A hexagonal fuel assembly of dispersion multilayer clad fuel fibers

Abstract

The application discloses a kind of dispersion multilayer coated fuel fiber hexagonal prism fuel assembly, and fuel assembly is composed of silicon carbide matrix and near cylindrical multilayer coated fuel fiber.Fuel fiber is the improved form of spherical coated fuel particle, and the manufacture and positioning of fiber are realized by 3D printing technology.The design of near cylindrical fuel fiber can weaken the influence of irradiation anisotropy of pyrolytic carbon layer, significantly reduce the tangential stress of silicon carbide layer, and enhance the integrity and safety of fiber;The gap between fuel fibers is related to the arrangement mode and needs to accommodate the irradiation deformation of fuel fiber, which reduces the mutual influence between fibers;3D printing technology can realize the accurate positioning of fiber, ensure the manufacturing quality of fiber, efficiently utilize the internal space of assembly, improve the fuel loading capacity and service performance parameters of assembly, and effectively improve the economic benefit.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nuclear reactor fuel element design, and particularly relates to a hexagonal prism fuel assembly with dispersed multi-layer coated fuel fibers. BACKGROUND

[0002] Since the Fukushima nuclear accident in Japan, a large number of and extensive researches on accident tolerant fuel have been carried out internationally. Accident tolerant fuel can withstand longer loss of coolant compared to traditional light water reactor fuel. Among them, the widely researched cylindrical fully ceramic micro-encapsulated (FCM) fuel element adopts a high-density silicon carbide matrix and internal dispersion of isotropic fuel particles (TRISO). The TRISO particle is a spherical multi-layer coated structure, with a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a silicon carbide layer, and an outer dense pyrolytic carbon layer successively coated outside the fuel core. This form of fuel particle is known for its high pressure-bearing capacity and strong ability to retain fission products, but the anisotropic radiation behavior of the pyrolytic carbon coating layer will reduce the service performance of the spherical TRISO particle.

[0003] In addition, the design of the FCM fuel is to ensure a high safety margin, and the fuel loading fraction is not high, which will limit the improvement of the nuclear reactor power and economy. Generally speaking, to increase the uranium loading, highly-enriched uranium (HEU) needs to be used, but this conventional method increases the risk of nuclear proliferation, the cost of fuel manufacturing and processing, and the international community has strict regulations on the concentration and use of highly-enriched uranium fuel.

[0004] For fuel elements using multi-layer coated fuel particles, if both the requirements of increasing the fuel loading fraction and the performance of the coated fuel are to be met, the existing solution can only be to start the design and research of new fuel element forms.

[0005] There are currently published related researches. For example, the United States Oak Ridge National Laboratory proposed a hexagonal fuel element for the Transformation Challenge Reactor (TCR). The fuel element uses silicon carbide as the material, establishes an element shell mold through 3D printing, directly pours TRISO particles into the mold, realizes a filling rate of TRISO particles as high as 64%, pours in silicon carbide powder, processes the mold through chemical vapor phase infiltration (CVI) technology, and obtains a complete new hexagonal fuel element. The fuel element used in the TCR reactor is still based on the existing spherical TRISO particles, and the main factors affecting the performance of the particles have not been solved. In the literature “Innovative accident tolerant fuel concept enabled through direct manufacturing technology[J]. Applied Energy. 264 (2020) 114742”, based on multi-layer coated fuel, the spherical coated fuel is improved into a near-cylindrical coated fiber form. According to the results of the model of the actual sample, it is shown that this fiber form can significantly improve the performance of the spherical particles, but in order to facilitate manufacturing, the position of the fuel core in the fiber is slightly below the center, which will cause the side of the fuel pellet containing a large number of fibers to be heated too high, causing local deformation to be too large. SUMMARY

[0006] In view of the problems existing in the prior art, based on the preliminary performance analysis of the fuel fiber under irradiation conditions in the above literature, the purpose of the present application is to provide a dispersed multi-layer coated fuel fiber hexagonal fuel assembly, which improves the irradiation performance of the TRISO particle dispersed fuel assembly and increases the uranium loading of the fuel assembly. The present application adopts a hexagonal fuel assembly form with a central cylindrical through hole, and a plurality of near-cylindrical multi-layer coated fuel fibers are arranged inside the assembly. The manufacturing process of the fuel fiber is realized through 3D printing technology, and the precise positioning of the fuel fiber position can meet the design requirements. The near-cylindrical coated form can significantly reduce the tangential stress of the pyrolytic carbon layer and the influence on the stress of the silicon carbide layer.

[0007] In order to achieve the above purpose, the present application realizes the following technical solutions:

[0008] The application discloses a hexagonal prism fuel assembly of dispersed multi-layer coated fuel fibers, and belongs to the technical field of nuclear fuel.

[0009] The gap between the dispersed multi-layer coated fuel fibers is related to the arrangement mode of the fuel fibers, and the influence of fiber deformation and interaction during reactor operation also needs to be considered, that is, in the hexagonal prism fuel assembly, the dispersed multi-layer coated fuel fibers can be arranged in a circular ring according to the shape of the coolant central channel or can be arranged in a hexagon according to the hexagonal shape of the assembly, and the gap between the dispersed multi-layer coated fuel fibers is determined by adding a safety margin to the minimum distance of the arrangement array.

