CN113061033A - Graphite sphere for high-temperature gas cooled reactor and preparation method thereof - Google Patents
Graphite sphere for high-temperature gas cooled reactor and preparation method thereof Download PDFInfo
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Abstract
The embodiment of the invention relates to a graphite sphere for a high-temperature gas cooled reactor and a preparation method thereof. The preparation method of the graphite spheres for the high-temperature gas cooled reactor provided by the embodiment of the invention comprises the following steps: mixing petroleum coke, asphalt, natural flake graphite, carbon black and spherical coke, isostatic pressing, densification, graphitization, high-temperature purification and machining. The embodiment of the invention provides a brand-new method for preparing a graphite sphere (a false sphere) for a high-temperature gas-cooled reactor, the method has few steps and low cost, and the prepared graphite sphere for the high-temperature gas-cooled reactor has high density, high strength and good stability, completely meets the requirements of a nuclear reactor, and has longer service life in the reactor.
Description
Technical Field
The invention relates to the field of graphite preparation, in particular to graphite spheres for a high-temperature gas cooled reactor and a preparation method thereof.
Background
The high-temperature gas cooled reactor is a fourth-generation nuclear reactor which is developed and successfully built by Qinghua university and has completely independent intellectual property rights. The high-temperature gas cooled reactor takes 'all-ceramic' type coated granular fuel spheres as fuel elements, takes graphite as moderator and core structure material, and takes helium as coolant, and has good inherent safety.
The graphite sphere for the high-temperature gas-cooled reactor has a shape completely consistent with that of a spherical fuel element for the high-temperature gas-cooled reactor, except that the graphite sphere for the high-temperature gas-cooled reactor does not contain nuclear fuel and does not participate in the reactor core reaction, so that the fuel element for the high-temperature gas-cooled reactor is called a 'true sphere', and the graphite sphere for the high-temperature gas-cooled reactor is also called a 'false sphere'. In order to avoid excessive fuel in the high-temperature gas-cooled reactor in the early period of the high-temperature gas-cooled reactor and over severe reaction, a certain amount of dummy balls are required to be added during design, and the dummy balls are only added in the initial period of the operation of the high-temperature gas-cooled reactor to play roles in adjusting the internal reactivity of the reactor and transferring heat.
Two ways can be generally considered for preparing the artificial ball, one way is a preparation method for completely simulating a real ball, each step and parameter in the method can refer to the design of the real ball, but the method has multiple preparation steps and high cost. The other method is to use artificial graphite to prepare the artificial ball, the preparation steps of the method are few, the cost is low, but the graphite balls prepared by the traditional method can not meet the requirements of nuclear reactors.
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 limiting the invention.
Disclosure of Invention
Object of the Invention
In order to overcome the defects in the prior art, the invention aims to provide a graphite sphere for a high-temperature gas cooled reactor and a preparation method thereof. The preparation method of the graphite spheres for the high-temperature gas-cooled reactor provided by the embodiment of the invention provides a brand-new method for preparing the graphite spheres (dummy spheres) for the high-temperature gas-cooled reactor, the steps of the method are few, the cost is low, the density of the prepared graphite spheres for the high-temperature gas-cooled reactor is high, the strength is high, the stability is good, the requirements of a nuclear reactor are completely met, the service life in the reactor is longer, the imported dummy spheres can be completely replaced, the localization of the dummy spheres is realized, and the domestic blank is filled.
