Hollow radioactive containment fuel containing burnable poison, preparation method therefor and use thereof

Abstract

Provided are a hollow radioactive containment fuel containing a burnable poison, a preparation method therefor and the use thereof. The hollow radioactive containment fuel containing a burnable poison comprises a hollow fuel area and a fuel-free protective layer covering the periphery of the fuel area; the hollow fuel area comprises a matrix, and a fuel element and a burnable poison which are distributed in the matrix, wherein the fuel element is an isotropic coated fuel particle, and the burnable poison is an isotropic coated burnable poison particle. The present invention can realize highly compact and safe radioactive containment of a reactor fuel, ensure that radioactive products, especially fission gas, are not released into the environment accidentally, stably provide a fission site for the core of a miniature nuclear power pile for a long period of time, effectively confine the radioactive fission products inside the fuel, and guarantee the safe and stable operation of a reactor.

Description

Hollow radioactive inclusion fuel containing combustible poison, preparation method and use Technical Field

[0001] The present invention relates to fuel, in particular to a hollow radioactive inclusion fuel containing combustible poison, a preparation method and application thereof. Background Art

[0002] Micro nuclear power sources are energy devices for use in oceans, space, and remote areas on land. Compared with conventional power sources, micro nuclear power sources have the advantages of high energy density, strong continuous high-power output capability, large power adjustment range, and low dependence on external materials (no need for oxidizers and large amounts of nuclear fuel reserves, etc.).

[0003] High reactor safety is essential for the safety review and commercial operation of micro-nuclear power plants. This requires the fuel to be highly tolerant of radioactive materials under accident conditions. Current pressurized water reactors (PWRs) use a conventional UO2+Zr alloy nuclear fuel system, which presents a potential risk of nuclear leakage under accident conditions. Fuel elements are exposed to high temperatures, high pressures, and severe corrosion, and are subject to rapid temperature and pressure fluctuations. This can lead to performance degradation and cracking, damaging the protective barrier and potentially leaking radioactive materials. Furthermore, the uneven arrangement of fuel rods and burnable poison rods results in a bulky reactor core, which fails to meet the high compactness requirements of micro-nuclear power plants. The conventional UO2+Zr alloy fuel system has a weak structural design for accident tolerance and cannot guarantee the mitigation of the risk of radioactive material leakage. Therefore, developing accident-tolerant fuel designs suitable for micro-nuclear power systems is of paramount importance.

[0004] Summary of the Invention

[0005] The pressureless sintering scheme used for accident-resistant fuel for micro-nuclear power plants differs from conventional UO2 fuel pellets in that it must fully meet requirements for the core, the distribution of burnable poisons, and safety. Considering the specific use cases of micro-nuclear power plants, this paper proposes a highly safe fuel preparation scheme. Therefore, it is necessary to comprehensively consider multiple factors, such as radiation shielding, thermodynamic properties, and manufacturing processes, to develop a design and preparation scheme for hollow radioactive enclosed fuel containing burnable poisons.

[0006] The present invention provides a hollow radioactive inclusion fuel containing a combustible poison, which has the characteristics of excellent radiation resistance, good fission gas inclusion, high thermal conductivity and excellent safety performance. At the same time, the present invention also provides a preparation method of the hollow radioactive inclusion fuel containing a combustible poison, which adopts a pressureless sintering method to prepare a dispersed fuel pellet containing the combustible poison, thereby greatly improving the preparation and production efficiency while achieving densification, and realizing the purpose of industrialized mass production.

[0007] The present invention provides a hollow radioactive inclusion fuel containing a combustible poison, comprising a hollow fuel region and a fuel-free protective layer covering the periphery of the fuel region;

[0008] The hollow fuel region includes a matrix and fuel elements and burnable poisons uniformly distributed in the matrix;

[0009] The matrix is, for example, a SiC matrix, the fuel elements are isotropically coated fuel particles, for example, tri-structural isotropic (TRISO) coated fuel particles, the combustible poison is isotropically coated combustible poison particles, for example, bi-structural isotropic (BISO) coated combustible poison particles, and the fuel-free protective layer is, for example, made of SiC.

[0010] Furthermore, the density of the substrate and the fuel-free protective layer is not less than 95%.

[0011] Furthermore, the TRISO coated fuel particle includes a fuel core and four protective layers coated outside the fuel core;

[0012] The four protective layers are, from inside to outside, a loose carbon layer (Buffer), an inner pyrolytic carbon (IPyC) layer, a SiC layer, and an outer pyrolytic carbon (OPyC) layer.

