A spatial nuclear reactor reactivity control device

Abstract

The application discloses a kind of space nuclear reactor reactivity control devices, including reactor vessel, reactor core assembly and action control module;Reactor core assembly includes reactor core and the reactor core cladding around the periphery of reactor core;Reactor core includes inner layer fuel assembly, and outer layer fuel assembly and reflector in turn surround the periphery of inner layer fuel assembly;Reflecting layer has several control drums in annular distribution;Reactor core is in cross-sectional direction, by multiple partitions is separated into multiple reactor core regions independent of each other;Action control module includes several action control mechanisms, and reactor core region is driven under the action of action control mechanism and reciprocates along the radial direction of reactor core, so that outer layer fuel assembly in reactor core region is far away or close to inner layer fuel assembly, realizes the regulation and control to the leakage or absorption of neutron in the reactor.The space nuclear reactor reactivity control device has multiple space reactor reactivity control means, solves the problem of insufficient residual reactivity control and lack of passive reactivity control means in the early stage of reactor core life.

Description

Technical Field

[0001] This application relates to the field of reactor technology, and more particularly to a space nuclear reactor reactivity control device for aerospace purposes, providing electric power for unmanned or unmanned deep space shuttles to and from Mars or other asteroids. Background Technology

[0002] Space nuclear propulsion is an ideal power and energy source for humankind's deep space exploration, space orbital cargo transport, and the construction of spaceborne bases. This is mainly due to the high energy density, high environmental adaptability, and extremely low fuel consumption of nuclear propulsion systems compared to traditional chemical propulsion systems. In the foreseeable future, chemical rocket engines will remain an ideal power source for near-Earth space payload launches due to their ability to output powerful thrust in a short period. However, deep space activities originating from near-Earth orbit will rely more heavily on space propulsion systems. As a type of space propulsion system, the core module of a space nuclear propulsion system is a space fission reactor. This reactor can be launched to near-Earth orbit by chemical-powered rockets, and the propulsion system can be modularly assembled in orbit according to mission requirements.

[0003] Reactivity control is a crucial means of controlling reactor start-up and shutdown, regulating power output, and maintaining normal operation; it is a fundamental guarantee for the safe and successful implementation of space missions. To ensure the safe and reliable operation of a nuclear reactor, a corresponding system is necessary to perform reactivity control and protection functions. A key function of the reactor reactivity control system is to ensure reactor safety, requiring the control and protection system to act quickly in the event of an accident or emergency to ensure a safe reactor shutdown.

[0004] Space nuclear reactors, due to their compact design, typically use control drums arranged within a reflector layer for core reactivity control. Typically, 12 control drums are evenly distributed around the core. Each drum's main body is made of reflective material (beryllium), and a neutron absorber (B4C) is positioned on a 120° fan-shaped section on its side. The control drums can rotate freely along their own axis. During reactor operation, the angle of the neutron absorber fan-shaped section towards the core is adjusted by rotating the drums, thereby regulating reactor reactivity. However, this control method generally suffers from insufficient residual reactivity control in the early stages of core life and the potential for drum jamming due to uneven radial heating. Furthermore, as an active reactivity control mechanism, the control drum may completely lose its reactivity control capability in the event of a power outage or failure of its control drive equipment, posing a significant threat to the operational safety of the reactor and spacecraft. To overcome the shortcomings of the control drum approach, a reactivity control mechanism with strong residual reactivity control capabilities and the ability to act passively is needed.

[0005] Therefore, existing methods for controlling the reactivity of space reactors are limited, and there is an urgent need to propose a new technical solution to address the problems existing in the current technology. Summary of the Invention

[0006] This application provides a space nuclear reactor reactivity control device to solve the problem that the existing space reactor reactivity control methods are limited, resulting in insufficient passive safety of the reactor.

