阅读说明：本技术 一种新型多孔陶瓷复合燃料芯块及其制备方法 (Novel porous ceramic composite fuel pellet and preparation method thereof ) 是由 张青 崔雪峰 栗尼娜 刘持栋 成来飞 李建鑫 刘豪 于 2021-08-17 设计创作，主要内容包括：本发明公开了一种新型多孔陶瓷复合燃料芯块及其制备方法,涉及核电技术领域。该燃料芯块包括多孔陶瓷及均匀分散于所述多孔陶瓷内的包覆燃料颗粒；所述包覆燃料颗粒占比为10～30wt％。本发明通过将燃料颗粒包覆到碳和碳化硅陶瓷复合结构中,并形成具有连续换热通道的多孔结构,可获得更加均匀的热场和更为优异的换热效率,结构可设计性强,制造工艺路线简单、成本低廉,同时有望使高温气冷堆堆芯结构得到简化,并可大幅降低系统体积和结构重量。(The invention discloses a novel porous ceramic composite fuel pellet and a preparation method thereof, and relates to the technical field of nuclear power. The fuel pellet comprises porous ceramics and coating fuel particles uniformly dispersed in the porous ceramics; the proportion of the coated fuel particles is 10-30 wt%. According to the invention, the fuel particles are coated in the carbon and silicon carbide ceramic composite structure to form the porous structure with the continuous heat exchange channel, so that a more uniform thermal field and more excellent heat exchange efficiency can be obtained, the structure designability is strong, the manufacturing process route is simple, the cost is low, meanwhile, the reactor core structure of the high-temperature gas cooled reactor is expected to be simplified, and the system volume and the structure weight can be greatly reduced.)

1. A novel porous ceramic composite fuel pellet is characterized by comprising porous ceramic and coating fuel particles uniformly dispersed in the porous ceramic; the proportion of the coated fuel particles is 10-30 wt%.

2. A novel porous ceramic composite fuel pellet as claimed in claim 1 wherein the porous ceramic is a silicon carbide porous ceramic.

3. The novel porous ceramic composite fuel pellet as claimed in claim 2, wherein the porosity of the porous ceramic is 70 to 90% and the pore diameter is 0.5 to 3 mm.

4. The novel porous ceramic composite fuel pellet of claim 1, wherein the coated fuel particles are tri-structure co-oriented (TRISO) particles or bi-structure co-oriented (BISO) coated fuel particles.

5. A preparation method of the novel porous ceramic composite fuel pellet as claimed in any one of claims 1 to 4, characterized by comprising the following steps:

uniformly dispersing ceramic powder, coated fuel particles, resin and a pore-forming agent in an organic solvent to obtain resin slurry; drying the obtained resin slurry, and sequentially carrying out curing, carbonization and graphitization treatment to obtain a porous graphite preform containing coated fuel particles;

and carrying out ceramic treatment on the obtained porous graphite preform containing the coated fuel particles by adopting a vapor deposition method to obtain the novel porous ceramic composite fuel pellet.

6. The method for preparing a novel porous ceramic composite fuel pellet as claimed in claim 5, wherein the ceramizing of the porous graphite preform containing the coated fuel particles is performed according to the following steps:

placing the porous graphite preform containing the coated fuel particles in a chemical vapor furnace, taking trichloromethylsilane (MTS) as a precursor, hydrogen as a carrier gas and a diluent gas, taking inert gas as a protective gas, wherein the deposition temperature is 900-1200 ℃, the total pressure of the deposition furnace is 0.5-5 kPa, and the deposition time is 20-200 h.

7. The preparation method of the novel porous ceramic composite fuel pellet as claimed in claim 6, wherein the volume ratio of trichloromethylsilane, hydrogen and inert gas is 1: 5-15: 10-20.

