A method for preparing high thermal conductivity coated particle dispersion fuel pellets

Abstract

The present invention provides a method for preparing coated particle dispersion fuel pellets, comprising the following steps: Step 1: adding graphene during the preparation of the coated particle dispersion fuel pellet powder; Step 2: placing the prepared coated particle dispersion fuel pellet powder into a steel mold and pressing it to produce a graphene-added coated particle dispersion fuel pellet green body; Step 3: hot-pressing and sintering the graphene-added coated particle dispersion fuel green body to obtain the coated particle dispersion fuel pellets. The preparation method provided by the present invention can effectively improve the high-temperature thermal conductivity of SiC by adding graphene, enhancing the thermal conductivity of the coated particle dispersion fuel pellets and further improving reactor safety.

Description

Technical Field

[0001] The invention relates to the technical field of accident-resistant fuel pellets, and in particular to a method for preparing high-thermal-conductivity coated particle dispersed fuel pellets. Background Art

[0002] Nuclear fuel elements are the core components of nuclear reactors, and their advancement and safety are crucial foundations for their advancement and safety. Following the Fukushima accident, the international community has placed higher demands on the safety, reliability, and economic efficiency of new-generation nuclear power plants and nuclear fuels. To address the issue of excessive core temperatures caused by the low thermal conductivity of traditional UO2 fuel pellets and further enhance nuclear power plant safety, the development of accident-tolerant fuel (ATF), a fuel that can tolerate accidents to a certain extent and possesses inherent safety, is emerging as a new direction in the international nuclear fuel field.

[0003] Coated particle dispersion fuel, first proposed by Oak Ridge National Laboratory in 2012, has become a crucial component of accident-tolerant fuel. Its fuel structure consists of dispersed fuel pellets consisting of three-dimensional TRISO (Tri-Structural Isotropic) coated particles embedded in a SiC matrix. Coated particle dispersion fuel pellets utilize SiC, a material with excellent thermal conductivity, as their matrix. This allows for faster heat transfer from the fuel through conduction, mitigating temperature gradients within the reactor and reducing core temperatures. Furthermore, the use of TRISO particles as the fuel phase leverages their superior fission product tolerance and higher burnup tolerance, enhancing reactor safety.

[0004] Although SiC material has a significant advantage in thermal conductivity over traditional UO2, its thermal conductivity decreases significantly with increasing temperature. The industry consensus is that a material with a thermal conductivity higher than UO2 has a high thermal conductivity. Table 1 shows the thermal conductivity of UO2. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing high-thermal conductivity coated particle dispersed fuel pellets to solve the problem of serious attenuation of high-temperature thermal conductivity of SiC materials in traditional coated particle dispersed fuel pellets. By adding graphene, the high-temperature thermal conductivity of SiC can be effectively improved, the thermal conductivity of the coated particle dispersed fuel pellets can be enhanced, and the safety of the reactor can be further improved.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a coated particle dispersion fuel pellet comprises the following steps: step 1: adding graphene during the preparation of the coated particle dispersion fuel pellet powder; step 2: placing the prepared coated particle dispersion fuel pellet powder into a steel mold and pressing it to obtain a graphene-added coated particle dispersion fuel pellet green body; step 3: hot-pressing and sintering the graphene-added coated particle dispersion fuel green body to obtain the coated particle dispersion fuel pellet.

[0008] Step 1 specifically includes:

[0009] Step 1.1: Add 30%-65% by weight of nano-sized SiC powder, 3%-10% by weight of nano-sized Al2O3-Y2O3 sintering aid, and 1%-10% by weight of graphene into a mixing tank;

[0010] Step 1.2: Add dispersant to the mixing tank, ultrasonically disperse the mixture for 12-24 hours, and use grinding balls to high-speed ball mill the mixture at 100 rpm-400 rpm for 4-10 hours;

[0011] Step 1.3: Drying the wet-milled powder, crushing the powder after drying, and then passing it through a 50-200 mesh sieve to obtain a SiC mixed powder;

[0012] Step 1.4: Infiltrate the TRISO particles with a mixture of anhydrous ethanol and glycerol in a volume ratio of 9:1. After infiltration, place the TRISO particles on the SiC mixed powder and slowly roll them so that the surface of the TRISO particles is evenly coated with the SiC mixed powder to obtain the dressed TRISO particles.

