Method for manufacturing UO2 mixed powder for nuclear fuel production using an IBC blender and UO2 mixed powder for nuclear fuel production manufactured by the same

Abstract

According to the method for producing UO2 mixed powder for nuclear fuel production of the present invention, the mixing time is short, and the produced UO2 mixed powder has excellent mixing degree and homogeneity. The present invention provides a method for producing UO2 mixed powder for nuclear fuel production, comprising the steps of: (a) measuring and sieving UO2 powder, a pore former, and a lubricant using an automatic feeding device, and feeding the UO2 powder, the pore former, and the lubricant into a UC container; and (b) mixing the UO2 powder, the pore former, and the lubricant using an IBC blender.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a UO2 mixed powder for nuclear fuel production using an IBC blender, and to a UO2 mixed powder for nuclear fuel production produced thereby. [Background technology]

[0002] Uranium dioxide (UO2) pellets are commonly used as nuclear fuel in nuclear power plants.

[0003] Uranium dioxide (UO2) pellets, a nuclear fuel, are manufactured from UO2 powder. More specifically, the process involves mixing UO2 powder with additives such as a pore former and a lubricant to manufacture a UO2 mixed powder, pressing the manufactured UO2 mixed powder to manufacture UO2 compacted pellets, sintering the powder to manufacture UO2 sintered pellets, and grinding the sintered pellets to a uniform diameter to manufacture UO2 ground pellets.

[0004] In the step of preparing the UO2 mixed powder, a pore former and a lubricant are generally added and mixed using a mixer to improve the flowability of the powder and to ensure excellent properties of the final pellets. The degree of mixing and homogeneity of the mixture have a significant effect on the properties and quality of the final pellets, so the performance of the mixer for mixing the powders is very important in the step of preparing the UO2 mixed powder.

[0005] Conventional methods for producing UO2 mixed powder for nuclear fuel generally use a screw mixer. As shown in Figure 1, an operator manually weighs and sifts additives and places them into a UC container 1. The UC container is then attached to a fit-up device 2 located above the screw mixer. The additives are then mixed using the screw mixer 3, and the mixed powder is stored in a separate container 4.

[0006] The conventional method for manufacturing UO2 mixed powder for nuclear fuel production requires approximately four hours of mixing time, and the lubricant must be added several times during the mixing process to ensure uniform distribution. This lengthens the mixing time, reduces the continuity of work, and requires workers to wait while adding the lubricant. Due to the nature of the nuclear fuel production process, which involves handling nuclear materials, various problems arise in terms of economy, efficiency, and safety. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-2004-0029408 (April 6, 2004) [Patent Document 2] Korean Patent Publication No. 10-1001202 (December 8, 2010) Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a method for producing UO2 mixed powder for nuclear fuel production, which requires a short mixing time and produces a UO2 mixed powder with excellent mixing and homogeneity. [Means for solving the problem]

[0009] The present invention provides a method for producing a UO2 mixed powder for nuclear fuel production, which includes the steps of: (a) weighing and sieving a pore-former and a lubricant using an automatic feeding device, and feeding the pore-former and lubricant into a UC container containing UO2 powder; and (b) mixing the UO2 powder, the pore-former, and the lubricant using an IBC blender.

[0010] The pore-forming agent may be U3O8 powder or ADCA (Azodicarbonamide, C2H4N4O2).

[0011] The lubricant is Acrawax (Ethylene distearamide, C 38 H 76 N2O2) or Zinc stearate (Zn-C 36 H 70 O4) may also be used.

[0012] The UO2 powder may be 10 to 500 kg, and may contain 0.08 to 10 parts by weight of the pore-forming agent and 0.05 to 1 part by weight of the lubricant relative to 100 parts by weight of the UO2 powder.

[0013] The automatic feeding device may include a 300 μm sieve to remove granules present in the pore-forming agent and lubricant, and add the pore-forming agent and lubricant at a weight ratio set according to the weight of the UO powder.

[0014] The step (b) may be carried out under the conditions of a rotation speed of 10 to 14 rpm, a powder filling rate in the container of 50 to 70 vol%, a mixing time of 20 to 30 minutes, and forward mixing.

[0015] Step (b) may further include back-mixing for 10 minutes.

[0016] The present invention can also provide a UO2 mixed powder for use in nuclear fuel production, which is produced by the method for producing a UO2 mixed powder for use in nuclear fuel production.

