A fuel cladding tube irradiation internal pressure creep test piece and method

Abstract

A fuel cladding tubular irradiation internal pressure creep test piece includes a sample cladding, a first support, a second support, an isothermal body and a tubular sample. The sample cladding forms a closed accommodating cavity, the tubular sample is fixedly connected in the accommodating cavity through the first support and the second support, and the isothermal body covers the surface of the tubular sample between the first support and the second support; the tubular sample is filled with pressurized gas to provide an internal pressure load. The test piece realizes the loading of the internal pressure load by filling the internal pressurized gas, so that the test piece can be simultaneously neutron irradiated and loaded with the internal pressure load during the test, so as to meet the actual service conditions of the fuel cladding tubular and improve the test accuracy. The present invention also provides a fuel cladding tubular irradiation internal pressure creep test method.

Description

Technical Field

[0001] The invention belongs to the field of nuclear power, and in particular relates to an irradiation internal pressure creep test piece and a method for a fuel cladding tube. Background Art

[0002] In nuclear power facilities, the fuel cladding in the reactor must continue to withstand the effects of neutron irradiation, high temperature and high pressure during service. The creep behavior of the fuel cladding under neutron irradiation conditions will have an important impact on the reliability and safety of the fuel assembly. Under long-term service conditions, the creep behavior of the fuel cladding under neutron irradiation conditions may cause deformation or even rupture of the fuel rods, seriously affecting the safety of the reactor. Therefore, during the research and development stage, it is necessary to test the high-temperature creep behavior of the fuel rod cladding material under neutron irradiation conditions to verify the creep behavior data under different neutron injections, temperatures and pressures. The existing technical solution applies internal pressure loads and high temperature environments to the pipes outside the reactor, and then sends them into the reactor for neutron irradiation after reaching certain test conditions. This is not completely consistent with the actual service conditions of the fuel cladding, and it is difficult to verify the equivalence of the test results with the actual creep behavior of the fuel cladding during service in the reactor. Therefore, providing a test piece that can simultaneously undergo high temperature, high pressure and neutron irradiation has positive significance for optimizing the design of the fuel cladding and improving the reliability of the fuel cladding. Summary of the invention

[0003] The purpose of the present invention is to provide a fuel cladding tube irradiation internal pressure creep test piece, so that the test process is closer to the actual service state. The present invention also provides a fuel cladding tube irradiation internal pressure creep test method.

[0004] According to an embodiment of one aspect of the present invention, there is provided a fuel cladding tube irradiation internal pressure creep test piece, comprising a sample cladding, a first support, a second support, an isothermal body and a tube sample. The sample cladding forms a closed accommodating cavity, and the first support and the second support are fixed in the accommodating cavity; the tube sample is configured as a fuel cladding tube to be tested with both ends welded and closed, and the interior of the tube sample contains pressurized gas to provide an internal pressure load; the two ends of the tube sample are respectively connected and fixed to the first support and the second support; the isothermal body covers the outer surface of the tube sample located between the first support and the second support.

[0005] The test piece is loaded with internal pressure by filling gas, thereby achieving the stress requirements of the internal pressure creep test; the test piece can be loaded as a whole into the test reactor for irradiation treatment, thereby achieving simultaneous loading of internal pressure load and neutron irradiation, which is more in line with the actual service status of the fuel cladding tube.

[0006] Furthermore, in some embodiments, the containing chamber is filled with an inert gas.

[0007] Furthermore, in some embodiments, the inert gas includes one or a combination of helium, neon, and nitrogen.

[0008] Furthermore, in some embodiments, the manufacturing material of the first support and the second support includes one or a combination of aluminum oxide, zirconium oxide, and silicon carbide.

[0009] Furthermore, in some embodiments, the manufacturing material of the isothermal body includes one or a combination of copper, graphite, and aluminum alloy.

[0010] Furthermore, in some embodiments, a gap of 1 mm to 4 mm is provided between the isothermal body and the sample enclosure.

[0011] Furthermore, in some embodiments, a gap of 0.3 mm to 0.7 mm is provided between the pipe sample and the isothermal body.

