Zirconium-containing coated graphite spheres for high temperature gas cooled reactors and methods of making the same

Abstract

The application discloses a high-temperature gas cooled reactor graphite sphere with a zirconium coating layer and a preparation method thereof. The graphite sphere with the zirconium coating layer comprises a graphite sphere substrate and a zirconium coating layer from inside to outside. The thickness of the zirconium coating layer is 0.25-0.50 mm. The graphite sphere with the zirconium coating layer can significantly reduce the amount of graphite dust in a high-temperature gas cooled reactor primary circuit without changing the characteristics of a reactor core, improve the operation safety of the high-temperature gas cooled reactor, and improve the economy and reliability of the high-temperature gas cooled reactor. The preparation method of the graphite sphere with the zirconium coating layer is simple and easy to operate.

Description

Technical Field

[0001] This invention belongs to the field of pebble bed type high-temperature gas-cooled reactor fuel element design. Specifically, this invention relates to a zirconium-coated graphite sphere for high-temperature gas-cooled reactors and its preparation method. Background Technology

[0002] High-temperature gas-cooled reactors (HTGRs) are nuclear reactors that use helium as a coolant and graphite as a neutron moderator. They are one of the fourth-generation advanced reactor types, and their significant feature is inherent safety.

[0003] A high-temperature gas-cooled reactor (HTGR) consists of a core, which, apart from a small amount of fuel and control materials, is almost entirely composed of graphite-based materials, such as graphite reflectors, carbon bricks, support components, and various conduits. Graphite serves as both a moderator and a structural material. Hundreds of thousands of graphite spheres are loaded into the initial and transition cores of the HTGR. During commissioning and operation, these graphite spheres are added to the reactor core through the top feed pipe and discharged through the bottom discharge pipe. However, during this circulation process, the graphite spheres experience friction and wear against themselves, as well as against the graphite core components, fuel loading and unloading system piping and equipment, generating graphite dust. The generation of graphite dust can trigger a series of new problems and may affect the safety and normal operation of the reactor. For example, relatively small graphite particles, carried by the helium coolant, flow through the reactor's primary coolant loop and deposit on its surface and in dead zones, causing inconvenience for equipment maintenance and repair. Relatively large graphite particles, under gravity, accumulate at the bottom of the reactor core, causing fuel spheres to bridging and become stuck in the pipes, affecting fuel element circulation. Furthermore, graphite dust can deposit on the surface of the evaporator heat exchange tubes, affecting their heat exchange efficiency. Fine metal dust and metal powder generated by the flow friction of graphite spheres in the pipes are subject to in-core irradiation, directly impacting the increase in in-core radiation levels. Moreover, graphite dust can also enter the air with helium leaks, causing environmental pollution. Therefore, further optimization of the graphite spheres in existing pebble bed high-temperature gas-cooled reactors is needed to reduce graphite dust generation. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, embodiments of the present invention propose a zirconium-coated graphite sphere for high-temperature gas-cooled reactors and a method for preparing the same, in order to reduce the amount of graphite dust generated in the primary loop of high-temperature gas-cooled reactors.

[0005] One embodiment of the present invention provides a zirconium-coated graphite sphere for a high-temperature gas-cooled reactor, wherein the zirconium-coated graphite sphere comprises, from the inside out, a graphite sphere matrix and a zirconium coating layer; the thickness of the zirconium coating layer is 0.25-0.50 mm.

[0006] The high-temperature gas-cooled reactor graphite spheres with zirconium cladding in this embodiment of the invention reduce the amount of graphite dust generated in the primary circuit of the high-temperature gas-cooled reactor without changing the core characteristics by coating the graphite sphere substrate with a zirconium alloy.

[0007] Because zirconium has a small thermal neutron capture cross section (0.180 ± 0.004 dahn, 1 dahn = 10 dahn), -24 cm 2 Zirconium has outstanding nuclear performance. Furthermore, since the melting point of zirconium is 1852℃, which is higher than the fuel temperature limit of 1620℃ for spherical fuel elements in high-temperature gas-cooled reactors, and the graphite spheres themselves do not generate heat, they will not melt under normal operation or accident conditions of the high-temperature gas-cooled reactor, nor will they affect the nuclear characteristics such as the power distribution of the high-temperature gas-cooled reactor core.

