CN116564562B - High-uranium-density dispersion fuel containing ZrC coating layer and preparation method thereof - Google Patents

Abstract

The present invention relates to the technical field of dispersion fuel for pressurized water reactors, gas-cooled reactors and research and test reactors. In view of the problems of low uranium content of existing dispersion fuel pellets and poor ability of dispersion fuel containing TRISO particles to withstand extremely high temperatures, the present invention provides A high uranium density dispersion fuel containing a ZrC coating layer and a preparation method thereof are disclosed. The present invention reduces the thickness of the outer dense pyrolytic carbon layer to 0~30 μm and changes the SiC layer in the TRISO particles to a ZrC layer. Through the above combination The design improves the overall uranium loading and high-temperature resistance of TRISO particle dispersion fuel, which will help promote the application of TRISO particle dispersion fuel in special-purpose reactors with high burn-up consumption and high outlet temperature, and achieve efficient and safe operation of the fuel.

Description

A high uranium density dispersion fuel containing ZrC coating and its preparation method

Technical field

The invention relates to the technical field of dispersion fuel for pressurized water reactors, gas-cooled reactors and research and test reactors, and specifically relates to a high uranium density dispersion fuel containing a ZrC coating layer and a preparation method thereof.

Background technique

The current important direction for the development of nuclear power technology is to improve the safety and reliability of nuclear power systems and avoid repeating the mistakes of Japan's Fukushima nuclear power accident. Currently, a universal accident-resistant fuel structure proposed internationally is to disperse triisotropic TRISO particles in a SiC matrix material, using the four-layer coating of TRISO particles to provide accommodation space for fission gases, and using thermal conductivity SiC material with good thermal expansion coefficient, low neutron absorption cross-section and excellent compatibility with cladding and fuel is used as the base material to improve the safety characteristics of the fuel.

Although TRISO particles dispersed in the SiC matrix have high safety characteristics, they will lead to a significant reduction in the uranium content in the fuel, thus affecting the economic applicability of the entire dispersed fuel.

At present, the four-layer coating structure of TRISO particles is composed of a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a SiC layer and an outer dense pyrolytic carbon layer from the inside to the outside. The third SiC layer is the key to withstand internal and external pressure and ensure the integrity of the fuel core. However, in order to further improve the economy of the reactor, increasing the outlet temperature of the reactor is an important means. SiC will undergo item transformation at 1800°C, from face-centered cubic β-SiC to hexagonal α-SiC. At the same time, the amount of ¹³⁷ Cs released by irradiation is also very high. This will not be conducive to increasing the operating temperature of the reactor and will affect the further promotion of the in-depth application of TRISO particle dispersion fuel.

Contents of the invention

The purpose of this invention is to provide a high uranium density dispersion fuel containing a ZrC coating layer and a preparation method thereof, which solves the problem of low uranium content in the dispersion fuel pellets and increases the uranium content in the dispersion fuel by 7% to 30%. , and solves the problem of poor ability of dispersion fuel containing TRISO particles to withstand extremely high temperatures (≥1800°C).

In order to achieve the above objects, the present invention provides the following technical solutions:

A high uranium density dispersion fuel containing a ZrC coating layer, including coated fuel particles, a matrix and a fuel-free zone. The coated fuel particles include a fuel core and loose heat coated outside the fuel core in turn. Decomposed carbon layer, inner dense pyrolytic carbon layer, ZrC layer, outer dense pyrolytic carbon layer, the thickness of the ZrC layer is 17~45 μm, and the thickness of the outer dense pyrolytic carbon layer is 0~30 μm.

Further, the fuel core is a UCO core with a diameter of 500~800 μm.

Further, the thickness of the loose pyrolytic carbon layer is 50~120 μm, and the thickness of the inner dense pyrolytic carbon layer is 30~60 μm.

Further, the thickness of the loose pyrolytic carbon layer is 90.7 μm, the thickness of the inner dense pyrolytic carbon layer is 38.6 μm, the thickness of the ZrC layer is 17.6 μm, and the thickness of the outer dense pyrolytic carbon layer is is 20.9μm.

Further, the fuel core is a UN core with a diameter of 500~800 μm.