[0013] The fuel core is one or more of UO2, UC, UN, U3Si2, U alloy or other arbitrary nuclear fuels, and the 235U enrichment of the UO2, UC, UN, U3Si2, U alloy or other nuclear fuels is 2-20%;

[0014] The density of the loose carbon layer is 1.1 g / cm 3 , with a thickness of 95 μm; in an alternative embodiment, the density of the loose carbon layer is 0.9-1.2 g / cm 3 , thickness is 80-110μm;

[0015] The density of the inner pyrolytic carbon layer is 1.9 g / cm 3 , thickness is 30-60 μm; in an alternative embodiment, the density of the inner pyrolytic carbon layer is 1.8-2.2 g / cm 3 , thickness is 30-60μm;

[0016] The density of the SiC layer is 3.18 g / cm 3, with a thickness of 25-55 μm; in an alternative embodiment, the density of the SiC layer is 2.9-3.3 g / cm 3 , thickness is 25-55μm;

[0017] The density of the outer pyrolytic carbon layer is 1.9 g / cm 3 , thickness is 30-60 μm; in an alternative embodiment, the density of the outer pyrolytic carbon layer is 1.8-2.2 g / cm 3 , thickness is 30-60μm;

[0018] The diameter of the TRISO coated fuel particles is 400-800 μm.

[0019] Furthermore, the BISO coated burnable poison particles include a burnable poison core and two protective layers coated outside the burnable poison core;

[0020] The two protective layers are a loose carbon layer and a dense pyrolytic carbon layer from the inside to the outside;

[0021] The burnable poison core is one or more of B4C, Gd2O3 or other burnable poisons;

[0022] The density of the loose carbon layer is 1.1 g / cm 3 , a thickness of 80-100 μm; in an alternative embodiment, the density of the loose carbon layer is 0.9-1.2 g / cm 3 , thickness is 80-100μm;

[0023] The density of the dense pyrolytic carbon layer is 1.9 g / cm 3 , a thickness of 80-100 μm; in an alternative embodiment, the density of the dense pyrolytic carbon layer is 1.8-2.2 g / cm 3 , thickness is 80-100μm;

[0024] The diameter of the coated combustible poison particles is 200-400 μm.

[0025] Furthermore, the volume fraction of the TRISO coated fuel particles in the fuel zone is 30-50%;

[0026] The volume fraction of the BISO-coated combustible poison particles in the fuel zone is 5-15%;

[0027] The thickness of the fuel-free protective layer is 0.2-2 mm.

[0028] The present invention provides a method for preparing a hollow radioactive inclusion fuel containing a combustible poison, comprising the following steps:

[0029] Step 1: Prepare SiC mixed slurry and SiC mixed powder;

[0030] Step 2: coating the SiC mixed slurry on the fuel particles and the combustible poison particles by spray deposition, wherein the binder is, for example, 10-15% by volume glycerol diluted with anhydrous ethanol;

[0031] Step 3: The SiC-coated fuel particles and combustible poison particles are molded to obtain a fuel zone blank;

[0032] Step 4: pressing the SiC mixed powder into a shape to obtain a fuel-free zone green billet;

[0033] Steps 2 and 3 serve together as the preparation of the fuel zone biscuits, and there is no strict order between them and the preparation of the non-fuel zone biscuits in step 4. In an alternative embodiment, the non-fuel zone biscuits may be prepared first and then the fuel zone biscuits, or the preparation of the non-fuel zone biscuits and the preparation of the fuel zone biscuits may be performed simultaneously.

[0034] Step 5: Composite-pressing the fuel region biscuit and the non-fuel region biscuit into a radioactive contained diffused pellet fuel biscuit containing combustible poisons;

[0035] Step 6: Pressurelessly sintering the radioactive inclusion dispersion fuel pellet containing combustible poison in a vacuum furnace to obtain a sintered blank;

[0036] Step 7: The sintered billet is machined into final size fuel pellets.

[0037] Furthermore, the SiC mixed slurry contains, by weight percentage, 85-95% of SiC, 1-10% of Al2O3, 1-10% of Y2O3, 0.5-10% of SiO2 and 0.5-5% of polyethyleneimine as a dispersant.

[0038] Furthermore, the components of the SiC mixed slurry are placed in a nylon ball mill, and 1-2 times the total mass of alcohol is added and mixed, and 2-5 times the total mass of zirconia grinding balls or alumina grinding balls are added and ball milled for 6-24 hours to obtain the SiC mixed slurry; more preferably, 2-3 times the total mass of zirconia grinding balls or alumina grinding balls are added; and more preferably, the ball milling is performed for 10-30 hours;

[0039] The SiC mixed slurry is dried to obtain SiC mixed powder.