[0013] Step 1.5: Dry mix a certain mass of coated TRISO particles and SiC mixed powder for 5 h to obtain coated particle dispersed fuel pellet powder.

[0014] In step 1.1, the mass ratio of Al2O3 in the sintering aid to the total sintering aid is 20%-70%.

[0015] In step 1.2, anhydrous ethanol is used as a dispersant, stainless steel balls are used as grinding balls, and the ratio of the mass of the grinding balls to the total mass of the SiC mixed powder is 3:1.

[0016] In step 1.4, the dispersed binder is evenly coated on the surface of the TRISO particles. The binder is prepared by mixing 15% by volume of propylene glycol and 85% by volume of anhydrous ethanol.

[0017] Furthermore, after coating, mixed SiC powder is used for bonding so that the volume of the TRISO particles after sintering accounts for 35% of the total volume of the core block, and the bonded TRISO particles and the SiC mixed powder are uniformly mixed.

[0018] In step 2, the prepared coated particle dispersion fuel pellet powder is placed in a steel mold with a pressing force of 8-15 kN, a pressure increase rate of 0.2-0.5 kN / s, and a pressure holding time of 10-20 seconds to obtain a graphene-added coated particle dispersion fuel pellet green body.

[0019] Step 3 specifically includes:

[0020] Step 3.1: Place the coated particle dispersion fuel pellet green body into a hot pressing graphite mold for assembly. After assembly, place the hot pressing graphite mold into a hot pressing sintering furnace at a sintering temperature of 1650-1750°C, a holding time of 1.5-3 hours, a heating rate of 10-20°C / min, and a pressure of 50-80 MPa.

[0021] Step 3.2: After sintering, remove the hot-pressed graphite mold and take out the coated particle dispersion fuel pellets.

[0022] The method for preparing high thermal conductivity coated particle dispersion fuel pellets further includes step 3.3: polishing with sandpaper to obtain finished coated particle dispersion fuel pellets.

[0023] In step 3.2, the coated particle dispersion fuel pellets are removed by demoulding or disassembly.

[0024] Compared with the prior art, the method for preparing the high thermal conductivity coated particle dispersion fuel pellets provided by the present invention has the following beneficial effects:

[0025] The present invention adds graphene during the preparation process of coated particle dispersion fuel pellets, thereby improving the high-temperature thermal conductivity of the coated particle dispersion fuel pellets, enhancing the heat transfer efficiency of the coated particle dispersion fuel pellets under normal operating conditions of the reactor, and further improving the overall power generation efficiency and safety performance of the reactor.

[0026] Compared with existing coated particle dispersion fuel pellets without graphene addition, the thermal conductivity of the coated particle dispersion fuel pellets with graphene addition is improved by 40%-100%, and the improvement is more significant compared with traditional UO2 fuel pellets, as shown in Table 1.

[0027] Table 1 Thermal conductivity of coated particle dispersion fuel pellets

[0028] DETAILED DESCRIPTION

[0029] The following is further explained in detail through specific implementation methods.

[0030] The present invention provides a method for preparing coated particle dispersion fuel pellets with high thermal conductivity, comprising the steps of preparing coated particle dispersion fuel pellet powder, forming coated particle dispersion fuel pellet green bodies, sintering coated particle dispersion fuel pellets and post-processing.

[0031] Step 1: Preparation of coated particle dispersed fuel pellet powder. Details are as follows:

[0032] Step 1.1: Add 30%-65% by weight of nano-scale SiC powder, 3%-10% by weight of nano-scale Al2O3-Y2O3 sintering aid mixed powder, and 1%-10% by weight of graphene into a mixing tank, wherein the mass proportion of Al2O3 powder in the sintering aid mixed powder is 20%-70% of the total sintering aid.

[0033] Step 1.2: Use anhydrous ethanol as the dispersant. Anhydrous ethanol has excellent dispersion effects, a low evaporation temperature, and is economical. Stainless steel balls are used as grinding balls. The mass ratio of grinding balls to total powder is 1:1 to 6:1. Ultrasonic dispersion and mixing are performed for 12-24 hours. High-speed ball milling (100-400 rpm) is then used for 4-10 hours. Alternatively, agate balls and zirconia balls can also be used as grinding balls.

