System and method for manufacturing nuclear fuel components with controlled number of core particles

Abstract

The optical counter of the present invention is used in a method and system for manufacturing a nuclear fuel component containing a uniformly distributed nuclear material in a known volume, and includes the following steps. Supply nuclear fuel particles along a channel provided with a conveyor configured to transport the nuclear fuel particles towards an outlet. Drive the conveyor until a target number of nuclear fuel particles pass through the outlet of the channel, and count the number of nuclear fuel particles passing through the outlet of the channel with an optical counter. After a target number of nuclear fuel particles have passed through the outlet of the channel, stop the conveyor. Supply the target number of nuclear fuel particles to a mold for shaping the nuclear fuel component, fill the remaining voids in the mold with a granular matrix material, uniformly distribute the target number of nuclear fuel particles within the granular matrix material, and convert the granular matrix material into a solid matrix material. By this method, a nuclear fuel component containing a uniformly distributed nuclear material can be manufactured in an accurate volume.

Description

[Technical Field]

[0001] Various embodiments disclosed herein generally relate to the preparation of nuclear fuel components consisting of particles of nuclear material uniformly distributed within a matrix. [Background technology]

[0002] Generally, nuclear fuel components are composed of particles of nuclear material distributed within a matrix. Nuclear fuel particles may include compounds of uranium, plutonium, or thorium. In various embodiments, the kernel of a nuclear fuel particle may include a ceramic kernel of a nuclear metal. In the case of uranium, such a ceramic kernel may include uranium oxide (UO), uranium oxycarbide (UCO), uranium carbide (UC or UC), or uranium nitride (UN). Nuclear fuel particles may include a kernel coated with a protective carbon or ceramic layer, or may include an uncoated kernel. In various embodiments, nuclear fuel particles may include a kernel of a uranium ceramic compound coated with a protective ceramic or carbon layer.

[0003] The nuclear fuel component may be a triple-structured isotropic (TRISO) fuel particle, which includes multiple layers of varying thickness and different chemical compositions (carbon, SiC, or ZrC). To produce the TRISO particle, a ceramic nuclear fuel kernel is sequentially coated as follows:

[0004] Porous carbon layer Inner pyrolytic carbon layer Ceramic layers (e.g., silicon carbide, tungsten carbide, zirconium carbide, or zirconium nitride layers) outer pyrolytic carbon layer

[0005] Nuclear fuel elements consist of a matrix of uniformly distributed particles of coated or uncoated nuclear fuel kernels. The matrix surrounding the fuel may be graphite, a ceramic such as SiC or ZrC, or a resin such as phenolic resin. Fuel elements may be formed into spheres, cubes, or cylinders. Fuel elements are classified as follows:

[0006] Generally homogeneous with uniformly distributed nuclear fuel particles Heterogeneous, with an inner core containing fuel particles dispersed in a matrix material and an outer layer consisting of a matrix material that does not contain nuclear fuel. A heterogeneous structure with an inner core and outer layer of matrix material that does not contain nuclear fuel, with a fuel-containing layer between them. Multi-layered and heterogeneous, with each layer containing different types or sizes of fuel particles

[0007] The fuel components may contain burnable poisons within the matrix material or as individual particles embedded within the matrix material, which prevent criticality from excess nuclear fuel early in the life of the fuel component and are consumed by neutron absorption as the nuclear fuel is consumed.

[0008] Nuclear fuel components containing TRISO particles may be used to produce nuclear chain reactions in which one nuclear reaction triggers one or more subsequent nuclear reactions. The neutron multiplication factor, k, represents the average number of neutrons from one fission reaction that triggers another, and is defined as:

[0009] k = (number of neutrons in one generation) / (number of neutrons in the previous generation)

[0010] In general, the value of k determines the progress of a nuclear reaction. Specifically, If k is greater than 1, the chain reaction is supercritical and the number of neutrons increases exponentially; if k is less than 1, the chain reaction is subcritical and the number of neutrons decreases exponentially; if k is 1, the chain reaction is critical and the number of neutrons remains constant. Summary of the Invention [Problem to be solved by the invention]

[0011] Because the total amount of fissile material present in the matrix material of a nuclear fuel element affects the value of the multiplication factor k, a system that produces fuel elements with a predictable mass loading is desirable. The fuel kernel should be uniformly distributed within the radioactive fuel element. [Means for solving the problem]

[0012] In view of the current need for improved methods for providing nuclear fuel components having a controlled distribution in the nuclear fuel kernel, a summary of various embodiments is presented. The following summary may include some simplifications and omissions, which are intended to highlight and introduce some aspects of the various embodiments, but are not intended to limit the scope of the invention.

[0013] In various embodiments disclosed herein, there is provided a method for producing a nuclear fuel component having a known volume of uniformly distributed nuclear material, comprising: feeding nuclear fuel particles having a predetermined particle size along a channel having an outlet, the channel comprising a conveyor configured to transport the nuclear fuel particles through the outlet; driving the conveyor until a target number of the nuclear fuel particles pass through the channel and reach the outlet; counting the number of the nuclear fuel particles passing through the outlet of the channel with an optical counter; after the target number of the nuclear fuel particles have passed through the channel, stopping the conveyor; feeding the target number of the nuclear fuel particles into a mold for forming the nuclear fuel component; filling the target number of the nuclear fuel particles in the mold with a granular matrix material; uniformly distributing the nuclear fuel particles within the granular matrix material; and converting the granular matrix material into a solid matrix material, wherein the volume of nuclear material within the target number of nuclear fuel particles is known, and the nuclear fuel particles having the predetermined particle size have an average kernel size of 200 to 800. micrometer and comprising a nuclear fuel kernel having an optional coating. Let's say.

[0014] According to various embodiments disclosed herein, the volume of the nuclear material in the nuclear fuel particles and the volume of the granular matrix material are required to be sufficient to fill voids in the mold after the target number of nuclear fuel particles are fed into the mold. component determining that the proportion of the volume of the solid matrix material in the

[0015] In various embodiments, the conveyor is a vibrating conveyor having a conveyor surface that runs along the length of the channel, and the motor is configured to vibrate the conveyor surface.

