Manufacturing method for nuclear fuel pellets

Abstract

To provide a low-cost and high-quality recycled material from a nuclear fuel scrap.SOLUTION: A method for recycling a nuclear fuel scrap includes: a grinding step of grinding a nuclear fuel scrap by a counter air flow type grinder; and a recover step of recovering particles with diameters of not larger than a predetermined particle diameter of the ground nuclear fuel scrap.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for recycling nuclear fuel scrap, a recycling apparatus, and a method for manufacturing nuclear fuel pellets using recycled materials. More specifically, the present invention relates to a method for recycling nuclear fuel scrap generated in the process of manufacturing nuclear fuel pellets, an apparatus for recycling nuclear fuel scrap, and a method for manufacturing nuclear fuel pellets using the recycled material obtained by the method or apparatus.

Background Art

[0002] Nuclear fuel pellets are manufactured through, for example, a process (S11: mixing process) of adding and mixing recycled materials to raw material powder to obtain mixed powder as shown in FIG. 6, a process (S12: pressure molding process) of pressure molding the mixed powder into a cylindrical shape to obtain a molded body, a process (S13: sintering process) of sintering the molded body at a high temperature to obtain a sintered body, a process (S14: grinding process) of grinding the sintered body to adjust its shape to obtain nuclear fuel pellets, and a process (S15: inspection process) of inspecting the nuclear fuel pellets. As will be described below, nuclear fuel scrap (hereinafter also simply referred to as "scrap") is generated in each process.

[0003] The properties of nuclear fuel scrap are classified into powder form, molded body form, and sintered body form. Powder scrap (powder scrap) includes end materials generated in the mixing process and grinding waste generated in the grinding process. Molded body scrap (molded body scrap) includes molded bodies that could not be molded under the molding pressure under predetermined conditions, molded bodies with problems in appearance and dimensions, and the like. Sintered body scrap (sintered body scrap) includes sintered bodies with a sintering density outside the predetermined range, nuclear fuel pellets that failed in the inspection process, and the like.

[0004] Nuclear fuel scrap is recovered as a recycled material through recycling treatment. The recycled material is used as raw material powder or mixed with raw material powder for manufacturing nuclear fuel pellets.

[0005] Nuclear fuel scrap recycling methods are broadly classified into wet recycling methods and dry recycling methods. Dry recycling methods include oxidation recycling and crushing recycling.

[0006] In the wet recycling method, regardless of the properties of the nuclear fuel scrap, the nuclear fuel scrap is dissolved in nitric acid or the like, and then subjected to precipitation, drying, reduction, etc., to produce a powder (see, for example, Patent Document 1). The powder obtained in this way is used as the recycled material. On the other hand, in the oxidation recycling method, the nuclear fuel scrap is oxidized in an air atmosphere at a predetermined temperature (for example, 1000°C or less) to produce a powder, and then crushed or sieved to remove coarse particles (see, for example, Patent Documents 2 to 5). The powder obtained in this way is used as the recycled material.

[0007] In the crushing recycling method, nuclear fuel scrap (molded body scrap and sintered body scrap) is crushed into particles of a few millimeters in a primary coarse crushing, and then crushed into particles of several hundred micrometers or less in a secondary coarse crushing. For example, a roll crusher with relatively wide gaps between the crushing rolls is used for the primary coarse crushing, and a roll crusher with relatively narrow gaps between the crushing rolls is used for the secondary coarse crushing. After that, the powder is sieved with a vibrating sieve to remove uncrushed material, and the powder from which uncrushed material has been removed is crushed into particles of submicron to several hundred microns using a fine crushing machine such as a jet mill or ball mill. After that, the powder is sieved with a vibrating sieve to remove coarse particles that have not been sufficiently crushed (see, for example, Patent Document 6). The powder obtained in this way is used as the recycled material. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Special Publication No. 3-19169 [Patent Document 2] Patent No. 3051355 [Patent Document 3] Patent No. 3739694 [Patent Document 4] Patent No. 4796041 [Patent Document 5] Japanese Patent Publication No. 2000-314790 [Patent Document 6] Special Publication No. 2002-536628 [Patent Document 7] Patent No. 3403960 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The wet recycling method, oxidation recycling method, and crushing recycling method described above each have the following challenges.

