Fuel element for high-temperature gas cooled reactor and preparation method of fuel element

Abstract

The invention belongs to the technical field of dispersion fuel elements, and particularly relates to a fuel element for a high-temperature gas cooled reactor and a preparation method of the fuel element. The invention relates to a fuel element for a high-temperature gas cooled reactor. The fuel element for the high-temperature gas cooled reactor structurally comprises a graphite layer, an inner zirconium carbide layer, a TRISO fuel bearing layer, an outer zirconium carbide layer and a protective layer in sequence from inside to outside. The fuel element for the high-temperature gas cooled reactor has the beneficial effects that the fuel element for the high-temperature gas cooled reactor is of a multi-layer composite structure design and has high corrosion resistance and compressive strength.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of dispersion fuel elements, and particularly relates to a fuel element for a high-temperature gas-cooled reactor and a preparation method thereof. BACKGROUND

[0002] In the development process of the high-temperature gas-cooled reactor, the performance of the fuel element plays a key role in the safe, economic and efficient operation of the reactor. The traditional fuel element structure still has certain limitations in the operation process of the advanced reactor, and has deficiencies in resisting high-temperature corrosion and diffusion of fission products. When the high-temperature gas-cooled reactor is operated, the coolant is usually helium, and even if the purity of helium is high, there may still be trace impurities in the high-temperature environment, which will chemically react with the fuel element and erode the element structure. At the same time, various products produced by fuel fission have different chemical activity and diffusion characteristics, and part of the fission products will diffuse to the outside of the fuel element, not only polluting the coolant, but also affecting the normal operation and safety of the reactor.

[0003] In addition, in terms of neutron economy, the traditional fuel element is difficult to achieve efficient utilization and precise control of neutrons. With the increase of reactor power and the extension of operation period, it becomes increasingly important to optimize the neutron spectrum and reduce neutron leakage, which leads to the fact that the current prismatic fuel element structure cannot fully meet the requirements of advanced reactors for neutron utilization efficiency. Moreover, in terms of mechanical performance, the existing fuel element is prone to structural deformation, crack propagation and other problems when subjected to high temperature, high pressure and stress generated by irradiation, which affects the service life and reliability of the fuel element. Therefore, it is urgent to develop a prismatic fuel element with a new structure. SUMMARY

[0004] The application provides a fuel element for a high-temperature gas-cooled reactor and a preparation method thereof, aiming to solve the problems of weak corrosion resistance, low neutron utilization rate and poor mechanical performance of the existing fuel element for a high-temperature gas-cooled reactor.

[0005] The first aspect of the application provides a fuel element for a high-temperature gas-cooled reactor, which comprises, from inside to outside, a graphite layer, an inner zirconium carbide layer, a TRISO fuel bearing layer, an outer zirconium carbide layer and a protective layer.

[0006] According to some embodiments of the fuel element for a high-temperature gas-cooled reactor, the TRISO fuel bearing layer comprises graphite and TRISO fuel.

[0007] According to some embodiments of the fuel element for a high-temperature gas-cooled reactor, the protective layer comprises graphite and carbon fibers.

[0008] According to some embodiments of the fuel element for a high-temperature gas-cooled reactor, the mass ratio of the graphite and the carbon fibers is (8-10):1.

[0009] According to some embodiments of the fuel element for high temperature gas-cooled reactor provided in the application, the thickness of the graphite layer is 0.5-1 mm.

[0010] According to some embodiments of the fuel element for high temperature gas-cooled reactor provided in the application, the thickness of the inner layer of zirconium carbide is 0.2-0.5 mm.

[0011] According to some embodiments of the fuel element for high temperature gas-cooled reactor provided in the application, the thickness of the TRISO fuel bearing layer is 6-12 mm.

[0012] According to some embodiments of the fuel element for high temperature gas-cooled reactor provided in the application, the thickness of the outer layer of zirconium carbide is 0.2-0.5 mm.

