Oxide nuclear fuel sintered body with microscopic precipitates distributed along the circumferential direction and manufacturing method thereof

Abstract

The present invention relates to an oxide nuclear fuel sintered body and a method for manufacturing the same. In a matrix of a uranium dioxide sintered body used as nuclear fuel for a nuclear power plant, microscopic plate-like precipitates are uniformly precipitated into the nuclear fuel sintered body structure to form annular precipitate clusters distributed therein. More specifically, the present invention aims to provide an oxide nuclear fuel sintered body and a method for manufacturing the same. In order to improve the thermal and physical properties of the uranium dioxide nuclear fuel sintered body, microscopic plate-like precipitates or annular two-dimensional precipitate clusters are uniformly precipitated and distributed within the nuclear fuel sintered body structure to achieve a high creep strain rate and improved thermal conductivity of the sintered body, thereby reducing sintered body-cladding interaction damage and the core temperature of the nuclear fuel in the event of an accident, thereby significantly improving the safety of the nuclear reactor.

Description

Technical Field

[0001] The present invention relates to an oxide nuclear fuel sintered body and a method for manufacturing the same. In a matrix of a uranium dioxide sintered body used as nuclear fuel for a nuclear power plant, microscopic plate-like precipitates are uniformly precipitated into the nuclear fuel sintered body structure to form annular precipitate clusters. More specifically, the present invention relates to an oxide nuclear fuel sintered body and a method for manufacturing the same. In order to improve the thermal and physical properties of the uranium dioxide nuclear fuel sintered body, microscopic plate-like precipitates or precipitate clusters forming annular two-dimensional structures are uniformly precipitated and distributed within the nuclear fuel sintered body structure to achieve a high creep strain rate and improved thermal conductivity of the sintered body, thereby reducing sintered body-cladding interaction damage and the core temperature of the nuclear fuel in the event of an accident, thereby significantly improving the safety of the nuclear reactor. Background Art

[0002] Nuclear power generation utilizes the heat generated by nuclear fission. Hundreds of fuel rods, each containing sintered uranium dioxide (UO2) as the nuclear fuel, are bundled together to create nuclear fuel assemblies. These fuel assemblies are assembled into the cores of pressurized light water reactors (PLWRs) and pressurized heavy water reactors (PHWRs). Heat generated by nuclear fission in the sintered assemblies is transferred through the cladding and the sintered cladding to the cooling water flowing around the fuel rods. The sintered assemblies, which serve as the heat source for nuclear power plants, are cylindrically formed and sintered from oxides or mixtures of uranium, plutonium, and thorium. Currently, uranium dioxide is the primary fuel used in commercial nuclear power plants worldwide.

[0003] This uranium oxide sintered body is made of uranium oxide powder as the starting material and mixed with lubricants, etc., and is heated to 1 ton (ton) / cm 2 A preform is formed under pressure to prepare a blank, which is then crushed to produce pellets. A lubricant is added and mixed into the pellets, and the pellets are then uniaxially pressed into shape. The compact is then sintered at a temperature of approximately 1780°C in a hydrogen-containing atmosphere to produce a sintered body. The uranium oxide sintered body produced by this process is typically cylindrical and has a density of approximately 95% of the theoretical density.

[0004] Furthermore, (U, Pu) O2 and (U, Th) O2 sintered bodies are produced by mixing plutonium oxide or thorium oxide powder with uranium oxide powder and following the same method as the uranium oxide production method. (U, Gd) O2 sintered bodies used as burnable absorber nuclear fuel can be produced by mixing gadolinium oxide powder with uranium oxide powder and following a method similar to the uranium oxide production method.

[0005] Uranium dioxide (UO2), a nuclear fuel used in commercial nuclear power plants, has an extremely high melting point of approximately 2850°C and minimal reactivity with cooling water, making it widely used as a nuclear fuel. However, UO2 has an extremely low thermal conductivity of approximately 2-3 W / mK within the operating temperature range of nuclear power plants, and its small grain size can accelerate the release of fission gases and fuel rod fracture caused by sinter-cladding interactions. In particular, UO2's low thermal conductivity prevents heat generated by nuclear fission from being easily transferred to the cooling water. The temperature of the sintered body rises significantly above that of the cooling water, causing the core temperature of the sintered body to rise and creating a large temperature gradient within the sintered body. This thermal characteristic accelerates all temperature-dependent reactions, significantly degrading material performance and reducing the safety margin of the nuclear power plant.