Further, the thickness of the loose pyrolytic carbon layer is 50~120 μm, the thickness of the inner dense pyrolytic carbon layer is 30~60 μm, and the thickness of the outer dense pyrolytic carbon layer is 0 μm.

Further, the thickness of the loose pyrolytic carbon layer is 52.2 μm, the thickness of the inner dense pyrolytic carbon layer is 36 μm, and the thickness of the ZrC layer is 44.7 μm.

Further, the matrix is a SiC matrix.

Further, after the inner dense pyrolysis carbon layer is prepared in the fluidized bed, hydrogen and ZrCl ₄ powder are introduced, the hydrogen gas introduction flow rate is 70~380L/min, and the ZrCl ₄ powder introduction speed is 70~190g/ min, after the input of hydrogen and ZrCl ₄ powder is stable, propylene is introduced to react with ZrCl ₄ powder. The propylene flow rate is 3~10L/min, the reaction time is 30~80min, and the ZrC layer is obtained after the reaction.

Further, after the ZrC layer is prepared, acetylene and propylene are introduced to react to obtain an outer dense pyrolysis carbon layer, and the particles are cooled to room temperature in a fluidized state and then discharged to obtain coated fuel particles; or after the ZrC layer is prepared, The particles are directly cooled to room temperature in a fluidized state and then discharged to obtain coated fuel particles.

Compared with the existing technology, the high uranium density dispersion fuel containing ZrC coating provided by the present invention and its preparation method have the following beneficial effects:

The present invention reduces the thickness of the outermost dense pyrolysis carbon layer of TRISO particles from 40 μm to 0~30 μm, which can reduce the diameter of TRISO particles and increase the uranium loading capacity of dispersion fuel under the same filling volume.

Taking the 500μm _UO2 core as an example, the thickness of the loose pyrolytic carbon is 95μm, the thickness of the inner dense pyrolytic carbon is 40μm, the thickness of SiC is 35μm, and the thickness of the outer dense pyrolytic carbon is 40μm and 0μm. Both TRISO particles are packed in pellets of Ф8.43mm×10.92mm. When the filling volume of TRISO particles is 40%, the fuel pellet with an outer dense pyrolysis carbon layer thickness of 0 μm has a higher uranium content than the outer one. The uranium content of fuel pellets with a dense pyrolysis carbon layer thickness of 40 μm has increased by 30%.

This invention changes the SiC layer in the TRISO particles to a ZrC layer, which can increase the operating temperature and outlet temperature of the reactor. The ZrC layer does not undergo phase change below 3540°C (the melting point of the ZrC layer), and can better protect the integrity of the TRISO particles. properties; at the same time, the ZrC layer hardly reacts with palladium and has good fission product containment capacity.

Description of the drawings

In order to more clearly explain the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments will be briefly introduced below.

Figure 1 is a schematic diagram of coated fuel particles provided by Embodiment 1 of the present invention;

Figure 2 is a schematic diagram of the dispersion fuel provided in Embodiment 1 of the present invention.

Explanation of reference symbols:

1. Fuel core; 2. Loose pyrolytic carbon layer; 3. Inner dense pyrolytic carbon layer; 4. ZrC layer; 5. Outer dense pyrolytic carbon layer; 6. TRISO particles; 7. SiC matrix; 8. None fuel area.

Detailed ways

The following is further described in detail through specific implementations.

The invention provides a high uranium density dispersion fuel containing a ZrC coating layer, which increases the uranium loading in the dispersion fuel and improves the high temperature resistance of the dispersion fuel.

By replacing the third SiC layer in TRISO particles with a ZrC layer, the present invention gives full play to the excellent anti-oxidation and high-temperature resistance of the ZrC material and further improves the high-temperature resistance of TRISO particle dispersion fuel at higher operating temperatures (above 1800°C). performance to promote the application of TRISO particle dispersion fuel in more harsh environments.

