阅读说明：本技术 一种大晶粒uo2陶瓷燃料及其制备方法和应用 (Large-grain UO2Ceramic fuel and preparation method and application thereof ) 是由 钟毅 张鹏程 杨振亮 高瑞 李冰清 白彬 褚明福 黄奇奇 王志毅 王昀 谢良 于 2021-09-03 设计创作，主要内容包括：本发明提供了一种大晶粒UO-(2)陶瓷燃料及其制备方法和应用,属于核燃料开发技术领域。本发明以添加剂作为晶粒生长助剂,在烧结过程中,添加剂会通过晶格电荷平衡(电荷态)和缺陷结构(间隙原子大小/配位关系)机制进入晶格间隙,从而提高铀的空位浓度,提升晶格扩散速率,促使UO-(2)晶格重排获得晶粒生长,加速UO-(2)燃料晶粒生长,快速有效地提高UO-(2)陶瓷燃料的平均晶粒尺寸(50～180μm)。而且,大晶粒尺寸的获得能够降低晶界比表面积,使UO-(2)具备低热膨胀系数、较高的高温蠕变性能以及对裂变产物更高的滞留性等特点,从而提高反应堆的经济性和安全性,可作为反应堆的新型核燃料。(The invention provides a large-grain UO 2 Ceramic fuel and a preparation method and application thereof, belonging to the technical field of nuclear fuel development. The invention takes the additive as the grain growth assistant, and the additive can enter into the crystal lattice gap through the mechanisms of crystal lattice charge balance (charge state) and defect structure (interstitial atom size/coordination relation) in the sintering process, thereby improving the vacancy concentration of uranium, promoting the crystal lattice diffusion rate and promoting UO 2 The crystal grain growth is obtained by the rearrangement of the crystal lattice, and the UO is accelerated 2 The grain growth of fuel can quickly and effectively raise UO 2 The average grain size of the ceramic fuel is 50 to 180 μm. Moreover, the large grain size can be obtained to reduce the specific surface area of the grain boundary, so that UO can be obtained 2 Has the characteristics of low thermal expansion coefficient, higher high-temperature creep property, higher retention of fission products and the likeThereby improving the economy and the safety of the reactor and being used as a novel nuclear fuel of the reactor.)

1. Large-grain UO₂The preparation method of the ceramic fuel is characterized by comprising the following steps:

mixing UO₂Ball-milling and mixing the powder, the additive and the lubricant to obtain mixed powder;

sintering the mixed powder to obtain large-grain UO₂A ceramic fuel;

the additive comprises metal oxide and/or metal simple substance; the metal oxide comprises one or more of manganese oxide, titanium oxide, niobium oxide, chromium oxide and vanadium oxide; the metal simple substance comprises one or more of niobium, chromium, manganese and vanadium;

the large crystal grain UO₂The average grain size of the ceramic fuel is 50 to 180 μm.

2. The method of claim 1, wherein the UO is present in a liquid phase₂The particle size of the powder is 100 nm-50 μm,²³⁵the U enrichment degree is 1-10%.

3. The method of claim 1, wherein the additive is present in the UO in a mass amount₂The mass percentage of the powder is 0.05-5%.

4. The method of claim 1, wherein the lubricant comprises Acer wax or zinc stearate, and wherein the lubricant comprises the UO by mass₂The mass percentage of the powder is 0.3%.

5. The method of claim 1, wherein the sintering comprises pressureless sintering, hot-press sintering, or spark plasma sintering.

6. The method of claim 5, wherein the pressureless sintering process comprises the steps of: molding the mixed powder to obtain UO₂A green body prepared by subjecting the UO to heat treatment₂Sintering the blank body without pressure to obtain large-grain UO₂A ceramic fuel; said die pressing intoThe pressure of the pressureless sintering is 100-400 MPa, the temperature of the pressureless sintering is 1500-1850 ℃, the heat preservation time is 1-40 h, and the heating rate of the pressureless sintering after heating to the temperature of the pressureless sintering is 1-20 ℃/min.

7. The preparation method according to claim 5, wherein the pressure of the hot-pressing sintering is 20-200 MPa, and the process of the hot-pressing sintering comprises the following steps: heating to 800 ℃ at the speed of 1-10 ℃/min, and preserving heat for 1h, and heating to 1300-1800 ℃ at the speed of 1-5 ℃/min, and preserving heat for 1-20 h.

8. The production method according to claim 5, wherein the atmospheric pressure of the spark plasma sintering is 10 to 70 kPa; the process of spark plasma sintering comprises the following steps: heating to 1100-1700 ℃ at a speed of 50-1000 ℃/min, sintering at a pressure of 20-200 MPa, and keeping the temperature for 1 min-2 h.