[0040] Furthermore, the operating temperature of step 2 is 70-100° C.;

[0041] The pressing pressure in step 3 is 20-60 MPa, and the resulting fuel zone blank is a hollow column;

[0042] The pressing pressure of the molding in step 4 is 20-60 MPa. The obtained fuel-free area blank includes upper and lower covers and an annular cylinder, has a thickness of 2-4 mm, and a clearance of 0.1-0.25 mm with the fuel area blank.

[0043] The pressure of the composite pressing in step 5 is higher than the pressing pressure of the molding in step 3 and the pressing pressure of the molding in step 4.

[0044] Furthermore, the pressure of the composite pressing in step 5 is 60-80 MPa.

[0045] Furthermore, in step 6, the temperature is first raised to 600°C at a rate of 5-10°C / min and kept at this temperature for 0.5-2h for degreasing. The vacuum degree is 10 -2 The furnace is heated to -10 kPa, then protected by argon at a pressure of 10-50 kPa, and the temperature is raised to 1700-1900°C at a rate of 2-10°C / min, held at that temperature for 1-5 hours, and then cooled. In an alternative embodiment, the temperature can be first raised to 600-650°C at a rate of 5-10°C / min and held at that temperature for 0.5-2 hours, with the remaining steps being the same as above.

[0046] The present invention also proposes a use of processing the hollow radioactive inclusion fuel containing combustible poison into nuclear fuel pellets according to the size of fuel assemblies in ultra-small nuclear reactors.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The hollow radioactive containment fuel containing combustible poisons proposed in the present invention can achieve highly compact and high-safety radioactive containment of reactor fuel, ensure that radioactive products, especially fission gases, are not released into the environment in the event of an accident, provide a fission site for the long-term stability of the micro-nuclear power supply core, and effectively confine radioactive fission products inside the fuel, providing a guarantee for the safe and stable operation of the reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0050] FIG1 is a schematic structural diagram of one direction of a hollow radioactive inclusion fuel containing a combustible poison according to an embodiment of the present invention;

[0051] FIG2 is a schematic structural diagram of another direction of the hollow radioactive inclusion fuel containing a combustible poison according to an embodiment of the present invention;

[0052] FIG3 is a flow chart of a method for preparing a hollow radioactive containment fuel containing a combustible poison according to an embodiment of the present invention.

[0053] In the picture:

[0054] 1 is the SiC fuel-free protective layer; 2 is the TRISO fuel particle; 3 is the BISO combustible poison particle; 4 is the hollow area; 5 is the dense SiC matrix. DETAILED DESCRIPTION

[0055] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0056] The present invention proposes a hollow radioactive containment fuel containing combustible poisons, which can achieve highly compact and high-safety radioactive containment of reactor fuel, ensure that radioactive products, especially fission gases, are not released into the environment in the event of an accident, provide a long-term and stable fission site for the core of a micro-nuclear power supply, and effectively confine radioactive fission products inside the fuel, providing a guarantee for the safe and stable operation of the reactor.

[0057] As shown in Figures 1 and 2, the hollow radioactive enclosed fuel containing a burnable poison of the present invention comprises a hollow annular fuel region and a fuel-free protective layer 1 surrounding the fuel region. The fuel-free protective layer 1 comprises upper and lower covers and an annular cylinder, with the inner layer of the annular cylinder containing a hollow region 4. The fuel region comprises a matrix 5, fuel elements 2 and burnable poison 3 uniformly distributed within the matrix 5. The matrix 5 is dense SiC, the fuel elements 2 are triple-layer isotropically coated fuel particles, referred to as TRISO-coated fuel particles, and the burnable poison 3 are double-layer isotropically coated burnable poison particles, referred to as BISO-coated burnable poison particles. The fuel-free protective layer 1 is made of SiC.

[0058] The density of the substrate 5 and the fuel-free protective layer 1 is not less than 95%.

