CN104810065A - Cobalt-containing coated particles and preparation method thereof - Google Patents

Abstract

The present invention proposes a cobalt-containing coated particle design for tracing different fuel elements in a reactor. The cobalt-containing traced coated particle has a multi-layer structure, and the core of the particle is a cobalt-containing ceramic particle. The ceramic The particles are carbide or oxide ceramics with dispersed elemental cobalt or cobalt compounds; the core size is 200-900 μm, and the core cobalt content is 0.1%-35%; from the core to the outside, it is low-temperature coating carbonization Silicon layer, inner pyrolytic carbon layer, high temperature coated silicon carbide layer and outer pyrolytic carbon layer. The present invention designs an all-ceramic multi-layer coated cobalt-containing coated particle form, and binds cobalt element inside the coated particle. In particular, the present invention designs a low-temperature coated silicon carbide layer as the innermost layer of the coating layer to prevent the precipitation of cobalt in the coating process and subsequent treatment, and avoid the influence of tracer particles on the internal environment of the reactor under the operating conditions of the reactor. Impact.

Description

Cobalt-containing coated particles and preparation method thereof

technical field

The invention belongs to the field of particle design and material preparation, and in particular relates to a cobalt-containing coated particle for tracing and a preparation method thereof.

Background technique

Energy is one of the material driving forces to promote social and economic development. The current dominant fossil energy has caused a large number of environmental problems such as large-scale and continuous smog pollution in the process of use. Therefore, it is necessary to establish a scientific and reasonable energy structure and develop new energy. The problem is becoming more and more urgent. As a clean energy nuclear energy, its research and application are also in a new stage of development. The operation of nuclear power plants is inseparable from nuclear fuel elements. At present, according to the different types of reactors, various types of fuel elements have been continuously designed. For the same stack type, the design parameters of its fuel elements can be changed, but its appearance and structure are the same, which requires certain technical means to distinguish different fuel elements. Especially for new fuel elements, in order to verify their performance in the reactor, it is often necessary to design nuclear fuel loads of different abundances or different qualities to achieve optimal power generation efficiency. How to distinguish fuel elements with different parameters has become an urgent problem to be solved.

The interior of the reactor is a highly radioactive environment, and the general method of differentiation is difficult to operate. Utilizing ⁵⁹ Co will become ⁶⁰ Co in neutron irradiation environment, usually a gamma spectrometer is installed on the circuit for burnup detection, and the characteristic gamma spectrum of ⁶⁰ Co can be detected well, so it can be used This method differentiates the different fuel elements in the reactor.

Contents of the invention

In view of the problems existing in this field, the object of the present invention is to propose the design of the core and coating layer of cobalt-containing coated particles, thereby proposing a cobalt-containing coated particle.

Another object of the present invention is to propose a method for the preparation of cobalt-containing coated particles.

A third object of the invention is to propose the use of said cobalt-containing coated particles.

The technical scheme that realizes the object of the present invention is:

A cobalt-containing coated particle, the cobalt-containing coated particle has a multi-layer structure, the core of the particle is a cobalt-containing ceramic particle, and the ceramic particle is based on an oxide or carbide, and the oxidation of cobalt or cobalt The material is dispersed in the carbide or oxide matrix, the core size is 200-900 μm, and the core cobalt content is 0.1%-35%; from the core to the outside, the low-temperature silicon carbide layer and the inner layer of pyrolytic carbon layer, high temperature silicon carbide layer and outer pyrolytic carbon layer.

Further, the ceramic particles are based on carbide, and cobalt is dispersed in the carbide matrix, and the mass fraction of cobalt in the ceramic particles is 1 to 20%; or, the ceramic particles are based on oxides, and the oxidation of cobalt In the material-dispersed oxide matrix, the mass fraction of cobalt element in the ceramic particles is 1-20%;

The oxide is sintered at high temperature and can be granulated, such as one or more of zirconia, aluminum oxide, and titanium oxide; the carbide is sintered at high temperature and can be granulated, such as titanium carbide, tantalum carbide, One or more of tungsten carbide.