[0012] Furthermore, in some embodiments, the first support is provided with a through hole, and the second support is provided with a blind hole, so as to allow the pipe sample to pass through the first support, be inserted into and fixed to the second support.

[0013] According to another aspect of the present invention, there is provided a method for irradiation internal pressure creep test of a fuel cladding tube. The method uses the irradiation internal pressure creep test piece of the fuel cladding tube provided in any of the above embodiments, and comprises the following steps:

[0014] Perform simulation calculations based on the test reactor parameters to determine the isothermal body size required to make the fuel cladding tube to be tested reach the temperature and pressure of the test design, and manufacture the corresponding isothermal body;

[0015] Providing the fuel cladding tube to be tested, filling the interior of the fuel cladding tube to be tested with pressurized gas and welding both ends to seal, inserting the tube sample into the isothermal body and loading it into the sample cladding;

[0016] The fuel cladding tube irradiation internal pressure creep test piece is integrally loaded into the irradiation channel of the test reactor for environmental loading to complete the internal pressure creep performance test.

[0017] Furthermore, in some embodiments, the simulation calculation is performed using ANSYS software. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the cross-sectional structure of a fuel cladding tube irradiation internal pressure creep test piece in one embodiment;

[0019] Figure 2 Schematic diagram of the cross-sectional structure of an isothermal body in one embodiment.

[0020] Meaning of the reference symbols:

[0021] 1-sample cladding; 2-first support; 3-second support; 4-isothermal body; 5-inert gas layer; 6-pipe sample; 7-mounting hole; 8-upper end plug.

[0022] The purpose of the above drawings is to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. For the sake of simplicity, the above drawings only schematically illustrate the structures related to the technical features of the present invention, and do not strictly follow the actual proportions to draw the complete structure and all details. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0024] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0025] In the description of this article, unless otherwise clearly specified and limited, the technical terms "installed", "connected", "connected" and the like should be understood in a broad sense, which can be a movable connection, a fixed connection or an integral connection. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of this application can be understood according to specific circumstances.

[0026] In the description of this document, terms indicating orientation or positional relationships, such as "up", "down", "left", "right", "horizontal", "vertical", "height", "length", and "width", are intended to accurately describe the embodiments and simplify the description, but are not intended to limit the parts or structures involved to have a specific orientation, be installed or operate in a specific orientation, and should not be construed as a limitation on the embodiments in this document.

[0027] In the description of this article, the terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order or primary and secondary relationship of the described technical features. In the description of this article, the meaning of "plurality" is at least two.

[0028] There are a large number of pressure pipe structures in the reactors of nuclear power facilities, such as the high-pressure pipelines in the primary circuit of the pressurized water reactor and the fuel rod cladding in the reactor core. These pipes play an important role in the safe operation of the reactor, as they support, carry, position, and provide fluid channels or solid component assembly interfaces. Due to the harsh operating conditions of the reactor core, these pipes need to serve for a long time under high temperature, high pressure and high neutron irradiation conditions. The evaluation of the durability of pipes under high temperature irradiation conditions has become an important issue in reactor safety design and management.

[0029] During the service in the reactor, the fuel rod cladding tubes will creep due to continuous neutron irradiation and high temperature stress. If the creep exceeds the limit during service, it may cause deformation or even rupture of the fuel rod cladding, which will not only fail to achieve the expected design function, but also may cause safety accidents. Therefore, conducting neutron irradiation and internal pressure creep tests on fuel rod cladding tubes has become a necessary step in the development of reactor fuel rod cladding tubes. Especially before being used in commercial reactors, it is necessary to conduct verification tests on fuel rod cladding tubes under different combinations of neutron injection rates, temperatures and stress conditions in the test reactor to obtain irradiation creep data to verify material properties and design solutions.

[0030] At present, the conventional test scheme is to load the test environment independently, that is, first examine the internal pressure creep performance of the tube under the internal pressure load of the reactor external component and the high temperature environment, and then load the tube into the reactor for neutron irradiation after certain conditions are met, and take it out to complete the test after reaching the predetermined irradiation dosage. However, in this test scheme, the internal pressure creep loading is separated from the neutron irradiation, which cannot fully restore the real service conditions of the fuel rod cladding tube, and it is difficult to verify the equivalence of the test results and the creep behavior of the fuel rod cladding tube during in-core service, which has limited guiding significance for the design and optimization of the fuel cladding tube.

