Preparation method of periodic TRISO particle dispersion fuel pellet and fuel pellet

Abstract

The invention relates to the technical field of nuclear fuel preparation, and discloses a periodic TRISO particle dispersion fuel pellet preparation method which comprises the following steps: laying matrix powder in a mold cavity of a fuel pellet mold, and compacting to form a substrate layer; tRISO particles are laid on the substrate layer layer by layer through a particle arrangement mold; wherein the TRISO particles in the TRISO particle layer of the Nth layer are arranged and distributed at a first position, and the TRISO particles in the TRISO particle layer of the (N + 1) th layer are arranged and distributed at a second position; after the layer number of the TRISO particle layers reaches a preset layer number, compacting the TRISO particle layers and packaging the fuel pellet mold; and sintering and demolding the packaged fuel pellet mold to obtain the fuel pellet. Therefore, the arrangement and spacing of TRISO particles in the axial direction and the radial direction can be accurately controlled, so that the temperature gradient in the pellet is reduced, the TRISO particles are effectively prevented from cracking and losing efficacy, and the compact structure of the pellet is ensured. The invention further discloses a fuel pellet.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear fuel preparation, and particularly relates to a preparation method of a periodic TRISO particle dispersed fuel pellet and a fuel pellet. BACKGROUND

[0002] At present, TRISO (tristructural-isotropic) particles are a kind of three-structural isotropic nuclear fuel, and its excellent safety performance is widely used in high-temperature gas-cooled reactors and other advanced nuclear reactor designs. The commonly used fully ceramic microencapsulated (FCM) TRISO particles are randomly distributed inside. The aggregation of part of the TRISO particles not only causes the internal temperature gradient of the fuel pellet to be too high, but also causes the stress generated by the direct contact of the TRISO particles to cause particle rupture, which is easy to cause the structure of the TRISO particles to be damaged, fail and release nuclear fission products, and the like. Thus, the operation safety and heat conduction efficiency of the reactor are affected.

[0003] In the related art, in order to adjust the distribution of the TRISO particles in the radial direction and the axial direction of the fuel pellet, a process is adopted to stack a perforated silicon carbide (SiC) green disc layer by layer, and after the stacked green disc is subjected to cold isostatic pressing, degassing, sintering and other process procedures, a fuel pellet with relatively uniform distribution in the radial direction and the axial direction is obtained.

[0004] In the process of implementing the embodiments of the present disclosure, it is found that at least the following problems exist in the related art:

[0005] The above-mentioned method can obtain a fuel pellet meeting the requirements, but in the preparation process, most of the processes introduce organic matter, which volatilizes to form pores in the subsequent sintering process, which will affect the densification degree of the fuel pellet to some extent; at the same time, the process of degassing is added, which makes the process more and more complex, thus the preparation time is longer, the production cycle is prolonged, and the production cost is further increased. In addition, the process of manufacturing the green disc is complex, and it is difficult to consolidate the green disc.

[0006] It should be noted that the information disclosed in the above background section is only used to strengthen the understanding of the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0007] To provide a simple overview of some aspects of the disclosed embodiments the following is a brief summary. The summary is not an extensive overview of all of the embodiments discussed in the present application. It is not intended to identify key / critical elements of the embodiments or to delineate the scope of the embodiments, but to present some aspects of the embodiments in a simplified form as a prelude to the more detailed description of the embodiments presented later.

[0008] The present disclosure provides a preparation method of a periodic TRISO particle dispersed fuel pellet and a fuel pellet, which can accurately control the arrangement and spacing of TRISO particles in the axial and radial directions, thereby effectively adjusting the fuel density, ensuring the compactness of the pellet structure, while effectively reducing the complexity of the process, shortening the preparation time and production cycle, and reducing the production cost.

[0009] In some embodiments, the preparation method of the periodic TRISO particle dispersed fuel pellet comprises the following steps:

[0010] (1) laying a matrix powder in the mold cavity of the fuel pellet mold to form a substrate layer after compaction;

[0011] (2) using a particle arrangement mold to lay TRISO particles layer by layer on the substrate layer;

[0012] wherein after laying each layer of TRISO particles, the matrix powder is filled and covers the TRISO particles, and a TRISO particle layer is formed after compaction; and the TRISO particles in the Nth layer of TRISO particle layer are arranged and distributed in a first position, and the TRISO particles in the N+1th layer of TRISO particle layer are arranged and distributed in a second position, wherein N is a positive integer greater than or equal to 1;

[0013] (3) after the number of TRISO particle layers laid reaches a preset number, the fuel pellet mold is packaged after compaction;

[0014] (4) sintering and demolding the packaged fuel pellet mold to obtain a fuel pellet.

[0015] In some embodiments, the fuel pellet comprises a fuel pellet prepared by the preparation method of the periodic TRISO particle dispersed fuel pellet as described in the foregoing embodiments.

[0016] The preparation method of the periodic TRISO particle dispersed fuel pellet and the fuel pellet provided by the embodiments of the present disclosure can achieve the following technical effects:

[0017] By using a particle arrangement mold to lay a preset number of TRISO particle layers on the substrate layer of the fuel pellet mold, the arrangement and spacing of TRISO particles in the axial and radial directions can be accurately controlled to prevent TRISO particles from contacting each other, while compared with random arrangement of TRISO particles, the temperature gradient inside the pellet is reduced, the heat conduction efficiency of the fuel is improved, and the TRISO particle rupture failure is effectively prevented. On this basis, the preparation method provided by the present application is relatively simple, and does not need to add organic matter and perform a glue removal process. In this way, the production cycle can be effectively shortened, and the production cost can be reduced. In addition, the load capacity of TRISO particles can also be effectively improved, and the pellet structure is more compact.