[0007] To achieve the above objectives, this application provides the following technical solution:

[0008] This application provides a space nuclear reactor reactivity control device, including a reactor vessel, a core assembly disposed within the reactor vessel, and an action control module;

[0009] The reactor core assembly includes a reactor core and a core cladding surrounding the reactor core; the reactor core includes an inner fuel assembly, and an outer fuel assembly and a reflector layer sequentially surrounding the inner fuel assembly; the reflector layer has a plurality of control drums arranged in a ring shape; a plurality of coolant channels are formed between the outer fuel assembly and the reflector layer; the reactor core is divided into multiple independent core regions by multiple partitions in the cross-sectional direction;

[0010] The motion control module includes several motion control mechanisms. Each motion control mechanism is connected to a core region. The core region moves back and forth along the radial direction of the core under the drive of the motion control mechanism, so that the outer fuel assembly in the core region moves away from or closer to the inner fuel assembly, thereby controlling the leakage or absorption of neutrons in the reactor.

[0011] In a preferred embodiment of the above technical solution, 12 control drums are uniformly distributed within the reflective layer. Each control drum has a rod-shaped structure, and its central axis is parallel to the central axis of the reactor vessel. A neutron absorber is disposed on one side of the outer wall of the control drum, and the neutron absorbers are concentrated in one-third of the outer wall region of the control drum. When the control drum rotates along its central axis, the neutron absorbers on it are rotated to gradually face the reactor core. As the control drum continues to rotate, the neutron absorbers on it are rotated to gradually move away from the reactor core. The reactivity of the reactor core is adjusted by regulating the area of ​​the neutron absorbers facing the reactor core.

[0012] Preferably, the inner fuel assembly includes six annularly distributed inner fuel units, and the outer fuel assembly includes twelve annularly distributed outer fuel units. The cross-sections of the inner and outer fuel units are hexagonal, and the inner and outer fuel assemblies are honeycomb-shaped.

[0013] Preferably, the core is divided into four independent core regions by four baffles in the cross-sectional direction. The cross-section of each core region is fan-shaped. Each core region includes three outer fuel units, three control drums, and a partial reflector layer located between two adjacent baffles. When the core undergoes geometric changes due to thermal expansion, the four core regions are moved outward in the radial direction by the motion control mechanism connected to them.

[0014] Preferably, the reactor vessel is a cylindrical structure, the reactor core assembly is a cylindrical structure, and the outer wall of the reactor core assembly and the inner wall of the reactor vessel form the working space of the motion control mechanism.

[0015] Preferably, the motion control mechanism includes a thermally expanded cadmium rod, a stainless steel conductive rod, a wedge-shaped slider, and a reset spring. The thermally expanded cadmium rod is arranged along the axial direction of the reactor core and close to the inner wall of the reactor vessel. One end of the stainless steel conductive rod is connected to the thermally expanded cadmium rod, and the other end is connected to the wedge-shaped slider. The reset spring is arranged between the wedge-shaped slider and the inner wall of the reactor vessel.

[0016] Preferably, the wedge-shaped slider has a sloping connecting surface, and one end of the stainless steel conductive rod is connected to the sloping connecting surface.

[0017] Preferably, in the cold reactor state, the outer fuel assemblies of the core region are pressed against the corresponding inner fuel assemblies under the action of the return spring. During reactor operation, the core temperature rises, and the thermally expanding cadmium rods expand due to heat. Their axial linear expansion is conducted to the wedge-shaped slider through the stainless steel conduction rods. Under the linear expansion of the thermally expanding cadmium rods, the wedge-shaped sliders move outward along the radial direction of the core, and the return springs are compressed. The wedge-shaped sliders drive the core region connected to them to move outward, and the outer fuel assemblies on the core region separate from the inner fuel assemblies, increasing neutron leakage. Furthermore, coolant channels are formed between the fuel assemblies, enhancing the absorption and moderation of neutrons by the coolant.

[0018] Preferably, the bottom surface of the reactor vessel is provided with a slide rail adapted to the wedge-shaped slider.

