Coated particle dispersion fuel and preparation method thereof

Abstract

The invention belongs to the technical field of nuclear fuel preparation, and discloses a coated particle dispersion fuel and a preparation method thereof.The preparation method comprises the steps that firstly, a powder atomic layer deposition device is started, inert gas is continuously introduced to remove gas in a reactor and a pipeline, and the powder atomic layer deposition device is prepared through the atomic layer deposition process; the method comprises the following steps: performing sintering aid coating deposition on silicon carbide powder in a fluidized state, including precursor adsorption, chemical reaction, inert gas purging and cyclic repetition until coating components and thickness reach the standard, depositing other types of sintering aids according to sintering aid component design requirements, performing coated particle dispersion fuel pellet forming, and performing densification sintering on the pellet, thereby obtaining the coated particle dispersion fuel pellet. The silicon carbide-based coated particle dispersion fuel is obtained; the coated particle dispersion fuel is prepared by the method. According to the preparation method, through SiC powder modification, the dosage of the sintering aid in the preparation process of the coated particle dispersion fuel is optimized.

Description

Technical Field

[0001] This application belongs to the field of nuclear fuel preparation technology, and in particular relates to a coated particulate dispersion fuel and its preparation method. Background Technology

[0002] Coated particulate dispersed fuels are currently a research hotspot in the international field of Accident Tolerant Fuels (ATFs). They utilize silicon carbide (SiC) as the matrix phase and TRISO particles as the fuel phase, employing a structure where TRISO-coated particulate fuels are dispersed within the SiC matrix. The SiC matrix is ​​chemically stable, has good compatibility with coolants, and possesses a high melting point, high thermal conductivity, and good radiation stability. The TRISO particles effectively prevent the release of fission products. The combination of the SiC matrix and TRISO particles significantly improves the accident tolerance performance of coated particulate dispersed fuels compared to traditional UO2.

[0003] Existing coated particulate dispersion fuels typically employ a preparation process of "uniform mixing of silicon carbide powder and sintering aid powder - uniform mixing of matrix powder and TRISO particles - green forming - densification sintering". However, SiC is a strongly covalently bonded high-temperature ceramic with a very low self-diffusion rate, which limits mass transport during sintering. Therefore, diffusion-controlled solid-state sintering alone is insufficient to achieve high densification. Existing sintering processes mainly improve the solid-state diffusion rate of SiC by adding sintering aids, generating a liquid glass phase to assist SiC particles in achieving viscous flow, and increasing sintering temperature and pressure to improve SiC density.

[0004] Silicon carbide nanoparticles have high surface energy and high sintering activity, which can reduce the sintering temperature. To prepare high-density SiC matrix materials, highly active nanoscale powders are usually selected as raw materials. Due to the small particle size of the raw material powder, dry mixing can easily cause powder agglomeration and clumping, making it difficult to mix evenly with sintering aids. Furthermore, if the sintering aids are not added evenly, SiC may shrink unevenly during sintering, leading to defects such as core cracking and deformation.

[0005] Furthermore, during the sintering process, the oxide layer on the surface of silicon carbide reacts with the silicon carbide to produce volatile components, making it difficult to sinter the ceramic into a dense structure. The large specific surface area of ​​silicon carbide nanoparticles increases the content of the surface oxide layer, which is also detrimental to the densification of silicon carbide during sintering. Summary of the Invention

[0006] The main objective of this invention is to provide a coated particulate dispersion fuel and its preparation method, thereby solving the problem of uniform mixing of silicon carbide powder and sintering aids during the preparation of coated particulate dispersion fuel.

[0007] Another objective of this invention is to provide a method for preparing coated particulate dispersion fuel, which solves the problem that excessive sintering aid dosage leads to a decrease in the thermal conductivity of coated particulate dispersion fuel.

[0008] Another objective of this invention is to provide a method for preparing coated particulate dispersion fuel, which solves the problem of controlling the phase transformation of silicon carbide during the densification process of coated particulate dispersion fuel.