[0018] The foregoing general description and the following detailed description are exemplary and explanatory only and are not intended to be limiting of the application. BRIEF DESCRIPTION OF DRAWINGS

[0019] One or more embodiments are illustrated by way of example in the figures that are not intended to be limiting of the application as defined by the claims and their equivalents. Identical reference numbers in the figures designate equivalent elements, and:

[0020] Figure 1 is a structural schematic diagram of a structure for using a particle arrangement mold in a fuel pellet mold provided by an embodiment of the present disclosure;

[0021] Figure 2 is a structural schematic diagram of a first base of a first kind provided by an embodiment of the present disclosure;

[0022] Figure 3 is a structural schematic diagram of a first base of a second kind provided by an embodiment of the present disclosure;

[0023] Figure 4 is a structural schematic diagram of a first base of a third kind provided by an embodiment of the present disclosure;

[0024] Figure 5 is a structural schematic diagram of a second base provided by an embodiment of the present disclosure;

[0025] Figure 6 is a structural schematic diagram of a first base of a second kind and a second base used in cooperation provided by an embodiment of the present disclosure;

[0026] Figure 7 is Figure 6 a structural schematic diagram in which a positioning channel segment and a positioning mating channel segment constitute a positioning channel;

[0027] Figure 8 is Figure 6 a structural schematic diagram in which a positioning channel segment and a positioning mating channel segment are staggered;

[0028] Figure 9 is a structural schematic diagram of a first base of a third kind and a second base used in cooperation provided by an embodiment of the present disclosure;

[0029] Figure 10 is Figure 9 a structural schematic diagram in which a positioning channel segment and a positioning mating channel segment constitute a positioning channel;

[0030] Figure 11 is Figure 9 a structural schematic diagram in which a positioning channel segment and a positioning mating channel segment are staggered;

[0031] Figure 12 is an X-ray scanning image of a fuel pellet provided by the embodiment of the present disclosure, which is perpendicular to the pressure direction;

[0032] Figure 13 is a flowchart of a preparation method of a periodic TRISO particle dispersed fuel pellet provided by the embodiment of the present disclosure.

[0033] Reference signs:

[0034] 100 - fuel pellet mold; 101 - lower pressing structure; 102 - graphite gasket; 103 - particle arrangement mold;

[0035] 200 - TRISO particle;

[0036] 10 - first base body; 11 - positioning plate; 12 - positioning channel segment; 13 - guide structure; 131 - guide cylinder; 132 - guide rod;

[0037] 20 - second base body; 21 - positioning fitting channel segment; 22 - guide groove. DETAILED DESCRIPTION

[0038] In order to enable a more detailed understanding of the features and technical content of the embodiments of the present disclosure, the implementation of the embodiments of the present disclosure will be described in detail below in conjunction with the drawings, which are only used for reference and do not limit the embodiments of the present disclosure. In the following technical description, in order to facilitate explanation, a plurality of details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. In other cases, in order to simplify the drawings, well-known structures and devices can be simplified.

[0039] The terms "first", "second", and the like in the specification and claims of the embodiments of the present disclosure and the above drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the embodiments of the present disclosure described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion.

[0040] In the embodiments of the present disclosure, the terms "upper", "lower", "inner", "middle", "outer", "front", "back" and the like indicate the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the embodiments of the present disclosure and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation. In addition, in addition to indicating the orientation or positional relationship, the above-mentioned part of the terms can also be used to represent other meanings, for example, the term "upper" can also be used to represent a certain dependent relationship or connection relationship in some cases. For those skilled in the art, the specific meaning of these terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0041] In addition, the terms "set", "connected", "fixed" should be broadly understood. For example, "connected" can be fixedly connected, detachably connected, or integrally configured; can be mechanically connected, or electrically connected; can be directly connected, or indirectly connected through an intermediate medium, or internal communication between two devices, elements or components. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0042] Unless otherwise specified, the term "a plurality of" means two or more.

[0043] In the embodiments of the present disclosure, the character " / " represents an "or" relationship between the objects before and after it. For example, A / B means: A or B.

[0044] The term "and / or" is a description of the association between objects, which means that there can be three relationships. For example, A and / or B means: A or B, or, A and B, the three relationships.

[0045] It should be noted that the embodiments in the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0046] At present, the fuel element used by the traditional high temperature gas cooled reactor is to disperse TRISO particles in the graphite matrix. After being subjected to neutron irradiation, the graphite matrix is prone to changes in microstructure and size, such as an increase in anisotropy and volume shrinkage. These changes in physical properties will affect the safety of the graphite material, and will also shorten its service life. Based on the advantages of SiC material, such as good irradiation stability, high thermal conductivity, and chemical stability, etc. Therefore, a SiC-based all-ceramic micro-encapsulated fuel is provided, that is, TRISO particles are dispersed in a SiC matrix to form an FCM fuel pellet.