[0019] Preferably, one end of the reactor core is provided with a plurality of control rods, and each control rod is plugged into an inner fuel unit or an outer fuel unit.

[0020] Preferably, the control rod is a columnar structure, with a cladding shell wrapped around its outer wall. A first rack is provided on the cladding shell, and a second rack corresponding to the first rack is provided on the inner or outer fuel unit that is connected to the control rod. Both the first and second racks mesh with gears. When the control rod is lowered and inserted into the reactor core under external force, the first rack on it meshes with the gear. After the gear rotates, it drives the second rack to move in the opposite direction to the movement direction of the first rack. The inner or outer fuel unit connected to the control rod moves upward under the drive of the second rack.

[0021] Preferably, the core cladding is a radiation shielding structure.

[0022] Preferably, the coolant channel is a helium-xenon coolant channel, which is used to remove heat from the reactor core.

[0023] Compared with the prior art, this application has the following advantages:

[0024] 1. The space nuclear reactor reactivity control device provided in this application can be used for reactor start-up and shutdown control, criticality control, and power regulation during operation. This reactor reactivity control device includes a reactor vessel, a core assembly disposed within the reactor vessel, and an actuation control module. The core includes inner fuel assemblies, and outer fuel assemblies and a reflector layer sequentially surrounding the inner fuel assemblies. In cross-sectional direction, the core is divided into multiple independent core regions by multiple partitions. Driven by the actuation control mechanism, the core regions reciprocate radially, causing the outer fuel assemblies within each core region to move away from or closer to the inner fuel assemblies. When the outer fuel assemblies within a core region move away from the inner fuel assemblies, the gap between the outer and inner fuel assemblies increases, the coolant (helium-xenon gas) increases, and the reactor reactivity decreases accordingly, forming a negative feedback with power and temperature. This negative feedback mechanism does not rely on active mechanisms and constitutes an important guarantee for the passive safety of the reactor. Furthermore, several control drums are arranged in a ring within the reflector layer. These control drums can rotate freely along their own axes. During reactor operation, the angle of the neutron absorber fan on the control drum towards the reactor core is adjusted by rotating the drum, thereby regulating the reactor reactivity and ultimately the core power. Therefore, the space nuclear reactor reactivity control device provided in this application possesses multiple space reactor reactivity control methods, enhancing the reactor's passive safety and improving the overall reliability of reactor operation.

[0025] 2. In addition to the two space reactor reactivity control methods mentioned above, this application also proposes another space reactor reactivity control method. This method achieves core burnup compensation by setting a plug-in control rod at one end of the core. The control rod is equipped with a first rack, and the fuel unit in the core is equipped with a second rack corresponding to the first rack. Both the first and second racks mesh with gears. When reactivity suppression is required, the control rod is inserted downwards, and the first rack on it meshes with the gear. After the gear rotates, it drives the second rack to move in the opposite direction to the movement of the first rack, and the fuel unit plugged into the control rod moves upwards. This reactivity control scheme cleverly utilizes the gear structure to make the control rod and fuel assembly move in opposite directions simultaneously, increasing the burnup effect control efficiency and achieving a superposition of dual reactivity control methods. This realizes core burnup compensation and solves the problem of insufficient remaining reactivity control in the early stage of core life.

[0026] 3. This application provides a diversified reactivity control scheme. This scheme uses a control drum as a means of normal reactor power regulation. Based on this, it introduces an additional residual reactivity control system to compensate for reactivity degradation during burnup, and a passive reactivity control system as a reactor safety guarantee in case of failure of the active reactivity control system. Residual reactivity control is implemented using axially movable control rods, while passive reactivity control is implemented using a variable core geometry scheme driven by material thermal expansion. Through these three independent control technologies, rapid, safe, and reliable adjustment of the basic control functions of the space reactor is achieved.

