Indirect heating type fuel rod simulation piece

Abstract

The utility model discloses an indirect heating type fuel rod simulation piece which comprises a cladding tube and an electric heating element, and the cladding tube is a corrosion product deposition test surface; the electric heating element is arranged in the cladding tube and is used for simulating heat generated by a nuclear fission reaction of the fuel pellet; high-purity helium is filled between the cladding tube and the electric heating element, and sealing of the fuel rod simulation piece is achieved through end plug welding at one end of the cladding tube and circumferential welding between the cladding tube and the electric heating element. According to the utility model, the actual structural characteristics and surface material properties of the fuel element are retained to the greatest extent while the surface thermal load state of the pressurized water reactor fuel element is simulated, so that the authenticity of corrosion product deposition test simulation and the reliability of obtaining test data are improved; and the method can also be used for experimental research on scale-caused accelerated corrosion after deposition of surface corrosion products.

Description

Technical Field

[0001] The utility model relates to the technical field of research on corrosion product release, migration and deposition in a reactor system, and particularly relates to an indirectly heated fuel rod simulator. Background Art

[0002] The fouling phenomenon is widespread in the energy industry and has various adverse effects on the stable and reliable operation of the system, and the pressurized water reactor is no exception. Corrosion products of materials such as nickel-based alloys of the heat transfer tubes of the steam generator and stainless steel of the main pipeline in the pressurized water reactor are released into the coolant, and the released corrosion products tend to migrate to the high-temperature area of the reactor core and deposit on the surface of the fuel element cladding. This phenomenon of corrosion product deposition on the surface of the fuel element brings a series of adverse effects to the stable operation of the pressurized water reactor system, including deterioration of the core thermohydraulic characteristics (affecting heat transfer and increasing flow resistance), axial power shift, fouling-induced accelerated corrosion, etc. In severe cases, it may lead to fuel element damage or even induce a reactor shutdown accident. In addition, the corrosion products deposited in the reactor core are easily neutron-activated to form radionuclides under irradiation conditions, thus significantly increasing the radiation field level of the primary loop system during reactor shutdown maintenance. At present, the pressurized water reactor is developing towards continuously improving the safety, reliability and power density of the nuclear reactor and extending the core life. The adverse effects caused by the long-term accumulation of corrosion product deposition may be more obvious. Therefore, studying the deposition behavior of corrosion products on the surface of pressurized water reactor fuel elements is of great significance for the safe and efficient development of nuclear energy.

[0003] Obtaining the fouling on the surface of the pressurized water reactor fuel element is an important prerequisite for studying the corrosion product deposition in the primary loop of the pressurized water reactor. Usually, two methods are adopted: First, obtaining it through a commercial pressurized water reactor; Second, obtaining it through an out-of-pile test loop that simulates the pressurized water reactor environment. The corrosion product migration and deposition test based on the actual pressurized water reactor can collect the corrosion product distribution on the surface of some equipment in the actual reactor to a certain extent. However, due to the strong radioactivity and extreme in-pile conditions, the test cost is high, there are difficulties in sampling and the research process, and the test conditions and test results are limited by the reactor type used, which is not suitable for exploring the influencing factors and laws of corrosion product behavior. Currently, the corrosion product deposition test based on the out-of-pile dynamic water loop is the main research method. The current technological development has been able to simulate the actual situation of the pressurized water reactor well, with high feasibility and relatively low test cost. The test conditions can cover different operating conditions and design ranges, and are suitable for carrying out the exploration of influencing factors and laws of corrosion product deposition and engineering verification tests.

[0004] Nucleate boiling on the surface of the fuel cladding is an important prerequisite and main factor for the deposition of corrosion products. How to prepare a self-heating fuel rod simulator, simulate the heating surface of the fuel cladding, and the nucleate boiling phenomenon is the key to the success or failure of the out-of-pile corrosion product deposition test. At present, most research institutions use directly heated fuel rod simulators to carry out out-of-pile corrosion product deposition tests. Although the preparation process is simple, the properties of the outer surface cladding material may be changed during the processing, so the prototype material and its process characteristics cannot be fully simulated.