Solution scheme
In order to achieve the purpose of the present invention, an embodiment of the present invention provides a preparation method of graphite spheres for a high temperature gas cooled reactor, where the preparation method includes the following steps:
mixing materials: mixing the raw materials to obtain a mixed material; the mixed material comprises the following components in parts by weight: 50-60 parts of petroleum coke, 35-45 parts of asphalt, 2-5 parts of natural crystalline flake graphite, 1-3 parts of carbon black and 1-2 parts of spherical coke;
isostatic pressing: the mixed material is subjected to isostatic pressing for 100-150 minutes under the pressure of 130-150 MPa;
densification treatment: taking out the product after isostatic compaction, and performing densification treatment, wherein the densification treatment is a step of performing one or more times of roasting and one or more times of soaking until the bulk density of the product reaches 1.65g/cm3The above;
graphitization and high-temperature purification: graphitizing and purifying the densified product by using a high-temperature purification furnace, paving calcium fluoride at the bottom of the furnace during charging, and introducing carbon tetrachloride when the temperature is raised to 2300 ℃; continuously heating to 3100-; cooling to obtain a graphite product; after the temperature rises to a certain temperature, the calcium fluoride is decomposed into fluorine gas and calcium oxide, the fluorine gas is used for purification, and the calcium oxide contacts air at the bottom of the furnace to generate calcium hydroxide and calcium carbonate;
and (3) machining: and processing the graphite product to the diameter of 59.9-60.2mm to obtain graphite spheres for the high-temperature gas cooled reactor.
In one possible implementation mode, the mixed material comprises the following components in parts by weight: 55 parts of petroleum coke, 40 parts of asphalt, 3 parts of natural crystalline flake graphite, 1 part of carbon black and 1 part of spherical coke.
In a possible implementation mode, before mixing materials, petroleum coke and natural crystalline flake graphite are ground to the granularity D50 of 35-40 μm; grading the powder to remove the parts with larger and smaller particle sizes; is favorable for uniform mixing.
In one possible implementation, the true density of the petroleum coke is not less than 2.08g/cm3The ash content is not more than 0.25 percent, the volatile content is not more than 0.5 percent, the moisture content is not more than 0.5 percent, and the sulfur content is not more than 0.4 percent.
In one possible mode of realization, the asphalt has a softening point of 115 ℃ and 120 ℃, an ash content of not more than 0.25%, an coking value of not less than 58%, a moisture content of not more than 4.0%, a toluene insoluble content of not less than 32%, and a quinoline insoluble content of 9 to 12%.
In one possible implementation, the natural crystalline flake graphite has a volatile content of less than 0.25% and a true density of greater than or equal to 2.23g/cm3The water content is less than 0.20 percent, the ash content is less than 0.25 percent, and the fixed carbon content is more than or equal to 99.4 percent.
In one possible implementation, the carbon black has a specific surface area of 80 to 120m2Oil absorption of 90-100cc/100 and ash content of less than 0.4%.
In one possible implementation, the carbon black has a particle size of 0.05 to 0.1 μm.
In one possible implementation, the shot coke has a volatile content of 5 to 11% and a true density of 2.03 to 2.14g/cm3The water content is less than 0.35 percent, and the ash content is less than 0.4 percent.
In one possible implementation, the shot coke has a particle size D50 of 10-18 μm.
In a possible implementation manner, the steps of isostatic pressing the mixed material under the conditions of the pressure of 130-150MPa for 100-120 minutes are as follows: and putting the mixed material into a rubber sleeve, vacuumizing the rubber sleeve, sealing when the vacuum degree in the rubber sleeve reaches 0.06MPa, putting the rubber sleeve into an isostatic press, and carrying out isostatic pressing for 100-fold 120 minutes under the condition that the pressure is 130-fold 150 MPa.
In one possible implementation, in the densification step: the highest temperature of the roasting is 1000-; the pressure of the impregnation is 3.5MPa, and the impregnation pressurization time is 2-3 hours each time.
In one possible implementation mode, during graphitization and high-temperature purification, the dosage of calcium fluoride is 20-30kg and the dosage of carbon tetrachloride is 30-40kg per ton of graphite product.
The embodiment of the invention also provides the graphite spheres for the high-temperature gas cooled reactor, which are prepared by the preparation method.