[0034] Step 1.3: Dry the wet ball-milled powder, crush it after drying, and then pass it through a 50-200 mesh sieve to obtain a mixed powder of SiC powder, sintering aid powder and graphene (SiC mixed powder).

[0035] Step 1.4: Infiltrate the TRISO particles with a mixture of anhydrous ethanol and glycerol in a volume ratio of 1:1 to 9:1. After infiltration, place the TRISO particles in the SiC powder mixture and slowly roll them to evenly coat the TRISO particles with the SiC powder mixture, creating a "coated" effect. Depending on the volume percentage of the TRISO particles in the coated particle dispersion fuel pellet, weigh a certain mass (e.g., 30% to 45% by volume) of the coated TRISO particles and the SiC powder mixture.

[0036] Step 1.5: The weighed coated TRISO particles and SiC mixed powder are mixed by dry mixing for 4-10 hours to obtain coated particle dispersed fuel pellet powder.

[0037] Step 2: Green Forming of Coated Particle Dispersion Fuel Pellets. Specifically, the prepared coated particle dispersion fuel pellet powder is placed in a steel mold. The compaction force is 8-15 kN, the pressure is increased at a rate of 0.2-0.5 kN / s, and the pressure is maintained for 10-20 seconds to produce green graphene-added coated particle dispersion fuel pellets. It should be noted that in this example, steel molds were used for molding, while graphite molds were used for sintering.

[0038] Step 3: Sintering and post-processing of the coated particle dispersion fuel pellets. Details are as follows:

[0039] Step 3.1: Place the coated particle dispersion fuel pellet green body into a hot pressed graphite mold for assembly, and place the assembled hot pressed graphite mold into a hot pressed sintering furnace with a sintering temperature of 1650-1750°C, a holding time of 1.5-3h, a heating rate of 10-20°C / min, and a pressure of 50-80MPa.

[0040] Step 3.2: After sintering, remove the hot-pressed graphite mold and remove the coated particle dispersion fuel pellets by demolding or disassembly.

[0041] Step 3.3: The coated particle dispersion fuel pellets are polished with sandpaper to obtain finished pellets.

[0042] This invention adds graphene during the preparation of coated dispersed fuel pellets, improving their thermal conductivity and heat transfer efficiency within the reactor, further enhancing the overall power generation efficiency and safety of the reactor. Compared to pellets without graphene, the thermal conductivity of the coated dispersed fuel pellets with graphene added is increased by 40%-100%.

[0043] For example, 50g of nano-sized SiC powder, 5g of nano-sized Al2O3-Y2O3 sintering aid, 2.5g of Al2O3 powder, 2.5g of Y2O3 powder, and 5g of graphene powder were added to a mixing tank. Anhydrous ethanol was used as the dispersant, and stainless steel balls weighing 180g were used as grinding balls. Ultrasonic dispersion and mixing were performed for 15 hours, followed by high-speed ball milling for 6 hours. The wet-milled powder was dried, crushed, and then passed through a 60-mesh sieve to obtain a SiC mixed powder. The dispersed binder was evenly coated on the surface of TRISO particles. The binder consisted of 15% by mass of glycerol as the binder and the remainder of anhydrous ethanol as the diluent (i.e., a mixture of 15% by volume of glycerol and 85% by volume of anhydrous ethanol). After coating, the TRISO particles were placed on the SiC mixed powder and slowly rolled to evenly coat the surface of the TRISO particles with the SiC mixed powder, thus producing the coated TRISO particles. Based on the percentage of the volume of TRISO particles in the total volume of the pellet being 35%, 24.15 g of dressed TRISO particles and 40.3 g of SiC mixed powder were weighed, and the weighed dressed TRISO particles and SiC mixed powder were dry-mixed for 5 hours to obtain coated particle dispersed fuel pellet powder.

[0044] The prepared powder was placed in a steel mold with a pressing force of 10 kN, a pressure increase rate of 0.3 kN / s, and a pressure holding time of 15 seconds to obtain a graphene-added coated particle dispersion fuel pellet green body.

[0045] The coated particle dispersion fuel green pellets are placed into a hot-pressed graphite mold for assembly. The mold is then placed into a hot-pressed sintering furnace. The sintering temperature is 1700°C, the holding time is 2 hours, the heating rate is 15°C / min, and the pressure is 60 MPa. After sintering, the hot-pressed mold is removed, and the coated particle dispersion fuel pellets are removed by demolding or disassembly. The finished pellets are then polished with sandpaper.