9. Large-grain UO prepared by the preparation method of any one of claims 1 to 8₂A ceramic fuel.

10. Large grain UO as claimed in claim 9₂Use of a ceramic fuel in a nuclear fuel.

Technical Field

The invention relates to the technical field of nuclear fuel development, in particular to a large-grain UO₂Ceramic fuel and a preparation method and application thereof.

Background

UO₂The ceramic fuel is used as the most widely applied nuclear fuel of the current commercial nuclear reactor, and has the remarkable advantages of high melting point, excellent thermal stability, good compatibility with a coolant and a cladding contact material, high irradiation stability, low thermal neutron capture cross section of chemical combination element oxygen and the like. However, at the same time the UO₂The ceramic fuel still has defects such as low thermal conductivity, swelling during irradiation, inhibition of burn-up deepening, and the like. The burn-up depth always restricts the utilization efficiency of nuclear fuelThe key factors of rate and cost are also the most interesting points for the commercial application of nuclear fuels. Therefore, the deepening of fuel pellet burnup in the service process becomes an important means for improving the economy of the commercial pressurized water reactor.

Large grain UO₂Has the traditional UO₂Is essentially the result of the larger average grain size of the fuel core compared to the conventional sintering mode.

Grain boundaries and through voids are the main diffusion channels for fission gases, and intergranular bubbles are also important sources of swelling during pellet irradiation. Under the same densification degree, the increase of the grain size can effectively reduce the specific surface area of the grain boundary and greatly improve the probability of pore distribution in the grain. This feature shows that the probability of the fission gas being stored in the pores inside the crystal grain is greatly increased relative to the pores dispersed at the grain boundary, which is very useful for improving the containment capability of the fission gas. Therefore, the path of diffusion of fission gases from the inside of the crystal grain to the crystal grain boundary or the gas channel is also increased correspondingly, so that the release rate of fission gases is also reduced with a high probability; on the other hand, increasing the grain size can also effectively reduce the swelling amount of the pellets during irradiation. During normal service, the interior of the fuel pellets are subjected to extremely high temperatures, the amount of thermal expansion of which is a significant source of swelling and deformation of the pellets. The study showed that the grain boundaries are limiting UO₂An important factor of thermal conductivity, the existence of grain boundaries reduces UO to some extent₂Thermal conductivity of (a); meanwhile, the increase of the grain size can also reduce the thermal expansion coefficient of the fuel pellet to a certain degree, and the large grain UO₂The creep property at high temperature will be much higher than that of UO with smaller grain size₂A fuel pellet.

To summarize, large grain UO₂Is helpful for improving the fission gas containing capability of the fuel pellet and reducing the fission gas release rate, can relieve the interaction between the fuel pellet and the cladding caused by overhigh temperature to a certain extent, thereby resisting the mechanical abrasion during service to maintain the integrity of the pellet, effectively preventing the accidents of pellet cracking, cladding damage and the like, and improving the fuel pelletThe economic efficiency and the safety of the fuel pellet in the service process are improved, thereby having unique advantages. Therefore, UO is further increased₂The grain size of (a) has an important meaning.

Disclosure of Invention

The invention aims to provide a large-grain UO₂Ceramic fuel, preparation method and application thereof, and prepared large-grain UO₂The average grain size of the ceramic fuel is 50 to 180 μm.

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

the invention provides a large-grain UO₂The preparation method of the ceramic fuel comprises the following steps:

mixing UO₂Ball-milling and mixing the powder, the additive and the lubricant to obtain mixed powder;

sintering the mixed powder to obtain large-grain UO₂A ceramic fuel;

the additive comprises metal oxide and/or metal simple substance; the metal oxide comprises one or more of manganese oxide, titanium oxide, niobium oxide, chromium oxide and vanadium oxide; the metal simple substance comprises one or more of niobium, chromium, manganese and vanadium;

the large crystal grain UO₂The average grain size of the ceramic fuel is 50 to 180 μm.

Preferably, the UO₂The particle size of the powder is 100 nm-50 μm,²³⁵the U enrichment degree is 1-10%.

Preferably, the mass of the additive accounts for the UO₂The mass percentage of the powder is 0.05-5%.

Preferably, the lubricant comprises Acer wax or zinc stearate, and the mass of the lubricant accounts for the UO₂The mass percentage of the powder is 0.3%.

Preferably, the sintering mode comprises pressureless sintering, hot-pressing sintering or spark plasma sintering.

