat release power, and improves the accuracy of the measurement of fuel rod bundle heat release power. Neither the helium screen nor the central helium pipeline is in contact with the higher temperature cooling water that cools the fuel rod bundle, which reduces the temperature of the helium pipeline and the tritium helium contained in the pipeline to a certain extent, thereby helping to reduce the penetration and leakage of tritium.

[0014] In order to meet the experimental requirements of different numbers of fuel rods, it is set as follows: when a number of the rod-shaped fuel elements cannot occupy the entire annular area, the rod-shaped fuel elements are evenly distributed on one side of the annular area in an annular direction and at equal intervals, and the remaining areas except the one side of the annular area are closed by structural components. In this scheme, if the number of fuel rods tested cannot occupy the entire annular area between the inner and outer tubes, the fuel rods are closely arranged on one side of the annular area while keeping the original spacing between the fuel rods unchanged, and the remaining areas of the annular area are closed by structural components to keep the cooling water flow rate in the middle flow channel that flushes and cools the fuel rod bundle to meet the test requirements.

[0015] In order to serve as a pressure boundary and form a coolant channel, a pressure tube is also included. The outer tube and the spiral tube helium shield are both located in the chamber of the pressure tube. The pressure tube has a cooling water inlet, and the cooling water inlet is located above the spiral tube helium shield; the lower end of the outer tube is connected to the bottom of the pressure tube, and the upper end of the outer tube is connected to the cooling water outlet. In this scheme, the pressure tube 3 is a thick-walled cylindrical structure made of stainless steel material, which serves as a pressure boundary to accommodate cooling water with typical pressurized water reactor environmental parameters (pressure of about 15MPa, temperature of about 280-330℃); in this way, cooling water can flow in from the upper cooling water inlet, flow downward along the outer flow channel, thereby cooling the pressure tube and the spiral tube helium shield, and then turn back upward at the bottom of the pressure tube and the outer tube, thereby passing through the middle flow channel and flowing out from the coolant outlet.

[0016] In order to completely separate the outer flow channel from the middle flow channel, a shunt pipe is also included, one end of which is connected to the upper end of the outer pipe through an intermediate joint, and the other end of the shunt pipe passes through the pressure pipe.

[0017] In order to reduce heat transfer, a protection tube is also included. The pressure tube and the protection tube are coaxial and arranged in sequence from the inside to the outside. The chamber between the inner side of the protection tube and the outer side of the pressure tube is a nitrogen chamber. In this solution, the protection tube is located outside the pressure tube and is also a cylindrical structure; there is a nitrogen chamber between the two, which is filled with nitrogen at normal pressure and is connected to the nitrogen inlet and the nitrogen outlet respectively.

[0018] In order to further reduce the heat exchange, so as to accurately obtain the temperature rise of the cooling water in the fuel area, it also includes an inner tube, the helium outlet pipe and the inner tube are coaxial, and are arranged in sequence from the inside to the outside, and the inner tube is located between the plurality of rod-shaped fuel elements; an annular inner flow channel is left between the inner side of the inner tube and the outer side of the helium outlet pipe, the lower end of the inner flow channel is connected to the bottom of the pressure pipe, and the upper end of the inner flow channel is connected to the cooling water outlet. In this scheme, an inner tube is coaxially provided outside the helium outlet pipe, and the inner flow channel is an annular area between the inner tube and the central helium outlet pipe, which is separated from the intermediate flow by the inner tube. The cooling water flows in from the cooling water inlet, flows downward along the outer flow channel, cools the pressure pipe and the spiral tube helium shield, and then turns upward at the bottom of the outer tube, flows into the intermediate flow channel and the inner flow channel respectively, and after flushing the cooling fuel rod bundle and the helium outlet pipe at the central position respectively, the cooling water of the two flow channels converges at the upper part of the device, and finally flows out from the cooling water outlet pipe.

[0019] In order to reduce the heat exchange between cooling water in different flow channels inside and outside the tube, the diverter tube, outer tube and inner tube all adopt a first double-layer tube structure, and the gap in the first double-layer tube structure is filled with nitrogen.

