Method for controlling content of carbon and oxygen impurities in nitride fuel and nitride fuel

Abstract

The embodiment of the invention relates to the technical field of binary compounds of nitrogen and metal, in particular to a method for controlling the content of carbon and oxygen impurities in nitride fuel and the nitride fuel. The invention provides a method for controlling the content of carbon and oxygen impurities in nitride fuel, which comprises the following steps: placing uranium dioxide powder in a reaction area, and introducing hydrogen to enable the molar ratio of oxygen to uranium in a reaction product to reach a preset value; mixing the reaction product with metal uranium powder and carbon powder to obtain a mixture; the mixture is placed in a nitriding area, nitrogen is input, temperature control and pressure control are conducted on the nitriding area, and the carbon content in the obtained nitride powder is reduced to a preset value; and mixing the nitride powder and the metal uranium powder, and then sintering, so that the oxygen content of the nitride fuel obtained by sintering is reduced to a preset value. The invention provides a nitride fuel. According to the method, the content of carbon and oxygen impurities in the nitride fuel can be accurately controlled, the high-purity nitride fuel is prepared, and the in-pile service performance of the nitride fuel can be improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of binary compounds of nitrogen and metals, and specifically to a method for controlling the carbon and oxygen impurity content in a nitride fuel and the nitride fuel. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] Nitride fuel, due to its high uranium density, high thermal conductivity, and excellent neutron economy, can significantly improve reactor safety margins when used in nuclear reactors. However, the carbon and oxygen impurity content in nitride fuel affects its performance in nuclear reactors, thereby affecting the serviceability of nuclear reactors. Carbon impurities in nitride fuel can form secondary phases such as UC and U2C3 at high temperatures, increasing the brittleness of the fuel matrix and exacerbating the interaction between the cladding and fuel pellets during irradiation swelling, leading to deformation or damage of the cladding tubes. Oxygen impurities react with fission products such as tellurium and cesium to form low-melting-point eutectics, such as Cs2TeO4, which can easily accelerate stress corrosion cracking of the cladding material encapsulating the fuel. Furthermore, impurity phases can reduce the thermal conductivity of the fuel, leading to a nonlinear increase in the fuel center temperature and increasing the risk of meltdown, thus seriously threatening the safe operation of the reactor.

[0004] However, the current nitride fuel production and process technology still has many technical defects in controlling the carbon and oxygen impurity content of the fuel, resulting in multiple safety risks in the prepared fuel during service, which is not conducive to the safe and stable operation of the reactor. Summary of the Invention

[0005] A brief overview of the present application is provided below to provide a basic understanding of certain aspects of the present application. It should be understood that this overview is not an exhaustive overview of the present application. It is not intended to identify key or important portions of the present application, nor is it intended to limit the scope of the present application. Its purpose is simply to present certain concepts in a simplified form as a prelude to the more detailed description that will be discussed later.

[0006] In a first aspect, an embodiment of the present application provides a method for controlling the carbon and oxygen impurity content in a nitride fuel, comprising the following steps: S10: placing uranium dioxide powder in a reaction area, introducing hydrogen into the reaction area, and reacting the uranium dioxide powder with the hydrogen so that the oxygen-uranium molar ratio in the reaction product reaches a predetermined value; S20: mixing the reaction product obtained in step S10 with metal uranium powder and carbon powder to obtain a mixture; S30: placing the mixture obtained in step S20 in a nitriding area, introducing nitrogen into the nitriding area, and controlling the temperature and pressure of the nitriding area so that the mixture reacts with the nitrogen and the carbon content in the obtained nitride powder is reduced to a predetermined value; S40: mixing the nitride powder obtained in step S30 with metal uranium powder and then sintering the mixture to reduce the oxygen content in the nitride fuel obtained by sintering to a predetermined value.

[0007] In a second aspect, an embodiment of the present application provides a nitride fuel, wherein the nitride fuel uses the control method of any embodiment of the first aspect of the present application to control carbon and oxygen impurities.

[0008] The control method in the embodiments of the present application can achieve precise control of the carbon and oxygen impurity content in the nitride fuel, prepare high-purity nitride fuel, and help improve the in-pile service performance of the nitride fuel and reduce the safety risks of fuel application. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other objects and advantages of the present application will become apparent from the following description of the embodiments of the present application with reference to the accompanying drawings, which will help to provide a comprehensive understanding of the present application.