In one possible implementation mode, the diameter of graphite spheres for the high-temperature gas cooled reactor is 59.9-60.2mm, and the density of the graphite spheres is 1.73-1.77g/cm3The total ash content is less than or equal to 50ppm, the lithium content is less than or equal to 0.05ppm, the total boron equivalent is less than or equal to 0.3ppm, the heat conductivity coefficient (1000 ℃) is more than or equal to 30W/(m.k), the abrasion rate (20 spheres, 100h) is less than or equal to 2 mg/(sphere.h), the crushing strength of graphite spheres is more than or equal to 20KN, the thermal expansion anisotropy (room temperature-400 ℃) is less than or equal to 1.3, the graphitization degree is more than or equal to 85%, and the surface has no notch defect with the length depth of 1 mm.
Advantageous effects
(1) The preparation method of the graphite spheres for the high-temperature gas-cooled reactor provided by the embodiment of the invention provides a brand-new method for preparing the graphite spheres (i.e. the dummy spheres) for the high-temperature gas-cooled reactor, the steps of the method are few, the cost is low, the density of the prepared graphite spheres for the high-temperature gas-cooled reactor is high, the strength is high, the stability is good, the requirements of a nuclear reactor are completely met, the service life in the reactor is longer, the imported dummy spheres can be completely replaced, the localization of the dummy spheres is realized, and the domestic blank is filled.
The preparation method takes petroleum coke, asphalt, natural crystalline flake graphite, carbon black and spherical coke in a specific proportion as raw materials, the petroleum coke is easy to graphitize, and the graphitization degree can be more than 90% under the condition of not very high temperature so as to ensure that the graphitization degree of the graphite spheres meets the design requirement; the addition of natural crystalline flake graphite, carbon black and spherical coke greatly improves the wear resistance, compression resistance and heat conductivity of graphite nodules, and the isotropy of the graphite nodules is better; the raw materials interact with each other, so that the prepared graphite nodule has excellent comprehensive performance.
(2) According to the preparation method of the graphite ball for the high-temperature gas-cooled reactor, provided by the embodiment of the invention, the raw materials are further selected, and the prepared graphite ball for the high-temperature gas-cooled reactor has the best performance under the optimal proportion.
During material mixing, the granularity D50 of the petroleum coke and the natural crystalline flake graphite is controlled to be 35-40 mu m, so that the material mixing is more uniform, and the quality of a finished product is more uniform.
(3) According to the preparation method of the graphite spheres for the high-temperature gas cooled reactor, provided by the embodiment of the invention, a large amount of researches are carried out on the used raw materials, the high-temperature purification is carried out by using calcium fluoride and carbon tetrachloride, the graphite can be purified to a nuclear purity level, the obtained graphite product is lower in impurity element content, boron element content and lithium element content, and the total boron equivalent of the obtained graphite (the content of other impurity elements is converted into the content of boron elements according to equivalent factors of the other impurity elements, and the sum of the boron equivalents of the elements is the total boron equivalent) is also lower. In a reactor, the total boron equivalent is an important parameter of a nuclear reactor material, and directly determines the reactivity of the reactor, because the area of a boron element for absorbing neutrons is the largest, the total boron equivalent exceeds the technical requirement, neutrons are excessively absorbed in the nuclear reaction process, and when the number of free neutrons is insufficient, the nuclear reaction is stopped.
(4) The preparation method of the graphite spheres for the high-temperature gas cooled reactor provided by the embodiment of the invention selects various parameters of the steps of material mixing, isostatic pressing, densification treatment, graphitization, high-temperature purification and machining, and the graphite spheres for the high-temperature gas cooled reactor prepared by the preparation method have good ash content and total boron equivalent, graphitization degree and heat conductivity coefficient effects.
(5) The graphite spheres for the high-temperature gas-cooled reactor prepared by the preparation method of the graphite spheres for the high-temperature gas-cooled reactor provided by the embodiment of the invention have excellent wear resistance, compression resistance, heat conductivity and isotropy of the graphite spheres, and can avoid the phenomena of crushing or large wear in the operation process and generation of more dust, and all performance indexes meet the requirements of a nuclear reactor.
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.
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.
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.
Example 1
A preparation method of graphite spheres for a high-temperature gas cooled reactor comprises the following specific processes:
1) mixing materials: putting 55 parts by weight of petroleum coke, 40 parts by weight of asphalt, 3 parts by weight of natural crystalline flake graphite, 1 part by weight of carbon black and 1 part by weight of spherical coke into a stirring device, and stirring for 7 hours to obtain a mixed material.