[0005] The indirectly heated fuel rod simulator generates heat by arranging electric heating elements inside the cladding and transferring the heat to the surface of the fuel cladding in a uniform heating manner. It can more realistically simulate the thermal load state of the fuel cladding surface, and at the same time can retain the material characteristics of the fuel cladding to the greatest extent, which is very suitable for the study of the deposition behavior of corrosion products. However, the preparation process of the indirectly heated fuel rod simulator is long and the process is complex. At present, domestic research institutions have not carried out the research and development work of indirectly heated fuel rod simulators specifically for corrosion product deposition tests. Therefore, there is an urgent need to develop an indirectly heated fuel rod simulator that can better simulate the characteristics of pressurized water reactor fuel elements. Summary of the Utility Model

[0006] The purpose of the present utility model is to provide an indirectly heated fuel rod simulator, which simulates the thermal load state on the surface of a pressurized water reactor fuel element, and at the same time retains the actual structural characteristics and surface material properties of the fuel element to the greatest extent, and is used to study the deposition characteristics of corrosion products and the scale-induced accelerated corrosion behavior of the cladding material under the multi-field coupling conditions of thermo-fluid-chemistry of the fuel element.

[0007] According to one aspect of the present utility model, there is provided an indirectly heated fuel rod simulator, comprising a fuel cladding tube and an electric heating element, wherein the fuel cladding tube provides a surface for corrosion product deposition tests, and the electric heating element is placed inside the fuel cladding tube and is used to simulate the heat generated by the nuclear fission reaction of the fuel pellets;

[0008] After the electric heating element is placed in the fuel cladding tube, a cavity is formed between the bottom of the electric heating element and the fuel cladding tube, and helium gas is filled in the cavity and sealed.

[0009] Optionally, the electric heating element includes a heating resistance wire, an insulating filling material, and a cladding tube; the heating resistance wire is uniformly distributed in the cladding tube, and the insulating filling material is filled in the gaps inside the cladding tube and compacted;

[0010] The electric heating element is sealed by plug welding with an electric heating element plug.

[0011] Optionally, the cavity is filled with at least 0.5 MPa high-purity helium gas.

[0012] Optionally, the bottom of the fuel cladding tube is pressed into the cladding tube end plug and sealed by the cladding tube end plug weld;

[0013] The upper end of the fuel cladding tube is connected to the electric heating element through the inner and outer tube circumferential welds to complete the overall sealing of the fuel rod simulator.

[0014] Optionally, the heating resistance wires are uniformly distributed in the cladding tube and enter and exit through the non-end plug end of the fuel cladding tube.

[0015] The utility model provides an indirectly heated fuel rod simulator, which realizes the self-heating condition and surface heat flux density simulation during the service of the fuel element, and retains the actual structural characteristics and surface material properties of the fuel element to the greatest extent, improving the authenticity of the corrosion product deposition test simulation and the reliability of obtaining test data.

[0016] The alloy composition and preparation process of the surface cladding of the indirectly heated fuel rod simulator provided by the utility model are consistent with those of the pressurized water reactor prototype, and the material properties of the surface cladding material can be easily obtained during the anatomical inspection process. On the basis of carrying out the corrosion product deposition test, it can be used to carry out the research on fouling-induced accelerated corrosion test, broadening the scope of corrosion test research.

[0017] The indirectly heated fuel rod simulator provided by the utility model is prepared by sealing both ends with welds and filling high-purity helium gas between the fuel cladding tube and the electric heating element. Compared with the prior art, on the one hand, high-purity helium gas can effectively prevent the inner surface of the fuel cladding tube from high-temperature oxidation, ensuring that its corrosion occurs in the outer surface service environment, improving the authenticity of the fouling-induced accelerated corrosion test simulation. On the other hand, filling high-purity helium gas pressure between the fuel cladding tube and the electric heating element can balance the pressure from the high-temperature and high-pressure water in the test environment to a certain extent, improving the use stability of the fuel rod simulator.