[0006] Furthermore, above 30 GWD / MTU, PCI (Precipitational Corrosion Inhibition) (PCI) damage to fuel rods begins when the cladding and sintered body come into contact. At this point, the sintered body applies external forces in the radial direction of the cladding, causing mechanical deformation and fracture. However, the sintered body, resulting from the addition of oxides, exhibits a large-grained microstructure that undergoes plastic deformation before causing deformation of the cladding, eliminating the mutual stresses with the cladding caused by thermal volume expansion. Furthermore, the reduced area of grain boundaries, which serve as escape routes for the various fission gases generated by the nuclear reaction, reduces the rate at which fission gases escape from the sintered body. Therefore, by trapping the fission gases that cause internal surface degradation of the fuel rods within the sintered body, the risk of fractures caused by stress corrosion cracking can be mitigated. As described above, the primary function of sintering additives to reduce PCI damage is to increase the grain size of the uranium dioxide sintered body. This occurs because the oxide additives promote the migration of uranium cations at the sintering temperature during uranium dioxide sintering. This developed microstructure improves combustion safety within the nuclear power plant reactor and enhances the plant's operating margin.

[0007] To this end, in order to improve the thermal conductivity of uranium dioxide as described above, Korean authorized patent 10-0609217 discloses a nuclear fuel containing a tungsten metal mesh and a method for manufacturing the same. Specifically, the method discloses a method of heating a molded body composed of nuclear fuel powder and tungsten oxide in a reducing gas atmosphere to produce a pre-sintered body, then heating the pre-sintered body in an oxidizing gas atmosphere to form a liquid network of tungsten oxide on the pre-sintered body, and reducing the liquid network of tungsten oxide to produce a nuclear fuel sintered body containing a tungsten metal mesh.

[0008] In addition, Korean authorized patent 10-1652729 discloses a method for manufacturing a nuclear fuel sintered body with excellent thermal conductivity by using microscopically sized thermally conductive metal powder to prevent oxidation of metal materials during the manufacture of sintered bodies, thereby solving the problem of reducing the thermal conductivity of the sintered body, and further improving the uniformity of the microstructure of the sintered body by using plate-shaped metal powder.

[0009] However, conventional techniques for uniformly distributing liquid oxides along the grain boundaries of sintered bodies do not take into account the oxidative properties of metal substances, resulting in the possibility of volatilization and the formation of undesirable microstructures on the surface of the sintered bodies, making mass production commercially impossible.

[0010] To this end, the inventors of the present invention, while studying a method for simultaneously improving the mechanical and thermal properties of nuclear fuel sintered bodies, discovered that microscopic plate-like precipitates are uniformly distributed in the circumferential direction within a uranium dioxide matrix and arranged in a ring-shaped two-dimensional cluster shape, thereby improving the thermal conductivity characteristics. Growing the grain size to more than 30 μm will greatly promote the compression creep characteristics of the sintered body and can also significantly improve the PCI impedance, thereby completing the present invention.

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: Korean Patent Gazette No. 10-0609217 (Grant Date: July 27, 2006)

[0014] Patent Document 2: Korean Patent Gazette No. 10-1652729 (Grant Date: August 25, 2016) Summary of the Invention

[0015] The object of the present invention is to provide a nuclear fuel sintered body having a structure in which microscopic plate-like precipitates are distributed in a circumferential direction and has a ring-shaped two-dimensional cluster shape so as to meet the resistance to creep deformation and excellent thermal conductivity characteristics and a manufacturing method thereof.

[0016] Means used to solve problems

[0017] According to one aspect of the present invention, a nuclear fuel sintered body is made of an oxide to which at least one selected from the group consisting of uranium (U), plutonium (Pu), gadolinium (Gd), and thorium (Th) is added, and the microstructure of the nuclear fuel sintered body includes precipitates produced from the sintering additives during the sintering process, and the precipitates are uniformly distributed along the circumferential direction.

