阅读说明：本技术 一种新型泡沫陶瓷复合燃料芯块、制备方法及应用 (Novel foamed ceramic composite fuel pellet, preparation method and application ) 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泡沫陶瓷复合燃料芯块、制备方法及应用,涉及核电技术领域。该方法包括以下步骤：将陶瓷粉料、石墨粉料、包覆燃料颗粒以及粘结剂、除泡剂、增塑剂和分散剂均匀分散于有机溶剂中,获得浆料；采用模板法,将一定尺寸的泡沫状模板浸入至获得的浆料中进行充分挂浆处理,干燥后,去除或不去除模板,获得含有包覆燃料颗粒的泡沫预制体；采用气相沉积法,将含有包覆燃料颗粒的泡沫预制体进行陶瓷化处理,即得所述新型泡沫陶瓷复合燃料芯块。本发明基于模板法,经挂浆、干燥、去除模板(可选),获得泡沫陶瓷复合燃料颗粒骨架,再结合化学气相沉积法,使骨架致密化,最终得到泡沫陶瓷复合核燃料芯块。(The invention discloses a novel foamed ceramic composite fuel pellet, a preparation method and application, and relates to the technical field of nuclear power. The method comprises the following steps: uniformly dispersing ceramic powder, graphite powder, coated fuel particles, a binder, a defoaming agent, a plasticizer and a dispersing agent in an organic solvent to obtain slurry; soaking a foam template with a certain size into the obtained slurry by adopting a template method for full slurry coating treatment, and removing or not removing the template after drying to obtain a foam prefabricated body containing the coated fuel particles; and (3) adopting a vapor deposition method to carry out ceramic treatment on the foam prefabricated body containing the coated fuel particles to obtain the novel foam ceramic composite fuel pellet. The invention is based on a template method, obtains a foamed ceramic composite fuel particle framework by coating slurry, drying and removing the template (optional), and then is combined with a chemical vapor deposition method to densify the framework to finally obtain the foamed ceramic composite nuclear fuel pellet.)

1. The preparation method of the novel foamed ceramic composite fuel pellet is characterized by comprising the following steps of:

uniformly dispersing ceramic powder, graphite powder, coated fuel particles, a binder, a defoaming agent, a plasticizer and a dispersing agent in an organic solvent to obtain slurry;

soaking a foam template with a certain size into the obtained slurry by adopting a template method for full slurry coating treatment, and removing or not removing the template after drying to obtain a foam prefabricated body containing the coated fuel particles;

and (3) adopting a vapor deposition method to carry out ceramic treatment on the foam prefabricated body containing the coated fuel particles to obtain the novel foam ceramic composite fuel pellet.

2. The method for preparing a novel ceramic foam composite fuel pellet as claimed in claim 1, wherein the foam-like template is an organic template or an inorganic template; the organic template is a polyurethane foam or resin foam template; the inorganic template is carbon foam, diatomite or zeolite.

3. The method for preparing a novel foamed ceramic composite fuel pellet as claimed in claim 2, wherein the foamed template is an organic template, and the template is removed by a pyrolysis-oxidation removal process, specifically, the removal of the template is performed according to the following steps:

and heating the foam preform to 200-350 ℃ from room temperature at a heating rate of 0.1-1 ℃/min in an air atmosphere, preserving heat for 1-4 h, then continuously heating to 400-600 ℃ at a heating rate of 0.1-1 ℃/min, and preserving heat for 1-4 h.

4. A method for the preparation of novel ceramic foam composite fuel pellets according to claim 1, characterized in that the ceramization of the foam preform containing the coated fuel particles is carried out according to the following steps:

placing the foam 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, and performing deposition at 900-1200 ℃, wherein the total pressure of the deposition furnace is 0.5-5 kPa, and the deposition time is 20-200 h.

5. The preparation method of the novel foamed ceramic composite fuel pellet as claimed in claim 4, wherein the volume ratio of trichloromethylsilane, hydrogen and inert gas is 1: 5-15: 10-20.

