Methods of preparing leach-resistant and durable radioactive waste cermet solids and radioactive waste cermet solids

Abstract

The present invention relates to a method for manufacturing a radioactive waste cermet solidified body with excellent leaching resistance and durability, and to a radioactive waste cermet solidified body. More specifically, in the manufacturing of the cermet solidified body, oxidation of the metal is prevented so that the generation of metal oxides and side reactions between the metal oxides and the radioactive waste do not occur, thereby resulting in a manufactured solidified body with excellent leaching resistance and durability. Furthermore, since no additional treatment is required to prevent oxidation, it is excellent in terms of process efficiency. Additionally, phase separation between the ceramic and the metal is prevented, and since high process temperatures are not required, large-sized solidified bodies can be manufactured, resulting in a manufactured solidified body with very excellent storage efficiency.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a radioactive waste cermet solidified body with excellent leaching resistance and durability, and to a radioactive waste cermet solidified body. More specifically, in the manufacturing of the cermet solidified body, oxidation of the metal is prevented so that the generation of metal oxides and side reactions between the metal oxides and the radioactive waste do not occur, thereby resulting in a manufactured solidified body with excellent leaching resistance and durability. Furthermore, since no additional treatment is required to prevent oxidation, it is excellent in terms of process efficiency. Additionally, phase separation between the ceramic and the metal is prevented, and since high process temperatures are not required, large-sized solidified bodies can be manufactured, resulting in a manufactured solidified body with very excellent storage efficiency. Background Technology

[0003] Various types of radioactive waste are generated during the operation, decommissioning, and spent nuclear fuel processing of nuclear power plants. To minimize the leakage of radionuclides into the environment, this radioactive waste must be solidified for disposal, and methods such as cement solidification, glass solidification, and ceramic solidification are being researched.

[0004] Cement-based solidified materials have the advantage of being manufactured without heat treatment, but they have the disadvantages of lower stability compared to glass or ceramic solidified materials and a low radionuclide loading capacity. Glass and ceramic solidified materials possess high stability and radionuclide loading capacities, but they have the disadvantages of requiring high temperatures and complex manufacturing processes. In particular, ceramic solidified materials are difficult to apply because they require powder compaction and high-temperature sintering to produce engineering-scale solidified materials.

[0006] To address these issues, cermet solidifications, which are ceramic-metal composites, are being researched for the safe disposal of high-level radioactive waste generated from spent nuclear fuel processing. Cermet solidifications possess characteristics that combine the high hardness, wear resistance, and heat resistance of ceramics with the high strength and toughness of metals. It is assessed that applying such cermet solidifications to the solidification of radioactive waste can secure manufacturing technology capable of satisfying the leaching resistance and mechanical strength requirements for radioactive waste during storage and disposal.

[0007] Cermet solidification technology can be manufactured through various heat treatment methods such as induction heating, arc plasma, and SPS (discharge plasma sintering). Conventional radioactive waste cermet solidifications were produced by mixing a metal with a radioactive nuclide in the form of an oxide, which is a ceramic precursor, to form a cermet. In this process, heating to a high process temperature was required to convert the radioactive nuclide in the form of an oxide into a ceramic phase. However, when forming a cermet solidification by heating to a high temperature as in the past, the high process temperature caused metal oxides to form as impurities, which lowered the strength of the cermet solidification and reduced the leaching index. Additionally, side reactions occurred between the formed metal oxides and the radioactive nuclides in the form of oxides, forming impurities that similarly lowered the strength and reduced the leaching index. At this time, to prevent metal oxidation, a reducing or inert atmosphere must be created. However, this not only requires very high process costs, but even if such an atmosphere is created, oxidation cannot be completely blocked. Furthermore, there was a problem in that it was not easy to manufacture large-sized solidifications due to the complexity of the process.

[0009] Furthermore, when the metal melts due to the high-temperature process, phase separation occurs between the ceramic and the metal, resulting in uneven mixing and preventing the realization of the advantages of the cermet solidified material. Additionally, when high-temperature processes are involved, it is difficult to manufacture large-sized solidified materials. In particular, since radioactive waste solidified materials require long-term storage, storage efficiency is a critical factor; however, the inability to manufacture large-sized solidified materials and thus fail to ensure excellent storage efficiency has been a major drawback of conventional cermet solidified material manufacturing methods.

[0011] Therefore, there is a need for a method to manufacture radioactive waste cermet solids that is excellent in terms of process efficiency because it prevents metal oxidation, thereby avoiding the generation of metal oxides and side reactions between metal oxides and radioactive waste, and does not require additional treatment for oxidation prevention; furthermore, it prevents phase separation between ceramics and metals and does not require high process temperatures, allowing for the production of large-sized solids, resulting in excellent storage efficiency. Prior art literature

