阅读说明：本技术 一种含碳化物-难熔金属包覆层的包覆燃料颗粒及其制备方法 (Coated fuel particle containing carbide-refractory metal coating and preparation method thereof ) 是由 刘荣正 程心雨 刘马林 邵友林 刘兵 于 2020-04-23 设计创作，主要内容包括：本发明实施例涉及核燃料领域,具体涉及一种含碳化物-难熔金属包覆层的包覆燃料颗粒及其制备方法。本发明实施例提供的包覆燃料颗粒,包括陶瓷燃料核芯及在所述陶瓷燃料核芯外依次包覆的疏松层、内过渡层、碳化物包覆层、外过渡层和难熔金属包覆层。本发明实施例提供的包覆燃料颗粒,为全新设计的引入了难熔金属包覆层的包覆燃料颗粒,为陶瓷-金属复合层结构,与金属基体的相容性好,热导率高,综合力学性能强,可抵抗塑性变形,抗摩擦磨损,并可在极高温下服役,拓宽了包覆燃料颗粒的应用领域,为下一代新型核能系统燃料元件的制备提供技术储备；并且,可简化包覆燃料颗粒弥散在基体中的制备过程。(The embodiment of the invention relates to the field of nuclear fuels, in particular to a coated fuel particle containing a carbide-refractory metal coating and a preparation method thereof. The coated fuel particle provided by the embodiment of the invention comprises a ceramic fuel core, and a loose layer, an inner transition layer, a carbide coating layer, an outer transition layer and a refractory metal coating layer which are sequentially coated outside the ceramic fuel core. The coated fuel particle provided by the embodiment of the invention is a brand-new coated fuel particle introduced with a refractory metal coating layer, has a ceramic-metal composite layer structure, has good compatibility with a metal matrix, high thermal conductivity and strong comprehensive mechanical property, can resist plastic deformation and friction and abrasion, can be used at a very high temperature, widens the application field of the coated fuel particle, and provides technical reserve for the preparation of a next-generation novel nuclear energy system fuel element; and, the preparation process of the coated fuel particles dispersed in the matrix can be simplified.)

1. A coated fuel particle, characterized by: the coated fuel particles comprise a ceramic fuel core, and a loose layer, an inner transition layer, a carbide coating layer, an outer transition layer and a refractory metal coating layer which are sequentially coated outside the ceramic fuel core.

2. The coated fuel particle of claim 1, wherein: the refractory metal coating layer comprises metal with a melting point more than or equal to 1650 ℃; the metal comprises one or more of zirconium, niobium, tantalum, titanium, molybdenum, vanadium, chromium and tungsten;

and/or the refractory metal coating layer has a thickness of 5-100 μm.

3. The coated fuel particle of claim 1, wherein: the loose layer comprises one or more of pyrolytic carbon or silicon carbide; the porosity of the loose layer is 30-70%, and the thickness is 20-150 μm;

and/or the inner transition layer comprises pyrolytic carbon or silicon carbide; the thickness of the inner transition layer is 5-50 μm;

and/or the carbide coating comprises one or more of silicon carbide, zirconium carbide, niobium carbide, tantalum carbide, titanium carbide, molybdenum carbide, vanadium carbide, chromium carbide or tungsten carbide; the thickness of the carbide coating layer is 5-200 mu m;

and/or, the outer transition layer comprises pyrolytic carbon; the thickness of the outer transition layer is 1-5 μm.

4. The coated fuel particle of claim 1, wherein: the ceramic fuel core comprises one or more of uranium oxide, uranium carbide, uranium oxycarbide, uranium nitride, thorium oxide, thorium carbide or thorium nitride; the ceramic core is a sphere with the diameter of 100-1200 mu m.

5. The method of producing coated fuel particles according to claim 1, characterized in that: the preparation method comprises the step of sequentially coating a loose layer, an inner transition layer, a carbide coating layer, an outer transition layer and a refractory metal coating layer outside a ceramic fuel core by adopting a fluidized bed chemical vapor deposition method.

6. The method of claim 5, wherein: the preparation method of the loose layer comprises the following steps: argon is taken as fluidizing gas, and acetylene or precursors containing carbon and silicon are coated with a loose layer at the temperature of 800-1450 ℃, wherein the coating time is 30-1200 s;

and/or the preparation method of the inner transition layer comprises the following steps: controlling the temperature of the fluidized bed reactor to be 1100-1400 ℃, introducing acetylene and propylene gas or a precursor containing carbon and silicon elements to coat the inner transition layer, wherein the coating time is 30-1500 s;

and/or the preparation method of the carbide coating layer comprises the following steps: heating a halogen compound precursor raw material, taking hydrogen or argon as a carrier gas, taking hydrogen or a mixed gas of argon and hydrogen as a fluidizing gas, and carrying out chemical vapor deposition for 1-10h at the temperature of 1200-1800 ℃; when the halogen compound precursor has no carbon source, propylene is simultaneously introduced as a carbon source gas.

