Preparation method and fixing device of fuel core with directional arrangement of TRISO particles

Abstract

The present invention belongs to the field of radioactive pollutant decontamination and protection technology, and specifically relates to a method for preparing a fuel core with TRISO particles arranged in a directional manner and a fixing device. The method comprises the following steps: S1: placing the matrix powder at a set position, and pre-pressing a flat blank by a press; S2: placing a fixing device with TRISO particles arranged in a set arrangement above the flat blank, wherein the TRISO particles and the flat blank are arranged without obstruction and the spacing is not greater than the diameter of the TRISO particles; S3: applying pressure to the side of the fixing device away from the flat blank by a press, so that the TRISO particles are detached from the fixing device and then embedded in the flat blank in a directional manner; S4: repeating steps S1-S3 to obtain a fuel blank containing multiple layers of TRISO particles; S5: after adjusting the fuel blank to a set shape, hot pressing and sintering the fuel blank to obtain a fuel pellet.

Description

Technical Field

[0001] The present invention belongs to the technical field of radioactive pollutant decontamination and protection, and specifically relates to a method for preparing a fuel core with TRISO particles arranged in a direction and a fixing device. Background Art

[0002] TRISO (Tristructural Isotropic), as the nuclear fuel of the nuclear core, will release radioactive pollutants itself. Although the buffer layer, IPyC layer, SiC layer and OPyC layer on the outside of the TRISO particle nuclear fuel will contain the radioactive fission products layer by layer and prevent the release of radioactive fission products, a certain amount of radioactive pollutants will still break through.

[0003] Even so, TRISO, as an ideal accident-tolerant nuclear fuel, is often used in a variety of reactor types, including high-temperature gas-cooled reactors. A typical high-temperature gas-cooled reactor contains more than 10,000 TRISO particles. The arrangement of these TRISO particles determines important properties such as the temperature distribution of the fuel elements and the release of fission gases. Therefore, the directional arrangement of TRISO particles is an important parameter for improving the safety of advanced reactors.

[0004] Commonly used dispersed fuel pellets are obtained by randomly distributing TRISO particles in a SiC or ZrC (CN117373704A) matrix and sintering them by hot pressing or spark plasma sintering (SPS). The volume fraction of TRISO particles in the fuel pellets obtained in this way is small, the temperature distribution in the reactor is uneven, and the dimensional accuracy is difficult to control during the processing after sintering, resulting in a low yield.

[0005] In recent years, in order to improve the efficiency of fuel use and increase the fuel loading capacity, the arrangement of fuel pellets has attracted much attention. Patent CN111199809A uses 3D printing to output a base unit with set arrangement grooves, and cooperates with a robotic arm to place multiple TRISO particles into the grooves one by one, achieving a reasonable distribution of TRISO particles. However, the number of TRISO particles that the robotic arm can put in at one time is limited, which is not conducive to the industrial production of large-sized pellets. Patent CN116417165A uses a screen to prepare a single-layer fuel microsphere layer, and obtains a fuel pellet with a density of 5%-60% by superimposing a fuel thin layer. However, this patent directly scatters the fuel microspheres on the mold. Later, when the matrix is ​​pre-pressed, the strength and thickness of the microsphere thin layer blank cannot be controlled. Patent CN117584239A uses a multi-station automatic rotation regular arrangement of TRISO particles, absorbs TRISO particles into fixed holes through vacuum negative pressure, stops the vacuum negative pressure at a certain height above the powder layer surface, and TRISO particles fall to the powder layer surface under the action of gravity. However, when the vacuum negative pressure is stopped, a certain degree of powder absorption will be caused, thereby hindering the landing of the small balls. In addition, the size and mass of the small balls are different, which will cause different landing states, resulting in the small balls failing to land at the predetermined position. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing a fuel core with directional arrangement of TRISO particles and a fixing device, so as to quickly complete the directional arrangement of a large number of TRISO particle pellets, and realize efficient, high-density, low-cost, industrialized precise and orderly arrangement of TRISO particles.