[0016] In various embodiments, the channel has a tubular or semi-cylindrical surface, the conveyor includes a rotating auger configured to drive the nuclear fuel particles along the tubular or semi-cylindrical surface, and a motor configured to rotate the rotating auger.

[0017] In various embodiments, the conveyor is an inclined metal conveyor, and the conveyor may be gravity fed, driven by a motor configured to vibrate the conveyor surface, or a combination thereof. If the conveyor is gravity fed, stopping the conveyor includes closing a gate at the outlet of the channel. If the conveyor is vibration driven, stopping the conveyor includes stopping the motor.

[0018] In various embodiments, the conveyor has at least two rollers and an endless belt supported by at least two of the rollers, the endless belt running along the length of the channel to the outlet, and the motor configured to rotate at least two of the rollers.

[0019] In the disclosed method, the optical counter includes a laser disposed at the outlet of the channel and a detector for detecting a light beam emitted from the laser. beam and a control circuit configured to receive the laser. The aforementioned a sensor configured to transmit a beam, the beam being interrupted each time the nuclear fuel particle passes through the channel; The aforementioned and configured to transmit a first signal whenever the beam is interrupted, the control circuitry comprising: The aforementioned Every time the beam is interrupted The aforementioned receiving a first signal from the sensor; The aforementioned Passing through the channel The aforementioned A number of nuclear fuel particles may be calculated, and when the target number of nuclear fuel particles has passed through the channel, a second signal may be sent to a motor driving the conveyor, the second signal causing the motor to stop.

[0020] In the disclosed method, the optical counter comprises a camera disposed at an exit of the conveyor and a control circuit, the camera configured to transmit a first signal for each nuclear fuel particle passing through the channel, the control circuit receiving the first signal from the camera for each nuclear fuel particle passing through the channel, counting the nuclear fuel particles passing through the channel, and transmitting a second signal to a motor driving the conveyor when the target number of nuclear fuel particles has passed through the channel, the second signal may cause the motor to stop.

[0021] In the disclosed method, the optical counter preferably comprises a high-power LED disposed at the outlet of the channel, a digital camera, and control circuitry, wherein the LED is configured to illuminate a path of particles passing through the channel, the digital camera is configured to receive the light from the LED and record a sequence of images, the control circuit analyzes each image in the sequence of images to confirm that each dark spot corresponds to a particle, records the total number of particles in the sequence of images until the target number of particles is achieved, and sends a signal to a motor driving a conveyor when the target number of particles is achieved, and the step of stopping the conveyor preferably includes stopping the motor driving the conveyor after the motor receives the signal.

[0022] In various embodiments disclosed herein, the step of converting the granular matrix material into a solid matrix material preferably comprises hot isostatic pressing, cold isostatic pressing, spark plasma sintering, or uniaxial pressing of the nuclear fuel particles and the granular matrix material in the mold. The granular matrix material may comprise graphite, a phenolic resin, or a metal carbide (e.g., SiC or ZrC), and preferably further comprises a binder. The granular matrix material in the mold may further comprise a polymer binder and / or a burnable poison, and suitable burnable poisons preferably include gadolinium, boron, hafnium, and / or compounds thereof.

[0023] In various embodiments disclosed herein, a system for producing nuclear fuel components having a known amount of nuclear material uniformly distributed therein comprises a channel having an outlet, the channel configured to receive nuclear fuel particles, the nuclear fuel particles having an average kernel size of between 200 and 800. micrometera conveyor including a nuclear fuel kernel having an optional coating and configured to transport the nuclear fuel particles along the channel and through the outlet; an optical counter configured to count the number of nuclear fuel particles passing through the outlet of the channel and to send a first signal when a target number of the nuclear fuel particles have passed through the channel; and a motor configured to drive the conveyor until the target number of nuclear fuel particles have passed through the channel and reached the outlet, and to stop the conveyor after receiving the first signal from the optical counter.

[0024] The system further includes a mold for receiving the target number of nuclear fuel particles and the granular matrix material and for uniformly distributing the target number of nuclear fuel particles within the granular matrix material, the mold being preferably a graphite mold, a metal mold, or a polymer or elastomer mold, and in various embodiments, achieving the uniform distribution of the target number of nuclear fuel particles by vibrating the mold while filling it with the nuclear fuel particles and the granular matrix material.

[0025] In various embodiments of the system, the conveyor is a vibrating conveyor having a conveyor surface that travels along the length of the channel, the motor being configured to vibrate the conveyor surface, and in various embodiments of the system, the conveyor may have at least two rollers and an endless belt supported by at least two of the rollers, the endless belt traveling along the length of the channel to the outlet, and the motor being configured to rotate at least two of the rollers.

[0026] The optical counter of the disclosed system may include a laser disposed at the exit of the conveyor, a sensor configured to receive a beam from the laser, and a control circuit, wherein the laser is configured to transmit the beam, the beam being interrupted each time the nuclear fuel particle passes through the channel, the sensor being configured to transmit a second signal each time the beam is interrupted, the control circuit receiving the second signal from the sensor each time the beam is interrupted, counting the nuclear fuel particles passing through the channel, and transmitting the first signal to the motor when the target number of nuclear fuel particles has passed through the channel.

[0027] The disclosed system may include the optical counter comprising a camera disposed at the outlet of the conveyor, and a control circuit, wherein the camera is configured to transmit the second signal for each nuclear fuel particle passing through the channel, the control circuit receiving the second signal from the camera for each nuclear fuel particle passing through the channel, counting the nuclear fuel particles passing through the channel, and transmitting the first signal to the motor when the target number of nuclear fuel particles has passed through the channel.