[0013] According to some embodiments of the fuel element for high temperature gas-cooled reactor provided in the application, the thickness of the protective layer is 1-2 mm.

[0014] According to some embodiments of the fuel element for high temperature gas-cooled reactor provided in the application, the fuel element for high temperature gas-cooled reactor is a prismatic fuel element.

[0015] The second aspect of the application provides a preparation method of the fuel element for high temperature gas-cooled reactor according to the first aspect of the application, comprising the following steps:

[0016] (1) depositing a ZrC layer on the outer surface of the graphite tube by chemical vapor deposition to form an inner layer of zirconium carbide;

[0017] (2) mixing graphite and TRISO fuel to obtain a middle layer slurry; coating the middle layer slurry on the inner layer of zirconium carbide, and then performing cold isostatic pressing and sintering treatment to obtain a TRISO fuel bearing layer;

[0018] (3) depositing a ZrC layer on the surface of the TRISO fuel bearing layer by chemical vapor deposition to form an outer layer of zirconium carbide;

[0019] (4) mixing graphite and carbon fibers to obtain a protective layer slurry; coating the protective layer slurry on the outer layer of zirconium carbide, and then sequentially performing die pressing, sintering and graphitization treatment to obtain the fuel element for high temperature gas-cooled reactor.

[0020] According to some embodiments of the preparation method of the fuel element for high temperature gas-cooled reactor provided in the application, in steps (1) and (3), the temperature of the chemical vapor deposition is independently 1500-1800℃, and the pressure of the chemical vapor deposition is independently 5-10 kPa.

[0021] According to some embodiments of the method for preparing the fuel element for a high-temperature gas-cooled reactor, in step (2), the sintering temperature is 2000-2200℃, and the sintering time is 1.5-2.5h.

[0022] According to some embodiments of the method for preparing the fuel element for a high-temperature gas-cooled reactor, in step (4), the sintering temperature is 2050-2250℃, and the sintering time is 2-3h.

[0023] According to some embodiments of the method for preparing the fuel element for a high-temperature gas-cooled reactor, in step (4), the graphitization temperature is 500-1150℃, and the graphitization time is 1-3h.

[0024] The beneficial effects of the present application include that the fuel element for a high-temperature gas-cooled reactor has a multi-layer composite structure design, and has high corrosion resistance and compressive strength. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 FIG. 1 is a structural schematic diagram of a cross section of the fuel element for a high-temperature gas-cooled reactor according to Embodiment 1 of the present application;

[0026] In the figure, 1 is a graphite layer, 2 is an inner layer of zirconium carbide, 3 is a TRISO fuel carrier layer, 4 is an outer layer of zirconium carbide, and 5 is a protective layer. DETAILED DESCRIPTION

[0027] The embodiments of the present application are described in detail below, and the examples of the embodiments are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0028] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0029] The embodiments of the present application provide a fuel element for a high-temperature gas-cooled reactor, which has a structure including, from inside to outside, a graphite layer, an inner layer of zirconium carbide, a TRISO fuel carrier layer, an outer layer of zirconium carbide, and a protective layer.

[0030] In some embodiments of the present application, the TRISO fuel bearing layer comprises graphite and TRISO fuel. In the TRISO fuel bearing layer, the TRISO fuel particles are uniformly dispersed in the graphite, and the graphite matrix serves to support and protect the TRISO fuel particles. In addition, the graphite matrix is also a good neutron moderator. The center of the TRISO fuel particle is a fuel core, usually low-enrichment uranium dioxide (UO2), and the surface is coated with a four-layer structure of low-density pyrolytic carbon, high-density isotropic pyrolytic carbon, SiC, and high-density isotropic pyrolytic carbon in turn, which can effectively block the release of fission products.

[0031] In some embodiments of the present application, the protective layer comprises graphite and carbon fibers; the protective layer compounded by graphite and carbon fibers has good mechanical strength and oxidation resistance, which can protect the internal structure of the fuel element from the external environment, while ensuring the overall structural stability of the fuel element.