[0010] First, in the case of wet recycling, there are many steps involved, and it is necessary to perform chemical treatments (dissolution, precipitation) and heat treatments (drying, reduction) that require relatively long processing times. As a result, the overall processing time for the recycling process is very long, and the processing costs are high. Furthermore, because water is used, additional costs are required for safety features to improve criticality safety and for wastewater treatment. In addition, because heat treatment is performed under flammable gas conditions for the reduction process, additional costs are required for safety features to improve safety against fire and explosion. For these reasons, wet recycling has many challenges compared to other methods, especially in terms of cost.

[0011] Next, in the case of oxidation recycling, although the number of steps is not large, it is necessary to raise and lower the temperature in order to oxidize the nuclear fuel scrap at high temperatures, resulting in a very long processing time. In addition, there is a problem that the recycling rate is not high because the nuclear fuel scrap may not be sufficiently oxidized by the heat treatment and may not be turned into fine powder.

[0012] Next, in the case of crushing recycling, since there is no chemical or heat treatment, the cost of ensuring safety is lower and the processing time tends to be shorter compared to wet recycling and oxidation recycling, but there are the following challenges.

[0013] Firstly, the process involves many steps. In other words, in conventional crushing and recycling methods, primary and secondary coarse crushing are performed, followed by sieving in some cases to remove particles that have not been sufficiently crushed. Then, fine crushing is performed to remove particles that have not been sufficiently finely crushed. Thus, conventional crushing and recycling methods require at least four steps to be performed sequentially.

[0014] Secondly, there is a large variation in the particle size of the recycled material. That is, while small particle sizes (for example, 70 μm or less) are desirable for recycled material, vibrating sieves can only efficiently sieve particles with a particle size of approximately 100 μm or larger. Therefore, in conventional crushing recycling methods, there is a large variation in the particle size of the recycled material, which can cause non-uniform sintering in the sintering process of nuclear fuel pellets (see Patent Documents 6 and 7). As a result, there is a large variation in sintering density, and it can cause cracks and irregularities in the nuclear fuel pellets. These lead to a decrease in the quality and yield of nuclear fuel pellets.

[0015] Thirdly, the cleaning costs of the fine powder grinder are high. When a ball mill is used as a fine powder grinder, particles of nuclear fuel scrap adhere to the inside of the grinder and the grinding medium (balls), resulting in longer cleaning times and higher cleaning costs. In addition, the recycling rate is low, and there is a risk of foreign matter contamination. When a jet mill is used as a fine powder grinder, the large number of parts means that the time required for disassembly and cleaning is long, resulting in high cleaning costs. Furthermore, because the cleaning time is long, there is also the challenge of increased management costs due to the need to strictly manage the radiation exposure of cleaning workers.

[0016] As described above, among the conventional methods for recycling nuclear fuel scrap, the wet recycling method and the oxidation recycling method have many challenges in terms of cost and other factors due to the chemical and thermal treatments involved. Furthermore, the conventional crushing recycling method has challenges such as a large number of steps, large variation in the particle size of the recycled material (low quality), a low recycling rate, high cleaning costs, and high management costs due to strict radiation exposure control.

[0017] The present invention has been made based on the above technical recognition, and one of the problems to be solved is to provide a recycling method and a recycling apparatus for nuclear fuel scrap to improve the pulverization recycling method and obtain a high-quality recycled material at low cost from nuclear fuel scrap.

[0018] Another problem to be solved by the present invention is to produce high-quality nuclear fuel pellets at low cost by using the recycled material obtained by the above recycling method or apparatus.

Means for Solving the Problems

[0019] The recycling method of nuclear fuel scrap according to the present invention is a method for recycling nuclear fuel scrap, comprising a pulverizing step of pulverizing nuclear fuel scrap by a counter-current airflow pulverizer, and a recovering step of recovering particles having a particle diameter of a predetermined value or less from the pulverized nuclear fuel scrap by a recovery machine. It is provided with.

[0020] Further, in the recycling method of the nuclear fuel scrap, the particle diameter of the nuclear fuel scrap pulverized by the counter-current airflow pulverizer may be 5 mm or less.

[0021] Further, in the recycling method of the nuclear fuel scrap, the predetermined particle diameter may be 70 μm or less.