[0027] 4. The space nuclear reactor reactivity control device provided in this application complements three reactivity control methods, forming a reliable control of core reactivity throughout its entire lifespan and under all operating conditions. Under normal reactor operation, the control drum provides routine reactivity regulation. Under normal conditions, the control rods are partially inserted into the core. When the fuel reaches a certain burnup depth, the control rods are raised, and simultaneously, the inner fuel assemblies surrounding the control rods are lowered into the core, introducing positive reactivity to compensate for the reactivity loss caused by burnup. In emergency conditions, the control rods are lowered into the core, and simultaneously, the surrounding inner fuel assemblies are raised, entering a state of greater negative reactivity, causing the core to enter a deep subcritical state. In accident conditions with a rapid increase in power, even if both the control drum and control rods fail, the variable core geometry control method can still be driven by thermal expansion, increasing the neutron absorption and leakage rate, effectively suppressing core reactivity, and ensuring reactor safety.

[0028] 5. The core power variation of the space nuclear reactor reactivity control device provided in this application is controlled by a control drum; the burnup effect is compensated by an axial control system, i.e., a reactivity control scheme in which control rods and fuel assemblies act in opposite directions via gears; temperature change control is part of inherent safety. When the temperature rises, the thermal expansion mechanism, composed of thermally expanding cadmium rods, stainless steel conductive rods, wedge-shaped sliders, and return springs, separates the outer fuel assemblies from the inner fuel assemblies in the core region, thereby providing negative reactivity and causing a decrease in reactivity. When the temperature drops, the thermal expansion mechanism presses the outer fuel assemblies against the inner fuel assemblies in the core region, providing positive reactivity and thus improving the reactivity level. Therefore, the space nuclear reactor reactivity control device provided in this application utilizes the thermal expansion effect caused by temperature changes to create negative feedback between core reactivity and power. This passive adjustment method greatly improves reactor safety. The overall triple reactivity control scheme, when superimposed, effectively improves the efficiency and reliability of reactivity control. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concepts disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, and size ratios of certain units (components).

[0030] Figure 1 This is a schematic diagram of the reactivity control device for a space nuclear reactor provided in this application in a disassembled state, in one embodiment. The dashed lines in the lower half of the figure are used to help illustrate the positional correspondence between the reactor core and the reactor vessel during installation, and the dashed lines in the upper half are used to help illustrate the positional correspondence between the control rods and a fuel unit in the reactor core.

[0031] Figure 2 This is a schematic diagram of the structure in which the control rods of the space nuclear reactor reactivity control device provided in this application are connected to a fuel unit in the reactor core via a gear and rack in one embodiment.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Outer fuel assembly; 2. Coolant passage; 3. Control drum; 4. Reflector layer; 5. Divider; 6. Central control rod; 7. Inner fuel assembly; 8. Reactor vessel; 9. Thermal expansion cadmium rod; 10. Stainless steel conduction rod; 11. Wedge slider; 12. Return spring; 13. Core cladding; 14. Axial control rod; 15. Fuel unit; 16. First rack; 17. Second rack; 18. Gear. Detailed Implementation

[0034] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] In the description of this application: unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," "third," etc., in this application are intended to distinguish the objects referred to and do not have any special meaning in terms of technical connotation (e.g., they should not be construed as an emphasis on importance or order). Expressions such as "comprising," "including," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0036] The terms used in this application, such as "upper," "lower," "left," "right," and "middle," are generally used to facilitate intuitive understanding by referring to the accompanying drawings, and are not absolute limitations on the positional relationships in the actual product. Changes in these relative positional relationships, without departing from the technical concept disclosed in this application, should also be considered within the scope of this application.

[0037] Example 1

[0038] In reactor design, reactivity control methods can be implemented using control rods. These rods are made of materials with a large neutron absorption cross section and are then inserted into the reactor core via a transmission mechanism to absorb neutrons within the core, thereby reducing core reactivity and enabling safe shutdown.