Wherein, the petroleum coke and the natural crystalline flake graphite are ground into powder with the granularity D50 of 36 mu m;
the true density of the petroleum coke is 2.12g/cm30.23 percent of ash, 0.25 percent of volatile matter, 0.19 percent of water content and 0.05 percent of sulfur; the softening point of the asphalt is 118 ℃, the ash content is 0.23%, the coking value is 65%, the moisture content is 1.20%, the toluene insoluble content is 36%, and the quinoline insoluble content is 11%;
the natural crystalline flake graphite has a volatile content of 0.15% and a true density of 2.24g/cm30.15% of water, 0.14% of ash and 99.68% of fixed carbon;
specific surface area of carbon Black 100m2Oil absorption 97cc/100, ash 0.29%, particle size 0.08 μm;
the shot coke had a volatile content of 9% and a true density of 2.11g/cm3Moisture content 0.25%, ash content 0.26%, particle size D50 was 15 μm.
2) Isostatic pressing: and putting the mixed material into a rubber sleeve, vacuumizing the rubber sleeve, sealing the rubber sleeve when the vacuum degree in the rubber sleeve reaches 0.06MPa, putting the rubber sleeve into an isostatic press, and carrying out isostatic pressing for 100 minutes under the condition that the pressure is 140 MPa.
3) Densification treatment: taking out the product after isostatic pressing, roasting at the high temperature of 1100 ℃ for 850 hours, impregnating the roasted product for 2.5 hours under the pressure of 3.5MPa, roasting the impregnated product again, and repeating the steps until the bulk density of the product reaches 1.65g/cm3The above.
4) Graphitization and high-temperature purification: graphitizing and purifying the densified product, paving calcium fluoride at the bottom of the furnace when charging, heating to 2300 ℃, introducing carbon tetrachloride with the amount of 35kg per ton of graphite product, continuously heating to 3150 ℃, carrying out high-temperature treatment for 60 hours, and cooling the product subjected to high-temperature treatment to obtain the graphite product.
5) And (3) machining: and (3) machining the graphite product to a diameter of 60mm by using a lathe to obtain the graphite ball for the high-temperature gas cooled reactor.
Example 2
A preparation method of graphite spheres for a high-temperature gas cooled reactor comprises the following specific processes:
1) mixing materials: putting 51 parts by weight of petroleum coke, 45 parts by weight of asphalt, 2 parts by weight of natural crystalline flake graphite, 1 part by weight of carbon black and 1 part by weight of spherical coke into a stirring device, and stirring for 6 hours to obtain a mixed material.
The raw material parameters were the same as in example 1.
2) Isostatic pressing: and putting the mixed material into a rubber sleeve, vacuumizing the rubber sleeve, sealing the rubber sleeve when the vacuum degree in the rubber sleeve reaches 0.06MPa, putting the rubber sleeve into an isostatic press, and carrying out isostatic pressing for 110 minutes under the condition that the pressure is 130 MPa.
3) Densification treatment: taking out the product after isostatic pressing, roasting at the high temperature of 1000 ℃ for 830 hours, impregnating the roasted product for 2.0 hours under the pressure of 3.5MPa, and roasting the impregnated product again until the bulk density of the product reaches 1.65g/cm3The above.
4) Graphitization and high-temperature purification: and (3) putting the densified product into a high-temperature purification furnace for heating and purification, laying calcium fluoride at the bottom of the furnace when charging, wherein the dosage of the calcium fluoride is 30kg per ton of the graphite product, carbon tetrachloride is introduced when the temperature is raised to 2300 ℃, the dosage of the carbon tetrachloride is 30kg per ton of the graphite product, the temperature is continuously raised to 3100 ℃, the high-temperature treatment is carried out for 72 hours, and then the product after the high-temperature treatment is cooled to obtain the graphite product.