[0010] Figure 1 4 is a flow chart of a method for controlling the carbon and oxygen impurity content in a nitrogen oxide fuel according to an embodiment of the present application.

[0011] It should be noted that the drawings are not necessarily drawn to scale, but are merely shown in a schematic manner that does not affect the reader's understanding. DETAILED DESCRIPTION

[0012] Exemplary embodiments of the present application will be described below with reference to the accompanying drawings. For the sake of clarity and conciseness, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the process of developing any such actual implementation in order to achieve the developer's specific goals, such as meeting those constraints related to the system and business, and these constraints may vary depending on the implementation. In addition, it should be understood that although the development work may be very complex and time-consuming, it is a routine task for those skilled in the art who benefit from the content of this application.

[0013] It is also necessary to point out here that, in order to avoid obscuring the present application due to unnecessary details, the accompanying drawings only show the device structure and / or processing steps that are closely related to the solution according to the present application, while other details that are not closely related to the present application are omitted.

[0014] The inventors of this application have discovered that in the prior art, nitride fuels are typically prepared by metal uranium nitriding or carbon thermal reduction nitriding. The metal uranium nitriding method uses metal uranium as a raw material. When the nitriding reaction is carried out in a temperature range of 800 to 1400°C, there are problems such as incomplete nitriding and the byproduct H2 of ammonia decomposition easily causing spontaneous combustion of the raw metal uranium. In addition, the metal uranium nitriding method is not suitable for industrial-scale fuel production. The carbon thermal reduction nitriding method uses UO2 and C as raw materials and reacts in a vacuum environment at a temperature of 1600°C. However, the residual carbon content in the nitride fuel prepared by this method is generally higher than 0.5wt%. In addition, due to the high initial oxygen content of UO2 as a raw material, the oxygen impurities in the prepared nitride fuel are usually difficult to be lower than 1000ppm.

[0015] Based on this, the embodiment of the present application provides a method for controlling the carbon and oxygen impurity content in a nitride fuel, such as Figure 1 As shown, Figure 1 A flow chart showing a method for controlling the carbon and oxygen impurity content in a nitrogen oxide fuel according to an embodiment of the present application is provided. The method includes the following steps S10 to S40:

[0016] S10: placing uranium dioxide powder in a reaction area, introducing hydrogen into the reaction area, and causing the uranium dioxide powder to react with the hydrogen so that the oxygen-uranium molar ratio in the reaction product reaches a predetermined value.

[0017] S20: mixing the reaction product obtained in step S10 with metallic uranium powder and carbon powder to obtain a mixture.

[0018] S30: placing the mixture obtained in step S20 in a nitriding area, inputting nitrogen into the nitriding area, and controlling the temperature and pressure of the nitriding area to allow the mixture to react with the nitrogen and reduce the carbon content in the obtained nitride powder to a predetermined value.

[0019] S40: The nitride powder obtained in step S30 is mixed with metal uranium powder and then sintered to reduce the oxygen content in the nitride fuel obtained by sintering to a predetermined value.

[0020] The control method provided in the embodiments of the present application allows uranium dioxide powder to react with hydrogen to prepare uranium dioxide precursor powder with an oxygen-uranium molar ratio reaching a predetermined value, thereby preliminarily controlling the content of oxygen impurities; a mixture of the uranium dioxide precursor powder, metallic uranium powder, and carbon powder is subjected to a nitridation reaction with nitrogen, and the temperature and pressure of the nitriding region are controlled to control the carbon impurity content of the nitride powder generated by the reaction to a predetermined value; and metallic uranium powder is introduced as a getter to sinter the nitride powder to control the oxygen impurity content of the nitride fuel generated by the reaction to a predetermined value, thereby achieving precise control of the carbon-oxygen impurity content in the nitride fuel and preparing high-purity nitride fuel, which is beneficial to improving the in-pile service performance of the nitride fuel and reducing the safety risks of fuel application.

[0021] In some embodiments, the uranium dioxide powder may be pretreated before step S10 to make the uranium dioxide powder reach a predetermined size.