[0007] To achieve the above object, the present invention provides a method for preparing a fuel core with directional TRISO particles, comprising the following steps:

[0008] S1: placing the base powder at a set position and pre-pressing it through a press to obtain a flat green blank;

[0009] S2: placing a fixture with TRISO particles arranged in a set arrangement above the planar blank, wherein the TRISO particles are arranged without any obstruction to the planar blank and the spacing between the TRISO particles is no greater than the diameter of the TRISO particles;

[0010] S3: applying pressure to the side of the fixture away from the planar blank by using a press, so that the TRISO particles are separated from the fixture and embedded in the planar blank in a directional manner;

[0011] S4: repeating steps S1-S3 to obtain a fuel blank containing multiple layers of TRISO particles;

[0012] S5: After adjusting the fuel billet to a set shape, hot pressing and sintering the fuel billet to obtain a fuel pellet.

[0013] As an embodiment of the present invention, when preparing a fuel billet having multiple layers containing TRISO particles, the arrangement positions of the TRISO particles in two adjacent layers are different; and / or the diameters of the TRISO particles in two adjacent layers are different.

[0014] As an embodiment of the present invention, when preparing a fuel blank having multiple layers containing TRISO particles, the arrangement mode and / or diameter of the fixing holes of the TRISO particles on the fixing devices of two adjacent layers are different.

[0015] As an embodiment of the present invention, adjusting the fuel billet to a set shape includes covering the fuel billet containing TRISO particles with multiple layers by increasing the matrix powder and pressurizing it to form a graphite cap; and / or preparing the fuel pellet containing TRISO particles with multiple layers into a column or a square body.

[0016] As an embodiment of the present invention, when hot pressing and sintering the fuel blank to obtain the fuel pellet, the hot pressing mold is preferably a graphite mold, the sintering temperature is 1600°C-1900°C, the sintering pressure is 5 MPa-60 MPa, and the holding time is 5 min-120 min.

[0017] As an embodiment of the present invention, the composition of the base powder includes, by mass percentage, 85-95 wt.% silicon carbide, 5-10 wt.% sintering aid, 0.5-1 wt.% dispersant, and 5-10 wt.% binder.

[0018] As an implementation mode of the present invention, the set arrangement mode is a unit cell lattice structure.

[0019] According to a second aspect of the present invention, a fixing device is provided, which is used in the method for preparing a fuel core with directionally arranged TRISO particles as described in the first aspect of the present invention, and the fixing device comprises: a first part, on which a plurality of fixing holes are arranged and penetrate the first part in a set arrangement, and the fixing holes match the TRISO particles; and a colloid, which is glued to the inner wall of the fixing hole and is used to make the TRISO particles detachably fixed in the fixing hole.

[0020] As an embodiment of the present invention, the colloid is polyvinyl ether or polyacrylate.

[0021] According to a third aspect of the present invention, a fixing device is provided, which is used in the method for preparing a fuel core with directionally arranged TRISO particles as described in the first aspect of the present invention, wherein the fixing device comprises a first part and a second part fixedly connected, and fixing holes formed on the first part and the second part, wherein a plurality of the fixing holes are arranged in a set arrangement, wherein the fixing holes are grooves and pass through the first part, and the second part is made of resin material.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: through the scheme of the present invention, not only the directional arrangement of TRISO particles in the fuel core is achieved, but also by setting a fixing device, a large number of TRISO particle pellets can be quickly arranged, and the fixing device can be used repeatedly, which greatly reduces the manufacturing cost of the core fuel, has good economy and operability, and greatly increases the loading capacity of TRISO fuel pellets. Achieve efficient, high-density, low-cost, industrialized precise and orderly arrangement of TRISO particles;

[0023] At the same time, in the present invention, TRISO particles are orderly arranged in the silicon carbide matrix through the structure of the unit cell lattice. On the one hand, the silicon carbide matrix can provide an additional barrier to block the release of radioactive fission products. At the same time, the spillage of different radioactive fission products can be prevented in all directions without dead ends through the appropriate unit cell lattice arrangement, thereby ensuring the safe and stable operation of the nuclear reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 It is a structural schematic diagram of a fixing device provided by the present invention;

[0026] Figure 2 This is a real picture of the blank of the single-layer TRISO particles arranged in a directional manner provided by the present invention;

[0027] Figure 3 The actual pictures of the plate, sheet and column of TRISO fuel core after sintering;

[0028] Figure 4 This is a top view of an X-ray 3D imaging of a fuel core with four layers of TRISO particles arranged in a directional manner.