5) And (3) machining: and (3) machining the graphite product to a diameter of 60mm by using a lathe to obtain the graphite ball for the high-temperature gas cooled reactor.
Example 3
A preparation method of graphite spheres for a high-temperature gas cooled reactor comprises the following specific processes:
1) mixing materials: putting 60 parts by weight of petroleum coke, 35 parts by weight of asphalt, 1 part by weight of natural crystalline flake graphite, 2 parts by weight of carbon black and 1 part by weight of spherical coke into a stirring device, and stirring for 8 hours to obtain a mixed material.
The raw material parameters were the same as in example 1.
2) Isostatic pressing: and putting the mixed material into a rubber sleeve, vacuumizing the rubber sleeve, sealing the rubber sleeve when the vacuum degree in the rubber sleeve reaches 0.06MPa, putting the rubber sleeve into an isostatic press, and carrying out isostatic pressing for 120 minutes under the condition that the pressure is 150 MPa.
3) Densification treatment: taking out the product after isostatic pressing, roasting at the high temperature of 1200 ℃ for 850 hours, impregnating the roasted product for 3 hours under the pressure of 3.5MPa, and roasting the impregnated product again to repeat until the bulk density of the product reaches 1.65g/cm3The above.
4) Graphitization and high-temperature purification: and (3) putting the densified product into a high-temperature purification furnace for heating and purifying, during charging, laying calcium fluoride at the bottom of the furnace, wherein the dosage of the calcium fluoride is 20kg per ton of the graphite product, when the temperature is raised to 2300 ℃, introducing carbon tetrachloride, the dosage of the carbon tetrachloride is 40kg per ton of the graphite product, continuously raising the temperature to 3200 ℃, performing high-temperature treatment for 48 hours, and then cooling the high-temperature treated product to obtain the graphite product.
5) And (3) machining: and (3) machining the graphite product to a diameter of 60mm by using a lathe to obtain the graphite ball for the high-temperature gas cooled reactor.
Comparative example 1
The difference from example 1 is only that in step 1), the mixture does not contain natural crystalline flake graphite.
Comparative example 2
The difference from example 1 is only that in step 1), the mixture contains no carbon black.
Comparative example 3
The only difference from example 1 is that in step 1), the mixture does not contain shot coke.
Comparative example 4
The difference from example 1 is only that in step 4), the graphitization and high temperature purification steps are: and (2) placing the densified product into a high-temperature purification furnace for heating and purification, introducing chlorine into the high-temperature purification furnace when the furnace temperature of the high-temperature purification furnace reaches 2100 ℃, introducing 20kg of chlorine into each ton of product averagely, introducing Freon into the high-temperature purification furnace when the furnace temperature of the high-temperature purification furnace reaches 2500 ℃, introducing 30kg of Freon into each ton of product averagely, treating at high temperature for 24 hours after the furnace temperature of the high-temperature purification furnace reaches 3000 ℃, and then cooling the product after high-temperature treatment to obtain the graphite product.
Test examples
The performance of the graphite spheres for the high temperature gas cooled reactor processed in examples 1 to 3 and comparative examples 1 to 4 was measured, and is shown in table 1.
TABLE 1
The bold part of the font in table 1 indicates that the index is abnormal, because the performance index of the graphite nodule is changed after the raw material formula is changed or one preparation step is changed in the graphite nodule preparation method, and the graphite nodule does not meet the technical requirements of the graphite nodule for the high-temperature gas cooled reactor.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. The preparation method of the graphite spheres for the high-temperature gas cooled reactor is characterized by comprising the following steps:
mixing materials: mixing the raw materials to obtain a mixed material; the mixed material comprises the following components in parts by weight: 50-60 parts of petroleum coke, 35-45 parts of asphalt, 2-5 parts of natural crystalline flake graphite, 1-3 parts of carbon black and 1-2 parts of spherical coke;
isostatic pressing: the mixed material is subjected to isostatic pressing for 100-150 minutes under the pressure of 130-150 MPa;
densification treatment: taking out the product after isostatic compaction, and performing densification treatment, wherein the densification treatment is a step of performing one or more times of roasting and one or more times of soaking until the bulk density of the product reaches 1.65g/cm3The above;
graphitization and high-temperature purification: graphitizing and purifying the densified product by using a high-temperature purification furnace, paving calcium fluoride at the bottom of the furnace during charging, and introducing carbon tetrachloride when the temperature is raised to 2300 ℃; continuously heating to 3100-; cooling to obtain a graphite product;
and (3) machining: and processing the graphite product to the diameter of 59.9-60.2mm to obtain graphite spheres for the high-temperature gas cooled reactor.
