Lead-based fast neutron high-flux research reactor

Abstract

The invention relates to the technical field of nuclear reactor design, and particularly discloses a lead-based fast neutron high-flux research reactor which comprises a container, a fuel assembly and a reactivity control system, and the fuel assembly is arranged in the container. The reactivity control system comprises an electric control device, a gas pressure control device and a gas volume control device; the electric control device, the gas pressure control device and the gas volume control device are sequentially arranged from inside to outside in the radial direction of the reactor core; the sum of the total reactivity values of the reactivity control systems is configured to be sufficient to enter and maintain the core at a prescribed subcritical depth under the worst residual reactivity conditions. Therefore, reactivity control means can be enriched, and the problem of limitation of a reactivity control mode of a nuclear reactor in a lead-based fast neutron high-flux research reactor can be solved.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor technology, specifically to a lead-based fast neutron high-flux research reactor. Background Technology

[0002] Lead-based fast neutron high-flux research reactors use high-temperature liquid lead-based alloys as coolants, offering significant advantages such as high neutron energy, strong irradiation capability, inherent safety, simple coolant system configuration and operation, and flexible experimental operation. This makes them a crucial direction for future high-flux research reactor development. Reactivity control, a core guarantee for the safe operation of nuclear reactors, exhibits characteristics distinct from conventional light water-cooled thermal neutron reactors in lead-based fast reactors. These characteristics include: 1) High core fuel enrichment and large loading capacity, resulting in a hard neutron spectrum, low delayed neutron fraction, and shorter neutron generation time; 2) The core contains no moderators, has an extremely low thermal neutron fraction, eliminates xenon poisoning effects, and exhibits relatively stable reactivity throughout its lifetime; 3) A long neutron mean free path leads to significant neutron leakage around the core; 4) The high density and opacity of lead-based coolants prevent the use of soluble poisons such as boric acid solutions for reactivity control. These characteristics place more stringent demands on the reliability and versatility of the reactivity control system in lead-based fast neutron high-flux research reactors.

[0003] According to my country's nuclear safety regulations HAF102-2016, "Safety Regulations for the Design of Nuclear Power Plants," safe shutdown mechanisms must be provided under both operational and accident conditions. The reactor shutdown system should consist of at least two diverse and independent systems to ensure that even when the core is at maximum reactivity, at least one system can reliably and independently maintain the reactor at a sufficiently deep subcritical state. Furthermore, to meet the installation, commissioning, operation, and testing requirements of various irradiation experimental devices, lead-based fast neutron high-flux research reactors require sufficient operating space at the reactor top. However, currently operating and under-construction metal-cooled fast neutron reactors and high-flux research reactors, such as Russia's BOR-60 and MBIR, the US VTR, and Belgium's MYRRHA, all follow a similar pressurized water reactor technology, placing the control rod drive mechanism at the reactor top, occupying a large amount of top space and severely restricting the layout and operational flexibility of irradiation experimental devices.

[0004] Therefore, given the limitations of existing reactivity control methods in lead-based fast neutron high-flux research reactors, it is urgent to explore reactivity control systems based on different principles to enrich reactivity control methods, meet more stringent safety design requirements, and provide strong support for engineering implementation. Summary of the Invention

[0005] The purpose of this invention is to provide a lead-based fast neutron high-flux research reactor to improve the limitations of reactivity control methods in lead-based fast neutron high-flux research reactors.

[0006] This invention is achieved through the following technical solution:

[0007] The lead-based fast neutron high flux research reactor includes a container, fuel assemblies, and a reactivity control system, wherein the fuel assemblies are disposed in the container; characterized in that the reactivity control system includes an electric control device, a gas pressure control device, and a gas volume control device;

[0008] The electric control device, gas pressure control device, and gas volume control device are arranged sequentially from the inside to the outside in the radial direction of the core; the sum of the total reactivity value of the reactivity control system is configured to be sufficient to allow the core to enter and maintain a specified subcritical depth under the worst residual reactivity conditions.

[0009] In one possible design, the electric control device includes a first guide tube, a first control rod, and an electric actuator. The first guide tube is a blind tube with a sealed upper end, which is inserted into the reactor core from the bottom of the container upwards, and its top end is flush with the top of the fuel assembly. The first control rod is disposed in the first guide tube, and the electric actuator is used to drive the first control rod to move axially in the first guide tube.

[0010] In one possible design, the first control rod is divided into a strong neutron absorber section, a gas cavity section, and a shielding section along the axial direction from top to bottom; the sum of the heights of the strong neutron absorber section and the gas cavity section is the same as the height of the active section of the reactor core fuel assembly.

[0011] In one possible design, a first sealing structure and a first heat insulation structure are provided between the first guide tube and the bottom of the container.

[0012] In one possible design, the gas pressure control device includes a second guide tube, a second control rod, and a pneumatic actuator. The second guide tube is a blind tube with a sealed upper end, which is inserted into the reactor core from the bottom of the container upwards, and its top end is flush with the top of the fuel assembly. The second control rod is disposed in the second guide tube. The pneumatic actuator is connected to a high-pressure gas source and is used to drive the second control rod to quickly insert upwards into the active section of the reactor core under accident conditions.

[0013] In one possible design, the high-pressure gas source is a high-pressure gas cylinder, and a normally closed electric valve is provided on the connecting pipeline between the cylinder and the pneumatic actuator.

[0014] In one possible design, a second sealing structure and a second heat insulation structure are provided between the second guide tube and the bottom of the container.

[0015] In one possible design, the gas volume control device includes a built-in safety component, which is a cylindrical structure sealed at both ends, forming a closed gas chamber inside, and having a coolant inlet and outlet at its lower end.

[0016] In one possible design, the built-in safety component is pre-charged with inert gas at a set pressure before installation; under normal operating conditions, its internal coolant level is flush with the height of the active section of the reactor core fuel assembly.

[0017] In one possible design, the gas volume control device includes multiple built-in safety components that are evenly distributed circumferentially around the core periphery.

[0018] In one possible design, the built-in safety component has a shape and radial dimensions similar to the core fuel assembly and also serves as a neutron reflector during normal operation.

