阅读说明：本技术 一种SiC基UCO核芯燃料芯块制备方法 (Preparation method of SiC-based UCO core fuel pellet ) 是由 刘文涛 隋政 郭波龙 梁方知 张靖雪 张宇 孟莹 于 2020-12-30 设计创作，主要内容包括：本发明属于SiC基核燃料芯块制备技术领域,具体涉及一种SiC基UCO核芯燃料芯块制备方法。将U-3O-8粉缓慢加入浓硝酸和去离子水的混合溶液中,将硝酸铀酰和尿素配置为增稠剂,向混合溶液加入增稠剂,静置后通过分散头进行分散凝胶制备UO-3/C凝胶球,再进行陈化、洗涤和干燥去除杂质和水分,最终在CO气氛中焙烧制备得到UO-2+UC-2的UCO微球；流化包覆制备得到的UCO包覆颗粒与SiC粉末混合均匀,选用钢模将混合粉末冷压成生坯,将生坯封装入热压模具中真空下进行热压烧结,烧结结束后取出热压模具将芯块取出,将外观进行打磨后得到成品芯块。制得芯块在密度、尺寸、热物理性能、力学性能等堆外性能测试方面均能达到入堆芯块技术条件要求。(The invention belongs to the technical field of preparation of SiC-based nuclear fuel pellets, and particularly relates to a preparation method of a SiC-based UCO core fuel pellet. Will U 3 O 8 Slowly adding the powder into a mixed solution of concentrated nitric acid and deionized water, preparing uranyl nitrate and urea into a thickening agent, adding the thickening agent into the mixed solution, standing, and dispersing gel through a dispersion head to prepare UO 3 Aging, washing and drying the/C gel balls to remove impurities and moisture, and finally roasting in a CO atmosphere to obtain UO 2 +UC 2 The UCO microspheres of (a); uniformly mixing UCO coating particles prepared by fluidization coating with SiC powder, selecting a steel die to cold press the mixed powder into a green body, packaging the green body into a hot pressing die to carry out hot pressing sintering under vacuum, taking out the hot pressing die after sintering is finished to take out the core block, and polishing the appearance to obtain a finished productAnd (3) a core block. The prepared core block can meet the requirements of the reactor core block technical conditions in the aspects of testing the out-of-reactor performance such as density, size, thermal physical property, mechanical property and the like.)

1. A preparation method of a SiC-based UCO core fuel pellet is characterized by comprising the following steps: will U₃O₈Slowly adding the powder into a mixed solution of concentrated nitric acid and deionized water, preparing uranyl nitrate and urea into a thickening agent, adding the thickening agent into the mixed solution, standing, and dispersing gel through a dispersion head to prepare UO₃Aging, washing and drying the/C gel balls to remove impurities and moisture, and finally roasting in a CO atmosphere to obtain UO₂+UC₂The UCO microspheres of (a); and uniformly mixing UCO coating particles obtained by fluidized coating preparation with SiC powder, selecting a steel die to carry out cold pressing on the mixed powder to obtain a green body, packaging the green body into a hot pressing die to carry out hot pressing sintering under vacuum, taking out the hot pressing die after sintering is finished to take out the pellets, and polishing the appearance to obtain finished pellets.

2. The method of preparing SiC-based UCO core fuel pellets according to claim 1, characterized in that: 1000gU₃O₈The powder was slowly added to a mixed solution of 440mL concentrated nitric acid and 835mL deionized water.

3. The method of preparing SiC-based UCO core fuel pellets according to claim 1, characterized in that: 100ml of uranyl nitrate and 37.8g of urea were formulated as a thickener.

4. The method of preparing SiC-based UCO core fuel pellets according to claim 1, characterized in that: the thickener amount was 90g to the mixed solution.

5. The method of preparing SiC-based UCO core fuel pellets according to claim 1, characterized in that: 23G is selected for a dispersion head, the flow rate of glue solution is 12ml/min, and the vibration frequency is 100-120 Hz during dispersion to prepare UO₃and/C gel balls.

6. The method of preparing SiC-based UCO core fuel pellets according to claim 1, characterized in that: and (3) uniformly mixing the UCO coated particles prepared by fluidization coating with SiC powder according to the volume ratio of 41 percent of the coated particles.