[0022] In some embodiments, the uranium dioxide powder can be ball-milled with a ball-milling speed of 600 rpm, a duration of 3 hours, and a ball-to-material ratio of 6:1 to obtain uranium dioxide powder with a particle size of 0.5-3 microns.

[0023] In this embodiment, before reacting the uranium dioxide powder with hydrogen, the uranium dioxide powder is first ball-milled to significantly reduce the particle size of the uranium dioxide powder used for the reaction, increase the contact area between the powder and the hydrogen, and improve the reaction rate. In addition, the original free carbon impurities in the uranium dioxide powder can be fully initially dissolved in the uranium dioxide powder, thereby reducing the difficulty of subsequent reactions.

[0024] In some embodiments, step S10 further includes the following steps:

[0025] S11: heating the reaction area to a predetermined temperature.

[0026] S12: Pure hydrogen is introduced into the reaction area.

[0027] S13: Maintaining the temperature for a predetermined time to allow the uranium dioxide powder to react with the pure hydrogen.

[0028] In this embodiment, the temperature of the reaction zone is controlled and the uranium dioxide powder is reacted with pure hydrogen to remove excess oxygen atoms in the uranium dioxide powder, thereby achieving preliminary control of oxygen impurities in the reaction products, which is beneficial for the subsequent reduction of the oxygen impurity content in the nitride fuel.

[0029] Specifically, in step S10, uranium dioxide powder with an O / U ratio of ≤2.05 is placed in a reaction area, the reaction area is heated to 2100°C, and pure hydrogen is introduced into the reaction area to react with the uranium dioxide powder and the pure hydrogen in a high temperature environment. The temperature is kept for 4 hours to allow the uranium dioxide powder and the hydrogen to react completely, thereby obtaining a uranium dioxide precursor powder with an O / U ratio in the range of 1.98-1.99, and obtaining a UO precursor with an O / U ratio of less than 2.0. 2-x The fuel contains oxygen vacancies, which will decompose metallic uranium under low temperature conditions so that the oxygen impurity content in the reaction products can be reduced through subsequent reactions.

[0030] In some embodiments, in step S20, when the reaction product obtained in step S10 is mixed with metal uranium powder and carbon powder, the mixing can be performed by ball milling. The reaction product, metal uranium powder with a particle size of ≤1 micron and carbon powder with a particle size of ≤0.5 micron are placed in a ball mill, the ball milling speed is set to 200 rpm, the duration is 2 hours, and the ball-to-material ratio is set to 3:1, so as to utilize the metal uranium powder to reduce the oxygen impurity content through oxygen absorption, and then accelerate the reaction rate through subsequent liquid phase sintering, thereby comprehensively reducing the oxygen content in the nitride fuel finally obtained; and, by simultaneously ball milling carbon powder and metal uranium powder, the process of the subsequent carbonization reaction can be accelerated and the oxygen impurity content in the reaction product can be reduced.

[0031] In some embodiments, step S30 further includes the following steps:

[0032] S31: nitrogen is input into the nitriding region, and the temperature of the nitriding region and the nitrogen input pressure are controlled to nitride the mixture obtained in step S20 to obtain nitride powder.

[0033] S32: Argon gas is introduced into the nitriding region, and the temperature of the nitriding region is controlled to nitridize the nitride powder obtained in step S31 again.

[0034] S33: hydrogen is introduced into the nitriding region, and the temperature of the nitriding region is controlled to reduce the carbon content in the nitride powder obtained in step S32 to a predetermined value.

[0035] In this embodiment, the mixture obtained in step S20 is reacted with nitrogen through a multi-atmosphere temperature control method to regulate the reaction progress of UO2, C and N2 in different temperature ranges, thereby achieving simultaneous carbonization and nitridation reactions, reducing the amount of C retained during the reaction process, and thus facilitating the reduction of the carbon content in the nitride powder to a predetermined value.

[0036] In some embodiments, before step S31, the mixture obtained in step S20 may be pressed into a compact, the compact placed in a nitriding area, and after step S31, the nitrided compact is cooled and crushed to obtain nitride powder. In this embodiment, by cooling and crushing the nitrided compact into nitride powder after step S31, the partially unreacted carbon is mixed and contacted with the matrix metal uranium powder and carbon powder again, and re-nitridation is achieved in step S32, thereby further removing carbon impurities.