[0019] In one possible design, the electric control device is located in the central region of the reactor core; the gas pressure control device is located at the edge of the active region of the reactor core; and the gas volume control device is located in the outermost reflector region of the reactor core.

[0020] In one possible design, the driving principles and triggering structures of the electric control device, the gas pressure control device, and the gas volume control device are different from each other.

[0021] In one possible design, when the control rods of both the electric control device and the gas pressure control device are operating at normal power, the strong neutron absorber sections of both devices are located outside the active section of the reactor core fuel assembly.

[0022] The advantages of this invention over the prior art are as follows:

[0023] The operation of this lead-based fast neutron high-flux research reactor is as follows:

[0024] Through the above technical solutions, since the three control devices are completely independent in terms of driving principle, triggering structure and spatial position, the possibility of all shutdown measures failing simultaneously due to common faults is eliminated. This creates a safety barrier for the reactor that is far beyond conventional defense in depth, and enhances its resilience in the face of internal faults and external disasters.

[0025] The gas pressure control device utilizes pre-stored high-pressure gas as its power source, while the gas volume control device directly uses temperature changes—the fundamental accident signal—as its trigger condition. Both can automatically activate without relying on external active equipment during accident conditions. This deep integration of passive safety features significantly reduces the risk of human error or system interaction failures, endowing the reactor with a naturally safe genetic makeup. Even under extreme beyond-design-baseline accidents, it can spontaneously tend towards a safe state through its physical structure. Neither its drive mechanism nor its main body occupies the top space of the reactor vessel. This provides ample and convenient top space for the installation, connection, operation, and maintenance of various irradiation test devices, meeting the core multi-purpose experimental functional requirements of high-flux research reactors and solving the inherent problems of overcrowding and limited experimental flexibility in existing technologies.

[0026] By arranging control devices with different functions in different radial regions of the reactor core according to their value and purpose, the core space resources are optimized. In particular, placing the gas volume control device on the outermost periphery allows it to also function as a highly efficient neutron reflector during normal operation, reducing neutron leakage, improving nuclear fuel utilization, and enhancing the economics of the reactor core. This integrated design avoids wasting functional areas, resulting in a more compact and efficient core structure. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0028] Figure 1 This is a top view of one embodiment of the lead-based fast neutron high-flux research reactor provided by the present invention.

[0029] Figure 2 This is a cross-sectional structural schematic diagram of the electric control device in a lead-based fast neutron high flux research reactor under one state, provided by the present invention.

[0030] Figure 3 This is a cross-sectional structural schematic diagram of the electric control device in a lead-based fast neutron high-flux research reactor under another state, provided by the present invention.

[0031] Figure 4 This is a cross-sectional structural schematic diagram of the gas pressure control device in the lead-based fast neutron high flux research reactor provided by the present invention in one state.

[0032] Figure 5This is a cross-sectional schematic diagram of the gas pressure control device in the lead-based fast neutron high flux research reactor provided by the present invention in another state.

[0033] Figure 6 This is a cross-sectional structural schematic diagram of the gas volume control device in the lead-based fast neutron high flux research reactor provided by the present invention in one state.

[0034] Figure 7 This is a cross-sectional schematic diagram of the gas volume control device in the lead-based fast neutron high flux research reactor provided by the present invention in another state.

[0035] The attached diagram shows the following components and their corresponding names: 1-Container, 2-Fuel assembly, 21-Upper gas chamber, 22-Active section, 23-Lower gas chamber, 3-Electric control device, 31-First guide tube, 32-First control rod, 321-Strong neutron absorber section, 322-Gas chamber section, 323-Shielding section, 33-Electric actuator, 4-Gas pressure control device, 41-Second guide tube, 42-Second control rod, 43-Pneumatic actuator, 44-High-pressure gas source, 45-Electric valve, 5-Gas volume control device, 51-Built-in safety component. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be noted that while the description of these embodiments is intended to aid in understanding the invention, it does not constitute a limitation thereof. The specific structural and functional details disclosed herein are only for describing exemplary embodiments of the invention. However, the invention can be embodied in many alternative forms and should not be construed as being limited to the embodiments described herein.

[0037] According to a first aspect of this disclosure, a lead-based fast neutron high-flux research reactor is provided. Wherein, Figures 1 to 7 Specific embodiments thereof are shown.

[0038] As attached Figure 1 As shown in the schematic diagram of the reactivity control system based on different principles, the electric control device 3 is arranged in the central region of the core active area, and is arranged alternately with the fuel assembly 2; the gas pressure control device 4 is arranged in the outer periphery of the core active area, and is arranged alternately with the fuel assembly 2; the gas volume control device 5 is arranged in the outermost region of the core, and is an important component of the core reflector.

[0039] As attached Figure 2As shown, the first control rod 32 in the electric control device 3 is inserted into the reactor core. The first guide tube 31, sealed at the top, enters and exits the reactor core from the bottom of the container 1, with its top flush with the top of the fuel assembly 2 and its bottom connected to the electric actuator 33. During reactor shutdown, the strong neutron absorber section 321 at the top of the first control rod 32 is flush with the active section 22 of the reactor core assembly, and the upper part of the first guide tube 31 is a cavity. During reactor startup or stable operation, the first control rod 32 moves slowly upward by the electric actuator 33. The strong neutron absorber section 321 of the first control rod 32 gradually moves upward and leaves the active section 22 of the reactor core fuel assembly 2 until it completely leaves the active section 22 of the reactor core, at which point the strong neutron absorber section 321 of the first control rod 32 is flush with the top of the upper gas cavity 21 of the fuel assembly 2.

[0040] As attached Figure 3 As shown in the diagram, the first control rod of the electric control device 3 is in the state of being ejected from the reactor core. The first control rod 32 reaches the top of the first guide tube 31, and the strong neutron absorber section 321 completely leaves the active section 22 of the reactor core. The gas cavity section 322 of the first control rod 32 is flush with the active section 22 of the reactor core, and the shielding section 323 of the first control rod 32 moves upward accordingly. If a plant power outage or other accident occurs that requires an emergency shutdown, the first control rod 32 falls rapidly under gravity until the strong neutron absorber section 321 of the first control rod 32 is flush with the active section 22 of the reactor core, which is the lowest position that the first control rod 32 can reach.