7. The method of claim 5, wherein: the preparation method of the outer transition layer comprises the following steps: controlling the temperature of the fluidized bed reactor at 1100-1400 ℃, and introducing acetylene or propylene gas to coat the outer transition layer for 1-20 s.

8. The method of claim 5, wherein: the preparation method of the refractory metal coating layer comprises the following steps: heating the metal halide raw material, taking hydrogen or argon as a carrier gas, taking hydrogen or a mixed gas of argon and hydrogen as a fluidizing gas, and carrying out chemical vapor deposition for 0.5-10h at the temperature of 500-1600 ℃.

9. A fuel element, characterized by: the fuel element comprises a fuel region and a fuel-free region; the fuel region comprising the coated fuel particle of claim 1 and a substrate;

optionally, the volume fraction of the encapsulated fuel particles in the fuel zone is between 30% and 70%.

10. A method of manufacturing a fuel element according to claim 9, wherein: the preparation method comprises the following steps: dispersing the coated fuel particles of claim 1 in a matrix to obtain a fuel zone; the fuel area is directly arranged in the metal cavity and is packaged to obtain the fuel element, or the outside of the fuel area is coated with matrix powder, pressed and sintered to obtain the fuel element.

Technical Field

The invention relates to the field of nuclear fuels, in particular to a coated fuel particle containing a carbide-refractory metal coating and a preparation method thereof.

Background

The high-temperature gas cooled reactor with inherent safety is one of the fourth generation advanced reactor types, and the important guarantee of the safety is to use all-ceramic type coated fuel particles to restrain various gas and solid fission products. The full-ceramic coated fuel particle comprises a nuclear fuel core, and a loose pyrolytic carbon layer, an inner compact pyrolytic carbon layer, a silicon carbide layer and an outer compact pyrolytic carbon layer which are sequentially coated outside the nuclear fuel core. The successful application of the coated fuel particles in the high-temperature gas cooled reactor also proves the important potential of the coated fuel particles in other nuclear energy systems, and the coated fuel particles are expected to be used in other reactor type commercial nuclear power stations and nuclear power propulsion systems in important scenes such as air, deep sea and the like.

In a fuel element comprising coated fuel particles, the performance index of the coated fuel particles themselves and the compatibility with a base material are important factors that restrict practical use thereof. At present, the coating fuel particles are successfully dispersed in a graphite matrix to obtain a spherical or columnar fuel element and dispersed in a silicon carbide matrix to obtain a full ceramic micro-packaging type fuel form. The metal matrix has the outstanding advantages of good mechanical property, good thermal conductivity and the like, but because the coated fuel particles are all-ceramic coating layers, the strength of the outer compact pyrolytic carbon layer is not high, and the whole particles are easy to damage in the pressure forming process; meanwhile, the outer layer of pyrolytic carbon is a sintered inert material, and has poor compatibility with a heterogeneous matrix, particularly a metal matrix, so that the application and popularization of the coated fuel particles are limited.

In order to realize the wider application of the coated fuel particles in a new generation nuclear energy system in the future, further consolidate the safety of the system and ensure the larger safety margin under the accident condition, the development of novel coated fuel particles which have good compatibility with metal matrix materials, high thermal conductivity and certain brittle fracture resistance is needed.

The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Disclosure of Invention

Object of the Invention

In order to solve the problems that the existing all-ceramic coated fuel particles are easy to damage in pressure forming, have low compatibility with a metal matrix and the like, the invention provides novel coated fuel particles containing carbide-refractory metal coating layers and a preparation method thereof. The coated fuel particle provided by the embodiment of the invention is a brand-new coated fuel particle introduced with a refractory metal coating, has a ceramic-metal composite layer structure, has good compatibility with a metal matrix, high thermal conductivity and strong comprehensive mechanical property, can resist plastic deformation and friction and abrasion, can be used at a very high temperature, widens the application field of the coated fuel particle, and provides technical reserve for the preparation of a next-generation novel nuclear energy system fuel element. In addition, when the coated fuel particles provided by the embodiment of the invention are used for preparing the fuel element, the preparation process of dispersing the coated fuel particles in the matrix can be simplified.