[0010] The material of the near-cylindrical fuel core 4 is a uranium compound or a composite nuclear fuel containing additives and / or dopants in the uranium compound; and the matrix material is silicon carbide, specifically chemical vapor infiltration CVI type silicon carbide or nano-infiltration eutectic transformation NITE type silicon carbide.

[0011] The uranium compound is an oxide, carbide or nitride of uranium, or a compound of uranium and thorium, aluminum, silicon, beryllium or the like, such as UN, UO2, U3Si2, U3O8 or UC.

[0012] The additive is a nano-molybdenum particle or a nano-SiC particle.

[0013] The dopant is a SiC whisker, a SiC particle, Mo, Zr, BeO, Ag, In, Cd, Hf, B4C, Dy2O3, Er2O3, Eu2O3 or Gd2O3.

[0014] The internal structure and positioning of the multi-layer coated fuel fiber 3 are realized by a 3D printing technology.

[0015] The application has the following advantages and beneficial effects:

[0016] 1. By the design of near-cylindrical fuel fiber, the irradiation anisotropy of pyrolytic carbon layer can be weakened, the tangential stress of silicon carbide layer can be significantly reduced, and the integrity and safety of the fiber can be enhanced. The gap between the fuel fibers is related to the arrangement and needs to accommodate the irradiation deformation of the fuel fibers, which can significantly reduce the influence of TRISO pyrolytic carbon layer on the working stress of silicon carbide layer and avoid the problems caused by spherical coating form.

[0017] 2. As a ceramic material, the near-cylindrical coating form can significantly reduce the tangential stress of silicon carbide. Even if the tangential stress changes from compressive stress to tensile stress, due to the deformation behavior of the pyrolytic carbon layer on both sides, the tangential stress of silicon carbide will change to compressive stress again. This new coating form design can fully exert the advantages of silicon carbide coating layer in bearing fission gas pressure and retaining fission products, and reduce the failure probability of silicon carbide.

[0018] 3. The use of near-cylindrical fuel core and multi-layer coating design can increase the volume fraction of the core in the fuel fiber and increase the uranium loading.

[0019] 4. The fuel fiber manufactured by 3D printing technology can ensure the manufacturing quality of the fiber.

[0020] 5. The distribution design of fuel fiber can be realized by 3D printing technology, which can realize high filling amount of fuel fiber and optimize the irradiation performance of fuel assembly (such as significantly reducing the matrix stress and failure risk). BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the internal structure of the hexagonal prism fuel assembly and fuel fiber of the present application. DETAILED DESCRIPTION

[0022] The present application will be further described in detail below in conjunction with the drawings.

[0023] As Figure 1As shown in the figure, the six-prism fuel assembly of the dispersed multi-layer coated fuel fiber of the present application is a six-prism structure 1, and the six-prism structure 1 has a cylindrical hole 2 in the center for the flow of coolant; the fuel assembly has a large number of regularly arranged multi-layer coated fuel fibers 3 inside, and the remaining space in the assembly is the matrix material; the multi-layer coated fuel fiber 3 is a multi-layer coated structure in the shape of a near-cylinder, which is composed of a near-cylinder fuel core 4 and a porous pyrolytic carbon layer 5, an inner dense pyrolytic carbon layer 6, a silicon carbide layer 7, and an outer dense pyrolytic carbon layer 8 that coat the near-cylinder fuel core 4 from the inside to the outside, wherein the volume fraction of the near-cylinder fuel core 4 accounts for 15-20% of the entire fuel fiber, the porous pyrolytic carbon layer 5 completely wraps the near-cylinder fuel core 4, and in the direction of the top and bottom of the fiber, it is a solid near-cylinder to guide the fission gas released by the near-cylinder fuel core 4 to flow axially and contain part of the fission gas, and to ensure that the inner dense pyrolytic carbon layer 6, the silicon carbide layer 7, and the outer dense pyrolytic carbon layer 8 are mainly subjected to axial stress.

[0024] As a preferred embodiment of the present application, the gap between the dispersed multi-layer coated fuel fibers is related to the arrangement of the fuel fibers, and the effects of fiber deformation and interaction during reactor operation also need to be considered, that is, in the six-prism fuel assembly, the dispersed multi-layer coated fuel fibers can be arranged in a circular ring according to the shape of the coolant central channel or can be arranged in a hexagonal shape according to the six-prism shape of the assembly, and the gap between the dispersed multi-layer coated fuel fibers is determined by adding a safety margin to the minimum spacing of the arrangement array.

[0025] As a preferred embodiment of the present application, the material of the near-cylinder fuel core 4 is a uranium compound or a composite nuclear fuel containing additives and / or dopants in the uranium compound; the matrix material is silicon carbide, specifically chemical vapor infiltration CVI type silicon carbide or nano-infiltration eutectic transformation technology NITE type silicon carbide, although the manufacturing techniques are different, but these two kinds of silicon carbide materials have strong mechanical properties, heat transfer properties and oxidation resistance, so that the fuel assembly can maintain high stability and integrity.

