Plate-shaped briquette and manufacturing method of nuclear fuel for research reactor using the same

Abstract

The present invention relates to a plate-shaped compact and a method for manufacturing nuclear fuel for a research reactor using the same. More specifically, the invention relates to a plate-shaped compact and a method for manufacturing nuclear fuel for a research reactor using the same, which can prevent localized power increase or external leakage of the nuclear fuel core due to the displacement of nuclear fuel particles by improving the dog-bone defect in which the nuclear fuel core is pushed to the edge region during the hot rolling process of the compact.

Description

Technology Field

[0001] The present invention relates to a plate-shaped compact and a method for manufacturing nuclear fuel for a research reactor using the same. More specifically, the invention relates to a plate-shaped compact and a method for manufacturing nuclear fuel for a research reactor using the same, which can prevent localized power increase or external leakage of nuclear fuel core material caused by the displacement of nuclear fuel powder by improving the dog-bone defect in which the core material of the nuclear fuel is pushed to the edge region during the hot rolling process of the compact. Background Technology

[0003] Unlike power generation reactors, research reactor fuel is designed to be suitable for high neutron flux and heat removal; therefore, it uses a dispersed fuel form in which powdered fuel material is evenly dispersed within a metal matrix such as aluminum. The nuclear fuel for the aforementioned research reactor generally takes the form of very thin plates with a thickness of just over 1 mm. Consequently, to manufacture such plate-shaped fuel, an aluminum alloy assembly containing the fuel compact must first be produced and subjected to a multiple hot rolling process.

[0004] However, during the hot rolling process for manufacturing nuclear fuel for conventional research reactors, a phenomenon in which the fuel core is pushed to the edges persists. This occurs because the flowability differs between the fuel core, where the fuel powder is dispersed, and the aluminum alloy material acting as the cladding. Due to the material ductility and morphological differences between the cladding and the fuel core, this problem is unavoidable.

[0005] More specifically, referring to FIGS. 1 to 4, a conventional method for manufacturing nuclear fuel for a general research reactor involves loading a mixture of aluminum powder and nuclear fuel powder into the lower die of a press, which is a forming machine, and then lowering the upper ram of the press to press it under high pressure to produce a compact. The compact produced at this time is in the form of a rectangular plate, and after inserting this compact into an aluminum alloy assembly, a number of hot rolling processes are performed. At this time, as mentioned earlier, a dog-bone defect occurs due to excessive displacement of the nuclear fuel core at the end of the fuel plate caused by the difference in physical properties between the nuclear fuel core region and the aluminum alloy cladding.

[0006] Such localized concentration of nuclear fuel powder can not only cause localized power increases but also lead to serious problems, such as leakage of the nuclear fuel core, as the thickness of the aluminum alloy cladding becomes significantly thinner in the affected area. In addition, it causes a decrease in yield and an increase in manufacturing costs.

[0007] Accordingly, there is an urgent need for research that can significantly increase the safety of research reactor fuel and simultaneously improve productivity and economic efficiency by drastically improving the generation of dog-bone defects during the manufacturing of research reactor fuel. Prior art literature

[0009] Republic of Korea Registered Patent No. 10-2027869 (September 26, 2019) The problem to be solved

[0010] The present invention was devised to overcome the aforementioned problems, and the objective of the present invention is to provide a plate-shaped nuclear fuel compact for a research reactor with an improved shape without changing the existing commercial manufacturing process procedures and equipment for research reactor nuclear fuel.

[0011] In addition, another problem that the present invention aims to solve is to provide a nuclear fuel plate-shaped compact for a research reactor with an improved shape that can ensure a uniform distribution of nuclear fuel core thickness across the entire fuel plate by preventing the formation of dog-bone defects occurring in existing commercial processes.

[0012] In addition, another problem that the present invention aims to solve is a method for manufacturing nuclear fuel for a research reactor that can prevent localized power increase or external leakage of the nuclear fuel core material caused by the uneven distribution of nuclear fuel powder by using the nuclear fuel plate-shaped compact of the improved shape of the research reactor above. means of solving the problem

[0014] The present invention provides a method for manufacturing nuclear fuel for a research reactor, comprising a first step of mixing base metal powder and nuclear fuel powder to solve the above-mentioned problem, a second step of loading the mixed powder into a mold and pressurizing it to manufacture a plate-shaped compact, and a third step of inserting the plate-shaped compact into an alloy assembly and then hot rolling, wherein the upper and lower surfaces of the plate-shaped compact have inclined ends having an angle of 8° to 30° in the longitudinal direction.