Solution scheme

To achieve the purpose of the present invention, the embodiment of the present invention provides a coated fuel particle, which includes a ceramic fuel core, and a loose layer, an inner transition layer, a carbide coating layer, an outer transition layer and a refractory metal coating layer which are sequentially coated outside the ceramic fuel core. The inner transition layer is a transition layer between the loose layer and the carbide coating layer and is used for providing a good transition interface between the loose layer and the carbide coating layer and preventing the stress mismatch between the loose layer and the carbide coating layer; the outer transition layer is a transition layer between the carbide coating layer and the refractory metal coating layer for depositing the refractory metal.

In one possible implementation of the above coated fuel particle, the refractory metal coating comprises a metal having a melting point of greater than or equal to 1650 ℃; optionally, the metal comprises one or more of zirconium, niobium, tantalum, titanium, molybdenum, vanadium, chromium, tungsten. The refractory metal coating is an environmental contact layer that coats the fuel particles. The refractory metal has extremely high melting point and can be applied to extremely high service environment (higher than 1600 ℃). And it has a low neutron absorption cross section, suitable for nuclear fuel use; the high-temperature mechanical property is excellent, and the mechanical property requirement of the fuel element can be met; meanwhile, the friction and abrasion resistant effect is good.

In one possible implementation of the above coated fuel particle, the refractory metal coating has a thickness of 5 to 100 μm. A thinner refractory metal coating may be achieved if compatibility with the substrate is only considered, but the thickness of the refractory metal coating may be further specifically selected based on the thickness of the carbide coating, the substrate material, and the service environment. For example, when the carbide coating layer is thinner as a structural support layer, the thickness of the refractory metal coating layer can be increased accordingly; if further improvement in resistance to plastic deformation is desired, the thickness can be increased accordingly.

In one possible implementation of the above coated fuel particle, the ceramic fuel core comprises one or more of uranium oxide, uranium carbide, uranium oxycarbide, uranium nitride, thorium oxide, thorium carbide, or thorium nitride; the ceramic core is a sphere with the diameter of 100-1200 mu m.

In one possible implementation of the above coated fuel particle, the porous layer comprises one or more of pyrolytic carbon or silicon carbide; optionally, the porosity of the porous layer is 30-70% and the thickness is 20-150 μm.

In one possible implementation of the above coated fuel particle, the inner transition layer comprises pyrolytic carbon or silicon carbide; optionally, the inner transition layer is pyrolytic carbon.

In one possible implementation of the above coated fuel particle, the thickness of the inner transition layer is 5 to 50 μm.

In one possible implementation of the above coated fuel particle, the carbide coating comprises one or more of silicon carbide, zirconium carbide, niobium carbide, tantalum carbide, titanium carbide, molybdenum carbide, vanadium carbide, chromium carbide, or tungsten carbide; optionally, the carbide coating has a thickness of 5-200 μm. The carbide coating is a structural support layer that coats the fuel particles. In the coated fuel particle of the present invention, the material of the carbide coating layer may be selected from a wide variety of materials, such as carbide materials that are more resistant to high temperatures.

In one possible implementation of the above-described coated fuel particle, the outer transition layer comprises pyrolytic carbon.

In one possible implementation of the above coated fuel particle, the thickness of the outer transition layer is 1 to 5 μm.

The embodiment of the invention also provides a preparation method of the coated fuel particle, and the preparation method adopts a fluidized bed chemical vapor deposition method to coat the ceramic fuel core with the loose layer, the inner transition layer, the carbide coating layer, the outer transition layer and the refractory metal coating layer in sequence.

In one possible implementation manner, the preparation method of the loose layer comprises the following steps: argon is used as fluidizing gas, and acetylene or precursors containing carbon and silicon are coated on the loose layer at the temperature of 800-1450 ℃, wherein the coating time is 30-1200 s.

In one possible implementation manner, the preparation method of the internal transition layer comprises the following steps: controlling the temperature of the fluidized bed reactor at 1100-1400 ℃, and introducing acetylene and propylene gas or precursors containing carbon and silicon elements to coat the inner transition layer, wherein the coating time is 30-1500 s.

In one possible implementation manner, the preparation method of the carbide coating layer comprises the following steps: heating a halogen compound precursor raw material, taking hydrogen or argon as a carrier gas, taking hydrogen or a mixed gas of argon and hydrogen as a fluidizing gas, and carrying out chemical vapor deposition for 1-10h at the temperature of 1200-1800 ℃; when the halogen compound precursor has no carbon source, propylene is simultaneously introduced as a carbon source gas.