[0032] In some embodiments of the present application, the mass ratio of the graphite and the carbon fibers is (8-10):1, for example, 8:1, 8.5:1, 9:1, 9.5:1, 10:1, etc.

[0033] In some embodiments of the present application, the thickness of the graphite layer is 0.5-1mm; for example, 0.5mm, 0.8mm, 0.9mm, 1mm, etc.

[0034] In some embodiments of the present application, the thickness of the inner layer of zirconium carbide is 0.2-0.5mm; for example, 0.2mm, 0.3mm, 0.4mm, 0.5mm, etc.

[0035] In some embodiments of the present application, the thickness of the TRISO fuel bearing layer is 6-12mm; for example, 6mm, 8mm, 10mm, 12mm, etc.

[0036] In some embodiments of the present application, the thickness of the outer layer of zirconium carbide is 0.2-0.5mm; for example, 0.2mm, 0.3mm, 0.4mm, 0.5mm, etc.

[0037] In some embodiments of the present application, the thickness of the protective layer is 1-2mm; for example, 1mm, 1.2mm, 1.5mm, 1.8mm, 2mm, etc.

[0038] In some embodiments of the present application, the fuel element for high-temperature gas-cooled reactors is a prismatic fuel element.

[0039] The embodiments of the present application also provide a preparation method of the fuel element for high-temperature gas-cooled reactors of the first aspect of the present application, comprising the following steps:

[0040] (1) depositing a ZrC layer on the outer surface of the graphite tube by chemical vapor deposition to form an inner zirconium carbide layer;

[0041] (2) mixing graphite and TRISO fuel to obtain a middle layer slurry; coating the middle layer slurry on the inner zirconium carbide layer, and then performing cold isostatic pressing and sintering to obtain a TRISO fuel bearing layer;

[0042] (3) depositing a ZrC layer on the surface of the TRISO fuel bearing layer by chemical vapor deposition to form an outer zirconium carbide layer;

[0043] (4) mixing graphite and carbon fibers to obtain a protective layer slurry; coating the protective layer slurry on the outer zirconium carbide layer, and then performing mold pressing, sintering and graphitization to obtain the fuel element for the high-temperature gas cooled reactor.

[0044] The preparation method described in the present application forms a firm bonding interface between adjacent layers at high temperature through atomic mutual diffusion, ensures that delamination does not occur between the layers in harsh environments such as high temperature and irradiation, and guarantees the structural integrity of the fuel element.

[0045] In some embodiments of the present application, in steps (1) and (3), the temperature of the chemical vapor deposition is independently 1500-1800℃, for example 1500℃, 1550℃, 1600℃, 1700℃, 1800℃, etc., and the pressure of the chemical vapor deposition is independently 5-10kPa, for example 5kPa, 6kPa, 7kPa, 9kPa, 10kPa, etc. The zirconium carbide layer has a high melting point, excellent corrosion resistance and a low neutron absorption cross section. In the high-temperature gas cooled reactor environment, the zirconium carbide layer can effectively block the erosion of impurities in the coolant on the internal structure, protecting the TRISO particle fuel in the middle layer. In addition, zirconium carbide has a certain moderation and reflection effect on neutrons, which helps to optimize the neutron spectrum and improve the neutron utilization efficiency.

[0046] In some embodiments of the present application, in step (2), the sintering temperature is 2000-2200℃, for example 2000℃, 2100℃, 2200℃, etc., and the sintering time is 1.5-2.5h, for example 1.5h, 2.0h, 2.2h, 2.5h, etc. Sintering makes the graphite matrix more dense, enhancing its mechanical properties and thermal conductivity.

[0047] In some embodiments of the present application, in step (4), the sintering temperature is 2050-2250℃, for example 2050℃, 2100℃, 2200℃, 2250℃, etc., and the sintering time is 2-3h, for example 2h, 2.2h, 2.5h, 2.8h, 3h, etc.