[0009] Another objective of this invention is to provide a method for preparing coated particulate dispersion fuel, which solves the problem of TRISO particles coming into contact with each other during the densification process of coated particulate dispersion fuel.

[0010] To achieve the above objectives, this application provides the following technical solution:

[0011] In a first aspect, this application provides a method for preparing coated particulate dispersion fuel, comprising:

[0012] Step 1: Start the powder atomic layer deposition apparatus and continuously introduce inert gas to remove gas from the reactor and pipelines;

[0013] Step 2: Atomic layer deposition process is used to deposit a sintering aid coating on silicon carbide powder in a fluidized state, including precursor adsorption, chemical reaction, inert gas purging and repeated cycles until the coating composition and thickness meet the requirements.

[0014] Step 3: Based on the design requirements of the sintering aid composition, repeat step 2 to deposit other types of sintering aids;

[0015] Step 4: Form coated particulate fuel pellets;

[0016] Step 5: Densification sintering of the pellets to obtain silicon carbide-based coated particulate dispersion fuel.

[0017] As one feasible approach, step 2 includes:

[0018] Step 2.1: Place silicon carbide powder into a powder atomic layer deposition apparatus, introduce inert gas to make the powder reach a stable fluidized state, and start deposition after the temperature of the reactor and gas pipeline stabilizes;

[0019] Step 2.2: The first gaseous precursor used to generate the sintering aid is introduced into the reaction chamber and undergoes a chemical adsorption reaction on the surface of the deposition substrate. After a certain deposition time, sufficient precursor molecules are provided to the surface of the powder substrate.

[0020] Step 2.3: Add a pressure holding process during ALD deposition to increase the adsorption time of the precursor on the powder surface;

[0021] Step 2.4: Inert gas is introduced into the reaction chamber to purge excess gaseous second precursor and byproducts for a certain period of time to ensure that all unreacted precursors are removed.

[0022] Step 2.5: Introduce a second precursor for the reaction to generate the sintering aid, which reacts chemically with the first precursor on the substrate surface to generate a sintering aid coating. Deposit for a certain period of time to provide sufficient precursor molecules to the surface of the powder substrate.

[0023] Step 2.6: Inert gas is introduced into the reaction chamber to purge excess gaseous second precursor and byproducts for a certain period of time to ensure that all unreacted precursors are removed.

[0024] Step 2.7: Repeat steps 2.2 to 2.6 until the thickness of the deposited sintering aid reaches the required level.

[0025] As an feasible approach, the sintering aid used to coat silicon carbide powder may be one or more of Al2O3, Y2O3, SiO2, CeO2, ZrO2, TiO2, La2O3, Sc2O3, MgO, AlN, and TiN.

[0026] As an feasible approach, the reaction temperature is set in the powder atomic layer deposition apparatus, the heating is turned on to preheat the reaction chamber, and the frequency and amplitude of the vibration table are adjusted.

[0027] As an feasible approach, the deposition time is 1–20 min and the purging time is 1–20 min.

[0028] As an feasible approach, the thickness of the sintering aid is selected based on the number of cycles in steps 2.2 to 2.6.

[0029] As an feasible approach, 10 to 100 cycles are used.

[0030] As one feasible approach, the mass percentage of the coated silicon carbide powder sintering aid is 1% to 12%.

[0031] As one feasible approach, step 4 includes:

[0032] Step 4.1: Add a small amount of anhydrous ethanol to the silicon carbide powder coated with the combustion aid and mix evenly. Then, put the mixture into a steel mold for the fuelless zone collar and cover plate and press it into shape to obtain the fuelless zone collar and cover plate of the pellet.

[0033] Step 4.2: Add a small amount of anhydrous ethanol to TRISO particles and silicon carbide powder coated with combustion aid and mix evenly. Then, load the mixture into a steel mold for the fuel compartment and press it into shape to obtain the fuel block.

[0034] Step 4.3: Insert the fuel pellet into the hollow fuelless zone ring, then place the two cover plates on the top and bottom of the ring respectively, and perform cold isostatic pressing under a certain pressure to obtain a coated particulate dispersed fuel green blank.

[0035] As an feasible approach, the cold isostatic pressure is 180–240 MPa.