[0018] The precipitates may form annular two-dimensional precipitate clusters.

[0019] The precipitates may be arranged along grain boundaries.

[0020] The precipitate may have a length of 3 μm to 30 μm and a thickness of 1 μm to 10 μm.

[0021] The sintering additive comprises copper (I) oxide (CuO), copper (II) oxide (Cu2O), chromium carbide (Cr 23 C6), at least one of the group consisting of molybdenum dioxide (MoO2), molybdenum trioxide (MoO3), molybdenum carbide (Mo2C), and molybdenum disilicide (MoSi2).

[0022] The sintering additive may also include titanium dioxide (TiO2).

[0023] The content of titanium dioxide (TiO2) may be 0.05 wt% to 0.70 wt% relative to the oxide for the nuclear fuel sintered body.

[0024] The content of the metal aluminum powder may be 0.01 wt % to 0.10 wt % relative to the oxide for the nuclear fuel sintered body.

[0025] Metal aluminum (Al) powder may also be included.

[0026] The content of the metal aluminum powder may be 0.01 wt % to 0.10 wt % relative to the oxide for the nuclear fuel sintered body.

[0027] According to another aspect of the present invention, a method for manufacturing an oxide nuclear fuel sintered body is provided, which is used to manufacture an oxide nuclear fuel sintered body in which microscopic plate-like precipitates are distributed in a circumferential direction, comprising: a step of mixing an oxide powder containing at least one selected from a group including uranium (U), plutonium (Pu), gadolinium (Gd), and thorium (Th) with a sintering additive powder to produce a mixed powder (step 1); a step of pre-pressing and crushing the mixed powder and then screening to produce a granulated powder (step 2); a step of uniaxially pressing the granulated powder at 300 to 500 MPa to produce a nuclear fuel molded body (step 3); a step of performing a primary sintering on the manufactured nuclear fuel molded body at a sintering temperature of approximately 700 to 1100°C and a hydrogen-containing reducing gas atmosphere (step 4); and a step of continuously performing a secondary sintering at a sintering temperature of 1700 to 1800°C and a hydrogen-containing reducing gas atmosphere after the primary sintering is completed (step 5).

[0028] The sintering additive powder may include copper (I) oxide (CuO), copper (II) oxide (Cu2O), chromium carbide (Cr 23C6), at least one of the group consisting of molybdenum dioxide (MoO2), molybdenum trioxide (MoO3), molybdenum carbide (Mo2C), and molybdenum disilicide (MoSi2).

[0029] The sintering additive may also include titanium dioxide (TiO2).

[0030] The content of titanium dioxide (TiO2) may be 0.05 wt% to 0.70 wt% relative to the oxide for the nuclear fuel sintered body.

[0031] The method for producing the oxide nuclear fuel sintered body may further include adding oxide metal aluminum (Al) powder.

[0032] In the primary sintering step, the sintering additive may be kept in a liquid state by heating at a heating rate of 1 to 10° C. / min and sintering at 300 to 1100° C. for 30 to 120 minutes.

[0033] In the secondary sintering step, cooling may not be performed after the primary sintering step is completed, and sintering may be performed at 1700 to 1800°C for 60 to 240 minutes at a heating rate of 1 to 10°C / min, so that the liquid sintering additives grow as microscopic plate-like precipitates along with the grain growth of the oxide nuclear fuel sintered body and are uniformly arranged along the circumferential direction.

[0034] When the sintering additive powder is copper (I) oxide (CuO) or copper (II) oxide (Cu2O), the sintering temperature of the primary sintering step (step 4) is 300 to 500°C and the sintering time is 30 to 120 minutes.

[0035] The hydrogen-containing reducing gas may include at least one selected from the group consisting of carbon dioxide, nitrogen, argon, and helium.

[0036] The hydrogen-containing reducing gas may consist only of hydrogen.

[0037] Effects of the Invention

[0038] According to the oxide nuclear fuel sintered body and its manufacturing method of the present invention, the nuclear fuel sintered body has a structure in which microscopic plate-like precipitates are distributed along the circumferential direction and has a ring-shaped two-dimensional cluster shape, so it has the effect of being able to simultaneously meet extremely high creep deformation characteristics and excellent thermal conductivity characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 FIG. 8 shows the microstructure of the uranium dioxide sintered body according to Example 1 of the present invention, which was photographed using an optical microscope (100 magnifications).