[0048] In some embodiments of the present application, in step (4), the temperature of the graphitization treatment is 500-1150℃, such as 500℃, 800℃, 930℃, 980℃, 1100℃, 1150℃, etc., and the time of the graphitization treatment is 1-3h, such as 1h, 2h, 3h, etc.

[0049] The technical solutions of the present application are further described below in combination with specific embodiments.

[0050] Embodiment 1

[0051] A method for preparing a fuel element for a high-temperature gas-cooled reactor, comprising the following steps:

[0052] (1) High-purity graphite powder with a particle size of 50μm is selected, and is molded under a pressure of 20MPa and calcined at 2500℃ to obtain a graphite layer; zirconium tetrachloride and methane with a mass ratio of 1:4 are deposited on the surface of the graphite layer by chemical vapor deposition at 1650℃ and 10KPa for 3.5h to form an inner layer of zirconium carbide;

[0053] (2) The graphite and TRISO fuel are mixed to obtain a middle layer slurry, which is coated on the inner layer of zirconium carbide, and cold isostatic pressing is performed under a pressure of 160MPa, followed by high-temperature sintering at 2100℃ for 2h to obtain a TRISO fuel bearing layer;

[0054] (3) Zirconium tetrachloride and methane with a mass ratio of 1:4 are deposited on the surface of the TRISO fuel bearing layer by chemical vapor deposition at 1650℃ and 10KPa for 3.5h to form an outer layer of zirconium carbide;

[0055] (4) Graphite and carbon fibers with a mass ratio of 9:1 are mixed to obtain a protective layer slurry, which is coated on the outer layer of zirconium carbide, and is molded under a pressure of 25MPa, followed by sintering treatment at a temperature of 2200℃ for 2h; then graphitization treatment is performed at a temperature of 500℃ for 2h to obtain a prismatic fuel element for a high-temperature gas-cooled reactor with a graphite layer thickness of 0.6mm, an inner layer of zirconium carbide thickness of 0.2mm, a TRISO fuel bearing layer thickness of 8mm, an outer layer of zirconium carbide thickness of 0.2mm, and a protective layer thickness of 1mm.

[0056] Embodiment 2

[0057] The method for preparing the fuel element for a high-temperature gas-cooled reactor described in Embodiment 2 differs from that of Embodiment 1 only in that the mass ratio of graphite and carbon fibers in the protective layer during the preparation process of the fuel element for a high-temperature gas-cooled reactor described in Embodiment 2 is 10:1.

[0058] The specific operation steps include:

[0059] (1) high-purity graphite powder with a particle size of 50 μm is selected, and is molded under a pressure of 20 MPa, and is calcined at 2500°C to obtain a graphite layer; zirconium tetrachloride and methane with a mass ratio of 1:4 are deposited on the surface of the graphite layer by chemical vapor deposition under the conditions of 1650°C and 10 KPa for 3.5 h to form an inner layer of zirconium carbide;

[0060] (2) the graphite and TRISO fuel are mixed to obtain a middle layer slurry, the middle layer slurry is coated on the inner layer of zirconium carbide, and cold isostatic pressing is performed under a pressure of 160 MPa, and then high-temperature sintering is performed at 2100°C for 2 h to obtain a TRISO fuel bearing layer;

[0061] (3) zirconium tetrachloride and methane with a mass ratio of 1:4 are deposited on the surface of the TRISO fuel bearing layer by chemical vapor deposition under the conditions of 1650°C and 10 KPa for 3.5 h to form an outer layer of zirconium carbide;

[0062] (4) graphite and carbon fibers with a mass ratio of 10:1 are mixed to obtain a protective layer slurry, the protective layer slurry is coated on the outer layer of zirconium carbide, and molding is performed under a pressure of 25 MPa, and then sintering treatment is performed at a temperature of 2200°C for 2 h; and then graphitization treatment is performed at a temperature of 500°C for 2 h to obtain a prismatic high-temperature gas-cooled reactor fuel element with a graphite layer thickness of 0.6 mm, an inner layer of zirconium carbide thickness of 0.2 mm, a TRISO fuel bearing layer thickness of 8 mm, an outer layer of zirconium carbide thickness of 0.2 mm, and a protective layer thickness of 1 mm.

