Dispersion type fuel core and preparation method thereof

Abstract

The invention discloses a dispersion type fuel core and a preparation method thereof. The preparation method comprises the following steps: S1, preparing a sphere with a core-shell structure through a microfluid control technology; the core part of the ball body is made of a fissile material, and the shell layer of the ball body is made of a functional material comprising at least one of an antioxidant material and a high thermal conductivity material; and S2, filling the spheres into a core body mold, sintering, enabling shell layers of the spheres to be mutually fused and connected to form a base body, and forming the fuel microspheres dispersed in the base body by core parts in the spheres. A sphere with a core-shell structure is prepared through a microfluid control technology, then the sphere is filled and sintered, shell layers of the sphere are mutually fused to form a base body of the fuel core body, fuel microspheres evenly dispersed in the base body are formed on the core part, and it is guaranteed that all the fuel microspheres are wrapped by the base body; the preparation process is high in efficiency and suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear fuel, and in particular to a dispersed fuel core and a preparation method thereof. Background Art

[0002] Dispersed fuel is a type of accident-tolerant nuclear fuel. By dispersing the fuel in the matrix medium to form a uniform dispersed structure, the heat generated by each fuel fission is small, and the matrix material used for dispersed fuel microspheres generally uses metals or metal oxides with thermal conductivity greater than that of the fuel, which has better thermal conductivity than ceramic fuel. In this way, the center temperature of the dispersed fuel is low, reducing the probability of accidents. The matrix material of the dispersed fuel can be made of chemically inert substances to reduce the risk of chemical reactions between the fuel and the coolant under extreme accident conditions. In addition, the ability of dispersed fuel to encapsulate fission gas is also stronger, which greatly improves the inherent safety of the reactor.

[0003] In order to achieve the preparation of uniformly dispersed fuel cores, the following technical means are currently available: 1. Mechanically mix the fuel and the matrix material. In this method, the fuel microspheres and the matrix material are mixed by ball milling. During the ball milling process, the material rubs and collides with the grinding balls and the container, which easily introduces impurities and oxidation. In addition, due to the difference in density and particle size between the two substances, it is difficult to evenly distribute the microspheres by mechanical mixing, and it cannot be guaranteed that the matrix can cover all the fuel microspheres. 2. Use a binder to wrap the matrix material on the surface of the fuel microspheres. The process is complicated, the uniformity is poor, and it is not convenient to control the size of the microspheres and the thickness of each layer; 3. Use a mold or other tools to accurately locate the position of the fuel, first use the mold to prepare a uniformly dispersed thin layer, and then use a stacking method to prepare the dispersed fuel core block. The process is difficult, the production efficiency is low, and the preparation cost is high. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an improved dispersed fuel core and a preparation method thereof.

[0005] The technical solution adopted by the present invention to solve the technical problem is: to provide a method for preparing a dispersed fuel core, comprising the following steps:

[0006] S1. Preparing a sphere with a core-shell structure by microfluidic control technology; the core of the sphere is formed of a fissile material, and the shell of the sphere is formed of a functional material including at least one of an anti-oxidation material and a high thermal conductivity material;

[0007] S2. The sphere is loaded into a core mold and sintered so that the shell layers of the sphere fuse and connect to form a matrix, and the core of the sphere forms fuel microspheres dispersed in the matrix.

[0008] In some embodiments, in the dispersed fuel core, the volume fraction of the fuel microspheres is 30% to 70%, and the volume fraction of the matrix is ​​30% to 70%.

[0009] In some embodiments, the fissile material includes at least one of UO2, PuO2, UN, PuN, U-Mo, U-Zr, and U3Si2;

[0010] The functional material includes at least one of Al, Zr, Cr, ZrO2, UO2, and U3O8.

[0011] In some embodiments, in the sphere, the diameter of the core is 100 μm to 600 μm, and the thickness of the shell is 1 / 2 to 1 / 8 of the radius of the core.

