Decoating system and decoating method for coated fuel particles

Abstract

When removing carbon from the cladding material of cladding fuel particles, it is possible to prevent carbon from remaining in the fuel kernel and suppress the amount of activated carbon gas released into the atmosphere. [Solution] A decoating system 10 for coated fuel particles, in which the fuel kernel is coated with a coating material, removes carbon contained in the coating material of coated fuel particles, comprising: a gasifier 11 that generates carbon monoxide gas by the reaction of carbon contained in the coating material with carbon dioxide gas; a carbon generator 12 that generates carbon and carbon dioxide gas by reacting the carbon monoxide gases generated in the gasifier at a lower temperature than the gasifier and in the absence of a fuel kernel; and a blower 13 that supplies carbon dioxide-containing gas, including carbon dioxide gas generated in the carbon generator, to the gasifier 11, and carbon monoxide-containing gas, including carbon monoxide gas generated in the gasifier, to the carbon generator 12, and is configured to recover and remove the carbon generated in the carbon generator.

Description

Technical Field

[0001] Embodiments of the present invention relate to a de-coating system for coated fuel particles and a method for de-coating coated fuel particles.

Background Art

[0002] At present, as the realization of carbon neutrality progresses, the importance of nuclear power generation that does not generate CO2 during power generation is being reexamined. Although light water reactors are currently the mainstream in nuclear power generation, the development of safer next-generation innovative reactors is being carried out in various countries. Among the next-generation innovative reactors, the high-temperature gas-cooled reactor that uses He gas, which is chemically stable as a coolant, and operates at high temperatures has not only a high power generation efficiency of 45% or more but also features such as the ability to produce hydrogen using the generated heat.

[0003] TRISO (Tri-structural isotropic) type coated fuel particles are used as the fuel for high-temperature gas-cooled reactors. Different from general light water reactor fuels, the nuclear fuel UO2 in this TRISO type coated fuel particle is multiply coated with a ceramic material having excellent heat resistance and a carbon material having high thermal conductivity. Therefore, it is said that even in the event of an accident, the fuel will not be damaged and the external release of radioactive substances is unlikely to occur.

[0004] In Japan, which is resource-poor and has a low energy self-sufficiency rate, as mentioned in the 6th Basic Energy Plan, it is important to realize a nuclear fuel cycle that not only ensures a stable energy supply by nuclear power generation but also effectively utilizes resources by reprocessing spent fuel. In the reprocessing of ordinary light water reactor fuels, the PUREX method is used, in which the fuel rods stored in the cladding tubes are directly sheared, dissolved in a nitric acid solution, and then various components are separated and purified and used again as fuel raw materials.

[0005] On the other hand, the fuel used in high-temperature gas reactors is UO2, the same as that used in light water reactors. However, as mentioned earlier, the fuel kernel, which is the particle of the nuclear fuel (UO2), is made up of spherical particles with a diameter of 0.8 to 1 mm coated with high-density pyrolysis carbon, low-density pyrolysis carbon, and silicon carbide. These coatings can contain radioactive materials even at 1600°C, have high chemical stability, and also possess high mechanical strength. For this reason, high-temperature gas reactor fuel is difficult to reprocess in its original state using the current PUREX method. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 3569659 [Patent Document 2] Special Publication No. 3-31235 [Overview of the project] [Problems that the invention aims to solve]

[0007] TRISO-type coated fuel particles used in high-temperature gas reactors are made of UO2, so if the pyrolysis carbon (PyC) and silicon carbide (SiC) coating the UO2 can be removed from the fuel particles, they can be reprocessed using the PUREX method.

[0008] A conventional method for removing pyrolysis carbon from TRISO-type coated fuel particles involves mechanically crushing the fuel particles and then burning the pyrolysis carbon in an 850°C vortex-flowbed furnace. 14 A method has been proposed to purify exhaust gases containing radioactive materials such as CO2 before releasing them into the atmosphere. In this conventional method, from the perspective of minimizing the release of radioactive materials into the environment, the exhaust gas contains 14 Ideally, CO2 should be fixed in the form of calcium carbonate or similar substances, but this would generate a large amount of exhaust gas, resulting in high costs.

[0009] As a method that does not involve combustion, Patent Document 1 proposes a method for separating fuel particles from structural materials by heating fuel elements for high-temperature gas reactors to about 650°C and allowing the carbon, which is the structural material of the fuel elements, to flow in a relaxed state. Patent Document 2 proposes a method for separating TRISO-type coated fuel particles by creating a fuel structure that makes it easy to separate the fuel part from the coating material when crushing TRISO-type coated fuel particles with a rotor disc. However, in the technologies described in Patent Documents 1 and 2, there is a possibility that the carbon-containing coating material may remain on the fuel particles.