6. The method for preparing a novel ceramic foam composite fuel pellet as claimed in claim 1, wherein the ceramic powder is silicon carbide ceramic powder;

the coated fuel particles are three-structure homodromous (TRISO) particles or two-structure homodromous (BISO) coated fuel particles;

the binder is polyvinyl butyral or polyvinyl alcohol;

the defoaming agent is n-butyl alcohol or ethylene glycol;

the plasticizer is dimethyl dioctyl phthalate or glycerol;

the dispersing agent is triethyl phosphate or ethyl orthosilicate.

7. The method for preparing the novel foamed ceramic composite fuel pellet as claimed in claim 6, wherein the ceramic powder, the graphite powder, the coated fuel particles, the binder, the defoaming agent, the plasticizer and the dispersant are calculated according to the following mass percentages: 5-30% of ceramic powder, 5-20% of graphite powder, 5-50% of coated fuel particles, 20-70% of organic solvent, 1-5% of binder, 1-5% of defoaming agent, 1-5% of plasticizer and 1-5% of dispersing agent.

8. The method for preparing a novel ceramic foam composite fuel pellet as claimed in claim 1, wherein the organic solvent is one or more of ethanol, butanone, toluene and isopropanol.

9. A novel foamed ceramic composite fuel pellet prepared by the method of claims 1-8, wherein the pellet has a void ratio of 70-90%.

10. Use of the novel ceramic foam composite fuel pellets according to claim 9 in high temperature gas cooled reactors.

Technical Field

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

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. The reactor core structure has the problems that the heat released by fuel cannot be quickly and effectively transferred, the further improvement of the power generation efficiency is hindered, and the development of a high-temperature gas cooled reactor is limited.

Disclosure of Invention

The invention aims to solve the defects in the background technology, and provides a preparation method of a novel foam ceramic composite fuel pellet, wherein coating fuel particles are innovatively introduced into a template with a foam structure and combined with silicon carbide and graphite, no sintering aid is required to be added in the preparation process, a foam ceramic composite fuel particle framework is obtained by carrying out slurry coating, drying and template removal (optional) on the basis of a template method, and then the silicon carbide ceramic is coated outside the composite fuel particle framework by combining a chemical vapor deposition method to densify the framework, so that the foam ceramic composite nuclear fuel pellet is finally obtained.

The invention aims to provide a preparation method of a novel foamed ceramic composite fuel pellet, which comprises the following steps:

uniformly dispersing ceramic powder, graphite powder, coated fuel particles, a binder, a defoaming agent, a plasticizer and a dispersing agent in an organic solvent to obtain slurry;

soaking a foam template with a certain size into the obtained slurry by adopting a template method for full slurry coating treatment, and removing or not removing the template after drying to obtain a foam prefabricated body containing the coated fuel particles;

and (3) adopting a vapor deposition method to carry out ceramic treatment on the foam prefabricated body containing the coated fuel particles to obtain the novel foam ceramic composite fuel pellet.

Preferably, the foam template is an organic template or an inorganic template; the organic template is a polyurethane foam or resin foam template; the inorganic template is carbon foam, diatomite or zeolite.

More preferably, the foam template is an organic template, and the template is removed by a pyrolysis-oxidation removal process, wherein the template removal is specifically performed according to the following steps:

and heating the foam preform to 200-350 ℃ from room temperature at a heating rate of 0.1-1 ℃/min in an air atmosphere, preserving heat for 1-4 h, then continuously heating to 400-600 ℃ at a heating rate of 0.1-1 ℃/min, and preserving heat for 1-4 h.

Preferably, the ceramization of the foam preform containing the coated fuel particles is carried out according to the following steps:

placing the foam 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, and performing deposition at 900-1200 ℃, wherein 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 ceramic powder is silicon carbide ceramic powder;

the coated fuel particles are three-structure homodromous (TRISO) particles or two-structure homodromous (BISO) coated fuel particles;

the binder is polyvinyl butyral or polyvinyl alcohol;

the defoaming agent is n-butyl alcohol or ethylene glycol;

the plasticizer is dimethyl dioctyl phthalate or glycerol;

the dispersing agent is triethyl phosphate or ethyl orthosilicate.