[0012] In some embodiments, step S1 includes:

[0013] S1.1, dispersing the fissile material powder and the functional material powder in a solvent respectively to form a first liquid phase and a second liquid phase; the solvent is a mixed liquid phase containing a cross-linking agent and an initiator;

[0014] S1.2, using a microfluidic control device, utilizing the shear force generated by continuous phase extrusion to separate the second liquid phase containing the first liquid phase into droplets of a core-shell structure; the droplets are gelled under the action of an initiator;

[0015] S1.3. The gelled droplets are washed and dried, and then sintered at 600°C to 800°C for 1 to 2 hours to form spheres with a core-shell structure.

[0016] In some embodiments, step S2 includes: placing the core mold with a sealed bottom end on a vibration table, fixing a feeding funnel at the upper end of the core mold, and the spheres enter the core mold from the feeding funnel at a constant rate through a powder feeder; during the filling process, the vibration table maintains vibration with a constant frequency and amplitude in the vertical direction.

[0017] In some embodiments, in step S2, the filling volume fraction of the spheres in the core mold is ≥80%.

[0018] In some embodiments, in step S2, the sintering is pressureless sintering, hot pressing sintering, spark plasma sintering or induction sintering.

[0019] In some embodiments, the dispersed fuel core has a diameter of 5 mm to 15 mm and a height of 10 mm to 1500 mm.

[0020] The present invention also provides a dispersed fuel core body, which is prepared by any of the preparation methods described above.

[0021] The beneficial effects of the present invention are as follows: a sphere with a core-shell structure is prepared by microfluidic control technology, and then the sphere is filled and sintered, and the shell layers of the sphere are fused with each other to form a matrix of the fuel core, and the core part of the sphere forms fuel microspheres uniformly dispersed in the matrix, ensuring that the matrix covers all the fuel microspheres; the shell thickness and core size of the sphere are easy to control and can be customized according to needs; the preparation process is efficient and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0023] Figure 1 It is a schematic diagram of the cross-sectional structure of a sphere in a method for preparing a dispersed fuel core according to an embodiment of the present invention;

[0024] Figure 2 It is a structural schematic diagram of a microfluidic control device in a method for preparing a dispersed fuel core according to an embodiment of the present invention;

[0025] Figure 3 yes Figure 2 An enlarged structural schematic diagram of the first T-shaped three-way and the second T-shaped three-way in the microfluidic control device shown;

[0026] Figure 4 It is a schematic diagram of the cross-sectional structure of a green body after spheres are filled in a method for preparing a dispersed fuel core according to an embodiment of the present invention;

[0027] Figure 5 It is a schematic diagram of the cross-sectional structure of a dispersed fuel core body obtained by a method for preparing a dispersed fuel core body according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0029] refer to Figures 1 to 5 The method for preparing a dispersed fuel core according to an embodiment of the present invention may include the following steps:

[0030] S1. Prepare spheres 10 with a core-shell structure by microfluidic control technology.

[0031] Among them, Figure 1As shown, the sphere 10 has a core 11 and a shell 12 covering the outer periphery of the core 11. The core 11 of the sphere 10 is formed of a fissile material; the fissile material includes at least one of UO2, PuO2, UN, PuN, U-Mo, U-Zr, U3Si2, etc. The shell 12 of the sphere 10 is formed of a functional material, and the functional material includes but is not limited to at least one of an anti-oxidation material and a high thermal conductivity material, and further includes but is not limited to at least one of Al, Zr, Cr, ZrO2, UO2, U3O8, etc.

[0032] Preferably, the core 11 and the shell 12 are formed of different materials.

[0033] In the sphere 10 , the diameter of the core 11 is 100 μm to 600 μm, and the thickness of the shell 12 is 1 / 2 to 1 / 8 of the radius of the core.

[0034] Step S1 may further include:

[0035] S1.1. Prepare a liquid phase corresponding to the core 11 and a liquid phase corresponding to the shell 12.

[0036] Specifically, the fissile material powder is dispersed in a solvent to form a first liquid phase; the particle size of the fissile material powder is 5 μm to 300 μm. The functional material powder is dispersed in a solvent to form a second liquid phase; the particle size of the functional material powder is 0.1 μm to 10 μm.

[0037] The solvent of the first liquid phase and the solvent of the second liquid phase are both mixed liquid phases containing a crosslinking agent and an initiator, wherein the initiator can act under conditions of temperature, pH value, light, etc. to gel the first liquid phase and the second liquid phase.

