阅读说明：本技术 一种二氧化铀-类石墨烯复合燃料芯块的制备方法 (Preparation method of uranium dioxide-graphene-like composite fuel pellet ) 是由 马浩然 张燕 朱礼洋 杨志红 杨素亮 田国新 郭波龙 隋政 冯海宁 于 2020-12-17 设计创作，主要内容包括：本发明属于核燃料制备技术领域,涉及一种二氧化铀-类石墨烯复合燃料芯块的制备方法。所述的制备方法包括如下步骤：(1)将聚丙烯腈用溶剂溶解后加入二氧化铀粉末,混合均匀后得到中间体；(2)蒸发中间体除去溶剂后得到二氧化铀-聚丙烯腈混合粉末；(3)将二氧化铀-聚丙烯腈混合粉末装入模具冷压成型,脱模,得到燃料芯块素坯；(4)将燃料芯块素坯在还原性气氛下进行烧结,得到二氧化铀-类石墨烯复合燃料芯块。利用本发明的二氧化铀-类石墨烯复合燃料芯块的制备方法,能够制备得到高导热性的新型复合燃料芯块,从而提高核反应堆运行时的经济性和安全性。(The invention belongs to the technical field of nuclear fuel preparation, and relates to a preparation method of a uranium dioxide-graphene composite fuel pellet. The preparation method comprises the following steps: (1) dissolving polyacrylonitrile by using a solvent, adding uranium dioxide powder, and uniformly mixing to obtain an intermediate; (2) evaporating the intermediate to remove the solvent to obtain uranium dioxide-polyacrylonitrile mixed powder; (3) loading the uranium dioxide-polyacrylonitrile mixed powder into a mould for cold press molding, and demoulding to obtain a fuel pellet biscuit; (4) and sintering the fuel pellet biscuit in a reducing atmosphere to obtain the uranium dioxide-graphene composite fuel pellet. By using the preparation method of the uranium dioxide-graphene composite fuel pellet, the novel composite fuel pellet with high thermal conductivity can be prepared, so that the economy and the safety of a nuclear reactor during operation are improved.)

1. A preparation method of a uranium dioxide-graphene composite fuel pellet is characterized by comprising the following steps:

(1) dissolving polyacrylonitrile by using a solvent, adding uranium dioxide powder, and uniformly mixing to obtain an intermediate;

(2) evaporating the intermediate to remove the solvent to obtain uranium dioxide-polyacrylonitrile mixed powder;

(3) loading the uranium dioxide-polyacrylonitrile mixed powder into a mould for cold press molding, and demoulding to obtain a fuel pellet biscuit;

(4) and sintering the fuel pellet biscuit in a reducing atmosphere to obtain the uranium dioxide-graphene composite fuel pellet.

2. The method of claim 1, wherein: in the step (1), the solvent is one or more selected from dimethylformamide, N-dimethylformamide and dimethyl sulfoxide.

3. The method of claim 1, wherein: in the step (1), the mass-to-volume ratio of the polyacrylonitrile to the solvent is 1-10g:100 ml.

4. The method of claim 1, wherein: in the step (1), the mass ratio of the polyacrylonitrile to the uranium dioxide powder is 0.3-20: 1000.

5. The method of claim 1, wherein: in the step (1), the dissolving temperature is 30-80 ℃.

6. The method of claim 1, wherein: in the step (1), the average grain diameter of the uranium dioxide powder is 0.1-10 μm.

7. The method of claim 1, wherein: in the step (2), the evaporation is reduced pressure evaporation, the pressure of the reduced pressure evaporation is 0.001-0.1Mpa, and the temperature is 40-110 ℃.

8. The method of claim 1, wherein: in the step (3), the pressure of the cold press molding is 300-800MPa, and the pressure maintaining time is 20-60 s.

9. The method of claim 1, wherein: in the step (4), the volume ratio of hydrogen to argon in the reducing atmosphere is 0.1-5: 95.

10. The method of claim 1, wherein: in the step (4), the sintering temperature is 1400-1850 ℃ and the time is 1-5 h.

Technical Field

The invention belongs to the technical field of nuclear fuel preparation, and relates to a preparation method of a uranium dioxide-graphene composite fuel pellet.

Background

UO₂High melting point and small radiation swelling, so worldwide, UO₂The pellet-Zr clad is the most prominent fuel system for commercial pressurized water reactors. But UO₂Low thermal conductivity, so that UO₂the-Zr fuel system generates larger temperature gradient in the operation process, so that thermal stress is generated in the pellets, the thermal stability of the pellets is reduced, and in extreme cases, the central temperature of the fuel pellets is too high, and even cladding breakage and core melting can be caused.