[0008] In some embodiments of the present invention, the diameter of the graphite sphere matrix is ​​6 ± 0.2 cm; the density is 1.70–1.80 g / cm³. 3 .

[0009] In some embodiments of the present invention, the zirconium cladding layer is made of any one of Zr-4 alloy, ZIRLO alloy, and M5 alloy.

[0010] In another aspect, the present invention also provides a method for preparing the above-mentioned zirconium-coated graphite spheres for high-temperature gas-cooled reactors, comprising the following steps:

[0011] S1, through melting and extrusion molding, two hemispherical zirconium alloy cladding layers are obtained;

[0012] S2, the two hemispherical zirconium alloy cladding layers are assembled on the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld is then ground, and the surface of the zirconium alloy cladding layer is ground and polished to obtain the zirconium-clad graphite sphere.

[0013] The features and advantages described above for zirconium-coated graphite spheres for high-temperature gas-cooled reactors also apply to the preparation method of zirconium-coated graphite spheres for high-temperature gas-cooled reactors, and will not be repeated here.

[0014] In some embodiments of the present invention, the melting temperature is 2000–2100°C; the melting time is 5–10 min.

[0015] In some embodiments of the present invention, the melting is carried out in a protective gas atmosphere, the protective gas including at least one of nitrogen, argon or helium.

[0016] In some embodiments of the present invention, the extrusion molding pressure is 20-25 MPa; the extrusion molding time is 30-60 s.

[0017] In some embodiments of the present invention, the welding is performed under a vacuum degree ≤8×10 -3 The welding is carried out in an environment of Pa, with a welding voltage of 60kV and an electron beam current of 6.0-8.0mA.

[0018] In some embodiments of the present invention, the grinding is performed sequentially using 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper.

[0019] In some embodiments of the present invention, the polishing liquid used is a mixture of anhydrous acetic acid, propionic acid and perchloric acid.

[0020] The present invention has the following advantages and beneficial effects:

[0021] In this embodiment of the invention, by coating the surface of a graphite sphere matrix with a layer of zirconium alloy, the amount of graphite dust in the primary loop of a high-temperature gas-cooled reactor (HTGR) can be significantly reduced without altering the core characteristics, thereby improving the operational safety of the HTGR. Simultaneously, it simplifies the graphite dust collection device, enhancing the economy and reliability of the HTGR. Furthermore, the preparation method of the zirconium-coated graphite spheres for HTGRs in this embodiment is simple, easy to operate, and has broad application prospects. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0024] In this article, the terms “about” or “around” refer to + / - 10% of the listed values.

[0025] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0026] One embodiment of the present invention provides a zirconium-coated graphite sphere for a high-temperature gas-cooled reactor, wherein the zirconium-coated graphite sphere comprises, from the inside out: a graphite sphere matrix and a zirconium coating layer; the thickness of the zirconium coating layer is 0.25-0.50 mm.

[0027] In this embodiment of the invention, by coating the surface of the graphite sphere matrix with a layer of zirconium alloy, the generation of graphite dust can be effectively prevented without changing the core characteristics.

[0028] Because zirconium has a small thermal neutron capture cross section (0.180 ± 0.004 dahn, 1 dahn = 10 dahn), -24 cm 2 Zirconium possesses outstanding nuclear performance. Furthermore, since zirconium has a melting point of 1852℃, exceeding the 1620℃ fuel temperature limit for spherical fuel elements in high-temperature gas-cooled reactors (HTGRs), and graphite spheres themselves do not generate heat, they will not melt under normal operation or accident conditions in HTGRs, nor will they affect the nuclear characteristics such as the power distribution of the HTGR core. In addition, zirconium and zirconium alloys have wide applications in various reactors; for example, zirconium alloys are widely used as fuel rod cladding materials and fuel assembly guide tube materials in pressurized water reactors and boiling water reactors. Therefore, China has a complete industrial chain for their production, and the price is not expensive, so it will not significantly increase the manufacturing cost of graphite spheres.