[0040] Figure 2] shows a SEM microstructure photograph of plate-like molybdenum precipitated along the grain boundaries of the uranium dioxide sintered body according to Example 1 of the present invention.

[0041] Figure 3 3 shows an SEM / EDS mapping photograph and an XRD pattern photograph of plate-like molybdenum precipitated along the grain boundaries of the uranium dioxide sintered body according to Example 1 of the present invention.

[0042] Figure 4 The photographs show molybdenum (white) and molybdenum oxide (black) precipitated in the uranium dioxide sintered body of Comparative Example 1 of the present invention according to the oxygen partial pressure.

[0043] Figure 5 This is an optical microscope microstructure photograph showing the results of adding metallic aluminum obtained by the aluminothermic method to the uranium dioxide sintered body of Example 1 of the present invention to maintain the soundness of molybdenum precipitates in the uranium dioxide sintered body matrix.

[0044] Figure 6 Graphs showing compression creep deformation over time after high-temperature compression creep tests of uranium dioxide sintered bodies according to Examples 1 to 4 of the present invention and Comparative Example 1.

[0045] Figure 7 This is a graph showing a comparison of thermal conductivity changes over time of uranium dioxide sintered bodies containing a sintering additive according to Examples 1 to 5 of the present invention and Comparative Example 1 and a conventional uranium dioxide sintered body. DETAILED DESCRIPTION

[0046] The specific structural and functional descriptions disclosed in the embodiments of the present invention are merely examples for illustrating embodiments of the concepts according to the present invention. Embodiments according to the concepts of the present invention may be implemented in a variety of ways and should not be construed as being limited to the embodiments described in this specification. Instead, they should be understood to encompass all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention.

[0047] According to one aspect of the present invention, a nuclear fuel sintered body is made of an oxide to which at least one selected from the group consisting of uranium (U), plutonium (Pu), gadolinium (Gd), and thorium (Th) is added, and the microstructure of the nuclear fuel sintered body includes precipitates produced by the sintering additives during the sintering process, and the precipitates are uniformly distributed along the circumferential direction.

[0048] The precipitates may form annular two-dimensional precipitate clusters.

[0049] The precipitates may be arranged along grain boundaries.

[0050] The precipitate may have a length of 3 μm to 30 μm and a thickness of 1 μm to 10 μm.

[0051] The sintering additive comprises copper (I) oxide (CuO), copper (II) oxide (Cu2O), chromium carbide (Cr 23 At least one of the group consisting of molybdenum dioxide (C6), molybdenum dioxide (MoO2), molybdenum trioxide (MoO3), molybdenum carbide (Mo2C), and molybdenum disilicide (MoSi2). During the sintering of uranium dioxide in a reducing atmosphere, the sintering additive is reduced and remains as a precipitate within the sintered body, thereby improving the thermal conductivity of the sintered body. Preferably, the amount of the sintering additive added relative to the oxide content of the nuclear fuel sintered body is 0.5 to 10.0 wt%.

[0052] The sintering additive may also include titanium dioxide (TiO2). Titanium dioxide can increase the grain size within the sintered body, thereby increasing the rate of compression creep deformation at high temperatures. This improves PCI properties and effectively reduces the pressure exerted on the cladding by the sintered body expansion. Preferably, the titanium dioxide (TiO2) content is 0.05wt% to 0.70wt% relative to the oxide used in the nuclear fuel sintered body.

[0053] The oxide nuclear fuel sintered body may also contain metal aluminum (Al) powder. The sintering additive reduced and precipitated in the uranium oxide sintered body serves to improve the thermal conductivity, but the reduced precipitates are reoxidized under high oxygen partial pressure conditions and lose their function. The metal aluminum powder reacts with oxygen to form aluminum oxide (Al2O3) and reduce the oxygen partial pressure, thereby preventing the reduced precipitates from oxidizing. Preferably, the content of the metal aluminum powder can be 0.01wt% to 0.10wt% relative to the oxide used in the nuclear fuel sintered body.