[0039] To ensure the reliably inserted control rods into the reactor core during an accident, the control rod drive mechanism must be able to insert the control rods into the core even in the event of a power outage, thereby ensuring core safety. In conventional reactors, gravity is the primary force; when the control rod drive mechanism loses power, the control rods will fall into the core under their own weight, achieving passive (without external driving force) shutdown.

[0040] For conventionally vertically arranged reactors, the flow of coolant and buoyancy within the core can affect the insertion of control rods, causing uncertainty in the insertion rate. For certain special-purpose reactors, the core may not be vertical under normal operating conditions, making it impossible for gravity-based control rods to insert smoothly in the core during an accident. This prevents passive shutdown and compromises reactivity safety. Therefore, alternative passive principles are needed to achieve control rod insertion and safe shutdown.

[0041] This application provides a space nuclear reactor reactivity control device, which uses control rods to achieve reactivity control. The structure and working principle of this space nuclear reactor reactivity control device are described in detail below.

[0042] The space nuclear reactor reactivity control device provided in this application includes a reactor vessel 8 and a core assembly disposed within the reactor vessel 8. The core assembly includes a core and a core cladding 13 surrounding the core; the core includes a central control rod 6, and an inner fuel assembly 7, an outer fuel assembly 1, and a reflector layer 4 sequentially surrounding the central control rod 6; a plurality of control drums 3 are arranged in a ring within the reflector layer 4; a plurality of coolant channels 2 are formed between the outer fuel assembly 1 and the reflector layer 4.

[0043] Twelve control drums 3 are evenly distributed within the reflector layer 4 (neutron reflector layer). Each control drum 3 has a rod-shaped structure, and its central axis is parallel to the central axis of the central control rod 6. A neutron absorber is installed on one side of the outer wall of the control drum 3, and the neutron absorbers are concentrated in one-third of the outer wall area of ​​the control drum 3. When the control drum 3 rotates along its central axis, the neutron absorbers on it are rotated to face the reactor core. As the control drum 3 continues to rotate, the neutron absorbers on it are rotated to face away from the reactor core. The reactor core reactivity is adjusted by adjusting the area of ​​the neutron absorbers facing the reactor core.

[0044] The inner fuel assembly 7 includes six annularly distributed inner fuel units, and the outer fuel assembly 1 includes twelve annularly distributed outer fuel units. The cross-sections of the inner and outer fuel units are hexagonal, and the inner fuel assembly 7 and the outer fuel assembly 1 are honeycomb-shaped.

[0045] In one embodiment, a plurality of control rods are provided at one end of the reactor core, and each control rod is plugged into an inner or outer fuel unit. See also Figure 1 A control rod is inserted into a fuel unit 15. The control rod is a cylindrical structure and, because it moves along the core axis, is called an axial control rod 14. See also... Figure 2The axial control rod 14 has a cladding shell surrounding its outer wall, on which a first rack 16 is mounted. A fuel unit 15, which is connected to the axial control rod 14, has a second rack 17 corresponding to the first rack 16. Both the first rack 16 and the second rack 17 mesh with a gear 18. When the axial control rod 14 is lowered and inserted into the reactor core under external force, the first rack 16 meshes with the gear 18. The rotation of the gear 18 drives the second rack 17 to move in the opposite direction to the movement of the first rack 16, causing the fuel unit 15 connected to the axial control rod 14 to move upwards. When reactivity suppression is required, the control rod is lowered, and its first rack meshes with the gear. The rotation of the gear drives the second rack to move in the opposite direction to the movement of the first rack, causing the fuel unit 15 connected to the control rod to move upwards.

[0046] The reactivity control scheme in this embodiment links the control rods and fuel assemblies via a gear structure. This ensures that when the control rods at the top of the core move, the corresponding fuel assemblies automatically move upwards without requiring additional control methods, reducing the probability of control strategy failure. This reactivity control scheme cleverly utilizes the gear structure to enable the control rods and fuel assemblies to move in opposite directions simultaneously, increasing the efficiency of burnup control and achieving a superposition of dual reactivity control methods. It is a residual reactivity control system that can compensate for the decrease in reactivity during burnup, thus achieving core burnup compensation.