[0029] In some specific embodiments, the thickness of the zirconium cladding layer is 0.25–0.50 mm, with non-limiting examples including 0.25 mm, 0.30 mm, 0.45 mm, and 0.50 mm. It should be noted that if the zirconium cladding layer is too thin, it will be detrimental to preventing the generation of graphite dust; if the zirconium cladding layer is too thick, it will excessively increase the weight of the graphite spheres, which is not conducive to the recycling of the graphite spheres in the fuel loading and unloading system. Therefore, in the embodiments of the present invention, the thickness of the zirconium cladding layer is controlled to be 0.25–0.50 mm.

[0030] In some specific embodiments, the diameter of the graphite sphere matrix is ​​6±0.2 cm; the density is 1.70~1.80 g / cm³. 3 Non-limiting examples include: 1.70 g / cm³ 3 1.75g / cm 3 1.80g / cm 3 wait.

[0031] In some specific embodiments, the zirconium cladding layer is made of any one of Zr-4 alloy, ZIRLO alloy, and M5 alloy.

[0032] In another aspect, the present invention also provides a method for preparing the above-mentioned zirconium-coated graphite spheres for high-temperature gas-cooled reactors, comprising the following steps:

[0033] S1, through melting and extrusion molding, two hemispherical zirconium alloy cladding layers are obtained;

[0034] S2, the two hemispherical zirconium alloy cladding layers are assembled on the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld is then ground, and the surface of the zirconium alloy cladding layer is ground and polished to obtain the zirconium-clad graphite sphere.

[0035] In some specific embodiments, the melting temperature is 2000-2100°C, and non-limiting examples include 2000°C, 2050°C, 2080°C, 2100°C, etc.; the melting time is 5-10 minutes, and non-limiting examples include 5 minutes, 8 minutes, 10 minutes, etc.

[0036] In some specific embodiments, the melting is carried out under vacuum conditions and in a protective gas atmosphere, the protective gas including at least one of nitrogen, argon or helium.

[0037] In some specific embodiments, the extrusion molding pressure is 20-25 MPa, and non-limiting examples include 20 MPa, 23 MPa, 24 MPa, 25 MPa, etc.; the extrusion molding time is 30-60 s, and non-limiting examples include 30 s, 45 s, 50 s, 60 s, etc.

[0038] In some specific embodiments, welding is performed at a vacuum level ≤ 8 × 10⁻⁶. -3 The welding is performed in an environment of Pa, and the welding parameters are as follows: voltage of 60kV; electron beam current of 6.0 to 8.0mA, with non-limiting examples such as 6.0mA, 6.5mA, 7.0mA, 8.0mA, etc.; rotation speed of 20 to 30r / min, with non-limiting examples such as 20r / min, 25r / min, 30r / min, etc.

[0039] In some specific embodiments, grinding is performed sequentially using 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper.

[0040] In some specific embodiments, the polishing fluid used for polishing is a mixture of anhydrous acetic acid, propionic acid and perchloric acid;

[0041] Specifically, the polishing slurry is prepared by adding a mixture of 90% anhydrous ethanol and 10% propionic acid to perchloric acid, with a volume ratio of 1:200 between the mixture and the perchloric acid.

[0042] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The following embodiments use conventional instruments and equipment in the art. Experimental methods not specifically described in the embodiments are conventional methods and conditions well known in the art, or methods and conditions recommended by the manufacturer. Unless otherwise stated, all raw materials used in the following embodiments are conventional commercially available products, or can be prepared by known methods.

[0043] Example 1

[0044] This embodiment provides a zirconium-coated graphite sphere for a high-temperature gas-cooled reactor. The zirconium-coated graphite sphere comprises, from the inside out: a graphite sphere matrix and a zirconium coating; wherein the graphite sphere matrix has a diameter of 6 cm and a density of 1.70 g / cm³. 3 The zirconium cladding is made of Zr-4 alloy and has a thickness of approximately 0.25 mm.