[0017] The present invention also provides a method for producing UO2 pellets, which includes a step of pressing the UO2 mixed powder for nuclear fuel production to produce UO2 shaped pellets, a step of sintering the UO2 shaped pellets to produce UO2 sintered pellets, and a step of grinding the sintered pellets to make the diameter of the sintered pellets uniform, wherein the defect rate is 5% or less and the density of the sintered pellets is 10.30 to 10.58 g / cm 3 The present invention provides a method for producing UO2 nuclear fuel. [Effects of the Invention]

[0018] According to the method for producing UO2 mixed powder for nuclear fuel production of the present invention, the mixing time is short, and the produced UO2 mixed powder has excellent mixing degree and homogeneity.

[0019] By using the UO2 mixed powder for nuclear fuel production manufactured by the method for manufacturing UO2 mixed powder for nuclear fuel of the present invention, the properties and quality of the UO2 pellets that are finally manufactured are excellent. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing a conventional method for mixing UO2 powder using a screw mixer. [Figure 2] FIG. 1 is a diagram showing the configuration of an IBC blender used in the present invention. [Figure 3] FIG. 10 is a diagram showing the Zn content and deviation in the UO2 mixed powder according to the mixing conditions at a rotation speed of 10 rpm in the IBC blender. [Figure 4] FIG. 10 is a diagram showing the Zn content and deviation in the UO2 mixed powder according to the mixing conditions at an IBC blender rotation speed of 14 rpm. [Figure 5] FIG. 1 shows the configuration of an automatic additive feeding device that automatically feeds additives into a UC container containing UO2 powder. The UC container is attached to the IBC blender shown in FIG. 2 and the powder is mixed. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in more detail below with reference to embodiments, examples, and drawings. It will be obvious to those skilled in the art that these embodiments and examples are merely for illustrating the present invention and should not be construed as limiting the scope of the present invention.

[0022] According to one embodiment, the present invention provides a method for producing a UO2 mixed powder for nuclear fuel production, the method comprising the steps of: (a) weighing and sieving a pore former and a lubricant using an automatic feeding device, and feeding the pore former and lubricant into a UC container containing UO2 powder; and (b) mixing the UO2 powder, the pore former, and the lubricant using an IBC blender.

[0023] The UO2 powder is a starting material for producing UO2 mixed powder for nuclear fuel production and nuclear fuel pellets. In one embodiment of the present invention, the specific surface area of the UO2 powder is 2.6 to 2.7 m 2 / g and the average particle size is 4.0 to 10 μm. In one embodiment of the present invention, the UO2 powder can be used in an amount of 10 to 500 kg.

[0024] The pore former is a compound that can adjust the sintering density of sintered pellets and control the size of pores inside the sintered pellets when the UO2 mixed powder is used to prepare molded pellets and then the molded pellets are sintered to produce sintered pellets. U3O8 powder or ADCA (azodicarbonamide, C2H4N4O2) can be used as the pore former. The pore former can be included in an amount of 0.08 to 10 parts by weight per 100 parts by weight of UO2 powder.

[0025] The lubricant is a compound added to form a thin coating on UO2 powder particles. It improves the fluidity of powder particles, allowing for consistent control of the amount of material fed into the die during powder compaction, and also increases the production rate of compacted pellets. It also reduces the pressure between powder particles and the frictional pressure between powder particles and the die wall during powder compaction, allowing for the desired compaction density to be achieved at the optimal compaction pressure, thereby extending the life of the die and punch. Acrawax (Ethylene distearamide, C 38 H 76 N2O2) or Zinc stearate (Zn-C36 H 70 The lubricant may be contained in an amount of 0.05 to 1 part by weight relative to 100 parts by weight of the UO2 powder.

[0026] The IBC blender (Intermediate Bulk Container Blender) refers to a blender that mixes the contents by rotating the container itself in various directions.

[0027] The automatic dosing device measures and sieves the pore former and lubricant and then dispenses them into the UC container containing UO powder. The automatic dosing device includes a 300 μm sieve to remove granules from the pore former and lubricant. The automatic dosing device is shown in FIG. 5. As shown in FIG. 5, the automatic dosing device includes a first additive dosing device 1, a second additive dosing device 2, and an additive measuring device 3, each of which includes a 300 μm sieve 4. The UC container is a 700-liter standard container (Uranium-C (standard order) container) certified by the Korea Institute of Nuclear Safety Technology and capable of handling uranium powder with a maximum enrichment of 5.0 w / o. The 300 μm sieve 4 is a sieve that can remove materials such as granules and particles larger than 300 μm.