Preferably, the pressureless sintering process comprises the following steps: molding the mixed powder to obtain UO₂A green body prepared by subjecting the UO to heat treatment₂Sintering the blank body without pressure to obtain large-grain UO₂A ceramic fuel; the pressure of the die forming is 100-400 MPa, the temperature of the pressureless sintering is 1500-1850 ℃, the heat preservation time is 1-40 h, and the heating rate of the temperature rising to the pressureless sintering temperature is 1-20 ℃/min.

Preferably, the pressure of the hot-pressing sintering is 20-200 MPa, and the process of the hot-pressing sintering comprises the following steps: heating to 800 ℃ at the speed of 1-10 ℃/min, and preserving heat for 1h, and heating to 1300-1800 ℃ at the speed of 1-5 ℃/min, and preserving heat for 1-20 h.

Preferably, the atmosphere pressure of the spark plasma sintering is 10-70 kPa; the process of spark plasma sintering comprises the following steps: heating to 1100-1700 ℃ at a speed of 50-1000 ℃/min, sintering at a pressure of 20-200 MPa, and keeping the temperature for 1 min-2 h.

The invention provides the large-grain UO prepared by the preparation method in the technical scheme₂A ceramic fuel.

The invention provides the large-grain UO in the technical scheme₂Use of a ceramic fuel in a nuclear fuel.

The invention provides a large-grain UO₂The preparation method of the ceramic fuel comprises the following steps: mixing UO₂Ball-milling and mixing the powder, the additive and the lubricant to obtain mixed powder; sintering the mixed powder to obtain large-grain UO₂A ceramic fuel; the additive comprises metal oxide and/or metal simple substance; the metal oxide comprises one or more of manganese oxide, titanium oxide, niobium oxide, chromium oxide and vanadium oxide; the metal simple substance comprises one or more of niobium, chromium, manganese and vanadium; the large crystal grain UO₂The average grain size of the ceramic fuel is 50 to 180 μm. The invention takes the additive as the grain growth auxiliary agent, and UO is applied in the high temperature environment of sintering₂Generating dislocation such as point defect, the additive can enter into crystal lattice gap through crystal lattice charge balance (charge state) and defect structure (gap atom size/coordination relation) mechanism, thereby improving vacancy concentration of uranium, increasing crystal lattice diffusion rate, and promoting UO₂The crystal grain growth is obtained by the rearrangement of the crystal lattice, and the UO is accelerated₂Grain growth of fuel, rapidEffectively improve UO₂The average grain size of the ceramic fuel is 50 to 180 μm.

The large-grain UO prepared by the invention₂The ceramic fuel not only inherits the traditional UO₂Ceramic fuels have the advantages of high melting point, high chemical stability and radiation resistance, and the large grain size can reduce the specific surface area of grain boundary, so that UO (oxygen-free) can be obtained₂The reactor has the characteristics of low thermal expansion coefficient, higher high-temperature creep property, higher retention of fission products and the like, thereby improving the economy and safety of the reactor and being used as novel nuclear fuel of the reactor.

Drawings

FIG. 1 shows a large-grained UO prepared in example 1₂Metallographic pictures of ceramic fuels;

FIG. 2 shows a large-grained UO prepared in example 2₂Metallographic pictures of ceramic fuels;

FIG. 3 shows a large-grained UO prepared in example 4₂Metallographic pictures of ceramic fuels;

FIG. 4 shows large-grained UO prepared in example 17₂Metallographic pictures of ceramic fuels;

FIG. 5 shows a large-grained UO prepared in example 20₂Metallographic pictures of ceramic fuels;

FIG. 6 is a conventional UO prepared in comparative example 1₂Metallographic pictures of ceramic fuels;

FIG. 7 is pure UO of comparative example 2₂Metallography of the powder;

FIG. 8 shows a large-grained UO prepared in example 1₂Ceramic fuel and conventional UO prepared in comparative example 1₂Thermal expansion profile of ceramic fuel.

Detailed Description

The invention provides a large-grain UO₂The preparation method of the ceramic fuel comprises the following steps:

mixing UO₂Ball-milling and mixing the powder, the additive and the lubricant to obtain mixed powder;

sintering the mixed powder to obtain large-grain UO₂A ceramic fuel;

the additive comprises metal oxide and/or metal simple substance; the metal oxide comprises one or more of manganese oxide, titanium oxide, niobium oxide, chromium oxide and vanadium oxide; the metal simple substance comprises one or more of niobium, chromium, manganese and vanadium;

the large crystal grain UO₂The average grain size of the ceramic fuel is 50 to 180 μm.

In the present invention, unless otherwise specified, all the starting materials required for the preparation are commercially available products well known to those skilled in the art.