[0015] In addition, according to one embodiment of the present invention, the mold of the second stage may further include a pressing member that applies pressure to the upper and lower surfaces of the plate-shaped compact so that the plate-shaped compact has two ends inclined in the longitudinal direction.

[0016] In addition, the thickness increase at both ends of the plate-shaped compact is offset during the hot rolling process of the third stage, so that no dog-bone defects occur.

[0017] In addition, the compact base metal powder may be characterized as being aluminum, Si solid solution aluminum, or an aluminum alloy.

[0018] In addition, a method for manufacturing nuclear fuel for a research reactor, characterized in that the nuclear fuel powder is at least one selected from the group consisting of U, U-Mo, U-Si, U-Al, UO, UN, U-Ti, U-Zr, and U-Nb compounds.

[0019] In addition, the average particle size of the base metal powder may be characterized as being 1 to 50 μm.

[0020] In addition, the present invention provides a plate-shaped compact for research reactor nuclear fuel that has improved dog-bone defects, comprising a base metal powder and nuclear fuel powder, and having two ends inclined so as to have an angle of 8° to 30° in the longitudinal direction on the upper and lower surfaces.

[0021] In addition, both ends of the plate-shaped compact may be characterized by having an area corresponding to 1 to 8% of the total length in the longitudinal direction that is inclined.

[0022] In addition, both ends of the plate-shaped compact may be characterized by having an area corresponding to 8 to 16% of the total thickness direction that is inclined.

[0023] In addition, the above plate-shaped compact may be characterized by satisfying the following relationship 1.

[0024] [Relationship 1]

[0025] 0.14 rad < Arctan(b / a) < 0.52 rad

[0026] At this time, a is the end region corresponding to 1 to 8% of the total length direction of the plate-shaped compact, b is the end region corresponding to 8 to 16% of the total thickness direction of the plate-shaped compact, and rad means radians. Effects of the invention

[0028] The present invention can provide a nuclear fuel plate-shaped compact for a research reactor with an improved shape that can ensure an even distribution of nuclear fuel core thickness across the entire fuel plate by preventing the formation of dog-bone defects occurring in existing commercial processes without changing existing commercial manufacturing process procedures and equipment for research reactor nuclear fuel. In addition, by preventing localized power increases or external leakage of nuclear fuel core material caused by the uneven distribution of nuclear fuel powder, the stability of the research reactor nuclear fuel can be significantly improved, and the productivity and economic efficiency of the research reactor nuclear fuel manufacturing process can be greatly enhanced. Brief explanation of the drawing

[0030] Figures 1 and 2 are schematic diagrams showing a method for manufacturing a compact as a general core material for conventional research reactor nuclear fuel. Figure 3 is a schematic diagram showing the hot rolling step in a general manufacturing method for nuclear fuel for a conventional research reactor. Figure 4 is a schematic diagram showing a dog-bone defect that appears according to the general manufacturing method of nuclear fuel for a conventional research reactor. Figure 5 is an image showing the difference in core material distribution between the dog-bone region and the nuclear fuel center region after final rolling when using a compact made of aluminum powder with an average powder size of 45 μm according to one embodiment of the present invention. Figure 6 is an image showing the difference in core material distribution between the dog-bone region and the nuclear fuel center region after final rolling when using a compact made of aluminum powder with an average powder size of 10 μm according to one embodiment of the present invention. FIGS. 7 and 8 are schematic diagrams illustrating a method for manufacturing nuclear fuel for a research reactor according to an embodiment of the present invention. FIG. 9 is a schematic diagram showing a nuclear fuel assembly manufactured by a method for manufacturing nuclear fuel for a research reactor according to one embodiment of the present invention. FIGS. 10 and 11 are schematic diagrams showing that no dog-bone defects occur after hot rolling in a method for manufacturing nuclear fuel for a research reactor according to one embodiment of the present invention. FIG. 12 is an image of the end portion of a nuclear fuel manufactured by the method for manufacturing nuclear fuel for a research reactor according to an embodiment of the present invention. FIG. 13 is a perspective view showing a compact body shape design according to one embodiment of the present invention. Specific details for implementing the invention

[0031] The embodiments of the present invention are described below in detail so that those skilled in the art can easily implement the invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0032] In this specification, "compact" may refer to a plate-shaped member manufactured by pressing a mixture of base metal powder and nuclear fuel particle powder, and "nuclear fuel core" may refer to the compact after inserting the plate-shaped compact into an alloy assembly and hot rolling.