Since the nuclear accident of fukushima, japan, the development of advanced nuclear fuels, particularly nuclear fuel pellets having high thermal conductivity characteristics, has become a new focus of international research.

Korean related research has proposed a metallic Mo-UO₂The results of the preparation method of the composite fuel pellet show that Mo is in UO₂The latticed heat conduction channels can be formed in the matrix, so that the heat conductivity of the composite fuel pellet is greatly increased. Related research in the United states has proposed a diamond-UO₂The research shows that the composite fuel pellet prepared by doping 10 wt% of diamond powder has a thermal conductivity improving effect of 30% of the total weight of the composition. Related researches in China also provide a method for preparing the composite fuel pellet by doping beryllium oxide, acetylene black or graphene, and in the research scope, obvious improvement of thermal conductivity is observed.

However, the disadvantages of the common technical characteristics include: firstly, the doping amount is large, which can cause the uranium loading amount of the fuel pellet and the pellet density to be obviously reduced; second, the doping phase is in UO₂Problems of uniform dispersion within the matrix. Therefore, the search and development of new doping materials and processes can bring about breakthrough progress.

Polyacrylonitrile (PAN) based carbon fiber materials are novel thin, light and strong high-thermal-conductivity carbon fiber materials, are excellent fiber reinforcement materials, and have wide application in the fields of aviation, aerospace, automobiles and the like.

Disclosure of Invention

The invention aims to provide a preparation method of a uranium dioxide-graphene-like composite fuel pellet, which can be used for preparing a novel composite fuel pellet with high thermal conductivity, so that the economy and the safety of a nuclear reactor during operation are improved.

To achieve the object, in a basic embodiment, the present invention provides a method for preparing a uranium dioxide-based graphene composite fuel pellet, the method comprising the steps of:

(1) dissolving Polyacrylonitrile (PAN) with a solvent, adding uranium dioxide powder, and uniformly mixing to obtain an intermediate;

(2) evaporating the intermediate to remove the solvent to obtain uranium dioxide-polyacrylonitrile mixed powder;

(3) loading the uranium dioxide-polyacrylonitrile mixed powder into a mould for cold press molding, and demoulding to obtain a fuel pellet biscuit;

(4) and sintering the fuel pellet biscuit in a reducing atmosphere to obtain the uranium dioxide-graphene composite fuel pellet.

In a preferred embodiment, the invention provides a preparation method of a uranium dioxide-based graphene composite fuel pellet, wherein in the step (1), the solvent is one or more selected from dimethylformamide, N-dimethylformamide and dimethyl sulfoxide.

In a preferred embodiment, the invention provides a preparation method of a uranium dioxide-graphene-like composite fuel pellet, wherein in the step (1), the mass volume ratio of polyacrylonitrile to the solvent is 1-10g:100 ml.

In a preferred embodiment, the invention provides a preparation method of a uranium dioxide-based graphene composite fuel pellet, wherein in the step (1), the mass ratio of polyacrylonitrile to uranium dioxide powder is 0.3-20: 1000.

In a preferred embodiment, the present invention provides a method for preparing uranium dioxide-based graphene composite fuel pellets, wherein the dissolution temperature in step (1) is 30 to 80 ℃.

In a preferred embodiment, the present invention provides a method for preparing a uranium dioxide-based graphene composite fuel pellet, wherein in the step (1), the average particle diameter of the uranium dioxide powder is 0.1 to 10 μm.

In a preferred embodiment, the invention provides a preparation method of the uranium dioxide-type graphene composite fuel pellet, wherein in the step (2), the evaporation is reduced pressure evaporation, the pressure of the reduced pressure evaporation is 0.001-0.1Mpa, and the temperature is 40-110 ℃.

In a preferred embodiment, the invention provides a preparation method of the uranium dioxide-graphene-like composite fuel pellet, wherein in the step (3), the pressure of cold press molding is 300-800Mpa, and the dwell time is 20-60 s.

In a preferred embodiment, the invention provides a preparation method of the uranium dioxide-graphene-like composite fuel pellet, wherein in the step (4), the volume ratio of hydrogen to argon in the reducing atmosphere is 0.1-5: 95.

In a preferred embodiment, the invention provides a preparation method of the uranium dioxide-graphene-like composite fuel pellet, wherein in the step (4), the sintering temperature is 1400-1850 ℃ and the time is 1-5 h.

The preparation method has the beneficial effects that the novel composite fuel pellet with high thermal conductivity can be prepared by using the preparation method of the uranium dioxide-graphene composite fuel pellet, so that the economy and the safety of a nuclear reactor during operation are improved.