[0047] Example 2

[0048] This application provides a space nuclear reactor reactivity control device. Compared with the space nuclear reactor reactivity control device provided in Embodiment 1, the space nuclear reactor reactivity control device provided in this embodiment adds another reactivity control scheme.

[0049] The space nuclear reactor reactivity control device provided in this embodiment also includes an action control module, which is actually a thermal expansion action mechanism. The core of this space nuclear reactor reactivity control device is divided into multiple independent core regions by multiple partitions 5 in the cross-sectional direction. The action control module includes several action control mechanisms, each connected to a core region. Driven by the action control mechanisms, the core region reciprocates along the radial direction of the core, causing the outer fuel assembly 1 within the core region to move away from or closer to the inner fuel assembly 7, thus achieving neutron leakage or absorption. The following is in conjunction with... Figure 1 The structure of the reactivity control device for the space nuclear reactor is described in detail.

[0050] See Figure 1In the cross-sectional direction, the core is divided into four independent core regions by four diaphragms 5. The cross-section of each core region is fan-shaped. Each core region contains three outer fuel units, three control drums 3, and a partial reflector layer 4 located between two adjacent diaphragms 5. When the core undergoes geometric changes due to thermal expansion, the four core regions are moved outward in the radial direction by the motion control mechanism connected to them.

[0051] In one embodiment, the reactor vessel 8 is a cylindrical structure, the core assembly is a cylindrical structure, the central axis of the central control rod 6 coincides with the central axis of the reactor vessel 8, and the outer wall of the core assembly and the inner wall of the reactor vessel 8 form an active space for the motion control mechanism.

[0052] In one embodiment, the motion control mechanism includes a thermally expanding cadmium rod 9, a stainless steel conductive rod 10, a wedge-shaped slider 11, and a return spring 12. The thermally expanding cadmium rod 9 is arranged along the axial direction of the reactor core and close to the inner wall of the reactor vessel 8. One end of the stainless steel conductive rod 10 is connected to the thermally expanding cadmium rod 9, and the other end is connected to the wedge-shaped slider 11. A return spring 12 is arranged between the wedge-shaped slider 11 and the inner wall of the reactor vessel 8. During specific installation, the return spring 12 can be placed horizontally between the reactor vessel 8 and the wedge-shaped slider 11. The wedge-shaped slider 11 has a sloping connecting surface, and one end of the stainless steel conductive rod 10 is connected to the sloping connecting surface. A slide rail adapted to the wedge-shaped slider 11 is provided on the bottom surface of the reactor vessel 8.

[0053] In the cold reactor state, the outer fuel assembly 1 in the core region is pressed against the corresponding inner fuel assembly 7 by the return spring 12. During reactor operation, the core temperature rises, and the thermal expansion cadmium rod 9 expands due to heat. Its axial linear expansion is conducted to the wedge slider 11 through the stainless steel conduction rod 10. Under the linear expansion of the thermal expansion cadmium rod 9, the wedge slider 11 moves outward along the radial direction of the core, the return spring 12 is compressed, and the wedge slider 11 drives the core region connected to it to move outward. The outer fuel assembly 1 and the inner fuel assembly 7 on the core region separate, which increases the leakage of neutrons. In addition, a coolant channel 2 is added between the fuel assemblies, which enhances the absorption and moderation of neutrons by the coolant.

[0054] In one embodiment, the aforementioned core cladding 13 is a radiation shielding structure; the coolant channel 2 is a helium-xenon coolant channel, which is used to remove heat from the core.

[0055] A nuclear reactor using the space nuclear reactor reactivity control device provided in this application can serve as a power source and energy source. The reactor is a fast neutron reactor, and the core is cooled by helium-xenon gas. The heat from the core is carried away by the coolant and the thermoelectric conversion device is driven by the Brayton cycle to generate electricity.