In the invention, the UO₂And ball-milling and mixing the powder, the additive and the lubricant to obtain mixed powder. In the present invention, the UO₂The particle size of the powder is preferably 100nm to 50 μm,²³⁵the U enrichment degree is preferably 1-10%.

In the present invention, the additive includes a metal oxide and/or a simple metal; the metal oxide comprises one or more of manganese oxide, titanium oxide, niobium oxide, chromium oxide and vanadium oxide, and is preferably chromium oxide, titanium oxide or niobium oxide; the metal simple substance comprises one or more of niobium, chromium, manganese and vanadium, and chromium or niobium is preferred. When the additives are preferably selected from the above types, the invention has no special limitation on the mixture ratio of different types of additives, and the mixture ratio can be any.

In the present invention, the particle size of the manganese oxide is preferably 30nm to 50 μm; the particle size of the titanium oxide is preferably 15 nm-40 μm; the grain size of the niobium oxide is preferably 20 nm-10 mu m; the particle size of the chromium oxide is preferably 60 nm-40 mu m; the particle size of the vanadium oxide is preferably 30 nm-50 mu m; the particle size of the niobium is preferably 1-200 μm; the particle size of the chromium is preferably 5-200 mu m; the particle size of the vanadium is preferably 1-200 mu m; the particle size of the manganese is preferably 80nm to 74 μm.

In the present invention, the additive preferably accounts for the UO in mass₂The mass percentage of the powder is 0.05-5%, and more preferably 0.3-3%.

In the present invention, the lubricant preferably includes Acer wax or zinc stearate, and the mass of the lubricant preferably accounts for the UO₂The mass percentage of the powder is 0.3%. The invention utilizes a lubricantPromoting fuel pellet formation.

In the present invention, the process of ball milling and mixing is preferably as follows: mixing UO₂Placing the powder, the additive and the lubricant in a tungsten carbide ball mill tank, adding zirconia grinding balls, and carrying out ball milling and mixing for 16h to obtain mixed powder; the mass ratio of the zirconia grinding balls to the mixed powder is preferably 3: 1. The rotation speed of the ball milling and mixing and the specification of the zirconia grinding balls are not particularly limited, and the zirconia grinding balls known in the field can be used according to the process known in the field.

The particle size of the mixed powder is not specially limited, and the mixed powder with the corresponding particle size can be obtained by ball milling according to the ball milling and mixing process.

After the mixed powder is obtained, the mixed powder is sintered to obtain the large-grain UO₂A ceramic fuel.

In the present invention, the sintering manner preferably includes pressureless sintering, hot-press sintering or spark plasma sintering.

In the present invention, when the sintering manner is pressureless sintering, the pressureless sintering process preferably includes the following steps: molding the mixed powder to obtain UO₂A green body prepared by subjecting the UO to heat treatment₂Sintering the blank body without pressure to obtain large-grain UO₂A ceramic fuel. In the invention, the pressure of the die forming is preferably 100-400 MPa, and more preferably 150-250 MPa; the time is preferably 5 s-2 min; the pressureless sintering is preferably carried out in an atmosphere sintering furnace.

Before the pressureless sintering, the invention preferably heats up to 800 ℃ at the speed of 10 ℃/min under the protection of vacuum or argon atmosphere, preserves the temperature for 1h for degreasing, then introduces hydrogen or hydrogen-carbon dioxide mixed gas to normal pressure, carries out pressureless sintering, and obtains large-grain UO after furnace cooling₂A ceramic fuel. In the invention, the volume ratio of carbon dioxide in the hydrogen-carbon dioxide mixed gas is preferably 1-10%. The invention burns the lubricant to be volatilized and removed through degreasing.

In the invention, the temperature of the pressureless sintering is preferably 1500-1850 ℃, more preferably 1600-1800 ℃, the heat preservation time is preferably 1-40 h, more preferably 5-30 h, and the heating rate of the pressureless sintering is preferably 1-20 ℃/min, more preferably 5-10 ℃/min.

In the present invention, when the sintering mode is hot-pressing sintering, the hot-pressing sintering is preferably performed in a graphite mold, and the graphite mold is not particularly limited in the present invention, and may be a graphite mold well known in the art.

The invention is preferably vacuumized to 5X 10 of vacuum degree^-2After the pressure is about 5Pa, continuously introducing hydrogen or hydrogen-carbon dioxide mixed gas (the volume ratio of carbon dioxide in the hydrogen-carbon dioxide mixed gas is preferably 1-10%), performing hot-pressing sintering, and cooling along with a furnace to obtain large-grain UO₂A ceramic fuel.