[0054] According to another aspect of the present invention, a method for manufacturing an oxide nuclear fuel sintered body is provided, which is used to manufacture an oxide nuclear fuel sintered body in which microscopic plate-like precipitates are distributed in a circumferential direction, comprising: a step of mixing an oxide powder containing at least one selected from a group including uranium (U), plutonium (Pu), gadolinium (Gd), and thorium (Th) with a sintering additive powder to produce a mixed powder (step 1); a step of pre-pressing and crushing the mixed powder and then screening to produce a granulated powder (step 2); a step of uniaxially pressing the granulated powder at 300 to 500 MPa to produce a nuclear fuel molded body (step 3); a step of performing a primary sintering on the manufactured nuclear fuel molded body at a sintering temperature of approximately 700 to 1100°C and a hydrogen-containing reducing gas atmosphere (step 4); and a step of continuously performing a secondary sintering at a sintering temperature of 1700 to 1800°C and a hydrogen-containing reducing gas atmosphere after the primary sintering is completed (step 5).

[0055] The sintering additive powder may include copper (I) oxide (CuO), copper (II) oxide (Cu2O), chromium carbide (Cr 23 C6), at least one of the group consisting of molybdenum dioxide (MoO2), molybdenum trioxide (MoO3), molybdenum carbide (Mo2C), and molybdenum disilicide (MoSi2).

[0056] The sintering additive may also include titanium dioxide (TiO2).

[0057] The content of titanium dioxide (TiO2) may be 0.05 wt% to 0.70 wt% relative to the oxide for the nuclear fuel sintered body.

[0058] The method for producing the oxide nuclear fuel sintered body may further include adding oxide metal aluminum (Al) powder.

[0059] In the primary sintering step, the sintering additive may be kept in a liquid state by heating at a heating rate of 1 to 10° C. / min and sintering at 300 to 1100° C. for 30 to 120 minutes.

[0060] In the secondary sintering step, cooling may not be performed after the primary sintering step is completed, and sintering may be performed at 1700 to 1800°C for 60 to 240 minutes at a heating rate of 1 to 10°C / min, so that the liquid sintering additives grow as microscopic plate-like precipitates along with the grain growth of the oxide nuclear fuel sintered body and are uniformly arranged along the circumferential direction.

[0061] When the sintering additive powder is copper (I) oxide (CuO) or copper (II) oxide (Cu2O), the sintering temperature of the primary sintering step (step 4) is 300 to 500°C and the sintering time is 30 to 120 minutes.

[0062] The hydrogen-containing reducing gas may include at least one selected from the group consisting of carbon dioxide, nitrogen, argon, and helium.

[0063] The hydrogen-containing reducing gas may consist only of hydrogen.

[0064] The present invention is described in detail below by way of examples and experimental examples, which are merely illustrative and do not limit the present invention in any way.

[0065] <Example 1> Production of uranium dioxide sintered body

[0066] Step 1: The method for producing a sintered oxide nuclear fuel body with microscopic plate-like precipitates distributed circumferentially is as follows: an oxide powder containing at least one selected from the group consisting of uranium (U), plutonium (Pu), gadolinium (Gd), and thorium (Th) is mixed with a sintering additive powder to produce a mixed powder. The oxide powder used in this example is uranium dioxide powder, and the amount of sintering additive added is shown in Table 1.

[0067] Step 2: The powder mixed in step 1 is pre-pressed (100 MPa) to produce a pre-pressed powder, which is then sieved to produce a granulated powder. The particle size of the granulated powder is about 400 μm to 800 μm.

[0068] Step 3: The granular powder produced in step 2 is placed in a quantitative molding die and uniaxially pressed at 300-400 MPa to produce a nuclear fuel molded body.

[0069] Step 4: The uranium dioxide molded body produced in step 3 is initially sintered at a sintering temperature of about 700-1100° C. in a hydrogen-containing reducing gas atmosphere for about 30-120 minutes.

[0070] Step 5: After the primary sintering in step 4 is completed, no cooling is performed, and a secondary sintering is performed at a sintering temperature range of 1700-1800°C for 60-240 minutes at a heating rate of 1-10°C / min to produce a uranium dioxide sintered body.