[0037] In some embodiments, step S31 further includes the following steps:

[0038] S311: heating the nitriding region to a first predetermined temperature, and inputting nitrogen into the nitriding region at a first predetermined pressure.

[0039] S312: Continuously heating the nitriding region to a second predetermined temperature, increasing the nitrogen input pressure to a second predetermined pressure, and inputting nitrogen into the nitriding region at the second predetermined pressure.

[0040] S313: Continuously heating the nitriding region to a third predetermined temperature, increasing the nitrogen input pressure to the third predetermined pressure, inputting nitrogen into the nitriding region at the third predetermined pressure, and maintaining the temperature for a first predetermined time.

[0041] In this embodiment, the temperature of the nitriding region is gradually increased to enhance the reaction extents at different carbonization and nitriding stages. Furthermore, the nitrogen pressure input to the nitriding region is determined based on the product produced at each reaction stage to provide optimal parameters for the carbonization and nitriding reactions at each stage, thereby accelerating the removal of carbon impurities.

[0042] In some embodiments, the first predetermined temperature and the second predetermined temperature, and the second predetermined temperature and the third predetermined temperature are of equal difference, and the first predetermined pressure and the second predetermined pressure, and the second predetermined pressure and the third predetermined pressure are of equal difference, so as to achieve gradient temperature and pressure increase in the nitriding area.

[0043] Specifically, in step S31, when controlling the temperature of the nitriding area and the nitrogen input pressure, the nitriding area is heated to 800°C, the nitrogen input pressure is set to 0.1 MPa, the nitriding area is continuously heated to 1200°C, the nitrogen input pressure is increased to 0.2 MPa, the nitriding area is continuously heated to 1600°C, the nitrogen input pressure is increased to 0.3 MPa, and the temperature is maintained for 3 hours while maintaining the nitrogen input pressure of 0.3 MPa to achieve a slow transition from slow to accelerated nitriding reaction, providing sufficient time for the removal of carbon impurities, thereby further ensuring that the carbon content in the nitride powder is reduced to a predetermined value.

[0044] In some embodiments, step S32 further includes the following steps:

[0045] S321: Argon gas is input into the nitriding area to convert the nitriding area into an argon atmosphere.

[0046] S322: Heating the nitriding area to a predetermined temperature and keeping the temperature for a predetermined time.

[0047] S323: Vacuum the nitriding area.

[0048] S324: Cooling the nitriding area to a temperature equal to the external temperature of the nitriding area at a predetermined speed.

[0049] Specifically, in step S32, the nitriding area is converted into an argon atmosphere. In the argon environment, the nitriding area is heated to 1200°C and kept warm for 3 hours. The nitriding area is vacuumed and cooled at a rate of 400°C / h until the temperature is equal to the external temperature of the nitriding area to prevent UN from transforming into U2N3 phase, so that the carbon impurities become free state, which is conducive to the removal of carbon impurities.

[0050] In some embodiments, step S33 further includes the following steps:

[0051] S331: Continuously input pure hydrogen into the nitriding area to transform the nitriding area into a flowing pure hydrogen environment.

[0052] S332: Heating the nitriding area to a predetermined temperature and keeping the temperature for a predetermined time.

[0053] Specifically, in step S33, the nitriding area is converted into a flowing pure hydrogen environment. In the flowing pure hydrogen environment, the nitriding area is heated to 1400° C. and kept warm for 4 hours to further achieve effective removal of carbon impurities through pure hydrogen.

[0054] In some embodiments, before step S33, the method further includes mixing the nitride powder obtained in step S32 with an ethanol solution and pulverizing the nitride powder to a predetermined size.

[0055] Specifically, the nitride powder obtained in step S32 can be pulverized by ball milling, with the ball milling speed set to 500 rpm, the duration being 4 hours, and the ball-to-material ratio being set to 8:1 to obtain nitride powder with a particle size of ≤0.5 microns, so as to further refine the nitride powder and facilitate the removal of trace carbon impurities in the nitride powder during the subsequent sintering process.

[0056] In some embodiments, step S40 further includes the following steps:

[0057] S41: placing the mixture of the nitride powder obtained in step S30 and the metal uranium powder in a sintering area.