[0047] The high temperature gas cooled reactor core is composed of about 10 9 ~ 10 10If a small number of TRISO particles are damaged, it will affect the operation and maintenance of the reactor; if a large number of TRISO particles fail, it will cause a large amount of radioactive fission products to leak, affecting the safe operation of the reactor.

[0048] There are four main TRISO particle failure mechanisms in the related art, one of which is the amoeba effect, that is, due to the temperature gradient inside the TRISO particle, the fuel kernel migrates to the high temperature side, eventually leading to the failure of the TRISO particle.

[0049] In most processes for preparing FCM fuel, TRISO particles are randomly distributed, so that the TRISO particles are unevenly distributed in the radial and axial directions of the fuel pellet, and some areas may have TRISO particles in contact with each other. Therefore, during the process of pressure sintering, the uneven distribution of TRISO particles in the radial and axial directions of the fuel pellet may reduce the heat conduction efficiency, resulting in a high temperature gradient inside the pellet, which may cause the SiC layer to phase change, decompose and reduce performance, and the kernel fuel to migrate, etc., causing damage, failure and release of nuclear fission products, etc.

[0050] In addition, the aggregation of some TRISO particles not only causes a high temperature gradient inside the fuel pellet, but also causes stress between the directly contacted TRISO particles, which may cause the particles to crack, etc., thereby seriously affecting the safe operation of the reactor. At the same time, the current process uses a perforated SiC green disc to stack layer by layer, and the stacked green disc is subjected to cold isostatic pressing, degassing, sintering and other process procedures. Therefore, the process of degassing is added, which is more complex and time-consuming, prolonging the production cycle and further increasing the production cost.

[0051] On this basis, TRISO particles are fixed on the SiC green disc by punching, but the dried SiC green disc is prone to cracking after punching and cutting, and the SiC green disc needs to be punched and cut multiple times, which is a tedious process. At the same time, during the process of stacking the SiC green disc layer by layer, the tightness between the SiC green discs needs to be ensured to make the overall structure of the fuel pellet dense. Therefore, the connection method between each layer of SiC green disc also needs to be considered.

[0052] Therefore, in combination with the problems in the related art, as shown in Figure 12 The present disclosure provides a preparation method of a periodic TRISO particle dispersed fuel pellet, which can accurately control the arrangement and spacing of TRISO particles in the axial and radial directions, effectively adjust the fuel density, ensure the densification of the pellet structure, and effectively reduce the complexity of the process, shorten the preparation time and production cycle, and reduce the production cost. Specifically, the method comprises the following steps:

[0053] (1) Laying matrix powder in the mold cavity of the fuel pellet mold and compacting it to form a base layer;

[0054] (2) Using a particle arrangement mold to lay TRISO particles layer by layer on the base layer;

[0055] After each layer of TRISO particles is laid, the matrix powder is filled and covered with TRISO particles, and a TRISO particle layer is formed after compaction; and the TRISO particles in the TRISO particle layer of the Nth layer are arranged and distributed in a first position, and the TRISO particles in the TRISO particle layer of the N+1th layer are arranged and distributed in a second position, wherein N is a positive integer greater than or equal to 1;

[0056] (3) After the number of TRISO particle layers reaches the preset number, the fuel pellet mold is encapsulated after compaction;

[0057] (4) Sintering and demoulding the encapsulated fuel pellet mold to obtain the fuel pellet.

[0058] The method for preparing the periodic TRISO particle dispersion fuel pellets provided by the embodiment of the present disclosure is adopted, and a preset number of TRISO particle layers are laid on the base layer of the fuel pellet mold by using a particle arrangement mold. In this way, the arrangement and spacing of the TRISO particles in the axial and radial directions can be precisely controlled to prevent the TRISO particles from contacting each other. At the same time, compared with the random arrangement of TRISO particles, the temperature gradient inside the pellet is reduced, the thermal conductivity efficiency of the fuel is improved, and the TRISO particles are effectively prevented from breaking and failing. On this basis, the preparation method provided by the present application has a relatively simple process and does not require processes such as adding organic matter and debinding. In this way, the production cycle can be effectively shortened while reducing production costs. In addition, the load capacity of the TRISO particles can also be effectively improved, making the pellet structure more compact.

[0059] In this embodiment, the fuel pellet mold includes a Spark Plasma Sintering (SPS) mold.

[0060] In this embodiment, combined with Figure 1 As shown, a downward pressure structure 101 is provided at a lower middle position of the fuel pellet mold 100, and an upward pressure structure (not shown in the figure) is provided at an upper middle position of the fuel pellet mold 100. After the matrix powder is laid in the mold cavity of the fuel pellet mold, it is compacted by the downward pressure structure 101 and the upward pressure structure to form a base layer.

[0061] Optionally, the particle arrangement mold has regularly arranged positioning channels, and the TRISO particles are laid through the positioning channels to form a regularly arranged TRISO particle layer; wherein the particle arrangement mold comprises a first particle arrangement mold and a second particle arrangement mold, and the positioning channels of the first particle arrangement mold and the second particle arrangement mold have the same arrangement mode but different arrangement positions.

[0062] In this way, the TRISO particles in the TRISO particle layer can be effectively constrained and fixed through the positioning channels of the first particle arrangement mold and the second particle arrangement mold, so that the TRISO particles are arranged periodically.

[0063] Here, the same arrangement mode of the positioning channels of the first particle arrangement mold and the second particle arrangement mold means that the positioning channels in the first particle arrangement mold and the second particle arrangement mold are arranged in an array in a uniform manner, and the number of the positioning channels is the same.