[0036] As one feasible approach, densification is carried out in step 5 by pressureless sintering, hot pressing sintering, or spark plasma sintering;

[0037] The maximum sintering temperature for pressureless sintering is 1700–2100℃, and the holding time is 1–4 hours.

[0038] The maximum sintering temperature for hot pressing is 1700–2100℃, the heating rate is 5–20℃ / min, and the maximum sintering pressure is 50–150MPa.

[0039] The maximum sintering temperature of spark plasma sintering is 1700–2100℃, the heating rate is 50–150℃ / min, and the maximum sintering pressure is 10–60MPa.

[0040] As a feasible approach, 4% Al2O3 and 4% Y2O3 were laminated onto the surface of SiC with two different particle sizes using atomic layer deposition technology, and then SiC chips were prepared by SPS sintering.

[0041] Secondly, this application provides a coated particulate dispersion fuel, which is prepared using the above-described method.

[0042] Compared with the prior art, the coated particulate dispersion fuel and its preparation method provided in this application have the following beneficial effects:

[0043] This application achieves uniform mixing of sintering aid powder and SiC powder through powder atomic layer deposition technology.

[0044] This application optimizes the amount of combustion aid used in the preparation of coated particulate dispersion fuel by modifying SiC powder.

[0045] This application achieves optimization of sintering temperature and control of silicon carbide phase transformation during the densification process of coated particulate dispersion fuel through SiC powder modification.

[0046] This application achieves optimization of sintering pressure during the densification process of coated particulate dispersion fuel through SiC powder modification. Attached Figure Description

[0047] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the technical description will be briefly introduced below.

[0048] Figure 1 A flowchart of the method for preparing coated particulate dispersion fuel provided in this application;

[0049] Figure 2 An image of alumina coating on a 60nm silicon carbide surface obtained using transmission electron microscopy, provided in this application.

[0050] Figure 3 The image provided in this application shows the effect of coating alumina onto a 60nm silicon carbide surface using TEM-EDS.

[0051] Figure 4 An image showing the effect of alumina coating on a 500nm silicon carbide surface obtained using transmission electron microscopy, provided for this application.

[0052] Figure 5 The image shows the effect of coating alumina on a 500nm silicon carbide surface obtained by TEM-EDS, which is provided in this application. Detailed Implementation

[0053] The following detailed description provides further details on specific implementation methods.

[0054] like Figure 1 As shown, this application provides a method for preparing coated particulate dispersed fuel, which is a method for preparing coated particulate dispersed fuel modified with silicon carbide powder based on atomic layer deposition (ALD) technology. In this method, after drying the silicon carbide powder, an additive is deposited on the surface of the silicon carbide powder using ALD. One ALD cycle includes a first precursor adsorption and reaction - inert gas purging - a second precursor adsorption and reaction - inert gas purging. The number of cycles is determined according to the required amount of additive; if multiple additives are required, they are deposited sequentially. After obtaining silicon carbide powder coated with additives, a fuel-free zone collar and cover plate are obtained by cold pressing. The silicon carbide powder is mixed with TRISO particles, and a fuel zone core is obtained by cold pressing. The fuel-free zone and fuel zone are assembled, and cold isostatic pressing is used to obtain a coated particulate dispersed fuel green body. The green body is densified by pressureless sintering, hot pressing sintering, or spark plasma sintering to obtain silicon carbide-based coated particulate dispersed fuel. This method specifically includes the following steps:

[0055] Step 1: Start the powder atomic layer deposition apparatus and continuously introduce inert gas (nitrogen or argon) for a period of time to remove other gases from the reactor and pipelines.

[0056] Step 2: Perform the silicon carbide powder atomic layer step. Step 2 includes:

[0057] Step 2.1: Place the silicon carbide powder, which has been dried in an oven beforehand, into the powder atomic layer deposition apparatus, set the reaction temperature, turn on the heating to preheat the reaction chamber, adjust the frequency and amplitude of the vibration table, and introduce an inert gas (nitrogen, argon, helium, etc.) to make the powder reach a stable fluidized state. After the temperature of the reactor and gas pipeline stabilizes, deposition begins. The sintering aid used to coat the silicon carbide powder can be one or more of Al2O3, Y2O3, SiO2, CeO2, ZrO2, TiO2, La2O3, Sc2O3, MgO, AlN, TiN, etc.

