TRISO fuel pellet manufacturing method and fuel pellet

Abstract

The invention discloses a TRISO fuel pellet manufacturing method and a fuel pellet, and belongs to the field of nuclear power. The manufacturing method of the TRISO fuel pellet comprises the following steps that graphite powder is laid in a fuel pellet mold, a graphite powder layer is compacted through a hemispherical working part with protrusions, a positioning hole is formed, a fuel ball is arranged in the positioning hole and covered with the graphite powder layer, and the fuel pellet mold is formed. And the steps of compacting to form the positioning holes and loading the fuel pellets are repeated until the graphite powder reaches the preset height, sintering is performed after overall compacting, and the TRISO fuel pellet is obtained. According to the method, the uniformity of the TRISO fuel pellet can be improved, and large-scale continuous production is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of nuclear power, and in particular relates to a TRISO fuel pellet manufacturing method and a fuel pellet. Background Art

[0002] Currently, TRISO (tristructural-isotropic) fuel is widely used in high temperature gas-cooled reactors (HTGR) and other advanced nuclear reactor designs due to its excellent safety performance. In the design of heat pipe micro-reactors, the reactor is often required to have excellent safety and mobility, so there are also high requirements for the safety of the fuel, which is very suitable for the use of fuel pellets based on TRISO fuel particles.

[0003] In the prior art, TRISO fuel particles are usually randomly dispersed in a graphite matrix, which may lead to uneven local fuel density, thereby affecting the fuel performance and the overall thermal characteristics of the core.

[0004] Patent CN116417166A discloses a method for manufacturing dispersed fuel pellets, which uses a vacuum adsorption device to implant fuel microspheres into the matrix powder of the fuel pellets layer by layer to achieve uniform distribution of the fuel microspheres in the pellets, and sinter them into dispersed fuel pellets after compression molding. This method can control the position of each layer of fuel microspheres through the vacuum adsorption device, and control the longitudinal distribution of the fuel microspheres by adjusting the layer thickness of the matrix powder. However, the vacuum adsorption device will inevitably absorb the matrix powder when implanting the fuel microspheres, resulting in uneven distribution of the matrix powder and contamination of the vacuum adsorption system, affecting production efficiency.

[0005] Therefore, providing a more efficient method for manufacturing TRISO fuel pellets has positive significance for improving production efficiency and optimizing economic efficiency. Summary of the invention

[0006] The object of the present invention is to provide a method for manufacturing TRISO fuel pellets to improve the continuous production efficiency of TRISO fuel pellets. The present invention also provides a fuel pellet.

[0007] According to an embodiment of one aspect of the present invention, a method for manufacturing a TRISO fuel pellet is provided, for manufacturing a TRISO fuel pellet composed of a graphite matrix and a fuel ball.

[0008] The method specifically comprises the following steps:

[0009] Step a): providing a fuel pellet mold, and laying a graphite powder layer in the fuel pellet mold;

[0010] Step b): providing a punching die, wherein the punching die has a punching working surface, and a raised hemispherical working portion is arranged on the punching working surface; using the punching die to compact the graphite powder layer and make the hemispherical working portion form a positioning hole in the graphite powder layer;

[0011] Step c): inserting the fuel ball into the positioning hole and covering the fuel ball with a graphite powder layer;

[0012] Step d): using the hole pressing die to compact the graphite powder layer laid in step c) and to form a positioning hole in the graphite powder layer by the hemispherical working part;

[0013] Step e): repeating step c) and step d) until the graphite powder reaches a preset thickness, compacting and sintering the graphite powder to obtain a TRISO fuel pellet.

[0014] The method realizes the layer-by-layer positioning of the fuel balls by forming positioning holes in the compacted graphite powder layer, without the need for a vacuum adsorption device, and can effectively avoid contamination caused by graphite powder mixing into the vacuum adsorption device; at the same time, the positioning holes can limit the fuel balls, and avoid uneven distribution of the fuel balls caused by deviation in the position of the fuel balls when the graphite powder is further covered.