[0020] In order to further prevent the tritium in the spiral tube helium shield and the connected helium pipeline from penetrating and leaking into the cooling water, the spiral tube helium shield, the helium inlet pipe and the helium outlet pipe all adopt a second double-layer tube structure with a filling layer, and the second double-layer tube structure includes an inner tube, a sponge-like metal titanium tube filling layer and an outer tube from the inside to the outside, and the inner tube and the outer tube are both made of stainless steel with a dense Al2O3 coating. In this solution, a helium pipeline with a double-layer stainless steel tube structure with an interlayer is adopted, and the double-layer tube is designed with Al2O3 coating. The inner tube contains helium containing tritium, which can prevent the tritium in the helium shield and the connected helium pipeline from penetrating and leaking into the cooling water, thereby effectively reducing the radioactive hazards caused by tritium leakage.

[0021] In order to monitor the thermal neutron injection rate near the fuel rods online, the inner side of the outer tube is equipped with measuring heads of several self-powered neutron detectors; wherein the measuring heads are preferably located between the several rod-shaped fuel elements and the inner tube.

[0022] In order to measure the temperature rise of the cooling water in the intermediate flow channel in the fuel area, several thermocouples are arranged above and below the fuel section of several rod-shaped fuel elements. In this scheme, several fuel section inlet thermocouples are arranged below the fuel section of the intermediate flow channel, and several fuel section outlet thermocouples are arranged above the fuel section to measure the temperature rise of the cooling water in the intermediate flow channel in the fuel area; the heat release power of the fuel rod bundle can be obtained by the heat balance method using the cooling water flow measured by the external system connected to the device and the diversion ratio of the intermediate flow and the internal flow channel.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] 1) The present invention provides a power transient irradiation device suitable for fuel rod bundles, which adopts a compact circular arrangement scheme and can carry multiple fuel rods at the same time; at the same time, it adopts the design of spiral tube helium screen and central helium pipeline, which can achieve a significant power jump and effectively reduce the power difference between different fuel rods.

[0025] 2) The present invention provides a power transient irradiation device suitable for a fuel rod bundle, wherein the outer tube, the inner tube and the diverter tube all adopt a double-layer tube structure design, which effectively reduces the heat exchange of cooling water between adjacent flow channels; at the same time, the helium shield and the central helium gas pipeline are both located outside the middle flow channel for cooling the fuel rod bundle, which reduces the influence of the heat release of helium-3 gas and its helium shield structural material on the fuel heat release power measurement, thereby improving the accuracy of the fuel rod bundle heat release power measurement.

[0026] 3) The present invention provides a power transient irradiation device suitable for a fuel rod bundle. The helium shield and the central helium pipeline are not in contact with the higher temperature cooling water for cooling the fuel rod bundle, which reduces the temperature of the helium pipeline and the tritium helium gas contained in the pipeline to a certain extent, thereby helping to reduce the penetration and leakage capacity of tritium.

[0027] 4) The present invention provides a power transient irradiation device suitable for a fuel rod bundle, which adopts a helium pipeline with a double-layer stainless steel tube structure with an interlayer, and the double-layer tube is designed with Al2O3 coating, which can prevent the tritium in the helium screen and the connected helium pipeline from penetrating and leaking into the cooling water, thereby effectively reducing the radioactive hazards caused by tritium leakage.

[0028] 5) The present invention can be applied to the design of in-pile device of a fuel power transient test loop using a helium-3 gas loop, and ultimately used to study the transient irradiation test of fuel bundle power with a large variation range and high power distribution uniformity in the pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0030] Figure 1 A schematic diagram of the structure of the power transient irradiation device provided by the present invention;

[0031] Figure 2 An AA cross-sectional view of the power transient irradiation device provided by the present invention;

[0032] Figure 3 A BB cross-sectional view of the power transient irradiation device provided by the present invention;

[0033] Figure 4 This is a schematic structural diagram of the spiral tube helium screen provided by the present invention.