The main function of the outermost dense pyrolytic carbon layer of TRISO particles (coated fuel particles) is to protect the third layer and provide support for it. This design is mainly due to the fact that the initial application of TRISO particles was on a graphite matrix. Pyrolytic carbon and graphite are homologous materials, so the outermost outer dense pyrolytic carbon layer can have good compatibility with the graphite matrix. After the present invention uses the ZrC layer to replace the SiC layer, considering that the thermal expansion coefficient of the outermost pyrolytic carbon layer is significantly different from that of the ZrC layer, the present invention proposes two solutions. One is to thin the outer dense layer of the outermost layer. The thickness of the pyrolysis carbon layer is 0 μm < the thickness of the outer dense pyrolysis carbon layer ≤ 30 μm, which can effectively increase the uranium loading in the dispersion fuel. The 30 μm thick outermost dense pyrolytic carbon layer is the standard thickness dimension for TRISO particles to wear. In the present invention, the 30 μm thick outermost dense pyrolytic carbon layer can be used as a spacer layer between TRISO particles to prevent During the filling and molding process, TRISO particles squeeze each other and cause deformation. The second is to remove the outermost outer dense pyrolytic carbon layer, which means that the thickness of the outer dense pyrolytic carbon layer is 0 μm. This can not only increase the uranium content in the dispersion fuel, but also improve the thermal conductivity between TRISO particles and the SiC matrix. Performance compatibility. Therefore, the thickness of the outer dense pyrolysis carbon layer of the outermost layer of the high uranium density dispersion fuel containing the ZrC coating provided by the present invention is 0~30 μm, that is, 0 μm ≤ the thickness of the outer dense pyrolysis carbon layer ≤ 30 μm.

Therefore, the present invention reduces the thickness of the outer dense pyrolytic carbon layer and changes the SiC layer in the TRISO particles to a ZrC layer. Through the above combination design, the overall uranium loading and high temperature resistance of the TRISO particle dispersion fuel can be improved, which will be beneficial to promotion. TRISO particle dispersion fuel is used in special-purpose reactors with high burn-up consumption and high outlet temperature to achieve efficient and safe fuel operation and promote wider applications.

In the present invention, the thickness of the loose pyrolytic carbon layer is 50~120 μm, the thickness of the inner dense pyrolytic carbon layer is 30~60 μm, and the thickness of the ZrC layer is 17~45 μm.

Example 1

A high uranium density dispersion fuel containing a ZrC coating. The coated fuel particles are shown in Figure 1. From the inside to the outside, the fuel core 1, the loose pyrolytic carbon layer 2, and the inner dense pyrolytic carbon are Layer 3, ZrC layer 4 and outer dense pyrolytic carbon layer 5.

The material composition of the fuel core 1 is UCO, and the diameter of the fuel core 1 is 500 μm. The thickness of the loose pyrolytic carbon layer 2 is 90.7 μm, the thickness of the inner dense pyrolytic carbon layer 3 is 38.6 μm, the thickness of the ZrC layer 4 is 17.6 μm, and the thickness of the outer dense pyrolytic carbon layer 5 is 20.9 μm. The coated fuel particles are dispersed in the SiC matrix, and the size of the overall pellet is Ф8.566mm×12.979mm. As shown in Figure 2, the components of the dispersion fuel are TRISO particles 6, SiC matrix 7 and fuel-free area 8.

A method for preparing high uranium density dispersion fuel containing ZrC coating, including the following steps:

Step 1: UCO core preparation. The UCO core is prepared through external gel and carbothermal reduction processes. The process flow is as follows: first, slowly add 5000g U ₃ O ₈ powder into a mixed solution of 2200 mL concentrated nitric acid and 4100 mL deionized water to obtain uranyl nitrate solution (HMTA). ; In addition, mix 2.3~2.5g hexamethylenetetramine and 1g urea to prepare a mixed solution of hexamethylenetetramine and urea; add the HMTA/urea mixed solution and 640g carbon powder to the prepared ADUN solution to form a glue solution . The mixed glue liquid after standing is dispersed through the dispersing head, where the glue flow rate is 12mL/min, and the vibration frequency is 100-120Hz to form UO ₃ /C gel balls, which are then aged, washed and dried, and finally in CO The UCO core was prepared by roasting at 1700°C in the atmosphere.