[0029] Description of reference numerals:

[0030] 100, fixing device; A, first part; 111, fixing hole; B, second part. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work belong to the scope of protection of the present invention. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. In the present invention, unless otherwise specified, the directional words used, such as "up", "down", "left", "right", "front", and "back", generally refer to the up, down, left, and right of the device in actual use or working state, specifically the drawing direction in the accompanying drawings.

[0032] It should be noted that the description order of the following embodiments is not intended to limit the preferred order of the embodiments of the present invention. In addition, in the following embodiments, the description of each embodiment has its own emphasis, and for parts not described in detail in one embodiment, reference can be made to the relevant description of other embodiments.

[0033] As mentioned above, the problem with preparing composite fuels of TRISO particles in the prior art is that it is impossible to achieve rapid directional arrangement of multiple TRISO particles at the same time, resulting in slow preparation efficiency during industrial production. Based on this, the present invention proposes a method for preparing a fuel core with directional arrangement of TRISO particles and a fixing device, so as to at least achieve a solution for rapid directional arrangement of TRISO particles, so as to be suitable for industrial production.

[0034] See also Figure 1 The present invention first provides a fixing device for fixing a plurality of TRISO particles. The fixing device 100 comprises a first fixed part A and a second fixed part B. A large number of through holes arranged in a set arrangement and adapted to the size of the TRISO particles are printed on the first part A by laser. The second part B is arranged on one side of the first part A. Figure 1 In this specific embodiment, the second part B is arranged on the lower side of the first part A, and the second part B on the lower side is a resin-type ultra-thin sheet that matches the first part A. The first part A and the second part B are fixed by bolts or adhesion. The second part B is also provided with grooves that match the shape of the TRISO particles, and the grooves correspond one by one to the through holes on the first part A. The through holes on the first part A and the grooves on the second part B together constitute a fixing hole 111. The fixing hole 111 matches the TRISO particles and is used to at least partially accommodate the TRISO particles. It is naturally understandable that a plurality of fixing holes 111 are provided.

[0035] The fixing hole 111 on the fixing device 100 is preferably prepared by laser drilling on the mold and then polishing. The advantage of such manufacturing is that the aperture accuracy of the fixing hole 111 can be guaranteed as much as possible.

[0036] As for the setting arrangement of the fixing holes 111 , since the arrangement of the TRISO particles is limited by the fixing device 100 , it is more convenient in actual industry, and the operator can freely choose according to the needs.

[0037] When the fixing device 100 is needed, firstly, the second part B is placed on a horizontal plane away from the first part A. Figure 1 In this specific embodiment, the bottom surface of the second part B is placed on a horizontal plane, and the first part A is arranged above the second part B. Then, a large number of TRISO particles are randomly spread on the first part A, so that all the fixing holes 111 are filled with TRISO particles. Then, the TRISO particles are relatively fixed in the fixing holes 111 by bonding, clamping or air pressure pressing. Then, the excess TRISO particles on the surface of the first part A are removed, and the first part A side of the fixing device 100 is placed on the silicon carbide blank and pressed, so that the TRISO particles are orderly embedded in the silicon carbide matrix, thereby realizing a large number of orderly arrangements of TRISO particles.

[0038] It can be understood that the second part B is preferably made of resin material, which has the advantage that, on the one hand, the second part B and the TRISO particles can be directly engaged, that is, the second part B and the TRISO particles are bonded, and the fixing device 100 and the TRISO can be relatively fixed without adding other devices. Naturally, in order to better achieve its fixation, a negative pressure device can also be set in the fixing hole 111 of the fixing device 100 to make the TRISO particles and the fixing device 100 negatively pressed to strengthen the degree of fixation. On the other hand, since the resin material itself has a certain elasticity, it can well protect the TRISO particles in the subsequent process of preparing the composite fuel, buffer the extrusion between the TRISO particles and the blank, and avoid the surface of the TRISO particles from being damaged. Please describe in detail later.