[0034] Marks and corresponding parts names in the attached drawings:

[0035] 1-protection tube; 2-nitrogen cavity; 3-pressure tube; 4-spiral tube helium shield; 5-outer tube; 6-rod-shaped fuel element; 7-outer flow channel; 8-middle flow channel; 9-diverter tube; 10-nitrogen inlet; 11-nitrogen outlet; 12-cooling water inlet; 13-cooling water outlet; 14-fuel section inlet thermocouple; 15-fuel section outlet thermocouple; 16-self-powered neutron detector; 17-helium inlet pipe; 18-helium outlet pipe; 19-inner tube; 20-inner flow channel. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0037] Example

[0038] This embodiment provides a power transient irradiation device suitable for a fuel rod bundle, such as Figure 1-Figure 4 As shown, including:

[0039] An outer tube 5, wherein the upper and lower ends of the outer tube 5 are open, and the inner cavity of the outer tube 5 is axially provided with a helium outlet pipe 18;

[0040] A spiral tube helium shield 4, wherein the spiral tube helium shield 4 is coaxially wound around the outer side of the outer tube 5, the upper end inlet of the spiral tube helium shield 4 is connected to the helium inlet pipe 17, the lower end outlet of the spiral tube helium shield 4 is connected to the lower end of the helium outlet pipe 18, and the upper end of the helium outlet pipe 18 is connected to an external device;

[0041] The annular area between the outer wall of the helium outlet pipe 18 and the inner wall of the outer tube 5 is an intermediate flow channel 8 for cooling water to pass through, and a plurality of rod-shaped fuel elements 6 are evenly distributed in an annular direction and at equal intervals in the intermediate flow channel 8; the spacing between adjacent rod-shaped fuel elements 6 is consistent with the spacing of fuel rods in the prototype fuel assembly; both ends of the fuel segment of the rod-shaped fuel element 6 are located between the two ends of the spiral tube helium shield 4.

[0042] Compared with the existing technology, tritium is an isotope of hydrogen, and tritium in gas state has strong permeability; tritium at a higher temperature can easily penetrate containers made of metal materials and leak into the environment; and because the gas pressure adjustment range provided by the helium-3 gas circuit is limited, generally 0.1 to 4.5 MPa; at the same time, the traditional helium shield structure adopts an annular gas cavity design and is far away from the test fuel rod. These two factors limit the power variation range of the test fuel element. On the other hand, in order to increase the number of fuel rods in a single power transient test, a fuel bundle is generally used to carry out the test; due to the difference in neutron injection rate distribution in the research reactor and the "mutual screen" effect of the fuel rod bundle, the power of the fuel rods at different positions in the bundle is quite different, which does not meet the requirement that the power of the fuel rods and its change conditions are as similar as possible in a single test. The present invention provides a power transient irradiation device suitable for a fuel rod bundle. By adopting this scheme, a plurality of fuel rods can achieve a large power jump at the same time, and the power difference of fuel rods at different positions is greatly reduced. During the test, the test parameters of different fuel rods are basically the same, so that a plurality of rod-shaped fuel elements 6 can be used to carry out power transient tests at the same time.