[0031] In order to solve the above problems, an embodiment of one aspect of the present invention provides a fuel cladding tube irradiation internal pressure creep test piece. The test piece has a structure as follows Figure 1 As shown, it includes a sample shell 1, which is cylindrical in shape as a whole and has a closed accommodating cavity formed inside, in which a first support 2 and a second support 3 are arranged; a pipe sample 6 is installed in the accommodating cavity, and the two ends of the pipe sample 6 are respectively connected and fixed to the first support 2 and the second support 3; the part of the pipe sample 6 located between the first support 2 and the second support 3 is passed through the isothermal body 4, and the isothermal body 4 covers the surface of the pipe sample 6; the pipe sample 6 is filled with high-pressure gas, and the gas pressure provides the internal pressure load in the internal pressure creep test. The gas pressure in the pipe sample 6 is determined according to the load design requirements of the internal pressure creep test, and the gas filled can be helium, neon or nitrogen.

[0032] Specifically, in a preferred embodiment, the containing cavity is filled with an inert gas to provide heat insulation. In different embodiments, the inert gas may be one or a mixture of helium, neon, and nitrogen. The sample envelope 1 itself may be made of nuclear grade aluminum alloy, pure aluminum, stainless steel, or nickel-based alloy.

[0033] The first support 2 and the second support 3 are used to provide end fixation for the pipe sample 6 and also play a role in heat preservation and heat insulation. In some embodiments, a through hole is provided on the first support 2 and a blind hole is provided on the second support 3. When installing the pipe sample 6, the pipe sample 6 is inserted through the through hole on the first support 2 and the isothermal body 4 and into the blind hole of the second support 3 to achieve installation and fixation. During the test, if the pipe sample 6 undergoes axial thermal expansion or radiation growth, the deformation generated is absorbed by allowing the pipe sample 6 to extend toward one end of the first support 2.

[0034] In other embodiments, the through hole on the first support 2 can also be replaced by a blind hole. During installation, the pipe sample 6 is installed first and then the first support 2 covers the end of the pipe sample 6, so that the end of the pipe sample 6 is inserted into the blind hole to achieve installation and fixation.

[0035] The first support 2 and the second support 3 should have sufficient strength under high temperature irradiation conditions and good thermal insulation properties. In different embodiments, they can be made of one or a combination of different materials including alumina, zirconium oxide or silicon carbide ceramic materials.

[0036] The function of the isothermal body 4 is to maintain uniform temperature distribution of the pipe sample 6 in the axial direction, so the isothermal body 4 needs to have good thermal conductivity. In different embodiments, the isothermal body is made of one or a combination of pure copper, graphite or aluminum alloy. In one embodiment, the cross-sectional structure of the isothermal body 4 is as follows: Figure 2 As shown, three mounting holes 7 are evenly spaced on the cross section of the isothermal body 4, and the positions of the mounting holes 7 correspond to the positions of the through holes / blind holes on the first support 2 and the second support 3 for mounting the tubular sample 6. A gap of 1mm-4mm (single side) is reserved between the isothermal body 4 and the sample cladding 1 to accommodate the thermal expansion of the isothermal body during the test and to provide space for accommodating inert gas. A difference of 0.2mm-0.5mm is reserved between the aperture of the mounting hole 7 of the isothermal body 4 and the outer diameter of the tubular sample 6, so that a gap of 0.2mm-0.5mm (single side) is formed when the tubular sample 6 is inserted into the mounting hole 7 to accommodate the thermal expansion of the tubular sample 6 during the test. In other embodiments, according to the test design requirements or the size of the irradiation channel of the test reactor, the number of tubular samples installed in a test piece can also be one or more.