[0039] It is naturally understood that, for the fixing device 100, as long as the multiple TRISO particles can be arranged in the fixing holes 111 according to the set arrangement and remain relatively fixed, there is no limitation on the specific relative fixing method. Figure 1 In this case, the fixing device 100 includes a first portion A and a second portion B, and the second portion is used to achieve relative fixation between the fixing device 100 and the TRISO particles. The first portion A is preferably a polished metal, and the second portion B is preferably a resin sheet.

[0040] In another alternative embodiment, the fixing device 100 includes only the first part A, and the fixing hole 111 is formed vertically through the first part A. The inner wall of the fixing hole 111 of the first part A is coated with polyvinyl ether or polyacrylate, so that the first part A is engaged with the TRISO particles, and due to the presence of polyvinyl ether or polyacrylate, the TRISO particles and the first part A maintain a certain adhesion force, thereby fixing the fixing device 100 and the TRISO particles relatively.

[0041] The following is a detailed description of a method for preparing a composite fuel based on the fixture 100 to further understand the role of the fixture 100 in preparing the composite fuel.

[0042] A method for preparing a fuel core with directional TRISO particles comprises the following steps:

[0043] S1: Place the base powder at a set position and pre-press it through a press to obtain a flat green blank.

[0044] For the matrix powder, it is preferably cubic phase silicon carbide micron powder or nano powder. The ingredients of the matrix powder are as follows: the content of silicon carbide is selected to be 85 wt.%~95 wt.%, the content of sintering aid is 5 wt.%~10 wt.%, the content of dispersant is 0.5 wt.%~1 wt.%, and the content of binder is 5 wt.%~10 wt.%. Sintering aids include Al2O3, Y2O3, Gd2O3, ZrO2, CaO, CaCO3, etc., and the ratio of Al2O3 to other sintering aids is 7:3~8:2. The above raw materials are ball-milled and mixed in anhydrous ethanol, the content of anhydrous ethanol is 50 wt.%~70 wt.%, and the ratio of grinding balls to powder is 1:1~3:1.

[0045] For pre-pressing by a press, an automatic press is preferably used to pre-press the matrix powder, and a certain amount of matrix powder is pre-pressed in the automatic press to form a flat blank. There are many solutions for automatic presses in the prior art, and the details are not repeated here.

[0046] It can be understood that, unlike the prior art, the solution of the present invention requires the blank to be pre-pressed into a planar blank. The purpose of this arrangement is that the inventors found in their research that if grooves matching TRISO particles are set on the blank, since a large number of TRISO particles need to be placed on the blank, and the TRISO particles themselves are relatively small, then the matching problem between TRISO and the blank grooves must be solved. However, since TRISO particles are small and numerous, it is very difficult to ensure that a large number of TRISO particles match a large number of grooves on the blank, and it is difficult to be suitable for industrial mass production.

[0047] Therefore, the inventor creatively proposes this solution, which can well realize rapid large-scale directional arrangement on the blank by setting the blank into a plane shape, combining the fixing device 100 and subsequent steps. The specific solution will gradually become clear with the discussion below.

[0048] S2: placing a fixture 100 with TRISO particles arranged in a set arrangement above a planar blank, wherein the fixture 100 and the planar blank remain relatively fixed, and there is no obstruction between the TRISO particles and the planar blank, and the spacing between the TRISO particles is no greater than the diameter of the TRISO particles.

[0049] When it is necessary to put TRISO particles in the fixture 100, in order to ensure that the fixing holes 111 of the fixture 100 are all filled with TRISO particles, a push rod device (not shown in the figure) can be provided on the fixture 100. The gap between the push rod device and the fixture 100 is not greater than the diameter of the TRISO particles. When it is necessary to put TRISO particles in the fixture 100, the fixture 100 is first placed in a large number of fuel TRISO particles, and then a push rod is provided on the surface of the fixture 100 on the side where the TRISO particles are exposed, and the push rod is reciprocated along a certain set direction to ensure that all the fixing holes 111 are filled with TRISO particles.