[0022] Further, in the recycling method of the nuclear fuel scrap, the predetermined particle diameter may be 40 μm or less.

[0023] Further, in the recycling method of the nuclear fuel scrap, the recovery step is A first dust collection step involves collecting particles of the pulverized nuclear fuel scrap that are smaller than or equal to the predetermined particle size using an airflow classifier or a cyclone dust collector, A second dust collection step involves using a filter-type dust collector to collect particles of nuclear fuel scrap that were not collected in the first dust collection step, specifically those with a particle size equal to or smaller than the predetermined particle size. It may be provided with such features.

[0024] Furthermore, in the aforementioned method for recycling nuclear fuel scrap, The nuclear fuel scrap to be pulverized by the aforementioned counter-airflow pulverizer may include powder scrap.

[0025] Furthermore, in the aforementioned method for recycling nuclear fuel scrap, The aforementioned nuclear fuel scrap may contain (U,Pu,Gd)O2.

[0026] The method for producing nuclear fuel pellets according to the present invention is: A method for producing nuclear fuel pellets using particles recovered by the above method as recycled material, A mixing step in which the recycled material is added to the raw material powder and mixed to form a mixed powder, A pressure molding step involves pressurizing the mixed powder into a cylindrical shape to form a molded body, A sintering step in which the molded body is sintered at a high temperature to form a sintered body, A grinding step in which the sintered body is ground to shape it, It is equipped with.

[0027] The nuclear fuel scrap recycling apparatus according to the present invention is A device for recycling nuclear fuel scrap, A counter-airflow crusher that crushes nuclear fuel scrap by placing it on a counter-airflow created by opposing impellers and causing them to collide, A recovery machine for recovering particles of a predetermined particle size or smaller from the pulverized nuclear fuel scrap, It is equipped with.

[0028] Furthermore, in the apparatus for recycling the aforementioned nuclear fuel scrap, The recovery machine may include at least one of the following: an airflow classifier, a cyclone dust collector, and a filter dust collector. [Effects of the Invention]

[0029] According to the present invention, high-quality recycled material can be obtained from nuclear fuel scrap at low cost. Furthermore, high-quality nuclear fuel pellets can be manufactured at low cost. [Brief explanation of the drawing]

[0030] [Figure 1] This is a diagram illustrating a method for recycling nuclear fuel scrap according to an embodiment of this invention. [Figure 2] This figure shows a schematic configuration of a nuclear fuel scrap recycling apparatus according to an embodiment of this invention. [Figure 3] This figure shows a schematic configuration of a counter-airflow type pulverizer according to an embodiment. [Figure 4] This graph shows the particle size distribution of recovered particles when using a counter-airflow type pulverizer (manufactured by Company A). [Figure 5] This graph shows the particle size distribution of recovered particles when using a counter-airflow type pulverizer (manufactured by Company B). [Figure 6] This is a flowchart illustrating the manufacturing process of nuclear fuel pellets. [Modes for carrying out the invention]

[0031] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0032] <Methods for recycling nuclear fuel scrap> Referring to Figure 1, a method for recycling nuclear fuel scrap according to an embodiment will be described.

[0033] First, the nuclear fuel scrap is coarsely crushed using a coarse crusher (S1: coarse crushing process). For example, a roll crusher is used as the coarse crusher. In this embodiment, molded body scrap and sintered body scrap are coarsely crushed. Here, molded body scrap refers to molded bodies that were deemed defective (defective molded bodies) obtained in the pressure molding process. Sintered body scrap includes at least one of the following: sintered bodies that were deemed defective (defective sintered bodies) obtained in the sintering process for manufacturing nuclear fuel pellets, and nuclear fuel pellets that were rejected in the inspection process for manufacturing nuclear fuel pellets (rejected nuclear fuel pellets).

[0034] The type of nuclear material in the nuclear fuel scrap to be processed is not particularly limited, but may include, for example, oxides of nuclear fuel materials (UO2, PuO2, etc.) or mixtures of oxides of two or more types of nuclear fuel materials, or said oxides or mixtures thereof to which gadolinium (Gd), a neutron absorber, has been added (hereinafter referred to as (U,Pu,Gd)O2).

[0035] In addition, in the coarse grinding step S1, only one of the molded body scrap or the sintered body scrap may be coarsely ground.