In the invention, the pressure of the hot-pressing sintering is preferably 20-200 MPa, and more preferably 50-150 MPa; the hot-pressing sintering process preferably comprises the following steps: heating to 800 ℃ at the speed of 1-10 ℃/min, and preserving heat for 1h, and heating to 1300-1800 ℃ at the speed of 1-5 ℃/min, and preserving heat for 1-20 h.

In the present invention, when the sintering method is spark plasma sintering, the spark plasma sintering is preferably performed in a graphite mold, and the graphite mold is not particularly limited in the present invention, and a graphite mold known in the art may be used.

In the invention, the atmosphere pressure of the spark plasma sintering is preferably 10-70 kPa, and more preferably 30-60 kPa; according to the invention, the graphite mold is preferably vacuumized to 5-50 Pa, and argon-carbon dioxide mixed gas (the volume ratio of carbon dioxide is preferably 1-10%) is filled to the atmosphere pressure.

In the present invention, the process of spark plasma sintering preferably comprises: heating to 1100-1700 ℃ at a heating rate of 50-1000 ℃/min, wherein the sintering pressure is 20-200 MPa, and the heat preservation time is 1 min-2 h; the heating rate is more preferably 100-300 ℃/min; preferably heating to 1300-1600 ℃; the sintering pressure is preferably 30-100 MPa; the heat preservation time is preferably 20 min-1.5 h.

Completing the discharge plasma firingAfter the solidification, the invention preferably carries out furnace cooling to obtain the large-grain UO₂A ceramic fuel.

The invention provides the large-grain UO prepared by the preparation method in the technical scheme₂A ceramic fuel.

The invention provides the large-grain UO in the technical scheme₂Use of a ceramic fuel in a nuclear fuel. The method of the present invention is not particularly limited, and the method may be applied according to a method known in the art. The invention preferably uses large-grain UO according to different requirements of reactor types₂The ceramic fuel is machined to the desired shape and size using grinding equipment. The process of the present invention is not particularly limited, and may be carried out according to a process known in the art.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the following examples, UO₂The particle size of the powder is 3-5 μm,²³⁵the enrichment degree of U is 5%; the addition amount of the lubricant accounts for UO₂Is 0.3% by mass.

Example 1

Will 100gUO₂Powder, 0.5g of chromium oxide powder (particle size 5-10 μm, addition amount of UO)₂0.5 percent) and 0.3g of Ackerite are placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 7g of the mixed powder, and carrying out die pressing forming under the pressing pressure of 200MPa to obtain UO₂The method comprises the following steps of carrying out pressureless sintering on a green body by using an atmosphere sintering furnace, vacuumizing the atmosphere sintering furnace, introducing argon atmosphere for protection, heating to 800 ℃ at the speed of 10 ℃/min, keeping the temperature for 1h for degreasing, continuously introducing a mixed gas of hydrogen and carbon dioxide (the volume ratio of the carbon dioxide is 1.8%) to normal pressure at the speed of 5 ℃/min is heated to 1700 ℃, the temperature is preserved for 4 hours, and the product is cooled to room temperature along with the furnace to obtain the large-grain UO₂A ceramic fuel.

Example 2

The only difference from example 1 is: the additive is chromium powder (grain diameter is 10-30 mu m, and the addition amount accounts for UO₂Mass fraction of (d) is 0.5%), the same as in example 1.

Example 3

The only difference from example 1 is: the additive is titanium oxide powder with the grain diameter of 30nm and the addition amount of UO₂0.25% of the mass fraction.

Example 4

Will 100gUO₂Powder, 0.25g niobium oxide powder (particle size 20-100 nm, addition amount is UO)₂0.25 percent) and 0.3g of Ackerite are placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 7g of the mixed powder, and carrying out die pressing forming under the pressing pressure of 200MPa to obtain UO₂Carrying out pressureless sintering on a green body by using an atmosphere sintering furnace, vacuumizing the atmosphere sintering furnace, filling argon for atmosphere protection, heating to 800 ℃ at the speed of 10 ℃/min, keeping the temperature for 1h for degreasing, continuously introducing hydrogen to the normal pressure, heating to 1650 ℃ at the speed of 5 ℃/min, keeping the temperature for 24h, and cooling to the room temperature along with the furnace to obtain the large-grain UO₂A ceramic fuel.

Example 5

The only difference from example 4 is: the additive is metal niobium powder with the grain diameter of 10-50 mu m and the addition amount of UO₂0.5 percent of the mass fraction.

Example 6

The only difference from example 1 is: the additive is manganese oxide powder with the particle size of 100-300 nm and the addition amount of UO₂The same as example 1 except that the amount of the component (B) was 0.5% by mass.