[0050] It can be understood that in the solution of the present invention, in order to facilitate industrial operation, it is preferred that the fixing holes 111 on the fixing device 100 have been arranged according to the set arrangement mode, and at this time, it is only necessary to make all TRISO particles fall into the fixing holes 111. Of course, in another alternative mode, the fixing holes 111 on the fixing device 100 are arranged according to conventional rules (such as a 20×20 square or other shapes). At this time, when the TRISO particles are arranged in the set arrangement mode, some of the fixing holes 111 do not need to accommodate TRISO particles. In order to arrange the TRISO particles in the set arrangement mode, the TRISO particles can be arranged in the set arrangement mode by manual or robot methods.

[0051] by Figure 1Taking the fixture 100 with the first and second fixed parts A and B as an example, when TRISO particles are placed in the fixture 100, the first part A is located above the second part B, and the TRISO particles enter the fixing hole 111 of the fixture 100 through the side of the first part A away from the second part B. When the fixture 100 with TRISO particles arranged in a set arrangement is placed on the flat blank, the fixture 100 needs to be flipped 180 degrees, that is, the second part B in the fixture 100 is located above the first part A, and the side of the first part A away from the second part B is arranged close to the flat blank, so that there is no obstruction between the TRISO particles and the flat blank.

[0052] Similarly, it can be understood that when the fixing device 100 has only the first part A, the fixing holes 111 corresponding to the TRISO particles arranged in the set arrangement are coated with glue such as polyvinyl ether or polyacrylate. At this time, since there is no second part B, there is no need to flip the first part A to achieve an unobstructed setting between the TRISO particles and the flat blank.

[0053] At the same time, the distance between the TRISO particles and the flat blank is no greater than the diameter of the TRISO particles. The purpose of this setting is to minimize the difference between the actual landing position of the TRISO particles and the set landing position caused by the interference of external factors during the gravity descent of the TRISO particles, which may cause the TRISO particles to fail to land at the predetermined position, resulting in poor performance of the entire fuel pellet.

[0054] It can be understood that in the actual process of preparing fuel pellets, it is necessary to set up multiple layers of planar blanks and TRISO particles. In order to ensure that the TRISO density in the obtained fuel pellets meets the requirements, it is necessary to ensure that the position of the TRISO particles in each layer is in the set position, otherwise it will affect the arrangement position of the TRISO particles on the subsequent layers, and the errors will be accumulated layer by layer, which will cause the entire fuel pellet to deviate from the set standard.

[0055] By ensuring that the distance between the TRISO particles and the planar blank is no greater than the diameter of the TRISO particles and superimposing other steps of the present invention, it is possible to ensure that all the TRISO particles fall at the set positions, thereby ensuring the design quality of the final fuel pellets.

[0056] Preferably, the distance between the TRISO particles and the planar green blank is not greater than the diameter of the TRISO particles and not less than the radius of the TRISO particles.

[0057] Preferably, in order to ensure the quality of the finally prepared fuel pellets, the diameter difference of the TRISO particles is controlled to be no greater than 0.3 mm. In this case, a screening procedure can be added before the TRISO particles are placed in the fixture 100. That is, a step is added after step S1 and before step S2 to screen the TRISO particles so that the diameter difference of the remaining TRISO particles is no greater than 0.3 mm.

[0058] S3: using a press machine to pressurize the side of the fixture away from the planar blank, so that the TRISO particles are separated from the fixture and embedded in the planar blank in a directional manner.

[0059] The mold with the TRISO particles arranged in a directional manner is placed on an automatic press, and pressure is applied to allow the TRISO particles to be released from the mold and directionally embedded in the silicon carbide blank.

[0060] The pressure applied by the automatic press to the TRISO particles should be less than the compressive strength of the fuel pellets, in order to avoid damage to the TRISO particles.

[0061] Preferably, the fixture 100 is a fixture 100 including a first part A and a second part B that are fixedly connected. At this time, when the press presses the TRISO particles, it directly contacts the second part B to achieve indirect pressurization of the TRISO particles. Since the second part B is made of resin material and has a certain elasticity, it can well protect the TRISO particles in the subsequent process of preparing composite fuel, buffer the extrusion between the TRISO particles and the blank, and avoid the surface of the TRISO particles from being damaged. Therefore, the TRISO particles can be better protected.