[0013] Korean Registered Publication No. 10-0426952 The problem to be solved

[0014] The present invention is proposed to solve the problems described above and aims to provide a radioactive waste cermet solidified body with excellent leaching resistance and durability, and a method for manufacturing the same. More specifically, the invention aims to provide a method for manufacturing a radioactive waste cermet solidified body and a radioactive waste cermet solidified body in which metal oxidation is prevented during manufacturing, thereby preventing the generation of metal oxides and side reactions between metal oxides and radioactive waste, resulting in a solidified body with excellent leaching resistance and durability, while also being excellent in terms of process efficiency as no additional treatment for oxidation prevention is required. Furthermore, the invention aims to provide a method for manufacturing a radioactive waste cermet solidified body and a radioactive waste cermet solidified body in which phase separation between ceramic and metal is prevented and high process temperatures are not required, allowing for the production of large-sized solidified bodies, thereby providing a solidified body with excellent storage efficiency. means of solving the problem

[0016] To solve the above-mentioned problem, the present invention provides a method for manufacturing a radioactive waste cermet solidified body, comprising: (1) a step of mixing a ceramic-type radioactive waste and a metal to form a mixture; and (2) a step of sintering the mixture at a temperature lower than the melting point of the metal to produce a cermet solidified body.

[0017] In addition, the above radioactive waste may not be a ceramic precursor.

[0018] In addition, the above step (2) may be sintering the mixture at a temperature 800 to 100°C lower than the melting point of the metal.

[0019] In addition, the above step (2) may be to sinter the mixture at a temperature of 200°C or higher and less than 600°C to produce a cermet solidified body.

[0020] In addition, in step (2) above, by-products of metal oxide and ceramic may not be formed.

[0021] In addition, the metal may be 50% by weight or more of the total mixture of step (1) above.

[0022] In addition, to solve the above-mentioned problem, the present invention comprises a metal; and M x AO y The present invention provides a radioactive waste cermet solidification characterized by comprising a ceramic-type radioactive waste including, and not including a metal oxide and by-products of the metal oxide and the ceramic. wherein, x is 0.1 to 3 and y is 1 to 10, A is one or more selected from the group consisting of Ti, Zr, Al, Si, P, W, Te, and Mo, and M is one or more selected from the group consisting of Sr, Ba, Cs, lanthanide and actinide elements as a radioactive nuclide.

[0023] In addition, the above metal and M x AO y The weight ratio of can be 85:15 to 95:5.

[0024] In addition, as a result of performing a leaching test on the above-mentioned solidified cermet at 90°C for 7 days using the ASTM 1220-10 test method, the normalized leaching rate of M was 0 g / m 2 · Exceeding 0.1g / m² per day 2 ·day or less, and the normalized leaching rate of A is 0 g / m 2 · day exceeding 1X10 -6 g / m 2 · It can be less than a day.

[0025] Also, the above metal is copper, and M x AO yis SrTiO3, and the 2θ values ​​according to XRD analysis have peaks at 21–24, 31–34, 38–41, 42–45, 45–48, 49–52, 56–59, 66–69, 74–76, and 76–79, and may not have peaks at 29–30, 48–49, 61–62, 37–38, and 62–63. Effects of the invention

[0027] Through the present invention, a radioactive waste cermet solidified body with excellent leaching resistance and durability and a method for manufacturing the same can be provided. More specifically, in the manufacturing of the cermet solidified body, oxidation of the metal is prevented so that the generation of metal oxides and side reactions between the metal oxides and the radioactive waste do not occur, thereby providing excellent leaching resistance and durability of the manufactured solidified body, while also being excellent in terms of process efficiency as no additional treatment for oxidation prevention is required. Furthermore, a method for manufacturing a radioactive waste cermet solidified body and a radioactive waste cermet solidified body can be provided, in which phase separation between the ceramic and the metal is prevented and high process temperatures are not required, allowing for the manufacture of large-sized solidified bodies, and thus the manufactured solidified body is highly excellent in terms of storage efficiency. Brief explanation of the drawing

[0029] FIGS. 1a to 1c are photographs of cermet solidified bodies formed in Examples 1 to 3 according to the present invention. FIGS. 2a to 2c show the XRD analysis results of the cermet solidified bodies formed in Examples 1 to 3 according to the present invention, compared with metallic copper and SrTiO3. FIGS. 3a to 3c illustrate SEM-EDS results of cermet solidified bodies formed in Examples 1 to 3 according to the present invention. Figure 4 shows the SEM imaging results of metallic copper. Figure 5 shows the results of evaluating the leaching characteristics of Examples 1 to 3 and the SrTiO3 ceramic solidified body according to the present invention using the ASTM 1220-10 test method. Figure 6 is a photograph of a cermet solidified body manufactured in various configurations by the manufacturing method of the present invention. Figure 7 shows the SEM-EDS analysis results of a cermet solidified body prepared by the manufacturing method of the present invention. Specific details for implementing the invention

[0030] Embodiments of the present invention are described below in detail so that those skilled in the art can easily implement them. The present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0032] As described above, in the manufacture of radioactive waste solids, conventional cement solids, glass solids, and ceramic solids had problems such as overly complex manufacturing processes, weak strength, low radioactive waste loading capacity, or poor stability. Accordingly, to address these issues, cermet solids have been reported by mixing metal and ceramic to possess the high strength of metal and the high wear resistance, heat resistance, and leaching resistance of ceramic. However, in the conventional method of manufacturing cermet solids, radioactive waste in oxide form was mixed with metal and subjected to a high-temperature process to form the radioactive waste into a ceramic phase while simultaneously forming the cermet solid; at this time, a very high temperature was required to form the radioactive waste in oxide form into a ceramic phase.