7. The method of preparing SiC-based UCO core fuel pellets according to claim 1, characterized in that: and cold-pressing the mixed powder into a green body under the pressure of 60MPa by using an 8.2mm steel die.

8. The method of preparing SiC-based UCO core fuel pellets according to claim 1, characterized in that: and after sintering, taking out the hot-pressing die, and taking out the core block in a demoulding or disintegration mode.

9. The method of preparing SiC-based UCO core fuel pellets according to claim 1, characterized in that: and polishing the appearance by using sand paper to obtain a finished product core block.

Technical Field

The invention belongs to the technical field of preparation of SiC-based nuclear fuel pellets, and particularly relates to a preparation method of a SiC-based UCO core fuel pellet.

Background

The U.S. oak ridge national laboratory developed a UCO system microsphere dispersed fuel. The preparation of the microsphere adopts an inner gel process and a carbothermic reduction process. The prepared microspheres are used for preparing high-temperature gas cooled reactor fuel.

Disclosure of Invention

The invention aims to provide a preparation method of a SiC-based UCO core fuel pellet, which is mainly applied to the preparation of the SiC-based UCO core fuel pellet, and the prepared pellet can meet the requirements of reactor core pellet technical conditions in the aspects of out-of-reactor performance tests such as density, size, thermophysical property, mechanical property and the like.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a process for preparing SiC-base UCO core fuel pellet includes such steps as providing U₃O₈Slowly adding the powder into a mixed solution of concentrated nitric acid and deionized water, preparing uranyl nitrate and urea into a thickening agent, adding the thickening agent into the mixed solution, standing, and dispersing gel through a dispersion head to prepare UO₃Aging, washing and drying the/C gel balls to remove impurities and moisture, and finally roasting in a CO atmosphere to obtain UO₂+UC₂The UCO microspheres of (a); and uniformly mixing UCO coating particles obtained by fluidized coating preparation with SiC powder, selecting a steel die to carry out cold pressing on the mixed powder to obtain a green body, packaging the green body into a hot pressing die to carry out hot pressing sintering under vacuum, taking out the hot pressing die after sintering is finished to take out the pellets, and polishing the appearance to obtain finished pellets.

1000gU₃O₈The powder was slowly added to a mixed solution of 440mL concentrated nitric acid and 835mL deionized water.

100ml of uranyl nitrate and 37.8g of urea were formulated as a thickener.

The thickener amount was 90g to the mixed solution.

23G is selected for a dispersion head, the flow rate of glue solution is 12ml/min, and the vibration frequency is 100-120 Hz during dispersion to prepare UO₃and/C gel balls.

And (3) uniformly mixing the UCO coated particles prepared by fluidization coating with SiC powder according to the volume ratio of 41 percent of the coated particles.

And cold-pressing the mixed powder into a green body under the pressure of 60MPa by using an 8.2mm steel die.

And after sintering, taking out the hot-pressing die, and taking out the core block in a demoulding or disintegration mode.

And polishing the appearance by using sand paper to obtain a finished product core block.

The beneficial effects obtained by the invention are as follows:

the method can realize the preparation of the SiC-based UCO core fuel pellet, the prepared pellet can meet the requirements of the technical conditions of the reactor core pellet in the aspects of out-of-reactor performance tests such as density, size, thermal physical performance, mechanical performance and the like, and the prepared pellet is mainly applied to the fuel reactor corresponding to the technical conditions and meets the use standard of nuclear fuel elements.

Detailed Description

The present invention will be described in detail with reference to specific examples.

The method mainly comprises the key process methods of UCO core preparation, TRISO particle preparation, green body preparation, pellet sintering and the like.