8. The preparation method of the novel porous ceramic composite fuel pellet as claimed in claim 5, wherein the curing is to treat the dried resin slurry in an air environment at 150-180 ℃ for 2-5 hours to fully cure the resin slurry; and in the carbonization step, the solidified resin slurry is heated to 600-900 ℃ at the heating rate of 0.5-5 ℃/min and is kept for 1-5 h under the protection of nitrogen or inert gas, so that the resin is completely carbonized and cracked, and the porous carbon preform containing the coated fuel particles is prepared.

9. The preparation method of the novel porous ceramic composite fuel pellet as claimed in claim 8, wherein the graphitization treatment is to preserve the porous carbon preform at 2000-2300 ℃ for 1-5 h.

10. The method for preparing the novel porous ceramic composite fuel pellet as claimed in claim 5, wherein the organic solvent is one or more of ethanol, butanone, toluene and isopropanol;

the resin is phenolic resin or epoxy resin; the pore-forming agent is polymethyl methacrylate;

the ceramic powder, the coated fuel particles, the resin, the organic solvent and the pore-forming agent are calculated according to the following mass percentages, wherein the ceramic powder is 5-30%, the coated fuel particles are 10-50%, the resin is 10-50%, the organic solvent is 10-40% and the pore-forming agent is 1-30%.

Technical Field

The invention relates to the technical field of nuclear power, in particular to a novel porous ceramic composite fuel pellet and a preparation method thereof.

Background

The high-temperature gas cooled reactor is a reactor type recognized by the international nuclear energy field and has good safety characteristics, the power generation efficiency of the high-temperature gas cooled reactor is about 25% higher than that of a pressurized water reactor nuclear power plant, the high-temperature gas cooled reactor has passive safety characteristics, so that the system is very simple, the inert gas is used as a coolant, the traditional risks of reactor core melting and the like cannot occur under the most serious accident condition, and the high-temperature gas cooled reactor is listed as one of six candidate reactor types of the future fourth generation nuclear energy system technology. At present, spherical fuel elements and cylindrical fuel elements are widely used as fuel elements in high-temperature gas cooled reactors. The spherical fuel element is prepared by making uranium fuel into small particles, coating a layer of low-density carbon, two layers of high-density carbon and a layer of silicon carbide outside each particle to form coated fuel particles, and then uniformly dispersing the coated fuel particles in a graphite slowing material to prepare the spherical fuel element with the diameter of 6 cm. The cylindrical fuel element is prepared by preparing the coating fuel particles, graphite powder and other auxiliary materials into annular pellets, loading the annular pellets into a graphite sleeve, sealing the graphite sleeve into a fuel rod by using a graphite end plug, and then inserting the fuel rod into a fuel pore in a hexagonal graphite upright post, or directly loading the coating fuel particles and the graphite particles into the fuel rod and then inserting the coating fuel particles and the graphite particles into the fuel pore. Above reactor core structure all has the fuel release heat to obtain the problem fast, effectively shift, has hindered the further promotion of generating efficiency, has restricted the development of high temperature gas cooled reactor, and in addition, traditional rod-like structure nuclear fuel reactor core need use full ceramic fuel rod to load the fuel granule, and granule dispersion is uneven in the fuel rod, easily leads to whole reactor core inside thermal field inhomogeneous, and inert gas can only circulate outside the fuel rod, and heat exchange efficiency is low.

Disclosure of Invention

The invention aims to solve the defects in the background technology, and provides a novel porous ceramic composite fuel pellet and a preparation method thereof. According to the method, the coating fuel particles are compounded into the porous ceramic by adopting a resin foaming combined chemical vapor deposition method, and the inert cooling gas can directly carry out heat transfer through the porous channel by forming the porous structure with the continuous channel, so that the heat loss of a fuel pipeline is reduced, the heat conduction efficiency of the fuel pellet can be greatly improved, and the efficiency of a high-temperature gas cooled reactor is improved.

The invention provides a novel porous ceramic composite fuel pellet, which comprises porous ceramic and coating fuel particles uniformly dispersed in the porous ceramic; the proportion of the coated fuel particles is 10-30 wt%.