[0038] Alternatively, the solvent may be a mixed liquid phase containing acrylamide and ammonium persulfate, or a mixed liquid phase containing tripropylene glycol diacrylate and azobisisobutyronitrile.

[0039] The solvent can be further adjusted to form a suspension by adding deionized water, polyvinyl alcohol, polyvinyl pyrrolidone, etc. according to the requirements of surface tension, density, viscosity, etc.

[0040] S1.2. Using a microfluidic control device, the shear force generated by continuous phase extrusion is used to separate the second liquid phase containing the first liquid phase into droplets of a core-shell structure; the droplets are gelled under the action of an initiator.

[0041] The continuous phase can be selected from dimethyl silicone oil, isoamyl alcohol and the like, which are liquids that provide shear force and can carry droplets.

[0042] S1.3. Wash and dry the gelled droplets, and then sinter them at 600° C. to 800° C. for 1 to 2 hours to solidify the droplets to form spheres 10 with a core-shell structure.

[0043] refer to Figure 2 and Figure 3 The microfluidic control device may include a first microfluidic delivery pump 21 for loading and delivering a first liquid phase, a second microfluidic delivery pump 22 for loading and delivering a second liquid phase, a third microfluidic delivery pump 23 for loading and delivering a continuous phase, a first T-shaped tee 30, a second T-shaped tee 40, and a droplet solidification mechanism 50. The first microfluidic delivery pump 21 and the second microfluidic delivery pump 22 are respectively connected to a first interface and a second interface perpendicular to the first T-shaped tee 30 through a pipeline, the third microfluidic delivery pump 23 is connected to the second interface of the second T-shaped tee 40 through a pipeline, the third interface of the first T-shaped tee 30 is connected to the first interface of the second T-shaped tee 40, and the third interface of the second T-shaped tee 40 is connected to the collector 60 through a pipeline. The droplet solidification mechanism 50 is arranged on the pipeline between the second T-shaped tee 40 and the collector 60, or is arranged on the collector 60.

[0044] In combination with the microfluidic control device, the specific operation of step S1 is as follows:

[0045] The first microfluidic delivery pump 21 pushes the first liquid phase to the first T-shaped tee 30 through the first capillary 211, and the first liquid phase flows from the first capillary 211 through the first T-shaped tee 30; the second microfluidic delivery pump 22 pushes the second liquid phase to the first T-shaped tee 30, and the second liquid phase is output from the third interface of the first T-shaped tee 30 and enters the second capillary 221 sleeved outside the first capillary 211. The first liquid phase and the second liquid phase flow through the second T-shaped tee 40 along the first capillary 211 and the second capillary 221 respectively, and the third microfluidic delivery pump 23 pushes the continuous phase to the second T-shaped tee 40.

[0046] The outlet ends of the first capillary 211 and the second capillary 221 are located at the third interface of the second T-shaped tee 40. At the third interface of the second T-shaped tee 40, the second liquid phase containing the first liquid phase forms droplets under the shear force generated by the continuous phase extrusion.

[0047] When the droplets flow through the droplet solidification mechanism 50 under the continuous phase carrier, the initiator in the droplets is activated by adjusting the temperature, pH value, light and other conditions, thereby causing the droplets to gel. The gelled droplets enter the collector 60 at the end under the continuous phase carrier. The droplet solidification mechanism 50 may include at least one of a heating sleeve, a dropper and a light source, respectively realizing temperature adjustment, pH value adjustment, light adjustment, etc. Alternatively, the collector 60 at the end is filled with an acid or alkali solution for adjusting the pH value, and the droplets enter the collector 60 and realize gelation at a certain pH value.

[0048] The connected first T-shaped tee 30 and the second T-shaped tee 40 are used as a droplet generation module. In order to improve the production capacity, two or more groups of droplet generation modules can be set up. The multiple groups of droplet generation modules are connected in parallel between the microfluidic delivery pump (including the first microfluidic delivery pump 21, the second microfluidic delivery pump 22 and the third microfluidic delivery pump 23) and the collector 60.

[0049] The gelled droplets are washed with a detergent containing one or more of trichloroethylene, alcohol, sodium alkylbenzene sulfonate, etc., and then placed in air for 12 hours to 48 hours to dry. Thereafter, the droplets are sintered at 600° C. to 800° C. for 1 hour to 2 hours to form a sphere 10 having a core-shell structure.