[0033] Due to these high process temperatures, metal oxides were formed during the cermet manufacturing process. Furthermore, the leaching resistance and durability of the solidified cermet were reduced due to by-products formed from the metal oxides reacting with radioactive waste. In addition, to prevent such metal oxidation, a reducing or inert atmosphere had to be established, which required very high process costs and prevented the manufacturing of solidified cermets in large sizes, thereby reducing storage efficiency. Moreover, the requirement for high process temperatures also prevented the manufacturing of solidified cermets in large sizes, and problems also arose where the advantages of the solidified cermet could not be realized because the metal melted during the manufacturing process, causing the ceramic phase and the metal phase to separate.

[0034] Accordingly, the present invention seeks to solve the aforementioned problems by providing a method for manufacturing a radioactive waste cermet solidified, comprising: (1) a step of mixing a ceramic-type radioactive waste and a metal to form a mixture; and (2) a step of sintering the mixture at a temperature lower than the melting point of the metal to produce a cermet solidified. As a result, oxidation of the metal is prevented during the manufacturing of the cermet solidified, thereby preventing the generation of metal oxides and side reactions between the metal oxides and the radioactive waste. Consequently, the manufactured solidified exhibits excellent leaching resistance and durability, while also being excellent in terms of process efficiency as no additional treatment, such as reduction or the creation of an inert atmosphere to prevent oxidation, is required. Furthermore, phase separation between the ceramic and the metal is prevented, and a high process temperature is not required, allowing for the production of a large-sized solidified, thereby providing a method for manufacturing a radioactive waste cermet solidified that is highly excellent in terms of storage efficiency.

[0036] First, as a (1) step, radioactive waste in the form of ceramic and metal are mixed to form a mixture.

[0037] More specifically, the radioactive waste may be manufactured in a ceramic form and mixed with metal. When the radioactive waste is pre-manufactured in a ceramic form and mixed with metal, high temperatures are not required to produce the solidified body during the sintering process described later. Consequently, the formation of metal oxides and the occurrence of side reactions are prevented, thereby allowing for the production of a cermet solidified body with excellent leaching resistance and durability. Furthermore, since high temperatures are not required during sintering and there is no need to form an atmosphere to prevent oxidation, the process efficiency is excellent, and a solidified body of a large size can be formed. Additionally, since the metal does not melt, an excellent cermet solidified body can be formed without phase separation between the metal and the ceramic.

[0038] In particular, considering the risk of exposure, high stability of the solidified body is required for radioactive waste, and since it must be stored for a long period, high storage efficiency is required. Therefore, a method for manufacturing a cermet solidified body that can be produced in a large size while having high leaching resistance and durability, as in the present invention, shows very superior performance compared to conventional methods, especially in the manufacture of solidified bodies for radioactive waste.

[0040] More specifically, the radioactive waste may be radioactive waste generated during the processing of spent nuclear fuel, although it is not limited to conventional radioactive waste. In this case, the radioactive waste contains radionuclides, and while the radionuclides are not particularly limited, they may be one or more selected from the group consisting of Sr, Ba, Cs, lanthanide, and actinide elements.

[0041] More specifically, the radioactive waste may be prepared in advance in the form of ceramic and mixed with metal. In this case, preferably, the radioactive nuclide contained in each radioactive waste may be prepared in a stable form of ceramic. For example, if the radioactive nuclide is Sr, it may be prepared in the form of stable ceramic such as SrTiO3, SrZrO3, or SrWO4; if the radioactive nuclide is Cs, it may be Cs pollucite (CsAlSi2O6); if the radioactive nuclide is a lanthanide (Nd, Ce), it may be NdPO4 or CePO4; and if the radioactive nuclide is an actinide (U), it may be UO2.

[0042] More preferably, the above-mentioned ceramic-type radioactive waste is more preferably M x AO y It can be in the form of.

[0043] At this time, M is a radioactive nuclide selected from the group consisting of Sr, Ba, Cs, lanthanide and actinide elements, A is selected from the group consisting of Ti, Zr, Al, Si, P, W, Te, and Mo, x can be 0.1 to 3, and y can be 1 to 10.

[0044] More specifically, in this case, M may include two or more types of radionuclides; for example, if M is strontium and barium, M is, for example, Sr 0.5 Ba 0.5 It can have a composition like that.

[0045] The above ceramic-shaped radioactive waste is M x AO y In the case of the form, when a cermet solid is formed, it can have superior durability and leaching resistance.

[0046] At this time, the method of manufacturing radioactive waste into ceramic is not limited to any method that typically involves manufacturing radionuclides in the form of ceramic.

[0048] More specifically, the above-mentioned ceramic-type radioactive waste may not be a ceramic precursor.

[0049] Conventionally, in forming cermet solids, radioactive waste was mixed with metal in the form of a ceramic precursor (oxide of radionuclides) and processed at very high temperatures. This process resulted in problems such as the metal melting and separating the ceramic and metal phases, the generation of metal oxides, and side reactions between the metal oxides and the radioactive waste, ultimately leading to reduced durability and leaching resistance of the cermet solid. On the other hand, while leaching resistance can be ensured by manufacturing the radionuclides into a stable single-phase ceramic solid, a high-temperature sintering process is essential for single-phase production. This process presents problems such as reduced process stability and increased manufacturing costs.