Step 2: TRISO particle preparation. Put 3000g of UCO core into the fluidized bed, heat the fluidized bed to 1150°C, introduce argon (flow rate: 67L/min) and acetylene (flow rate: 175L/min), reaction time is 2min, and obtain loosening heat Decompose carbon; pass in acetylene (flow rate: 60L/min) and propylene (60L/min), react for 10 minutes to obtain internally dense pyrolysis carbon; pass in hydrogen (flow rate: 72L/min), ZrCl ₄ powder (70g/min ) and propylene (flow rate is 3L/min), the reaction time is 30 minutes, and the ZrC layer is obtained; acetylene (flow rate is 30L/min) and propylene (30L/min), the reaction time is 5 minutes, and the outer dense pyrolysis carbon layer is obtained. After the coating is completed, the TRISO particles are cooled in the furnace in a fluidized state, cooled to room temperature, and then discharged from the bottom to obtain TRISO particles.

Step 3: Preparation of fuel pellets. The particles containing the ZrC coating layer are evenly mixed with SiC powder and 3 to 7% sintering aid powder (Al ₂ O ₃ and Y ₂ O ₃ ). The volume proportion of the ZrC coating layer particles is 41%. Use a one-way press with a steel mold to make a green body from the composite powder filled into the steel mold at 1~1.5KN. The prepared green body is packaged into a graphite mold. After the packaging is completed, the graphite mold is placed in a hot-pressing sintering furnace. The temperature of the hot-pressing sintering furnace is controlled at 1650-1750°C, and sintering is performed under a protective atmosphere or vacuum; or The graphite mold is placed in a discharge plasma sintering furnace. The temperature of the discharge plasma sintering furnace is controlled at 1750~1850°C, and sintering is performed in a protective atmosphere or vacuum. After sintering, the graphite mold is taken out and the dispersed fuel is taken out by demolding or disintegrating. Finally, the high uranium density dispersed fuel containing the ZrC coating is obtained by grinding the outer surface.

Example 2

A high uranium density dispersion fuel containing a ZrC coating layer, consisting of a fuel core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a ZrC layer and an outer dense pyrolytic carbon layer from the inside to the outside.

The material composition of the fuel core is UCO, and the diameter of the fuel core is 650 μm. The thickness of the loose pyrolytic carbon layer is 111.3 μm, the thickness of the inner dense pyrolytic carbon layer is 41.4 μm, the thickness of the ZrC layer is 27.8 μm, and the thickness of the outer dense pyrolytic carbon layer is 29.5 μm. The coated fuel particles are dispersed in the SiC matrix, and the size of the overall pellet is Ф8.566mm×12.979mm. The components of the dispersion fuel are TRISO particles, SiC matrix and fuel-free zone.

A method for preparing high uranium density dispersion fuel containing ZrC coating, including the following steps:

Step 1: UCO core preparation. The UCO core is prepared through external gel and carbothermal reduction processes. The process flow is as follows: first, slowly add 5000g U ₃ O ₈ powder into a mixed solution of 2200 mL concentrated nitric acid and 4100 mL deionized water to obtain uranyl nitrate solution (HMTA). ; In addition, mix 2.3~2.5g hexamethylenetetramine and 1g urea to prepare a mixed solution of hexamethylenetetramine and urea; add the HMTA/urea mixed solution and 640g carbon powder to the prepared ADUN solution to form a glue solution . The mixed glue liquid after standing is dispersed through the dispersing head, where the glue flow rate is 12mL/min, and the vibration frequency is 100-120Hz to form UO ₃ /C gel balls, which are then aged, washed and dried, and finally in CO The UCO core was prepared by roasting at 1700°C in the atmosphere.

Step 2: TRISO particle preparation. Put 3000g UCO core into the fluidized bed, heat the fluidized bed to 1150°C, introduce argon (flow rate: 60L/min) and acetylene (flow rate: 171L/min), reaction time is 2min, and obtain loosening heat Decompose carbon; pass in acetylene (flow rate: 84L/min) and propylene (88L/min), react for 10 minutes to obtain internally dense pyrolysis carbon; pass in hydrogen (flow rate: 216L/min), ZrCl ₄ powder (123g/min ) and propylene (flow rate is 5L/min), the reaction time is 40 minutes, and the ZrC layer is obtained; acetylene (flow rate is 75L/min) and propylene (96L/min), the reaction time is 7 minutes, and the outer dense pyrolysis carbon layer is obtained. After the coating is completed, the TRISO particles are cooled in the furnace in a fluidized state, cooled to room temperature, and then discharged from the bottom to obtain TRISO particles.