[0037] In a preferred embodiment, using a structure such as Figure 1 , Figure 2The process of conducting the irradiation internal pressure creep test of the fuel cladding tube shown in the figure is as follows:

[0038] Provide the fuel cladding pipe to be tested. Depending on the test object, the fuel cladding pipe can be a zirconium alloy pipe or a heat-resistant stainless steel pipe of different specifications. Install end plugs at both ends of the fuel cladding pipe, one end is the lower end plug, and the other end is the upper end plug 8. After welding and sealing, high-pressure helium is filled into the pipe from one side of the upper end plug 8 and then welded and sealed to obtain a pipe sample 6. The inflation pressure is determined according to the load requirements of the internal pressure creep test. When inflated at room temperature, the inflation pressure is lower than the design pressure under the test conditions.

[0039] Next, a nuclear-grade 6061 aluminum alloy sample cladding 1 is provided. The sample cladding 1 is cylindrical, with an axial length of 250 mm, a bottom thickness of 6 mm, a side wall thickness of 3 mm, and an outer diameter of 39 mm. A second support 3 is installed at the bottom of the sample cladding 1. The second support 3 is made of alumina. Three blind holes evenly arranged in the circumference are provided on the second support 3. The inner diameter of the blind holes is 9.5 mm and the depth is 15 mm, so as to allow the lower end plug of the pipe sample 6 to be inserted and fixed, and at the same time separate the pipe sample 6 from the bottom of the sample cladding 1 to prevent heat from being conducted to the bottom of the sample cladding 1. Furthermore, in some embodiments, the second support 3 has an axial thickness of 21 mm, and a depression with a depth of 3 mm and a diameter of 29 mm is opened at the bottom to further reduce the contact area with the sample cladding 1 and enhance the thermal insulation effect.

[0040] ANSYS software is used for simulation analysis to calculate the heat transfer resistance of the isothermal body 4 that can meet the test conditions under the test conditions of 300°C, and then determine the structural size information that the isothermal body 4 needs to meet. The isothermal body 4 is manufactured according to the calculation results. Subsequently, the isothermal body 4 is installed. The isothermal body 4 is made of pure copper, with an outer diameter of 30 mm and a height of 74 mm. Three axially penetrating mounting holes 7 with a diameter of 10.5 mm are processed in the isothermal body 4, and the mounting holes 7 are aligned with the blind holes on the second support 3 respectively.

[0041] Next, install the first support 2, which is made of alumina and has an axial height of 21 mm. It is provided with three through holes with an inner diameter of 9.5 mm to allow the pipe sample 6 to penetrate, and at the same time allow the pipe sample 6 to extend through the first support 2 to release strain during axial thermal expansion and radiation growth. The positions of the through holes are aligned with the blind holes of the second support 3 and the mounting holes 7 of the isothermal body 4, respectively.

[0042] Next, insert one end of the lower end plug of the tubular sample 6 through the through hole of the first support 2, so that the tubular sample 6 passes through the first support 2 and the isothermal body 4 in sequence, and is inserted and fixed in the blind hole of the second support 3. After the tubular sample 6 is inserted, a 0.5mm gas gap (single-side gap 0.25mm) is left on the side between the tubular sample 6 and the isothermal body 4 to accommodate the subsequent thermal expansion, irradiation growth and creep deformation of the tubular sample 6. Helium is filled into the sample cladding 1 to form an inert gas layer 5 in the gap between the isothermal body 4 and the sample cladding 1 (single-side gap 1.5mm), and finally a top cover is installed on the upper end of the sample cladding 1 and welded closed, wherein the thickness of the top cover is 14mm, and the assembly of the irradiation internal pressure creep test piece of the fuel cladding tube is completed.

[0043] In different embodiments, the pressures in different pipe samples 6 in the same test piece can be the same or different; the materials and size specifications of different pipe samples 6 in the same test piece can also be the same or different. Setting different pipe samples 6 in the same test piece to the same conditions can obtain multiple sets of parallel data for verification, so as to reduce the influence of random errors on the test results; and setting different materials, sizes or internal pressure loads of different pipe samples 6 in the same test piece to different, it is possible to obtain multiple test results representing different test conditions in the same test, or provide control test samples, thereby improving the test efficiency.