[0064] The different arrangement positions of the positioning channels of the first particle arrangement mold and the second particle arrangement mold means that the first particle arrangement mold is arranged in an array in a uniform manner with the center axis as the reference, and the second particle arrangement mold is arranged in an array in a uniform manner with the position deviating from the center axis as the reference.

[0065] In an embodiment of the present application, the TRISO particles are laid on the substrate layer layer by layer using the particle arrangement mold, comprising: laying the TRISO particles by alternately and repeatedly using the first particle arrangement mold and the second particle arrangement mold until the number of the laid TRISO particle layers reaches a preset number, so that the TRISO particles in the fuel pellet are arranged periodically.

[0066] In this way, the TRISO particles in each TRISO particle layer are arranged at different positions by alternately and repeatedly using the first particle arrangement mold and the second particle arrangement mold. Here, the first particle arrangement mold needs to be removed from the fuel pellet mold after the first particle arrangement mold is used, and the second particle arrangement mold needs to be removed from the fuel pellet mold after the second particle arrangement mold is used, so as to be alternately and repeatedly used.

[0067] Here, the TRISO particles are arranged at specific positions by the first particle arrangement mold and the second particle arrangement mold, so that the TRISO particles are arranged uniformly in the axial and radial directions. Therefore, the prepared fuel pellet has high densification and few defects such as pores, and the heat conduction efficiency of the fuel pellet is improved.

[0068] In the embodiment, after each layer of TRISO particles is laid, matrix powder is filled and covers the TRISO particles, and after compaction, a layer of TRISO particles is formed. In this way, the TRISO particles can be separated by the matrix powder to form a layer of TRISO particles in which the TRISO particles are regularly arranged and mixed in the matrix powder.

[0069] In the embodiment, in the vertical direction, the positions of the TRISO particles in the adjacent layers of TRISO particles are different. For example, the TRISO particles in the Nth layer of TRISO particles are arranged in a first position, and the TRISO particles in the N+1th layer of TRISO particles are arranged in a second position. In this way, the arrangement and spacing of the TRISO particles in the axial and radial directions can be accurately controlled, thereby effectively adjusting the fuel density and ensuring the compactness of the pellet structure.

[0070] Optionally, the mold cavity of the fuel pellet mold is provided with a positioning structure, and the first particle arrangement mold and the second particle arrangement mold are each provided with a positioning matching structure. In the process of alternately and repeatedly using the first particle arrangement mold and the second particle arrangement mold, the positions of the first particle arrangement mold and the second particle arrangement mold are determined by the positioning structure and the positioning matching structure, thereby determining the positions of the TRISO particles in different layers of TRISO particles.

[0071] In the embodiment, the positioning structure includes a first scale in the mold cavity of the fuel pellet mold, and the positioning matching structure includes a second scale or a positioning protrusion on the first particle arrangement mold and / or the second particle arrangement mold. In this way, in the process of laying different layers of TRISO particles, the positions of the first particle arrangement mold and the second particle arrangement mold are adjusted by the positioning structure and the positioning matching structure, thereby effectively adjusting the position distribution of the TRISO particles in different layers of TRISO particles.

[0072] In one embodiment of the present application, in the process of laying each layer of TRISO particles, the matrix powder is allowed to fall through a screen onto the surface of the TRISO particles to prevent the TRISO particles from moving. Until all the TRISO particles in the entire plane are covered, after compaction, a layer of TRISO particles containing the matrix powder and the TRISO particles is formed. The next layer of TRISO particles is laid to isolate the TRISO particles in the layer of TRISO particles from each other by the matrix powder.

[0073] After each layer of TRISO particles is laid, the matrix powder is also covered on all the TRISO particles through a screen. In this way, the TRISO particles in the horizontal direction can be isolated by the matrix powder, and the TRISO particles in the vertical direction can also be isolated by the matrix powder.

[0074] In one specific embodiment, a screen is placed above the fuel pellet mold. Matrix powder is poured onto the screen in small amounts and repeatedly. The screen is gently shaken, allowing the matrix powder to pass through the screen and gently float into the mold cavity of the fuel pellet mold. It then settles on the surface of the TRISO particles until it covers them. This prevents the matrix powder from shifting the TRISO particles during pouring. A matching indenter is then used to compact the matrix powder, completing the laying of a layer of TRISO particles.

[0075] In one embodiment of the present application, during the process of laying each TRISO particle layer, it also includes: squeezing the TRISO particles through the positioning channel through the push rod group so that part of the TRISO particles are embedded in the base powder of the base layer or the lower TRISO particle layer.

[0076] In one specific embodiment, the ejector pin assembly includes one or more ejector pins. In the case of multiple ejector pins, the multiple ejector pins may be fixedly mounted on a fixed plate. To further define the position of each TRISO particle, after the TRISO particle is placed into the mold cavity through the positioning channel, an ejector pin is passed through the positioning channel and applied with a certain pressure, so that the top of the ejector pin presses against the TRISO particle, forcing a portion of the TRISO particle to embed within the base powder of the base layer or the underlying TRISO particle layer. This further ensures the position of the TRISO particle.