[0043] In the specific scheme, it includes an outer tube 5, a spiral tube helium shield 4, a helium inlet pipe 17 and a helium outlet pipe 18. The spiral tube helium shield 4 is spiral and coaxially wound around the outer side of the outer tube 5, that is, the helium shield is formed by spirally winding the helium pipeline of the above structure around the outer tube 5. At this time, the upper end of the spiral tube helium shield 4 is connected to the helium inlet pipe 17, and the lower end of the spiral tube helium shield 4 is bent and enters the inner part of the outer tube 5 from the open part of the lower end of the outer tube 5, thereby forming the helium outlet pipe 18. In this way, helium can be filled into the spiral tube helium shield 4 and the helium outlet pipe 18 through the helium inlet pipe 17. 3He gas), helium-3 gas enters from the helium inlet pipe 17, flows through the spiral tube helium shield 4, and finally flows out through the helium outlet pipe 18 at the center position; in addition, there is an annular area between the outer wall of the helium outlet pipe 18 and the inner wall of the outer tube 5, that is, the intermediate flow channel 8 for cooling water to pass through, and a number of rod-shaped fuel elements 6 are arranged circumferentially in the annular area, that is, N fuel rods are circumferentially evenly spaced to form a circle, and the position of each rod is kept fixed by a corresponding fixed structure, and the spacing between the fuel rods is consistent with the spacing of the fuel rods in the prototype fuel assembly where they are located. In this way, through the circumferentially evenly spaced rod-shaped fuel elements 6, the spiral tube helium shield 4 arranged in an external spiral, and the helium outlet pipe 18 located in the center, while multiple fuel rods are simultaneously able to achieve a large power jump, the power difference of fuel rods at different positions is greatly reduced, so that the test parameters of different fuel rods during the test are basically consistent. The above rod-shaped fuel elements 6 adopt a shortened fuel rod design, generally overlapping the fuel area of ​​the fuel rod with the flat area of ​​the axial distribution of the core thermal neutron injection rate. The axial position of the helical tube helium shield 4 is substantially the same as the axis around which the fuel segments of the plurality of rod-shaped fuel elements 6 are disposed, that is, the axis around which the plurality of rod-shaped fuel elements 6 are disposed is coaxial with the helical tube helium shield 4, and the length of the helium shield is slightly greater than the length of the fuel segment, thereby accommodating the fuel segment therein.

[0044] The above scheme aims to achieve: by adopting a compact circular arrangement scheme, multiple fuel rods can be carried at the same time; at the same time, the design of the spiral tube helium screen 4 and the central helium pipeline can achieve a significant power jump and effectively reduce the power difference between different fuel rods. In addition, the spiral tube helium screen 4 and the central helium pipeline are both located outside the middle flow channel 8 for cooling the fuel rod bundle, which reduces the influence of the heat release of helium-3 gas and its helium screen structural materials on the measurement of the fuel heat release power, and improves the accuracy of the measurement of the fuel rod bundle heat release power. Neither the helium screen nor the central helium pipeline is in contact with the higher temperature cooling water for cooling the fuel rod bundle, which reduces the temperature of the helium pipeline and the tritium helium gas contained in the pipeline to a certain extent, thereby helping to reduce the penetration and leakage capacity of tritium.

[0045] In order to meet the experimental requirements of different numbers of fuel rods, it is set as follows: when a number of the rod-shaped fuel elements 6 cannot occupy the entire annular area, the rod-shaped fuel elements 6 are evenly distributed on one side of the annular area in an annular direction and at equal intervals, and the remaining areas except the one side of the annular area are closed by structural components. In this scheme, if the number of fuel rods tested cannot occupy the entire annular area between the inner and outer tubes 5, the fuel rods are closely arranged on one side of the annular area while keeping the original spacing between the fuel rods unchanged, and the remaining areas of the annular area are closed by structural components to keep the cooling water flow rate in the intermediate flow channel 8 that flushes and cools the fuel rod bundle to meet the test requirements.

[0046] In order to serve as a pressure boundary and form a coolant channel, a pressure tube 3 is also included. The outer tube 5 and the spiral tube helium shield 4 are both located in the chamber of the pressure tube 3. The pressure tube 3 is provided with a cooling water inlet 12, and the cooling water inlet 12 is located above the spiral tube helium shield 4. The lower end of the outer tube 5 is connected to the bottom of the pressure tube 3, and the upper end of the outer tube 5 is connected to the cooling water outlet 13. In this scheme, the pressure tube 33 is a thick-walled cylindrical structure made of stainless steel material, which serves as a pressure boundary to accommodate cooling water with typical pressurized water reactor environmental parameters (pressure of about 15MPa, temperature of about 280-330°C); in this way, the cooling water can flow in from the upper cooling water inlet 12, flow downward along the outer flow channel 7, thereby cooling the pressure tube 3 and the spiral tube helium shield 4, and then turn back upward at the bottom of the pressure tube 3 and the outer tube 5, thereby passing through the intermediate flow channel 8 and flowing out from the coolant outlet.