[0034] As described above, according to the conventional method for manufacturing nuclear fuel for research reactors, dog-bone defects inevitably occur during hot rolling, where the fuel core is pushed to the edge region, which poses a problem in that the stability of the fuel cannot be guaranteed and limits the improvement of production yield and economic efficiency.

[0035] Accordingly, the present invention seeks to solve the aforementioned problem by providing a method for manufacturing nuclear fuel for a research reactor, comprising a first step of mixing base metal powder and nuclear fuel powder, a second step of loading the mixed powder into a mold and pressurizing it to produce a plate-shaped compact, and a third step of inserting the plate-shaped compact into an alloy assembly and then hot rolling, wherein the upper and lower surfaces of the plate-shaped compact have inclined ends having an angle of 8° to 30° in the longitudinal direction.

[0036] Through this, the present invention can ensure stability and significantly improve economic efficiency and productivity by improving the dog-bone defect in which the nuclear fuel core is pushed to the edge region, thereby preventing localized power increase or external leakage of the nuclear fuel core caused by the displacement of nuclear fuel powder.

[0038] The present invention will be described in detail below with reference to the drawings.

[0039] In the present invention, a nuclear reactor refers to a device that controls a chain reaction to release a large amount of mass defect energy instantaneously as a result of a chain reaction of nuclear materials, thereby utilizing the thermal energy generated from nuclear fission as power.

[0040] Furthermore, in the present invention, nuclear fuel refers to a material that can be loaded into a nuclear reactor to cause a chain reaction of nuclear fission to obtain usable energy, and means atomic fuel.

[0042] Method for manufacturing nuclear fuel for a research reactor

[0043] The first step of the method for manufacturing nuclear fuel for a research reactor according to the present invention is to mix base metal powder and nuclear fuel powder, and the second step is to manufacture a plate-shaped compact by loading the mixed powder, in which the base metal powder and nuclear fuel powder are mixed, into a mold and applying pressure.

[0044] The above nuclear fuel powder may be one or more powders selected from the group consisting of uranium, uranium alloys, uranium silicides, and aluminides. Specifically, the above nuclear fuel powder may be one or more selected from the group consisting of U, U-Mo, U-Si, U-Al, UO, UN, U-Ti, U-Zr, and U-Nb compounds. In this case, the particle center diameter of the above nuclear fuel powder may be in the range of 10㎛ to 100㎛, but is not limited to the above examples and larger particles may also be used.

[0045] The above base metal powder is mixed with the above nuclear fuel powder, and any known conventional base metal powder may be used as long as it is suitable for the purpose of the invention. The above base metal powder may be, for example, one or more selected from the group consisting of aluminum, aluminum with Si solution, or aluminum alloys.

[0046] Meanwhile, according to FIGS. 1 and 2, which describe a general method for manufacturing nuclear fuel for research reactors, a mixture of aluminum alloy powder and nuclear fuel powder is loaded into the lower die of a press, and the upper ram of the press is lowered to apply pressure and manufacture a compact. The compact manufactured at this time is in the form of a rectangular plate, and this nuclear fuel compact is inserted into an aluminum alloy assembly to undergo multiple hot rolling processes. At this time, in the general hot rolling process shown in FIG. 3, local displacement of the nuclear fuel core material occurs, which may result in dog-bone defects at both ends of the compact as described above. FIG. 4 is a schematic cross-sectional view illustrating a compact exhibiting dog-bone defects. As shown in FIG. 4, a dog-bone defect refers to a defect in which the nuclear fuel core material is deformed convexly. If such a dog-bone defect occurs, it can cause a localized increase in power output due to fuel displacement. In addition, because the thickness of the aluminum alloy cladding at the site of the dog-bone defect becomes significantly thinner, it can cause serious problems such as the leakage of the fuel core.