[0063] Performance research of the high-temperature gas-cooled reactor fuel element described in embodiments 1-2 of the present application:

[0064] Corrosion resistance: the high-temperature gas-cooled reactor fuel elements described in embodiments 1-2 of the present application are respectively placed in a 1Vo1% H2O-He environment, and are corroded at 1000°C for 10 h to study the corrosion rate; the research results are shown in Table 1.

[0065] Table 1

[0066] Corrosion rate Crushing strength Example 1 1.0 mg / cm 2 • h]] 20 kN Example 2 0.9 mg / cm 2 ·h]]> 25 kN

[0067] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and changes, modifications, replacements and variations of the above embodiments made by those of ordinary skill in the art are within the protection scope of the present application.

Claims

1. A fuel element for a high temperature gas-cooled reactor, characterized in that: The fuel element structure for a high-temperature gas-cooled reactor includes, from the inside to the outside, a graphite layer, an inner zirconium carbide layer, a TRISO fuel bearing layer, an outer zirconium carbide layer, and a protective layer.

2. The fuel element for a high temperature gas-cooled reactor according to claim 1, characterized in that: The TRISO fuel carrying layer includes graphite and TRISO fuel.

3. The fuel element for a high temperature gas-cooled reactor according to claim 1, characterized in that: The protective layer includes graphite and carbon fiber; Preferably, the mass ratio of the graphite to the carbon fiber is (8-10):

1.

4. The fuel element for a high temperature gas-cooled reactor according to claim 1, characterized in that: The thickness of the graphite layer is 0.5-1 mm; And / or, the thickness of the inner layer of zirconium carbide is 0.2-0.5 mm; and / or, the thickness of the TRISO fuel bearing layer is 6-12 mm; and / or, the thickness of the outer layer of zirconium carbide is 0.2-0.5 mm; And / or, the thickness of the protective layer is 1-2 mm.

5. The fuel element for a high temperature gas-cooled reactor according to claim 1, characterized in that: The fuel element for the high temperature gas-cooled reactor is a prismatic fuel element.

6. The method for preparing a fuel element for a high temperature gas-cooled reactor according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Depositing a ZrC layer on the outer surface of the graphite tube by chemical vapor deposition to form an inner layer of zirconium carbide; (2) mixing graphite and TRISO fuel to obtain a middle layer slurry; coating the middle layer slurry on the inner layer zirconium carbide, and performing cold isostatic pressing and sintering to obtain a TRISO fuel bearing layer; (3) depositing a ZrC layer on the surface of the TRISO fuel carrier layer by chemical vapor deposition to form an outer layer of zirconium carbide; (4) Graphite and carbon fiber are mixed to obtain a protective layer slurry; the protective layer slurry is coated on the outer layer of zirconium carbide, and then subjected to compression molding, sintering and graphitization treatment in sequence to obtain the fuel element for the high temperature gas-cooled reactor.

7. The method for preparing a fuel element for a high temperature gas-cooled reactor according to claim 6, characterized in that: In step (1) and step (3), the temperature of the chemical vapor deposition is independently 1500-1800° C., and the pressure of the chemical vapor deposition is independently 5-10 kPa.

8. The method for preparing a fuel element for a high temperature gas-cooled reactor according to claim 6, characterized in that: In step (2), the sintering temperature is 2000-2200° C., and the sintering time is 1.5-2.5 hours.

9. The method for preparing a fuel element for a high temperature gas-cooled reactor according to claim 6, characterized in that: In step (4), the sintering temperature is 2050-2250° C., and the sintering time is 2-3 hours.

10. The method for preparing a fuel element for a high temperature gas-cooled reactor according to claim 10, characterized in that: In step (4), the temperature of the graphitization treatment is 500-1150° C., and the time of the graphitization treatment is 1-3 hours.

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