Preferably, the thickness of the low-temperature silicon carbide layer is 10-90 μm, the thickness of the inner pyrolytic carbon layer is 20-120 μm, the thickness of the high-temperature silicon carbide layer is 20-90 μm, and the thickness of the outer pyrolytic carbon layer is 20 μm. ~100 μm. The inner pyrolytic charcoal layer and the outer pyrolytic charcoal layer are independently one of a dense pyrolytic charcoal layer, a loose pyrolytic charcoal layer, and a composite pyrolytic charcoal layer with a loose inner layer and a dense outer layer.

Pyrolytic carbon is divided into loose and dense pyrolytic carbon due to different densities. The density of loose pyrolytic carbon is less than 1.1g/cm ³ , and the density of dense pyrolytic carbon is generally 1.8-2.0g/cm ³ . In terms of function, the loose pyrolytic carbon layer mainly absorbs the swelling of the core particles and stores the gas generated by the core. The inner dense pyrolytic carbon provides a good interface for the deposition of SiC, and the outer dense pyrolytic carbon protects the particles from the external environment. The sequence of coating can determine whether the inner layer of the composite pyrolytic carbon layer is loose and the outer layer is dense or vice versa. However, according to actual needs, the composite pyrolytic carbon layer designed in the present invention has an inner layer of loose pyrolytic carbon layer and The layer is a structure of dense pyrolytic carbon layer.

Wherein, the low-temperature silicon carbide layer is obtained by chemical vapor deposition of chlorinated silane at 1200-1450°C; the high-temperature silicon carbide layer is obtained by chemical vapor deposition of chlorinated silane at 1550-1650°C. Low-temperature SiC is different from high-temperature SiC. Here, in order to prevent overflow of cobalt during the coating process, the innermost SiC coating temperature is lower.

Chlorosilane refers to methyltrichlorosilane, dimethyldichlorosilane or trimethylmonochlorosilane.

The preparation method of the cobalt-containing coated particles proposed by the present invention comprises the steps of:

1) The fluidized bed reactor is heated to 1000-1200°C under an argon atmosphere, and cobalt-containing ceramic particles are placed;

2) The fluidized bed reactor is heated to 1200-1450°C, and one of methyltrichlorosilane, dimethyldichlorosilane or trimethylmonochlorosilane is used as the precursor raw material, heated to steam, and the precursor raw material The steam is fed into the fluidized bed reactor with hydrogen as the carrier gas, and the low-temperature silicon carbide layer is obtained by chemical vapor deposition. The time for chemical vapor deposition is 1 to 6 hours;

3) The temperature of the fluidized bed reactor is controlled at 1100-1400°C, and acetylene or propylene gas is introduced to coat the inner pyrolytic carbon layer;

4) Raise the temperature of the fluidized bed reactor to 1500-1650°C, the precursor raw material vapor is passed into the fluidized bed reactor with hydrogen as the carrier gas, and chemical vapor deposition is carried out to obtain a high temperature silicon carbide layer, and the chemical vapor deposition is carried out The time is 1~4h;

5) The temperature of the fluidized bed reactor is controlled at 1100-1400° C., and acetylene or propylene gas is introduced to coat the outer pyrolytic carbon layer.

Wherein, the precursor raw material in the step 2) is heated to steam at 25-60°C; the fluidizing gas is argon and/or hydrogen, the hydrogen is the carrier gas of the precursor vapor, and the carrier gas and the fluidizing gas The flow ratio is 0.01 to 0.2.