[0047] In one example, the dog-bone defect may be formed depending on the size of the base metal powder mixed for the dispersion of the nuclear fuel powder. Referring to FIGS. 5 and 6, it can be seen that when the average size of the base metal powder mixed in the first step is small, the tendency for dog-bone defects to occur is more pronounced during the hot rolling process. That is, the average particle size of the base metal powder may be 1 to 50 μm. In this case, if the average particle size of the base metal powder is less than 1 μm, mixing with the nuclear fuel powder is not smooth, which may result in reduced bonding strength and localized clumping. Additionally, if the average particle size of the base metal powder exceeds 50 μm, the distribution of the nuclear fuel powder becomes uneven, which may result in a decrease in homogeneity.

[0048] In another example, the dog-bone defect may be affected by the shape of the compact. As previously mentioned, when the compact is inserted into an aluminum alloy assembly and hot-rolled, dog-bone defects may occur more frequently if the compact is in the form of a cuboidal plate. To prevent dog-bone defects caused by the shape of the compact, the mold for manufacturing the compact in the second step may further include an aluminum or aluminum alloy pressing member that applies pressure to the upper and lower surfaces of the plate-shaped compact so that the plate-shaped compact has two ends inclined in the longitudinal direction.

[0049] More specifically, referring to FIGS. 7 and 8, which represent an embodiment of the present invention, a lower pressurizing member A is first positioned at the bottom of the compaction mold, and then a mixture of nuclear fuel and aluminum powder is loaded. After covering with the upper pressurizing member B, the upper press ram is lowered to form a high-density compaction body. In this case, as shown in FIG. 7, an assembly can be manufactured in which the thickness decreases while having a certain slope at the edge of the plate-shaped compaction body. By using this assembly and performing hot rolling according to FIG. 8, a nuclear fuel can be manufactured in which the thickness does not increase even if the central nuclear fuel core region is pushed toward the end of the nuclear fuel plate. That is, as shown in FIG. 11, it can be seen that no dog-bone defects appear. This result is possible because the thickness of the end of the core of the compaction body is reduced in advance, so even if a displacement phenomenon of the nuclear fuel core occurs later, it does not exceed the thickness of the central part of the core excessively.

[0050] At this time, in order to determine specific specifications for the shape of the end of the plate-shaped compact according to one embodiment of the present invention, changes in the physical properties of the plate-shaped compact itself during the manufacturing process must be considered. Referring to FIG. 9, the upper and lower surfaces of the plate-shaped compact according to the present invention may be set to have inclined ends with an angle of 8° to 30° in the longitudinal direction. FIG. 10 is a schematic diagram showing the process of hot rolling the plate-shaped compact of FIG. 9, and FIG. 11 schematically illustrates the shape of the end of the compact after hot rolling. When manufacturing nuclear fuel using the method for manufacturing nuclear fuel for a research reactor according to the present invention, even if a displacement phenomenon of the core material occurs during the hot rolling process, the thickness of the central part of the core material does not become excessive as shown in FIG. 11, and the formation of dog-bone defects at both ends can be prevented. At this time, if the upper and lower surfaces of the plate-shaped compact have an angle of less than 8° in the longitudinal direction, the effect of preventing the formation of dog-bone defects may be minimal, and if the upper and lower surfaces of the plate-shaped compact have an angle exceeding 30° in the longitudinal direction, there may be a problem in that the distribution of nuclear fuel powder in the end region of the core material is significantly reduced and the uniformity of the nuclear fuel powder is not guaranteed.

[0051] More specifically, as shown in FIG. 13, the above-described compact may have a shape (θ) in which the two end regions (a) corresponding to 1 to 8% of the total length in the longitudinal direction and the two end regions (b) corresponding to 8 to 16% of the total thickness in the thickness direction are inclined. In this case, if the portion (θ) inclined in the longitudinal direction is less than 1% of the total length or the portion inclined in the thickness direction is less than 8% of the total thickness, the effect of preventing the formation of dog-bone defects may be negligible. Furthermore, if the portion inclined in the longitudinal direction exceeds 8% of the total length or the portion inclined in the thickness direction exceeds 16% of the total thickness, the distribution of nuclear fuel powder in the end regions of the core material is significantly reduced, and there is a problem in that the uniformity of the nuclear fuel powder is not guaranteed. The end regions (a) along the longitudinal direction of the above plate-shaped compact may be 8% or less, 7% or less, 6% or less, 5% or less, or 4.6% or less, but are not limited thereto.