[0036] Next, the coarse powder of nuclear fuel scrap obtained in step S1 is finely ground using a counter-airflow pulverizer (S2: fine grinding step). By using a counter-airflow pulverizer, it is possible to finely grind nuclear fuel scrap with larger particle sizes compared to conventional pulverizers (ball mill, jet mill). The specific configuration of the counter-airflow pulverizer will be explained in detail later with reference to Figures 2 and 3.

[0037] The particle size of nuclear fuel scrap crushed by the counter-airflow crusher is several millimeters, for example, between 0.5 mm and 5 mm. Therefore, in this embodiment, there is no need to perform secondary coarse crushing as in conventional crushing and recycling methods, and the nuclear fuel scrap obtained from primary coarse crushing can be directly crushed to fine particles.

[0038] In the present invention, the particle size of the coarsely ground particles is a value obtained by the method specified in JIS Z 8825 (Particle size analysis - Laser diffraction and scattering method) or JIS Z 8827-1 (Particle size analysis - Image analysis method - Part 1: Static image analysis method).

[0039] Furthermore, when measuring the particle size of coarse particles, both standards may be used. Specifically, first, the particle size may be measured using the method of JIS Z 8825, which is applicable to relatively small particles, and if there are particles outside the applicable range, the particle size may be measured using JIS Z 8827-1, which is applicable to relatively large particles.

[0040] In step S2, as shown in Figure 1, the powder scrap may be finely ground together with the molded body scrap and sintered body scrap. Here, the powder scrap includes at least one of the scraps generated in the mixing process for manufacturing nuclear fuel pellets and the grinding slag generated in the grinding process for manufacturing nuclear fuel pellets. Alternatively, in step S2, only the powder scrap may be finely ground.

[0041] Next, particles smaller than a predetermined particle size are recovered from the nuclear fuel scrap that was finely pulverized in step S2 (S3: recovery step). This step is carried out using an airflow classifier or a dust collector. Examples of dust collectors include cyclone-type dust collectors and filter-type dust collectors (bag filters, air filters, etc.). In this embodiment, the dust collector is used to separate and recover particles with a particle size of 40 μm or less, so that 95% or more of the volume is obtained.

[0042] In step S3, the predetermined particle size is, for example, 70 μm or less, and preferably 40 μm or less in order to produce high-quality nuclear fuel pellets. Note that the smaller the particle size, the higher the quality of the recycled material, but the lower limit of the particle size is, for example, 0.1 μm.

[0043] In this invention, the particle size of the finely ground particles is obtained by the method specified in JIS Z 8825 (Particle size analysis - Laser diffraction and scattering method).

[0044] The coarse grinding step in step S1 may be omitted if a counter-airflow type grinder capable of directly grinding molded body scrap or sintered body scrap is used in step S2.

[0045] Furthermore, the recovery process in step S3 may consist of multiple steps. For example, step S3 may include a first dust collection step using an airflow classifier or a cyclone dust collector, and a second dust collection step in which particles that were not recovered in the first dust collection step and are smaller than a predetermined particle size are collected by a filter dust collector. This reduces the load on the filter of the subsequent filter dust collector.

[0046] Nuclear fuel pellets are manufactured using recycled materials obtained by the above-described method of recycling nuclear fuel scrap. The manufacturing method for nuclear fuel pellets includes at least a mixing step of adding and mixing recycled materials with raw material powder to form a mixed powder, a pressure molding step of pressurizing the mixed powder into a cylindrical shape to form a molded body, a sintering step of sintering the molded body at a high temperature to form a sintered body, and a grinding step of grinding the sintered body to adjust its shape. By using high-quality and low-cost recycled materials, high-quality nuclear fuel pellets can be manufactured at a low cost.

[0047] In the mixing process, it is desirable to mix recycled material with the raw material powder up to a maximum of 40% by weight. When recycled material is added to the raw material powder, the density of the nuclear fuel pellet decreases compared to when only the raw material powder is used. However, with the above mixing ratio, it is possible to produce nuclear fuel pellets with a stable density.