[0071] <Examples 2 to 10>

[0072] A sintered oxide nuclear fuel body with microscopic plate-like precipitates distributed circumferentially was manufactured using the same method as in Example 1, with the difference being the chemical composition of the uranium dioxide powder and the sintering additive. The chemical composition of the sintering additive added to the sintered oxide nuclear fuel body with microscopic plate-like precipitates distributed circumferentially is shown in Table 1.

[0073] [Table 1]

[0074] distinguish <![CDATA[MoO2]]> <![CDATA[Mo2C]]> <![CDATA[Cr 23 C6]]> CuO <![CDATA[Cu2O]]> <![CDATA[TiO2]]> Al Example 1 5 - - - - 0.1 0.01 Example 2 3 - - - - 0.1 0.05 Example 3 - 5 - - - 0.1 - Example 4 - 3 - - - 0.1 - Example 5 - - - - 3 0.1 - Example 6 - - - - 5 0.1 - Example 7 - - 5 - - - - Example 8 - - 3 - - - - Example 9 - - - 5 - 0.1 - Example 10 - - - 3 - 0.1 -

[0075] <Comparative Example 1> Production of Existing Commercial Uranium Dioxide Sintered Body

[0076] As the commercial uranium dioxide sintered body used as nuclear fuel in commercial nuclear power plants, a uranium dioxide sintered body currently commercially supplied and manufactured using a uranium dioxide sintered body manufacturing process is used.

[0077] <Comparative Example 2> Production of Uranium Dioxide Sintered Body Containing No Aluminum

[0078] The production was carried out in the same manner as in Example 1, except that no aluminum was added to the components of the sintering additive.

[0079] <Experimental Example 1> Microstructure Analysis

[0080] In order to analyze the microstructure of the sintered body of the oxide nuclear fuel in which microscopic plate-like precipitates are distributed in the circumferential direction according to Example 1 of the present invention, the microstructure was analyzed using an optical microscope and a scanning electron microscope. Figure 1 and Figure 2 The microstructure of the sintered body with the addition of molybdenum dioxide, titanium dioxide and metal aluminum is shown. Figure 1 and Figure 2 As shown, the addition of molybdenum dioxide during sintering confirms that, due to the growth of the UO2 sintered body's grains induced by titanium dioxide and the chemical reaction between molybdenum dioxide and hydrogen, plate-like metallic molybdenum precipitates along the grain boundaries. In particular, the plate-like metallic molybdenum precipitates are uniformly distributed in a two-dimensional ring-like pattern. These two-dimensional rings and the metallic molybdenum contribute to the improvement in thermal conductivity. Figure 3 Scanning electron microscopy (SEM / EDS) and XRD analysis of the microstructure and elements of the precipitates confirmed the presence of plate-like molybdenum deposits along the grain boundaries of the uranium dioxide. Furthermore, XRD analysis, using an analytical instrument used to analyze trace impurities and crystal structure, confirmed that the precipitates within the uranium dioxide matrix were all metallic molybdenum deposited from the molybdenum dioxide additive.

[0081] <Experimental Example 2> Evaluation of the Soundness of Molybdenum Precipitates Based on Sintering Atmosphere

[0082] In order to evaluate the soundness of precipitates in the sintered body of the oxide nuclear fuel in which microscopic plate-like precipitates are distributed in the circumferential direction according to Comparative Example 1 and Example 1 of the present invention, the soundness of the precipitates was evaluated according to the sintering atmosphere. Figure 4 The precipitates in the microstructure of uranium dioxide of Comparative Example 1 manufactured under the sintering atmosphere conditions of oxygen partial pressure of CO2 / H2=3% and 5% are shown in FIG. Figure 4As shown, increasing oxygen partial pressure can lead to oxidation or volatilization of molybdenum precipitates. This is because residual oxygen in the sintering furnace and trace amounts of oxygen in the uranium dioxide increase the oxygen partial pressure, causing the precipitated molybdenum to be reoxidized into molybdenum oxides such as molybdenum trioxide (MoO3) or molybdenum dioxide (MoO2), which then volatilize. Therefore, to prevent residual oxygen from causing oxidation of the metallic molybdenum precipitates, a small amount of aluminum can be added. Aluminothermic treatment can be used to allow the residual oxygen to react with the aluminum first, significantly reducing the oxygen partial pressure in the sintering furnace and preventing molybdenum oxidation. Figure 5 The figure shows the test results of adding a trace amount of metal aluminum to maintain the soundness of the precipitate as in Example 1. The dark black part is molybdenum oxide, and the bright white part is molybdenum. Figure 4 , Figure 5 A large number of white spots, which are molybdenum, are distributed in the sample, and it was confirmed that the oxidation of molybdenum can be prevented by adding aluminum.