[0028] Various embodiments disclosed herein relate to a method for producing a nuclear fuel component having a predictable multiplication factor k, comprising: feeding nuclear fuel particles along a channel having an outlet, the channel comprising a conveyor configured to transport the nuclear fuel particles through the outlet; driving the conveyor until a target number of the nuclear fuel particles pass through the channel and reach the outlet; counting the number of the nuclear fuel particles passing through the outlet of the channel with an optical counter; stopping the conveyor after the target number of nuclear fuel particles have passed through the channel; filling a mold with the target number of nuclear fuel particles and a granular matrix material; vibrating the mold to uniformly distribute the nuclear fuel particles within the granular matrix material; and converting the granular matrix material into a solid matrix material, the nuclear fuel particles having an average kernel size of 200 to 800. micrometerand characterized in that it comprises a nuclear fuel kernel having an optional coating. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a diagram illustrating a system for filling molds for nuclear fuel components, including a conveyor for receiving nuclear fuel particles and an optical counter for counting the nuclear fuel particles. [Figure 2A] FIG. 2A illustrates a method for classifying nuclear fuel particles using a screen. [Figure 2B] FIG. 2B illustrates a method for classifying nuclear fuel particles using roller classification. [Figure 3] FIG. 3 illustrates a method for preparing a nuclear fuel component by applying heat and / or pressure to a mold containing nuclear fuel particles and precursors of a solid matrix material. [Figure 4] 4A and 4B illustrate an embodiment of a vibrating conveyor for use in the system of FIG. [Figure 5] 5A and 5B illustrate an alternative embodiment of a conveyor for use in the system of FIG. [Figure 6] FIG. 6 shows an endless belt conveyor for use in the system of FIG. [Figure 7] FIG. 7 illustrates a method for preparing a nuclear fuel component by cold isostatic pressing a mold containing nuclear fuel particles and precursors of a solid matrix material. [Figure 8] FIG. 8 illustrates a method for preparing a nuclear fuel component by hot isostatic pressing a mold containing nuclear fuel particles and precursors of a solid matrix material. [Figure 9] FIG. 9 illustrates a method for preparing a nuclear fuel component by subjecting a mold containing nuclear fuel particles and precursors of a solid matrix material to spark plasma sintering. [Figure 10] FIG. 10 illustrates a method for preparing a nuclear fuel component by applying uniaxial compression to a mold containing nuclear fuel particles and precursors of a solid matrix material. DETAILED DESCRIPTION OF THE INVENTION

[0030] Referring to the drawings, wherein like numbers refer to like parts or steps, broad aspects of various embodiments are disclosed.

[0031] As used herein, the term "about" encompasses "plus or minus 10%" of the stated value. The term "substantially" may allow for up to a 15% variation on the value.

[0032] As used herein, the term "uniform distribution" means that the particles within the matrix are evenly distributed, indicating that any two sections of the same volume through the matrix material have substantially the same number of particles.

[0033] When discussing nuclear fuel particles, the term "kernel" refers to a radioactive ceramic particle. The term "particle" refers to the kernel or a particle produced by coating the kernel with a carbon layer, a ceramic layer, or a combination thereof. The term "TRISO particle" refers to a specific class of kernels sequentially coated with a porous carbon layer, an inner pyrolytic carbon layer, a ceramic layer (e.g., a metal carbide, oxide, or nitride layer), and an outer pyrolytic carbon layer.

[0034] In various embodiments, the present disclosure describes systems and methods for producing multiple nuclear fuel components containing a precisely determined amount of uranium in each fuel component. Each fuel component contains approximately the same number of nuclear fuel kernels as the other fuel components. Each nuclear fuel kernel has approximately the same volume and mass as the other nuclear fuel kernels. The mass of each nuclear fuel kernel is within ±10% of a target mass M. The number of nuclear fuel kernels in each fuel component is counted using an optical counter. Nuclear fuel kernels, each with a mass M ±10%, are counted until a target number N is reached, and then fuel components containing N kernels are prepared, resulting in fuel components containing a predictable amount of nuclear material. The fuel components are manufactured to contain kernels uniformly distributed within each fuel component. Each fuel component contains the same number of kernels within a matrix of substantially identical kernels uniformly distributed. The kernels may include a ceramic and / or carbon coating, but each kernel has a substantially identical mass.

[0035] Conventional processes use nuclear fuel particles with a defined total mass, rather than a defined particle count or particle volume. In such systems, particle counts cannot be easily predicted because particles can contain a mixture of small and large particles. Furthermore, particles often have a kernel coated with a carbon layer, a ceramic layer, or a combination of carbon and ceramic layers. The mass of each particle includes contributions from the kernel and the coating layer, each with its own uncertainty. As a result, the error in determining the amount of nuclear material by measuring mass is greater than the error from counting a predetermined number of particles.

[0036] As described above, measuring the amount of nuclear material based on mass can produce fuel components with kernels of variable size. When kernels have different surface areas, i.e., when small and large kernels are mixed, the total kernel surface area decreases. Under this condition, k-infinity increases. This disclosure describes a system for counting nuclear fuel kernels of approximately identical size and mass to produce fuel components with uniform kernel size and low k-infinity. The various counting processes disclosed herein can be performed very quickly, and measuring the amount of nuclear material based on particle count can be performed without significantly sacrificing productivity while improving accuracy compared to measuring based on particle mass.

[0037] FIG. 1 illustrates a system for filling a mold 7 with nuclear fuel pellets or particles 2 and granular matrix material 9. A first hopper 1 contains nuclear fuel pellets 2 (e.g., uranium oxide particles, uranium carbide particles, uranium oxycarbide particles, or TRISO particles). The nuclear fuel pellets 2 enter a channel 3 in the direction of arrow A and are fed into a channel 3 containing a vibrating conveyor 4. A motor 16 connected to the conveyor 4 by an actuator 15 vibrates the conveyor 4, moving the particles 2 along the conveyor 4 toward the output opening 3a of the channel 3. As the particles 2 leave the channel 3, they enter a passage 8, which feeds the particles 2 into the mold 7 through the output 8a. Simultaneously, a second hopper 10 contains granular matrix material 9 and feeds the granular matrix material 9 into a second passage 11, which feeds the granular matrix material 9 into the mold 7. After the mold 7 is filled with the granular matrix material 9 and particles 2, a mass flow controller (e.g., valve 12) can be used to stop the flow of the matrix material 9 into the mold 7. The mould 7 is used to prepare the nuclear fuel components.