Example 7

The only difference from example 1 is: the additive is metal vanadium powder with the grain diameter of 74 mu m, and the addition amount is UO₂The same as example 1 except that the amount of the component (B) was 0.5% by mass.

Example 8

The only difference from example 1 is: the additive is metal vanadium powder with the grain diameter of 74 mu m, and the addition amount is UO₂0.3% of mass fraction; and vanadium oxide powder with the particle size of 30-100 nm and the addition amount of UO₂0.2% of the mass fraction.

Example 9

Will 100gUO₂Powder and 0.5g of chromium oxide powder (the particle size is 5-10 mu m, and the addition amount accounts for UO)₂0.5 percent) and 0.3g of Ackerite are placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 11g of the mixed powder, placing the mixed powder into a graphite die for hot-pressing sintering, wherein the sintering process is as follows: vacuumizing to the vacuum degree of 0.1Pa, continuously introducing a mixed gas of hydrogen and carbon dioxide (the volume ratio of the carbon dioxide is 2.0%), heating to 800 ℃ at the speed of 10 ℃/min, preserving heat for 1h, heating to 1500 ℃ at the speed of 5 ℃/min, preserving heat for 2h, applying the pressure of 50MPa in the sintering process, cooling to room temperature along with the furnace to obtain the large-grain UO₂A ceramic fuel.

Example 10

Will 100gUO₂Powder and 0.3g of metal chromium powder (the particle size is 10-30 mu m, and the addition amount is UO)₂0.3 percent of the mass fraction) of the powder is placed in a tungsten carbide ball milling tank, zirconia grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 11g of the mixed powder, placing the mixed powder into a graphite die for hot-pressing sintering, wherein the sintering process is as follows: vacuumizing to the vacuum degree of 0.1Pa, continuously introducing a mixed gas of hydrogen and carbon dioxide (the volume ratio of the carbon dioxide is 2.0%), heating to 800 ℃ at the speed of 10 ℃/min, preserving heat for 1h, heating to 1500 ℃ at the speed of 5 ℃/min, preserving heat for 4h, applying the pressure of 50MPa in the sintering process, cooling to the room temperature along with the furnace to obtain the large-grain UO₂A ceramic fuel.

Example 11

Will 100gUO₂Powder and 0.5g of niobium metal powder (the particle size is 10-50 mu m, and the addition amount accounts for UO)₂0.5%) was placed in a tungsten carbide ball mill pot, and 3 times the mass of the resultant mixture was added with oxidationZirconium grinding balls are mixed for 16 hours to obtain mixed powder;

weighing 11g of the mixed powder, placing the mixed powder into a graphite die for hot-pressing sintering, wherein the sintering process is as follows: vacuumizing to the vacuum degree of 0.1Pa, continuously introducing a mixed gas of hydrogen and carbon dioxide (the volume ratio of the carbon dioxide is 2.0%), heating to 800 ℃ at the speed of 10 ℃/min, preserving heat for 1h, heating to 1400 ℃ at the speed of 5 ℃/min, preserving heat for 24h, applying the pressure of 50MPa in the sintering process, cooling to the room temperature along with the furnace to obtain the large-grain UO₂A ceramic fuel.

Example 12

Will 100gUO₂Powder and 0.25g niobium oxide powder (particle size 20-100 nm, addition amount of UO)₂0.25 percent) of the powder is placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 11g of the upper mixed powder, placing the upper mixed powder in a graphite die for hot-pressing sintering, wherein the sintering process is as follows: vacuumizing to the vacuum degree of 0.1Pa, continuously introducing a mixed gas of hydrogen and carbon dioxide (the volume ratio of the carbon dioxide is 2.0%), heating to 800 ℃ at the speed of 10 ℃/min, preserving heat for 1h, heating to 1500 ℃ at the speed of 5 ℃/min, preserving heat for 10h, applying the pressure of 50MPa in the sintering process, cooling to the room temperature along with the furnace to obtain the large-grain UO₂A ceramic fuel.

Example 13

Only the difference from example 10; the additive is titanium oxide powder with particle size of 30nm and added amount of UO₂0.25% of mass fraction; otherwise, the same procedure as in example 10 was repeated.

Example 14

The only difference from example 11 is: the additive is manganese oxide powder with the particle size of 100-300 nm and the addition amount of UO₂0.5 percent of the mass fraction.

Example 15

The only difference from example 10 is that: the additive is metal vanadium powder with the grain diameter of 74 mu m, and the addition amount is UO₂0.3% of mass fraction; vanadium oxide powder with particle size of 30-100 nm and addition amount of UO₂0.2% of mass fraction; otherwise, the same procedure as in example 10 was repeated.