[0056] To control the initial residual reactivity of the reactor core and to reactivity-compensate for fuel burnup, see [reference needed]. Figure 1 The reactor core is equipped with an axially movable control rod reactivity control system. In order to passively adjust the reactor according to the power conditions, the core is designed with a variable geometry structure, that is, the core structure is changed by the thermal expansion effect (the outer fuel assembly 1 and the inner fuel assembly 7 in the core area are separated or compressed), thereby changing the leakage and absorption of neutrons in the core.

[0057] In summary, the core reactivity control system consists of three control schemes, the specific working principles of which are described below:

[0058] 1. Using a control drum as a means of regulating reactor power under normal conditions:

[0059] Twelve rod-shaped control drums are evenly arranged circumferentially within the outer reflector layer of the reactor core. These control drums can rotate around their axis. Each control drum is made of beryllium reflective material and has a neutron absorber (B4C) on its 120° side fan-shaped surface. By adjusting the area (angle) of the absorber facing the reactor core, the reactor core reactivity can be adjusted, thereby regulating the reactor core power.

[0060] 2. Residual reactivity control scheme to compensate for the decrease in reactivity during the fuel consumption process:

[0061] The reactor top contains several control rod assemblies arranged from top to bottom. The control rod assemblies are cylindrical and covered with a cladding shell, on which racks are installed. The core contains movable fuel assemblies, which are fuel units that are connected to the control rod assemblies and have corresponding racks and gears. The fuel assemblies are hexagonal cylindrical structures. When reactivity suppression is required, the control rods are inserted downwards, and the corresponding fuel assemblies are moved upwards by the gears and racks, achieving a superposition of dual reactivity control methods to compensate for core burnup.

[0062] 3. Passive reactivity control scheme based on variable core geometry driven by material thermal expansion:

[0063] When the reactor core undergoes geometric changes due to thermal expansion, the four core regions, acting as independent structures, can simultaneously move radially. The linear expansion of the cadmium rods in the thermal expansion mechanism transforms the wedge-shaped slider into a radially outward sliding motion, simultaneously pulling the connected core regions outward. This sliding causes separation between the outer and inner fuel assemblies, increasing neutron leakage. It also increases the flow channels for helium-xenon coolant between fuel assemblies, increasing the proportion of new internal coolant and thus enhancing neutron absorption and moderation. The combined effect is that the core size increases with temperature, and the core reactivity decreases, achieving a negative reactivity feedback effect. Simultaneously, the core cladding provides a certain degree of shielding against neutrons, minimizing radiation damage to the thermal expansion mechanism and extending its service life.

[0064] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

[0065] The present application has been described in a relatively specific and detailed manner above through general descriptions and specific embodiments. It should be understood that, based on the technical concept of the present application, several conventional adjustments or further innovations can be made to these specific embodiments; however, as long as they do not depart from the technical concept of the present application, the technical solutions obtained by these conventional adjustments or further innovations also fall within the protection scope of the claims of the present application.

Claims

1. A space nuclear reactor reactivity control device, characterized in that, This includes the reactor vessel, the core assembly housed within the reactor vessel, and the motion control module; The reactor core assembly includes a reactor core and a core cladding surrounding the reactor core; the reactor core includes an inner fuel assembly, and an outer fuel assembly and a reflector layer sequentially surrounding the inner fuel assembly; the reflector layer has a plurality of control drums arranged in a ring shape; a plurality of coolant channels are formed between the outer fuel assembly and the reflector layer; the reactor core is divided into multiple independent core regions by multiple partitions in the cross-sectional direction; The motion control module includes several motion control mechanisms. Each motion control mechanism is connected to a core region. The core region moves back and forth along the radial direction of the core under the drive of the motion control mechanism, so that the outer fuel assembly in the core region moves away from or closer to the inner fuel assembly, thereby controlling the leakage or absorption of neutrons in the reactor. The reactor core is divided into four independent core regions by four baffles in the cross-sectional direction. Each core region has a fan-shaped cross-section and contains three outer fuel units, three control drums, and a partial reflector layer located between two adjacent baffles. When the reactor core undergoes geometric changes due to thermal expansion, the four core regions are moved outward in the radial direction by the motion control mechanism connected to them. The reactor vessel has a cylindrical structure, the reactor core assembly has a cylindrical structure, and the outer wall of the reactor core assembly and the inner wall of the reactor vessel form the working space of the motion control mechanism. The motion control mechanism includes a thermally expanded cadmium rod, a stainless steel conductive rod, a wedge-shaped slider, and a return spring.