The precursor raw material vapor can be generated by electric heating or constant temperature water bath,

Wherein, the inner pyrolytic carbon layer and the outer pyrolytic carbon layer are independently one of a dense pyrolytic carbon layer, a loose pyrolytic carbon layer, and a composite pyrolytic carbon layer with a loose inner layer and a dense outer layer;

Among them, the coating temperature of the loose pyrolytic carbon layer is 1100-1250°C, the coating time is 20-400s, the fluidization gas is argon, the reaction gas is acetylene, and the volume flow ratio of the fluidization gas to the reaction gas is 0.2-4.0 ;

The covering temperature of dense pyrolytic carbon layer is 1300-1400 ℃, and the covering time is 40-600s. Covering the loose pyrolytic carbon layer and then covering the dense pyrolytic carbon layer can obtain a composite pyrolytic carbon layer with a loose inner layer and a dense outer layer.

Wherein, in the step 4), Ar and _H2 are used as the fluidization gas, and the volume flow ratio range of the two gases Ar/ _H2 is 0-0.9. The volume flow ratio of the carrier gas to the fluidization gas ranges from 0.01 to 0.2.

Further, after the step 5) coating is completed, the particles are cooled with the furnace in a fluidized state, and then unloaded from the bottom after cooling to room temperature.

The application of the cobalt-containing coated particles proposed in the present invention specifically includes placing the cobalt-containing coated particles in nuclear fuel elements, and performing trace and identification of the fuel elements in the reactor.

The beneficial effects of the present invention are:

The present invention proposes an all-ceramic multi-layer coated cobalt-containing coated particle form, and the cobalt element is bound inside the coated particle. In particular, the present invention designs a low-temperature silicon carbide layer as the innermost layer of the cladding layer to prevent the precipitation of cobalt during the cladding process and subsequent treatment, and to avoid the influence of tracer particles on the internal environment of the reactor under operating conditions in the reactor .

The invention has the advantages of simple technological process, convenient technological operation and low cost, and can continuously realize multi-layer coating in a vertical fluidized bed, which is beneficial to realizing industrialized mass production.

Description of drawings

Fig. 1 is a schematic diagram of the design of cobalt-containing coated particles of the present invention;

Fig. 2 is the scanning electron micrograph of the obtained cobalt-containing particle of embodiment 1 of the present invention;

Figure 3 is a line scan of the cross-sectional element distribution of cobalt-containing particles obtained in Example 1 of the present invention;

Fig. 4 is a surface scan of the cross-sectional element distribution of cobalt-containing particles obtained in Example 1 of the present invention.

Detailed ways

The present invention is now illustrated with the following examples, which are not intended to limit the scope of the present invention. The means used in the examples, unless otherwise specified, are conventional means in the art.

The form of tracer particles designed by the present invention is shown in FIG. 1 . From the inside to the outside, it is designed as an inner low-temperature SiC layer, an inner pyrolytic carbon layer, an outer high-temperature SiC layer, and an outer pyrolytic carbon layer. The pyrolytic carbon layer may include loose pyrolytic carbon and dense pyrolytic carbon, and the form of pyrolytic carbon may be a single layer or two or more layers.

Example 1:

The fluidized bed reactor is heated to 1100°C under an argon atmosphere; the mixed gas of Ar and H ₂ is used as the fluidizing gas, the flow rate of H ₂ is 6L/min, the flow rate of Ar is 1.0L/min, 40g ZrO ₂ - CoO (based on the total mass of the particles, the mass fraction of CoO is 3%) particles are placed in the fluidized bed at 1100° C. in the fluidized bed reaction zone for fluidization, and the average diameter of the particles is 600 μm.

Methyltrichlorosilane vapor, constant temperature at 35°C, methyltrichlorosilane vapor is fed into the fluidized bed reaction zone when the temperature continues to rise to 1430°C, _H2 is the carrier gas, and the flow rate of the carrier gas is 0.6L/min, The reaction time is 2h, and a low-temperature silicon carbide layer is obtained. Lower the temperature to 1150°C, adjust the flow rate of Ar to 4.0L/min, the flow rate of acetylene to 5L/min, and the reaction time to 40s to obtain a loose pyrolytic carbon layer. The temperature of the fluidized bed reaction zone was raised to 1350°C, the flow rate of Ar was adjusted to 4.0L/min, the flow rate of propylene to 2.5L/min, and the reaction time was 160s to obtain dense pyrolytic carbon layer, loose pyrolytic carbon layer and dense pyrolytic carbon layer Composite to form the inner pyrolytic carbon layer.