[0046] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention are intended to be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection of the claims.

Claims

1. A method for preparing a high thermal conductivity coated particle dispersion fuel pellet, characterized in that: The following steps are involved: Step 1: adding graphene during the preparation of the coated particle dispersion fuel pellet powder; Step 1 specifically includes: Step 1.1: Add 30%-65% by weight of nano-sized SiC powder, 3%-10% by weight of nano-sized Al2O3-Y2O3 sintering aid, and 1%-10% by weight of graphene into a mixing tank; Step 1.2: Add dispersant to the mixing tank, ultrasonically disperse the mixture for 12-24 hours, and use grinding balls to high-speed ball mill the mixture at 100 rpm-400 rpm for 4-10 hours; Step 1.3: Drying the wet-milled powder, crushing the powder after drying, and then passing it through a 50-200 mesh sieve to obtain a SiC mixed powder; Step 1.4: Infiltrate the TRISO particles with a mixture of anhydrous ethanol and glycerol in a volume ratio of 9:

1. After infiltration, place the TRISO particles on the SiC mixed powder and slowly roll them so that the surface of the TRISO particles is evenly coated with the SiC mixed powder to obtain the dressed TRISO particles. Step 1.5: Dry-mix a certain amount of coated TRISO particles and SiC mixed powder for 5 hours to obtain coated particle dispersed fuel pellet powder; Step 2: placing the prepared coated particle dispersion fuel pellet powder into a steel mold and pressing it to obtain a graphene-added coated particle dispersion fuel pellet green body; Step 3: hot pressing and sintering the graphene-added coated particle dispersion fuel green body to obtain coated particle dispersion fuel pellets.

2. The method for preparing a high thermal conductivity coated particle dispersion fuel pellet according to claim 1, characterized in that: In step 1.1, the mass ratio of Al2O3 in the sintering aid to the total sintering aid is 20%-70%.

3. The method for preparing a high thermal conductivity coated particle dispersion fuel pellet according to claim 1, characterized in that: In step 1.2, anhydrous ethanol is used as a dispersant, stainless steel balls are used as grinding balls, and the ratio of the mass of the grinding balls to the total mass of the SiC mixed powder is 3:

1.

4. The method for preparing a high thermal conductivity coated particle dispersion fuel pellet according to claim 1, characterized in that: In step 1.4, the dispersed binder is evenly coated on the surface of the TRISO particles. The binder is prepared by mixing 15% by volume of propylene glycol and 85% by volume of anhydrous ethanol.

5. The method for preparing a high thermal conductivity coated particle dispersion fuel pellet according to claim 4, characterized in that: After coating, mixed SiC powder is used for bonding so that the volume of the TRISO particles after sintering accounts for 35% of the total volume of the core block, and the bonded TRISO particles and the SiC mixed powder are uniformly mixed.

6. The method for preparing a high thermal conductivity coated particle dispersion fuel pellet according to claim 1, characterized in that: In step 2, the prepared coated particle dispersion fuel pellet powder is placed in a steel mold with a pressing force of 8-15 kN, a pressure increase rate of 0.2-0.5 kN / s, and a pressure holding time of 10-20 seconds to obtain a graphene-added coated particle dispersion fuel pellet green body.

7. The method for preparing a high thermal conductivity coated particle dispersion fuel pellet according to claim 1, characterized in that: Step 3 specifically includes: Step 3.1: Place the coated particle dispersion fuel pellet green body into a hot pressing graphite mold for assembly. After assembly, place the hot pressing graphite mold into a hot pressing sintering furnace at a sintering temperature of 1650-1750°C, a holding time of 1.5-3 hours, a heating rate of 10-20°C / min, and a pressure of 50-80 MPa. Step 3.2: After sintering, remove the hot-pressed graphite mold and take out the coated particle dispersion fuel pellets.

8. The method for preparing a high thermal conductivity coated particle dispersion fuel pellet according to claim 7, characterized in that: The method further includes step 3.3: polishing with sandpaper to obtain finished coated particle dispersion fuel pellets.

9. The method for preparing high thermal conductivity coated particle dispersion fuel pellets according to claim 7, characterized in that: In step 3.2, the coated particle dispersion fuel pellets are removed by demoulding or disassembly.

Images