[0083] <Experimental Example 3> High Temperature Compression Creep Test

[0084] In order to understand the high-temperature deformation characteristics of the oxide nuclear fuel sintered bodies having microscopic plate-like precipitates distributed in the circumferential direction according to Examples 1 to 4 of the present invention and Comparative Example 1, a high-temperature compression creep test as described below was carried out. After manufacturing a uranium dioxide sintered body having the composition of Examples 1 to 4 and Comparative Example 1, a high-temperature compression creep test specimen was produced. After the end faces of the sintered body specimens were evenly cut, the diameter and length of the specimens were measured to evaluate the deformation of the specimens after the high-temperature compression creep test. The high-temperature compression creep test was carried out using a special purpose high-temperature creep test equipment manufactured by the German Zwick / Roell company, applying a compressive load of 40 MPa for about 20 hours at a temperature of 1450°C and a hydrogen atmosphere. In the high-temperature compression creep test, the deformation over time when a compressive load of 40 MPa was applied was measured in real time using a non-contact laser extensometer and stored. As Figure 6 As shown, it can be confirmed that the high-temperature compressive creep deformation of Examples 1 to 4 of the present invention is at least 5 to 20 times faster than the high-temperature compressive creep deformation of the commercial uranium dioxide sintered body given as Comparative Example 1.

[0085] <Experimental Example 4> Thermal Conductivity Evaluation Test

[0086] The thermal conductivity of uranium dioxide sintered compacts is affected by factors such as density, porosity, chemical equivalence, temperature, and impurity concentration. Thermal conductivity, a thermophysical property, is an inherent material property and is calculated as a function of the component's density, specific heat, and thermal diffusivity. To evaluate the thermal conductivity of uranium dioxide, thermal diffusivity was determined using the laser flash method. Thermal diffusivity was measured using the Netzsch LFA427 model, density was determined using the buoyancy method, and specific heat was calculated using the composite specific heat calculation method. The temperature-dependent thermal conductivity was calculated by multiplying density, specific heat, and thermal diffusivity. Figure 7 The following table shows the results of a comparative evaluation of the thermal conductivity of the sintered bodies of Examples 1 to 5 of the present invention and Comparative Example 1. As shown, the thermal conductivity of Examples 1 to 5 is approximately 40% to 70% higher than that of Comparative Example 1. This result is believed to be due to the precipitation of molybdenum oxides, chromium carbides, and the like into plate-like metallic molybdenum during the sintering process, resulting in a significant increase in thermal conductivity due to the two-dimensional annular distribution effect.

[0087] The present invention described above is not limited to the above embodiments and drawings, and various substitutions, deformations and changes can be made without departing from the technical scope of the present invention. This is obvious to ordinary technicians in the technical field to which the present invention belongs.

Claims

1. A sintered oxide nuclear fuel body, comprising an oxide to which at least one selected from the group consisting of uranium (U), plutonium (Pu), gadolinium (Gd), and thorium (Th) is added, characterized in that: The microstructure of the nuclear fuel sintered body contains precipitates generated by sintering additives during the sintering process, and the precipitates are uniformly distributed along the circumferential direction; The sintering additive comprises copper (I) oxide (CuO), copper (II) oxide (Cu2O), chromium carbide (Cr 23 C6), at least one of the group consisting of molybdenum dioxide (MoO2), molybdenum trioxide (MoO3), molybdenum carbide (Mo2C), molybdenum disilicide (MoSi2) and metallic aluminum (Al) powder.

2. The oxide nuclear fuel sintered body according to claim 1, characterized in that: The precipitates form ring-shaped two-dimensional precipitate clusters.