[0048] In the pressure molding process, the molding pressure is set to 1 to 5 tons / cm². 2It is desirable that the molding pressure be within the above range. If the molding pressure is high, the raw material powder is more easily compressed than the recycled material powder, making it easier to produce non-uniform nuclear fuel pellets. As a result, variations in the density of the nuclear fuel pellets and cracks are induced, leading to a decrease in quality and yield. On the other hand, if the molding pressure is low, the strength of the molded body is low, making it prone to chipping and reducing the yield. Considering these points, it is desirable that the molding pressure be within the above range.

[0049] In the sintering process, it is desirable to sinter the molded body at a temperature of 1650°C to 1850°C for 0.5 hours or more in a mixed gas atmosphere in which an inert gas, a reducing gas, and a small amount of water vapor are mixed in any ratio. Here, the inert gas is, for example, argon (Ar), nitrogen (N2), carbon dioxide (CO2), etc., and the reducing gas is, for example, hydrogen (H2), carbon monoxide (CO), etc. The gas mixing ratio, temperature, and time are adjusted according to the characteristics of the raw material powder, the amount of recycled material added, and the molding pressure.

[0050] By adopting the above manufacturing conditions, it becomes possible to minimize the impact on sintering caused by the non-uniformity of particle size in the recycled material. As a result, the density of the nuclear fuel pellets can be kept small (within ±2%) relative to the nominal value, and the manufacturing yield can be increased to a high yield (over 92%).

[0051] <Nuclear fuel scrap recycling equipment> Next, an example of a recycling apparatus for performing the above recycling method will be described with reference to Figures 2 and 3. The recycling apparatus 1 according to this embodiment is an apparatus for recycling nuclear fuel scrap to obtain recycled material.

[0052] As shown in Figure 2, the recycling device 1 comprises a coarse crusher 10, a counter-airflow crusher 20, a recovery unit 30, and an exhaust fan 40. In this embodiment, the counter-airflow crusher 20, the recovery unit 30, and the exhaust fan 40 are connected via pipes. When the exhaust fan 40 is driven, an exhaust flow is generated from the inlet of the counter-airflow crusher 20 towards the outlet of the recovery unit 30. The coarse crusher 10 may also be connected to the counter-airflow crusher 20 via pipes.

[0053] The coarse crusher 10 is configured to crush molded body scrap and / or sintered body scrap. As shown in Figure 2, the coarse crusher 10 is a roll crusher and has two crushing rolls 11 arranged with a predetermined gap between them. Nuclear fuel scrap fed into the coarse crusher 10 is crushed to a particle size corresponding to the size of the gap between the crushing rolls 11. In this embodiment, the coarse crusher 10 crushes molded body scrap and sintered body scrap to produce particles P1. The particle size of particles P1 is, for example, 0.5 mm or more and 5 mm or less.

[0054] The counter-airflow type pulverizer 20 is configured to finely pulverize the coarse particles discharged from the coarse pulverizer 10, and to discharge particles smaller than a predetermined particle size. A more detailed explanation follows.

[0055] As shown in Figure 3, the counter-airflow type pulverizer 20 has two impellers 21A and 21B arranged opposite each other, two motors 23 connected to the impellers 21A and 21B respectively via a shaft 22, an inlet 24, and an outlet 25. The impellers 21A and 21B rotate in opposite directions relative to each other by the motors 23 to which they are connected, thereby generating a counter-airflow.

[0056] Particles P1 introduced into the inlet 24 of the counter-airflow pulverizer 20 are finely pulverized by collisions with each other in the counter-airflow generated by the rotation of impellers 21A and 21B. Subsequently, the particles are cyclone-classified by the centrifugal force of impeller 21B, and particles P3 (in this case, particles with a particle diameter of 40 μm or less) smaller than a predetermined particle size are carried by the exhaust flow and removed from the outlet 25, and guided into the subsequent recovery machine 30.

[0057] Particles P2 that have not been sufficiently pulverized (in this case, particles with a diameter larger than 40 μm) remain in the counter-airflow pulverizer 20. These residual particles are collected when they have accumulated to a certain extent (for example, when cleaning the counter-airflow pulverizer 20) and are then fed back in through the inlet 24.

[0058] Furthermore, the opposing airflow type pulverizer 20 may also be configured in which one motor rotates and drives two impellers, although this will reduce its fine pulverization capacity.

[0059] As described above, the counter-airflow type pulverizer 20 has three functions: mechanical pulverization by the impeller 21A, airflow pulverization by collision of particles in a high-speed airflow, and centrifugal classification.