[0038] In various embodiments, the nuclear fuel pellets or particles 2 have a defined average particle size and / or a defined particle size range. Based on information about the size of such particles 2, knowing the number of nuclear fuel pellets or particles 2 contained in the nuclear fuel component allows for a good estimation of the amount of nuclear material present in the nuclear fuel component prepared in the mold 7. Furthermore, using a known number of nuclear fuel pellets or particles 2 with a controlled average particle size or particle size range provides a nuclear fuel component with a controlled surface area. When all particles have a similar surface area, the total kernel surface area is maximized. Under this condition, k-infinity, i.e., the proportion of neutrons from current generation fission in an infinitely sized system, is minimized.

[0039] To address this, the system of FIG. 1 uses an optical sensor to count the number of particles entering mold 7. As particles 2 move from channel opening 3a into passageway 8 in the direction of arrow B, they pass through the optical sensor. The optical sensor includes a light source 5 and a sensor 6. In various embodiments, light source 5 is a laser that transmits a beam in the direction of arrow C to sensor 6, which records the intensity of the beam from light source 5. Sensor 6 is configured to communicate with control circuitry 6a.

[0040] The term "control circuitry" as used herein refers to any type of information processing unit. The control circuitry may be a central processing unit (CPU) external to the optical sensor that can communicate with the optical sensor over a wired or wireless communication network. The control circuitry may be a microprocessor contained within the optical sensor, particularly within sensor 6. The control circuitry may be logic circuits or logic gates contained in an integrated circuit within sensor 6. The control circuitry may be a combination of logic gates and a CPU or microprocessor contained in an integrated circuit within sensor 6.

[0041] Each time a particle 2 passes through the beam of the laser 5, the intensity of the beam decreases and the sensor 6 sends a signal to the control circuit 6a. The control circuit 6a records the number of signals received from the sensor 6 and counts the number of particles passing through the sensor 6. Once the target number of particles has passed through the sensor 6, the control circuit 6a sends a signal to the motor 16 to stop the motor 16, which stops the vibrating conveyor 4. This allows the correct number of nuclear fuel pellets or particles 2 to enter the mold 7. The control circuit can be implemented using logic gates implemented in an integrated circuit or using a CPU or microprocessor.

[0042] The control circuit 6a may be a sequential logic circuit implemented on an integrated circuit that counts particles leaving the channel 3 until a target number is reached, and then sends a signal to stop the motor 16. The logic circuit may be designed to reset the particle count to zero after sending the signal to the motor 16.

[0043] The control circuit 6a may include a logic circuit implemented on an integrated circuit and a CPU or microprocessor. The logic circuit sends a signal to the CPU or microprocessor each time a particle leaves the channel 3, and the CPU or microprocessor counts the number of particles until a target number is reached, then sends a signal to stop the motor 16. In various embodiments, the logic circuit may be a NOT gate that sends a signal each time a particle 2 passes through the beam of the laser 5. In various embodiments, the logic circuit may be a two-input logic gate. For example, the sensor 6 may be configured to detect both the decrease in laser intensity as the particle 2 passes through the beam of the laser 5 and the time T until the laser returns to its original intensity. This allows for filtering out false signals due to temporary fluctuations in laser intensity. The two-input logic gate may be, for example, an AND gate that sends a signal each time a particle 2 passes through the beam of the laser 5 when the following condition is met: If the laser intensity is below the reference intensity, and If the time it takes for the laser intensity to return to its original intensity exceeds a minimum time T. The two-input logic gate may be an OR gate that sends a signal whenever particle 2 passes through the beam of laser 5 when any of the following conditions are met: When the laser intensity decreases to the target value, or If the laser intensity decreases beyond the target time. One-input or two-input logic gates can be constructed from networks of connected NAND gates.

[0044] The control circuit 6a may include a CPU or microprocessor configured to record the output from the sensor 6, count the particles leaving the channel 3 based on this output, and send a signal to stop the motor 16 when a target number is reached.

[0045] In various embodiments, the optical sensor includes a light source 5 and a sensor 6, which may be a camera positioned at the exit of the conveyor. The camera is configured to send a first signal each time a nuclear fuel particle exits the channel. The optical sensor includes control circuitry configured to receive the first signal from the camera each time a nuclear fuel particle exits the channel and to calculate the number of nuclear fuel particles exiting the channel. The control circuitry sends a second signal to a motor driving the conveyor when a target number of nuclear fuel particles exiting the channel is reached, and the second signal stops the motor.

[0046] In various embodiments, the optical sensor includes an LED as the light source 5 and a camera as the sensor 6. The camera is positioned at the exit of the conveyor and configured to record a series of images of the particle stream exiting the conveyor. The camera is configured to sequentially transmit each image in the series to a control circuit. The control circuit is configured to sequentially analyze each image and detect dark spots, i.e., spots where the image brightness is below a threshold. Each dark spot corresponds to a particle. The control circuit counts the number of particles in each image and calculates the total number of nuclear fuel particles exiting the channel in the series of images. When the total number of nuclear fuel particles exiting the channel reaches a target value, the control circuit sends a signal to a motor driving the conveyor, which, upon receiving the signal, causes the motor to stop the conveyor.

[0047] In various embodiments, the control circuitry is configured to analyze the diameter or area, typically particle size, of each dark spot. The control circuitry may send a warning signal if a threshold number or percentage of particles are outside a target size range. Because the number of nuclear fuel pellets or particles 2 entering the mold 7 is known and the average particle size or particle size range of the nuclear fuel pellets or particles 2 is known, a good estimate of the number of pellets 2 and total volume of nuclear fuel material can be made.