[0050] Accordingly, in the present invention, since the radioactive waste in the form of ceramic does not contain a ceramic precursor, there is no need to perform a process requiring a very high temperature for conversion into a ceramic solid (pellet) in the manufacture of a cermet solid, and accordingly, the occurrence of the aforementioned problems is prevented, and a solid with excellent durability and leaching resistance can be formed.

[0051] More specifically, in the past, to form a cermet solidified body, radioactive waste in the form of an oxide, which is a ceramic precursor, was mixed with a metal. In this case, the radioactive waste in the form of an oxide is in a form in which oxygen is bonded to a radionuclide, such as SrO or Cs2O. This is a common form that can be obtained from spent nuclear fuel, and since radioactive waste in this form has a high leaching index, it must be formed into a ceramic phase to form a stable solidified body. However, in the present invention, the radioactive waste in the form of a ceramic precursor can be converted into a ceramic phase beforehand to form a cermet solidified body, and accordingly, the radioactive waste mixed with the metal may not contain the ceramic precursor.

[0053] More specifically, the above-mentioned ceramic-type radioactive waste may be included in the mixture in an amount of 5 to 95 weight percent.

[0055] More specifically, the metal may be one or more selected from the group consisting of Cu, Fe, Cr, Ni, Zr, Zn, Ti, Sn, Mo, W, Zr, Ta, and SUS and Inconel alloys including these, preferably one or more selected from the group consisting of Cu, Fe, Zr, SUS, and Inconel alloys, and more preferably Cu. More specifically, when the metal is one or more selected from the group consisting of Cu, Fe, Cr, Ni, Zr, Zn, Ti, Sn, Mo, W, Zr, Ta, and SUS and Inconel alloys including these, a solidified body with excellent leaching resistance and durability can be formed due to the absence of metal oxide formation and side reactions, and in particular, when the metal is copper, a cermet solidified body with significantly excellent leaching resistance and durability can be manufactured.

[0057] In this case, the metal may be metal waste generated during the operation and decommissioning of a nuclear power plant. Since metal waste generated during the operation and decommissioning of a nuclear power plant is also waste that must be treated as radioactive waste, if the metal is used as such radioactive waste, the radioactive waste in metallic form can also be simultaneously manufactured into a solidified cermet and treated, which can be highly effective in terms of radioactive waste treatment efficiency.

[0059] More specifically, the metal may be included in the mixture in an amount of 5% to 95% by volume. In this case, if the metal is included in an amount of 50% or less by volume, the radioactive waste in the form of ceramic is included in an amount of 50% or more by volume. In this case, when the cermet solidified body is finally manufactured, it may be in a form where the metal is encapsulated inside the ceramic. In this case, although the existing ceramic is exposed to the outside, it has a higher thermal conductivity compared to conventional ceramic solidified bodies due to the encapsulated metal inside, so heat generated inside the solidified body is easily released during storage, which may be excellent in terms of storage stability. In this case, if the metal is included in an amount of less than 5% by volume, the amount of metal is too small, so the effect of increasing thermal conductivity is insufficient, and it may not be excellent in terms of storage stability.

[0060] In this case, more preferably, the metal may be included in the mixture at a volume of 50% or more. In this case, the ceramic-type radioactive waste is included at a volume of less than 50%, and accordingly, when the cermet solidified body is finally formed, it is manufactured in a form in which the ceramic-type radioactive waste is encapsulated inside the metal. With this structure, external exposure of the ceramic-type radioactive waste is minimized, which can be excellent in terms of leaching resistance, and since the high-strength metal surrounds the outside of the radioactive waste, it can simultaneously be excellent in terms of durability. However, if the metal is included in the mixture at a volume of more than 95%, the amount of the radioactive waste is too small, so it may not be excellent in terms of storage efficiency.

[0062] More specifically, when the metal is included in the mixture at a volume of 50% or more, the metal may be included in the mixture at a weight of 85% to 95%. When the metal is included in the mixture at a weight of 85% to 95%, the cermet solidified body produced may be excellent in terms of leaching resistance, as the leaching index of radionuclides and ceramic components is very low, and may also be excellent in terms of strength.

[0064] More specifically, the radioactive waste in the form of ceramic and the metal included in the mixture may exist in a mixed powder state, wherein the radioactive waste and the metal may be provided in powder form prior to mixing, or may be manufactured in powder form during the mixing process.

[0065] At this time, when the ceramic-type radioactive waste and metal included in the mixture are in powder form, the range of particle sizes is not particularly limited, but in the case of ceramic-type radioactive waste, the average particle size may be 10 nm to 1 mm, and in the case of metal, the average particle size may be 10 nm to 1 mm.

[0066] At this time, the method of mixing the above-mentioned ceramic-type radioactive waste and metal is not particularly limited, but, for example, methods such as mechanical milling, ball milling, powder mixer, and mechanical blender may be used.

[0068] Next, in step (2), the mixture is sintered at a temperature lower than the melting point of the metal to produce a cermet solidified body.