[0060] Unlike conventional fine powder mills (ball mills, jet mills), the counter-airflow type pulverizer 20 can finely pulverize particles with relatively large particle sizes. In the case of a jet mill, a nozzle is provided to accelerate the material being processed, but because the inner diameter of the nozzle is small, large particles cannot be pulverized. In contrast, in the case of a counter-airflow type pulverizer, the particles are accelerated by the counter-airflow, so an acceleration nozzle is not necessary, and even relatively large particles can be pulverized. In this embodiment, the counter-airflow type pulverizer 20 pulverizes nuclear fuel scrap with a particle size of 5 mm or less.

[0061] The recovery machine 30 is configured to recover particles of a predetermined particle size or smaller (40 μm or less in this embodiment) from the nuclear fuel scrap that has been crushed by the counter-airflow crusher 20. The recovery machine 30 has at least one of the following: an airflow classifier, a cyclone dust collector, and a filter dust collector.

[0062] As shown in Figure 2, in this embodiment, the recovery machine 30 includes a cyclone-type dust collector (first recovery machine) 30A that recovers particles of a predetermined particle size or smaller from the nuclear fuel scrap (particles P3) that have been crushed by the counter-airflow type crusher 20, and a filter-type dust collector (second recovery machine) 30B that recovers the particles P3 that were not collected by the cyclone-type dust collector 30A.

[0063] The cyclone-type dust collector 30A is configured to collect particles of a predetermined particle size or smaller by designing and adjusting the exhaust volume, the dimensions of the cyclone inner cylinder, etc. The filter-type dust collector 30B is configured to collect particles of a predetermined particle size or smaller by selecting or designing the type and characteristics of the filter, etc.

[0064] As described above, the recovery rate of fine particles can be improved by having the recovery unit 30 in a multi-stage configuration. Furthermore, the multi-stage configuration can reduce the load on the filter 31 of the subsequent filter-type dust collector 30B.

[0065] Furthermore, the recovery machine 30 is not limited to a two-stage configuration; it may also have a one-stage configuration or a configuration of three or more stages.

[0066] Furthermore, the type of recovery machine is not limited to those described above; the first recovery machine may be an airflow classifier or a filter-type dust collector, and the second recovery machine may be an airflow classifier or a cyclone-type dust collector. However, in order to prevent particles from being discharged to the outside, it is desirable that the final recovery machine be a filter-type dust collector.

[0067] The exhaust fan 40 is connected downstream of the recovery unit 30 and has an impeller (not shown). As this impeller rotates, exhaust air flows through the recycling device 1, and the air that has flowed out of the filter 31 of the filter-type dust collector 30B is exhausted to the outside. Note that if the exhaust fan 40 is provided as part of the filter-type dust collector 30B, it does not need to be provided separately. [Examples]

[0068] The verification results of the recycling apparatus according to the above embodiment will now be explained. However, since it is currently extremely difficult to use plutonium-containing (U,Pu,Gd)O2 material as nuclear fuel scrap due to manufacturing equipment limitations, etc., cerium oxide (CeO2), which is commonly used as a simulant material, was used here. Cerium oxide has properties very similar to those of the material in question (Reference 1: AT Nelson, DR Rittman, JT White et al., “An evaluation of the thermophysical properties of stoichiometric CeO2in comparison to UO2 and PuO2,” J. Am. Ceram. Soc., 97

[11] , 3652-3659; Reference 2: B. Ye, A. Oaks, M. Kirk et al., “Irradiation effects in UO2 and CeO2,” J. Nucl. Mater., 441, 525-529).

[0069] Figures 4 and 5 show the particle size distribution of the recycled material (powder) recovered by the recycling device 1. Figures 4 and 5 show different types (manufacturers) of counter-air pulverizers used. While each counter-air pulverizer differs in device size and impeller shape, their basic configuration is the same.

[0070] As can be seen from Figures 4 and 5, the particle size of the particles collected by both the cyclone-type dust collector 30A and the filter-type dust collector 30B was 40 μm or less. Thus, it was confirmed that similar good results could be obtained even when using counter-airflow pulverizers from different manufacturers. Furthermore, the amount of insufficiently pulverized powder (particles with a particle size greater than 40 μm) was less than 1%, confirming a very high recycling rate.