[0077] Here, the circumferential diameter of the ejector pin is smaller than the aperture of the positioning channel. Meanwhile, the thickness of the base layer and the thickness of the matrix powder of the TRISO particle layer are at least greater than the radius of the TRISO particles. This prevents the TRISO particles from contacting each other after extrusion.

[0078] In one specific embodiment, after the particle arrangement mold is placed into the fuel pellet mold and before the TRISO particles are placed into the positioning channels, a push rod can be used to directly squeeze the base powder of the base layer or the underlying TRISO particle layer to create positioning holes. The top of the push rod is spherical or hemispherical, with a diameter less than or equal to the diameter of the TRISO particles. In this way, after the positioning holes are created, the TRISO particles are poured from the positioning channels into the mold cavity, so that each TRISO particle falls into its corresponding positioning hole.

[0079] Combine Figure 1 and Figure 2As shown, in one embodiment of the present application, the particle arrangement mold comprises: a first base body 10, comprising a positioning plate 11 and a guide structure 13 arranged on the positioning plate 11, the positioning plate 11 has regularly arranged positioning channel segments 12; wherein the guide structure 13 comprises a guide cylinder 131, which can cooperate with the mold cavity of the fuel pellet mold 100, so that the positioning plate 11 is located on the substrate layer or the TRISO particle layer, and the TRISO particles are laid on the substrate layer or the TRISO particle layer through the positioning channel segments 12.

[0080] Here, the particle arrangement mold comprises a first particle arrangement mold and a second particle arrangement mold, and the structures of the first particle arrangement mold and the second particle arrangement mold can be the same or different. When the structures of the first particle arrangement mold and the second particle arrangement mold are different, only the form of the positioning structure on the guide structure 13 is different; for example, the first particle arrangement mold is provided with a second scale, and the second particle arrangement mold is provided with a positioning protrusion. The rest of the structures are the same.

[0081] In this embodiment, whether the structures of the first particle arrangement mold and the second particle arrangement mold are the same or different, the arrangement positions of the positioning channels are different. Here, the first particle arrangement mold is taken as an example, and the second particle arrangement mold will not be described again. Specifically, it comprises a first base body 10, which comprises a positioning plate 11 and a guide structure 13 arranged on the positioning plate 11, wherein the positioning plate 11 has regularly arranged positioning channel segments 12 (the positioning channel segments 12 in the other second particle arrangement mold are different from the position in this embodiment), and the guide structure 13 comprises a guide cylinder 131, which can make the positioning plate 11 located on the substrate layer or the TRISO particle layer along the guide direction of the mold cavity of the fuel pellet mold 100, and finally the TRISO particles are laid on the substrate layer or the TRISO particle layer through the positioning channel segments 12. Thus, the laying of the TRISO particles is completed, and then the base powder is put in to complete the laying of the TRISO particle layer.

[0082] In addition, the particle arrangement mold can also have other structures. In combination with the above description of the first particle arrangement mold and the second particle arrangement mold, the particle arrangement mold can have other structures. Figures 3 to 11 As shown, the guide structure 13 comprises a guide rod 132, or the guide structure 13 comprises a guide cylinder 131 and a guide rod 132 arranged on the inner wall of the guide cylinder 131; the particle arrangement mold further comprises: a second base body 20, which is a column structure, and the two end faces of the column are provided with positioning matching channel segments 21 which are used in cooperation with the positioning channel segments 12; the side surface of the column is provided with a guide groove 22 which is used in cooperation with the guide rod 132, wherein the guide groove 22 and the guide rod 132 have a set distance therebetween.

[0083] The positioning channel is formed by the complete matching of the positioning channel section 12 of the first base body 10 and the positioning matching channel section 21 of the second base body 20, so that the TRISO particles can be laid into a regularly arranged TRISO particle layer in the mold cavity of the fuel pellet mold through the positioning channel; the guide structure 13 of the first base body 10 and the guide groove 22 of the second base body 20 are moved relative to each other, so that the positioning channel section 12 and the positioning matching channel section 21 are staggered, and the TRISO particles in the positioning channel section 12 and the positioning matching channel section 21 are isolated.

[0084] In an optional embodiment, as shown in Figure 3 , Figures 5 to 8 , the guide structure 13 includes a guide rod 132, and the guide rod 132 of the first base body 10 is used in cooperation with the guide groove 22 of the second base body 20. Here, reference can be made to Figure 7 , the positioning channel section 12 and the positioning matching channel section 21 completely match to form the positioning channel, and when the TRISO particles are fed into the fuel pellet mold, the TRISO particles can be laid into a regularly arranged TRISO particle layer in the mold cavity of the fuel pellet mold through the positioning channel.

[0085] After the laying is completed, the guide rod 132 and the guide groove 22 have a set spacing, that is, the guide structure 13 of the first base body 10 and the guide groove 22 of the second base body 20 are moved relative to each other. Here, reference can be made to Figure 8 , the guide rod 132 is moved, so that the positioning channel section 12 and the positioning matching channel section 21 are staggered. In this way, the TRISO particles in the positioning channel section 12 and the positioning matching channel section 21 can be isolated, so that the entire particle arrangement mold can be taken out and replaced with another particle arrangement mold.