[0015] Furthermore, in some embodiments, the punching dies are provided with two, and when the two punching dies are coaxially arranged, the projection positions of the respective hemispherical working parts are staggered with each other;

[0016] Adjacent graphite powder layers are compacted using different punching dies.

[0017] The use of different punching dies can stagger the positions of the fuel balls between two adjacent layers, avoiding the fuel balls from being squeezed and crushed during the compaction process, while also increasing the density of the fuel balls.

[0018] Furthermore, in some embodiments, when the graphite powder layer is laid, the thickness of the graphite powder layer after compaction is not less than the diameter of the fuel ball.

[0019] Furthermore, in some embodiments, the method for loading the fuel balls into the positioning holes is as follows: the fuel balls having the same number as the positioning holes are sprinkled on the graphite powder layer formed with the positioning holes, and the fuel balls are made to fall into the positioning holes by vibration.

[0020] Furthermore, in some embodiments, the method further provides a filling mold, wherein the filling mold is provided with a filling hole, the filling hole corresponds to the positioning hole one by one, and allows the fuel ball to be clamped in the filling hole;

[0021] The method of inserting the fuel ball into the positioning hole is as follows:

[0022] The fuel ball is inserted into the filling hole of the filling mold, and the fuel ball is sent into the positioning hole through the filling mold.

[0023] Further, in some embodiments, the fuel pellet mold used in the method is provided with a lifting mechanism at the bottom, and the method of inserting the fuel ball into the positioning hole is as follows:

[0024] Fuel balls of a number not less than the number of the positioning holes are sprinkled on the graphite powder layer formed with the positioning holes, and fuel balls are made to fall into each of the positioning holes by vibration; the compacted graphite powder blank is lifted to the top of the fuel core block mold by a lifting mechanism, so that the fuel balls that have not fallen into the positioning holes are rolled out of the graphite powder layer.

[0025] Furthermore, in some embodiments, the hemispherical working portion and the fuel ball have the same radius.

[0026] Furthermore, in some embodiments, the radius of the positioning hole is 0.8 mm-1.0 mm.

[0027] According to another embodiment of the present invention, there is provided a fuel pellet, which includes a graphite matrix and a fuel ball, and adopts the TRISO fuel pellet manufacturing method provided in any of the above embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of a punching die in one embodiment;

[0029] Figure 2 Schematic diagram of the fuel ball positioning process in one embodiment.

[0030] Meaning of the reference symbols:

[0031] 1-Pressing die;

[0032] 2-hemispherical working part;

[0033] 3-Fuel ball;

[0034] 4-graphite powder layer;

[0035] 5- Positioning holes.

[0036] 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

[0037] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0038] 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.

[0039] 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, for example, it 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.

[0040] 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.

[0041] 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.

[0042] In order to solve the problem of uneven distribution of fuel particles in TRISO fuel and realize continuous and efficient production of TRISO fuel pellets, an embodiment of one aspect of the present invention provides a method for manufacturing TRISO fuel pellets, which can ensure the uniformity of fuel particle distribution in TRISO fuel pellets, improve the thermal conductivity and radiation resistance of the fuel pellets, and is suitable for large-scale continuous production.

[0043] The method uses graphite powder and spherical fuel particles as raw materials and includes the following steps:

[0044] Step a): providing a fuel pellet mold, the fuel pellet mold is used to press the fuel pellets into shape, and a graphite powder layer is laid in the fuel pellet mold.

[0045] Step b): Provide Figure 2The punching die 1 shown in the figure. The punching die matches the internal dimensions of the fuel pellet mold. The punching die 1 cooperates with the fuel pellet mold to fully compact the graphite powder in the fuel pellet mold. The punching die 1 has a working surface for compacting the graphite powder. The working surface is provided with a convex hemispherical working part 2. Figure 2 In the process of compacting the graphite powder layer 4 , the hemispherical working part 2 can form a positioning hole 5 in the graphite powder layer 4 .