[0059] The TRISO coated fuel particle comprises a fuel core and four protective layers coated on the outside of the fuel core, wherein the four protective layers are, from the inside to the outside, a loose carbon layer, an inner pyrolytic carbon layer, a SiC layer and an outer pyrolytic carbon layer; wherein the fuel core is one or more of UO2, UC, UN, U3Si2, U alloy or other nuclear fuels, and the UO2, UC, UN, U3Si2, U alloy or other nuclear fuels are selected from the group consisting of: 235 U enrichment is 2-20%; the density of the loose carbon layer is 1.1g / cm 3 , thickness is 95 μm, and the density of the inner pyrolytic carbon layer is 1.9 g / cm3 , the thickness is 30-60 μm, and the density of the SiC layer is 3.18 g / cm 3 , thickness is 25-55 μm, and the density of the outer pyrolytic carbon layer is 1.9 g / cm 3 The diameter of the TRISO coated fuel particles is 400-600 μm. In an alternative embodiment, the density of the loose carbon layer is 0.9-1.2 g / cm 3 , with a thickness of 80-110 μm. In an alternative embodiment, the density of the inner pyrolytic carbon layer is 1.8-2.2 g / cm 3 , with a thickness of 30-60 μm. In an alternative embodiment, the density of the SiC layer is 2.9-3.3 g / cm 3 , with a thickness of 25-55 μm. In an alternative embodiment, the density of the outer pyrolytic carbon layer is 1.8-2.2 g / cm 3 , thickness is 30-60μm.

[0060] The BISO coated combustible poison particles include a combustible poison core and two protective layers coated outside the combustible poison core, and the two protective layers are a loose carbon layer and a dense pyrolytic carbon layer from the inside to the outside. The combustible poison core is one or more of B4C, Gd2O3 or other combustible poisons; the density of the loose carbon layer is 1.1g / cm3 and the thickness is 80-100μm, and the density of the dense pyrolytic carbon layer is 1.9g / cm3 and the thickness is 80-100μm. The diameter of the BISO coated combustible poison particles is 200-240μm. In an alternative embodiment, the density of the loose carbon layer is 0.9-1.2g / cm 3 , with a thickness of 80-100 μm. In an alternative embodiment, the density of the dense pyrolytic carbon layer is 1.8-2.2 g / cm 3 , thickness is 80-100μm.

[0061] The volume fractions of the TRISO-coated fuel particles and the BISO-coated combustible poison particles in the fuel zone are 30-50% and 5-15% respectively, and the thickness of the fuel-free protective layer is 0.2-2 mm.

[0062] In a preferred embodiment of the present invention, a hollow radioactive inclusion fuel containing a burnable poison comprises mainly 30-50 vol.% TRISO-coated fuel particles and 5-15 vol.% BISO-coated burnable poison particles, a dense SiC matrix, and a fuel-free protective layer. The TRISO-coated fuel particles use one or more of UO2, UC, UN, U3Si2, U alloy, or other nuclear fuels as the fuel core, and are sequentially composed of a loose carbon layer, an inner pyrolytic carbon layer, a SiC layer, and a The invention comprises an outer pyrolytic carbon layer; BISO-coated burnable poison particles, with one or more of B4C, Gd2O3, or other burnable poisons as the burnable poison core, and are composed, from the inside out, of a loose carbon layer and a dense pyrolytic carbon layer. The dense SiC matrix and SiC fuel-free protective layer each have a density of no less than 95%, preferably greater than 95%. The integrity of the fuel particles and burnable poison particles is well maintained, and the dense SiC matrix is ​​tightly bonded to the interfaces of the TRISO-coated fuel particles and the BISO-coated burnable poison particles. The hollow radioactive containment fuel containing a burnable poison in the present invention has good thermal conductivity and radiation resistance, sufficient mechanical strength, and excellent fission gas containment. Compared to conventional UO2 pellets and Zr alloy fuel assemblies, it offers significantly improved safety and can be used as fuel assemblies for ultra-compact reactors in micro-nuclear power sources, showing broad industrial prospects.

[0063] As shown in FIG3 , in one embodiment of the present invention, a method for preparing a hollow radioactive inclusion fuel containing a combustible poison comprises the following steps:

[0064] Step 1: Prepare SiC mixed slurry and SiC mixed powder;

[0065] Step 2: coating the SiC mixed slurry on the fuel particles and the combustible poison particles by spray deposition, wherein the binder is 10-15% glycerol diluted with anhydrous ethanol;

[0066] Step 3: The SiC-coated fuel particles and combustible poison particles are molded to obtain a fuel zone blank;

[0067] Step 4: pressing the SiC mixed powder into a shape to obtain a fuel-free zone green billet;

[0068] In an alternative embodiment, the fuel-free zone biscuits may be prepared first and then the fuel zone biscuits, or the fuel-free zone biscuits and the fuel zone biscuits may be prepared simultaneously.

[0069] Step 5: Composite-pressing the fuel area biscuit and the non-fuel area biscuit into a hollow radioactive inclusion fuel biscuit containing combustible poisons;

[0070] Step 6: Pressurelessly sintering the hollow radioactive inclusion fuel blank containing combustible poison in a vacuum furnace to obtain a sintered blank;

[0071] Step 7: The sintered billet is machined into final size fuel pellets.