[0010] The embodiments of the present invention have been made in consideration of the above circumstances, and aim to provide a decoating system and a decoating method for coated fuel particles that can prevent carbon from remaining on the fuel kernel when removing carbon from the coating material from coated fuel particles, and can also suppress the amount of activated carbon gas released into the atmosphere. [Means for solving the problem]

[0011] The decoating system for coated fuel particles in an embodiment of the present invention is a decoating system for coated fuel particles that removes carbon contained in the coating material of coated fuel particles formed by coating a fuel kernel with a coating material, and is characterized in that it comprises: a gasifier that generates carbon monoxide gas by the reaction of carbon contained in the coating material of the coated fuel particles with carbon dioxide gas; a carbon generator that generates carbon and carbon dioxide gas by reacting the carbon monoxide gases generated in the gasifier at a lower temperature than the gasifier and in the absence of the fuel kernel; and a blower that supplies the carbon dioxide-containing gas, including the carbon dioxide gas generated in the carbon generator, to the gasifier, and the carbon monoxide-containing gas, including the carbon monoxide gas generated in the gasifier, to the carbon generator, and is configured to recover and remove the carbon generated in the carbon generator.

[0012] The decoating method for coated fuel particles in an embodiment of the present invention is a method for decoating coated fuel particles that removes carbon contained in the coating material of coated fuel particles formed by coating a fuel kernel with a coating material, characterized in that the gasification device generates carbon monoxide gas by the reaction of carbon contained in the coating material of the coated fuel particles with carbon dioxide gas; the carbon generation device generates carbon and carbon dioxide gas by reacting the carbon monoxide gases generated in the gasification device with each other at a lower temperature than the gasification device and in the absence of the fuel kernel; and the blower supplies carbon dioxide-containing gas, including the carbon dioxide gas generated in the carbon generation device, to the gasification device, thereby recovering and removing the carbon generated in the carbon generation device. [Effects of the Invention]

[0013] According to embodiments of the present invention, when removing carbon from the coating material from coated fuel particles, it is possible to prevent carbon from remaining in the fuel kernel and to suppress the amount of activated carbon gas released into the atmosphere. [Brief explanation of the drawing]

[0014] [Figure 1] A block diagram showing the configuration of a decoating system for coated fuel particles according to the first embodiment. [Figure 2] Figure 1 is a schematic diagram showing the structure of coated fuel particles that are processed by the coated fuel particle decoating system. [Figure 3] Figure 1 shows a graph illustrating the temperature dependence of the gas concentration when chemical reaction equilibrium is reached in the decoating system for coated fuel particles. [Figure 4] Figure 1 shows a graph illustrating the temperature dependence of pressure when chemical reaction equilibrium is reached in the decoating system for coated fuel particles. [Figure 5] Figure 1 is an explanatory diagram illustrating the processing status at the start (A) and end (B) of the decoating system for coated fuel particles. [Figure 6] A block diagram showing the configuration of a decoating system for coated fuel particles according to the second embodiment. [Figure 7] Flowchart showing the processing procedure of the coating removal system for coated fuel particles in FIG. 6.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments for carrying out the present invention will be described based on the drawings.

[0016] [A] First Embodiment (FIGS. 1 to 5) FIG. 1 is a block diagram showing the configuration of a coating removal system for coated fuel particles according to the first embodiment. The coating removal system 10 for coated fuel particles shown in FIG. 1 removes carbon contained in the coating material of coated fuel particles (for example, TRISO - type coated fuel particles) used in a high - temperature gas reactor, and is composed of a gasification device 11, a carbon generation device 12, a blower 13, a system housing 14, a hopper 15, a gas supply unit 16, a densitometer 17, a pressure gauge 18, and a control device 19. This coating removal system 10 for coated fuel particles is a pretreatment device contributing to the reprocessing of coated fuel particles.

[0017] Here, the structure of the coated fuel particles, which are the processing target of the coating removal system 10 for coated fuel particles, will be described. FIG. 2 is a schematic structural diagram of a currently mainstream TRISO - type coated fuel particle. This coated fuel particle 1 has a nuclear fuel (UO2) particle called a fuel kernel 2 at the center, and this fuel kernel 2 is sequentially coated with a buffer layer 3 made of low - density pyrolytic carbon, an inner high - density pyrolytic carbon (IPyC) layer 4, a silicon carbide (SIC) layer 5, and an outer high - density pyrolytic carbon (OPyC) layer 6. These buffer layer 3, inner high - density pyrolytic carbon layer 4, silicon carbide layer 5, and outer high - density pyrolytic carbon layer 6 form a coating material 7.