[0048] Finally, returning to FIG. 1 , mold 7 may be placed on a vibration table 41 that is vibrated by motor 42 during the filling process. The vibration evenly distributes the nuclear fuel pellets or particles 2 within matrix material 9. Thus, after filling of mold 7 is complete, a known number of nuclear fuel pellets or particles 2 with a known particle size are evenly distributed within a known amount of matrix material 9. The matrix material 9 within the mold is solidified by sintering and / or compaction to produce a nuclear fuel component with a known amount of uranium particles or pellets evenly distributed within a known amount of matrix material.

[0049] In various embodiments, the mold includes a core element that is devoid of a nuclear fuel kernel before being filled with nuclear fuel particles and matrix material. The nuclear fuel particles and matrix material are added to the mold to surround the core element, and the final fuel composition includes a zone without nuclear fuel particles and a zone with nuclear fuel particles uniformly distributed within the matrix material. The core element may be cylindrical, spherical, or cubic. The core element has a hollow bore, with a first zone containing uniformly distributed nuclear fuel particles within the hollow bore of the core element and a second zone surrounding the outer surface of the core element containing uniformly distributed nuclear fuel particles.

[0050] Efficient distribution of fuel particles within the matrix is ​​important, and k-infinity increases when: When the distance between kernels decreases When the average distance between the kernel and the edge of the fuel component decreases When fuel kernels are very close together, they behave as a single large kernel. Kernels near the edge of the fuel element and far from other kernels also increase k-infinity. Uniformly distributed kernels of roughly the same size produce a more controllable nuclear chain reaction with reduced k-infinity.

[0051] Prior art procedures fill molds for nuclear fuel components with a known mass of uranium particles, rather than a known number of particles with a known particle size. Such systems may contain a small number of large particles and a large number of small particles that contribute disproportionately to the total mass. Even when the mold is vibrated during filling, such systems may not have a uniform particle size distribution, resulting in an inconsistent distribution of uranium particles or pellets within the matrix material.

[0052] Furthermore, the disclosed method counts nuclear fuel kernels or coated nuclear fuel particles with a narrow kernel size distribution. Counting such particles allows for accurate total mass determination of fissile material. Simply weighing particles, as in the prior art, is less accurate than particle counting because the particle size distribution is not well controlled. Furthermore, in the case of coated particles, determining the target amount of fissile material by weighing the coated particle mass is inaccurate due to uncertainties in the kernel mass and coating mass of each particle. TRISO particles and other coated particle fuels contain significant amounts of non-fissile material. Even if the total mass of the particle is known, significant uncertainty remains in the kernel mass of each coated fuel particle due to the uncertainty in the combination of the kernel mass and coating mass.

[0053] In various embodiments disclosed herein, the average fissile mass and particle size per each kernel are known before any non-fissile mass (e.g., coating layers) is added. The distribution of kernel size and / or kernel mass is very narrow (e.g., ±10%), making the average kernel mass very representative. In various embodiments, the number of fuel particles in each fuel element is determined by dividing the target fissile mass of each fuel element by the known fissile mass per particle. This provides more accurate results than simply measuring the total mass of the fuel particles. Because the mass of fissile material per each kernel is precisely known, a wider range of coated fuel particle sizes can be accommodated while maintaining the precision and accuracy of the fissile mass of the fuel element.

[0054] When coated particles are measured by total mass, the number of kernels and the mass of fissile material per kernel are not precisely known, and the range of particle sizes that can be accepted is narrow. For example, large particles may be rejected because they may have oversized kernels. Some of these particles may simply have a thick coating.

[0055] Granular matrix material 9 is fed from a hopper 10 into the mould 7 until the mould is filled. Since the total volume of nuclear fuel material in the mould is known, the volume of matrix material in the mould 7 is also known. This allows the ratio of the volume of nuclear fuel material to the volume of matrix material to be determined.

[0056] In various embodiments, the nuclear fuel pellets or particles 2 should have a substantially uniform size. For TRISO particles, the average kernel size is approximately 200-800 mm in diameter. micrometer , 300~700 micrometer , or 350-500 micrometer The average multi-coated TRISO particle size is approximately 500-1500 mm in diameter. micrometer , 600~1200 micrometer , or 800-1000 micrometer If a set of particles is determined to have an unacceptably wide particle size range, such as containing unacceptably large particles 2a and unacceptably small particles 2b, as shown in Figure 2A, the particles may be processed to remove particles outside the optimal size range. As shown in Figure 2A, the particle size range can be narrowed by sieving. Nuclear fuel pellets or particles are passed through a high-mesh screen 39, which retains the large particles 2a, and then through a low-mesh screen 40, which retains particles of the desired size and allows the small particles 2b to pass. This allows the average size of the uranium kernels to be estimated. As previously mentioned, the optical counter in the apparatus of Figure 1 can directly measure the number of particles being added to the mold 7.

[0057] In various embodiments, the particle size range can be narrowed with a roller classifier, as shown in FIG. 2B. Nuclear fuel pellets or particles 2 are fed into a hopper 43 and then into a chute 44, which directs them toward a pair of classifying rolls 45 with diverging axes and a gap between them. At the beginning of the classifying rolls 45, small particles 2b pass through the gap, while larger particles 2 and 2a are retained by the classifying rolls. The small particles 2b are conveyed by the first classifying chute 47 to a first container 48b. At the end of the classifying rolls, the largest particles 2a are conveyed by a chute 49 to a container 48a for oversized particles. Particles 2 of the target diameter pass through the gap at a point whose width corresponds to the target diameter and are delivered through the classifying chute 47 to a container 48 for receiving particles with the target diameter. One or more containers 48n may be positioned at different locations on the rolls 45 and configured to receive particles with different target diameters from different classifying chutes 47. Intermediate size particles pass through gaps at intermediate positions along the classifying roll and are conveyed by the appropriate classifying chute to the appropriate container, allowing the collection of particles with a very narrow size range.