[0041] As attached Figure 4 As shown, this is a schematic diagram of the gas pressure control device 4 in full-rod configuration. The top-sealed second guide pipe 41 enters and exits the reactor core from the bottom of container 1, with its top flush with the top of fuel assembly 2, and its bottom connected to the pneumatic actuator 43. Each second control rod 42 is equipped with one high-pressure gas cylinder and one electric valve 45. During normal shutdown, startup, and operation, the second control rod 42 is not in the active region of the reactor core, and its top is flush with the lower end of the lower gas chamber 23 of fuel assembly 2.

[0042] As attached Figure 5 As shown in the diagram, the gas pressure control device 4 is in the fully inserted state. If an emergency shutdown accident occurs, the electric valve 45 will automatically open, and the pressure generated by the high-pressure gas cylinder will drive the pneumatic actuator 43 to quickly insert the second control rod 42 upward into the reactor core, introduce reactivity into the reactor core, and maintain the inserted state.

[0043] As attached Figure 6The diagram shows the normal operating condition of the gas volume control device 5. The upper and lower ends of the built-in safety component 51 are completely sealed, preventing the flow of coolant and forming a closed space inside. Several lead-based coolant inlet and outlet holes are provided at the lower end. Under normal operating conditions, the gas chamber pressure of the built-in safety component 51 is balanced with the external lead-based coolant pressure, and the liquid level of the lead-based coolant is level with the height of the active section 22 of the reactor core fuel assembly 2.

[0044] As attached Figure 7 The diagram shows a schematic of the gas volume control device 5 under accident conditions. When an accident occurs that causes a rapid rise in coolant temperature, the pressure in the gas chamber at the upper end of the built-in safety component 51 rises accordingly, forcing the internal lead coolant level to drop rapidly. This significantly increases the neutron leakage rate in the reactor core, introducing negative reactivity and reducing reactor power, thus ensuring reactor safety.

[0045] See Figures 1 to 7 As shown, the lead-based fast neutron high-flux research reactor includes a container 1, a fuel assembly 2, and a reactivity control system. The fuel assembly 2 is disposed in the container 1. The reactivity control system includes an electric control device 3, a gas pressure control device 4, and a gas volume control device 5. The electric control device 3, the gas pressure control device 4, and the gas volume control device 5 are arranged from the inside to the outside in the radial direction of the reactor core. The sum of the total reactivity value of the reactivity control system is configured to be sufficient to allow the reactor core to enter and maintain a specified subcritical depth under the worst residual reactivity conditions.

[0046] Based on the setup of three different systems—electric control device 3, gas pressure control device 4, and gas volume control device 5—which operate on three completely different physical principles (mechanical drive, gas pressure drive, and thermodynamic effects)—a triple independent and diverse safety barrier can be formed. Since the three control devices are arranged sequentially from the core center outwards, it is beneficial to improve the neutron flux density field and reactivity value of the core.

[0047] The working process of the lead-based fast neutron high flux research reactor is as follows:

[0048] 1. Start-up and Power Operation: During this stage, precise reactivity control is primarily achieved through the electric control unit 3. Its precise axial movement compensates for the negative temperature feedback effect of the core transitioning from a cold to a hot state, the reactivity loss due to fuel combustion, and enables fine-tuning of power output. At this time, the gas pressure control unit 4 is in a non-interventional standby state, with its control elements located outside the active zone of the core; while the gas volume control unit 5 operates as a static reflector component, with its internal medium in a state of equilibrium.

[0049] 2. Normal and Emergency Shutdown: When a shutdown is required, the electric control unit 3 will quickly activate using drive power or gravity to insert its strong neutron absorber into the reactor core, introducing negative reactivity. If this system fails to respond fully for any reason, or if a design-baseline accident occurs such as loss of external power, the gas pressure control unit 4 will be passively triggered. High-pressure gas will be used as a power source to rapidly push its control elements into the active zone of the reactor core, providing a second, independent shutdown capability.

[0050] 3. Passive Accident Response: For more extreme transient accidents (such as a sudden surge in power causing a rapid rise in coolant temperature), the gas volume control device 5 will play a crucial role. The internal gas pressure increases due to coolant heating, forcing the liquid level to drop. This process directly leads to an increase in the neutron leakage rate around the core, thereby introducing strong negative reactivity into the core. The entire process is driven spontaneously by physical laws, requiring no external signals, power sources, or human intervention, achieving the highest level of inherent safety.

[0051] Through the above technical solutions, since the three control devices are completely independent in terms of driving principle, triggering structure and spatial position, the possibility of all shutdown measures failing simultaneously due to common faults is eliminated. This creates a safety barrier for the reactor that is far beyond conventional defense in depth, and enhances its resilience in the face of internal faults and external disasters.

[0052] Among them, the gas pressure control device 4 uses pre-stored high-pressure gas as power, and the gas volume control device 5 directly uses temperature change, the accident's fundamental signal, as a trigger condition. Both can automatically start working without relying on external active equipment under accident conditions. This deep integration of passive safety characteristics significantly reduces the risk of human error or system interaction failure, giving the reactor a naturally safe genetic makeup. Even under extreme over-design-baseline accidents, it can spontaneously tend towards a safe state through its physical structure. Neither its drive mechanism nor its main body occupies the top space of the reactor vessel 1. This provides ample and convenient top space for the installation, connection, operation, and maintenance of various irradiation test devices, meeting the core multi-purpose experimental function requirements of high-flux research reactors and solving the problems of overcrowding at the reactor top and limited experimental flexibility in existing technologies.

[0053] By arranging control devices with different functions in different radial regions of the reactor core according to their value and purpose, the core space resources are optimized. In particular, placing the gas volume control device 5 on the outermost edge allows it to also function as a highly efficient neutron reflector during normal operation, reducing neutron leakage, improving nuclear fuel utilization, and enhancing the neutron economy of the reactor core. This integrated functional design avoids wasting functional areas, resulting in a more compact and efficient core structure.