[0018] In the coating removal system 10 for coated fuel particles in the present embodiment, the coating removal utilizes the Boudouard reaction represented by the following chemical formula to remove carbon from the coated fuel particle 1. C + CO2⇔2CO ··· (1)

[0019] The above reaction equation (1) shows a significant equilibrium shift from room temperature to around 1100°C, with carbon monoxide (CO) being more readily produced at higher temperatures and carbon (C) and carbon dioxide (CO2) being more readily produced at lower temperatures. The decoating system 10 for coated fuel particles utilizes this characteristic to remove carbon from the coated fuel particles 1 by converting the carbon contained in the coating material 7 of the coated fuel particles 1 into carbon monoxide gas, and then converting the carbon monoxide gas back into carbon in the absence of the fuel kernel 2.

[0020] The gasifier 11 generates carbon monoxide gas through a reaction between the carbon contained in the coating material 7 of the crushed coated fuel particles (solid A in Figure 5), which are obtained by crushing the coated fuel particles 1, and the carbon dioxide gas contained in the carbon dioxide-containing gas. The temperature of the gasifier 11 is 500 to 1100°C, preferably 700 to 1000°C. The minimum temperature of the gasifier 11 is the lower limit temperature required to obtain a realistic reaction rate when proceeding to the right in reaction equation (1), and the maximum temperature is set based on the integrity of the materials constituting the gasifier 11.

[0021] The amount of carbon dioxide supplied to the gasifier 11 from the gas supply unit 16 and the blower 13 is 1 to 3 times, preferably 1 to 1.2 times, the molar amount of carbon in the crushed coated fuel particles (solid A). The minimum amount of carbon dioxide supplied to the gasifier 11 is determined based on the quantifiable amounts required to convert carbon into carbon monoxide. Although increasing the molar amount of carbon dioxide relative to the molar amount of carbon makes the reaction equation (1) proceed more easily to the right, it reduces the proportion of carbon derived from the coated fuel particles that can be reconverted in the carbon generator 12. Therefore, it is desirable that the molar amount of carbon in the crushed coated fuel particles (solid A) and the molar amount of carbon dioxide gas in the carbon dioxide-containing gas supplied from the gas supply unit 16 and the blower 13 be as equal as possible.

[0022] The carbon generator 12 reacts carbon monoxide gases produced in the gasifier 11 at a lower temperature than that of the gasifier 11 (described later) and in the absence of coated fuel particles 1 to produce carbon and carbon dioxide gas. The temperature of the carbon generator 12 is 200°C or higher and lower than that of the gasifier 11. The temperature of the carbon generator 12 needs to be lower than that of the gasifier 11 in order to advance reaction equation (1) to the left, and is preferably 600°C or lower. The minimum temperature of the carbon generator 12 is the lower limit temperature required to obtain a realistic reaction rate when advancing reaction equation (1) to the left. The carbon produced in this carbon generator 12 (solid C in Figure 5) is recovered, thereby removing carbon from the coated fuel particle fragments (solid A).

[0023] The blower 13 circulates and supplies gas, supplying carbon dioxide-containing gas, including carbon dioxide gas produced in the carbon generator 12, to the gasifier 11, and carbon monoxide-containing gas, including carbon monoxide gas produced in the gasifier 11, to the carbon generator 12. The blower 13 is a general-purpose blower that corresponds to the temperature range of the decoating system 10 for coated fuel particles. Depending on the specifications of the blower 13, a cooler may be provided before the blower 13 and a heater after it.

[0024] The system enclosure 14 houses the gasifier 11, carbon generator 12, blower 13, and hopper 15, and is designed to minimize the scattering of radioactive materials outside the decoating system 10. The hopper 15 is used to feed the crushed coated fuel particles (solid A) into the gasifier 11.

[0025] The gas supply unit 16 supplies carbon dioxide-containing gas, including carbon dioxide gas, to the gasification device 11. As described above, the gas supply unit 16 ensures that the amount of carbon dioxide supplied from the gas supply unit 16 and the blower 13 to the gasification device 11 is 1 to 3 times, preferably 1 to 1.2 times, the molar amount of carbon in the crushed coated fuel particles (solid A).

[0026] The concentration meter 17 is installed in the gasification device 11 and measures the concentration of at least one of the carbon monoxide concentration and carbon dioxide concentration inside the gasification device 11. The pressure gauge 18 is installed in the carbon generation device 12 and measures the pressure inside the carbon generation device 12.