The preparation process of the UCO core is to carry out the preparation of the UCO core by an inner gel and carbothermic reduction process, and the process flow is as follows: firstly, U is firstly₃O₈Slowly adding the powder into a mixed solution of concentrated nitric acid and deionized water to obtain a uranyl nitrate solution with the volume concentration of 33-40%; mixing (2.3-2.5) g of hexamethylenetetramine with 1g of urea to prepare a mixed solution of hexamethylenetetramine and urea; and adding the HMTA/urea mixed solution and the C powder into the prepared ADUN solution to prepare a glue solution, wherein the adding amount of the mixed solution is (50-65)% of the mass ratio of the total glue solution. Dispersing the mixed glue solution after standing by a dispersion head for gelation, wherein the dispersion head selects 23G, the glue solution flow is 12ml/min, and the vibration frequency is 100-120 Hz to prepare UO₃The gel balls are aged, washed and dried to remove impurities and waterRespectively, and finally roasting in CO atmosphere to prepare UO₂+UC₂The UCO microspheres of (1).

The sintering process is shown in Table 1

TABLE 1 UCO microsphere calcination Process

The preparation process of the TRISO particles refers to a UCO microsphere coating preparation process, wherein the UCO microsphere coating preparation process is to coat the surface of the UCO particles with a coating by adopting a fluidized bed-chemical vapor deposition technology. In the coating process, different atmospheres, coating temperatures and time are selected according to different coating layers, substances introduced into a furnace chamber are used for determining the coated substances, the decomposition rate and the deposition effect are controlled by adjusting the coating temperature, and the thickness, the density and the like of the coating layer are controlled by adjusting the coating time.

The preparation process of the green body comprises the steps of mixing SiC powder, coating and mixing SiC and TRISO particles and pressing the green body, wherein firstly, sintering aid powder with the impurity doping amount ratio of (3-7)% is uniformly mixed by a ball milling wet mixing mode to obtain matrix powder, the matrix powder and the TRISO particles are uniformly mixed by using a coating machine or the same principle method to obtain composite powder, a one-way press is matched with a steel die, and the composite powder filled into the steel die is made into the green body under the pressure of (45-70) MPa according to a preset pressing curve.

The core block sintering process is realized through a hot-pressing sintering process or an SPS sintering process, the prepared green body is packaged in a graphite mold, after the packaging is finished, the graphite mold is placed in a hot-pressing sintering furnace (1650-1750) DEG C or an SPS sintering furnace (1750-1850) DEG C to be sintered under a protective atmosphere or vacuum, and the sintering process is shown in Table 2. And after sintering, taking out the mold, taking out the core block in a demolding or disintegration mode, and polishing the appearance by using sand paper to obtain a finished product core block.

TABLE 2 UCO pellet sintering Process

The SiC-based UCO core fuel pellet prepared by the method can meet the requirements of reactor core pellet technical conditions in the aspects of out-of-reactor performance tests such as density, size, thermophysical properties, mechanical properties and the like.

1000gU₃O₈Slowly adding mixed solution of 440mL of concentrated nitric acid and 835mL of deionized water into the powder, preparing thickening agent by adding uranyl nitrate with the volume of 100mL and the adding amount of urea of 37.8G into the mixed solution, adding the thickening agent into the mixed solution with the adding amount of 90G, selecting a dispersion head with the volume of 23G, controlling the flow rate of glue solution to be 12mL/min, and preparing UO with the vibration frequency of 100-120 Hz during dispersion₃Aging, washing and drying the/C gel balls to remove impurities and moisture, and finally roasting in a CO atmosphere to obtain UO₂+UC₂The UCO microspheres of (1). The UCO coated particles prepared by fluidization coating are uniformly mixed with SiC powder according to the volume ratio of 41% vol of the coated particles, and are selectedAnd cold-pressing the mixed powder into a green body by using a steel die under the pressure of 60MPa, packaging the green body into a hot-pressing die, carrying out hot-pressing sintering under vacuum, taking out the die after sintering, taking out the core block by using a demolding or disintegration mode, and polishing the appearance by using sand paper to obtain the finished core block.

The method can realize the preparation of the SiC-based UCO core fuel pellet. The purpose of preparing the core block is achieved by several key process methods such as UCO core preparation, TRISO particle preparation, green body preparation, core block sintering and the like. The prepared pellet can meet the requirements of the reactor core block technical conditions in the aspects of out-of-reactor performance tests such as density, size, thermal physical properties, mechanical properties and the like, and the prepared pellet is mainly applied to fuel stacks corresponding to the technical conditions and meets the use standards of nuclear fuel elements.