[0069] Conventionally, in the manufacture of cermet solids, the metal was melted at a temperature higher than its melting point to form a ceramic phase. However, when cermet solids are manufactured at temperatures above the metal's melting point in this manner, problems arose, such as phase separation between the metal and the ceramic due to the melting of the metal, or the formation of metal oxides due to the high temperature, which resulted in the deterioration of physical properties of the final solidified body, including leaching resistance and durability.

[0070] Accordingly, the present invention solves the aforementioned problems by manufacturing a cermet solidified body by sintering a mixture at a temperature lower than the melting point of the metal. In this invention, a mixture of metal and radioactive waste in the form of ceramic is heat-treated, and since the radioactive waste is preferentially formed in the form of ceramic, high-temperature melting as in conventional methods is not required. Therefore, a cermet solidified body can be manufactured by sintering at a temperature lower than the melting point of the metal without melting the metal; consequently, phase separation between the metal and ceramic does not occur, and metal oxides are not formed, so the leaching resistance and durability of the final solidified body can be excellent.

[0071] More specifically, when a mixture containing metal is heat-treated at a temperature above the melting point of the metal, the metal melts, raising concerns about phase separation. In contrast, when a mixture containing metal is heat-treated at a temperature below the melting point of the metal, the mixture is sintered. Sintering refers to the process where metal particles stick together and bond to reduce surface energy as the temperature rises, rather than the metal completely changing into a liquid state as in melting. When sintered, there is no concern about phase separation, and the uniformly mixed mixture can be manufactured into a cermet solid while maintaining its form. Consequently, the ceramic and metal contained in the final solidified body can be evenly mixed. Furthermore, a cermet solidified body with such a uniform interior is superior to the case of melting in that it has excellent leaching resistance and durability due to the absence of localized imbalances.

[0073] More specifically, the method of sintering the mixture in step (2) above is not limited to any method of heat treatment typically used to manufacture a cermet solidified body, but may use one or more methods selected from the group consisting of, for example, cold pressing, hot pressing, induction heating, and spark plasma. In this case, when sintering is performed using a cold pressing or hot pressing method, the pressure range is not particularly limited but may be in the range of 1 to 1000 MPa.

[0075] More specifically, the sintering time is not specifically limited, but can be performed for 0.5 to 24 hours.

[0077] More specifically, the above step (2) may be to sinter the mixture at a temperature 800 to 100°C lower than the melting point of the metal to produce a cermet solidified body, more preferably at a temperature 800 to 300°C lower than the melting point of the metal, and even more preferably at a temperature 800 to 500°C lower than the melting point of the metal.

[0078] When the above mixture is sintered at a temperature 800 to 100°C lower than the melting point of the metal, the sintering temperature is not excessively high, so the formation of metal oxides and phase separation are prevented, and the sintering temperature is not excessively low, so it is a sufficient temperature for the formation of a cermet solidified body, and it may also be advantageous in terms of process efficiency. At this time, when the sintering temperature is in the range of 800 to 300°C lower than the melting point of the metal, the formed cermet solidified body may be very excellent in terms of leaching resistance and durability, and when the sintering temperature is in the range of 800 to 500°C lower than the melting point of the metal, the formed cermet solidified body may be significantly excellent in terms of leaching resistance and durability.

[0080] More specifically, the above step (2) may be to sinter the mixture at a temperature of 200°C or higher and less than 600°C to produce a cermet solidified body.

[0081] At this time, when the above mixture is sintered at a temperature of 200°C or higher and less than 600°C, the temperature is sufficient for the cermet solidification to be formed through sintering, and the manufacturing process of the cermet solidification is excellent in terms of process efficiency. Furthermore, metal oxides are not generated during the manufacturing process, and thus the formation of byproducts between metal oxides and radioactive waste is prevented, so the finally formed cermet solidification can be excellent in terms of durability and leaching resistance compared to conventional methods.

[0083] More specifically, in step (2) above, by-products of metal oxide and ceramic may not be formed.

[0084] As described above, the present invention forms a cermet solidified body by sintering a metal at a temperature higher than its melting point, rather than melting it, thereby preventing the formation of metal oxides. If metal oxides are formed, side reactions occur between the metal oxides and the ceramic, resulting in the formation of byproducts; both the metal oxides and the byproducts act as factors that reduce the leaching resistance and durability of the finally manufactured cermet solidified body. In other words, the present invention prevents both the generation of such metal oxides and the side reactions between the metal oxides and the ceramic, thereby enabling the formation of a cermet solidified body with excellent leaching resistance and durability.

[0086] More specifically, in performing step (2) above, a reducing or inert atmosphere may be created. Since metals such as Fe, which have a high melting point and high oxidation reactivity, may generate some metal oxides even when using the method of the present invention, a reducing or inert atmosphere may be created to prevent the generation of such metal oxides. If a reducing or inert atmosphere is additionally created in performing step (2) above, metal oxides and side reactions between metal oxides and ceramics are completely prevented, and a cermet solidified body with excellent leaching resistance and durability can be formed.

[0087] More specifically, the above reducing or inert atmosphere can be used in a manner typically used to create a reducing or inert atmosphere, but for example, the reducing atmosphere can be created by supplying a reducing gas such as CO, H2, CH4, NH3, etc. to the reactor where step (2) is performed, and the inert atmosphere can be created by supplying inert gases such as Ne, Ar, etc. to the reactor.