[0027] The control device 19 compares the carbon monoxide concentration and carbon dioxide concentration at the chemical reaction equilibrium of reaction equation (1) corresponding to the environment (temperature) of the gasification device 11 with the concentration measurement value of at least one of the carbon monoxide concentration and carbon dioxide concentration measured by the concentration meter 17, and determines that the time when the concentration measurement value reaches a predetermined concentration is the end of the decoating treatment (decarbonization treatment) of the coated fuel particle crushed material (solid A).

[0028] In other words, as shown in Figure 3, for example, let's assume that the chemical reaction is in equilibrium when the carbon monoxide concentration rises to 89.0% and the carbon dioxide concentration decreases to 11.0% at 800°C. In this case, the control device 19 determines that the chemical reaction has reached equilibrium and that the decoating (decarbonization) treatment of the coated fuel particle fragments (solid A) is complete when, after a predetermined time has elapsed at 800°C inside the gasification device 11, the carbon monoxide concentration measured by the concentration meter 17 reaches a predetermined concentration near 89.0% and the carbon dioxide concentration measures a predetermined concentration near 11.0%.

[0029] Furthermore, the control device 19 compares the pressure inside the carbon generation device 12, which is assumed to be at the chemical reaction equilibrium of reaction equation (1) corresponding to the environment (temperature) of the carbon generation device 12, with the pressure measurement value inside the carbon generation device 12 obtained by the pressure gauge 18, and determines that the time when the pressure measurement value reaches a predetermined pressure is the end of the decoating treatment (decarbonization treatment) of the coated fuel particle fragments (solid A).

[0030] In other words, as shown in Figure 4, the total amount of carbon monoxide gas and carbon dioxide gas increases as the chemical reaction of reaction equation (1) progresses inside the carbon generator 12, and the chemical reaction is considered to be at equilibrium when the pressure inside the carbon generator 12 reaches, for example, 1.8 atm at 800°C. In this case, the control device 19 determines that the chemical reaction has reached equilibrium and that the decoating (decarbonization) process of the coated fuel particle fragments (solid A) is complete when the pressure measured by the pressure gauge 18 reaches a predetermined pressure of approximately 1.8 atm after a predetermined time has elapsed at 800°C inside the carbon generator 12.

[0031] While the timing for determining when the decoating process for coated fuel particle fragments (solid A) is complete can be determined by weight, volume, etc., concerns exist regarding the accuracy of weight measurements in a high-temperature atmosphere containing highly chemically active carbon monoxide, and concerns about the density of carbon generated in the carbon generator 12 changing depending on the environment. Therefore, it is preferable to use at least one of carbon monoxide concentration, carbon dioxide concentration, and pressure as the criteria for determination.

[0032] The control device 19 starts heating the gasifier 11 and carbon generator 12 and activates the blower 13 when the decoating (decarbonization) treatment of the coated fuel particle fragments (solid A) begins. Furthermore, as described above, when the control device 19 determines that the decoating (decarbonization) treatment of the coated fuel particle fragments (solid A) is complete, it stops the heating operation of the gasifier 11 and carbon generator 12 and stops the blower 13.

[0033] Here, the stopping of the gasification device 11, carbon generation device 12, and blower 13 based on the control device 19's determination that the decoating process is complete is performed at, for example, the later of the determination of the decoating process completion time based on the concentration measurement of at least one of the carbon monoxide concentration and carbon dioxide concentration measured by the concentration meter 17, and the determination of the decoating process completion time based on the pressure measurement in the carbon generation device 12 measured by the pressure gauge 18.

[0034] Next, we will explain the decoating process using Figure 5. At the start of the decoating process shown in Figure 5(A), when removing carbon from the coated fuel particle fragments (solid A), a predetermined amount of coated fuel particle fragments (solid A) is first introduced into the gasifier 11, and a carbon dioxide-containing gas containing a molar amount of carbon dioxide gas corresponding to the molar amount of carbon contained in the solid A is supplied from the gas supply unit 16. After the gasifier 11, carbon generator 12, and blower 13 are filled with a predetermined amount of carbon dioxide-containing gas, the supply of carbon dioxide-containing gas and exhaust are stopped.

[0035] Next, the control device 19 starts the blower 13 to circulate the carbon dioxide-containing gas in the gasifier 11 and the carbon generator 12, while heating the gasifier 11 and the carbon generator 12 to their respective predetermined temperatures.

