Method and system for controlling the source strength of a reactor antimony beryllium neutron source during startup

Abstract

The present disclosure relates to a reactor antimony beryllium neutron source start-up source intensity control method and control system, and relates to the technical field of nuclear power, the reactor start-up source intensity control method optimizes the relative position between the neutron source and the detector by system integration of the structure parameters of the secondary source rod, the core layout parameters and the position of the out-of-core detector, and improves the neutron count rate; the reactor start-up source intensity control method comprises: determining the structure parameters of the secondary source rod and the first layout parameters in the fuel assembly based on the target neutron source intensity through iterative optimization; determining the second layout parameters of the secondary source rod in the target fuel assembly position from a plurality of fuel assemblies based on the core neutron parameters and the fuel management data; determining the third layout parameters of the detector and the target fuel assembly based on the estimated neutron count rate; calculating the secondary source intensity and the neutron count rate after the preset cycle irradiation according to the parameters determined in the above steps.

Description

Technical Field

[0001] This disclosure relates to the field of nuclear power technology, and in particular to a method and control system for controlling the start-up source strength of a reactor antimony-beryllium neutron source. Background Technology

[0002] During reactor loading and startup, the subcritical state of the reactor core must be monitored in real time, and the rate of reactivity introduction must be strictly controlled. This monitoring is achieved by measuring the number of fission neutrons released from the core. Although nuclear fuel itself contains spontaneous fission neutrons, their yield is extremely low, and neutrons are slowed down and absorbed by coolant, reactor internals, and pressure vessels before being detected, resulting in extremely weak signals. Especially for external detectors, the neutron count rate is extremely low after penetrating the thick barriers, easily creating monitoring blind spots and posing potential risks to reactor safety.

[0003] Neutron sources are typically introduced during the initial fuel loading phase to raise the neutron background level, ensuring that detectors can effectively record fission neutrons from the start of loading. This allows for real-time monitoring of the introduction of positive reactivity, guaranteeing that the effective multiplication factor of the reactor core remains within the expected control range. Based on their usage characteristics, neutron sources can be categorized into primary and secondary neutron sources. Primary neutron sources are used only during the first full-core irradiation cycle, while secondary neutron sources, activated after the first cycle of core irradiation, can be reused in subsequent cycles.

[0004] Currently, the widely used secondary neutron source is the antimony-beryllium (Sb-Be). This neutron source must be irradiated for a sufficient time at a certain power level to activate it before its source strength can meet the lower limit requirement for starting monitoring. Existing designs are prone to problems such as material waste, insufficient source strength, unsatisfactory count rate, or short detector life. Summary of the Invention

[0005] To address the aforementioned technical problems, this disclosure provides a method for controlling the start-up source strength of an antimony-beryllium neutron source in a reactor. This method integrates the structural parameters of the secondary source rods, the core layout parameters, and the positions of the external detectors to optimize the relative positions between the neutron source and the detectors, thereby improving the neutron count rate.

[0006] In a first aspect, this disclosure provides a method for controlling the start-up source intensity of an antimony-beryllium neutron source in a reactor. The reactor control method includes: determining, through iterative optimization, structural parameters of a secondary source rod and first layout parameters within a fuel assembly based on a target neutron source intensity; the structural parameters include diameter, length, and number of rods; the first layout parameters include the placement position within a fuel assembly guide tube; determining, based on core neutronics parameters and fuel management data, second layout parameters of the secondary source rod at the target fuel assembly position from multiple fuel assemblies; determining, based on an estimated neutron count rate, third layout parameters of a detector and the target fuel assembly; the third layout parameters include the circumferential, radial, and axial positions of the detector; calculating, based on the first, second, and third layout parameters determined in the above steps, the secondary source intensity and neutron count rate after a preset cyclic irradiation; determining whether the neutron count rate meets a preset requirement; if not, iteratively adjusting at least one of the first, second, and third layout parameters, and recalculating the secondary source intensity and neutron count rate after the preset cyclic irradiation.

[0007] Based on the above scheme, this application provides a method for controlling the start-up source strength of an antimony-beryllium neutron source in a reactor. This control method improves the neutron count rate by systematically integrating the structural parameters of the secondary source rods, the core layout parameters, and the position of the external detectors, thereby optimizing the relative position between the neutron source and the detectors. First, by iteratively optimizing the structural parameters (diameter, length, number of rods) of the secondary source rods and their first layout parameters within the fuel assembly, the optimal balance between material cost and source term efficiency is achieved while meeting the target source strength. Second, based on the core neutronics parameters and fuel management data, the second layout parameters of the source rods in the core are determined, ensuring that the secondary source is placed in the correct position. The optimal position, which has a high subflux rate and enables the detector signal to truly reflect the global state of the reactor core, simultaneously improves the activation efficiency of the source and the accuracy of the monitoring signal. Furthermore, by determining the third layout parameters of the detector and the target fuel assembly based on the pre-estimated flux rate, the contradiction between the signal strength during startup and the irradiation damage to the detector during power operation is balanced, significantly extending the detector's lifespan. Finally, by integrating all parameters and simulating and verifying the actual performance of the system after a complete irradiation cycle, and by introducing an iterative adjustment mechanism, the reliability and safety of the design scheme under long-term operating conditions are fundamentally ensured, overcoming the performance limitations caused by traditional step-by-step design and reliance on experience.