[0058] Step 2.2: The first gaseous precursor used to generate the sintering aid is introduced into the reaction chamber, where it undergoes a chemical adsorption reaction on the surface of the deposition substrate. Deposition takes place for a certain period, providing sufficient precursor molecules to the surface of the powder substrate. The deposition time is, for example, 1–20 min.

[0059] Step 2.3: For powders with a large specific surface area, deposition is more difficult. A "holding pressure" process can be added during ALD deposition to increase the adsorption time of the precursor on the powder surface. The holding pressure time is, for example, 1 to 20 minutes.

[0060] Step 2.4: Inert gas (nitrogen, argon, helium, etc.) is introduced into the reaction chamber to purge excess gaseous secondary precursors and byproducts for a certain period of time to ensure that all unreacted precursors are removed. The purging time is, for example, 1 to 20 minutes.

[0061] Step 2.5: Introduce a second precursor for the reaction to generate the sintering aid, which reacts chemically with the first precursor on the substrate surface to form a sintering aid coating. Deposition is carried out for a certain period to provide sufficient precursor molecules to the surface of the powder substrate. The deposition time is, for example, 1–20 minutes.

[0062] Step 2.6: Inert gas (nitrogen, argon, helium, etc.) is introduced into the reaction chamber to purge excess gaseous secondary precursors and byproducts for a certain period of time to ensure that all unreacted precursors are removed. The purging time is, for example, 1 to 20 minutes.

[0063] Step 2.7: Repeat steps 2.2 to 2.6 until the deposited sintering aid thickness reaches the required level. The sintering aid thickness depends on the number of cycles in steps 2.2 to 2.6, for example, 10 to 100 cycles.

[0064] Step 3: Based on the design requirements for the sintering aid composition, repeat Step 2 to deposit other types of sintering aids (one or more of Al2O3, Y2O3, SiO2, CeO2, ZrO2, TiO2, La2O3, Sc2O3, MgO, AlN, TiN, etc.). The mass percentage of the coated silicon carbide powder sintering aid is, for example, 1% to 12%.

[0065] Step 4: Form coated particulate fuel pellets.

[0066] Step 4.1: Add a small amount of anhydrous ethanol to the silicon carbide powder coated with the combustion aid and mix evenly. Then, put the mixture into a steel mold for the fuelless zone collar and cover plate (the inner wall of the steel mold is coated with zinc stearate or carbon tetrachloride as a release lubricant). After cold pressing, the fuelless zone collar and cover plate of the pellet are obtained.

[0067] Step 4.2: Mix TRISO pellets (or coated TRISO pellets) with silicon carbide powder coated with combustion aids, add a small amount of anhydrous ethanol and mix evenly. Then, load the mixture into a steel mold for the fuel zone (the inner wall of the steel mold is coated with zinc stearate or carbon tetrachloride as a release lubricant). After cold pressing, the pellet fuel zone is obtained.

[0068] Step 4.3: Insert the fuel pellet into the hollow fuel-free ring, then place the two cover plates on top and bottom respectively, and perform cold isostatic pressing under a certain pressure to obtain the coated particulate dispersed fuel green compact. The cold isostatic pressing pressure is, for example, 180-240 MPa.

[0069] Step 5: Perform core sintering, densifying the core through pressureless sintering, hot pressing sintering, or spark plasma sintering.

[0070] The maximum sintering temperature for pressureless sintering is 1700–2100℃, with a holding time of 1–4 hours. The maximum sintering temperature for hot pressing is 1700–2100℃, with a heating rate of 5–20℃ / min and a maximum sintering pressure of 50–150 MPa. The maximum sintering temperature for spark plasma sintering is 1700–2100℃, with a heating rate of 50–150℃ / min and a maximum sintering pressure of 10–60 MPa. For hot pressing and spark plasma sintering, graphite paper must be added to the sidewalls of the graphite mold. The green blank is placed into the mold, and graphite paper is added to its top and bottom faces to prevent adhesion between the green blank and the graphite mold during sintering. After sintering and densification, silicon carbide-based coated particulate dispersion fuel is obtained.