[0086] In another optional embodiment, as shown in Figure 4 , Figure 5 , Figures 9 to 11 , the guide structure 13 includes a guide cylinder 131 and a guide rod 132 arranged on the inner wall of the guide cylinder 131, and the second base body 20 is located in the guide cylinder 131 of the first base body 10, and the guide rod 132 of the first base body 10 is used in cooperation with the guide groove 22 of the second base body 20. Here, reference can be made to Figure 10 , the positioning channel section 12 and the positioning matching channel section 21 completely match to form the positioning channel, and when the TRISO particles are fed into the fuel pellet mold, the TRISO particles can be laid into a regularly arranged TRISO particle layer in the mold cavity of the fuel pellet mold through the positioning channel. After the laying is completed, reference can be made to Figure 8The moving guide rod 132 can disengage the positioning channel section 12 from the positioning mating channel section 21. In this way, the TRISO particles in the positioning channel section 12 and the positioning mating channel section 21 can be isolated, so that the entire particle arrangement mold can be removed and replaced with another particle arrangement mold.

[0087] In one embodiment of the present application, the thickness of the positioning plate 11 is 1:1 of the particle size of the TRISO particles. Here, the thickness of the positioning plate 11 is 0.8mm-1.2mm. In this way, it is convenient to lay and fix the TRISO particles. The length of the guide structure 13 is greater than the length of the column structure, and the difference between the length of the guide structure 13 and the length of the column structure is 8mm-15mm. In this way, it is convenient to move the first base 10 or the second base 20.

[0088] In one embodiment of the present application, the set distance between the groove bottom of the guide groove 22 and the first surface of the guide rod 132 is 1:2 of the particle size of the TRISO particles; the set distance between the groove wall of the guide groove 22 and the second surface of the guide rod 132 is 1:2 of the particle size of the TRISO particles.

[0089] In this embodiment, as shown in Figure 7 and Figure 8 , the groove wall of the guide groove 22 is arranged opposite to the second surface of the guide rod 132. In this way, in the case that there is a set distance between the groove wall of the guide groove 22 and the second surface of the guide rod 132, the first base 10 or the second base 20 can be moved in the direction of the set distance, so that the groove wall of the guide groove 22 and the second surface of the guide rod 132 are in contact or separated.

[0090] In this embodiment, as shown in Figure 10 and Figure 11 , the groove bottom of the guide groove 22 is arranged opposite to the first surface of the guide rod 132. In this way, in the case that there is a set distance between the groove bottom of the guide groove 22 and the first surface of the guide rod 132, the first base 10 or the second base 20 can be moved in the direction of the set distance. The groove bottom of the guide groove 22 and the first surface of the guide rod 132 are in contact or separated.

[0091] In this embodiment, the wall thickness of the guide cylinder 131 is 1.0mm-2.0mm.

[0092] Here, the cylinder diameter of the guide cylinder 131 is greater than the diameter of the second base 20. At the same time, the height of the guide rod 132 is less than the depth of the guide groove 22, so that through the difference, the guide rod 132 of the first base 10 and the guide groove 22 of the second base 20 can be moved relative to each other.

[0093] In an embodiment of the present application, the particle arrangement mold and the ejector pin can be made of resin material or metal material. In the case of the particle arrangement mold and the ejector pin made of resin material, the mold can be prepared by 3D printing technology. In the case of the particle arrangement mold and the ejector pin made of metal material, the corresponding mold can be prepared by machining.

[0094] In an embodiment of the present application, the first base body 10 of the particle arrangement mold prepared by 3D printing technology specifically includes: adding support to the first base body model, importing the sliced first base body model file into the 3D printer, pouring resin into the transparent film, and running the program. The exposure time is 2s-5s, and the exposure power is 5mW / cm 3 ~10mW / cm 3 After the program ends, the residual resin is washed away by using anhydrous ethanol ultrasonic cleaning for 10-15min, and then the mold is cured by using an ultraviolet lamp for 1-3h. After curing, the support of the first base body model is removed, and the surface is polished.

[0095] In the related art, most of the organic matters such as dispersants, binders and plasticizers are added, and the content is as high as 10%-20%. Therefore, the process problem of removing the organic matters before sintering is involved. Here, the removal process needs to completely remove the above-mentioned organic matters by using appropriate parameters. Therefore, these parameters will affect the performance of the fuel pellet, and the removal process flow is too complex and tedious, and the densification degree of the fuel pellet will be affected to some extent during the removal process.

[0096] In an embodiment of the present application, the base body powder is prepared by the following method: the slurry prepared by mixing and configuring the raw material powder and the dispersant is ball milled, and then dried, ground and sieved to obtain the mixed and uniform base body powder. The raw material powder includes SiC powder, Y2O3 powder and Sc2O3 powder weighed according to a preset ratio.

[0097] In an embodiment of the present application, the mass fraction of Y2O3 powder and Sc2O3 powder in the raw material powder is 3%-10%, and the dispersant includes anhydrous ethanol, and the proportion of anhydrous ethanol is 50wt%-60wt%.

[0098] In this way, since the anhydrous ethanol is completely volatilized during the drying process, the base body powder provided by the embodiment of the present application does not contain organic matter, and therefore, the removal problem is not involved, which not only simplifies the preparation process and shortens the preparation time, but also improves the densification of the fuel pellet.

[0099] In one embodiment of the present application, the slurry prepared by mixing the raw material powder and the dispersant is ball milled, and then dried, ground and sieved to obtain the uniformly mixed matrix powder, including: ball milling the slurry prepared by mixing the raw material powder and the dispersant by a ball mill, the ball milling time being 24h; drying the matrix slurry after ball milling, the drying temperature being 120°C and the drying time being 12h; grinding the matrix slurry after drying, and sieving to obtain the uniformly mixed matrix powder.