[0018] The technical solution of the utility model will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0019] The drawings are used to provide a further understanding of the utility model, and constitute a part of the specification. Together with the embodiments of the utility model, they are used to explain the utility model, and do not constitute a limitation to the utility model. In the drawings:

[0020] Figure 1 It is a schematic structural diagram of the fuel rod simulator provided by the embodiment of the utility model;

[0021] Figure 2 It is an installation schematic diagram of the fuel rod simulator of the embodiment of the utility model;

[0022] Figure 3Schematic diagram of the operation of the fuel rod simulator according to the embodiment of the present invention;

[0023] Among them, 1 - insulating filling material; 2 - circumferential weld of inner and outer pipes; 3 - cladding tube; 4 - heating resistance wire; 5 - electric heating element; 6 - fuel cladding tube; 7 - plug of electric heating element; 8 - helium cavity; 9 - end plug of cladding tube; 10 - weld of end plug of cladding tube; 11 - sealing flange; 12 - outlet of test medium; 13 - fuel rod simulator; 14 - test section cylinder; 15 - inlet of test medium. Specific embodiments

[0024] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0025] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0026] In the present invention, unless otherwise clearly defined and limited, the terms "mounted", "connected", "connected to", "fixed" and other terms should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] The following is a description of the preferred embodiments of the present invention with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not used to limit the present invention.

[0028] The embodiment of the present invention provides an indirectly heated fuel rod simulator, as Figure 1As shown in the figure, the indirectly heated fuel rod simulator of this embodiment includes a fuel cladding tube 6 and an electric heating element 5. The fuel cladding tube 6 provides a surface for corrosion product deposition test. The electric heating element 5 is placed inside the fuel cladding tube 6 and is used to simulate the heat generated by the nuclear fission reaction of the fuel pellets. After the electric heating element 5 is placed inside the fuel cladding tube 6, a cavity 8 is formed between the bottom of the electric heating element 5 and the fuel cladding tube. Helium is filled in the cavity 8 and sealed. Optionally, during sealing, it is sealed by the cladding tube end plug weld 10. The bottom of the fuel cladding tube 6 is pressed into the cladding tube end plug 9 and sealed by the cladding tube end plug weld 10. The upper end of the fuel cladding tube 6 is connected to the electric heating element 5 through the inner and outer tube circumferential weld 2 to complete the overall sealing of the fuel rod simulator.

[0029] As Figure 1 shown in the figure, the electric heating element 5 of this embodiment includes a heating resistance wire 4, an insulating filling material 1, and a cladding tube 3. The heating resistance wire 4 is evenly distributed inside the cladding tube 3, and the voids inside the cladding tube 3 are filled with the insulating filling material 1 and compacted. The electric heating element plug 7 is used for plug welding and sealing of the electric heating element 5.

[0030] The heating resistance wire 4 is evenly distributed inside the cladding tube 3, the voids are filled with the insulating filling material 1 and compacted. Continuing to refer to Figure 1 , the heating resistance wire 4 is evenly distributed inside the cladding tube 3, enters and exits from the non-end plug end of the fuel cladding tube 6, the voids are filled with the insulating filling material 1 and compacted. The heating resistance wire 4 is energized to generate heat and is used to simulate the heat generated by the nuclear fission reaction of the fuel pellets. The cladding tube 3 is prepared with the same material as the fuel cladding tube to achieve weldability between the electric heating element 5 and the fuel cladding tube 6. In addition, by preparing the cladding tube 3 and the electric heating element plug 7 with the same material as the fuel cladding tube 6, the electric heating element 5 is subjected to plug welding and sealing. That is to say, the bottom end of the electric heating element 5 is sealed by the electric heating element plug 7.

[0031] In some alternative embodiments, the cavity 8 between the fuel cladding tube 6 and the electric heating element 5 is filled with at least 0.5 MPa high-purity helium, which not only ensures the uniformity of heat transfer but also prevents excessive oxidation and collapse of the inner surface of the cladding. The cladding tube end plug 9 is pressed into one end of the fuel cladding tube 6 and connected through the cladding tube end plug weld 10, and the other end of the fuel cladding tube 6 is connected to the electric heating element 5 through the inner and outer tube circumferential weld 2 to achieve the sealing of the fuel rod simulator. The indirectly heated fuel rod simulator provided by this embodiment can well simulate the prototype materials and their process characteristics, thus retaining the actual structural characteristics and surface material properties of the fuel element to the greatest extent, and improving the authenticity of the corrosion product deposition test simulation and the reliability of obtaining test data.