[0045] The preparation method of the zirconium-coated graphite spheres for the high-temperature gas-cooled reactor includes the following steps:

[0046] S1, Zr-4 alloy was vacuum melted at 2000℃ for 10 min under argon atmosphere protection, and then extruded at 23MPa for 45 s to obtain two hemispherical zirconium alloy coating layers.

[0047] S2, the two hemispherical zirconium alloy cladding layers are assembled on the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld is then ground, and the surface of the zirconium alloy cladding layer is then ground sequentially with 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper. Finally, after polishing, the zirconium-clad graphite sphere is obtained.

[0048] Example 2

[0049] This embodiment provides a zirconium-coated graphite sphere for a high-temperature gas-cooled reactor. The zirconium-coated graphite sphere comprises, from the inside out: a graphite sphere matrix and a zirconium coating; wherein the graphite sphere matrix has a diameter of 6 cm and a density of 1.75 g / cm³. 3 The zirconium cladding is made of ZIRLO alloy and is approximately 0.25 mm thick.

[0050] The preparation method of the zirconium-coated graphite spheres for the high-temperature gas-cooled reactor includes the following steps:

[0051] S1, ZIRLO alloy was vacuum melted at 2100℃ for 8 minutes under argon atmosphere protection, and then extruded at 25MPa for 30 seconds to obtain two hemispherical zirconium alloy coating layers.

[0052] S2, the two hemispherical zirconium alloy cladding layers are assembled on the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld is then ground, and the surface of the zirconium alloy cladding layer is then ground sequentially with 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper. Finally, after polishing, the zirconium-clad graphite sphere is obtained.

[0053] Example 3

[0054] This embodiment provides a zirconium-coated graphite sphere for a high-temperature gas-cooled reactor. The zirconium-coated graphite sphere comprises, from the inside out: a graphite sphere matrix and a zirconium coating; wherein the graphite sphere matrix has a diameter of 6 cm and a density of 1.80 g / cm³. 3 The zirconium cladding is made of M5 alloy and has a thickness of approximately 0.25 mm.

[0055] The preparation method of the zirconium-coated graphite spheres for the high-temperature gas-cooled reactor includes the following steps:

[0056] S1, M5 alloy was vacuum melted at 2050℃ for 5 minutes under argon atmosphere protection, and then extruded at 20MPa for 60s to obtain two hemispherical zirconium alloy coating layers.

[0057] S2, the two hemispherical zirconium alloy cladding layers are assembled on the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld is then ground, and the surface of the zirconium alloy cladding layer is then ground sequentially with 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper. Finally, after polishing, the zirconium-clad graphite sphere is obtained.

[0058] Example 4

[0059] This embodiment provides a zirconium-coated graphite sphere for a high-temperature gas-cooled reactor. The zirconium-coated graphite sphere comprises, from the inside out: a graphite sphere matrix and a zirconium coating; wherein the graphite sphere matrix has a diameter of 6 cm and a density of 1.70 g / cm³. 3 The zirconium cladding is made of Zr-4 alloy and has a thickness of approximately 0.50 mm.

[0060] The preparation method of the zirconium-coated graphite spheres for the high-temperature gas-cooled reactor includes the following steps:

[0061] S1, Zr-4 alloy was vacuum melted at 2100℃ for 10 min under argon atmosphere protection, and then extruded at 25MPa for 45s to obtain two hemispherical zirconium alloy coating layers.

[0062] S2, the two hemispherical zirconium alloy cladding layers are assembled on the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld is then ground, and the surface of the zirconium alloy cladding layer is then ground sequentially with 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper. Finally, after polishing, the zirconium-clad graphite sphere is obtained.

[0063] Example 5

[0064] This embodiment provides a zirconium-coated graphite sphere for a high-temperature gas-cooled reactor. The zirconium-coated graphite sphere comprises, from the inside out: a graphite sphere matrix and a zirconium coating; wherein the graphite sphere matrix has a diameter of 6 cm and a density of 1.75 g / cm³. 3 The zirconium cladding is made of ZIRLO alloy and has a thickness of approximately 0.50 mm.