[0058] In various embodiments, the nuclear fuel kernels are classified with a roller classifier or a screen classifier to produce kernels with a narrow size distribution. As a result, the mass of nuclear material contained in each particle is known. The kernels may then be coated with a ceramic layer, a carbon layer, or a mixture thereof. The coating may introduce some variation in the overall size of the particles, but each particle will have substantially the same kernel size. Optionally, after coating the kernels, the coated particles are classified with a screen classifier or a roller classifier to produce particles with a narrow size distribution, providing nuclear fuel particles with the following properties: Effectively constant kernel size Substantially constant total coating thickness This allows for the production of substantially homogeneous nuclear fuel particles.

[0059] The spherical uranium oxide kernels have an average diameter of approximately 500 mm. micrometer If it is known that the volume of uranium oxide contained in each kernel is about 0.52 mm 3 Based on the exact number of nuclear fuel pellets or particles 2, the volume of uranium oxide in the mold 7 for the nuclear fuel component is known. Furthermore, if the volume of uranium oxide in the mold or the volume of coated uranium oxide particles, e.g., TRISO particles, is known, the amount of granular matrix material 9 to be added to the mold 7 can be determined, and the ratio of nuclear material to matrix material can be accurately determined. Specifically, an amount of granular matrix material can be added to the mold 7 equal to the void volume remaining in the mold after the nuclear fuel pellets or particles 2 have been added to the mold 7.

[0060] FIG. 3 illustrates the conversion of a defined number of nuclear fuel pellets or particles 2 and a defined amount of granular matrix material 9 into a nuclear fuel component. The mold 7 containing the particles 2 and granular matrix material 9 is sealed with a closure element 7a, and heat and / or pressure are applied to fuse the granular matrix material 9 into a solid matrix 13, e.g., a solid mass of sintered particles. The mold 7 and closure element 7a are removed, leaving the nuclear fuel component containing the nuclear fuel pellets or particles 2 and solid matrix 13. The nuclear fuel pellets or particles 2 may be bare kernels, ceramic-coated kernels, carbon-coated kernels, or kernels coated with a carbon and ceramic layer (e.g., TRISO particles). Various materials that may be used as inert matrix materials for nuclear fuel include: Ceramic (e.g. MgO, ZrO2, CeO2, or SiC) Refractory materials (e.g. graphite) Ceramic-metal composites (cermets) Composite materials (ceramics) made of two or more types of ceramics Metal (e.g., stainless steel, zirconium, molybdenum, or tungsten)

[0061] In various embodiments, the granular matrix material 9 may include a small amount of a burnable poison. The burnable poison has a high neutron absorption cross section, but is converted to a substance with a relatively low absorption cross section upon combustion in the reactor. The negative reactivity of the burnable poison decreases over time. Suitable burnable poisons include gadolinium, boron, hafnium, or compounds thereof.

[0062] FIG. 4A shows an apparatus including a first embodiment of a vibrating conveyor. A tongue 4a on the conveyor 4 has a hole through which a first end of a cable or rope 20 is fixed to a solid surface (e.g., the floor) and a second end is fixed to the end of a first wheel 18. The cable or rope 20 passes through the hole in the tongue 4a, and a spring 21 may be incorporated into the cable or rope. A motor 16 rotates a second wheel 17, and a belt 19 driven by wheel 17 rotates wheel 18. As wheel 18 rotates, spring 21 alternately expands and contracts, causing the conveyor 4 to oscillate vertically.

[0063] Figure 4B shows an apparatus including a second embodiment of a vibrating conveyor. Conveyor 4 is attached to springs 23. Motor 16 is connected to actuator 22, which transfers the vibratory motion from motor 16 to conveyor 4. Springs 23 allow conveyor 4 to vibrate up and down.

[0064] In various embodiments, the system of Figure 1 may be modified by replacing the vibratory conveyor with a rotating auger. The channel has a tubular or semi-cylindrical conveyor surface 50 running along the length of the channel to an outlet, as shown in Figure 5A, with a screw auger 51 mounted therein. The conveyor is driven by rotating the screw auger 51, which carries particles 2 within the helical threads 52 of the auger 51 along the conveyor surface 50 to the outlet. A motor 53 is configured to rotate the screw auger 51.

[0065] In various embodiments, the system of FIG. 1 may be modified by replacing the vibratory conveyor with an inclined metal conveyor surface. The channel has an inclined metal conveyor surface 54 that runs along the length of the channel to the outlet, as shown in FIG. 5B. The conveyor may be gravity fed, driven by a motor 55 configured to vibrate the conveyor surface, or a combination thereof. If the conveyor is gravity fed, stopping the conveyor includes closing a gate 56 at the channel outlet. If the conveyor is vibration driven, stopping the conveyor includes stopping the motor.

[0066] FIG. 6 illustrates an apparatus including an endless belt conveyor. Conveyor 4b is a flexible belt carried by rollers 25 and 25a. Conveyor 4b is driven by motor 16, which includes actuator 24 that rotates roller 25. Roller 25a may be rotated by conveyor 4b moving around roller 25. Alternatively, roller 25a may be rotated by a second motor. As rollers 25 and 25a drive the flexible belt of conveyor 4b, particles 2 are carried along channel 3 and reach exit 3a. As particles fall from exit 3a, they pass light source 5 and sensor 6, which sends a signal to control circuit 6a each time a particle passes sensor 6. When a predetermined number of particles are detected, control circuit 6a sends a signal to motor 16, which stops the rotation of roller 25 and the movement of the endless belt conveyor.

[0067] Once the mold 7 is filled with nuclear fuel pellets or particles 2 and a defined amount of granular matrix material 9, its contents are heated and / or pressured to convert the granular matrix material 9 into solid matrix material 13 (see Figure 3). This can be done by several techniques.