[0028] The step (b) may be performed under the conditions of a rotation speed of 10 to 14 rpm, a powder container filling rate of 50 to 70 vol%, a mixing time of 20 to 30 minutes, and forward mixing. The step (b) may further include mixing in the reverse direction for 10 minutes.

[0029] In one embodiment of the present invention, the method includes a step of pressing UO mixed powder for nuclear fuel production to produce UO compact pellets, a step of sintering the UO compact pellets to produce UO sintered pellets, and a step of grinding the sintered pellets to make the diameter of the sintered pellets uniform, and the defect rate is 5% or less, and the density of the sintered pellets is 10.30 to 10.58 g / cm. 3 It is possible to provide a method for producing UO2 nuclear fuel,

[0030] In this specification, the term "defective rate" refers to the number of defective pellets generated in each step among all pellets manufactured from UO mixed powder through molding, sintering, and grinding processes. A pellet is judged as defective if it does not meet the design conditions or specifications.

[0031] Example 1 In order to further improve the degree of mixing and homogeneity of UO2 mixed powder for nuclear fuel manufacturing, various modifications of the conditions for the mixing method using an IBC blender were studied.

[0032] For this study, a certain amount (here, 5 parts by weight per 100 parts by weight of UO2 powder) of U3O8 powder, which was made by oxidizing pellet scrap generated during the UO2 pellet manufacturing process, was added to and mixed with UO2 powder. Adding and mixing U3O8 powder not only improves economic efficiency by recycling scrap, but also acts as a pore-forming agent, allowing for control of the density of the UO2 pellets and the size and number of pores present within the pellets depending on the amount added. Furthermore, to improve the powder flowability and pellet compactibility, which affect pellet quality, a certain amount of lubricant (here, 0.4 parts by weight per 100 parts by weight of UO2 powder and U3O8 powder, and 0.38 parts by weight per 100 parts by weight of UO2 powder) was added and mixed. The lubricant used was Zn-stearate (Zn-C 36 H 70 UO2+U3O8 powder was used. Zn-stearate has a Zn content of 10%. The Zn content of the (UO2+U3O8) powder was measured to be approximately 20 ppm. Therefore, if 0.4 parts by weight of Zn-stearate is added to the (UO2+U3O8) powder for every 100 parts by weight of UO2 powder and U3O8 powder, the Zn content of the mixed powder is theoretically 420 ppm.

[0033] As shown in Table 1 below, the experimental conditions for verifying the mixing performance of the IBC blender were the mixing time, mixing direction (forward and reverse), container fill rate, and rotation speed of the IBC blender. The container fill rate is expressed as the volume percent of powder relative to the total volume of the container. The Zn content and deviation of the mixed powder were analyzed. For this purpose, one mixed powder was produced for each experimental condition, and five samples were taken from each mixed powder to measure the Zn content and deviation. The Zn content was measured using inductively coupled plasma emission spectroscopy (ICP-OES). The degree of mixing was evaluated by comparing the measured Zn content with the theoretical Zn content, and the degree of homogeneity was evaluated from the deviation of the measured Zn content.

[0034] The degree of mixing refers to the degree of mixing of the additives. The better the mixing, the closer the measured degree of mixing is to the theoretical content. The lower the degree of mixing, the more unmixed additives there are.

[0035] The homogeneity indicates how uniformly the additives present in the mixed powder are mixed. In this specification, the homogeneity is evaluated from the deviation of the measured Zn content, and the lower the deviation, the higher the homogeneity.

[0036] Table 1 below shows the Zn content and deviation in the UO2 mixed powder under each experimental condition.

[0037] [Table 1]

[0038] The forward and backward rotation directions mean relatively opposite directions, and the forward direction may mean a clockwise or counterclockwise direction, and the backward direction may mean a counterclockwise or clockwise direction that is the opposite direction of the forward direction.

[0039] The results of Table 1 are shown in FIGS. 3 and 4 according to the rotation speed.