[0072] The SiC mixed slurry contains, by weight percentage, 85-95% of SiC, 1-10% of Al2O3, 1-10% of Y2O3, 0.5-10% of SiO2 and 0.5-5% of polyethyleneimine as a dispersant.

[0073] The above components are placed in a nylon ball mill, and based on the total mass of the above components, 1-2 times the total mass of alcohol is added and mixed, 2-3 times the total mass of zirconia grinding balls or alumina grinding balls are added and ball milled for 6-24 hours to obtain SiC mixed slurry, and SiC mixed powder is obtained after drying.

[0074] The operating temperature of step 2 is 70-100°C; the pressing pressure of the molding in step 3 is 10-60 MPa, the holding time is 10-20s, and the obtained fuel zone billet is a hollow column; the pressing pressure of the molding in step 4 is 10-60 MPa, and the obtained fuel-free zone billet includes upper and lower covers and an annular cylinder with a thickness of 2-4 mm and a fitting clearance with the fuel zone billet of 0.1-0.25 mm; the pressure of the composite pressing in step 5 is higher than the pressing pressure of the molding in step 3 and the pressing pressure of the molding in step 4.

[0075] The pressure of the composite pressing in step 5 is 60-80 MPa. In step 6, the temperature is first raised to 600°C at a rate of 5-10°C / min and kept at this temperature for 0.5-2h to perform degreasing treatment. The vacuum degree is 10 -2 The furnace is heated to -10 kPa, then protected by argon at a pressure of 20-60 kPa, and the temperature is raised to 1600-2000°C at a rate of 2-10°C / min, held at that temperature for 1-5 hours, and then cooled. In an alternative embodiment, the temperature can be first raised to 600-650°C at a rate of 5-10°C / min and held at that temperature for 0.5-2 hours, with the remaining steps being the same as above.

[0076] The preparation method of the present invention uses SiC, Y2O3, SiO2, and polyethyleneimine to prepare SiC mixed slurry and SiC mixed powder. The SiC mixed slurry is coated on fuel particles and burnable poison particles by spray deposition to form a dense SiC matrix to produce a fuel region biscuit. The SiC mixed powder is molded into a fuel-free region biscuit. The fuel region biscuit and the fuel-free region biscuit are then composite-pressed to form a hollow radioactive enclosed fuel biscuit containing the burnable poison. The hollow radioactive enclosed fuel biscuit containing the burnable poison is then pressurelessly sintered at high temperature in a vacuum furnace. After cooling the furnace, the sintered biscuit is machined to the required size to form a fuel assembly for a water reactor. The present invention uses a pressureless sintering method to prepare the hollow radioactive enclosed fuel containing the burnable poison, achieving densification while significantly improving preparation and production efficiency, effectively achieving the goal of industrialized mass production.

[0077] The hollow radioactive inclusion fuel containing combustible poison prepared by the preparation method can be processed into a pressurized water reactor fuel assembly by a purely mechanical method according to the size of a water reactor fuel assembly in a nuclear reactor.

[0078] In order to further illustrate the present invention, several preferred embodiments are provided below.

[0079] Example 1:

[0080] Step 1: Weigh the following powders according to the following specifications and proportions: SiC, 85 wt.%, Al2O3, 5 wt.%, Y2O3, 5 wt.%, SiO2, 3 wt.%, and polyethyleneimine (molecular weight 800, 2 wt.%). Mix these powders with an equal amount of alcohol and place them in a nylon ball mill using zirconium oxide balls at a 3:1 ball-to-powder ratio. Mill for 24 hours to produce a SiC mixed slurry. Divide this slurry into equal parts: one portion is used to coat the fuel and combustible poison particles; the other portion is dried at 60-100°C for 16-24 hours and sieved to obtain the SiC mixed powder.

[0081] Step 2: The SiC mixed slurry is spray-deposited onto the fuel and burnable poison particles. The binder is 12% glycerol diluted with anhydrous ethanol. The fuel and burnable poison particles are rolled on a vibrator and heated to 70°C. The SiC mixed slurry prepared in Step 1 is used to form a mist slurry through a spray generator, which is then deposited onto the surfaces of the fuel and burnable poison particles. The desired atomization effect is achieved by adjusting parameters such as the spray generator angle, opening size, spray pressure, and flow rate. By coating different masses of SiC mixed slurry, different volume fractions of TRISO-coated fuel particles and BISO-coated burnable poison particles can be obtained.

[0082] Step 3: The SiC-coated fuel particles and combustible poison particles are molded to form a fuel zone blank. A hollow cylindrical mold is designed according to the fuel zone size requirements and molded under a pressure of 20 MPa.