[0032] The embodiment of the present utility model also provides a preparation method of an indirectly heated fuel rod simulation component, and the method includes:

[0033] S1. Prepare the electric heating element 5: Determine the power of the electric heating element 5 according to the surface heat flux density requirement, and prepare the electric heating element 5.

[0034] Further, the step of preparing the electric heating element 5 in step S1 includes: determining the power of the electric heating element 5 according to the surface heat flux density requirement; determining the material, size and quantity of the heating resistance wire 4 according to the power, uniformly arranging the heating resistance wire 4 in the cladding tube 3, filling the insulating filling material 1 and then compacting; preparing the cladding tube 3 and the plug 7 with the same material as the fuel cladding tube, and performing plug welding and sealing on the electric heating element 5.

[0035] For example, if the surface heat flux density requirement is Q = 30 W / cm 2 , the length of the heating section L = 30 cm, and the diameter D = 8.36 mm, then Q * L * D * 3.14 = 2.35 KW (heat flux density multiplied by the heating area), that is, the power of the electric heating rod is 2.35 KW. Since the size of the fuel rod simulation component is basically determined, the greater the heat flux density, the greater the power, and then the higher the requirements for the heating resistance wire.

[0036] The working temperature of the heating resistance wire determined by the power, for example, when the heat flux density is 30 W / cm 2 , when the working temperature is less than 1000 °C, use nickel-chromium or iron-chromium-aluminum heating wire, and fill magnesium oxide powder around; the working temperature of the heating resistance wire determined by the power, when the heat flux density is 100 W / cm 2 , when the working temperature is much higher than 1000 °C, the oxidation resistance of nickel-chromium or iron-chromium-aluminum heating resistance wire is insufficient, and a graphite heating rod needs to be used, and BN powder is filled around. The specific design is determined according to specific working requirements, and this embodiment does not limit this.

[0037] S2. Prepare the test unit: Cut the fuel cladding tube 6, and seal one end of the fuel cladding tube 6 by welding the cladding tube end plug 9.

[0038] Further, the step of preparing the test unit in step S2 includes: cutting a tubular sample unit with an appropriate length in the length direction of the fuel cladding tube 6 by using a cutting machine; pressing the cladding tube end plug 9 into one end of the fuel cladding tube 6, and completing the connection between the cladding tube end plug 9 and one end of the fuel cladding tube 6 by means of circumferential welding; wherein, air holes are left on the cladding tube end plug 9.

[0039] S3. Assemble the fuel rod simulation component 13: Insert the electric heating element 5 into the fuel cladding tube 6 to assemble the fuel rod simulation component 13.

[0040] Further, the steps of assembling the fuel rod simulator 13 in step S3 include: inserting the electrical heating element 5 into the fuel cladding tube 6 via the test unit by interference fit, and connecting the electrical heating element 5 and the unsealed end of the fuel cladding tube 6 by circumferential welding; injecting at least 0.5 MPa of high-purity helium gas into the fuel rod simulator through the air hole of the cladding tube end plug 9, and then completing the sealing by spot welding.

[0041] After the above step S3, there is also step S4 of installing the fuel rod simulator 13: machining a tubular test section and assembling the fuel rod simulator 13 into the tubular test section. Further, the specific steps of step S4 of installing the fuel rod simulator include: machining a tubular corrosion product deposition test section, vertically installing the fuel rod simulator 13 at both ends of the test section, and realizing the sealing between the fuel rod simulator 13 and the test section through a seal and a hoop; the fuel rod simulator 13 and the test section together form a fluid channel, and the test medium enters the fluid channel from one side of the test section cylinder 14, flows through the surface of the simulator, and flows out from the other side of the test section cylinder 14.

[0042] During actual use, the fuel cladding tube 6 is placed inside the test section cylinder 14 and serves as the surface for corrosion product deposition test; the fuel cladding tube 6 is a small-diameter thin-walled tube with through holes at both ends, and the inner and outer diameter dimensions are standard dimensions for nuclear power plants, and the alloy composition and preparation process are the same as those of the pressurized water reactor prototype.