[0047] In order to completely separate the outer flow channel 7 from the middle flow channel 8, a shunt pipe 9 is also included. One end of the shunt pipe 9 is connected to the upper end of the outer pipe 5 through an intermediate joint, and the other end of the shunt pipe 9 passes through the pressure pipe 3.

[0048] In order to reduce heat transfer, a protection tube 1 is also included. The pressure tube 3 and the protection tube 1 are coaxial and arranged in sequence from the inside to the outside. The chamber between the inner side of the protection tube 1 and the outer side of the pressure tube 3 is a nitrogen chamber 2. In this solution, the protection tube 1 is located outside the pressure tube 3 and is also a cylindrical structure; between the two is a nitrogen chamber 2, which is filled with nitrogen at normal pressure and is connected to a nitrogen inlet 10 and a nitrogen outlet 11 respectively.

[0049] In order to further reduce heat exchange and accurately obtain the temperature rise of cooling water in the fuel area, an inner tube 19 is also included. The helium outlet pipe 18 and the inner tube 19 are coaxial and arranged in sequence from the inside to the outside. The inner tube 19 is located between the plurality of rod-shaped fuel elements 6. An annular inner flow channel 20 is left between the inner side of the inner tube 19 and the outer side of the helium outlet pipe 18. The lower end of the inner flow channel 20 is connected to the bottom of the pressure pipe 3, and the upper end of the inner flow channel 20 is connected to the cooling water outlet 13. In this solution, the inner tube 19 is coaxially provided outside the helium outlet pipe 18. The inner flow channel 20 is an annular area between the inner tube 19 and the central helium outlet pipe 18, and is separated from the intermediate flow by the inner tube 19. The cooling water flows in from the cooling water inlet 12, flows downward along the outer flow channel 7, cools the pressure tube 3 and the spiral tube helium shield 4, then turns back upward at the lower part of the outer tube 5, flows into the middle flow channel 8 and the inner flow channel 20 respectively, flushes and cools the fuel rod bundle and the helium outlet pipe 18 at the center respectively, and then the cooling water of the two flow channels converges at the upper part of the device and finally flows out from the cooling water outlet pipe 13.

[0050] In order to reduce the heat exchange between the cooling water in different flow channels inside and outside the tube, the diverter tube 9, the outer tube 5 and the inner tube 19 all adopt a first double-layer tube structure, and the gap in the first double-layer tube structure is filled with nitrogen.

[0051] In order to further prevent the tritium in the spiral tube helium shield 4 and the connected helium pipeline from penetrating and leaking into the cooling water, the spiral tube helium shield 4, the helium inlet pipe 17 and the helium outlet pipe 18 all adopt a second double-layer tube structure with a filling layer, and the second double-layer tube structure includes an inner tube, a sponge-like metal titanium tube filling layer and an outer tube from the inside to the outside, and the inner tube and the outer tube are both made of stainless steel with a dense Al2O3 coating. In this solution, a helium pipeline with a double-layer stainless steel tube structure with an interlayer is adopted, and the double-layer tube is designed with Al2O3 coating. The inner tube contains tritium-containing helium, which can prevent the tritium in the helium shield and the connected helium pipeline from penetrating and leaking into the cooling water, thereby effectively reducing the radioactive hazards caused by tritium leakage.

[0052] In order to monitor the thermal neutron injection rate near the fuel rods online, the inner side of the outer tube 5 is equipped with measuring heads of several self-powered neutron detectors 16 ; wherein the measuring heads are preferably located between the several rod-shaped fuel elements 6 and the inner tube 19 .

[0053] In order to measure the temperature rise of the cooling water in the intermediate flow channel 8 in the fuel area, several thermocouples are arranged above and below the fuel section of several rod-shaped fuel elements 6. In this scheme, several fuel section inlet thermocouples 14 are arranged below the fuel section of the intermediate flow channel 8, and several fuel section outlet thermocouples 15 are arranged above the fuel section to measure the temperature rise of the cooling water in the intermediate flow channel 8 in the fuel area; the heat release power of the fuel rod bundle can be obtained by using the cooling water flow measured by an external system connected to the device, and the diversion ratio of the intermediate flow and the internal flow channel 20 using the heat balance method.