2. The preparation method of claim 1, wherein the mixed material comprises the following components in parts by weight: 55 parts of petroleum coke, 40 parts of asphalt, 3 parts of natural crystalline flake graphite, 1 part of carbon black and 1 part of spherical coke.
3. The preparation method of claim 1, wherein the petroleum coke and the natural crystalline flake graphite are ground to a particle size D50 of 35-40 μm before mixing.
4. The process of claim 1 wherein the petroleum coke has a true density of not less than 2.08g/cm3The ash content is not more than 0.25 percent, the volatile content is not more than 0.5 percent, the moisture content is not more than 0.5 percent, and the sulfur content is not more than 0.4 percent; and/or the softening point of the asphalt is 115 ℃ and 120 ℃, and the ash content isNot less than 0.25%, not less than 58%, not less than 4.0%, not less than 32% and 9-12% in content of insoluble substances.
5. The preparation method according to claim 1, wherein the natural crystalline flake graphite has a volatile content of less than 0.25% and a true density of 2.23g/cm or more3The water content is less than 0.20 percent, the ash content is less than 0.25 percent, and the fixed carbon content is more than or equal to 99.4 percent;
and/or the specific surface area of the carbon black is 80 to 120m2(ii)/g, oil absorption of 90-100cc/100, ash content less than 0.4%; the particle size of the carbon black is 0.05-0.1 μm;
and/or the spherical coke has a volatile content of 5-11% and a true density of 2.03-2.14g/cm3The water content is less than 0.35 percent, and the ash content is less than 0.4 percent; the shot coke has a particle size D50 of 10-18 μm.
6. The preparation method as claimed in claim 1, wherein the step of isostatic pressing the mixture under the pressure of 130-150MPa for 100-120 minutes comprises: and putting the mixed material into a rubber sleeve, vacuumizing the rubber sleeve, sealing when the vacuum degree in the rubber sleeve reaches 0.06MPa, putting the rubber sleeve into an isostatic press, and carrying out isostatic pressing for 100-fold 120 minutes under the condition that the pressure is 130-fold 150 MPa.
7. The preparation method as claimed in claim 1, wherein the calcination temperature is 1000-1200 ℃, and the calcination time is 800-850 hours each time; the pressure of the impregnation is 3.5MPa, and the impregnation pressurization time is 2-3 hours each time.
8. The method according to claim 1, wherein the amount of calcium fluoride and carbon tetrachloride is 20-30kg and 30-40kg per ton of graphite product during graphitization and high temperature purification.
9. Graphite spheres for high temperature gas cooled reactor prepared by the method of any one of claims 1 to 8.
10. The graphite ball for high temperature gas cooled reactor according to claim 9, wherein the graphite ball for high temperature gas cooled reactor has a diameter of 59.9-60.2mm and a density of 1.73-1.77g/cm3The total ash content is less than or equal to 50ppm, the lithium content is less than or equal to 0.05ppm, the total boron equivalent is less than or equal to 0.3ppm, the heat conductivity coefficient (1000 ℃) is more than or equal to 30W/(m.k), the abrasion rate (20 spheres, 100h) is less than or equal to 2 mg/(sphere.h), the crushing strength of graphite spheres is more than or equal to 20KN, the thermal expansion anisotropy (room temperature-400 ℃) is less than or equal to 1.3, the graphitization degree is more than or equal to 85%, and the surface has no notch defect with the length depth of 1 mm.
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