Adjust the flow rate of gas entering the fluidized bed reaction zone, the flow rate of _H2 is 6L/min, the flow rate of Ar is 1.0L/min, the temperature is raised to 1580°C and methyltrichlorosilane vapor is introduced, _H2 is the carrier gas, and the The gas flow rate is 0.6L/min, and the reaction time is 2h to obtain a high-temperature silicon carbide layer. The temperature in the fluidized bed reaction zone was lowered to 1350°C, the flow rate of Ar was adjusted to 4.0L/min, the flow rate of propylene was 2.5L/min, and the reaction time was 160s to obtain an outer dense pyrolytic carbon layer. After the coating is completed, the particles are cooled with the furnace in a fluidized state, and the material is discharged from the bottom after cooling to room temperature.

The scanning electron microscope photos of the coated particles after mounting and polishing are shown in Figure 2 (Figure 2a is magnified by 40 times and Figure 2b is magnified by 270 times), and the multi-layer coating structure can be clearly seen. The inner layer is the core of the ceramic matrix with a core size of 600 μm, which is covered with a low-temperature silicon carbide layer (thickness 30-40 μm) in order from the core to the outside. The inner layer is a loose pyrolytic carbon layer (thickness 40-50 μm), pyrolytic carbon layer (thickness 40-50μm), high-temperature silicon carbide layer (thickness 30-40μm) and outer pyrolytic carbon layer (thickness 40-50μm).

The element line distribution and surface distribution of each layer are shown in Figure 3 and Figure 4. It can be seen that the cobalt element only exists in the core and is not detected in each cladding layer, indicating that the cobalt element is bound in the core inside without spreading outward.

Example 2

The fluidized bed reactor is heated to 1100°C under an argon atmosphere; the mixed gas of Ar and _H2 is used as the fluidization gas, the flow rate of _H2 is 8L/min, the flow rate of Ar is 0.6L/min, _40gZrO2 -CoO (Based on the total mass of the particles, the mass fraction of CoO is 6%). The particles are placed in a fluidized bed at 1100° C. for fluidization, and the average diameter of the particles is 800 μm.

Methyltrichlorosilane is made into steam at 35°C with a constant temperature water bath, and the fluidized bed continues to heat up to 1430°C to feed methyltrichlorosilane steam, _H2 is the carrier gas, and the flow rate of the carrier gas is 0.6L/min. The time is 3 hours, and a low-temperature silicon carbide layer is obtained. Cool the fluidized bed to 1150°C, adjust the Ar flow rate to 4.0 L/min, the acetylene flow rate to 5 L/min, and the reaction time to 40 s to obtain a loose pyrolytic carbon layer. Adjust the flow rate of gas entering the fluidized bed reaction zone, the flow rate of _H2 is 8L/min, the flow rate of Ar is 0.6L/min, the temperature is raised to 1600°C and methyltrichlorosilane vapor is introduced, _H2 is the carrier gas, and the The gas flow rate is 0.6L/min, and the reaction time is 2h to obtain a high-temperature silicon carbide layer. Lower the temperature to 1400°C, adjust the flow rate of Ar to 4.0L/min, the flow rate of propylene to 3.5L/min, and the reaction time to 200s to obtain an outer dense pyrolytic carbon layer. After the coating is completed, the particles are cooled with the furnace in a fluidized state, and the material is discharged from the bottom after cooling to room temperature.

After coating, the particles are cut open, and the multi-layer coating structure can be clearly seen. The inner layer is the core of the ceramic matrix, the core size is 800 μm, and it is coated with a low-temperature silicon carbide layer (thickness 50-60 μm) in order from the core outward, and the inner layer is loose pyrolytic carbon layer (thickness 50-60 μm), high-temperature silicon carbide layer layer (thickness 40-50 μm) and outer pyrolytic carbon layer (thickness 50-60 μm).