[0040] Figure 3 shows the results obtained when the IBC blender was rotated at 10 rpm. As shown in Figure 3, when the IBC blender was rotated at 10 rpm and mixed only in the forward direction, the average Zn content of the samples mixed for 20 and 30 minutes was 416 rpm and 422 rpm, respectively, which is close to the theoretical value (420 ppm), and the deviation was small. However, the average Zn content was closer to the theoretical value and the deviation was smaller when the mixing time was 30 minutes than when it was 20 minutes. In contrast, when the mixing time was increased to 60 minutes, the average Zn content deviated from the theoretical value and the deviation became larger. This is thought to be due to the segregation of some of the added materials when the mixing time was too long.

[0041] Meanwhile, when rotating in the forward direction for 10 minutes, the results were closer to the theoretical value than when mixing only in the forward direction, with a smaller deviation. This is thought to be because rotating in the reverse direction after rotating in one direction for a certain period of time reduces the amount of unmixed additives. These results were similar regardless of the filling rate. However, since a 50% filling rate shows better homogeneity than a 70% filling rate, it is preferable to set the filling rate to 50%.

[0042] Figure 4 shows the results obtained when the IBC blender was rotated at 14 rpm. As shown in Figure 4, when the IBC blender was rotated at 14 rpm and mixed only in the forward direction, the average Zn content of the samples mixed for 20 and 30 minutes was 421 rpm and 419 rpm, respectively. This is close to the theoretical value (420 ppm), and the deviation is small. However, the average Zn content is closer to the theoretical value and the deviation is smaller when the mixing time is 30 minutes than when the mixing time is 20 minutes. On the other hand, when the mixing time is increased beyond 30 minutes to 60 minutes, the average Zn content deviates from the theoretical value and the deviation becomes larger. This is thought to be due to the segregation of some of the added materials when the mixing time is too long.

[0043] On the other hand, when the mixture was rotated in the forward direction for 10 minutes, the results were closer to the theoretical value and the deviation was smaller than when the mixture was mixed only in the forward direction. This is thought to be because the amount of unmixed additive material decreases when the mixture is rotated in the reverse direction after rotating in one direction for a certain period of time. These results were similar regardless of the filling rate. However, since a 50% filling rate shows better homogeneity than a 70% filling rate, it is preferable to set the filling rate to 50%.

[0044] Example 2 The characteristics of UO2 pellets produced from the UO2 mixed powder produced by the conventional method for producing UO2 mixed powder for nuclear fuel production and the method for producing UO2 mixed powder for nuclear fuel production of the present invention are compared.

[0045] In the process of producing UO2 pellets from UO2 powder, all other steps except for the process of producing UO2 mixed powder for nuclear fuel production are carried out in the same manner. The results of comparing the conventional manufacturing method with the manufacturing method of the present invention are shown in Table 2 below.

[0046] In the conventional method for producing UO2 mixed powder for nuclear fuel production and the method for producing UO2 mixed powder for nuclear fuel production of the present invention, 50 kg of (UO2 + U3O8) powder and 200 g (= 0.4 parts by weight) of lubricant powder were added to each mixer. Other mixing conditions are shown in Table 2 below.

[0047] In addition, in order to compare the physical properties of the molded pellets and sintered pellets produced from the UO2 mixed powder produced by the conventional production method and the production method of the present invention, 100 pellets of each type were produced.

[0048] The UO2 mixed powder was filled into a punch and a die and pressed to produce a molded pellet, and the molded pellet was heat-treated in a gas environment for a certain period of time to produce a sintered pellet.

[0049] For compacted pellets, only the length was measured, taking into account the flowability of the powder, and the deviation was calculated. Because the compacted pellets were produced using a punch and die of the same diameter, the effect on the diameter was not taken into consideration. For sintered pellets, the length, diameter, and density were measured, and the deviation was calculated.

[0050] [Table 2]

[0051] As shown in Table 2, it was confirmed that the compacted pellets and sintered pellets produced from the UO2 mixed powder for nuclear fuel production of the present invention exhibit superior properties to those produced from the UO2 mixed powder for nuclear fuel production produced using a screw mixer. More specifically, it was confirmed that the compacted pellets and sintered pellets produced from the UO2 mixed powder for nuclear fuel production have good fluidity, resulting in small deviations in length and density, and therefore small deviations in density. The quality standard for sintered pellets is 95.0% to 95.7% of the theoretical density. Compared to sintered pellets produced by conventional methods, the density deviation of sintered pellets produced by the method of the present invention is smaller, making quality control easier.