[0071] In addition, this application also provides a coated particulate dispersion fuel, which is prepared by the above method.

[0072] Example 1

[0073] This embodiment describes the main process for preparing a coated particulate dispersion fuel. Atomic layer deposition (ALD) technology is used to laminate 4% Al₂O₃ and 4% Y₂O₃ onto the surfaces of two different SiC particle sizes, replacing traditional mechanical mixing. SiC pellets are then prepared by SPS sintering. The measured theoretical density of the SiC pellets is 96.26%, and the thermal conductivity reaches 67 W / (m·K) at 100 °C and remains at 30 W / (m·K) at 1000 °C. Compared to traditional mechanical mixing followed by sintering, both density and thermal conductivity are improved.

[0074] Example 2

[0075] This embodiment describes the atomic layer deposition (ALD) process for Al2O3 on SiC powder. Trimethylaluminum (TMA)-water (H2O) was selected as the precursor for the Al2O3 coating film. Through analysis of parameters such as deposition temperature and precursor pulse time, the optimal Al2O3 coating process was ultimately chosen for 60nm and 500nm SiC.

[0076] Deposition temperature 150℃, 15s (TMA)-240s (holding pressure)-120s (cleaning)-15s (H2O)-240s (holding pressure)-120s (cleaning), and 5s (TMA)-120s (holding pressure)-90s (cleaning)-5s (H2O)-120s (holding pressure)-90s (cleaning).

[0077] This embodiment achieved stable linear coating of Al2O3 films on SiC surfaces, with a coating rate of 0.09 nm / cycle. Figures 2 to 5 As shown, TEM and EDS characterization demonstrate the uniformity of Al2O3 deposition on the SiC surface.

[0078] Example 3

[0079] This embodiment describes the atomic layer deposition (ALD) process of Y₂O₃ on SiC powder. N,N-diisopropylacetamidinate (Yttrium tris(N,N'-diisopropylacetamidinate))-water (H₂O) was selected as the precursor for the Y₂O₃ coating film. Through analysis of parameters such as deposition temperature and precursor pulse time, the optimal Y₂O₃ coating process was ultimately chosen for 60nm and 500nm SiC.

[0080] 60s (Y precursor) - 900s (holding pressure) - 480s (cleaning) - 60s (O3) - 900s (holding pressure) - 480s (cleaning), and 30s (Y precursor) - 420s (holding pressure) - 240s (cleaning) - 30s (O3) - 420s (holding pressure) - 240s (cleaning).

[0081] This embodiment achieves stable linear coating of Y2O3 film on SiC surface, with coating rates of 0.016 nm / cycle and 0.019 nm / cycle.

[0082] In summary, this application describes a method for modifying the matrix material of particulate dispersed fuel using atomic layer deposition (ALD) technology. The matrix material is not limited to silicon carbide, a mixture of silicon carbide and silicon carbide whiskers, a mixture of silicon carbide and silicon carbide fibers, or other silicides. The coating material is not limited to one or more of Al₂O₃, Y₂O₃, SiO₂, CeO₂, ZrO₂, TiO₂, La₂O₃, Sc₂O₃, MgO, AlN, and TiN.

[0083] The above description is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application.

Claims

1. A method for preparing coated particulate dispersion fuel, characterized in that, include: Step 1: Start the powder atomic layer deposition apparatus and continuously introduce inert gas to remove gas from the reactor and pipelines; Step 2: Atomic layer deposition process is used to deposit a sintering aid coating on silicon carbide powder in a fluidized state, including precursor adsorption, chemical reaction, inert gas purging and repeated cycles until the coating composition and thickness meet the requirements. Step 3: Based on the design requirements of the sintering aid composition, repeat step 2 to deposit other types of sintering aids; Step 4: Form coated particulate fuel pellets; Step 5: Densification sintering of the pellets to obtain silicon carbide-based coated particulate dispersion fuel.