[0044] Finally, the irradiation internal pressure creep test piece of the fuel cladding tube is sent into the irradiation channel of the test reactor to receive the designed dose of neutron irradiation, and at the same time, the internal part of the tube sample 6 is heated and pressurized to generate the internal pressure load required by the test design, and the neutron irradiation and internal pressure creep synchronous loading test is carried out. After reaching the preset test time, the test piece is taken out of the irradiation channel of the test reactor, and the tube sample 6 is characterized and evaluated, so as to obtain the irradiation internal pressure creep performance test results of the fuel cladding tube.

[0045] The irradiated internal pressure creep test piece of the fuel cladding tube provided in the above-mentioned embodiment can realize the synchronous loading of neutron irradiation and internal pressure load, restore the real service conditions of the fuel cladding tube, and improve the accuracy of the test evaluation; the test piece has a simple structure and low manufacturing cost, and can be tested directly in the test reactor without rebuilding a new test circuit or modifying the original circuit.

[0046] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, the optimization or equivalent replacement of the part structure or method steps involved, and the combination of implementation methods in different embodiments without conflict of structure and principle, all fall within the protection scope of the present invention.

Claims

1. A fuel cladding tube irradiation internal pressure creep test piece, characterized in that: It includes a sample cladding, a first support, a second support, an isothermal body and a pipe sample, wherein: The sample shell forms a closed accommodating cavity, and the first support and the second support are fixed in the accommodating cavity; The pipe sample is configured as a fuel cladding pipe to be tested with both ends welded and closed, and the interior of the pipe sample contains pressurized gas, which is filled at room temperature and heated and pressurized in the irradiation channel to provide an internal pressure load; The two ends of the pipe sample are respectively connected and fixed to the first support and the second support; the isothermal body covers the outer surface of the pipe sample located between the first support and the second support.

2. The irradiation internal pressure creep test piece for fuel cladding tube according to claim 1, characterized in that: The accommodating chamber is filled with inert gas.

3. The irradiation internal pressure creep test piece for fuel cladding tube according to claim 2, characterized in that: The inert gas includes one or a combination of helium, neon and nitrogen.

4. The irradiation internal pressure creep test piece for fuel cladding tube according to claim 1, characterized in that: The manufacturing material of the first support and the second support includes one or a combination of aluminum oxide, zirconium oxide, and silicon carbide.

5. The irradiation internal pressure creep test piece for fuel cladding tube according to claim 1, characterized in that: The manufacturing material of the isothermal body includes one or a combination of copper, graphite, and aluminum alloy.

6. The irradiation internal pressure creep test piece for fuel cladding tube according to claim 5, characterized in that: A gap of 1 mm to 4 mm is provided between the isothermal body and the sample cladding.

7. The irradiation internal pressure creep test piece for fuel cladding tube according to claim 5 or 6, characterized in that: A gap of 0.2 mm to 0.5 mm is provided between the pipe sample and the isothermal body.

8. The irradiation internal pressure creep test piece for fuel cladding tube according to claim 1, characterized in that: The first support is provided with a through hole, and the second support is provided with a blind hole, so as to allow the pipe sample to pass through the first support, be inserted into the second support and be fixed to the second support.

9. A fuel cladding tube irradiation internal pressure creep test method, characterized in that: The fuel cladding tube irradiation internal pressure creep test piece according to any one of claims 1 to 8 is used, and the steps are as follows: Perform simulation calculations based on the test reactor parameters to determine the isothermal body size required to make the fuel cladding tube to be tested reach the temperature and pressure designed for the test, and manufacture the corresponding isothermal body; Providing the fuel cladding tube to be tested, filling the interior of the fuel cladding tube to be tested with pressurized gas and welding both ends to seal, inserting the tube sample into the isothermal body and loading it into the sample cladding; The fuel cladding tube irradiation internal pressure creep test piece is integrally loaded into the irradiation channel of the test reactor for environmental loading to complete the internal pressure creep performance test.

10. The irradiation internal pressure creep test method for fuel cladding tubes according to claim 9, characterized in that: The simulation calculations were performed using ANSYS software.

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