[0052] Furthermore, it was confirmed that micropores were uniformly distributed in the microstructure of the sintered pellets, which means that U3O8, which acts as a pore-former, was uniformly distributed in the UO2 mixed powder. The absence of coarse pores is due to the uniform distribution of the lubricant without clustering. In contrast, in the case of sintered pellets made from the UO2 mixed powder for nuclear fuel production produced using a screw mixer, some coarse pores were present in the microstructure. This means that the pore-former and lubricant were not uniformly distributed in the UO2 mixed powder.

[0053] The method for producing UO2 mixed powder for nuclear fuel production according to the present invention uses an IBC blender, which allows lubricant to be added only once at the beginning, shortening the mixing time, preventing unmixed lubricant from being generated due to reverse rotation, improving the degree of mixing and homogeneity, improving powder fluidity, and enabling continuous operation. Furthermore, since there is no need for workers to wait to add the lubricant, the method is economical, efficient, and safe.

[0054] The defect rate observed in the UO2 pellet manufacturing process was 5-10% in the conventional method (molding process defect rate: 1-2%, grinding process defect rate: 5-8%), while it was 3-5% in the present invention (molding process defect rate: 0%, grinding process defect rate: 3-5%).

[0055] Pellet defects generally occur primarily during the molding process, in which UO2 mixed powder is pressed to produce compacted pellets, and the grinding process, in which sintered pellets are ground. Defects during the molding process occur when the compacted pellet breaks or its length exceeds the specified range during compact production. Defects during the grinding process occur due to damage caused by unground areas, cracks, or pores on the surface of the ground pellets. The molding process defect rate was 1-2% with the conventional method, while it was 0% with the present invention. Furthermore, the grinding process defect rate was 5-8% with the conventional method, while it was 3-5% with the present invention. The low defect rate for ground pellets produced using the present invention is due to the absence of unground areas on the pellet surface and damage caused by pores. The absence of unground areas is due to the small reduction in molding pressure caused by friction when compacting powder particles with a uniformly dispersed lubricant. In addition, damage caused by pores is a phenomenon that occurs when lubricant remains after sintering due to poor mixing, and the pellets produced by this technology had less of this type of damage.

[0056] As described above, the UO2 mixed powder for nuclear fuel production using an IBC blender has a uniform distribution of lubricants and pore formers, which improves the pellet characteristics and quality of the molded pellets, sintered pellets, and ground pellets produced from the UO2 mixed powder.

[0057] As described above, when mixing is performed using the IBC blender device of the present invention, the degree of mixing and homogeneity are better than when mixing using a conventional screw mixer, and the properties and quality of the final UO pellets produced are excellent.

Claims

1. UO for nuclear fuel production ２ A method for producing a mixed powder, comprising: (a) The pore former and lubricant are weighed and sieved using an automatic feed device, and UO ２ adding the powder to a UC container; (b) Using an IBC Blender, ２ mixing the powder, the pore former, and the lubricant; The step (b) is carried out under the conditions of a rotation speed of 10 to 14 rpm, a powder container filling rate of 50 to 70 vol%, a mixing time of 20 to 30 minutes, and forward mixing; The UO ２ The powder is 10 to 500 kg, and the UO ２ 100 parts by weight of the powder, the pore former is 0.08 to 10 parts by weight and the lubricant is 0.05 to 1 part by weight. ２ Method for producing mixed powder.

2. The pore-forming agent is U ３ O ８ Powder or ADCA (Azodicarbonamide, C ２ H ４ N ４ O ２ 2. The UO 2 for nuclear fuel production according to claim 1, ２ Method for producing mixed powder.

3. The lubricant is Acrawax (Ethylene distearamide, C ３８ H ７６ N ２ O ２ ) or Zinc stearate (Zn-C ３６ H ７０ O ４ 2. The UO 2 for nuclear fuel production according to claim 1, ２ Method for producing mixed powder.

4. The automatic feeding device includes a 300 μm sieve to remove granules present in the pore former and lubricant, and ２ 2. The UO powder for nuclear fuel production according to claim 1, wherein a pore former and a lubricant are added in a weight ratio set according to the weight of the powder. ２ Method for producing mixed powder.

5. 2. The UO 2 for nuclear fuel fabrication according to claim 1, wherein step (b) further comprises mixing in the reverse direction for 10 minutes. ２ Method for producing mixed powder.

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