The invention takes Polyacrylonitrile (PAN) as a raw material, generates a graphene-like carbon fiber material in situ in the sintering process of pellet preparation, and dopes the carbon fiber material as a second phase to UO₂In the pellet, the process is simple and convenient, the efficiency is high, the economy is good, and the performance of the prepared composite fuel pellet is good.

The invention is in UO₂Polyacrylonitrile (PAN) material is uniformly attached to the surfaces of the fuel particles, and the PAN incorporation amount is less. After cold press molding, PAN is uniformly dispersed in UO₂In the matrix; during the fuel sintering process, the PAN can generate a qualitative chemical change to generate a graphene-like material, and the graphene-like material is uniformly distributed in the fuel pellet core.

Therefore, the method can prepare the UO based on the PAN carbon fiber with high uranium loading capacity and high thermal conductivity₂The fuel pellet meets the technical conditions of the existing reactor fuel pellet and can be used as a novel nuclear reactor fuel pellet.

Detailed Description

The following examples further illustrate specific embodiments of the present invention.

Example 1: preparation of uranium dioxide-graphene-like composite fuel pellet

(1) Preparation of PAN-N, N-Dimethylformamide (DMF) solution

Weighing 0.4g of PAN powder, measuring 20ml of DMF solvent, pouring the PAN powder into DMF, fully stirring, and heating the container to 40 ℃ to promote the dissolution of PAN until the PAN powder is completely dissolved in the DMF.

(2) Preparation of UO₂-PAN-DMF intermediate

Weighing UO₂100g of powder (average particle diameter: 2 μm) was poured into the PAN-DMF solution obtained in step (1), and thoroughly mixed and stirred to obtain UO₂-PAN-DMF intermediate.

(3) Preparation of UO₂-PAN Mixed powder

The UO obtained in the step (2)₂-PAN-DMVacuum evaporating the intermediate F, and evaporating DMF at 80 deg.C to obtain UO₂-PAN mixed powder.

(4) Preparation of Fuel pellet biscuit

And (3) taking 10g of the mixed powder obtained in the step (3), placing the mixed powder in a forming die, carrying out cold press forming under the pressure of 500Mpa for 30s, and demoulding to obtain the fuel pellet biscuit.

(5) Preparation of Fuel pellets

Heating the fuel pellet biscuit obtained in the step (4) to 1750 ℃, preserving heat for 4 hours, and sintering in Ar-5% (v/v) H atmosphere₂Mixed gas is sintered to obtain UO based on PAN carbon fiber₂-graphene-like fuel pellets.

Example 2: UO₂Analytical testing of-PAN Mixed powder and uranium dioxide-graphene-like composite Fuel pellets

UO prepared in example 1₂PAN mixed powder and uranium dioxide-based graphene composite fuel pellets were tested as follows:

(1) powder specific surface area measurement

According to GB/T11847 + 2008 BET volumetric method for determining specific surface area of uranium dioxide powder, raw material UO is subjected to₂Powder and preparation of UO₂The specific surface area of the PAN mixed powder is 3.01m²In g, the latter is 3.79m²/g。

(2) Powder oxygen-uranium atomic ratio detection

According to GB/T11842-89 thermogravimetry for determining atomic ratio of uranium oxide to uranium dioxide powder and pellet, for raw material UO₂Powder and preparation of UO₂The PAN mixed powder was tested for the atomic ratio of oxygen to uranium of 2.12 for the former and 2.09 for the latter.

(3) Uranium dioxide-graphene-like composite fuel pellet appearance detection

According to EJ/T787-93 & lt inspection method for the physical dimension and roughness of sintered uranium dioxide, the appearance of the prepared uranium dioxide-graphene composite fuel pellet is inspected, and the composite fuel pellet is gray black and has no phenomena of cracking, corner falling and the like.

(4) Fuel pellet thermal conductivity detection

Selecting raw material UO₂Powder as a single starting Material starting with UO as the starting material, analogous to the experimental procedure in step (4) of example 1₂Powder compaction to UO₂Fuel pellet biscuit, again analogous to the experimental procedure in step (5) of example 1, UO₂And further sintering the fuel pellet biscuit to obtain the uranium dioxide fuel pellet. The thermal conductivity of the uranium dioxide fuel pellet and the uranium dioxide-graphene composite fuel pellet obtained in example 1 was measured by the laser flash method specified in GB/T5598-2015 beryllium oxide ceramic thermal conductivity measurement method, and as a result, the former was 0.9W/m K and the latter was 1.6W/m K at 1000 ℃.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations. The foregoing examples or embodiments are merely illustrative of the present invention, which may be embodied in other specific forms or in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. The scope of the invention should be indicated by the appended claims, and any changes that are equivalent to the intent and scope of the claims should be construed to be included therein.