[0054] It should be noted that directional terms such as "inner" and "outer" refer to "inner" and "outer" relative to the outline of the component; "inner" refers to the direction towards the component, and "outer" refers to the direction away from it. Furthermore, terms such as "first" and "second" are used to distinguish one element from another and do not indicate sequence or importance. Also, in the accompanying drawings, the same reference numerals in different drawings represent the same element. It should be noted that "and / or" in the text refers to A and / or B, indicating that there are three possible scenarios: only A, only B, or both A and B. Conversely, " / and" in the text refers to A and B, indicating that there are two possible scenarios: only A and both A and B.

[0055] In one embodiment provided in this disclosure, the electric control device 3 includes a first guide tube 31, a first control rod 32, and an electric actuator 33. The first guide tube 31 is a blind tube with a sealed upper end, which is inserted into the reactor core from the bottom of the container 1 upwards, and the top end is flush with the top of the fuel assembly 2. The first control rod 32 is disposed in the first guide tube 31, and the electric actuator 33 is used to drive the first control rod 32 to move axially in the first guide tube 31.

[0056] Before reactor startup or during shutdown, the first control rod 32 is at its lower limit of travel, with its strong neutron absorber section 321 facing the active core region, ensuring the reactor is in a deep subcritical state. During reactor startup, the electric actuator 33 receives a command and drives the first control rod 32 to slowly move upwards within the sealed first guide tube 31, gradually removing its strong neutron absorber section 321 from the active core region. Reactivity then slowly increases until it reaches criticality and is raised to the target power level. During power operation, the electric actuator 33 performs minute axial displacements on the first control rod 32 to precisely regulate reactor power and compensate for slow changes in reactivity caused by fuel consumption and fission product accumulation. When a normal shutdown is required or an emergency shutdown signal is triggered, the electric actuator 33 is de-energized, and the first control rod 32 falls rapidly along the guide tube under gravity, allowing its strong neutron absorber section 321 to fully re-enter the active core region in the shortest possible time, rapidly introducing negative reactivity and achieving a safe shutdown.

[0057] All drive and actuator mechanisms of the system are integrated at the bottom of reactor vessel 1, without occupying any space above the reactor core. This provides unprecedented convenience and flexibility for the vertical installation, remote operation and maintenance of various irradiation test devices, and solves the bottleneck problem in the prior art where the control rod top drive mechanism occupies valuable reactor top space and restricts experimental functions.

[0058] The sealed guide tube design at the top completely isolates the first control rod 32 from the high-temperature, high-density lead-based coolant, effectively preventing corrosion and erosion of the control rod material by the coolant, as well as the impact of the enormous buoyancy that the control rod may experience during movement. This eliminates the potential risk of lead-based coolant leakage and ensures the reliability of the operation. Secondly, the emergency shutdown relies on gravity descent, which is an inherently passive safety structure. Even in extreme accident conditions such as a complete power outage, it can be automatically triggered without external power, ensuring reactor safety.

[0059] The system employs an electric motor drive, enabling precise control of the insertion depth of the first control rod 32, thus achieving fine and stable adjustment of reactor reactivity. This not only meets the stability requirements of the research reactor under different power operating modes but also provides crucial technical support for conducting physics experiments requiring precise control of neutron flux levels. As a complete reactivity control unit that intervenes from the reactor bottom, the system is structurally independent, has minimal interference with other systems within the reactor, and is easy to install, debug, and maintain independently, thereby improving the engineering feasibility and maintainability of the entire reactor system.

[0060] Specifically, the first control rod 32 is divided into a strong neutron absorber section 321, a gas cavity section 322, and a shielding section 323 along the axial direction from top to bottom; the sum of the heights of the strong neutron absorber section 321 and the gas cavity section 322 is the same as the height of the active section 22 of the fuel assembly 2.

[0061] The axial segmented structure of the first control rod 32, combined with its precise movement within the guide tube, constitutes a reactivity control structure. When the reactor is in a cold shutdown or requires an emergency shutdown, the control rod is at its lowest point of travel. At this time, the strong neutron absorber segment 321 completely covers and axially aligns with the active segment 22 of the core fuel assembly 2, introducing maximum negative reactivity into the core and ensuring that the reactor is in a safe subcritical state.

[0062] When the reactor starts up and requires a power increase, the electric actuator 33 drives the control rods upward along the guide tube. This process causes the strong neutron absorber section 321 to gradually withdraw from the active section 22 of the core, while the gas cavity section 322 below it simultaneously enters the active region space previously occupied by the absorber. Since the neutron absorption cross-section of the gas cavity section 322 is much lower than that of the strong neutron absorber material, this replacement process is equivalent to continuously removing neutron poison, thereby achieving a smooth and linear increase in reactivity. During power operation, precise power control can be achieved by accurately adjusting the control rods to the center position along the axial direction.

[0063] When the reactor reaches the end of its service life and requires maximum positive reactivity, the control rods are raised to the highest operating position. In this state, the strong neutron absorber section 321 is completely withdrawn and positioned above the active section 22 of the core, while the gas cavity section 322 completely fills the axial space corresponding to the entire active section 22. At this point, the negative reactivity introduced by the control rods is minimized, and the core reactivity reaches its maximum value within its operating cycle. Regardless of the operating condition under which an emergency shutdown signal is received, the control rods can rapidly fall under the influence of gravity, causing the strong neutron absorber section 321 to quickly reset and completely cover the active section 22, achieving a rapid and safe shutdown.

[0064] In this way, by precisely matching the sum of the heights of the strong neutron absorber section 321 and the gas cavity section 322 to the height of the core active section 22, a highly linear correspondence between the neutron absorption cross-section and displacement within the active region is ensured throughout the movement of the control rods. This design makes the introduction and release rates of reactivity predictable and controllable, facilitating reactor startup, power regulation, and operation management, effectively avoiding nonlinear abrupt changes in reactivity value, and improving operational stability and control precision.

[0065] During operation, the gas cavity section 322 enters the active region. Its low neutron absorption characteristics locally increase the neutron flux in the corresponding region, which helps to flatten the axial power distribution of the core and reduce the local power peak factor. This not only improves operational safety, allowing the reactor to operate at a higher average power density, but also promotes more uniform fuel combustion, helps to improve fuel burnup during unloading, extends refueling cycles, and thus improves the core's economics.