Preferably, the porous ceramic is a silicon carbide porous ceramic.

More preferably, the porosity of the porous ceramic is 70-90%, and the pore diameter is 0.5-3 mm.

Preferably, the coated fuel particles are tri-structure homodromous (TRISO) particles or bi-structure homodromous (BISO) coated fuel particles.

The second purpose of the invention is to provide a preparation method of the novel porous ceramic composite fuel pellet, which comprises the following steps:

uniformly dispersing ceramic powder, coated fuel particles, resin and a pore-forming agent in an organic solvent to obtain resin slurry; drying the obtained resin slurry, and sequentially carrying out curing, carbonization and graphitization treatment to obtain a porous graphite preform containing coated fuel particles;

and carrying out ceramic treatment on the obtained porous graphite preform containing the coated fuel particles by adopting a vapor deposition method to obtain the novel porous ceramic composite fuel pellet.

Preferably, the ceramization treatment of the porous graphite preform containing the coated fuel particles is performed according to the following steps:

placing the porous graphite preform containing the coated fuel particles in a chemical vapor furnace, taking trichloromethylsilane (MTS) as a precursor, hydrogen as a carrier gas and a diluent gas, taking inert gas as a protective gas, wherein the deposition temperature is 900-1200 ℃, the total pressure of the deposition furnace is 0.5-5 kPa, and the deposition time is 20-200 h.

More preferably, the volume ratio of the trichloromethylsilane to the hydrogen to the inert gas is 1: 5-15: 10-20.

Preferably, the curing is to treat the dried resin slurry for 2-5 hours in an air environment at 150-180 ℃ so as to fully cure the resin slurry; and in the carbonization step, the solidified resin slurry is heated to 600-900 ℃ at the heating rate of 0.5-5 ℃/min and is kept for 1-5 h under the protection of nitrogen or inert gas, so that the resin is completely carbonized and cracked, and the porous carbon preform containing the coated fuel particles is prepared.

More preferably, the graphitization treatment is to preserve the porous carbon preform at 2000-2300 ℃ for 1-5 h.

Preferably, the organic solvent is one or more of ethanol, butanone, toluene and isopropanol;

the resin is phenolic resin or epoxy resin; the pore-forming agent is polymethyl methacrylate;

the ceramic powder, the coated fuel particles, the resin, the organic solvent and the pore-forming agent are calculated according to the following weight percentage: 5-30% of ceramic powder, 10-50% of coated fuel particles, 10-50% of resin, 10-40% of organic solvent and 1-30% of pore-forming agent.

Compared with the prior art, the invention has the beneficial effects that:

the invention provides a novel porous ceramic composite fuel pellet and a preparation method thereof, the fuel pellet is formed by coating fuel particles in a carbon and silicon carbide ceramic composite structure and forming a porous structure with continuous heat exchange channels, so that a more uniform thermal field and more excellent heat exchange efficiency can be obtained, the structure designability is strong, the manufacturing process route is simple, the cost is low, and meanwhile, the reactor core structure of a high-temperature gas cooled reactor is expected to be simplified, and the system volume and the structure weight can be greatly reduced. The method adopts a resin foaming combined chemical vapor deposition method to compound the coating fuel particles into the porous ceramic, specifically, the silicon carbide ceramic is deposited into the porous graphite by the chemical vapor deposition method to form a graphite and silicon carbide composite material, and the inert cooling gas can directly carry out heat transfer through the porous channel by forming a porous structure with continuous channels, so that the heat loss of a fuel pipeline is reduced, the heat conduction efficiency of the fuel pellet can be greatly improved, and the efficiency of the high-temperature gas cooled reactor is improved.

According to the preparation method of the porous ceramic composite fuel pellet, the coating fuel particles are innovatively compounded into the porous carbon preform by adopting a resin foaming method, and the porous carbon structure is vitrified by combining a chemical vapor deposition method, so that the ceramic composite fuel pellet is finally obtained, and no sintering aid is required to be added in the whole process.