[0036] Subsequently, the control device 19 determines the completion of the carbon treatment (decoating treatment) of the coated fuel particle fragments (solid A) based on the measurement value of the concentration meter 17 installed in the gasification device 11 or the measurement value of the pressure meter 18 installed in the carbon generation device 12, and stops heating of the gasification device 11 and the carbon generation device 12, and stops the blower 13 (Figure 5(B)). After this decoating treatment is completed, the carbon-removed coated fuel particle fragments (solid B) present in the gasification device 11 and the carbon (solid C) present in the carbon generation device 12 are recovered, respectively.

[0037] As configured as described above, this first embodiment provides the following effects (1) and (2). (1) Even if carbon-removed coated fuel particle fragments (solid B) containing the fuel kernel 2 remain in the gasification unit 11, the gasification unit 11 is at a higher temperature than the carbon generation unit 12, so carbon is not produced by the reaction of carbon monoxide gases. Furthermore, carbon-removed coated fuel particle fragments (solid B) containing the fuel kernel 2 do not exist in the carbon generation unit 12, where carbon monoxide gases react to produce carbon. Therefore, it is possible to prevent carbon from adhering to and remaining on the fuel kernel 2.

[0038] (2) The carbon generator 12 generates solid carbon and carbon dioxide gas from the carbon monoxide gas generated in the gasifier 11, and the carbon dioxide-containing gas, including the carbon dioxide gas generated in the carbon generator 12, is supplied to the gasifier 11 by the blower 13. Therefore, when the coated fuel particles 1 are spent fuel, the amount of activated carbon gas (carbon monoxide gas, carbon dioxide gas) released into the atmosphere can be suppressed.

[0039] [B] Second embodiment (Figures 6 and 7) Figure 6 is a block diagram showing the configuration of a decoating system for coated fuel particles according to the second embodiment. In this second embodiment, parts that are the same as in the first embodiment are denoted by the same reference numerals as in the first embodiment, and their explanation is simplified or omitted.

[0040] The difference between the decoating system 20 for coated fuel particles in this second embodiment and the first embodiment is that the fuel partial separation device 21, fuel partial recovery device 22, and pressure reducing device 23 are located downstream of the gasifier 11 and upstream of the carbon generator 12, while the carbon separation device 24, carbon recovery device 25, and pressure reducing device 26 are located downstream of the carbon generator 12 and upstream of the blower 13.

[0041] In this coated fuel particle decoating system 20, the carbon-removed coated fuel particle fragments (solid B) present in the gasifier 11 as the fuel portion are separated from the carbon monoxide-containing gas, including the carbon monoxide gas produced in the gasifier 11, by the fuel portion separation device 21, and made recoverable by the fuel portion recovery device 22. Furthermore, the carbon (solid C) produced in the carbon generator 12 is separated from the carbon dioxide-containing gas, including the carbon dioxide gas produced in the carbon generator 12, by the carbon separation device 24, and made recoverable by the carbon recovery device 25.

[0042] The fuel partial separation unit 21 separates the carbon-removed coated fuel particle fragments (solid B), which are the fuel portion from which carbon has been removed in the gasifier 11, from the carbon-monoxide-containing gas, which includes the carbon monoxide gas generated in the gasifier 11. The carbon-removed coated fuel particle fragments (solid B) contain the fuel kernel 2. The fuel partial separation unit 21 also guides the separated carbon-monoxide-containing gas to the carbon generator 12. In this fuel partial separation unit 21, general gas-solid separation methods can be used to separate the carbon monoxide gas from the carbon-removed coated fuel particle fragments (solid B), such as a method that utilizes the flow of gas, such as a cyclone that can be operated at a temperature similar to that of the gasifier 11, or a method that utilizes shielding materials such as inorganic filters.

[0043] The fuel partial recovery unit 22 receives the carbon-removed coated fuel particulate fragments (solid B) from the fuel partial separation unit 21 and makes them recoverable to the outside. The fuel partial recovery unit 22 is in communication with the fuel partial separation unit 21 except when recovering the carbon-removed coated fuel particulate fragments (solid B). When the fuel partial recovery unit 22 recovers the carbon-removed coated fuel particulate fragments (solid B) to the outside, the communication between the fuel partial separation unit 21 and the fuel partial recovery unit 22 is cut off by closing the on / off valve 28 provided in the fuel partial recovery unit 22.

[0044] The depressurizing device 23 sucks in the carbon monoxide-containing gas inside the fuel partial recovery device 22 and moves it to the carbon generation device 12 when the fuel partial recovery device 22 closes the on / off valve 28 to recover the carbon-removed coated fuel particle fragments (solid B) to the outside.