[0046] Step c): insert the fuel ball 3 into the positioning hole, and continue to lay the graphite powder layer to completely cover the fuel ball 3.

[0047] Step d): using the punching die 1 to continue compacting the graphite powder layer applied in step c) and forming positioning holes 5 .

[0048] Step e): repeating step c) and step d) until the graphite powder reaches a predetermined thickness, fully compacting the graphite powder and sintering it to obtain a TRISO fuel pellet.

[0049] In a preferred embodiment, two punching dies 1 are provided. When the two punching dies 1 are coaxially arranged, the projection positions of their respective hemispherical working parts 2 are staggered. In the pellet manufacturing process, the two punching dies 1 are used alternately. In this way, the positions of the fuel balls 3 of two adjacent layers in the thickness direction can be staggered to avoid the graphite powder from being directly contacted and crushed during the compaction process. In a further preferred embodiment, the fuel balls 3 are arranged in a body-centered cubic or face-centered cubic manner in the graphite powder to further improve the effective density of the fuel in the TRISO fuel pellets.

[0050] In different embodiments, the fuel ball 3 can be installed into the positioning hole 5 in different ways.

[0051] In some preferred embodiments, after the graphite powder layer 4 is compacted and the positioning holes 5 are formed, the same number of fuel balls 3 as the positioning holes 5 are sprinkled on the graphite powder layer 4 and the fuel balls 3 are naturally dropped into the positioning holes 5 by vibration.

[0052] In some preferred embodiments, the fuel ball 3 is loaded into the positioning hole 5 on the graphite powder layer 4 by a filling mold. Specifically, a filling hole is provided on the filling mold, and the filling mold is manufactured according to the structural design of the hole pressing mold so that the filling hole and the positioning hole 5 are overlapped and correspond one to one. The filling hole is similar in size to the fuel ball 3, so that the fuel ball 3 can be snapped into the filling hole. In this way, the fuel ball 3 is loaded into each filling hole of the filling mold, and the fuel ball 3 is sent into the fuel core block mold by using the filling mold, and the fuel ball 3 is discharged to load the fuel ball 3 into the positioning hole 5 corresponding to the filling hole, thereby completing the setting of the fuel ball 3. In different embodiments, different methods can be used to discharge the fuel ball 3 from the filling hole: for example, in some embodiments, a mechanical device can be used to push the fuel ball 3 out of the filling hole; in other embodiments, a blowing device can be used to blow the fuel ball 3 out of the filling hole by air pressure.

[0053] In some preferred embodiments, a lifting mechanism is provided at the bottom of the fuel pellet mold, and the lifting mechanism can lift the compacted graphite powder to the top of the fuel pellet mold. In this embodiment, after the graphite powder layer 4 is compacted, a number of fuel balls 3 not less than the positioning holes 5 are loaded into the fuel pellet mold, and a fuel ball 3 is placed in each positioning hole 5 by vibration. Subsequently, the compacted graphite powder is lifted up by the lifting mechanism, so that the upper surface of the graphite powder layer 4 is not lower than the top edge of the fuel pellet mold. Finally, the excess fuel balls that have not fallen into the positioning holes 5 are rolled off the surface of the graphite powder layer 4 by blowing or the like, and the arrangement of the fuel balls 3 is completed.

[0054] In a preferred embodiment, the radius of the hemispherical working portion 2 is the same as that of the fuel ball 3, so that the size of the formed positioning hole 5 matches that of the fuel ball 3. Further, the positioning hole 5 and the fuel ball 3 are set to a radius of 0.9 mm.

[0055] In a preferred embodiment, in order to prevent the fuel balls 3 between different layers from contacting each other and causing crushing during the compaction process, the thickness of the compacted graphite powder layer 4 should not be less than the diameter of the fuel ball 3. Specifically, the thickness of the compacted graphite powder layer 4 under different pressures can be determined by experimental testing to determine the loading amount of graphite powder in each graphite powder layer 4.