[0089] More specifically, the volume of the formed cermet solid is not particularly limited, but is 1 to 300,000 cm³ 3 It can be within the range of.

[0091] To solve the above-mentioned problem, the present invention comprises: a metal; and M x AO y The present invention provides a radioactive waste cermet solidification characterized by including a ceramic-type radioactive waste containing [a specific component] and not including metal oxides and by-products of the metal oxides and ceramics.

[0092] At this time, x is 0.1 to 3 and y is 1 to 10, and

[0093] A is one or more selected from the group consisting of Ti, Zr, Al, Si, P, W, Te, and Mo, and

[0094] M is a radioactive nuclide and is one or more selected from the group consisting of Sr, Ba, Cs, lanthanide and actinide elements.

[0096] Next, the cermet solidified body provided by the present invention will be described. Accordingly, details that overlap with the above-described method for manufacturing the cermet solidified body will be omitted, but are not limited thereto.

[0098] More specifically, as above, metal and M x AO y In the case of including radioactive waste in the form of ceramics, which includes metal oxides and by-products of metal oxides and ceramics, a cermet solidified body with excellent leaching resistance and durability can be provided, which has both the excellent strength of metal and the excellent leaching resistance of ceramics, and does not have a degradation of physical properties due to impurities such as metal oxides or by-products.

[0099] At this time, the above cermet solidified body is, for example, a metal and M x AO yIt can be manufactured by mixing radioactive waste in the form of ceramics containing [the metal] and then sintering it at a temperature below the melting point of the metal. When manufactured in this way, the formation of metal oxides can be prevented due to the low temperature, and the formation of by-products of the reaction between the metal oxide and the ceramic can also be prevented.

[0101] More specifically, the metal may be one or more selected from the group consisting of Cu, Fe, Cr, Ni, Zr, Zn, Ti, Sn, Mo, W, Zr, Ta, and alloys such as SUS and Inconel containing these, preferably one or more selected from the group consisting of alloys such as Cu, Fe, and SUS, and more preferably Cu. When the metal is one or more selected from the group consisting of Cu, Fe, Cr, Ni, Zr, Zn, Ti, Sn, Mo, W, Zr, Ta, and alloys such as SUS and Inconel containing these, a solidified body with excellent leaching resistance and durability can be formed because there is no formation of metal oxides or side reactions during the formation process of the cermet solidified body, and in particular, when the metal is copper, the leaching resistance and durability of the cermet solidified body may be significantly superior.

[0103] More specifically, the above metal and M x AO y The weight ratio of can be 95:5 to 95:5, preferably 50:50 to 95:5, and more preferably 85:15 to 95:5. In the above cermet solidified body, the metal and M x AO y When the weight ratio is 85:15 to 95:5, it can be very excellent in terms of leaching resistance, as the leaching index of radioactive nuclides and ceramic components is very low, and it can also be very excellent in terms of strength.

[0105] More specifically, as a result of performing a leaching test on the cermet solidified body at 90°C for 7 days using the ASTM 1220-10 test method, the normalized leaching rate of M was 0 g / m² 2 · Exceeding 0.1g / m² per day 2 ·day or less, and the normalized leaching rate of A is 0 g / m 2 · day exceeding 1X10 -6 g / m 2 · It can be less than a day.

[0106] The above cermet solidified body is metal and M as described above x AO y It includes, and when it does not contain metal oxides and by-products of metal oxides and ceramics, it exhibits excellent leaching resistance, such that the normalized leaching rate of the ceramic component (A) and radionuclide (M) contained therein is 0 g / m² 2 · Exceeding 10 days -6 g / m 2 ·day or less, M is 0g / m² 2 · Exceeding 0.1g / m² per day 2 It can have a very low value of less than 1 day. Since the solidified radioactive waste must be stored for a very long time due to the very long half-life of the radionuclides, it must therefore possess very high storage stability. Accordingly, the present invention has a very low leaching rate value as described above, making it particularly excellent as a solidified radioactive waste.

[0108] More specifically, the volume of the above-mentioned solidified cermet is not particularly limited, but is 1 to 300,000 cm³ 3 It can be within the range of.

[0110] In addition, to solve the above-mentioned problem, the present invention provides a radioactive waste cermet solidified body comprising copper and SrTiO3, characterized in that the 2θ values ​​according to XRD analysis have peaks at 21 to 24, 31 to 34, 38 to 41, 42 to 45, 45 to 48, 49 to 52, 56 to 59, 66 to 69, 74 to 76, and 76 to 79, and do not have peaks at 29 to 30, 48 to 49, 61 to 62, 37 to 38, and 62 to 63.