[0066] This structure establishes a direct and clear correspondence between the physical position of the control rods and their reactivity state. For example, when the lower end face of the absorber section is flush with the lower end face of the active section 22, it provides a clear and unambiguous visual or positional indication of "full rod insertion," explicitly indicating that the reactor is in a safe shutdown state. This provides operators with an intuitive and reliable safety criterion, reducing the risk of misjudgment and misoperation.

[0067] The shielding section 323, located at the bottom, can follow the control rods into the guide tube area at the bottom of the reactor core when they are lifted. This effectively shields the neutrons and gamma radiation from the reactor core, protecting the precision equipment such as the electric actuator 33 below from strong radiation damage. This improves the long-term operational reliability and service life of the drive mechanism, reduces the maintenance needs and operational risks caused by equipment irradiation failure, and enhances the robustness of the entire control device.

[0068] In this disclosure, a first sealing structure and a first heat insulation structure are provided between the first guide pipe 31 and the bottom of the container 1. The first sealing structure can effectively prevent the main coolant in the container 1 from leaking through the annular gap between the first guide pipe 31 and the bottom of the container 1, eliminating serious safety problems such as main circuit contamination and radioactive material leakage that may be caused by coolant leakage, and ensuring the integrity of the reactor primary circuit pressure boundary.

[0069] The first thermal insulation structure can block the conduction of high core temperature to the lower part of the container 1 and the electric actuator 33. On the one hand, this prevents the electric actuator 33 from failing, aging faster, or degrading due to long-term overheating, ensuring the accuracy and reliability of its operation; on the other hand, it also avoids the problem of reduced material strength that may be caused by excessively high local temperature, ensuring the mechanical integrity of the support structure.

[0070] Effective thermal insulation significantly reduces the operating temperature of components such as the electric actuator 33 located below the reactor vessel 1. This allows for the use of more conventional and lower-cost electrical components and materials, eliminating the need for specialized materials with extreme high-temperature resistance, thus reducing system manufacturing costs and maintenance complexity. Simultaneously, a temperature-controlled environment facilitates condition monitoring and maintenance of the drive mechanism, improving the overall maintainability of the system.

[0071] In one embodiment provided in this disclosure, the gas pressure control device 4 includes a second guide tube 41, a second control rod 42, and a pneumatic actuator 43. The second guide tube 41 is a blind tube with a sealed upper end, which is inserted into the reactor core from the bottom of the container 1 upwards, and its top end is flush with the top of the fuel assembly 2. The second control rod 42 is disposed in the second guide tube 41. The pneumatic actuator 43 is connected to a high-pressure gas source 44 and is used to drive the second control rod 42 upwards and quickly insert it into the active section 22 of the reactor core under accident conditions.

[0072] During normal reactor shutdown, startup, steady state, or power operation, the gas pressure control device 4 remains on standby. At this time, the second control rod 42 is at its lowest point of travel, with its top end flush with the lower end of the gas chamber 23 of the fuel assembly 2, completely outside the active section 22 of the core, and does not participate in the daily regulation of reactivity, thereby avoiding functional overlap or interference with the dominant electric control device 3.

[0073] Once the reactor monitoring system detects an accident signal requiring emergency shutdown (such as earthquake, overpower, or loss of current), it will issue an opening command to the system's electrically operated valve 45 (or automatically open upon power failure). Upon opening, the inert high-pressure gas pre-stored in the high-pressure cylinder is instantly released and enters the pneumatic actuator 43. The high-pressure gas acts as the driving medium, propelling the pneumatic actuator 43, which in turn pushes the second control rod 42 upwards at high speed along the second guide tube 41. The second control rod 42 overcomes gravity and fluid resistance, rapidly penetrating the lower gas cavity 23 of the reactor core, ultimately ensuring that its strong neutron absorber section 321 is fully inserted into the active section 22 of the core. This introduces a significant negative reactivity into the core, rapidly suppressing the chain fission reaction and achieving a safe shutdown. After insertion, the system maintains the control rod in the inserted state through a self-locking mechanism or continuous gas pressure, ensuring the shutdown depth.

[0074] Based on the differences between the driving principle (high-pressure gas power) of gas pressure control device 4 and that of electric control device 3 (motor drive) and gas volume control device 5 (thermodynamic effect), the diverse shutdown methods required by the "Safety Regulations for Nuclear Power Plant Design" can be achieved. Its independent gas source, actuator, and triggering structure ensure that even in extreme accident conditions such as a complete plant power outage that could cause electric control device 3 to fail, it can still be reliably triggered as a completely independent system, enhancing the reactor's ability to cope with common-cause failures.

[0075] The gas pressure control device 4 relies on pre-charged high-pressure gas as its power source, which is stored continuously during the standby period. When activated, it requires no external power grid or emergency diesel generators; a simple signal triggers the valve to open, and the subsequent process directly converts the stored potential energy into mechanical energy, achieving passive actuation. This not only simplifies the system configuration but also ensures extremely high inherent reliability due to its independence from external energy sources, guaranteeing rapid response capabilities under extreme accident conditions.

[0076] Similar to the electric control unit 3, all components of this system, including the guide tubes, control rods, and pneumatic actuator 43, are integrated into the bottom of the reactor vessel 1. This design also frees up valuable top space, facilitating the arrangement and operation of the irradiation experiment apparatus.

[0077] For most of the reactor's lifespan, this system remains in a silent standby state. Its simple structure means that the high-pressure gas cylinders and pneumatic actuators 43 do not require continuous operation, resulting in a low failure rate and minimal maintenance requirements. The sealed guide tube at the top also isolates the control rods from the active coolant, preventing contact between the control rods and the high-temperature, corrosive coolant during standby, ensuring component integrity and functional reliability, and thus enabling deterministically fulfilling its safety functions when necessary.

[0078] Specifically, the high-pressure gas source 44 is a high-pressure gas cylinder, and a normally closed electric valve 45 is provided on the connecting pipeline between it and the pneumatic actuator 43.

[0079] As a sealed pressure vessel 1, the high-pressure gas cylinder can stably store high-pressure inert gas for a long period without consuming external energy, providing an independent mechanical energy reserve that is always available for the gas pressure control device 4. This energy storage method is unaffected by the state of the power system, ensuring that a huge amount of driving energy can be released instantaneously when needed throughout the entire fuel cycle of the reactor, guaranteeing the rapid insertion of control rods.