[0062] Regarding the directionally embedding of the TRISO particles into the planar blank after the TRISO particles are separated from the fixture 100, in one embodiment, no embedding force may be applied to the TRISO particles. Based on the gravity of the TRISO particles themselves, the TRISO particles are "slightly embedded" into the planar blank. In this case, the planar blank itself is preferably "softer".

[0063] In another embodiment, the distance over which the press applies force to the TRISO particles can be slightly greater than the distance between the TRISO particles and the planar blank. Specifically, by adjusting the distance between the TRISO particles and the planar blank, and by the displacement of the press applying pressure to the TRISO particles, the press can simultaneously apply an "embedding force" to the TRISO particles, so that the TRISO particles can be more firmly embedded in the planar blank. At this time, since the distance between the TRISO particles and the planar blank is not greater than the diameter of the TRISO particles, the distance over which the press applies force to the TRISO particles is not greater than the diameter of the TRISO particles.

[0064] In a preferred embodiment, the distance between the TRISO particles and the planar blank is slightly smaller than the diameter of the TRISO particles, and the distance at which the press applies force to the TRISO particles is exactly the diameter of the TRISO particles, so that the TRISO particles can be well embedded in the planar blank.

[0065] S4: Repeat steps S1-S3 to obtain a fuel blank containing multiple layers of TRISO particles.

[0066] When arranging the first layer of planar blanks, the set position at this time can be, for example, a specific position, such as a flat table on an automatic press. When arranging planar blanks with multiple layers, the set position where the matrix powder is placed at this time is the planar blank that has been embedded with TRISO particles before, and then the planar blank of this layer is obtained again through pre-pressing by the press, and the preparation on this layer of planar blank is completed through S1-S3.

[0067] It is naturally understandable that in a specific embodiment, when preparing a fuel blank containing multiple layers of TRISO particles, the arrangement positions of the TRISO particles of two adjacent layers are different, which can be achieved by directly replacing the fixture 100 with a corresponding arrangement mode and then loading the TRISO particles into the fixture 100. For example, the TRISO particles of the second layer are arranged at the corresponding position between two adjacent TRISO particles of the first layer. The advantage of such an arrangement is that the number of layers of TRISO particles in the fuel pellet can be further increased, thereby increasing the density of TRISO particles and better meeting the different requirements of the fuel pellet.

[0068] It is naturally also understandable that, in a specific embodiment, the sizes of the TRISO particles of two adjacent layers are different, which can be achieved by directly replacing the fixing device 100 with the fixing holes 111 that can accommodate the corresponding TRISO particles, and then loading the TRISO particles into the fixing device 100, thereby making the TRISO particles of the two adjacent layers different, and obtaining fuel core blocks with diversified sizes.

[0069] Preferably, the content of TRISO particles in the fuel pellets is 40 vol% to 70 vol%, and the density of the fuel pellets is 80% to 99%.

[0070] S5: After adjusting the fuel billet to a set shape, sinter the fuel billet to obtain a fuel pellet.

[0071] Adjusting the fuel billet to a set shape may include covering the fuel billet containing TRISO particles with multiple layers to form a graphite cap by increasing the matrix powder and applying pressure; or may include preparing the fuel core blocks containing TRISO particles with multiple layers to a desired shape, such as a plate, sheet or column, by a hollow drill bit or other equipment. The hollow drill bit may be, for example, a cylinder or a square.

[0072] As for the internal structure of the fuel pellets, by utilizing different arrangements of TRISO particles between two adjacent layers, fuel pellets with different internal structures can be obtained. The internal arrangement of the fuel pellets is arranged according to the unit cell lattice structure, such as cubic, hexagonal and orthogonal. For example, when it is necessary to obtain a cubic internal layout structure, the arrangement of the TRISO particles and the thickness of each layer of matrix powder are determined based on the specific structure. By adjusting the amount of powder added, the spacing and edge length of each layer of TRISO particles can be controlled, thereby realizing the arrangement of the face-centered cubic crystal structure. Similarly, other crystal structures can also be arranged in the same way.