The ceramic composite fuel pellet prepared by the invention does not relate to a fuel rod and a support structure thereof, so that the internal structure of a reactor core can be greatly simplified, and the weight can be remarkably reduced; and a uniform thermal field can be formed by the design of the porous structure, and meanwhile, a heat exchange channel is provided, so that the heat exchange efficiency is greatly improved.

Compared with the traditional nuclear fuel pellet, the porous ceramic composite nuclear fuel pellet has more excellent heat conduction efficiency, excellent designability in the aspects of porosity, loading capacity and the like, simple manufacturing process route and low cost.

Drawings

Fig. 1 is a schematic structural diagram of the novel porous ceramic composite fuel pellet provided by the invention.

Detailed Description

In order to make the technical solutions of the present invention better understood and implemented by those skilled in the art, the present invention is further described below with reference to the following specific embodiments and the accompanying drawings, but the embodiments are not meant to limit the present invention.

It should be noted that the experimental methods in the following examples are all conventional methods unless otherwise specified; the reagents and materials used are commercially available, unless otherwise specified.

The grain size of the high-purity silicon carbide ceramic powder selected in the following embodiment is 0.005-10 mu m, and the purity is more than 90%; the diameter of the crystal whisker is 1-5 mu m, the length-diameter ratio is 5-15, and the purity is more than 90%.

The coated fuel particles selected for use in the following examples are tri-structure homodromous (TRISO) particles, having a diameter of 1mm or less, available from BWXT, USA.

The resin used in the following examples is phenolic resin or epoxy resin;

the pore former used in the following examples was polymethyl methacrylate.

Example 1

A novel porous ceramic composite fuel pellet is shown in figure 1, and comprises porous ceramic and coated fuel particles uniformly dispersed in the porous ceramic; the coated fuel particles were present in a proportion of 10 wt%.

The porous ceramic is silicon carbide porous ceramic;

the porosity of the porous ceramic is 70%, and the pore diameter is 0.5 mm;

the coated fuel particles are tri-structure homodromous (TRISO) particles.

The novel porous ceramic composite fuel pellet is prepared by the following steps:

(1) TRISO particles, high-purity silicon carbide powder (the particle diameter d50 is 0.05 mu m, the purity is 99%), phenolic resin, ethanol and polymethyl methacrylate, and the mass ratio of the components is 30 wt%: 10 wt%: 30 wt%: 15 wt%: mixing 15 wt% of the raw materials, and stirring the mixture in a stirring tank for 1 hour;

(2) pouring the uniformly mixed resin slurry into a mold, placing the mold in an air environment at 60 ℃ for curing for 2h, then placing the mold in a high-temperature furnace, taking nitrogen as protective atmosphere, raising the temperature to 700 ℃ at a heating rate of 0.5 ℃/min, keeping the temperature for 2h to completely carbonize the resin, and then continuing to raise the temperature to 2200 ℃ and keep the temperature for 1h to obtain a porous graphite preform containing fuel particles;

(3) placing a porous graphite preform containing fuel particles in a chemical vapor furnace for ceramic formation, wherein trichloromethylsilane (MTS) is used as a precursor, hydrogen is used as a carrier gas anddiluent gas, argon as protective gas, MTS: H₂The ratio of Ar to Ar is 1:12:10, the deposition temperature is 1000 ℃, the total air pressure of a deposition furnace is 0.6kPa, and the deposition time is 60 hours. Finally obtaining the porous ceramic composite nuclear fuel pellet.

Example 2

A novel porous ceramic composite fuel pellet is shown in figure 1, and comprises porous ceramic and coated fuel particles uniformly dispersed in the porous ceramic; the coated fuel particles accounted for 30 wt%.

The porous ceramic is silicon carbide porous ceramic.

The porosity of the porous ceramic is 90%, and the pore diameter is 3 mm;

the coated fuel particles are tri-structure homodromous (TRISO) particles.