More preferably, the ceramic powder, the graphite powder, the coated fuel particles, the binder, the defoaming agent, the plasticizer and the dispersant are calculated according to the following mass percentages: 5-30% of ceramic powder, 5-20% of graphite powder, 5-50% of coated fuel particles, 20-70% of organic solvent, 1-5% of binder, 1-5% of defoaming agent, 1-5% of plasticizer and 1-5% of dispersing agent.

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

The second purpose of the invention is to provide a novel foamed ceramic composite fuel pellet, wherein the porosity of the pellet is 70-90%.

The third purpose of the invention is to provide the application of the novel foamed ceramic composite fuel pellet in the high-temperature gas-cooled reactor.

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

the invention provides a preparation method of a novel foamed ceramic composite fuel pellet, which is characterized in that coating fuel particles are innovatively introduced into a template with a foam structure and combined with silicon carbide and graphite, no sintering aid is required to be added in the preparation process, a foam ceramic composite fuel particle framework is obtained by carrying out slurry coating, drying and template removal (optional) on the basis of a template method, and then the silicon carbide ceramic is coated outside the composite fuel particle framework by combining a chemical vapor deposition method to densify the framework, so that the foamed ceramic composite nuclear fuel pellet is finally obtained.

The pellet provided by the invention forms a more excellent thermal efficiency and more uniform thermal field by compounding the coated fuel particles into the foamed ceramic, has strong designability of structure, simple manufacturing process route and low cost, is expected to simplify the reactor core structure of the high-temperature gas cooled reactor, and can greatly reduce the volume and the structural weight of the system.

The foamed ceramic composite nuclear 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 obviously reduced; meanwhile, the framework of the foamed ceramic forms a uniform thermal field and provides a heat exchange channel, so that the heat exchange efficiency is greatly improved.

Compared with the traditional nuclear fuel pellet, the foamed 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 ceramic foam composite fuel pellet provided by the invention.

Fig. 2 is a diagram of an embodiment of the novel ceramic foam composite fuel pellet provided in example 1.

Fig. 3 is a diagram of an embodiment of the novel ceramic foam composite fuel pellet provided in example 2.

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 high-purity graphite powder selected in the following embodiment has the grain diameter of 1-200 mu m and the purity of more than 95 percent, and plays the role of a moderator.

The coated fuel particles selected for use in the following examples are tri-structure homodromous (TRISO) particles available from BWXT, Inc., USA.

The binder used in the following examples is polyvinyl butyral or polyvinyl alcohol;

the defoaming agent is n-butyl alcohol or ethylene glycol;

the plasticizer is o-dimethyl dioctyl phthalate or glycerol;

the dispersant is triethyl phosphate or ethyl orthosilicate.

Example 1

A preparation method of a novel foamed ceramic composite fuel pellet comprises the following steps:

(1) the method comprises the following steps of mixing TRISO particles, high-purity silicon carbide powder (the particle size d50 is 0.05 mu m, and the purity is 99%), high-purity graphite powder (the particle size d50 is 10 mu m, and the purity is 99%), ethanol, polyvinyl butyral, n-butanol, dimethyl dioctyl phthalate and triethyl phosphate in a mass ratio of 20 wt%: 15 wt%: 15 wt%: 40 wt%: 3 wt%: 2 wt%: 3 wt%: 2 wt% of the mixture is put into a stirring tank to be stirred for 10 hours;

(2) cutting polyurethane foam with the average pore diameter of 1mm into a square shape to be used as a template, soaking and hanging slurry, removing redundant slurry by adopting an extrusion method, placing in an air environment at 30 ℃ for 72 hours, and fully drying to obtain a foam preform;