[0083] Step 4: The SiC powder mixture is pressed into shape to form a fuel-free zone blank. This blank, consisting of upper and lower covers and an annular cylinder, is 2 mm thick and has a clearance of 0.1 mm with the fuel zone. The mold is designed based on the specific fuel-free zone dimensions and pressed into shape at a pressure of 40 MPa.

[0084] Step 5: The fuel area blank and the fuel-free area are combined and pressed into a hollow radioactive fuel blank containing combustible poisons. A mold is designed according to the specific dimensions and pressed at a pressure of 60 MPa.

[0085] Step 6: Pressureless sintering in a vacuum furnace. First, heat the furnace to 600°C at a rate of 5°C / min and hold for 0.5 h. Degrease the alloy. Vacuum to 10-2 Pa. Then, introduce argon protection at a pressure of 50 kPa. Heat the furnace to 1700°C at a rate of 10°C / min, hold for 1 h, and cool.

[0086] Step 7: Grind away the excess fuel-free area according to the pellet size requirements to obtain the final size of the pellet fuel.

[0087] Example 2:

[0088] Step 1: Weigh the following powders according to the following specifications and proportions: SiC, 86 wt.%, Al2O3, 2 wt.%, Y2O3, 4 wt.%, SiO2, 3 wt.%, and polyethyleneimine (molecular weight 1800, 5 wt.%). Mix these powders with twice the weight of alcohol and place them in a nylon ball mill using alumina balls at a ball-to-powder ratio of 3:1. Mill for 24 hours to produce a SiC mixed slurry. This slurry is divided equally: one portion is used to coat the fuel and combustible poison particles; the other portion is dried at 80°C for 24 hours and sieved to obtain the SiC mixed powder.

[0089] Step 2: The SiC mixed slurry is spray-deposited onto the fuel and burnable poison particles. The binder is 10% glycerol diluted with anhydrous ethanol. The fuel and burnable poison particles are rolled on a vibrator and heated to 100°C. The SiC slurry prepared in Step 1 is used to form a mist slurry through a spray generator, which is then deposited onto the surfaces of the fuel and burnable poison particles. The desired atomization effect is achieved by adjusting parameters such as the spray generator angle, opening size, spray pressure, and flow rate. By coating different masses of SiC mixed slurry, different volume fractions of TRISO-coated fuel particles and BISO-coated burnable poison particles can be achieved.

[0090] Step 3: The SiC-coated fuel particles and combustible poison particles are molded to form a fuel zone blank. A hollow cylindrical mold is designed according to the fuel zone size requirements and molded under a pressure of 60 MPa.

[0091] Step 4: The SiC powder mixture is pressed into shape to form a fuel-free zone blank. This blank, consisting of upper and lower covers and an annular cylinder, is 4 mm thick and has a clearance of 0.25 mm with the fuel zone. The mold is designed based on the specific fuel-free zone dimensions and pressed into shape at a pressure of 30 MPa.

[0092] Step 5: The fuel area blank and the fuel-free area are combined and pressed into a hollow radioactive fuel blank containing combustible poisons. A mold is designed according to the specific dimensions and pressed at a pressure of 60 MPa.

[0093] Step 6: Pressureless sintering in a vacuum furnace. First, heat the furnace to 600°C at a rate of 10°C / min and hold for 2 hours. Degrease the alloy and apply a vacuum of 1 Pa. Then, apply argon protection at a pressure of 10 kPa. Heat the furnace to 1900°C at a rate of 2°C / min, hold for 5 hours, and then cool.

[0094] Step 7: Grind away the excess fuel-free area according to the pellet size requirements to obtain the final size of the pellet fuel.

[0095] Example 3:

[0096] Step 1: Weigh the following powders according to the following specifications and proportions: SiC, 92 wt.%, Al2O3, 1 wt.%, Y2O3, 1 wt.%, SiO2, 5 wt.%, and polyethyleneimine (molecular weight 1800), 1 wt.%. Mix these powders with 1.5 times the weight of alcohol and place them in a nylon ball mill using alumina balls at a ball-to-powder ratio of 3:1. Mill for 24 hours to obtain a SiC mixed slurry. This slurry is divided equally: one portion is used to coat the fuel and combustible poison particles; the other portion is dried at 80°C for 24 hours and sieved to obtain the SiC mixed powder.

[0097] Step 2: The SiC mixed slurry is spray-deposited onto the fuel and burnable poison particles. The binder is 13% glycerol diluted with anhydrous ethanol. The fuel and burnable poison particles are rolled on a vibrator and heated to 85°C. The SiC slurry prepared in Step 1 is used to form a mist slurry through a spray generator, which is then deposited onto the surfaces of the fuel and burnable poison particles. The desired atomization effect is achieved by adjusting parameters such as the spray generator angle, opening size, spray pressure, and flow rate. By coating different masses of SiC mixed slurry, different volume fractions of TRISO-coated fuel particles and BISO-coated burnable poison particles can be obtained.