[0054] Specific working principle:

[0055] The invention provides a power transient irradiation device suitable for fuel rod bundles. Figure 1 and Figure 2 As shown in the figure, the device is installed in the core area of ​​the research reactor and is part of the fuel power transient test system; the cooling water inlet and outlet, helium inlet and outlet pipes, and nitrogen inlet and outlet of the device are connected to the external equipment of the test system, and the external equipment provides cooling water that meets the test requirements and helium with adjustable pressure ( 3He gas) and nitrogen source. From outside to inside, the main structural parts of the device include a protective tube 1, a pressure tube 3, a shunt tube 9 and an outer tube 5, an inner tube 19, and an air cavity or fluid domain separated by the above structure. The nitrogen cavity 2 between the protective tube 1 and the pressure tube 3 is mainly used for heat preservation and to reduce the heat transfer from the pressure tube 3 to the protective tube 1; at the same time, the nitrogen cavity 2 is connected to external equipment through the nitrogen inlet and outlet, realizing the circulation and quality detection of nitrogen, thereby realizing the online detection of the integrity of the pressure tube 3 (whether there is cooling water leakage). The cooling water in the device is driven by an external device, and flows into the outer flow channel 7 after entering from the cooling water inlet 12, flows from top to bottom to the bottom of the outer tube 5, and then turns back upward, flowing into the middle flow channel 8 and the inner flow channel 20 respectively; the cooling water flows independently in these two flow channels, and converges at the top of the device, and then flows out of the device through the cooling water outlet 13. As for the helium-3 gas, it is also driven by an external device to flow in from the helium inlet pipe 17, flow through the spiral tube helium screen 4, enter the helium outlet pipe 18 at the middle position of the fuel rod bundle through the connecting pipe, and finally flow out of the device.

[0056] A plurality of (usually 5 to 9) fuel rods, i.e., rod-shaped fuel elements 6, are arranged in a circle with equal circumferential spacing, and the positions of the rods are kept fixed by corresponding fixed structures. The spacing between the fuel rods is consistent with the spacing between the fuel rods in the prototype fuel assembly in which they are located. The length of the fuel segment core section can be 30 to 60 cm, and the fuel area is overlapped with the flat area of ​​the axial distribution of the core thermal neutron injection rate. A helium screen with a double-layer tube structure with a filling layer is adopted, and its axial position is basically the same as the fuel segment of the fuel rod, and the length of the helium screen is slightly larger than the length of the fuel segment. In this way, by adopting a compact circular arrangement scheme, multiple fuel rods can be carried at the same time; at the same time, the design of the spiral tube helium screen 4 and the central helium pipeline is adopted, which can achieve a large power jump and effectively reduce the power difference between different fuel rods. In addition, the spiral tube helium screen 4 and the central helium pipeline are both located outside the middle flow channel 8 for cooling the fuel rod bundle, which reduces the influence of the heat release of helium-3 gas and its helium screen structural material on the measurement of the fuel heat release power, and improves the accuracy of the measurement of the fuel rod bundle heat release power. Neither the helium shield nor the central helium pipeline comes into contact with the higher temperature cooling water that cools the fuel rod bundle, which to a certain extent reduces the temperature of the helium pipeline and the tritium helium contained in the pipeline, thereby helping to reduce the penetration and leakage ability of tritium.

[0057] A plurality of thermocouples are arranged below and above the fuel section of the intermediate flow channel 8, respectively, to measure the temperature rise of the cooling water in the fuel area of ​​the intermediate flow channel 8; the heat release power of the fuel rod bundle can be obtained by the heat balance method using the cooling water flow measured by an external system connected to the device, and the diversion ratio of the intermediate flow and the inner flow channel 20 (obtained by fluid mechanics calculation or hydraulic test).