Example 3

The fluidized bed reactor is heated to 1100°C under an argon atmosphere; the mixed gas of Ar and H ₂ is used as the fluidizing gas, the flow rate of H ₂ is 6L/min, the flow rate of Ar is 1.0L/min, 40g ZrO ₂ - CoO (based on the total mass of the particles, the mass fraction of CoO is 8%) particles were placed in a fluidized bed at 1100° C. for fluidization, and the average diameter of the particles was 600 μm.

The dimethyldichlorosilane vapor is kept at 30°C with a constant temperature water bath, and the temperature is continuously raised to 1380°C to feed the dimethyldichlorosilane vapor, _H2 is the carrier gas, the flow rate of the carrier gas is 0.4L/min, and the reaction time is 2h, a low-temperature silicon carbide layer was obtained. The temperature of the fluidized bed reaction zone was raised to 1350°C, the flow rate of Ar was adjusted to 4.0L/min, the flow rate of propylene was 2.0L/min, and the reaction time was 160s to obtain an inner dense pyrolytic carbon layer. Adjust the gas flow rate, the flow rate of _H2 is 6L/min, the flow rate of Ar is 1.0L/min, the temperature is raised to 1550°C and dimethyldichlorosilane vapor is introduced, _H2 is the carrier gas, and the flow rate of the carrier gas is 0.6L /min, the reaction time is 2h, and a high temperature silicon carbide layer is obtained. Lower the temperature to 1350°C, adjust the flow rate of Ar to 4.0L/min, the flow rate of propylene to 2.0L/min, and the reaction time to 160s to obtain an outer dense pyrolytic carbon layer. After the coating is completed, the particles are cooled with the furnace in a fluidized state, and the material is discharged from the bottom after cooling to room temperature.

After coating, the particles are cut open, and the multi-layer coating structure can be clearly seen. The inner layer is the core of the ceramic matrix with a core size of 600 μm, which is covered with a low-temperature silicon carbide layer (thickness 30-40 μm) and an inner dense pyrolytic carbon layer (thickness 30-40 μm) and high-temperature silicon carbide layer from the core outward. layer (thickness 40-50 μm) and outer pyrolytic carbon layer (thickness 30-40 μm).

Example 4

The fluidized bed reactor is heated to 1100°C under an argon atmosphere; the mixed gas of Ar and H ₂ is used as the fluidizing gas, the flow rate of H ₂ is 2L/min, the flow rate of Ar is 3.0L/min, 40g ZrO ₂ - CoO (based on the total mass of the particles, the mass fraction of CoO is 6%) particles were placed in a fluidized bed at 1100° C. for fluidization, and the average diameter of the particles was 700 μm.

Methyltrichlorosilane vapor is kept at 35°C with a constant temperature water bath, and the temperature is continuously raised to 1450°C to feed methyltrichlorosilane vapor, _H2 is the carrier gas, the flow rate of the carrier gas is 0.5L/min, and the reaction time is 5h. A low-temperature silicon carbide layer is obtained. The temperature of the reaction zone of the fluidized bed was lowered to 1400°C, the flow rate of Ar was adjusted to 3.0L/min, the flow rate of propylene was 5.0L/min, and the reaction time was 260s to obtain an inner dense pyrolytic carbon layer. Adjust the gas flow rate, the flow rate of _H2 is 2L/min, the flow rate of Ar is 2.0L/min, the temperature is raised to 1580°C and methyltrichlorosilane vapor is introduced, _H2 is the carrier gas, and the flow rate of the carrier gas is 0.6L/min min, the reaction time is 3h, and a high temperature silicon carbide layer is obtained. Lower the temperature to 1400°C, adjust the flow rate of Ar to 3.0L/min, the flow rate of propylene to 5.0L/min, and the reaction time to 260s to obtain an outer dense pyrolytic carbon layer. After the coating is completed, the particles are cooled with the furnace in a fluidized state, and the material is discharged from the bottom after cooling to room temperature.