[0073] It is naturally understandable that the shaping of a specific shape can be completed when the matrix powder is pre-pressed directly by a press to obtain a flat blank, and the details will not be repeated.

[0074] The obtained green billet is then hot pressed and sintered to obtain a fuel pellet. The hot pressing mold is preferably a graphite mold, the sintering temperature is 1600°C-1900°C, the sintering pressure is 5 MPa-60 MPa, and the holding time is 5 min-120 min.

[0075] In summary, the scheme of the present invention not only realizes the directional arrangement of TRISO particles in the fuel core, but also can quickly complete the directional arrangement of a large number of TRISO particle pellets by setting the fixture 100, and the fixture 100 can be used repeatedly, which greatly reduces the manufacturing cost of the core fuel, has good economy and operability, and greatly increases the loading capacity of TRISO fuel pellets. It realizes efficient, low-cost, industrialized precise and orderly arrangement of TRISO particles.

[0076] At the same time, by setting the fixing device 100, the effect of placing the TRISO particles at the set position can be well achieved. Compared with the prior art, the solution of the present invention solves the problem that there is an error in using gravity to make the TRISO particles reach the predetermined position due to the mass difference caused by the size difference of the same batch of TRISO particles, which in turn causes a large deviation in the overall effect of the multi-layer fuel pellet.

[0077] At the same time, by providing different fixing devices 100, different effects of TRISO particles in different layers of the fuel pellets can be well achieved, thereby obtaining fuel pellets with multiple sizes, thereby better improving the safety of the reactor.

[0078] At the same time, since the present invention has relatively low requirements for planar billets, the scheme of the present invention can be designed to process composite fuel billets of various shapes for sintering, which greatly reduces the processing cost of composite fuel parts after sintering.

[0079] Embodiment: In order to further illustrate the scheme of the present invention, it is specifically described below through embodiment.

[0080] S210: Polyvinyl ether or polyacrylate is loaded into a 3D printer, and the polyvinyl ether or polyacrylate is outputted on the inner side wall of the fixing hole 111 of the fixing device for accommodating TRISO particles by the 3D printer. The fixing device is placed among a large number of TRISO particles, and the TRISO fuel pellets are fixed in the fixing hole 111 by the polyvinyl ether or polyacrylate, so that the TRISO particles are arranged in a direction on the fixing device, and the excess TRISO fuel pellets are removed.

[0081] S220: placing the matrix powder on an automatic press, and pre-pressing a silicon carbide flat blank of a certain thickness through the automatic press.

[0082] S230: placing a fixture with TRISO fuel pellets fixed on the automatic press, adjusting the distance between the fixture and the flat blank to the diameter of the TRISO pellets, and fixing the TRISO fuel pellets at specific positions of the silicon carbide blank by applying pressure, such as Figure 2 shown.

[0083] S240: Add a certain amount of silicon carbide matrix powder to the flat blank in which TRISO particles have been embedded, and press and mold to form a new flat blank.

[0084] S250: Repeat steps 230-250 to finally produce a composite fuel plate with directional TRISO particles.

[0085] S260: A composite fuel of a desired shape is prepared by using a hollow drill bit with a specific shape.

[0086] S270: The final composite fuel blank is placed in a graphite mold and sintered in a hot press furnace at a sintering temperature of 1750°C, a holding time of 60 min, and a hot press pressure of 40 MPa. Figure 3 The top view of the four-layer TRISO composite fuel observed by high-resolution X-ray is shown in Figure 4 As shown, the TRISO arrangement is a close-packed hexagonal structure.

[0087] The scheme of the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

[0088] References throughout this specification to "one embodiment," "an embodiment," or "a specific embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, and not necessarily in all embodiments. Thus, various appearances of the phrases "in one embodiment," "in an embodiment," or "in a specific embodiment" in different places throughout this specification do not necessarily refer to the same embodiment. In addition, the particular features, structures, or characteristics of any specific embodiment of the invention may be combined with one or more other embodiments in any suitable manner. It should be understood that other variations and modifications of the embodiments of the invention described and illustrated herein may be possible in light of the teachings herein and are to be considered part of the spirit and scope of the invention.