[0043] As Figures 2 - 3 shown, the fuel rod simulator 13 is vertically installed at both ends of the test section cylinder 14, and the sealing between the fuel rod simulator 13 and the test section cylinder 14 is realized through a sealing flange 11 and other means; the fuel rod simulator 13 and the test section cylinder 14 together form a fluid channel. During the test, as Figures 2 - 3 indicated by the arrow, the test medium carrying corrosion products enters the fluid channel from the test medium inlet 15, flows through the surface of the fuel rod simulator 13, generates heat by energizing the heating resistance wire 4, realizes the simulation of the heating surface of the fuel element and the nucleate boiling phenomenon, so that the corrosion products are deposited on the outer surface of the fuel cladding tube 6. Subsequently, the test medium flows out from the test medium outlet 12.

[0044] After the test, take out the fuel rod simulator; by carrying out microscopic analysis and chemical analysis of the corrosion product deposition layer on the outer surface of the fuel cladding tube 6, study the corrosion product deposition behavior on the surface of the fuel element; by carrying out microscopic structure characterization and chemical composition analysis of the oxide film generated during the corrosion product deposition process of the fuel cladding tube 6, study the scale-induced accelerated corrosion behavior of the fuel cladding.

[0045] The alloy composition and preparation process of the surface cladding of the indirectly heated fuel rod simulator provided by the embodiment of the present utility model are consistent with those of the pressurized water reactor prototype, and the material properties of the surface cladding material can be easily obtained during the anatomical inspection process. On the basis of carrying out the corrosion product deposition test, it can be used to carry out the research on fouling-induced accelerated corrosion test, broadening the scope of corrosion test research.

[0046] Obviously, those skilled in the art can make various changes and modifications to the present utility model without departing from the spirit and scope of the present utility model. Thus, if these modifications and variations of the present utility model fall within the scope of the claims of the present utility model and its equivalent technologies, the present utility model is also intended to include these changes and modifications.

Claims

1. An indirectly heated fuel rod simulator, characterized in that, It includes a fuel cladding tube (6) and an electric heating element (5). The fuel cladding tube (6) provides a deposition test surface for corrosion products. The electric heating element (5) is placed inside the fuel cladding tube (6) and is used to simulate the heat generated by the nuclear fission reaction of fuel pellets. After the electric heating element (5) is placed inside the fuel cladding tube (6), a cavity (8) is formed between the bottom of the electric heating element (5) and the fuel cladding tube (6). Helium gas is filled in the cavity (8) and sealed.

2. The indirectly heated fuel rod simulator according to claim 1, characterized in that, The electric heating element (5) includes a heating resistance wire (4), an insulating filling material (1), and a cladding tube (3). The heating resistance wire (4) is distributed inside the cladding tube (3), and the insulating filling material (1) is filled in the voids inside the cladding tube (3) and compacted.

3. The indirectly heated fuel rod simulator according to claim 2, characterized in that, An electric heating element plug (7) is used to perform plug welding and sealing on the electric heating element (5).

4. The indirectly heated fuel rod simulator according to claim 1, wherein At least 0.5 MPa of high-purity helium gas is filled in the cavity (8).

5. The indirectly heated fuel rod simulator according to any one of claims 1-4, characterized in that The bottom of the fuel cladding tube (6) is pressed into a cladding tube end plug (9) and connected and sealed through a cladding tube end plug weld (10).

6. The indirectly heated fuel rod simulator according to claim 5, wherein The upper end of the fuel cladding tube (6) is connected to the electric heating element (5) through an inner and outer tube circumferential weld (2) to complete the overall sealing of the fuel rod mock-up.

7. The indirectly heated fuel rod simulator according to claim 5, characterized in that, Air holes are provided on the cladding tube end plug (9).

8. The indirectly heated fuel rod simulator according to claim 2, wherein The heating resistance wire (4) is uniformly distributed inside the cladding tube (3) and enters and exits through the non-end plug end of the fuel cladding tube (6).

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