(3) placing the foamed prefabricated body after the slurry coating and drying in a tubular furnace, carrying out pyrolysis-oxidation treatment in the air atmosphere, wherein the heating rate is 0.5 ℃/min, heating to 300 ℃ from room temperature, preserving heat for 2 hours, then continuously heating to 450 ℃ at 0.5 ℃/min, and preserving heat for 2 hours to obtain a foamed ceramic composite fuel particle skeleton consisting of silicon carbide powder, graphite powder and TRISO particles;

(4) the ceramic composite fuel particle skeleton is placed in a chemical vapor furnace for silicon carbide ceramic densification, trichloromethylsilane (MTS) is used as a precursor, hydrogen is used as carrier gas and diluent gas, and argon is used as a protective gasShielding 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 50 h. Finally obtaining a foamed ceramic composite nuclear fuel pellet; its porosity was 70%; as shown in fig. 1 and 2.

Example 2

A preparation method of a novel foamed ceramic composite fuel pellet comprises the following steps:

(1) the method comprises the following steps of mixing TRISO particles, silicon carbide whiskers (diameter is 1 mu m, length-diameter ratio is 10-15, purity is 99%), high-purity graphite powder (particle diameter d50 is 50 mu m, purity is 99%) and ethanol, butanone, polyvinyl alcohol, ethylene glycol, glycerol and ethyl orthosilicate in a mass ratio of 25 wt%: 10 wt%: 15 wt%: 30 wt%: 12 wt%: 2 wt%: 2 wt%: 2 wt%: 2 wt% of the mixture is put into a stirring tank to be stirred for 12 hours;

(2) cutting polyurethane foam with the average pore diameter of 3mm into a square shape to be used as a template, soaking and hanging slurry, removing redundant slurry by adopting an extrusion method, placing the slurry in a drying box at 50 ℃ for 48 hours, and fully drying the slurry to obtain a foam preform;

(3) placing the foamed prefabricated body after the slurry coating and drying in a tubular furnace, carrying out pyrolysis-oxidation treatment in the air atmosphere, wherein the heating rate is 0.5 ℃/min, heating to 300 ℃ from room temperature, preserving heat for 2 hours, then continuously heating to 450 ℃ at 0.5 ℃/min, and preserving heat for 2 hours to obtain a foamed ceramic composite fuel particle skeleton consisting of silicon carbide whiskers, graphite powder and TRISO particles;

(4) the ceramic composite fuel particle skeleton is placed in a chemical vapor furnace for silicon carbide ceramic densification, 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, the ratio of MTS to H2 to Ar is 1:12:10, the deposition temperature is 1000 ℃, the total pressure of the deposition furnace is 0.6kPa, and the deposition time is 50H. Finally obtaining the foamed ceramic composite nuclear fuel pellet with the porosity of 90 percent; as shown in fig. 1 and 3.

The invention provides a preparation method of a novel foamed ceramic composite fuel pellet, which is characterized in that coating fuel particles are innovatively introduced into a template with a foam structure and combined with silicon carbide and graphite, no sintering aid is required to be added in the preparation process, a foam ceramic composite fuel particle framework is obtained by carrying out slurry coating, drying and template removal (optional) on the basis of a template method, and then the silicon carbide ceramic is coated outside the composite fuel particle framework by combining a chemical vapor deposition method to densify the framework, so that the foamed ceramic composite nuclear fuel pellet is finally obtained.

The pellet provided by the invention forms a more excellent thermal efficiency and more uniform thermal field by compounding the coated fuel particles into the foamed ceramic, has strong designability of structure, simple manufacturing process route and low cost, is expected to simplify the reactor core structure of the high-temperature gas cooled reactor, and can greatly reduce the volume and the structural weight of the system.

The foamed ceramic composite nuclear 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 obviously reduced; meanwhile, the framework of the foamed ceramic forms a uniform thermal field and provides a heat exchange channel, so that the heat exchange efficiency is greatly improved.

Compared with the traditional nuclear fuel pellet, the foamed 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.