[0098] Step 3: The SiC-coated fuel particles and combustible poison particles are molded to form a fuel zone blank. A hollow cylindrical mold is designed according to the fuel zone size requirements and molded under a pressure of 40 MPa.

[0099] Step 4: The SiC powder mixture is pressed into shape to form a fuel-free zone blank. This blank, consisting of upper and lower covers and an annular cylinder, is 2 mm thick and has a clearance of 0.1 mm with the fuel zone. The mold is designed based on the specific fuel-free zone dimensions and pressed into shape at a pressure of 60 MPa.

[0100] Step 5: The fuel area blank and the fuel-free area are combined and pressed into a hollow radioactive fuel blank containing combustible poisons. A mold is designed according to the specific dimensions and pressed at a pressure of 40 MPa.

[0101] Step 6: Pressureless sintering in a vacuum furnace. First, heat the furnace to 600°C at a rate of 8°C / min and hold for 1 hour. Degrease the alloy and maintain a vacuum of 10 Pa. Then, apply argon protection at a pressure of 30 kPa. Heat the furnace to 1800°C at a rate of 5°C / min, hold for 3 hours, and cool.

[0102] Step 7: Grind away the excess fuel-free area according to the pellet size requirements to obtain the final size of the pellet fuel.

[0103] Example 4:

[0104] Step 1: Weigh the following powders according to the following specifications and proportions: SiC, 95 wt.%, Al2O3, 1.5 wt.%, Y2O3, 2 wt.%, SiO2, 1 wt.%, and polyethyleneimine (molecular weight 1800), 0.5 wt.%. Mix these powders with 1.8 times the weight of alcohol and place them in a nylon ball mill using alumina balls at a ball-to-powder ratio of 3:1. Mill for 24 hours to obtain a SiC mixed slurry. This slurry is divided equally: one portion is used to coat the fuel and combustible poison particles; the other portion is dried at 80°C for 24 hours and sieved to obtain the SiC mixed powder.

[0105] Step 2: The SiC mixed slurry is spray-deposited onto the fuel and burnable poison particles. The binder is 15% glycerol diluted with anhydrous ethanol. The fuel and burnable poison particles are rolled on a vibrator and heated to 90°C. The SiC slurry prepared in Step 1 is used to form a mist slurry through a spray generator, which is then deposited onto the surfaces of the fuel and burnable poison particles. The desired atomization effect is achieved by adjusting parameters such as the spray generator angle, opening size, spray pressure, and flow rate. By coating different masses of SiC mixed slurry, different volume fractions of TRISO-coated fuel particles and BISO-coated burnable poison particles can be obtained.

[0106] Step 3: The SiC-coated fuel particles and combustible poison particles are molded to obtain a fuel zone blank. The mold is designed according to the fuel zone size requirements and molded at a pressure of 45 MPa.

[0107] Step 4: The SiC powder mixture is pressed into shape to form a fuel-free zone blank. This blank, consisting of upper and lower covers and an annular cylinder, is 3 mm thick and has a clearance of 0.15 mm with the fuel zone. The mold is designed based on the specific fuel-free zone dimensions and pressed into shape at a pressure of 55 MPa.

[0108] Step 5: The fuel area biscuit and the fuel-free area are combined and pressed into a hollow radioactive fuel biscuit containing combustible poisons. A hollow cylindrical mold is designed according to the specific dimensions and molded at a pressure of 70 MPa.

[0109] Step 6: Pressureless sintering in a vacuum furnace. First, heat the furnace to 600°C at a rate of 8°C / min and hold for 1.5 hours. Degrease the part at a vacuum of 10 Pa. Then, apply argon protection at a pressure of 20 kPa. Heat the furnace to 1850°C at a rate of 5°C / min, hold for 2 hours, and then cool.

[0110] Step 7: Grind away the excess fuel-free area according to the pellet size requirements to obtain the final size of the pellet fuel.

[0111] The hollow radioactive inclusion fuel containing combustible poisons in the embodiment of the present invention has the characteristics of excellent radiation resistance, good fission gas inclusion, high thermal conductivity, and excellent safety performance. The preparation method is scientific and the process flow is simple. The hollow radioactive inclusion fuel containing combustible poisons is prepared by a pressureless sintering method, which greatly improves the preparation and production efficiency while achieving densification, and can achieve the purpose of industrial mass production. It has outstanding substantial characteristics and significant progress.