2. The method for preparing coated particulate dispersion fuel according to claim 1, characterized in that, Step 2 includes: Step 2.1: Place silicon carbide powder into a powder atomic layer deposition apparatus, introduce inert gas to make the powder reach a stable fluidized state, and start deposition after the temperature of the reactor and gas pipeline stabilizes; Step 2.2: The first gaseous precursor used to generate the sintering aid is introduced into the reaction chamber and undergoes a chemical adsorption reaction on the surface of the deposition substrate. After a certain deposition time, sufficient precursor molecules are provided to the surface of the powder substrate. Step 2.3: Add a pressure holding process during ALD deposition to increase the adsorption time of the precursor on the powder surface; Step 2.4: Inert gas is introduced into the reaction chamber to purge excess gaseous second precursor and byproducts for a certain period of time to ensure that all unreacted precursors are removed. Step 2.5: Introduce a second precursor for the reaction to generate the sintering aid, which reacts chemically with the first precursor on the substrate surface to generate a sintering aid coating. Deposit for a certain period of time to provide sufficient precursor molecules to the surface of the powder substrate. Step 2.6: Inert gas is introduced into the reaction chamber to purge excess gaseous second precursor and byproducts for a certain period of time to ensure that all unreacted precursors are removed. Step 2.7: Repeat steps 2.2 to 2.6 until the thickness of the deposited sintering aid reaches the required level.

3. The method for preparing coated particulate dispersion fuel according to claim 2, characterized in that, The sintering aid used for coating silicon carbide powder is one or more of Al2O3, Y2O3, SiO2, CeO2, ZrO2, TiO2, La2O3, Sc2O3, MgO, AlN, and TiN.

4. The method for preparing coated particulate dispersion fuel according to claim 2, characterized in that, The deposition time is 1–20 min, and the purging time is 1–20 min.

5. The method for preparing coated particulate dispersion fuel according to claim 2, characterized in that, The mass percentage of the coated silicon carbide powder sintering aid is 1% to 12%.

6. The method for preparing coated particulate dispersion fuel according to claim 1, characterized in that, Step 4 includes: Step 4.1: Add a small amount of anhydrous ethanol to the silicon carbide powder coated with the combustion aid and mix evenly. Then, put the mixture into a steel mold for the fuelless zone collar and cover plate and press it into shape to obtain the fuelless zone collar and cover plate of the pellet. Step 4.2: Add a small amount of anhydrous ethanol to TRISO particles and silicon carbide powder coated with combustion aid and mix evenly. Then, load the mixture into a steel mold for the fuel compartment and press it into shape to obtain the fuel block. Step 4.3: Insert the fuel pellet into the hollow fuelless zone ring, then place the two cover plates on the top and bottom of the ring respectively, and perform cold isostatic pressing under a certain pressure to obtain a coated particulate dispersed fuel green blank.

7. The method for preparing coated particulate dispersion fuel according to claim 6, characterized in that, The cold isostatic pressure is 180–240 MPa.

8. The method for preparing coated particulate dispersion fuel according to claim 1, characterized in that, In step 5, densification is carried out by pressureless sintering, hot pressing sintering or spark plasma sintering; The maximum sintering temperature for pressureless sintering is 1700–2100℃, and the holding time is 1–4 hours. The maximum sintering temperature for hot pressing is 1700–2100℃, the heating rate is 5–20℃ / min, and the maximum sintering pressure is 50–150MPa. The maximum sintering temperature of spark plasma sintering is 1700–2100℃, the heating rate is 50–150℃ / min, and the maximum sintering pressure is 10–60MPa.

9. The method for preparing coated particulate dispersion fuel according to claim 1, characterized in that, SiC cores were prepared by stacking 4% Al2O3 and 4% Y2O3 on the surface of two different particle sizes using atomic layer deposition technology, followed by SPS sintering.

10. A coated particulate dispersion fuel, characterized in that, Prepared using the method described in any one of claims 1 to 9.

Images