[0080] An electrically operated valve 45 is used in a normally closed state. Under normal circumstances, this valve remains closed, isolating the high-pressure gas source 44 from the actuator and keeping the system on standby. In case of an accident, the valve can be designed to open automatically upon a power failure signal (i.e., automatically opening when power is cut off). This power failure operation mode is a typical fail-safe design, meaning that in the most extreme accident conditions (such as a plant-wide power outage), precisely when the triggering condition must be met, the system can automatically start without relying on any external power, enhancing its deterministic operation and inherent reliability.

[0081] In a specific embodiment of this disclosure, a second sealing structure and a second heat insulation structure are provided between the second guide tube 41 and the bottom of the container 1.

[0082] The second sealing structure effectively blocks any leakage path of the high-temperature, high-density liquid lead-based alloy inside reactor vessel 1 through the second guide tube 41, ensuring the integrity of the reactor primary circuit pressure boundary and preventing the risk of radioactive coolant leakage. It completely isolates the internal environment of the second control rod 42 and its guide tube from the external active coolant, preventing the control rod from being chemically corroded, physically eroded, or having impurities deposited during long-term standby, preventing potential jamming, and ensuring that the control rod can be quickly and unimpededly inserted into the reactor core when needed.

[0083] The second thermal insulation structure reduces the heat transferred to the bottom area of ​​container 1 and the pneumatic actuator 43, preventing the precision components such as seals and pistons inside the pneumatic actuator 43 from aging, hardening, or failing due to long-term high temperatures, and avoiding sluggish operation or jamming caused by thermal stress. At the same time, it prevents abnormal pressure increases in the high-pressure gas pipeline that may be caused by local overheating, ensuring the stability of the system's energy storage state.

[0084] Furthermore, in this disclosure, the first and second sealing structures employ the same structure to achieve sealing. Specifically, the sealing structure is a threaded seal, a flange-metal gasket static seal, or a stuffing box seal (as a backup or auxiliary). Those skilled in the art can select any suitable existing sealing structure based on actual needs.

[0085] As for the thermal insulation structure, the first and second thermal insulation structures use the same structure to achieve thermal insulation. Specifically, the thermal insulation device includes any suitable thermal insulation method such as a multi-layer reflective screen thermal insulation component, a ceramic matrix composite thermal insulation ring / sleeve, or a vacuum thermal insulation cavity. Those skilled in the art can also choose any suitable existing thermal insulation structure.

[0086] In one embodiment provided in this disclosure, the gas volume control device 5 includes a built-in safety component 51, which is a cylindrical structure sealed at both the upper and lower ends, forming a sealed gas cavity inside, and having a coolant inlet and outlet at the lower end.

[0087] During operation, the gas volume control device 5 functions automatically under different operating conditions based on the principle of thermodynamic equilibrium. During normal reactor operation, high-temperature liquid lead-based coolant flows naturally into the built-in safety assembly 51 through the coolant inlet / outlet port at its lower end until the internal gas chamber pressure reaches equilibrium with the static pressure of the external main loop coolant and the system pressure. At this point, the coolant level inside the assembly is maintained at a stable position comparable to the height of the active section 22 of the reactor core. In this state, because the assembly is filled with liquid metal, it can effectively scatter neutrons and can act as part of the core reflector, reducing neutron leakage and improving neutron economy.

[0088] When a transient accident occurs that causes a rapid rise in the core coolant temperature (such as loss of flow or accidental introduction of positive reactivity), the coolant temperature inside the assembly connected to the main loop rises accordingly, heating the inert gas in the sealed gas chamber through heat conduction. The increased gas pressure disrupts the original pressure balance. The increased pressure in the gas chamber forces some of the liquid coolant back into the main loop through the inlet / outlet ports at the bottom, causing a rapid drop in the coolant level inside the assembly. This drop in level transforms the area previously occupied by liquid metal into a gas chamber, drastically weakening its shielding and reflection of neutrons, thus significantly increasing the neutron leakage rate around the core. This physical change is equivalent to introducing negative reactivity into the core, spontaneously inhibiting chain fission reactions, reducing reactor power, and forming an inherent negative feedback structure until a new equilibrium is established under new temperature and pressure conditions.

[0089] The activation, operation, and termination of the gas volume control device 5 are directly driven by the physical effects (temperature rise) generated by the accident itself, without relying on external detection signals, power supply, or the operation of any mechanical transmission mechanism. This negative feedback structure based on inherent physical principles decouples safety functions from human intervention and the reliability of active equipment, providing the highest level of safety assurance, and is especially valuable in dealing with transient accidents where emergency shutdown is not possible.

[0090] Secondly, the structure and triggering mechanism are highly reliable, requiring extremely low maintenance. The system has no moving mechanical parts; its core is a static, pre-charged, sealed container 1. This extremely simple structure means that there are no parts in the system that will wear out, jam, or require periodic operation, thus possessing a near-infinite service life and extremely high inherent reliability. Throughout the reactor's entire lifespan, the gas volume control device 5 requires almost no maintenance, only periodic monitoring of its pre-charged gas pressure, significantly reducing the overall life-cycle maintenance costs and risks.

[0091] The cylindrical structure of the gas volume control device 5 allows it to be positioned on the outermost edge of the reactor core, similar to conventional fuel assemblies 2 or reflector assemblies. During normal operation, the gas volume control device 5 acts as a highly efficient neutron reflector, improving fuel utilization; in accident conditions, it transforms into a highly efficient safety injection system. This multi-functional design optimizes the utilization efficiency of core space and achieves optimized structural utilization.

[0092] Specifically, the built-in safety component 51 is pre-charged with inert gas at a set pressure before installation; under normal operating conditions, the internal coolant level is flush with the height of the active section 22 of the core fuel assembly 2.