[0089] It should also be understood that one or more of the elements shown in the figures may also be implemented in a more separate or more integrated manner, or even removed because they are inoperable in certain circumstances or provided because they may be useful depending on the application.

[0090] In addition, unless otherwise explicitly indicated, any marking arrows in the drawings should be regarded as exemplary only and not limiting. In addition, unless otherwise indicated, the term "or" used herein is generally intended to mean "and / or". In the case where the term is not clear because it is anticipated that the ability to separate or combine is provided, the combination of components or steps will also be regarded as indicated.

Claims

1. A method for preparing a fuel core with directional TRISO particles, characterized in that: The steps include: S1: placing the base powder at a set position and pre-pressing it through a press to obtain a flat green blank; S2: placing a fixture with TRISO particles arranged in a set arrangement above the planar blank, wherein the TRISO particles are arranged without any obstruction to the planar blank and the spacing between the TRISO particles is no greater than the diameter of the TRISO particles; S3: applying pressure to the side of the fixture away from the planar blank by using a press, so that the TRISO particles are separated from the fixture and embedded in the planar blank in a directional manner; S4: repeating steps S1-S3 to obtain a fuel blank containing multiple layers of TRISO particles; S5: After adjusting the fuel billet to a set shape, hot pressing and sintering the fuel billet to obtain a fuel pellet.

2. The method for preparing a fuel core with directional TRISO particles according to claim 1, characterized in that: When preparing a fuel billet having multiple layers containing TRISO particles, the arrangement positions of the TRISO particles in two adjacent layers are different; And / or, the diameters of the TRISO particles in two adjacent layers are different.

3. The method for preparing a fuel core with directional TRISO particles according to claim 1, characterized in that: When preparing a fuel blank having multiple layers containing TRISO particles, the arrangement mode and / or diameter of the fixing holes of the TRISO particles on the fixing devices of two adjacent layers are different.

4. The method for preparing a fuel core with directional TRISO particles according to claim 1, characterized in that: Adjusting the fuel billet to a set shape, including covering the fuel billet containing TRISO particles formed with multiple layers by increasing the matrix powder and applying pressure to form a graphite cap; And / or, the fuel pellets containing multiple layers of TRISO particles are prepared into a plate, sheet or column shape.

5. The method for preparing a fuel core with directional TRISO particles according to claim 1, characterized in that: When the fuel blank is hot pressed and sintered to obtain the fuel pellet, the hot pressing mold is a graphite mold, the sintering temperature is 1600°C-1900°C, the sintering pressure is 5 MPa-60 MPa, and the holding time is 5 min-120 min.

6. The method for preparing a fuel core with directional TRISO particles according to any one of claims 1 to 5, characterized in that: The matrix powder comprises, by mass percentage, 85-95 wt.% of silicon carbide, 5-10 wt.% of a sintering aid, 0.5-1 wt.% of a dispersant, and 5-10 wt.% of a binder.

7. The method for preparing a fuel core with directional TRISO particles according to any one of claims 1 to 5, characterized in that: The set arrangement mode is a unit cell lattice structure.

8. A fixing device used in the method for preparing a fuel core with directional TRISO particles as claimed in any one of claims 1 to 7, characterized in that: The fixing device comprises: A first part, wherein the first part is provided with a plurality of fixing holes arranged in a set arrangement and penetrating the first part, and the fixing holes match the TRISO particles; The colloid is glued to the inner wall of the fixing hole and is used to make the TRISO particles detachably fixed in the fixing hole.

9. The fixing device according to claim 8, characterized in that: The colloid is polyvinyl ether or polyacrylate.

10. A fixing device used in the method for preparing a fuel core with directional TRISO particles as claimed in any one of claims 1 to 7, characterized in that: The fixing device comprises a first part and a second part fixedly connected, and fixing holes formed on the first part and the second part, wherein a plurality of the fixing holes are arranged in a set arrangement, wherein The fixing hole is a groove and passes through the first part; the second part is made of resin material.

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