3. The oxide nuclear fuel sintered body according to claim 1, characterized in that: The precipitates are arranged along the grain boundaries.

4. The oxide nuclear fuel sintered body according to claim 1, characterized in that: The precipitate has a length of 3 μm to 30 μm and a thickness of 1 μm to 10 μm.

5. The oxide nuclear fuel sintered body according to claim 1, characterized in that: The sintering additive also includes titanium dioxide (TiO2).

6. The oxide nuclear fuel sintered body according to claim 5, characterized in that: The content of titanium dioxide (TiO2) is 0.05 wt% to 0.70 wt% relative to the oxide for nuclear fuel sintered body.

7. The oxide nuclear fuel sintered body according to claim 1, characterized in that: The content of the sintering additive is 0.5 wt % to 10.0 wt % relative to the oxide for nuclear fuel sintered body.

8. The oxide nuclear fuel sintered body according to claim 1, characterized in that: The content of the metal aluminum (Al) powder is 0.01 wt % to 0.10 wt % relative to the oxide for nuclear fuel sintered body.

9. A method for producing an oxide nuclear fuel sintered body, for producing an oxide nuclear fuel sintered body having microscopic plate-like precipitates distributed along the circumferential direction, characterized in that: include: a step of mixing oxide powder containing at least one selected from the group consisting of uranium (U), plutonium (Pu), gadolinium (Gd), and thorium (Th) with sintering additive powder to produce a mixed powder (step 1); a step of preparing granulated powder by pre-pressing and pulverizing the mixed powder and then screening it (step 2); a step of subjecting the granulated powder to uniaxial pressing at 300 to 500 MPa to produce a nuclear fuel molded body (step 3); a step of performing a primary sintering of the manufactured nuclear fuel molded body at a sintering temperature of 700 to 1100° C. in a hydrogen-containing reducing gas atmosphere (step 4); as well as After the primary sintering is completed, a secondary sintering step is continuously performed at a sintering temperature of 1700-1800° C. in a hydrogen-containing reducing gas atmosphere (step 5); The sintering additive comprises copper (I) oxide (CuO), copper (II) oxide (Cu2O), chromium carbide (Cr 23 C6), at least one of the group consisting of molybdenum dioxide (MoO2), molybdenum trioxide (MoO3), molybdenum carbide (Mo2C), molybdenum disilicide (MoSi2) and metallic aluminum (Al) powder.

10. The method for producing a sintered oxide nuclear fuel body according to claim 9, wherein: The sintering additive also includes titanium dioxide (TiO2).

11. The method for producing a sintered oxide nuclear fuel body according to claim 10, wherein: The content of the added titanium dioxide (TiO2) is 0.05 wt% to 0.70 wt% relative to the oxide for nuclear fuel sintered body.

12. The method for producing a sintered oxide nuclear fuel body according to claim 9, wherein: In the primary sintering step, the sintering additive is kept in a liquid state by heating at a heating rate of 1 to 10° C. / min and sintering at 300 to 1100° C. for 30 to 120 minutes.

13. The method for producing a sintered oxide nuclear fuel body according to claim 9, wherein: In the secondary sintering step, no cooling is performed after the primary sintering step is completed, and the sintering is performed at 1700 to 1800°C for 60 to 240 minutes at a heating rate of 1 to 10°C / min, so that the liquid sintering additive grows as microscopic plate-like precipitates along with the grain growth of the oxide nuclear fuel sintered body and is uniformly arranged along the circumferential direction.

14. The method for producing a sintered oxide nuclear fuel body according to claim 12, wherein: When the sintering additive powder is copper (I) oxide (CuO) or copper (II) oxide (Cu2O), in the primary sintering step (4th step), the sintering temperature is 300 to 500°C and the sintering time is 30 to 120 minutes.

15. The method for producing a sintered oxide nuclear fuel body according to claim 9, wherein: The hydrogen-containing reducing gas includes at least one selected from the group consisting of carbon dioxide, nitrogen, argon, and helium.

16. The method for producing a sintered oxide nuclear fuel body according to claim 9, wherein: The hydrogen-containing reducing gas consists only of hydrogen.

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