[0052] When these results are combined, the plate-shaped compact according to the present invention can satisfy the following relationship 1.

[0053] [Relationship 1]

[0054] 0.15 rad < Arctan(b / a) < 0.54 rad

[0055] At this time, a is the end region corresponding to 1 to 8% of the total length direction of the plate-shaped compact, b is the end region corresponding to 8 to 16% of the total thickness direction of the plate-shaped compact, and rad means radians.

[0056] The above a may be 8% or less, 7% or less, 6% or less, 5% or less, or 4.6% or less, but is not limited thereto.

[0057] Through this, the present invention can significantly improve the occurrence of dog-bone defects by offsetting the thickness increase at both ends of the plate-shaped compact during the third stage hot rolling process. At this time, the hot rolling process is not particularly limited, as it may be a known conventional hot rolling process as long as it meets the purpose of the present invention.

[0059] Research reactor nuclear fuel plate compact

[0060] Next, a plate-shaped compact of research reactor fuel according to the present invention will be described. However, to avoid duplication, descriptions regarding content identical in technical concept to the manufacturing method of the research reactor fuel described above will be omitted.

[0061] The research reactor nuclear fuel plate-shaped compact according to the present invention is a plate-shaped compact with improved dog-bone defects, comprising base metal powder and nuclear fuel powder, and having two ends inclined to have an angle of 8° to 30° in the longitudinal direction on the upper and lower surfaces.

[0062] At this time, both ends of the plate-shaped compact may be inclined in an area corresponding to 1 to 8% of the total length direction and an area corresponding to 8 to 16% of the total thickness direction.

[0063] In addition, the end regions along the longitudinal direction of the plate-shaped compact may be 8% or less, 7% or less, 6% or less, 5% or less, or 4.6% or less, but are not limited thereto.

[0065] Hereinafter, preferred embodiments of the present invention and their effects will be described with reference to specific examples. The following examples are illustrative to facilitate understanding of preferred embodiments of the present invention and do not limit the scope of the present invention. People skilled in the art may implement the invention by adding, changing, or deleting configurations other than the essential configurations of the invention described in the claims of the present invention, and such embodiments are also within the scope of the present invention.

[0067] Examples

[0068] In order to determine specific specifications for the shape of the end of the plate, changes in the physical properties of the nuclear fuel core itself during the manufacturing process must be considered. The present invention confirmed that the shape of the compact and dog-bone defects are formed depending on the size of the base metal powder mixed for the dispersion of the nuclear fuel powder. More specifically, referring to Figures 5 and 6, it can be seen that when the size of the base metal powder (pure aluminum powder) mixed in the first step is small, the tendency for dog-bone defects to occur during the hot rolling process is more pronounced.

[0069] Therefore, regarding the plate-shaped compact according to the present invention based on the aluminum powder size, it can be seen that when the average size of the aluminum matrix powder is 45 μm, the tendency for dog-bone defects to appear is less than when it is 10 μm or less, so the reduction value of the end thickness of the plate-shaped compact must also be different. In other words, in order to secure an appropriate coating thickness in the dog-bone region, the shape of the plate-shaped compact can be inversely estimated.

[0070] To trace the shape of the plate-shaped compact, a mixture of nuclear fuel powder and base metal powder was loaded into a compaction mold and pressed to produce a plate-shaped compact specimen. The produced plate-shaped compact specimen had a thickness of 4.30 mm, a length of 94.10 mm, and a width of 43.40 mm.

[0071] The manufactured specimen was hot-rolled as shown in Fig. 10 to observe the shape change of the end of the compact. As a result of the observation, when the average size of the aluminum matrix powder is 45 μm, the thickness reduction at the end of the plate-shaped compact should be 0.38 mm at each end (8.8% of the thickness of the initial compact). At this time, the section where the dog-bone occurs is 10 to 35 mm after the last rolling, so it can be expected to be in the range of 1.23 to 4.3 mm in the longitudinal direction of the initial compact (1.3% to 4.6% of the length of the initial compact). At this time, the triangular shape of the end in pressing members A and B also matches the shape of the compact.