[0045] The carbon separation unit 24 separates the carbon produced in the carbon generator 12 from the carbon dioxide-containing gas, which also contains carbon dioxide gas produced in the carbon generator 12. The carbon separation unit 24 also guides the separated carbon dioxide-containing gas to the blower 13. In the carbon separation unit 24, the method for separating carbon dioxide gas and carbon (solid C) can be the same as in the fuel partial separation unit 21, and general gas-solid separation methods such as using gas flow methods such as cyclones or using shielding materials such as inorganic filters can be used, and its operating temperature is the same as that of the carbon generator 12.

[0046] The carbon recovery device 25 accepts carbon (solid C) from the carbon separation device 24 and recovers it to the outside. The carbon recovery device 25 is in communication with the carbon separation device 24 when not recovering carbon (solid C). When the carbon recovery device 25 recovers the carbon (solid C) separated by the carbon separation device 24 to the outside, the communication between the carbon separation device 24 and the carbon recovery device 25 is cut off by closing the on / off valve 29 provided in the carbon recovery device 25.

[0047] When the carbon recovery device 25 closes the on / off valve 29 to recover carbon to the outside, the pressure reducing device 26 sucks in the carbon dioxide-containing gas inside the carbon recovery device 25 and moves it to the blower 13.

[0048] The aforementioned fuel partial separation device 21, fuel partial recovery device 22, depressurization device 23, carbon separation device 24, carbon recovery device 25, and depressurization device 26 are housed together with the gasifier 11, carbon generator 12, blower 13, and hopper 15 within the system housing 30, thereby minimizing the scattering of radioactive materials outside the decoupling system 20.

[0049] Furthermore, the decoating system 20 for coated fuel particles includes a concentration meter 17 installed in one of the gasifier 11, the partial fuel separation unit 21, or the partial fuel recovery unit 22 (for example, the gasifier 11). This concentration meter 17 measures the concentration of at least one of carbon monoxide or carbon dioxide in the installed unit and transmits the information to the control unit 27. Additionally, a pressure gauge 18 is installed in one of the carbon generator 12, the carbon separation unit 24, or the carbon recovery unit 25 (for example, the carbon generator 12). This pressure gauge 18 measures the pressure in the installed unit and transmits the information to the control unit 27.

[0050] The control device 27 starts heating the gasifier 11 and the carbon generator 12 and activates the blower 13 when the decoating (decarbonization) treatment of the coated fuel particle fragments (solid A) begins.

[0051] Furthermore, the control device 27 compares the carbon monoxide concentration and carbon dioxide concentration at the chemical reaction equilibrium of reaction equation (1) corresponding to the environment (temperature) of the gasification device 11 with the concentration measurement value of at least one of the carbon monoxide concentration and carbon dioxide concentration measured by the concentration meter 17, and determines that it is time to recover the carbon-removed coated fuel particle fragments (solid B) from the fuel partial recovery device 22 when the concentration measurement value reaches a predetermined concentration similar to that of the first embodiment. When recovering the carbon-removed coated fuel particle fragments (solid B) from the fuel partial recovery device 22, the control device 27 closes the on / off valve 28 of the fuel partial recovery device 22 to cut off the communication between the fuel partial separation device 21 and the fuel partial recovery device 22, and moves the carbon monoxide-containing gas in the fuel partial recovery device 22 to the carbon generation device 12 using the pressure reducing device 23.

[0052] Furthermore, the control device 27 compares, for example, the pressure inside the carbon generator 12, which is assumed to occur at the chemical reaction equilibrium of reaction equation (1) corresponding to the environment (temperature) of the carbon generator 12, with, for example, the pressure measurement inside the carbon generator 12 by the pressure gauge 18, and determines that it is time to recover carbon (solid C) from the carbon recovery device 25 when the pressure measurement reaches a predetermined pressure similar to that of the first embodiment. When recovering carbon (solid C) from the carbon recovery device 25, the control device 27 closes the on-off valve 29 of the carbon recovery device 25 to cut off communication between the carbon separation device 24 and the carbon recovery device 25, and moves the carbon dioxide-containing gas inside the carbon recovery device 25 to the blower 13 using the depressurization device 26.

[0053] Furthermore, the removal of carbon-removed coated fuel particle fragments (solid B) from the fuel partial recovery unit 22 is performed after the pressure is restored by the fuel partial recovery unit 22 taking in the gas phase from the system housing 30. Similarly, the removal of carbon (solid C) from the carbon recovery unit 25 is performed after the pressure is restored by the carbon recovery unit 25 taking in the gas phase from the system housing 30.