[0100] In one embodiment of the present application, before laying the matrix powder in the mold cavity of the fuel pellet mold, the graphite gasket and the graphite paper are placed in the mold cavity of the fuel pellet mold. In this way, the graphite gasket is arranged to make the sintered fuel pellet more flat, and the graphite paper is arranged to facilitate the demolding of the sintered fuel pellet.

[0101] In one embodiment of the present application, the sintering of the packaged fuel pellet mold includes: sintering the packaged fuel pellet mold under vacuum conditions, the sintering temperature being 1700-1850°C, the sintering pressure being 15-30MPa, and the pressure holding time being 10-20min.

[0102] In one embodiment of the present application, during the sintering and demolding of the sintered fuel pellet mold, the process includes: taking out the fuel pellet mold after sintering, taking out the fuel pellet inside the fuel pellet mold, polishing the surface graphite paper with sandpaper, and finally obtaining the finished fuel pellet. The X-ray scanning diagram of the cut and polished fuel pellet is shown in Figure 12

[0103] In one embodiment of the present application, the face spacing d of the adjacent TRISO particle layer is calculated according to the face-centered cubic arrangement, specifically, calculated by the following formula:

[0104]

[0105] Wherein, x is the spacing between each TRISO particle.

[0106] In one embodiment of the present application, the mass m of the matrix powder added in each layer of TRISO particle layer is calculated by the following formula:

[0107] m = p p r 2 d

[0108] Wherein, p is the density of the matrix powder; r is the radius of the mold cavity of the fuel pellet mold.

[0109] ​In a specific embodiment, a positioning scale is provided on the edge of the cavity opening of the fuel pellet mold, so that the first particle arrangement mold and the second particle arrangement mold can ensure the accuracy of their positions through the positioning scale. Figure 1 As shown, a downward pressure structure 101 is positioned at the lower center of the fuel pellet mold 100, and an upward pressure structure (not shown) is positioned at the upper center of the fuel pellet mold 100. Compaction is achieved through these structures. A graphite gasket 102 is placed on the downward pressure structure 101. After a base layer is laid over the graphite gasket 102, a particle arrangement mold 103 is placed on the base layer, and then TRISO particles 200 are placed.

[0110] In one embodiment of the present application, the method for preparing fuel pellets and the particle arrangement mold involved provided in the present application include but are not limited to spark plasma sintering, and are also applicable to sintering methods such as hot pressing sintering and pressureless sintering.

[0111] The present invention is further explained below with reference to the following examples.

[0112] Example 1

[0113] Combine Figure 13 As shown, Example 1 provides a fuel pellet, which is prepared by the following method:

[0114] Preparation of matrix powder: A slurry prepared by mixing raw material powders and anhydrous ethanol is ball-milled for 24 hours. The milled matrix slurry is then dried at 120°C for 12 hours. The slurry is then ground and sieved to obtain a uniformly mixed matrix powder. The raw material powder comprises SiC powder, Y2O3 powder, and Sc2O3 powder, with the mass fraction of Y2O3 and Sc2O3 in the raw material powder being 5%. The proportion of anhydrous ethanol is 50 wt%.

[0115] Preparation of particle arrangement mold: Prepare the first particle arrangement mold and the second particle arrangement mold, using Figure 2 The structure shown. Two sets of first substrates were prepared using 3D printing technology. Specifically, support was added to the first substrate model, the sliced ​​first substrate model file was imported into the 3D printer, resin was poured into the transparent film, and the program was run. The exposure time was 3s and the exposure power was 6mW / cm 3 After the process is complete, ultrasonic cleaning with anhydrous ethanol for 12 minutes is performed to remove any residual resin, and the mold is then cured with a UV lamp for 1 hour. After curing, the supports of the first matrix model are removed and the surface is polished to obtain two sets of first matrices.

[0116] Determine the interplanar spacing d between adjacent TRISO particle layers in a fuel pellet:

[0117]

[0118] wherein x is the spacing between each TRISO particle.

[0119] Determine the matrix powder mass:

[0120] m = p p r 2 d

[0121] wherein p is the density of the matrix powder; r is the radius of the cavity of the fuel pellet mold.

[0122] In this example, the spacing between each TRISO particle is 1.1140 mm, and the matrix powder mass is 2.20 g.

[0123] S201, lay the matrix powder in the cavity of the SPS mold, and form a substrate layer after compaction;

[0124] S202, place the first particle arrangement mold into the inner cavity of the SPS mold, control the first scale on the SPS mold to align with the second scale line on the first particle arrangement mold, lay the TRISO particles through the first particle arrangement mold, extrude the TRISO particles through the positioning channel with the ejector rod, embed part of the TRISO particles into the substrate layer, and take out the first particle arrangement mold;

[0125] S203, the matrix powder falls through the screen onto the surface of the TRISO particles until it covers all the TRISO particles in the entire plane, and is compacted to form a TRISO particle layer;

[0126] S204, place the second particle arrangement mold into the inner cavity of the SPS mold, control the first scale on the SPS mold to align with the positioning protruding edge line on the second particle arrangement mold, lay the TRISO particles through the second particle arrangement mold, extrude the TRISO particles through the positioning channel with the ejector rod, embed part of the TRISO particles into the TRISO particle layer, and take out the second particle arrangement mold;

[0127] S205, the matrix powder falls through the screen onto the surface of the TRISO particles until it covers all the TRISO particles in the entire plane, and is compacted to form a TRISO particle layer;

[0128] S206, alternately use the first particle arrangement mold and the second particle arrangement mold to lay the TRISO particles until the number of layers of the laid TRISO particle layer reaches 8.