[0111] More specifically, regarding 2θ values ​​according to XRD analysis, Cu metal has peaks at 42–45, 49–52, and 74–76; SrTiO3 has peaks at 21–24, 31–34, 38–41, 45–48, 56–59, 66–69, and 76–79; metal oxide CuO peaks have peaks at 32–33, 38–39, 46–47, 48–49, 51–52, 53–54, 58–59, 61–62, 65–69, 72–73, and 75–76; and Cu2O has peaks at 29–30, 37–38, 42–43, and 62–63. It has a peak at 74 to 75. Therefore, when the cermet solidified contains copper and SrTiO3, the cermet solidified stably contains the metal and SrTiO3 while simultaneously not containing impurities such as copper oxide and by-products, so it may not contain peaks for CuO and Cu2O, and thus has peaks at 21 to 24, 31 to 34, 38 to 41, 42 to 45, 45 to 48, 49 to 52, 56 to 59, 66 to 69, 74 to 76, and 76 to 79, and may not have peaks at 29 to 30, 48 to 49, 61 to 62, 37 to 38, and 62 to 63. In this case, the leaching resistance and durability of the cermet solidified can be very excellent.

[0113] More specifically, the weight ratio of copper to SrTiO3 in the above cermet solidified body may be 5:95 to 95:5, preferably 50:50 to 95:5, and more preferably 85:15 to 95:5.

[0115] More specifically, the volume of the above-mentioned solidified cermet is not particularly limited, but is 1 to 300,000 cm³ 3 It could be.

[0117] The present invention will be explained more specifically through the following examples, but the following examples are not intended to limit the scope of the invention and should be interpreted as being for the purpose of aiding understanding of the invention.

[0119] <Example 1>

[0120] 90 g of copper powder and 10 g of SrTiO3 powder were mixed to form a mixture such that the copper powder constituted 90% by weight of the mixture. In this case, non-radioactive Sr, which has the same chemical properties as radioactive strontium, was used. Subsequently, the mixture was placed into a blender and homogenized at 34,000 rpm for 5 minutes. The homogenized sample was placed into a 4 cm diameter punch / die and hot-pressed at 400°C for 5 hours under a pressure of 150 MPa to obtain a cermet solidified body. The formed solidified body was then photographed and is shown in Fig. 1a.

[0122] <Example 2>

[0123] A cermet solidified body was obtained by performing the same procedure as in Example 1, except that a mixture was formed by mixing 80 g of copper powder and 20 g of SrTiO3 powder so that the copper powder constituted 80% by weight of the mixture. The formed solidified body was then photographed and is shown in Fig. 1b.

[0125] <Example 3>

[0126] A cermet solidified body was obtained by performing the same procedure as in Example 1, except that a mixture was formed by mixing 70 g of copper powder and 30 g of SrTiO3 powder so that the copper powder constituted 70% by weight of the mixture. The formed solidified body was then photographed and is shown in Fig. 1c.

[0128] <Experimental Example 1 - XRD Analysis of Cermet Solids>

[0129] X-ray diffraction (XRD) analysis was performed on the cermet solidified bodies obtained according to Examples 1 to 3, and the results were compared with the XRD analysis results of copper and SrTiO3. Subsequently, the results for Example 1 are shown in FIG. 2a, for Example 2 in FIG. 2b, and for Example 3 in FIG. 2c.

[0130] As can be seen from FIGS. 2a to 2c, the cermet solidified bodies formed in Examples 1 to 3 all have peaks at 21–24, 31–34, 38–41, 42–45, 45–48, 49–52, 56–59, 66–69, 74–76, and 76–79 according to XRD analysis results, and do not have peaks at 29–30, 48–49, 61–62, 37–38, and 62–63, which corresponds to the peak positions of copper and SrTiO3, respectively. Through this, it can be seen that metal oxides and by-products of the reaction between metal oxides and ceramics are not formed during the formation process of the cermet solidified body formed through the present invention, and therefore, the corresponding materials are not included in the final solidified body.

[0132] <Experimental Example 2 - SEM-EDS Analysis>

[0133] In order to determine whether the internal cermet structure was well formed in Examples 1 to 3, Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) analysis was performed to map the Cu, Sr, and Ti elements, and the results were compared with copper metal. At this time, the analysis results of Examples 1 to 3 are shown in Figures 3a to 3c, respectively, and the analysis results of metallic copper are shown in Figure 4.

[0134] Referring to FIGS. 3a to 3c and FIG. 4, first, it can be seen that the copper metal present inside the cermet solidified body of Examples 1 to 3 has the same form as the copper metal in FIG. 4, which means that the copper was successfully sintered in forming the cermet solidified body. In addition, it can be seen that the radioactive nuclide Sr and the ceramic component Ti are encapsulated between the copper in the cermet solidified body, which means that the metal and ceramic phases are well separated and formed, and that no by-products are formed between them. Furthermore, because the ceramic phase is encapsulated inside the metal, the durability of the solidified body is excellent due to the influence of the high-strength metal, and the leakage of radioactive nuclides is blocked, which means that the leaching resistance is excellent.

[0136] <Experimental Example 3 - Evaluation of Leaching Characteristics>

[0137] In the cermet solidified bodies formed according to Examples 1 to 3, the leaching characteristics of each element were evaluated using the ASTM 1220-10 test method. The leaching characteristics were evaluated by conducting a leaching experiment at 90°C for 7 days, and the concentration of the leached elements was measured using ICP-MS (Inductively Coupled Plasma-Mass Spectrometry), and the leaching characteristics were evaluated based on this. In addition, the same evaluation was performed on SrTiO3 ceramic solidified bodies sintered at 1400°C, and the results are shown in Fig. 5.