[0054] Furthermore, after carbon-removed coated fuel particle fragments (solid B) have been recovered from the fuel partial recovery device 22 and carbon (solid C) has been recovered from the carbon recovery device 25, the control device 27 activates the hopper 15 to feed the coated fuel particle fragments (solid A) into the gasifier 11. The control device 27 then supplies carbon dioxide-containing gas from the gas supply unit 16 to the gasifier 11 so that the amount of carbon dioxide in the gasifier 11 corresponds to the amount of carbon contained in the coated fuel particle fragments (solid A) that have been fed into the gasifier 11. This allows the coated fuel particle decoating (deoxygenation) treatment to be performed again by the coated fuel particle decoating system 20.

[0055] Next, the procedure for decoating (decarbonizing) coated fuel particles using the decoating system 20 will be explained with reference to Figure 7. First, a predetermined amount of coated fuel particle crushed material (solid A) is fed from the hopper 15 into the gasifier 11 (S1). Next, carbon dioxide-containing gas is fed from the gas supply unit 16 into the gasifier 11 in a molar amount corresponding to the molar amount of carbon contained in the coated fuel particle crushed material (solid A) (S2).

[0056] After the gasifier 11, fuel partial separation unit 21, carbon generation unit 12, carbon separation unit 24, and blower 13 are filled with carbon dioxide-containing gas, the control device 27 heats the gasifier 11 and carbon generation unit 12 to their respective predetermined temperatures and starts the blower 13. As a result, the gasifier 11 reacts the carbon contained in the coating material 7 of the coated fuel particle crushed material (solid A) with carbon dioxide gas to produce carbon monoxide gas (S3).

[0057] Next, the fuel partial separation unit 21 separates the carbon monoxide-containing gas, which includes the carbon monoxide gas produced in the gasification unit 11, from the carbon-removed coated fuel particle fragments (solid B) which constitute the fuel portion (S4). The carbon-removed coated fuel particle fragments (solid B) separated in the fuel partial separation unit 21 fall into the fuel partial recovery unit 22 and are received, while the separated carbon monoxide-containing gas is led to the carbon generation unit 12.

[0058] Next, the carbon generator 12 reacts the carbon monoxide in the carbon monoxide-containing gas introduced from the fuel partial separation unit 21 to produce carbon and carbon dioxide gas (S5). Next, the carbon separation unit 24 separates the carbon produced in the carbon generator 12 from the carbon dioxide-containing gas, which also contains carbon dioxide gas produced in the carbon generator 12 (S6). The carbon separated in the carbon separation unit 24 falls into the carbon recovery unit 25 and is received, and the separated carbon dioxide-containing gas is sent to the gasification unit 11 via the blower 13 (S7).

[0059] In step S4, during the process in which the carbon-removed coated fuel particle fragments (solid B), which are the fuel portion separated by the fuel partial separation device 21, are received by the fuel partial recovery device 22, when the concentration measurement value of at least one of the carbon monoxide concentration and carbon dioxide concentration in, for example, the gasification device 11, measured by the concentration meter 17, reaches a predetermined concentration (S8), the control device 27 closes the on-off valve 28 of the fuel partial recovery device 22 and activates the pressure reducing device 23, causing the fuel partial recovery device 22 to recover the carbon-removed coated fuel particle fragments (solid B) as the fuel portion (S9).

[0060] In step S6, during the process in which the carbon (solid C) separated in the carbon separation device 24 is received into the carbon recovery device 25, when the pressure measurement in, for example, the carbon generation device 12, measured by the pressure gauge 18, reaches a predetermined pressure (S10), the control device 27 closes the on-off valve 29 of the carbon recovery device 25 and activates the pressure reducing device 26 to recover the carbon (solid C) in the carbon recovery device 25 (S11).

[0061] As configured as described above, this second embodiment provides the same effects as the first embodiment (1) and (2), as well as the following effect (3).

[0062] (3) The carbon-removed coated fuel particle crushed material (solid B), from which carbon has been removed in the gasifier 11, is separated from the carbon monoxide-containing gas, including the carbon monoxide gas produced in the gasifier 11, by the fuel partial separation device 21, and is also provided for recovery by the fuel partial recovery device 22. In addition, the carbon (solid C) produced in the carbon generator 12 is separated from the carbon dioxide-containing gas, including the carbon dioxide gas produced in the carbon generator 12, by the carbon separation device 24, and is also provided for recovery by the carbon recovery device 25. As a result, even before the completion of the decoating (decarbonization) treatment of the coated fuel particle crushed material (solid A) using the gasifier 11, carbon generator 12 and blower 13, the carbon-removed coated fuel particle crushed material (solid B) can be independently recovered by the fuel partial recovery device 22, and the carbon (solid C) can be independently recovered by the carbon recovery device 25, so that each (solid A and solid B) can be quickly transferred to subsequent processing.