[0112] The above embodiment is only one of the preferred implementation methods of the present invention and should not be used to limit the scope of protection of the present invention. Any changes or modifications that have no substantive meaning made to the main design concept and spirit of the present invention, as long as the technical problems solved are still consistent with the present invention, should be included in the scope of protection of the present invention.

[0113] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A hollow radioactive inclusion fuel containing a combustible poison, characterized in that: include: A hollow fuel region and a fuel-free protective layer covering the periphery of the fuel region; The hollow fuel area includes a matrix and fuel elements and combustible poisons distributed in the matrix; The fuel element is an isotropic coated fuel particle, and the combustible poison is an isotropic coated combustible poison particle.

2. The hollow radioactive inclusion fuel containing a combustible poison according to claim 1, characterized in that: The density of the substrate and the fuel-free protective layer is not less than 95% respectively.

3. The hollow radioactive inclusion fuel containing a combustible poison according to claim 1, characterized in that: The coated fuel particle comprises a fuel core and a first protective layer coated outside the fuel core; The first protective layer at least includes, from inside to outside, a loose carbon layer, an inner pyrolytic carbon layer, a SiC layer and an outer pyrolytic carbon layer.

4. The hollow radioactive inclusion fuel containing a combustible poison according to claim 1, characterized in that: The coated burnable poison particle comprises a burnable poison core and a second protective layer coated outside the burnable poison core; The second protective layer includes a loose carbon layer and a dense pyrolytic carbon layer from the inside to the outside.

5. The hollow radioactive inclusion fuel containing a combustible poison according to claim 1, characterized in that: The diameter of the coated fuel particles is 400-800 μm; The diameter of the coated combustible poison particles is 200-400 μm; The thickness of the fuel-free protective layer is 0.2-2 mm.

6. A method for preparing a hollow radioactive inclusion fuel containing a combustible poison, characterized in that: The following steps are involved: Step S1: preparing SiC mixed slurry and SiC mixed powder; Step S2: coating the SiC mixed slurry on the fuel particles and the combustible poison particles by spray deposition, and pressing the SiC-coated fuel particles and the combustible poison particles into a fuel zone blank; and, pressing the SiC mixed powder into a fuel-free zone blank; Step S3: Composite-pressing the fuel region biscuit and the non-fuel region biscuit into a radioactive inclusion diffused pellet fuel biscuit containing combustible poisons; Step S4: pressurelessly sintering the radioactive inclusion dispersion type fuel pellet containing combustible poison in a vacuum furnace to obtain a sintered pellet; Step S5: machining the sintered billet into fuel pellets of final size.

7. The method for preparing hollow radioactive inclusion fuel containing combustible poison according to claim 6, characterized in that: The SiC mixed slurry contains, by weight percentage, 85-95% of SiC, 1-10% of Al2O3, 1-10% of Y2O3, 0.5-10% of SiO2 and 0.5-5% of polyethyleneimine as a dispersant.

8. The method for preparing hollow radioactive inclusion fuel containing combustible poison according to claim 7, characterized in that: The components of the SiC mixed slurry are placed in a nylon ball mill, and based on the total mass, 1-2 times the total mass of alcohol is added and mixed, and 2-5 times the total mass of zirconium oxide grinding balls or aluminum oxide grinding balls are added and ball milled for 10-30 hours to obtain the SiC mixed slurry; The SiC mixed powder is obtained by drying the SiC mixed slurry.

9. The method for preparing hollow radioactive inclusion fuel containing combustible poison according to claim 6, characterized in that: In the step S2, the operating temperature of coating the SiC mixed slurry on the fuel particles and the combustible poison particles by spray deposition is 70-100°C; In the operation of molding the SiC-coated fuel particles and the combustible poison particles, the compression pressure of the molding is 20-60 MPa, and the obtained fuel zone blank is a hollow columnar shape; In the operation of molding the SiC mixed powder, the pressing pressure of the molding is 20-60 MPa; the obtained fuel-free zone blank includes upper and lower covers and an annular cylinder, the thickness is 2-4 mm, and the matching clearance with the fuel zone blank is 0.1-0.25 mm; The pressure of the composite pressing in step S3 is higher than the pressing pressure of the molding of the fuel particles and the combustible poison particles coated with SiC and the pressing pressure of the molding of the SiC mixed powder in step S2.

10. A fuel use, characterized in that: The hollow radioactive inclusion fuel containing a burnable poison as claimed in any one of claims 1 to 5 is processed into a nuclear fuel pellet according to the size of a fuel assembly in an ultra-small nuclear reactor.

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