[0068] FIG. 7 illustrates the preparation of nuclear fuel components by cold isostatic pressing, which illustrates the wet bag technique. A mold 7 containing nuclear fuel pellets or particles 2 and granular matrix material 9 is placed in a container 27. The mold 7 is a flexible mold and may be made of an elastomeric material (e.g., rubber). The mold opening is closed with a closure element 7a. In some embodiments, the mold 7 is a disposable mold, and the closure element 7a may have a smaller diameter than the interior of the mold 7. In some embodiments, the mold 7 is a reusable mold, and the closure element 7a has the same diameter as the interior of the mold 7, allowing the nuclear fuel components to be retrieved without damaging the mold.

[0069] After the mold 7 is placed in the container 27, the container 27 is filled with a liquid material 26 (e.g., water) under high pressure through a pipe 28. Once the desired pressure is reached, a valve 29 on the pipe 28 is closed and pressure from the high-pressure liquid 26 is applied to the contents of the elastomeric mold 7 until the granular matrix material 9 sinters into a solid mass of solid matrix material 13. In some embodiments, the liquid material 26 can be heated, and both heat and pressure can be applied to the mold 7. The use of a pressurized heated liquid may enhance the sintering process. Dry bag isostatic pressing is known in the art and may be used to form nuclear fuel components.

[0070] 8 illustrates the preparation of nuclear fuel components by hot isostatic pressing. A flexible elastomeric mold 7 containing nuclear fuel pellets or particles 2 and granular matrix material 9 is placed in a container 27. The mold opening is closed with a closure element 7a. In some embodiments, the mold 7 is a disposable mold, and the closure element 7a may have a smaller diameter than the interior of the mold 7. In some embodiments, the mold 7 is a reusable mold, and the closure element 7a has the same diameter as the interior of the mold 7, allowing the nuclear fuel components to be retrieved without damaging the mold.

[0071] After mold 7 is placed in container 27, container 27 is filled with gas 30 (e.g., air, nitrogen, argon, or other inert gas) under high pressure through pipe 28. Once the desired pressure is reached, valve 29 on pipe 28 is closed and the pressure of pressurized gas 30 is applied to the contents of elastomeric mold 7, and gas 30 is heated to a sintering temperature. The heated pressurized gas 30 applies both heat and pressure to mold 7 until granular matrix material 9 sinters into a solid mass of solid matrix material 13.

[0072] Figure 9 illustrates the preparation of a nuclear fuel component by spark plasma sintering. A hollow mold 33 is filled with nuclear fuel pellets or particles 2 and granular matrix material 9. A lid 32 is placed on the mold 33 and pressed against the mold contents. The mold 33 and lid 32 are made of a resistive material, such as graphite. An electrical circuit 35 is connected to the mold 33 and lid 32. A power source 34 and a switch 36 may be included in the circuit 35. When the switch 36 is closed, current flows through the mold 33 and lid 32 in the direction of arrow F. The mold 33 and lid 32 are resistively heated, heating the matrix material 9 and sintering it into a solid matrix material 13. Once the sintering process is complete, the switch 36 is opened to stop the current to the mold. Once the mold and its contents have cooled, the lid 32 is removed from the mold 33, and the finished fuel component, containing nuclear fuel particles 2 within the sintered solid matrix 13, can be removed from the mold.

[0073] FIG. 10 illustrates the preparation of nuclear fuel components by uniaxial compression. A hollow mold 38 is filled with nuclear fuel pellets or particles 2 and granular matrix material 9. A lid 37 is placed on the mold 38 and forced against the contents of the mold in the direction of arrow G by a piston or other device 37a. This applies pressure to the particles 2 and granular matrix material 9, compressing them until they are converted into solid matrix material 13. In various embodiments, the mold may be heated to aid in solidifying or sintering the granular matrix material 9. While FIG. 10 illustrates compression from one direction, the contents of the mold may be compressed by a piston driven in the opposite direction.

[0074] In the processes of forming nuclear fuel components by hot or cold isostatic pressing, spark plasma sintering, and uniaxial compression, the mold may be of any shape, such as spherical, cylindrical, or cubic.

[0075] While various embodiments have been described in detail with particular reference to certain aspects, it should be understood that the invention is capable of other embodiments and its details are capable of modifications in various obvious respects. Variations and modifications can be made within the spirit and scope of the invention, as will be apparent to those skilled in the art. Accordingly, the foregoing disclosure, description, and figures are intended to be illustrative and not limiting of the invention, which is defined solely by the claims. [Explanation of symbols]

[0076] 1...first hopper, 2...nuclear fuel pellets (particles), 2a...large particles, 2b...small particles, 3...channel, 3a...output opening, 4...conveyor, 5...light source, 6...sensor, 6a...control circuit, 7...mold, 8...passage, 8a...output, 9...granular matrix material, 13...solid matrix, 10...hopper, 11...second passage, 12...valve, 15...actuator, 16...motor, 39...high mesh screen, 40...low mesh screen, 41...vibration table, 42...motor,

Claims

1. 1. A method for producing a nuclear fuel element having a known volume of uniformly distributed nuclear material, comprising: feeding nuclear fuel particles having a predetermined particle size along a channel having an outlet, the channel comprising a conveyor configured to transport the nuclear fuel particles through the outlet; driving the conveyor until a target number of the nuclear fuel particles have passed through the channel and reached an outlet; counting the number of nuclear fuel particles passing through the outlet of the channel with an optical counter; stopping the conveyor after a target number of the nuclear fuel particles have passed through the channel; providing a target number of said nuclear fuel particles to a mold for forming a nuclear fuel component; Filling the target number of nuclear fuel particles in the mold with a granular matrix material, uniformly distributing the nuclear fuel particles within the granular matrix material; converting the particulate matrix material into a solid matrix material; the volume of nuclear material within the target number of nuclear fuel particles is known; 10. The method of claim 1, wherein the nuclear fuel particles having the predetermined particle size comprise a nuclear fuel kernel having an average kernel size of 200 to 800 micrometers and having an optional coating.