[0093] The pre-charge setting pressure matches the coolant static pressure and system pressure in the core area under normal operating conditions, ensuring the liquid level is precisely stabilized at the same level as the active section 22. In this configuration, if a coolant temperature rise accident occurs, the gas volume control device 5 can respond immediately without overcoming any initial action threshold. Any temperature increase will directly lead to an increase in gas chamber pressure, rapidly disrupting this precise balance and immediately initiating coolant discharge. This minimizes the system's response time and ensures that negative reactivity is rapidly introduced.

[0094] By setting the liquid level at the same height as the active section 22 during normal operation, the built-in safety assembly 51 is filled with liquid coolant. This allows it to function as a highly efficient and complete neutron reflector during normal reactor operation, reducing neutron leakage around the core and improving neutron economy and fuel utilization. Conversely, during accident conditions when the liquid level drops, it can effectively introduce negative reactivity by increasing the neutron leakage rate. This design cleverly achieves optimal functional switching of the same structure under different operating conditions.

[0095] By precisely controlling the initial pressure of the pre-charged gas, the temperature / pressure threshold for the system startup response can be set directly and reliably, making the behavior pattern of the gas volume control device 5 predetermined and calculable, and the value of its safety function predictable.

[0096] Preferably, the gas volume control device 5 includes multiple built-in safety components 51, which are evenly distributed circumferentially around the reactor core. This ensures that regardless of the azimuth of the reactor core where an accident-induced power distortion or temperature rise occurs, the adjacent built-in safety components 51 can sense almost synchronous temperature and pressure changes and respond rapidly. This effectively avoids shadowing effects or protection blind spots that might result from concentrated placement of safety components, ensuring that in any anticipated transient accident, negative reactivity can be uniformly and symmetrically introduced from the entire periphery of the reactor core, thereby preventing localized power peaks, maintaining the overall stability of the reactor core, and improving the comprehensiveness and reliability of safety protection.

[0097] The use of multiple independent components working in parallel constitutes a redundant design. Even if a single or very few built-in safety components 51 fail to fully perform their preset functions due to manufacturing deviations or extreme operating conditions, the vast majority of the remaining normally functioning components can still work together to provide sufficient reactive control value, ensuring that the overall safety function of the system is realized. This improves the robustness and fault tolerance of the safety system, enabling it to reliably perform its safety mission even in the face of component-level uncertainties.

[0098] Multiple circumferentially distributed built-in safety components 51 collectively form a complete, continuous, and uniform radial neutron reflector layer during normal operation. This uniformity helps to create a flatter radial power distribution in the core, reducing the power peak factor, thereby improving core economics and creating better conditions for the safe and stable operation of the reactor. Under accident conditions, this uniform arrangement also ensures that the neutron leakage rate increases synchronously and consistently in all directions of the core, avoiding core physical disturbances that may be caused by asymmetric introduction of reactivity.

[0099] Furthermore, the built-in safety component 51 has a similar shape and radial dimensions to the core fuel assembly 2, and also serves as a neutron reflector during normal operation.

[0100] This allows the built-in safety assembly 51 to be integrated as a standardized structural unit into the existing grid location on the outermost edge of the core, eliminating the need for separate design and allocation of additional dedicated space. Structurally, it is a component of the core skeleton; functionally, it serves as a highly efficient neutron reflector during normal operation and as a passive safety system in accident conditions. This avoids increasing the core diameter or sacrificing the number of fuel assemblies 2 to establish a separate safety system, thereby maximizing the optimization and utilization of valuable core space resources while ensuring a high level of safety.

[0101] Because the built-in safety components 51 are similar in shape and size to the fuel assembly 2, these uniformly arranged built-in safety components 51 together form a complete, continuous, and efficient radial neutron reflector. This reflector can effectively scatter neutrons that would otherwise leak out of the reactor core back into the active region of the core, thereby reducing the neutron leakage rate, improving neutron utilization, reducing the consumption of fissile nuclides, and enhancing the economics of the reactor. At the same time, it also helps to flatten the radial power distribution of the reactor core, reduce local power peaks, and create a better physical basis for the safe and stable operation of the reactor.

[0102] Similar in size and uniform distribution to fuel assembly 2, this ensures that, under accident conditions, when the internal coolant level drops, the resulting neutron leakage effect can occur synchronously and uniformly throughout the entire periphery of the core. This avoids asymmetric disturbances to the core's physical properties that may be caused by differences in the shape, size, or location of safety components, and ensures that negative reactivity is introduced in a predictable and controllable manner. This, in turn, guarantees the stability of the core's behavior and the certainty of the system's safety functions during an accident.

[0103] In one embodiment provided in this disclosure, the electric control device 3 is arranged in the central region of the reactor core; the gas pressure control device 4 is arranged at the edge of the active region of the reactor core; and the gas volume control device 5 is arranged in the outermost reflector layer region of the reactor core.

[0104] Because the neutron flux is highest in the core center region, the value per unit length of control rod (the differential value of the control rod) is greatest. Placing the electrically powered control unit 3, which performs the main fine-tuning and shutdown functions, here allows for the maximum reactivity compensation depth with the fewest control rods, achieving optimal control efficiency. The gas pressure control unit 4, serving as an important accident backup measure, is placed at the edge of the active zone. Although its value per unit is lower than at the center, its reasonable quantity is sufficient to provide reliable safe shutdown capability, while avoiding competition for space with experimental access routes in the core high-value area. This layout principle based on value gradients ensures the most economical and efficient use of the limited core space.

[0105] This layout spatially separates the physical locations of the three systems, effectively reducing the likelihood that a single localized failure (such as component cooling failure or mechanical shock) could simultaneously affect multiple different reactive control systems, thus reducing the risk of common-cause failures. The three systems are located in three different radial zones within the reactor core, each functioning independently, together forming a reliable shutdown network with defense in depth, extending from the center to the periphery.

[0106] Placing the gas volume control device 5 in the outermost reflector region is the optimal choice for its passive function. This location allows it to directly sense changes in the overall power and temperature of the reactor core, resulting in a more sensitive response. This layout naturally integrates the gas volume control device 5 into the reactor core reflector structure, serving as a highly efficient reflector to improve economic efficiency during normal operation, and increasing neutron leakage by altering the composition of this region during accidents. Its safety function is closely integrated with the reactor core physics processes, demonstrating a high degree of design ingenuity.