[0063] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, such as the separation of carbon used as structural material from fuel elements for high-temperature gas reactors, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention, and such substitutions, modifications, and combinations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0064] 1...Coated fuel particles, 7...Coating material, 10...Coated fuel particle decoating system, 11...Gasifier, 12...Carbon generation device, 13...Blower, 17...Concentration meter, 18...Pressure gauge, 20...Coated fuel particle decoating system, 21...Fuel partial separation device, 22...Fuel partial recovery device, 24...Carbon separation device, 25...Carbon recovery device.

Claims

1. A decoating system for coated fuel particles, which removes carbon contained in the coating material of coated fuel particles formed by coating a fuel kernel with a coating material, A gasification device that generates carbon monoxide gas by the reaction of carbon contained in the coating material of the coated fuel particles with carbon dioxide gas, A carbon generator that reacts carbon monoxide gases produced in this gasification device at a lower temperature than the gasification device and in the absence of the fuel kernel to produce carbon and carbon dioxide gas, This carbon generator has a blower that supplies carbon dioxide-containing gas, including carbon dioxide gas produced by this carbon generator, to the gasification device, and carbon monoxide-containing gas, including carbon monoxide gas produced by this gasification device, to the carbon generator. A decoating system for coated fuel particles, characterized in that it is configured to recover and remove the carbon generated in the carbon generation device.

2. A decoating system for coated fuel particles, which removes carbon contained in the coating material of coated fuel particles formed by coating a fuel kernel with a coating material, A gasification device that generates carbon monoxide gas by the reaction of carbon contained in the coating material of the coated fuel particles with carbon dioxide gas, This gasification device removes carbon and separates the fuel portion, including the fuel kernel, from the carbon monoxide-containing gas, including the carbon monoxide gas generated in the gasification device. A fuel recovery device is provided to allow the fuel portion separated by this fuel portion separation device to be recovered to the outside, A carbon generator that reacts carbon monoxide gases produced in the gasification device at a lower temperature than the gasification device and in the absence of the fuel kernel to produce carbon and carbon dioxide gas, A carbon separation device separates the carbon produced by this carbon generation device from a carbon dioxide-containing gas that includes the carbon dioxide gas produced by the carbon generation device. A carbon recovery device is provided to allow the carbon separated by this carbon separation device to be recovered to the outside, A blower supplies carbon dioxide-containing gas, including carbon dioxide gas produced in the carbon generation device, to the gasification device, and carbon monoxide-containing gas, including carbon monoxide gas produced in the gasification device, to the carbon generation device. A decoating system for coated fuel particles, characterized in that the carbon generated in the carbon generation device is separated by the carbon separation device and recovered and removed by the carbon recovery device.

3. The decoating system for coated fuel particles according to claim 1 or 2, characterized in that the temperature of the gasification device is set to 500°C or higher, and the temperature of the carbon generation device is set to 200°C or higher and lower than the temperature of the gasification device.

4. The decoating system for coated fuel particles according to claim 1, characterized in that the gasification device is equipped with a concentration meter for measuring the concentration of at least one of carbon monoxide and carbon dioxide in the gasification device.

5. The decoating system for coated fuel particles according to claim 1, characterized in that the carbon generating device is equipped with a pressure gauge for measuring the pressure inside the carbon generating device.

6. The decoating system for coated fuel particles according to claim 2, characterized in that the gasification device, the fuel partial separation device, or the fuel partial recovery device is equipped with a concentration meter for measuring the concentration of at least one of carbon monoxide and carbon dioxide in any of the devices installed therein.

7. The decoating system for coated fuel particles according to claim 2, characterized in that the carbon generating device, the carbon separation device, or the carbon recovery device is equipped with a pressure gauge for measuring the pressure inside any of the devices installed therein.

8. A method for decoating coated fuel particles, wherein a fuel kernel is coated with a coating material to remove carbon contained in the coating material of coated fuel particles, The gasification device comprises the steps of generating carbon monoxide gas by the reaction of carbon contained in the coating material of the coated fuel particles with carbon dioxide gas, The carbon generation device includes the step of reacting carbon monoxide gases produced in the gasification device at a lower temperature than the gasification device and in the absence of the fuel kernel to produce carbon and carbon dioxide gas, The blower sequentially performs the following steps: supplying the carbon dioxide-containing gas, including the carbon dioxide gas produced in the carbon generation device, to the gasification device. A method for decoating coated fuel particles, characterized by recovering and removing the carbon generated in the carbon generation device.

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