[0026] As a preferred embodiment of the present application, the uranium compound is an oxide, carbide, or nitride of uranium, or a compound of uranium with thorium, aluminum, silicon, beryllium, etc., such as UN, UO2, U3Si2, U3O8, or UC, which has the advantages of higher melting point and stronger stability under high temperature and high radiation conditions.

[0027] As a preferred embodiment of the present application, the additive refers to the modification and modification on the surface of the fuel in order to enhance the compatibility of the interface and improve the strength and other properties of the whole, and the material used is a nano-sized particle of the matrix material or functional material, which can be nano-molybdenum particles or nano-SiC particles.

[0028] As a preferred embodiment of the present application, the dopant is SiC whisker, SiC particle, Mo, Zr, or dopant burnable poison particle such as BeO, Ag, In, Cd, Hf, B4C, Dy2O3, Er2O3, Eu2O3 or Gd2O3, which can improve the thermal conductivity of nuclear fuel, provide good control ability of reactor long-term reactivity and power, and improve fuel utilization.

[0029] As a preferred embodiment of the present application, the internal structure and positioning of the multi-layer coated fuel fiber 3 are realized by 3D printing technology. The 3D printing technology can realize accurate positioning of the fiber, ensure the quality of fiber manufacturing, efficiently utilize the internal space of the assembly, improve the fuel loading capacity and service performance parameters of the assembly, and effectively improve the economic benefits.

[0030] The above is a further detailed description of the present application in combination with specific preferred embodiments, and it cannot be considered that the specific embodiments of the present application are limited to this. For ordinary skilled persons in the art to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be considered to belong to the present application, and the scope of patent protection is determined by the submitted claims.

Claims

1. A hexagonal prism fuel assembly with dispersed multilayer coated fuel fibers, characterized in that: The fuel assembly has a hexagonal prism structure (1), with a cylindrical channel (2) in the center for coolant flow; the fuel assembly contains a large number of regularly arranged multi-layered coated fuel fibers (3), and the remaining space inside the assembly is the matrix material; the multi-layered coated fuel fibers (3) are a near-cylindrical multi-layered coated structure, consisting of a near-cylindrical fuel core (4) and a porous pyrolytic carbon layer (5) covering the near-cylindrical fuel core (4) from the inside out, an inner dense pyrolytic carbon layer (6), a silicon carbide layer (7), and an outer layer. The fiber is composed of a dense pyrolytic carbon layer (8), in which the volume fraction of the near-cylindrical fuel core (4) accounts for 15-20% of the entire fuel fiber. The porous pyrolytic carbon layer (5) completely encloses the near-cylindrical fuel core (4), and is a solid near-cylindrical in the direction of the top and bottom of the fiber, so as to guide the fission gas released by the near-cylindrical fuel core (4) to flow axially and accommodate part of the fission gas, ensuring that the inner dense pyrolytic carbon layer (6), silicon carbide layer (7), and outer dense pyrolytic carbon layer (8) are mainly subjected to axial force.

2. The hexagonal prism fuel assembly with dispersed multilayer coated fuel fibers as described in claim 1, characterized in that: The gaps between the dispersed multilayer coated fuel fibers are related to the arrangement of the fuel fibers. The effects of fiber deformation and interaction during reactor operation also need to be considered. Specifically, within the hexagonal prism fuel assembly, the dispersed multilayer coated fuel fibers are arranged in a ring according to the shape of the coolant central channel or in a hexagonal arrangement according to the hexagonal prism shape of the assembly. The gaps between the dispersed multilayer coated fuel fibers are determined by the minimum spacing of the array plus a safety margin.

3. The hexagonal prism fuel assembly with dispersed multilayer coated fuel fibers as described in claim 1, characterized in that: The material of the near-cylindrical fuel core (4) is uranium compound or composite nuclear fuel containing additives and / or dopants in uranium compound; the matrix material is silicon carbide, specifically chemical vapor infiltration CVI type silicon carbide or nano-infiltration eutectic transformation technology NITE type silicon carbide.

4. The hexagonal prism fuel assembly with dispersed multilayer coated fuel fibers as described in claim 3, characterized in that: The uranium compound is an oxide, carbide, or nitride of uranium, or a compound of uranium with thorium, aluminum, silicon, or beryllium.

5. The hexagonal prism fuel assembly with dispersed multilayer coated fuel fibers as described in claim 3, characterized in that: The additive is nano-molybdenum particles or nano-SiC particles.

6. The hexagonal prism fuel assembly with dispersed multilayer coated fuel fibers as described in claim 3, characterized in that: The dopant is SiC whisker, SiC particles, Mo, Zr, BeO, Ag, In, Cd, Hf, B4C, Dy2O3, Er2O3, Eu2O3 or Gd2O3.

7. The hexagonal prism fuel assembly with dispersed multilayer coated fuel fibers as described in claim 1, characterized in that: The internal structure and positioning of the multi-layer coated fuel fiber (3) are achieved by 3D printing technology.

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