[0072] Meanwhile, test results confirm that the tendency for dog-bone defects to occur becomes more pronounced when the average size of the aluminum powder is fine, which is 10 μm or less. The initial thickness of the plate-shaped compact should be further reduced by 0.67 mm at each end (approximately 15.5% of the initial compact thickness). Since the section where the dog-bone occurs is 10 to 35 mm after the last rolling, it can be formed in the range of 1.23 to 4.3 mm along the length of the initial compact (approximately 1.3% to 4.6% of the initial compact length). Similarly, the triangular shape at the ends of pressing members A and B also matches the shape of the compact.

[0073] FIG. 12 is an image of a cross-section of the end portion of nuclear fuel manufactured in an embodiment of the present invention. As shown in FIG. 12, nuclear fuel manufactured by the method for manufacturing research reactor nuclear fuel according to the present invention may not have dog-bone defects.

[0074] Although embodiments of the present invention have been described in detail above, the present invention is not limited by the aforementioned embodiments and accompanying drawings, but is intended to be limited by the appended claims. Accordingly, various substitutions, modifications, and changes may be made by those skilled in the art within the scope of the technical concept of the present invention as described in the claims, and such are also to be considered to fall within the scope of the present invention. Explanation of the symbols

[0076] -

Claims

Claim 1 A method for manufacturing nuclear fuel for a research reactor, comprising: a first step of mixing base metal powder and nuclear fuel powder; a second step of loading the mixed powder into a mold and pressurizing it to produce a plate-shaped compact; and a third step of inserting the plate-shaped compact into an alloy assembly and then hot rolling; wherein the upper and lower surfaces of the plate-shaped compact have inclined ends having an angle of 8° to 30° in the longitudinal direction, and the two ends of the plate-shaped compact have an inclined area corresponding to 1 to 8% of the total length in the longitudinal direction. Claim 2 A method for manufacturing nuclear fuel for a research reactor according to claim 1, wherein the mold of the second stage further comprises a pressurizing member that presses the upper and lower surfaces of the plate-shaped compact so that the plate-shaped compact has two ends inclined in the longitudinal direction. Claim 3 A method for manufacturing nuclear fuel for a research reactor according to claim 1, characterized in that the increase in thickness at both ends of the plate-shaped compact is offset in the hot rolling process of the third step, so that no dog-bone defects occur. Claim 4 A method for manufacturing nuclear fuel for a research reactor according to claim 1, characterized in that the base metal powder is aluminum, Si solid solution aluminum, or an aluminum alloy. Claim 5 A method for manufacturing nuclear fuel for a research reactor according to claim 1, wherein the nuclear fuel powder is at least one selected from the group consisting of U, U-Mo, U-Si, U-Al, UO, UN, U-Ti, U-Zr, and U-Nb compounds. Claim 6 A method for manufacturing nuclear fuel for a research reactor, characterized in that, in claim 1, the average particle size of the base metal powder is 1 to 50 μm. Claim 7 A plate-shaped compact for research reactor nuclear fuel with improved dog-bone defects, comprising a base metal powder and nuclear fuel powder, wherein the upper and lower surfaces have inclined ends having an angle of 8° to 30° in the longitudinal direction, and the two ends of the plate-shaped compact are characterized by having an area corresponding to 1 to 8% of the total length in the longitudinal direction. Claim 8 delete Claim 9 A research reactor nuclear fuel plate-shaped compact according to claim 7, characterized in that both ends of the plate-shaped compact have an area corresponding to 8 to 16% of the total thickness direction inclined. Claim 10 In claim 7, the above-mentioned plate-shaped compact is a research reactor nuclear fuel plate-shaped compact characterized by satisfying the following relationship 1. [Relationship 1] 0.15 rad < Arctan(b / a) < 0.54 rad where a is the end region corresponding to 1 to 8% of the total length direction of the plate-shaped compact, b is the end region corresponding to 8 to 16% of the total thickness direction of the plate-shaped compact, and rad means radian.

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