After coating, the particles are cut open, and the multi-layer coating structure can be clearly seen. The inner layer is the core of the ceramic matrix, the core size is 700μm, and it is covered with a low-temperature silicon carbide layer (thickness 70-80μm) in order from the core to the outside, and the inner layer is a dense pyrolytic carbon layer (thickness 60-70μm), high-temperature silicon carbide layer layer (thickness 60-70 μm) and outer dense pyrolytic carbon layer (thickness 60-70 μm).

Example 5

The fluidized bed reactor is heated to 1050°C under an argon atmosphere; the mixed gas of Ar and _H2 is used as the fluidization gas, the flow rate of _H2 is 18L/min, the flow rate of Ar is 2.0L/min, 60g WC-Co (Based on the total mass of the particles, the mass fraction of CoO is 6%). The particles are placed in a fluidized bed at 1050° C. for fluidization, and the average diameter of the particles is 600 μm. Methyltrichlorosilane is kept at a constant temperature of 35°C, and the temperature is continuously raised to 1400°C to pass through methyltrichlorosilane, _H2 is the carrier gas, the flow rate of the carrier gas is 0.6L/min, and the reaction time is 2h to obtain a low-temperature silicon carbide layer . Lower the temperature to 1350°C, adjust the flow rate of Ar to 6.0L/min, the flow rate of propylene to 4.5L/min, and the reaction time to 160s to obtain an inner dense pyrolytic carbon layer. Adjust the gas flow rate, the flow rate of _H2 is 18L/min, the flow rate of Ar is 2.0L/min, the temperature is raised to 1580°C and methyltrichlorosilane is introduced, _H2 is the carrier gas, and the flow rate of the carrier gas is 0.6L/min , the reaction time is 2h, and a high-temperature silicon carbide layer is obtained. Lower the temperature to 1350°C, adjust the flow rate of Ar to 6.0L/min, the flow rate of propylene to 4L/min, and the reaction time to 160s to obtain an outer dense pyrolytic carbon layer.

After coating, the particles are cut open, and the multi-layer coating structure can be clearly seen. The inner layer is the core of the ceramic matrix, the core size is 600μm, and the inner layer is covered with a low-temperature silicon carbide layer (thickness 40-50μm), an inner dense pyrolytic carbon layer (thickness 40-50μm), and a high-temperature silicon carbide layer. layer (thickness 40-50 μm) and outer dense pyrolytic carbon layer (thickness 40-50 μm).

The above embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, ordinary engineers and technicians in the field may make various modifications to the technical solutions of the present invention. and improvements, all should fall within the scope of protection determined by the claims of the present invention.

Claims (9)