2. The space nuclear reactor reactivity control device according to claim 1, characterized in that, The reflector layer contains 12 uniformly distributed control drums, each a rod-shaped structure. The central axis of each control drum is parallel to the central axis of the reactor vessel. A neutron absorber is disposed on one side of the outer wall of each control drum, concentrated in one-third of the outer wall region. As the control drum rotates along its central axis, the neutron absorbers on it gradually face the reactor core. As the control drum continues to rotate, the neutron absorbers on it gradually move away from the reactor core. The reactivity of the reactor core is adjusted by regulating the area of ​​the neutron absorbers facing the reactor core.

3. The space nuclear reactor reactivity control device according to claim 2, characterized in that, The inner fuel assembly includes six annularly distributed inner fuel units, and the outer fuel assembly includes twelve annularly distributed outer fuel units. The cross-sections of the inner and outer fuel units are hexagonal, and the inner and outer fuel assemblies are honeycomb-shaped.

4. The space nuclear reactor reactivity control device according to claim 1, characterized in that, The thermal expansion cadmium rod is arranged along the axial direction of the reactor core and close to the inner wall of the reactor vessel. One end of the stainless steel conductive rod is connected to the thermal expansion cadmium rod, and the other end is connected to the wedge-shaped slider. The reset spring is arranged between the wedge-shaped slider and the inner wall of the reactor vessel. The wedge-shaped slider has a sloping connecting surface, and one end of the stainless steel conductive rod is connected to the sloping connecting surface.

5. The space nuclear reactor reactivity control device according to claim 4, characterized in that, In the cold reactor state, the outer fuel assemblies of the core region are pressed against the corresponding inner fuel assemblies by the return springs. During reactor operation, the core temperature rises, and the thermally expanding cadmium rods expand due to heat. Their axial linear expansion is conducted to the wedge-shaped slider through the stainless steel conduction rods. Under the linear expansion of the thermally expanding cadmium rods, the wedge-shaped sliders move outward along the radial direction of the core, compressing the return springs. The wedge-shaped sliders drive the core region connected to them to move outward, separating the outer fuel assemblies from the inner fuel assemblies on the core region. This increases neutron leakage, and coolant channels are formed between the fuel assemblies, enhancing the absorption and moderation of neutrons by the coolant.

6. The space nuclear reactor reactivity control device according to claim 4, characterized in that, The bottom surface of the reactor vessel is provided with a slide rail adapted to the wedge-shaped slider.

7. The space nuclear reactor reactivity control device according to claim 3, characterized in that, One end of the reactor core is provided with several control rods, and each control rod is plugged into an inner fuel unit or an outer fuel unit. The control rod is a columnar structure with a cladding shell wrapped around its outer wall. A first rack is provided on the cladding shell, and a second rack corresponding to the first rack is provided on the inner or outer fuel unit that is connected to the control rod. Both the first and second racks mesh with gears. When the control rod is lowered and inserted into the reactor core under external force, the first rack on it meshes with the gear. After the gear rotates, it drives the second rack to move in the opposite direction to the movement direction of the first rack. The inner or outer fuel unit connected to the control rod moves upward under the drive of the second rack.

8. The space nuclear reactor reactivity control device according to claim 1, characterized in that, The core cladding is a radiation shielding structure; The coolant channel is a helium-xenon coolant channel, which is used to remove heat from the reactor core.

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