[0058] S42: nitrogen is input into the sintering area to transform the sintering area into a trace nitrogen environment.

[0059] S43: Heating the sintering area to a predetermined temperature to sinter the mixture.

[0060] In this embodiment, metallic uranium powder is introduced as a getter and mixed with the nitride powder obtained in step S30. Then, a sintering treatment is performed in a trace nitrogen atmosphere so that the oxygen impurities in the solid solution state in the nitride powder are first removed by reacting with U and then reacting with the carbon impurities and nitrogen in the nitride powder. Thus, the carbon impurities and oxygen impurities are removed simultaneously to obtain a high-purity nitride fuel.

[0061] Specifically, in step S40, the nitride powder obtained in step S30 is mixed with 1 wt% of ultrafine metal uranium powder for 3 hours, where the particle size of the metal uranium powder is 10-100 microns. The obtained mixture is pressed into shape and placed in a sintering area. The sintering area is heated to 1800°C in a nitrogen atmosphere of 200-500 ppm to sinter the mixture into a nitride fuel with a 90% TD.

[0062] An embodiment of the present application further provides a nitride fuel, wherein the carbon and oxygen impurities in the nitride fuel are controlled using the control method of any embodiment of the first aspect of the present application.

[0063] The following further describes the process of controlling the carbon and oxygen impurity content in the nitride fuel according to the present invention.

[0064] The uranium dioxide powder with an O / U ratio of ≤2.05 was ball-milled at a speed of 600 rpm for 3 hours with a ball-to-material ratio of 6:1 to obtain a uranium dioxide powder with a particle size of 0.5-3 microns, which was placed in a reaction area, heated to 2100°C, and then pure hydrogen was introduced into the reaction area to react the uranium dioxide powder with pure hydrogen under a high temperature environment. The temperature was kept for 4 hours to allow the uranium dioxide powder to react completely with the hydrogen to obtain a uranium dioxide precursor powder with an O / U ratio in the range of 1.98-1.99; the uranium dioxide precursor powder was mixed with metal uranium powder with a particle size of ≤1 micron and a particle size of ≤0.5 The micron carbon powder is placed in a ball mill and ball milled at a speed of 200 rpm for 2 hours with a ball-to-material ratio of 3:1 to obtain a mixture; the mixture is pressed into a Φ15mm×5mm green compact, the green compact is placed in a nitriding area, nitrogen is input into the nitriding area, the nitriding area is heated to 800°C, the nitrogen input pressure is set to 0.1MPa, the nitriding area is continuously heated to 1200°C, the nitrogen input pressure is increased to 0.2MPa, the nitriding area is continuously heated to 1600°C, the nitrogen input pressure is increased to 0.3MPa, and the temperature is kept for 3 hours while maintaining a nitrogen input pressure of 0.3MPa to make the green compact nitrogen After the nitrided compact is cooled, it is crushed and ball-milled to obtain nitride powder. The nitride powder is placed in a nitriding area, argon gas is introduced into the nitriding area to convert the nitriding area into an argon atmosphere, the nitriding area is heated to 1200°C and kept at this temperature for 3 hours, the nitriding area is vacuumed, and then the nitriding area is cooled at a rate of 400°C / h until the temperature is equal to the external temperature of the nitriding area, thereby obtaining a re-nitrided nitride powder. The re-nitrided nitride powder is mixed with an ethanol solution and ball-milled at a speed of 500 rpm for 4 hours with a ball-to-powder ratio of 8:1 to obtain a particle size of ≤0. 5 micron nitride powder; placing the nitride powder in a nitriding area, continuously supplying pure hydrogen to the nitriding area to transform the nitriding area into a flowing pure hydrogen environment, heating the nitriding area to 1400°C, and keeping it warm for 4 hours to obtain nitride powder with the carbon impurity content reduced to a predetermined value; mixing the nitride powder with 1wt% ultrafine metal uranium powder for 3 hours, pressing the obtained mixture into a shape, placing it in a sintering area, heating the sintering area to 1800°C in a nitrogen atmosphere of 200-500ppm to reduce the oxygen impurity content in the mixture to a predetermined value, and sintering it into a nitride fuel with 90% TD.

[0065] Regarding the embodiments of the present application, it should also be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other to obtain new embodiments.