[0056] Through the method provided in the above embodiment, TRISO fuel pellets with uniform fuel particle distribution can be manufactured, which are suitable for reactors with high requirements on fuel safety, such as heat pipe micro-reactors.

[0057] The TRISO fuel pellet manufacturing method provided in the above embodiment can improve the uniformity of fuel particle distribution in the TRISO fuel pellet, improve the thermal conductivity and radiation resistance of the fuel pellet, and improve the reliability of the fuel pellet. At the same time, it also reduces the risk of TRISIO particles being exposed on the surface in the manufacturing process of randomly mixing fuel particles with matrix powder for sintering, and there is no need to set up a process for preparing a fuel-free area on the surface.

[0058] 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 method steps involved, and the combination of the implementation methods in different embodiments without conflict of structure and principle, all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a TRISO fuel pellet, wherein the TRISO fuel pellet comprises a graphite matrix and a fuel ball, characterized in that: The following steps are involved: Step a): providing a fuel pellet mold, and laying a graphite powder layer in the fuel pellet mold; Step b): providing a punching die, wherein the punching die has a punching working surface, and a raised hemispherical working portion is arranged on the punching working surface; using the punching die to compact the graphite powder layer and make the hemispherical working portion form a positioning hole in the graphite powder layer; Step c): inserting the fuel ball into the positioning hole and covering the fuel ball with a graphite powder layer; Step d): using the hole pressing die to compact the graphite powder layer laid in step c) and to form a positioning hole in the graphite powder layer by the hemispherical working part; Step e): repeating step c) and step d) until the graphite powder reaches a preset thickness, compacting and sintering the graphite powder to obtain a TRISO fuel pellet.

2. The method for manufacturing TRISO fuel pellets according to claim 1, characterized in that: There are two punching dies, and when the two punching dies are coaxially arranged, the projection positions of the hemispherical working parts of the two punching dies are staggered with each other; Adjacent graphite powder layers are compacted using different punching dies.

3. The method for manufacturing TRISO fuel pellets according to claim 1 or 2, characterized in that: When the graphite powder layer is laid, the thickness of the graphite powder layer after compaction is not less than the diameter of the fuel ball.

4. The method for manufacturing TRISO fuel pellets according to claim 1 or 2, characterized in that: The method for loading the fuel balls into the positioning holes is as follows: the fuel balls having the same number as the positioning holes are spread on the graphite powder layer formed with the positioning holes, and the fuel balls are made to fall into the positioning holes by vibration.

5. The method for manufacturing TRISO fuel pellets according to claim 1 or 2, characterized in that: Providing a filling mold, wherein the filling mold is provided with filling holes, the filling holes correspond to the positioning holes one by one, and allow the fuel balls to be clamped in the filling holes; The method of inserting the fuel ball into the positioning hole is as follows: The fuel ball is inserted into the filling hole of the filling mold, and the fuel ball is sent into the positioning hole through the filling mold.

6. The method for manufacturing TRISO fuel pellets according to claim 1 or 2, characterized in that: The bottom of the fuel pellet mold is provided with a lifting mechanism, and the method for inserting the fuel ball into the positioning hole is as follows: Fuel balls of a number not less than the number of the positioning holes are sprinkled on the graphite powder layer formed with the positioning holes, and fuel balls are made to fall into each of the positioning holes by vibration; the compacted graphite powder blank is lifted to the top of the fuel core block mold by a lifting mechanism, so that the fuel balls that have not fallen into the positioning holes are rolled out of the graphite powder layer.

7. The method for manufacturing TRISO fuel pellets according to claim 1 or 2, characterized in that: The hemispherical working portion and the fuel ball have the same radius.

8. The method for manufacturing TRISO fuel pellets according to claim 1 or 2, characterized in that: The radius of the positioning hole is 0.8mm-1.0mm.

9. A fuel pellet comprising a graphite matrix and a fuel ball, characterized in that: The fuel pellets are manufactured using the TRISO fuel pellet manufacturing method according to any one of claims 1 to 7.

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