[0071] <Effects and Effects> The following explains the operation and effects of the nuclear fuel scrap recycling methods and equipment described above.

[0072] In this embodiment, in the fine grinding step S2, the counter-airflow type pulverizer 20 grinds particles with a relatively large particle size of at least several millimeters. Therefore, there is no need to perform secondary coarse grinding in the coarse grinding step S1. Furthermore, since particles P2 that have not been sufficiently finely ground in step S2 remain in the counter-airflow type pulverizer 20, there is no need to perform a separate sieving step after the fine grinding step S2. Thus, the number of steps can be reduced compared to conventional grinding and recycling methods.

[0073] Furthermore, in this embodiment, in the recovery process of step S3, the recovery machine 30 recovers particles of a predetermined particle size or smaller from the nuclear fuel scrap that has been finely pulverized by the counter-airflow pulverizer 20. As a result, it is possible to recover only particles with a smaller particle size (approximately 70 μm or less) than in conventional pulverization recycling methods. Consequently, high-quality recycled material with relatively small particle size variations can be obtained. Therefore, high-quality nuclear fuel pellets can be manufactured using the recycled material obtained in this embodiment. In other words, by manufacturing nuclear fuel pellets using the recycled material obtained in this embodiment, the occurrence of cracks and irregularities can be prevented, and the quality and yield of nuclear fuel pellets can be improved.

[0074] Furthermore, in this embodiment, since a counter-airflow type pulverizer without a pulverizing medium is used as a fine pulverizer, the recycling rate can be improved (for example, a recycling rate of 98% or more can be achieved). Also, since the counter-airflow type pulverizer has fewer parts than fine pulverizers such as ball mills and jet mills, the time required for disassembly and cleaning can be reduced. As a result, cleaning work can be performed easily.

[0075] Therefore, according to this embodiment, high-quality recycled material can be obtained at a lower cost compared to conventional crushing and recycling methods.

[0076] Based on the above description, those skilled in the art may conceive of additional effects and various modifications of the present invention, but the embodiments of the present invention are not limited to those described above. Various additions, modifications, and partial deletions are possible without departing from the conceptual idea and spirit of the present invention derived from the claims and their equivalents. [Explanation of Symbols]

[0077] 1. Recycling device 10 Coarse crusher 11. Grinding Rolls 20. Opposing airflow type pulverizer 21A, 21B Impeller 22 shafts 23 Motor 24 Inlet 25 Outlet 30 Recovery Machines 30A Cyclone Dust Collector 30B Filter-type dust collector 31 filters 40 Exhaust fan P1,P2,P3 particles

Claims

1. A pulverization step of pulverizing nuclear fuel scrap using an opposing airflow pulverizer, A recovery process in which particles of a predetermined particle size or smaller from the pulverized nuclear fuel scrap are recovered by a recovery machine as recycled material for manufacturing nuclear fuel pellets, A mixing step in which the recycled material is added to the raw material powder and mixed to form a mixed powder, A pressure molding step involves pressurizing the mixed powder into a cylindrical shape to form a molded body, A sintering step in which the molded body is sintered at a high temperature to form a sintered body, A grinding step in which the sintered body is ground to shape it, A method for manufacturing nuclear fuel pellets, comprising:

2. The method according to claim 1, wherein the particle size of the nuclear fuel scrap to be crushed by the counter-airflow type crusher is 5 mm or less.

3. The method according to claim 1, wherein the predetermined particle size is 70 μm or less.

4. The method according to claim 1, wherein the predetermined particle size is 40 μm or less.

5. The aforementioned recovery process is, A first dust collection step involves collecting particles of the pulverized nuclear fuel scrap that are smaller than or equal to the predetermined particle size using an airflow classifier or a cyclone dust collector, A second dust collection step involves using a filter-type dust collector to collect particles of nuclear fuel scrap that were not collected in the first dust collection step, specifically those with a particle size equal to or smaller than the predetermined particle size. The method according to claim 1, comprising:

6. The method according to claim 1, wherein the nuclear fuel scrap to be pulverized by the counter-airflow type pulverizer includes powder scrap.

7. The method according to claim 1, wherein the nuclear fuel scrap includes (U, Pu, Gd) O2.

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