Example 16

The only difference from example 10 is that: the additive is vanadium oxide powder with the particle size of 100-300 nm, and the addition amount of the additive is 0.5 percent of the mass fraction of UO 2; otherwise, the same procedure as in example 10 was repeated.

Example 17

Will 100gUO₂Powder and 0.5g of chromium oxide powder (the particle size is 5-10 mu m, and the addition amount is UO)₂0.5 percent of the mass fraction) of the powder is placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 6g of the mixed powder, placing the mixed powder in a graphite mold for spark plasma sintering, vacuumizing the graphite mold to 25Pa, and filling a mixed gas of argon and carbon dioxide (the volume ratio of the carbon dioxide is 1.0%) to 70 kPa; heating to 1500 deg.C at a rate of 100 deg.C/min, sintering under 30MPa, maintaining for 20min, cooling to room temperature to obtain large-grain UO₂A ceramic fuel.

Example 18

Will 100gUO₂Powder, 0.5g chromium powder (grain diameter 10-30 μm, addition amount is UO)₂0.5 percent of the mass fraction) of the powder is placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 6g of the mixed powder, placing the mixed powder in a graphite mold for spark plasma sintering, vacuumizing the graphite mold to 25Pa, and filling a mixed gas of argon and carbon dioxide (the volume ratio of the carbon dioxide is 1.0%) to 70 kPa; heating to 1600 deg.C at a rate of 100 deg.C/min, maintaining the sintering pressure at 30MPa for 20min, cooling to room temperature to obtain large-grain UO₂A ceramic fuel.

Example 19

Will 100gUO₂Powder, 0.4g titanium oxide powder (particle size 30nm, addition amount is UO)₂0.4 percent of the mass fraction) of the powder is placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 6g of the mixed powder, placing the mixed powder in a graphite mold for spark plasma sintering, vacuumizing the graphite mold to 25Pa, and filling argon and carbon dioxideThe mixed gas (the volume ratio of the carbon dioxide is 1.0 percent) is 70 kPa; heating to 1500 deg.C at a rate of 100 deg.C/min, sintering at 30MPa, maintaining for 30min, cooling to room temperature to obtain large-grain UO₂A ceramic fuel.

Example 20

Will 100gUO₂Powder, 0.5g manganese oxide powder (particle size 100-300 nm, addition amount is UO)₂0.5 percent of the mass fraction) of the powder is placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 6g of the mixed powder, placing the mixed powder in a graphite mold for spark plasma sintering, vacuumizing the graphite mold to 25Pa, and filling a mixed gas of argon and carbon dioxide (the volume ratio of the carbon dioxide is 1.0%) to 70 kPa; heating to 1700 ℃ at a temperature of 100 ℃/min, keeping the sintering pressure at 30MPa, keeping the temperature for 20min, and cooling to room temperature along with the furnace to obtain large-grain UO₂A ceramic fuel.

Example 21

Will 100gUO₂Powder, 0.25g niobium oxide powder (particle size 20-100 nm, addition amount is UO)₂0.25 percent of the mass fraction) of the powder is placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 6g of the mixed powder, placing the mixed powder in a graphite mold for spark plasma sintering, vacuumizing the graphite mold to 25Pa, and filling a mixed gas of argon and carbon dioxide (the volume ratio of the carbon dioxide is 1.0%) to 70 kPa; heating to 1600 deg.C at a rate of 100 deg.C/min, maintaining the sintering pressure at 30MPa for 30min, cooling to room temperature to obtain large-grain UO₂A ceramic fuel.

Example 22

Will 100gUO₂Powder and 0.5 metal niobium powder (particle size is 10-50 μm, addition amount is UO)₂0.5 percent of the mass fraction) of the powder is placed in a tungsten carbide ball milling tank, zirconium oxide grinding balls with the mass being 3 times that of the obtained mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 6g of the mixed powder, placing the mixed powder in a graphite mold for spark plasma sintering, vacuumizing the graphite mold to 25Pa, and filling argonThe gas and carbon dioxide mixed gas (the volume ratio of the carbon dioxide is 1.0 percent) is 70 kPa; heating to 1500 deg.C at a rate of 100 deg.C/min, sintering at 30MPa, maintaining for 30min, cooling to room temperature to obtain large-grain UO₂A ceramic fuel.

Example 23

The only difference from example 22 is that: the additive is metal vanadium powder with the grain diameter of 74 mu m, and the addition amount is UO₂The same as example 22 except that the amount of the polymer is 0.5% by mass.