Step 3: Preparation of fuel pellets. The particles containing the ZrC coating layer are evenly mixed with SiC powder and 3 to 7% sintering aid powder (Al ₂ O ₃ and Y ₂ O ₃ ). The volume proportion of the ZrC coating layer particles is 41%. Use a one-way press with a steel mold to make a green body from the composite powder filled into the steel mold at 1~1.5KN. The prepared green body is packaged into a graphite mold. After the packaging is completed, the graphite mold is placed in a hot-pressing sintering furnace. The temperature of the hot-pressing sintering furnace is controlled at 1650-1750°C, and sintering is performed under a protective atmosphere or vacuum; or The graphite mold is placed in a discharge plasma sintering furnace. The temperature of the discharge plasma sintering furnace is controlled at 1750~1850°C, and sintering is performed in a protective atmosphere or vacuum. After sintering, the graphite mold is taken out and the dispersed fuel is taken out by demolding or disintegrating. Finally, the high uranium density dispersed fuel containing the ZrC coating is obtained by grinding the outer surface.

Example 3

A high uranium density dispersion fuel containing a ZrC coating layer, which consists of a fuel core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer and a ZrC layer from the inside to the outside. Example 3 does not cover the outer dense pyrolytic carbon layer with the ZrC layer.

The material composition of the fuel core is UN, and the diameter of the fuel core is 800 μm. The thickness of the loose pyrolytic carbon layer is 52.2 μm, the thickness of the inner dense pyrolytic carbon layer is 36 μm, and the thickness of the ZrC layer is 44.7 μm. The coated fuel particles are dispersed in the SiC matrix, and the size of the overall pellet is Ф21.6mm×22.2mm. The components of the dispersion fuel are TRISO particles, SiC matrix and fuel-free zone.

A method for preparing high uranium density dispersion fuel containing ZrC coating, including the following steps:

Step 1: UN core preparation. The UN core is prepared through external gelling, carbothermal reduction and nitriding processes. The process flow is as follows: first, slowly add 5000g U ₃ O ₈ powder into a mixed solution of 2200 mL concentrated nitric acid and 4100 mL deionized water to obtain a uranyl nitrate solution. (HMTA); in addition, mix 2.3~2.5g hexamethylenetetramine and 1g urea to form a mixed solution of hexamethylenetetramine and urea; add the HMTA/urea mixed solution and 530g carbon powder to the prepared ADUN solution Glue liquid. The mixed glue liquid after standing is dispersed through the dispersing head, where the glue flow rate is 12mL/min, and the vibration frequency is 100-120Hz to form UO ₃ /C gel balls, which are then aged, washed and dried, and finally in N The UN core was prepared by roasting at 1900°C in ₂ atmosphere.

Step 2: TRISO particle preparation. Put 3000g UN core into the fluidized bed, heat the fluidized bed to 1150°C, introduce argon (flow rate 20L/min) and acetylene (60L/min), reaction time is 2min, and obtain loose pyrolysis carbon ; Pour in acetylene (flow rate 35L/min) and propylene (35L/min), reaction time 7min, obtain internal dense pyrolysis carbon; Pour in hydrogen (flow rate 380L/min), ZrCl ₄ powder (185g/min) and Propylene (flow rate is 10L/min), reaction time is 75min, and ZrC layer is obtained. After the coating is completed, the TRISO particles are cooled in the furnace in a fluidized state, cooled to room temperature, and then discharged from the bottom to obtain TRISO particles.