The novel porous ceramic composite fuel pellet is prepared by the following steps:

(1) the preparation method comprises the following steps of (1) mixing TRISO particles, silicon carbide whiskers (the diameter is 1 mu m, the length-diameter ratio is 10-15, and the purity is 99%), epoxy resin, ethanol and polymethyl methacrylate in a mass ratio of 30 wt%: 15 wt%: 25 wt%: 13 wt%: after 17 wt% of the mixture is mixed, putting the mixture into a stirring tank and stirring the mixture for 1 hour;

(2) pouring the uniformly mixed resin slurry into a mold, placing the mold in an air environment at 60 ℃ for curing for 1.5h, then placing the mold in a high-temperature furnace, taking nitrogen as protective atmosphere, raising the temperature to 800 ℃ at a heating rate of 2 ℃/min, preserving the heat for 2h to completely carbonize the resin, and then continuing to raise the temperature to 2300 ℃ and preserve the heat for 0.5h to obtain a porous graphite preform containing fuel particles;

(3) placing a porous graphite preform containing fuel particles in a chemical vapor furnace for ceramic formation, wherein trichloromethylsilane (MTS) is used as a precursor, hydrogen is used as a carrier gas and a diluent gas, argon is used as a protective gas, and MTS: H₂The ratio of Ar to Ar is 1:12:10, the deposition temperature is 1000 ℃, the total air pressure of a deposition furnace is 0.6kPa, and the deposition time is 80 hours. Finally obtaining the porous ceramic composite nuclear fuel pellet.

The porosity of the fuel pellet prepared by the method is 60-85%. Specifically, the open porosity of the material is measured by an Archimedes drainage method: firstly, cleaning and drying a sample to be testedDry, measure its weight m in air₁Then, putting the sample to be tested into water to be boiled for 3-5 hours to fully saturate the water in the sample to test the weight m of the sample containing saturated water₂Then putting the sample into water to measure the weight m of the sample in the water₃. The porosity P of the sample was calculated using the following formula_op(％)

In conclusion, the novel porous ceramic composite fuel pellet provided by the invention has the advantages that the fuel particles are coated in the carbon and silicon carbide ceramic composite structure, the porous structure with the continuous heat exchange channels is formed, the more uniform thermal field and the more excellent heat exchange efficiency can be obtained, the structure designability is strong, the manufacturing process route is simple, the cost is low, the core structure of the high-temperature gas cooled reactor is expected to be simplified, and the volume and the structural weight of the system can be greatly reduced.

According to the preparation method provided by the invention, the coating fuel particles are compounded into the porous ceramic by adopting a resin foaming combined chemical vapor deposition method, and the inert cooling gas can directly carry out heat transfer through the porous channel by forming the porous structure with the continuous channel, so that the heat loss of a fuel pipeline is reduced, the heat conduction efficiency of the fuel pellet can be greatly improved, and the efficiency of a high-temperature gas cooled reactor is improved.

According to the preparation method of the porous ceramic composite fuel pellet, the coating fuel particles are innovatively compounded into the porous carbon preform by adopting a resin foaming method, and the porous carbon structure is vitrified by combining a chemical vapor deposition method, so that the ceramic composite fuel pellet is finally obtained, and no sintering aid is required to be added in the whole process.

The ceramic composite fuel pellet prepared by the invention does not relate to a fuel rod and a support structure thereof, so that the internal structure of a reactor core can be greatly simplified, and the weight can be remarkably reduced; and a uniform thermal field can be formed by the design of the porous structure, and meanwhile, a heat exchange channel is provided, so that the heat exchange efficiency is greatly improved.

Compared with the traditional nuclear fuel pellet, the porous ceramic composite nuclear fuel pellet has more excellent heat conduction efficiency, excellent designability in the aspects of porosity, loading capacity and the like, simple manufacturing process route and low cost.

The present invention describes preferred embodiments and effects thereof. Additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.