2. 10. The method of claim 1, 1. A method for manufacturing a nuclear fuel component, comprising determining that the ratio of the volume of the nuclear material in the nuclear fuel particles to the volume of the solid matrix material in the nuclear fuel component is known, with the requirement that the volume of the granular matrix material is sufficient to fill voids in the mold after the target number of nuclear fuel particles have been delivered to the mold.

3. 10. The method of claim 1, comprising: the conveyor is a vibratory conveyor having a conveyor surface that runs along the length of the channel; A method for producing nuclear fuel components, wherein a motor is configured to vibrate the conveyor surface.

4. 10. The method of claim 1, the channel has a tubular or semi-cylindrical surface, the conveyor includes a rotating auger configured to drive the nuclear fuel particles along the tubular or semi-cylindrical surface; a motor configured to rotate the rotary auger;

5. 2. The method of claim 1, wherein said conveyor is an inclined metal conveyor.

6. 10. The method of claim 1, the optical counter comprises a laser disposed at an outlet of the channel, a sensor configured to receive a beam from the laser, and a control circuit; the laser is configured to transmit the beam, the beam being interrupted each time the nuclear fuel particle passes through the channel; the sensor is configured to transmit a first signal each time the beam is interrupted; the control circuit receives a first signal from a sensor each time the beam is interrupted, calculates the number of nuclear fuel particles passing through the channel, and sends a second signal to a motor driving the conveyor when the target number of nuclear fuel particles has passed through the channel, the second signal causing the motor to stop.

7. 10. The method of claim 1, The optical counter includes a camera disposed at an exit of the conveyor and a control circuit; the camera is configured to transmit a first signal for each nuclear fuel particle passing through the channel; a control circuit for receiving a first signal from the camera for each nuclear fuel particle passing through the channel, counting the nuclear fuel particles passing through the channel, and sending a second signal to a motor driving the conveyor when the target number of nuclear fuel particles has passed through the channel, the second signal causing the motor to stop.

8. 10. The method of claim 1, wherein the step of converting the granular matrix material into a solid matrix material comprises subjecting the nuclear fuel particles and the granular matrix material in the mold to hot isostatic pressing, cold isostatic pressing, spark plasma sintering, or uniaxial pressing.

9. 10. The method of claim 1, wherein the particulate matrix material comprises graphite, a phenolic resin, or a metal carbide.

10. 10. The method of claim 9, wherein the metal carbide comprises SiC or ZrC.

11. 10. The method of claim 9, wherein the particulate matrix material further comprises a binder.

12. 10. The method of claim 1, wherein the particulate matrix material further comprises a burnable poison selected from gadolinium, boron, hafnium, and compounds thereof.

13. 1. A system for producing nuclear fuel components having a known amount of uniformly distributed nuclear material, the system comprising: a channel having an outlet, the channel configured to receive nuclear fuel particles; the nuclear fuel particles have an average kernel size of 200 to 800 micrometers and include a nuclear fuel kernel with an optional coating; a conveyor configured to transport the nuclear fuel particles along the channel and through the outlet; an optical counter configured to count the number of nuclear fuel particles passing through the outlet of the channel and to transmit a first signal when a target number of the nuclear fuel particles have passed through the channel; a motor configured to drive the conveyor until the target number of nuclear fuel particles has passed through the channel and reached the outlet, and to stop the conveyor after receiving the first signal from the optical counter. A system for producing nuclear fuel components.

14. 14. The system of claim 13, 1. A system for manufacturing a nuclear fuel component, comprising: a mold for receiving the target number of nuclear fuel particles and a granular matrix material, and for uniformly distributing the target number of nuclear fuel particles within the granular matrix material.

15. 14. The system of claim 13, the conveyor is a vibratory conveyor having a conveyor surface running along the length of the channel; The system for producing nuclear fuel components, wherein the motor is configured to vibrate the conveyor surface.

16. 14. The system of claim 13, wherein the conveyor includes at least two rollers and an endless belt supported by at least two of the rollers, the endless belt running along the length of the channel to the outlet; The system for manufacturing nuclear fuel components, wherein the motor is configured to rotate at least two of the rollers.

17. 14. The system of claim 13, wherein the optical counter comprises a laser disposed at the exit of the conveyor, a sensor configured to receive a beam from the laser, and control circuitry; the laser is configured to transmit the beam, the beam being interrupted each time the nuclear fuel particle passes through the channel; the sensor is configured to transmit a second signal each time the beam is interrupted; The control circuit receives the second signal from the sensor each time the beam is interrupted, counts the nuclear fuel particles passing through the channel, and sends the first signal to the motor when the target number of nuclear fuel particles has passed through the channel.

18. 14. The system of claim 13, wherein the optical counter comprises a camera located at the exit of the conveyor; and control circuitry; the camera is configured to transmit a second signal for each nuclear fuel particle passing through the channel; The control circuit receives the second signal from the camera for each nuclear fuel particle passing through the channel, counts the nuclear fuel particles passing through the channel, and sends the first signal to the motor when the target number of nuclear fuel particles has passed through the channel.

19. 14. The system for manufacturing nuclear fuel components according to claim 13, wherein the mold is a metal mold, a graphite mold, or a rubber mold.

20. 1. A method for producing nuclear fuel components having a predictable multiplication factor k, comprising: supplying nuclear fuel particles along a channel having an outlet, the channel comprising a conveyor configured to transport the nuclear fuel particles through the outlet; driving the conveyor until a target number of the nuclear fuel particles have passed through the channel and reached the outlet; counting the number of nuclear fuel particles passing through the outlet of the channel with an optical counter; stopping the conveyor after the target number of nuclear fuel particles has passed through the channel; filling a mold with the target number of nuclear fuel particles and granular matrix material and vibrating the mold to uniformly distribute the nuclear fuel particles within the granular matrix material; 10. A method for producing a nuclear fuel component, comprising converting said granular matrix material into a solid matrix material, said nuclear fuel particles having an average kernel size of 200 to 800 micrometers and comprising a nuclear fuel kernel with an optional coating.

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