[0065] The preparation method of the zirconium-coated graphite spheres for the high-temperature gas-cooled reactor includes the following steps:

[0066] S1, ZIRLO alloy was vacuum melted at 2100℃ for 10 min under argon atmosphere protection, and then extruded at 25MPa for 60 s to obtain two hemispherical zirconium alloy coating layers.

[0067] S2, the two hemispherical zirconium alloy cladding layers are assembled on the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld is then ground, and the surface of the zirconium alloy cladding layer is then ground sequentially with 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper. Finally, after polishing, the zirconium-clad graphite sphere is obtained.

[0068] Example 6

[0069] This embodiment provides a zirconium-coated graphite sphere for a high-temperature gas-cooled reactor. The zirconium-coated graphite sphere comprises, from the inside out: a graphite sphere matrix and a zirconium coating; wherein the graphite sphere matrix has a diameter of 6 cm and a density of 1.80 g / cm³. 3 The zirconium cladding is made of M5 alloy and has a thickness of approximately 0.50 mm.

[0070] The preparation method of the zirconium-coated graphite spheres for the high-temperature gas-cooled reactor includes the following steps:

[0071] S1, M5 alloy was vacuum melted at 2050℃ for 10 min under argon atmosphere protection, and then extruded at 20MPa for 60 s to obtain two hemispherical zirconium alloy coating layers.

[0072] S2, the two hemispherical zirconium alloy cladding layers are assembled on the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld is then ground, and the surface of the zirconium alloy cladding layer is then ground sequentially with 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper. Finally, after polishing, the zirconium-clad graphite sphere is obtained.

[0073] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0074] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A zirconium-coated graphite sphere for a high-temperature gas-cooled reactor, characterized in that, From the inside out, it comprises: a graphite sphere matrix and a zirconium cladding layer; the thickness of the zirconium cladding layer is 0.25–0.50 mm; The zirconium-coated graphite spheres are prepared by a method comprising the following steps: S1, through melting and extrusion molding, two hemispherical zirconium alloy cladding layers are obtained; S2, the two hemispherical zirconium alloy cladding layers are assembled onto the surface of the graphite sphere substrate, and the two hemispherical zirconium alloy cladding layers are welded together using a vacuum electron beam. The weld seam is then ground, and the surface of the zirconium alloy cladding layer is further ground and polished to obtain the zirconium-clad graphite sphere; wherein, the welding is performed under a vacuum degree ≤8×10 - 3 The welding is carried out in an environment of Pa, with a welding voltage of 60kV and an electron beam current of 6.0-8.0mA; the grinding is performed sequentially using 400-grit, 600-grit, 800-grit, and 1200-grit sandpaper.

2. The zirconium-coated graphite spheres for high-temperature gas-cooled reactors according to claim 1, characterized in that, The graphite sphere matrix has a diameter of 6 ± 0.2 cm and a density of 1.70–1.80 g / cm³. 3 .

3. The zirconium-coated graphite spheres for high-temperature gas-cooled reactors according to claim 1, characterized in that, The zirconium cladding layer is made of any one of Zr-4 alloy, ZIRLO alloy, or M5 alloy.

4. The zirconium-coated graphite spheres for high-temperature gas-cooled reactors according to claim 1, characterized in that, The melting temperature is 2000–2100℃; the melting time is 5–10 min.

5. The zirconium-coated graphite spheres for high-temperature gas-cooled reactors according to claim 1, characterized in that, The melting is carried out in a protective gas atmosphere, which includes at least one of nitrogen, argon or helium.

6. The zirconium-coated graphite spheres for high-temperature gas-cooled reactors according to claim 1, characterized in that, The extrusion molding pressure is 20-25 MPa; the extrusion molding time is 30-60 s.

7. The zirconium-coated graphite spheres for high-temperature gas-cooled reactors according to claim 1, characterized in that, The polishing solution used is a mixture of anhydrous acetic acid, propionic acid, and perchloric acid.