Example 24

Will 100gUO₂Powder, 0.3g of metal vanadium powder (particle size 74 μm, addition amount is UO)₂0.3 percent of mass fraction), 0.2g of vanadium oxide powder (the particle diameter is 30-100 nm, and the addition amount is UO₂0.2 percent of the mass fraction) is placed in a tungsten carbide ball milling tank, zirconia grinding balls with the mass being 3 times that of the mixture are added, and the mixture is mixed for 16 hours to obtain mixed powder;

weighing 6g of the mixed powder, placing the mixed powder in a graphite mold for spark plasma sintering, vacuumizing the graphite mold to 25Pa, and filling a mixed gas of argon and carbon dioxide (the volume ratio of the carbon dioxide is 1.0%) to 70 kPa; heating to 1500 deg.C at a rate of 100 deg.C/min, sintering at 20MPa for 30min, cooling to room temperature to obtain large-grain UO₂A ceramic fuel.

Comparative example 1

The only difference from example 1 is: without addition of chromium oxide additives, conventional UO is obtained₂Ceramic fuel, the other examples are the same as example 1.

Comparative example 2

With pure UO₂The powder was used as comparative example 2.

Performance testing

1) Metallographic treatment was performed on the ceramic fuels prepared in examples 1, 2, 4, 17 and 20 and comparative examples 1 to 2, under the condition that silicon carbide sand paper was sequentially used for grinding, wherein the mesh numbers were 180 mesh, 500 mesh, 800 mesh, 1200 mesh and 2000 mesh, and the grinding time for each mesh number was 1 min; then polishing by using polishing cloth, and adding the diamond suspension intermittently for 4 times in 30s for 2 min; then the volume fraction is 1:1:1 (hydrogen peroxide: concentrated sulfuric acid: deionization)Water) to obtain ceramic fuel after metallographic treatment, and measuring different UOs after metallographic treatment by adopting an intercept point method according to standard GB/T6394 plus 2017 metal average grain size determination method₂The average grain size of the ceramic fuel, the measurement results are shown in table 1; the obtained metallographic photograph is shown in the figures 1-7; FIGS. 1 to 5 show the sequence of the large-grain UO prepared in examples 1, 2, 4, 17 and 20₂Metallographic pictures of ceramic fuels; 6-7 are metallographic photographs of the ceramic fuels of comparative example 1 and comparative example 2 in this order; wherein, the process sequence marked below the figure is sintering temperature, heat preservation time, sintering atmosphere and components; h₂(CO₂) Or Ar (CO)₂) Represents H₂Or mixing CO in Ar atmosphere₂A gas.

TABLE 1 average grain size of ceramic fuels prepared in examples 1, 2, 4, 17 and 20 and comparative examples 1-2

Case(s)	Sintering process	Composition (I)	Additive content	Average grain size
					Example 1	1700℃-4h-H2(CO2)	UO2(chromium oxide)	0.5wt.％	180μm
Examples2	1700℃-4h-H2(CO2)	UO2(chromium)	0.5wt.％	123μm
					Example 4	1700℃-4h-H2(CO2)	UO2(niobium oxide)	0.25wt.％	108μm
Example 17	1700℃-20min-Ar(CO2)	UO2(chromium oxide)	0.5wt.％	62μm
					Example 20	1700℃-20min-Ar(CO2)	UO2(manganese oxide)	0.5wt.％	52μm
Comparative example 1	1700℃-4h-H2(CO2)	UO2	--	18μm
					Comparative example 2	1700℃-20min-Ar(CO2)	UO2	--	12μm

As can be seen from Table 1 and FIGS. 1 to 7, the method of the present invention is based on addition of a grain growth promoter (additive) to UO₂The growth of crystal grains has promoting effect and can obviously increase UO₂Grain size of the ceramic fuel.

2) The large-grain UO prepared in example 1 was subjected to a thermal expansion tester manufactured by German Kaisha thermal analysis₂Ceramic fuel and conventional UO prepared in comparative example 1₂The thermal expansion coefficient of the ceramic fuel was measured, and the results are shown in FIG. 8, and the specific thermal expansion values are shown in Table 2.

TABLE 2 conventional UO₂With large grain UO₂(0.5wt.％Cr₂O₃) Thermal expansion value of

As is clear from FIG. 8 and Table 2, the large-grain UO prepared in example 1₂The ceramic fuel has a thermal expansion coefficient of 200-1200 ℃ higher than that of the conventional UO₂The reduction is 11.8-16.9%, which shows that the large-grain UO prepared by the invention₂Ceramic fuels have a low coefficient of expansion.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.