Step 3: Preparation of fuel pellets. The particles containing the ZrC coating layer are evenly mixed with SiC powder and 3 to 7% sintering aid powder (Al ₂ O ₃ and Y ₂ O ₃ ). The volume proportion of the ZrC coating layer particles is 41%. Use a one-way press with a steel mold to make a green body from the composite powder filled into the steel mold at 1~1.5KN. The prepared green body is packaged into a graphite mold. After the packaging is completed, the graphite mold is placed in a hot-pressing sintering furnace. The temperature of the hot-pressing sintering furnace is controlled at 1650-1750°C, and sintering is performed under a protective atmosphere or vacuum; or The graphite mold is placed in a discharge plasma sintering furnace. The temperature of the discharge plasma sintering furnace is controlled at 1750~1850°C, and sintering is performed in a protective atmosphere or vacuum. After sintering, the graphite mold is taken out and the dispersed fuel is taken out by demolding or disintegrating. Finally, the high uranium density dispersed fuel containing the ZrC coating is obtained by grinding the outer surface.

The preparation method provided by the invention realizes the preparation of high uranium density dispersion fuel pellets containing ultra-high temperature coating layer ZrC layer. The purpose of preparing pellets is achieved through several key processes such as core preparation, TRISO particle preparation with ultra-high temperature coating, green body preparation, and pellet sintering. The prepared pellets can meet the technical requirements for reactor pellets in terms of density, size, thermophysical properties, mechanical properties and other external performance tests. The prepared pellets are mainly used in fuel reactors corresponding to the technical conditions to meet the requirements of nuclear fuel elements. Use standards.

The present invention can improve the problem of low uranium content in current dispersion fuel and improve the overall economic characteristics of the fuel. The invention improves the high temperature resistance of the dispersion fuel, extends the fuel refueling cycle, accelerates the commercial application of the fuel, and can promote the use of fuel in ultra-high temperatures. Applications in gas-cooled reactors, gas-cooled micro-reactors and nuclear thermal rocket engines.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention. should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (8)

1. The high uranium density dispersion fuel comprises coated fuel particles, a SiC matrix and a fuel-free region, and is characterized in that the coated fuel particles comprise a fuel core, a loose pyrolytic carbon layer, an inner dense pyrolytic carbon layer, a ZrC layer and an outer dense pyrolytic carbon layer which are sequentially coated outside the fuel core, the thickness of the ZrC layer is 17-45 mu m, and the thickness of the outer dense pyrolytic carbon layer is 0 mu m, so that uranium loading in the dispersion fuel is improved, and compatibility of the coated fuel particles and heat conducting performance of the SiC matrix is improved.

2. The high uranium density dispersion fuel containing a ZrC cladding according to claim 1, wherein the fuel core is a UCO core having a diameter of 500-800 μm.

3. The high uranium density dispersion fuel containing a ZrC cladding according to claim 2, wherein the loose pyrolytic carbon layer has a thickness of 50 to 120 μm and the inner dense pyrolytic carbon layer has a thickness of 30 to 60 μm.

4. The high uranium density dispersion fuel containing a ZrC cladding according to claim 1, wherein the fuel core is a UN core having a diameter of 500 to 800 μm.

5. The high uranium density dispersion fuel containing a ZrC cladding of claim 4, wherein the loose pyrolytic carbon layer is 50 to 120 μm thick, the inner dense pyrolytic carbon layer is 30 to 60 μm thick, and the outer dense pyrolytic carbon layer is 0 μm thick.

6. The high uranium density dispersion fuel containing a ZrC cladding of claim 5, wherein the loose pyrolytic carbon layer has a thickness of 52.2 μm, the inner dense pyrolytic carbon layer has a thickness of 36 μm, and the ZrC layer has a thickness of 44.7 μm.

7. A process for preparing a high uranium density dispersion fuel containing a ZrC cladding layer as claimed in any one of claims 1 to 6, characterized in that after preparing an inner dense pyrolytic carbon layer in a fluidized bed, hydrogen and ZrCl are introduced ₄ Powder, wherein the flow rate of hydrogen is 70-380L/min, zrCl ₄ The powder is introduced at a speed of 70-190 g/min until hydrogen and ZrCl are introduced ₄ After the powder is input stably, propylene and ZrCl are introduced ₄ The powder is reacted, the propylene flow is 3-10L/min, the reaction time is 30-80 min, and the ZrC layer is obtained after the reaction.

8. The method for preparing a high uranium density dispersion fuel containing a ZrC coating according to claim 7, wherein after the ZrC coating is prepared, the ZrC coating is directly cooled to room temperature in a fluidized state and then discharged to obtain coated fuel particles.