[0138] As can be seen from FIG. 5, it can be confirmed that the cermet solidified bodies formed according to Examples 1 to 3 have a leaching index similar to that of ceramic solidified bodies. This implies that the cermet solidified bodies are superior in that they possess high strength and durability while exhibiting leaching resistance similar to that of ceramic solidified bodies, which are known for their particularly excellent leaching resistance among conventional solidified bodies. In particular, in the case of Example 1, the normalized leaching rate of Sr is 0.1 g / m² 2 It is less than 1 / day, and the normalized leaching rate of Ti is 1X10 -6 g / m 2 It has a normalized leaching rate of less than one day, which is lower than that of conventional ceramic solidified bodies, and this means that when a cermet solidified body is prepared as in Example 1, the leaching index is excellent.

[0140] <Example 4 - Formation of Cermet Solids of Various Compositions>

[0141] Cu (70 wt%) + LABS glass (30 wt%), Cu (40 wt%) + Ba 0.5 Sr 0.5Cermet solids were formed with a total of two compositions of TiO3 (60 wt%). In the case of the cermet solid using 70 wt% copper, the solid was formed using the same method as in Example 1, and in the case of the cermet solid using 40 wt% copper, the solid was formed using the same method as in Example 1, except that the sintering temperature was set to 1000°C. A reducing atmosphere or an inert atmosphere may be applied depending on the degree of metal oxidation. A photograph of the formed cermet solid is shown in Fig. 6. Additionally, Cu (50 wt%) + Ba 0.5 Sr 0.5 A cermet solidified body composed of TiO3 (50 wt%) was formed in the same manner as in Example 1, except that the sintering temperature was 1000°C, and then SEM-EDS analysis was performed, and the results are shown in Fig. 7.

[0142] Looking at FIG. 6, it can be seen that a cermet solidified body is easily formed even when the type of metal, the type of ceramic, and the weight ratio of the metal to the ceramic vary. Also, looking at FIG. 7, it can be confirmed that when a cermet solidified body is manufactured by the method of the present invention even with a different composition, a cermet solidified body in which the metal and ceramic are uniformly mixed is formed.

Claims

Claim 1 (1) a step of mixing radioactive waste in the form of ceramic and metal to form a mixture; and (2) a step of sintering the mixture at a temperature lower than the melting point of the metal to produce a cermet solidified body; a method for manufacturing a radioactive waste cermet solidified body. Claim 2 A method for manufacturing a radioactive waste cermet solidified body according to claim 1, characterized in that the radioactive waste is not a ceramic precursor. Claim 3 A method for manufacturing a radioactive waste cermet solidified body, wherein, in claim 1, step (2) is characterized by sintering the mixture at a temperature 100 to 800°C lower than the melting point of the metal to produce a cermet solidified body. Claim 4 A method for manufacturing a radioactive waste cermet solidified body, wherein, in claim 1, step (2) is characterized by sintering the mixture at a temperature of 200°C or higher and less than 600°C to produce a cermet solidified body. Claim 5 A method for manufacturing a radioactive waste cermet solidified body, characterized in that, in step (2) above, no by-products of metal oxide and ceramic are formed. Claim 6 A method for manufacturing a cermet solidified body according to claim 1, characterized in that the metal is 50 volume% or more of the total mixture of step (1). Claim 7 Metal; and M x AO y A radioactive waste cermet solidified body characterized by comprising: a ceramic-type radioactive waste containing; and not comprising metal oxides and by-products of the reaction between the metal oxide and the ceramic. (wherein x is 0.1 to 3 and y is 1 to 10, A is one or more selected from the group consisting of Ti, Zr, Al, Si, P, W, Te, and Mo, and M is one or more selected from the group consisting of Sr, Ba, Cs, lanthanide and actinide elements as a radioactive nuclide.) Claim 8 In Clause 7, the above metal and M x AO y A radioactive waste cermet solidified body characterized by a weight ratio of 85:15 to 95:

5. (wherein x is 0.1 to 3 and y is 1 to 10, A is one or more selected from the group consisting of Ti, Zr, Al, Si, P, W, Te, and Mo, and M is a radioactive nuclide selected from one or more selected from the group consisting of Sr, Ba, Cs, lanthanide and actinide elements.) Claim 9 In claim 7, as a result of performing a leaching test on the cermet solidified body at 90°C for 7 days using the ASTM 1220-10 test method, the normalized leaching rate of M was 0 g / m 2 · Exceeding 0.1g / m² per day 2 ·day or less, and the normalized leaching rate of A is 0 g / m 2 · day exceeding 1X10 -6 g / m 2 A radioactive waste cermet solidified body characterized by having a duration of less than or equal to 1 day. (wherein A is one or more selected from the group consisting of Ti, Zr, Al, Si, P, W, Te, and Mo, and M is one or more radionuclides selected from the group consisting of Sr, Ba, Cs, lanthanide and actinide elements.) Claim 10 A radioactive waste cermet solidified body comprising copper and SrTiO3, characterized by having 2θ values ​​according to XRD analysis peaks at 21–24, 31–34, 38–41, 42–45, 45–48, 49–52, 56–59, 66–69, 74–76, and 76–79, and not having peaks at 29–30, 48–49, 61–62, 37–38, and 62–63.

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