[0107] In one embodiment provided in this disclosure, the driving principles and triggering structures of the electric control device 3, the gas pressure control device 4, and the gas volume control device 5 are different from each other.

[0108] The three systems operate based on electromechanical, pneumatic, and thermodynamic principles, respectively, and their triggering structures rely on active control signals, power failure / accident signals, and inherent temperature changes, respectively. This heterogeneity in principle ensures that no single common failure mode can simultaneously cause all reactive control mechanisms to fail.

[0109] The three systems form a response hierarchy: the electric control unit 3 serves as an active daily control mechanism; the gas pressure control unit 4 is a passive (energy-dependent) dedicated safety facility; and the gas volume control unit 5 serves as a completely passive (energy-dependent) final inherent safety barrier. This gradient design ensures that the reactor always has one or more matching safety barriers in place to address accidents of varying severity.

[0110] While each principle has its own advantages and disadvantages, their combination creates a complementary system. Electric motors offer precision but rely on external power; high-pressure gas drives are fast and powerful but single-use; and the thermal expansion and contraction effect, while less precise, is completely autonomous and repeatable. Integrating them into a single system, the electric system handles fine-tuning daily operations, the gas pressure system provides rapid and deterministic emergency shutdowns, and the gas volume system addresses long-term temperature transients and provides the ultimate safety floor. This synergy ensures the reactor possesses an optimal reactivity control strategy suitable for any hypothetical operating condition.

[0111] In one embodiment provided in this disclosure, the strong neutron absorber sections 321 of both the electric control device 3 and the gas pressure control device 4 are located outside the active section 22 of the fuel assembly 2 during normal power operation. This ensures that the reactor can reach its maximum potential reactivity at the beginning of its lifespan, allowing both types of control rods to introduce a complete, pre-reserved negative reactivity into the core under accident conditions. The electric control device 3 performs fine-tuning of reactivity compensation and adjustment through axial movement during operation. During an accident, both control rods insert from the outside in to perform a safe shutdown function. This functional separation avoids mutual interference between normal operation and safety functions. In particular, the gas pressure control device 4 does not participate in routine operation and is only triggered under the most extreme accident conditions.

[0112] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0113] Finally, it should be noted that this invention is not limited to the optional embodiments described above, and anyone can derive other various forms of products under the guidance of this invention. The specific embodiments described above should not be construed as limiting the scope of protection of this invention, which should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A lead-based fast neutron high-flux research reactor, comprising a container, fuel assemblies, and a reactivity control system, wherein the fuel assemblies are disposed within the container; characterized in that, The reactive control system includes an electric control device, a gas pressure control device, and a gas volume control device. The electric control device, gas pressure control device, and gas volume control device are arranged sequentially from the inside to the outside in the radial direction of the core; the sum of the total reactivity value of the reactivity control system is configured to be sufficient to allow the core to enter and maintain a specified subcritical depth under the worst residual reactivity conditions.

2. The lead-based fast neutron high-flux research reactor according to claim 1, characterized in that, The electric control device includes a first guide tube, a first control rod, and an electric actuator. The first guide tube is a blind tube with a sealed upper end, which is inserted into the reactor core from the bottom of the container upwards, and its top end is flush with the top of the fuel assembly. The first control rod is disposed in the first guide tube, and the electric actuator is used to drive the first control rod to move axially in the first guide tube.

3. The lead-based fast neutron high-flux research reactor according to claim 2, characterized in that, The first control rod is divided into a strong neutron absorber section, a gas cavity section, and a shielding section along the axial direction from top to bottom; the sum of the heights of the strong neutron absorber section and the gas cavity section is the same as the height of the active section of the reactor core fuel assembly.

4. The lead-based fast neutron high-flux research reactor according to claim 2, characterized in that, A first sealing structure and a first heat insulation structure are provided between the first guide tube and the bottom of the container.

5. The lead-based fast neutron high-flux research reactor according to claim 1, characterized in that, The gas pressure control device includes a second guide tube, a second control rod, and a pneumatic actuator. The second guide tube is a blind tube with a sealed upper end, which is inserted into the reactor core from the bottom of the container upwards, and its top end is flush with the top of the fuel assembly. The second control rod is disposed in the second guide tube. The pneumatic actuator is connected to a high-pressure gas source and is used to drive the second control rod to quickly insert upwards into the active section of the reactor core under accident conditions.

6. The lead-based fast neutron high-flux research reactor according to claim 5, characterized in that, The high-pressure gas source is a high-pressure gas cylinder, and a normally closed electric valve is provided on the connecting pipeline between the cylinder and the pneumatic actuator.

7. The lead-based fast neutron high-flux research reactor according to claim 5, characterized in that, A second sealing structure and a second heat insulation structure are provided between the second guide tube and the bottom of the container.

8. The lead-based fast neutron high-flux research reactor according to claim 1, characterized in that, The gas volume control device includes a built-in safety component, which is a cylindrical structure sealed at both the top and bottom, forming a closed gas cavity inside, and has a coolant inlet and outlet at the lower end.

9. The lead-based fast neutron high-flux research reactor according to claim 8, characterized in that, The built-in safety component is pre-charged with inert gas at a set pressure before installation; under normal operating conditions, the internal coolant level is level with the height of the active section of the reactor core fuel assembly.

10. The lead-based fast neutron high-flux research reactor according to claim 8, characterized in that, The gas volume control device includes multiple built-in safety components, which are evenly distributed circumferentially around the reactor core.

11. The lead-based fast neutron high-flux research reactor according to claim 8, characterized in that, The built-in safety component has a shape and radial dimensions similar to the core fuel assembly and also serves as a neutron reflector during normal operation.

12. The lead-based fast neutron high-flux research reactor according to any one of claims 1-11, characterized in that, The electric control device is located in the central region of the reactor core; the gas pressure control device is located at the edge of the active region of the reactor core; and the gas volume control device is located in the outermost reflector region of the reactor core.

13. The lead-based fast neutron high-flux research reactor according to any one of claims 1-11, characterized in that, When the control rods of the electric control device and the gas pressure control device are operating at normal power, the strong neutron absorber sections of both the electric control device and the gas pressure control device are located outside the active section of the reactor core fuel assembly.

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