[0058] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A power transient irradiation device suitable for a fuel rod bundle, characterized in that: include: An outer tube (5), wherein the upper and lower ends of the outer tube (5) are both open, and the inner cavity of the outer tube (5) is axially provided with a helium outlet pipe (18); A helical tube helium shield (4), wherein the helical tube helium shield (4) is coaxially wound around the outer side of the outer tube (5), the upper inlet of the helical tube helium shield (4) is connected to a helium inlet pipe (17), the lower outlet of the helical tube helium shield (4) is connected to a lower end of the helium outlet pipe (18), and the upper end of the helium outlet pipe (18) is connected to an external device; The annular region between the outer wall of the helium outlet pipe (18) and the inner wall of the outer pipe (5) is an intermediate flow channel (8) for cooling water to pass through, and a plurality of rod-shaped fuel elements (6) are evenly distributed in an annular direction and at equal intervals in the intermediate flow channel (8); the spacing between adjacent rod-shaped fuel elements (6) is consistent with the spacing between fuel rods in the prototype fuel assembly; Both ends of the fuel section of the rod-shaped fuel element (6) are located between the two ends of the spiral tube helium shield (4).

2. A power transient irradiation device suitable for a fuel rod bundle according to claim 1, characterized in that: When the plurality of rod-shaped fuel elements (6) cannot occupy the entire annular region, the plurality of rod-shaped fuel elements (6) are evenly distributed in an annular direction and at equal intervals on one side of the annular region, and except for the one side of the annular region, the remaining area is closed by a structural component.

3. A power transient irradiation device suitable for a fuel rod bundle according to claim 1, characterized in that: It also comprises a pressure tube (3), wherein the outer tube (5) and the spiral tube helium shield (4) are both located in the chamber of the pressure tube (3), the pressure tube (3) is provided with a cooling water inlet (12), and the cooling water inlet (12) is located above the spiral tube helium shield (4); the lower end of the outer tube (5) is connected to the bottom of the pressure tube (3), and the upper end of the outer tube (5) is connected to the cooling water outlet (13).

4. A power transient irradiation device suitable for a fuel rod bundle according to claim 3, characterized in that: It also comprises a shunt pipe (9), one end of which is connected to the upper end of the outer pipe (5) via an intermediate joint, and the other end of which passes through the pressure pipe (3).

5. The power transient irradiation device suitable for a fuel rod bundle according to claim 3, characterized in that: It also comprises a protection tube (1), the pressure tube (3) and the protection tube (1) being coaxial and arranged in sequence from the inside to the outside, and the chamber between the inside of the protection tube (1) and the outside of the pressure tube (3) being a nitrogen chamber (2).

6. A power transient irradiation device suitable for a fuel rod bundle according to claim 4, characterized in that: It also includes an inner tube (19), the helium outlet tube (18) and the inner tube (19) are coaxial and arranged in sequence from the inside to the outside, and the inner tube (19) is located between the plurality of rod-shaped fuel elements (6); an annular inner flow channel (20) is left between the inner side of the inner tube (19) and the outer side of the helium outlet tube (18), the lower end of the inner flow channel (20) is connected to the bottom of the pressure tube (3), and the upper end of the inner flow channel (20) is connected to the cooling water outlet (13).

7. A power transient irradiation device suitable for a fuel rod bundle according to claim 6, characterized in that: The diverter tube (9), the outer tube (5) and the inner tube (19) all adopt a first double-layer tube structure, and the gap in the first double-layer tube structure is filled with nitrogen.

8. The power transient irradiation device suitable for a fuel rod bundle according to claim 1, characterized in that: The spiral tube helium shield (4), the helium inlet tube (17) and the helium outlet tube (18) all adopt a second double-layer tube structure with a filling layer, the second double-layer tube structure comprises, from the inside to the outside, an inner tube, a sponge-like titanium metal inter-tube filling layer and an outer tube, and the inner tube and the outer tube are both made of stainless steel material with a dense Al2O3 coating.

9. The power transient irradiation device suitable for a fuel rod bundle according to claim 1, characterized in that: The inner side of the outer tube (5) is provided with measuring heads of a plurality of self-powered neutron detectors (16).

10. The power transient irradiation device suitable for a fuel rod bundle according to claim 1, characterized in that: A plurality of thermocouples are arranged above and below the fuel sections of the plurality of rod-shaped fuel elements (6).

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