[0050] In the sphere 10 , the diameter of the core 11 and the thickness of the shell 12 can be controlled by changing parameters such as the viscosity and flow rate of the liquid phase.

[0051] S2, such as Figures 4 to 5 As shown, a number of spheres 10 are loaded into a core mold and sintered so that the shells 12 of the spheres 10 fuse and connect to form a matrix 100, and the cores 11 in the spheres 10 form fuel microspheres 110 dispersed in the matrix 100; after sintering, a dispersed fuel core is obtained.

[0052] The specific steps of filling may include: placing the core mold with a sealed bottom end on a vibration table or clamping it on a vibration table, fixing a feeding funnel at the upper end of the core mold, and allowing the spheres 10 to enter the core mold from the feeding funnel at a constant rate through a powder feeder; the filling volume fraction of the spheres in the core mold is ≥80%.

[0053] During the filling process, the vibration table maintains a constant frequency and amplitude vibration in the vertical direction to ensure the filling density of the spheres. The constant frequency can be 10Hz to 100Hz, and the amplitude can be 0.5mm to 5mm.

[0054] After the spheres 10 are filled, they are sintered. The sintering method can be at least one of pressureless sintering, hot pressing sintering, spark plasma sintering or induction sintering. Figure 4 shown.

[0055] During sintering, the shells 12 of the spheres 10 melt at high temperature, so that the shells 12 between the spheres 10 can fuse and connect with each other. The shells 12 of all the spheres 10 in the core mold are connected into one body after being fused with each other, that is, forming a matrix 100, and the cores 11 in all the spheres 10 form fuel microspheres 110 dispersed in the matrix 100. Figures 4 to 5 shown.

[0056] The sintering method and parameters are selected according to the material of the shell layer 12 of the sphere 10 .

[0057] Take the case where the shell 12 of the sphere 10 is Al and pressureless sintering is used as an example: the core mold is transferred as a whole into the sintering furnace, and an inert or reducing gas is introduced. During sintering, the specific process parameters are: heating to 600°C to 650°C at a rate of 5°C / min to 10°C / min, keeping the temperature for 30min to 120min, and cooling to room temperature at a rate of 10°C / min to 30°C / min or cooling with the furnace.

[0058] Take the case where the shell 12 of the sphere 10 is Zr and induction sintering is used as an example: the core mold is transferred as a whole to the sintering furnace, and an inert or reducing gas is introduced. During sintering, the specific process parameters are: heating to 1500°C to 1700°C at a rate of 3°C / s to 10°C / s, keeping the temperature for 30min to 120min, and cooling to room temperature at 10°C / min to 30°C / min or cooling with the furnace.

[0059] Take the case where the shell 12 of the sphere 10 is ZrO2 and spark plasma sintering is used as an example: the core mold is transferred as a whole to the sintering furnace, and an inert or reducing gas is introduced. During sintering, the specific process parameters are: applying a uniaxial pressure of 5MPa to 30MPa, heating to 1400°C to 1600°C at a rate of 50°C / min to 200°C / min, keeping the temperature for 2min to 10min, and cooling to room temperature at a rate of 10°C / min to 100°C / min or cooling with the furnace.

[0060] Take the shell 12 of the sphere 10 as UO2 and hot pressing sintering as an example: the core mold is transferred as a whole into the sintering furnace, and an inert or reducing gas is introduced. During sintering, the specific process parameters are: applying 5MPa to 30MPa uniaxial pressure, heating to 1600℃ to 1800℃ at a rate of 10℃ / min to 20℃ / min, keeping warm for 30min to 120min, cooling at 10℃ / min to 30℃ / min or cooling to room temperature with the furnace.

[0061] In some embodiments, in order to reduce the gaps between the spheres 10 and improve the density of the dispersed fuel core after sintering, the spheres 10 may be mixed with a matrix powder of no more than 20% by volume before loading the spheres 10, so that during sintering, the matrix powder can be fused between the spheres and also constitute part of the matrix. The matrix powder is made of the same material as the shell. Alternatively, appropriate pressure may be applied during sintering (such as hot pressing sintering) to increase the bonding degree of the spheres after fusion and reduce the gaps.