[0066] The above are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto. The protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for controlling the carbon and oxygen impurity content in a nitride fuel, characterized in that: It includes the following steps: S10: placing uranium dioxide powder in a reaction area, introducing hydrogen into the reaction area, and reacting the uranium dioxide powder with the hydrogen so that the oxygen-uranium molar ratio in the reaction product reaches a predetermined value; S20: mixing the reaction product obtained in step S10 with metallic uranium powder and carbon powder to obtain a mixture; S30: placing the mixture obtained in step S20 in a nitriding area, introducing nitrogen into the nitriding area, and controlling the temperature and pressure of the nitriding area so that the mixture reacts with the nitrogen and the carbon content in the obtained nitride powder is reduced to a predetermined value; S40: The nitride powder obtained in step S30 is mixed with metal uranium powder and then sintered to reduce the oxygen content in the nitride fuel obtained by sintering to a predetermined value.

2. The method according to claim 1, characterized in that In step S30, the following steps are also included: S31: inputting nitrogen into the nitriding region and controlling the temperature and nitrogen input pressure of the nitriding region to nitride the mixture obtained in step S20 to obtain nitride powder; S32: introducing argon gas into the nitriding region and controlling the temperature of the nitriding region to nitridize the nitride powder obtained in step S31 again; S33: hydrogen is introduced into the nitriding region, and the temperature of the nitriding region is controlled to reduce the carbon content in the nitride powder obtained in step S32 to a predetermined value.

3. The method according to claim 2, characterized in that In step S31, the following steps are also included: S311: heating the nitriding region to a first predetermined temperature, and inputting nitrogen into the nitriding region at a first predetermined pressure; S312: continuously heating the nitriding region to a second predetermined temperature, increasing the nitrogen input pressure to a second predetermined pressure, and inputting nitrogen into the nitriding region at the second predetermined pressure; S313: continuously heating the nitriding region to a third predetermined temperature, increasing the nitrogen input pressure to a third predetermined pressure, inputting nitrogen into the nitriding region at the third predetermined pressure, and maintaining the temperature for a first predetermined time.

4. The method according to claim 3, characterized in that The first predetermined temperature and the second predetermined temperature, and the second predetermined temperature and the third predetermined temperature are equidistant from each other, and The first predetermined pressure and the second predetermined pressure are of equal difference, and the second predetermined pressure and the third predetermined pressure are of equal difference.

5. The method according to claim 2, characterized in that In step S32, the following steps are also included: S321: Inputting argon gas into the nitriding region to transform the nitriding region into an argon atmosphere; S322: heating the nitriding region to a predetermined temperature and maintaining the temperature for a predetermined time; S323: vacuuming the nitriding area; S324: Cooling the nitriding region to a temperature equal to the external temperature of the nitriding region at a predetermined speed.

6. The method according to claim 2, characterized in that In step S33, the following steps are also included: S331: Continuously inputting pure hydrogen into the nitriding region to transform the nitriding region into a flowing pure hydrogen environment; S332: heating the nitriding region to a predetermined temperature and maintaining the temperature for a predetermined time.

7. The method according to claim 2, characterized in that Before step S33, the following steps are also included: The nitride powder obtained in step S32 is mixed with an ethanol solution and pulverized to make the nitride powder reach a predetermined size.

8. The method according to claim 1, characterized in that In step S40, the following steps are also included: S41: placing the mixture of the nitride powder obtained in step S30 and the metal uranium powder in a sintering area; S42: nitrogen is introduced into the sintering area to transform the sintering area into a trace nitrogen environment; S43: heating the sintering region to a predetermined temperature to sinter the mixture.

9. The method according to claim 1, characterized in that In step S10, the following steps are also included: S11: heating the reaction area to a predetermined temperature; S12: introducing pure hydrogen into the reaction area; S13: Maintaining the temperature for a predetermined time to allow the uranium dioxide powder to react with the pure hydrogen.

10. The method according to claim 1, characterized in that Before step S10, the uranium dioxide powder is pretreated to make the uranium dioxide powder reach a predetermined size.

11. A nitride fuel, characterized in that: The nitride fuel is controlled for carbon and oxygen impurities using the control method described in any one of claims 1 to 10.

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