[0129] S207, package the fuel pellet mold;

[0130] S208, sintering and demolding the packaged fuel pellet mold, wherein the sintering temperature is 1800 DEG C, the sintering pressure is 15 MPa, and the pressure holding time is 10 min, to obtain the fuel pellet.

[0131] The present disclosure further discloses a fuel pellet prepared by the preparation method of the periodically TRISO particle dispersed fuel pellet as described in the foregoing embodiments.

[0132] In some embodiments, the specific structure of the fuel pellet refers to the foregoing embodiments, and since the present fuel pellet adopts all the technical solutions of the foregoing embodiments, it at least has all the technical effects brought by the technical solutions of the foregoing embodiments, which will not be described one by one here.

[0133] The above description and drawings sufficiently illustrate the embodiments of the present disclosure to enable one skilled in the art to practice them. Other embodiments can include structural and other changes. The embodiments represent only the possible variations. Individual components and functions are optional unless explicitly required, and the order of operations can be changed. Parts and features of some embodiments can be included or replaced by parts and features of other embodiments. The embodiments of the present disclosure are not limited to the structures described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method of making a periodic TRISO particle dispersed fuel pellet, characterized in that, The method comprises the following steps: (1) laying a base powder in a mold cavity of a fuel pellet mold to form a base layer after compaction; (2) using a particle arrangement mold to lay TRISO particles on the base layer layer by layer; wherein after laying each layer of TRISO particles, the base powder is filled and the TRISO particles are covered, and a TRISO particle layer is formed after compaction; and the TRISO particles in the Nth layer of TRISO particle layer are arranged in a first position, and the TRISO particles in the N+1th layer of TRISO particle layer are arranged in a second position, wherein N is a positive integer greater than or equal to 1; (3) after the number of TRISO particle layers laid reaches a preset number, the fuel pellet mold is encapsulated after compaction; (4) sintering and demolding the encapsulated fuel pellet mold to obtain a fuel pellet.

2. The production method according to claim 1, characterized by, The particle arrangement mold comprises a first particle arrangement mold and a second particle arrangement mold; wherein the first particle arrangement mold and the second particle arrangement mold both have regularly arranged positioning channels, and the arrangement modes of the positioning channels of the first particle arrangement mold and the second particle arrangement mold are the same, and the arrangement positions of the positioning channels of the first particle arrangement mold and the second particle arrangement mold are different, and the TRISO particles are laid through the positioning channels.

3. The preparation method according to claim 2, characterized in that The method of laying TRISO particles on the base layer layer by layer using the particle arrangement mold comprises: The TRISO particles are laid by alternately and repeatedly using the first particle arrangement mold and the second particle arrangement mold until the number of TRISO particle layers laid reaches a preset number, so that the TRISO particles in the fuel pellet present a periodic arrangement.

4. The production method according to claim 3, characterized by, The mold cavity of the fuel pellet mold is provided with a positioning structure, and the first particle arrangement mold and the second particle arrangement mold are provided with a positioning matching structure, so that the positions of the first particle arrangement mold and the second particle arrangement mold are determined through the positioning structure and the positioning matching structure during the alternately using of the first particle arrangement mold and the second particle arrangement mold.

5. The production method according to any one of claims 1 to 4, characterized by, The particle arrangement mold comprises: A first base body comprising a positioning plate and a guide structure arranged on the positioning plate, the positioning plate having regularly arranged positioning channel segments, and the TRISO particles are laid through the positioning channel segments.

6. The production method according to claim 5, characterized by, The guide structure comprises a guide cylinder, or the guide structure comprises a guide cylinder and a guide rod arranged on the inner wall of the guide cylinder; The particle arrangement mold further comprises: A second base body in the form of a column, both end faces of the column being provided with positioning matching channel segments for matching the positioning channel segments; and a side face of the column being provided with a guide groove for matching the guide rod, wherein the guide groove and the guide rod have a set distance therebetween.

7. The preparation method according to claim 6, characterized in that The positioning channel segments of the first base body and the positioning matching channel segments of the second base body completely match to form the positioning channel; and the guide rod of the first base body and the guide groove of the second base body move relative to each other to enable the positioning channel segments and the positioning matching channel segments to be staggered and isolate the TRISO particles in the positioning channel segments and the positioning matching channel segments.

8. The preparation method according to claim 5, characterized in that The thickness of the positioning plate and the particle size of the TRISO particles are in a ratio of 1:

1.

9. The production method according to any one of claims 1 to 4, characterized by, The raw material powder comprises SiC powder, Y2O3 powder and Sc2O3 powder weighed according to a preset ratio, and the mass fraction of the Y2O3 powder and the Sc2O3 powder in the raw material powder is 3% to 10%.

10. A fuel pellet characterized by A fuel pellet comprising a dispersion of the periodic TRISO particles of any one of claims 1 to 9. A fuel pellet prepared by the method of preparing a dispersion of periodic TRISO particles.

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