1. A cobalt-containing coated particle is characterized in that the cobalt-containing coated particle has a multilayer structure, and the core of the particle is a cobalt-containing ceramic particle, and the ceramic particle is based on carbide or oxide , cobalt or cobalt oxides are dispersed in carbide or oxide matrix; the core size is 200-900 μm, and the mass fraction of cobalt in the core is 0.1%-35%; the silicon carbide layer is coated at low temperature from the core to the outside , inner pyrolytic carbon layer, high temperature coated silicon carbide layer and outer pyrolytic carbon layer. 2. The cobalt-containing coated particle according to claim 1, wherein the ceramic particle is based on carbide, and in the elemental cobalt dispersed carbide matrix, the mass fraction of elemental cobalt in the ceramic particle is 1%～ 20%; or, the ceramic particles are based on oxides, cobalt oxides are dispersed in the oxide matrix, and the mass fraction of cobalt element in the ceramic particles is 1% to 20%; The oxide is one or more of zirconia, aluminum oxide and titanium oxide; the carbide is one or more of titanium carbide, tantalum carbide and tungsten carbide. 3. The cobalt-containing coated particles according to claim 1, characterized in that, the thickness of the low-temperature silicon carbide layer is 10-90 μm, the thickness of the inner pyrolytic carbon layer is 20-120 μm, and the thickness of the high-temperature silicon carbide layer is 10-90 μm. The thickness is 20-90 μm, and the thickness of the outer pyrolytic carbon layer is 20-100 μm; the inner pyrolytic carbon layer and the outer pyrolytic carbon layer are independently dense pyrolytic carbon layer, loose pyrolytic carbon layer, One of the composite pyrolytic carbon layers with a loose inner layer and a dense outer layer. 4. The cobalt-containing coated particles according to claim 1, characterized in that, the low-temperature silicon carbide layer is obtained by chlorinated silane through a fluidized bed-chemical vapor deposition method at 1200-1450 ° C; the high-temperature carbonization The silicon layer is obtained by chlorinated silane at 1550-1650° C. through a fluidized bed-chemical vapor deposition method. 5. The method for preparing cobalt-containing coated particles according to any one of claims 1 to 4, characterized in that it comprises the steps of: 1) The fluidized bed reactor is heated to 1000-1200°C under an argon atmosphere, and cobalt-containing ceramic particles are placed; 2) The fluidized bed reactor is heated to 1200-1450°C, and one of methyltrichlorosilane, dimethyldichlorosilane or trimethylmonochlorosilane is used as the precursor raw material, heated to steam, and the precursor raw material The steam is fed into the fluidized bed reactor with hydrogen as the carrier gas, and the low-temperature silicon carbide layer is obtained by chemical vapor deposition. The time for chemical vapor deposition is 1 to 6 hours; 3) The temperature of the fluidized bed reactor is controlled at 1100-1400°C, and acetylene or propylene gas is introduced to coat the inner pyrolytic carbon layer; 4) Raise the temperature of the fluidized bed reactor to 1500-1650°C, the precursor raw material vapor is passed into the fluidized bed reactor with hydrogen as the carrier gas, and chemical vapor deposition is carried out to obtain a high temperature silicon carbide layer, and the chemical vapor deposition is carried out The time is 1~4h; 5) The temperature of the fluidized bed reactor is controlled at 1100-1400° C., and acetylene or propylene gas is introduced to coat the outer pyrolytic carbon layer. 6. The preparation method according to claim 5, characterized in that, in the step 2), the precursor raw material is heated to steam at 25-60°C; the fluidization gas is argon and/or hydrogen, and hydrogen is the precursor The carrier gas of the steam, the volume flow ratio of the carrier gas to the fluidization gas is 0.01-0.2. 7. The preparation method according to claim 5, characterized in that, the inner pyrolytic carbon layer and the outer pyrolytic carbon layer are independently dense pyrolytic carbon layer, loose pyrolytic carbon layer, loose inner layer One of the outer dense composite pyrolytic carbon layers; Among them, the coating temperature of the loose pyrolytic carbon layer is 1100°C-1250°C, the coating time is 20-400s, the fluidization gas is argon, the reaction gas is acetylene, and the flow ratio of fluidization gas to reaction gas is 0.2-4.0 ; The coating temperature of dense pyrolytic carbon layer is 1300~1400℃, and the coating time is 40~600s. The fluidization gas is argon, the reaction gas is propylene, and the flow ratio of fluidization gas to reaction gas is 0.2~4.0; The loose pyrolytic carbon layer is then coated with a dense pyrolytic carbon layer to obtain a composite pyrolytic carbon layer with a loose inner layer and a dense outer layer. 8. preparation method according to claim 5, it is characterized in that, in described step 4), adopt argon gas and hydrogen to be fluidization gas, the flow ratio scope Ar/H of two kinds of gases _2Be 0～0.9; The flow ratio of gas to fluidizing gas ranges from 0.01 to 0.2. 9. The application of the cobalt-containing tracer coated particles according to any one of claims 1 to 4, characterized in that the cobalt-containing coated particles are placed in fuel elements, and the nuclear fuel elements are traced and identified in the reactor.