[0062] In the dispersed fuel core prepared by the present invention, the volume fraction of the fuel microspheres 110 is 30% to 70%, and the volume fraction of the matrix 100 is 30% to 70%. Figure 5As shown in the cross-sectional schematic diagram, the dispersed fuel core structure comprises a matrix 100 and fuel microspheres 110 dispersed in the matrix 100. The matrix 100 is formed by fusion and connection of the shell layer 12 of the sphere 10, and the fuel microsphere 110 is formed by the core 11 in the sphere 10.

[0063] The fuel microspheres 110 can all be covered by the matrix 100, which has strong anti-oxidation ability, and prevents the fuel microspheres 110 from being exposed to the outside of the core and corroded by water. The matrix 100 can improve the thermal conductivity of the core by selecting a material with high thermal conductivity. In the matrix 100, the spacing between the fuel microspheres 110 can be achieved by adjusting the thickness of the shell layer 12 of the sphere 10.

[0064] In terms of size, the diameter of the dispersed fuel core may be, but not limited to, 5 mm to 15 mm, and the height may be, but not limited to, 10 mm to 1500 mm.

[0065] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a dispersed fuel core, characterized in that: The following steps are involved: S1. Preparing a sphere with a core-shell structure by microfluidic control technology; the core of the sphere is formed of a fissile material, and the shell of the sphere is formed of a functional material including at least one of an anti-oxidation material and a high thermal conductivity material; S2. The sphere is loaded into a core mold and sintered so that the shell layers of the sphere fuse and connect to form a matrix, and the core of the sphere forms fuel microspheres dispersed in the matrix.

2. The method for preparing a dispersed fuel core according to claim 1, characterized in that: In the dispersed fuel core, the volume fraction of the fuel microspheres is 30% to 70%, and the volume fraction of the matrix is ​​30% to 70%.

3. The method for preparing a dispersed fuel core according to claim 1, characterized in that: The fissile material includes at least one of UO2, PuO2, UN, PuN, U-Mo, U-Zr, and U3Si2; The functional material includes at least one of Al, Zr, Cr, ZrO2, UO2, and U3O8.

4. The method for preparing a dispersed fuel core according to claim 1, characterized in that: In the sphere, the diameter of the core is 100 μm to 600 μm, and the thickness of the shell is 1 / 2 to 1 / 8 of the radius of the core.

5. The method for preparing a dispersed fuel core according to claim 1, characterized in that: Step S1 includes: S1.1, dispersing the fissile material powder and the functional material powder in a solvent respectively to form a first liquid phase and a second liquid phase; the solvent is a mixed liquid phase containing a cross-linking agent and an initiator; S1.2, using a microfluidic control device, utilizing the shear force generated by continuous phase extrusion to separate the second liquid phase containing the first liquid phase into droplets of a core-shell structure; the droplets are gelled under the action of an initiator; S1.

3. The gelled droplets are washed and dried, and then sintered at 600°C to 800°C for 1 to 2 hours to form spheres with a core-shell structure.

6. The method for preparing a dispersion fuel core according to any one of claims 1 to 5, characterized in that: Step S2 includes: placing the core mold with a sealed bottom end on a vibration table, fixing a feeding funnel at the upper end of the core mold, and the spheres enter the core mold from the feeding funnel at a constant rate through the powder feeder; during the filling process, the vibration table maintains vibration with a constant frequency and amplitude in the vertical direction.

7. The method for preparing a dispersion fuel core according to any one of claims 1 to 5, characterized in that: In step S2, the filling volume fraction of the spheres in the core mold is ≥80%.

8. The method for preparing a dispersion fuel core according to any one of claims 1 to 5, characterized in that: In step S2, the sintering is pressureless sintering, hot pressing sintering, spark plasma sintering or induction sintering.

9. The method for preparing a dispersion fuel core according to any one of claims 1 to 5, characterized in that: The diameter of the dispersed fuel core is 5 mm to 15 mm, and the height is 10 mm to 1500 mm.

10. A dispersed fuel core, characterized in that: The method is prepared by the preparation method according to any one of claims 1 to 9.

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