In one possible implementation manner, the preparation method of the outer transition layer comprises the following steps: controlling the temperature of the fluidized bed reactor at 1100-1400 ℃, and introducing acetylene or propylene gas to coat the outer transition layer for 1-20 s.

In one possible implementation manner, the preparation method of the refractory metal coating layer comprises the following steps: heating the metal halide raw material, taking hydrogen or argon as a carrier gas, taking hydrogen or a mixed gas of argon and hydrogen as a fluidizing gas, and carrying out chemical vapor deposition for 0.5-10h at the temperature of 500-1600 ℃.

Embodiments of the present invention also provide a fuel element, which includes a fuel region and a fuel-free region; the fuel zone comprises the coated fuel particles and a matrix; optionally, the substrate is a metal.

In one possible implementation of the above fuel element, the volume fraction of the encapsulated fuel particles in the fuel region is 30% to 70%. With the coated fuel particles of the present invention comprising a refractory metal coating, the volume fraction of the coated fuel particles is high, i.e. the loading is high.

The embodiment of the invention also provides a preparation method of the fuel element, which comprises the following steps: burning and dispersing the coated fuel particles in a matrix to obtain a fuel area; the fuel area is directly arranged in the metal cavity and is packaged to obtain the fuel element, or the outside of the fuel area is coated with matrix powder, pressed and sintered to obtain the fuel element.

Advantageous effects

(1) The coated fuel particle provided by the embodiment of the invention is a brand-new coated fuel particle introduced with a refractory metal coating, has a ceramic-metal composite layer structure, has good compatibility with a metal matrix, high thermal conductivity and strong comprehensive mechanical property, can resist plastic deformation and friction and abrasion, can be used at a very high temperature, widens the application field of the coated fuel particle, and provides technical reserve for the preparation of a next-generation novel nuclear energy system fuel element.

In addition, when the coated fuel particles provided by the embodiment of the invention are used for preparing the fuel element, the preparation process of dispersing the coated fuel particles in the matrix can be simplified. The traditional coating fuel particles with the outer layer made of pyrolytic carbon or other carbides need to be sintered with a base material, but the carbide ceramic material is extremely difficult to be sintered, so that the prepared material has a porous structure and is difficult to form a high-strength pellet; in addition, a part of the sintering process also needs pressure, and the addition of the pressure is easy to cause the breakage of the coated particles. However, the outer layer of the coated particles is metal, a preparation process of the metal can be adopted when the coated particles are dispersed in a matrix, solid solution is easily formed between the metal and the metal, and the sintering difficulty can be reduced to a certain extent; the metal has good shaping and lower requirement on the pressurizing process; in addition, the metal has good electrical conductivity and thermal conductivity, and is beneficial to rapid forming during sintering.

(2) The coated fuel particles provided by the embodiment of the invention further optimize the design of each layer, weaken the functions of the inner and outer compact pyrolytic carbon layers of the existing coated fuel particles by designing the inner transition layer and the outer transition layer, and are beneficial to reducing the overall diameter of the particles. The inner transition layer is used for providing a good transition interface between the loose layer and the carbide coating layer, so that the stress mismatching of the loose layer and the carbide coating layer is prevented, the high density is not required, and the density is only between the loose layer and the carbide coating layer; nor too thick. The outer transition layer is used for making refractory metal easier to deposit, and does not need high density or thicker.

(3) The preparation method of the coated fuel particles provided by the embodiment of the invention has the advantages of convenient and fast process operation and coherent process flow, can continuously realize multilayer coating in a vertical fluidized bed, and is favorable for industrial mass production.

(4) According to the fuel element provided by the embodiment of the invention, the volume fraction of the fuel particles covered in the fuel area is large, and the filling amount is high.

Drawings

One or more embodiments are illustrated by the corresponding figures in the drawings, which are not meant to be limiting. The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

FIG. 1 is a schematic structural view of a coated fuel particle according to example 1 of the present invention.

FIG. 2 is a scanning electron micrograph of the silicon carbide and zirconium metal layers of the coated fuel particles obtained in example 1 of the present invention.

FIG. 3 is an energy spectrum of a zirconium layer of a coated fuel particle obtained in example 1 of the present invention.

FIG. 4 is a schematic structural view of a fuel element according to example 4 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. 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. Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.

Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a better understanding of the present invention. It will be understood by those skilled in the art that the present invention may be practiced without some of these specific details. In some embodiments, materials, elements, methods, means, and the like that are well known to those skilled in the art are not described in detail in order to not unnecessarily obscure the present invention.