[0008] Optionally, the step of determining the structural parameters of the secondary source rod and the first layout parameters within the fuel assembly through iterative optimization based on the target neutron source intensity includes: setting initial values ​​for the diameter, length, number of rods, and placement position of the secondary source rod; calculating the initial neutron source intensity based on historical neutronics parameters; analyzing the degree of influence of the structural parameters and the first layout parameters on the initial neutron source intensity, and identifying the parameters affecting the initial neutron source intensity; and adjusting the values ​​of the structural parameters and the first layout parameters based on the analysis results of the degree of influence.

[0009] Optionally, the second layout parameter for determining the location of the secondary source rod at the target fuel assembly based on core neutronics parameters and fuel management data includes: analyzing the neutronics parameters of each fuel assembly location after excluding control rod assembly locations based on the fuel management data; and selecting, based on the neutronics parameters, the fuel assembly location that can simultaneously improve the secondary source activation efficiency and the final neutron count rate as the target fuel assembly from among the multiple fuel assembly locations.

[0010] Optionally, determining the third layout parameters of the detector and the target fuel assembly based on the estimated neutron count rate includes: setting an initial position of the detector; calculating the neutron count rate at the initial position based on the first and second layout parameters; and adjusting the circumferential, radial, and axial positions of the detector when the neutron count rate meets a preset requirement, thereby determining the third layout parameters.

[0011] Optionally, when the neutron count rate meets the preset count rate, adjusting the circumferential, radial, and axial positions of the detector to determine the third layout parameters includes: reducing neutron irradiation damage to the detector during power operation when the preset count rate is met; and ensuring that the arrangement of the secondary source rods can provide a neutron count signal of the overall reactor status.

[0012] Secondly, this disclosure provides a start-up source strength control system for an antimony-beryllium neutron source in a reactor. This control system includes: a source rod parameter optimization module, an assembly position selection module, a detector positioning module, a simulation calculation module, and an iterative control module. The source rod parameter optimization module is used to determine the structural parameters of the secondary source rod and its first layout parameters within the fuel assembly through iterative optimization based on the target neutron source strength. The structural parameters include diameter, length, and number of rods, and the first layout parameters include the placement position within the fuel assembly guide tube. The assembly position selection module is used to select and determine the second layout parameters of the secondary source rod at the target fuel assembly position from multiple fuel assemblies based on core neutronics parameters and fuel management data. The detector... The positioning module is used to determine the third layout parameters of the detector and the target fuel assembly based on the estimated neutron count rate; the third layout parameters include the position of the detector in the circumferential, radial, and axial directions; the simulation calculation module is used to calculate the secondary source intensity and neutron count rate after a preset cycle of irradiation based on the first, second, and third layout parameters determined by the source rod parameter optimization module, the assembly position screening module, and the detector positioning module; the iterative control module is used to determine whether the neutron count rate meets the preset requirements; if not, it triggers at least one of the source rod parameter optimization module, the assembly position screening module, and the detector positioning module to adjust its parameters and starts the simulation calculation module to recalculate.

[0013] Optionally, the source rod parameter optimization module includes: a parameter initialization unit, an initial calculation unit, a sensitivity analysis unit, and a parameter adjustment unit; the parameter initialization unit is used to set the initial values ​​of the diameter, length, number of rods, and placement position of the secondary source rod; the initial calculation unit is used to calculate the initial neutron source intensity based on historical neutronics parameters; the sensitivity analysis unit is used to analyze the degree of influence of the structural parameters and the first layout parameters on the initial neutron source intensity and identify the parameters affecting the initial neutron source intensity; the parameter adjustment unit is used to adjust the values ​​of the structural parameters and the first layout parameters based on the analysis results of the degree of influence.

[0014] Optionally, the component location filtering module is further configured to: analyze the neutron parameters of each fuel component location after excluding the control rod component location based on the fuel management data; and select, from the multiple fuel component locations, the fuel component location that can simultaneously improve the secondary source activation efficiency and the final neutron count rate as the target fuel component based on the neutron parameters.

[0015] Optionally, the detector positioning module includes: a position initialization unit, a count rate estimation unit, and a position optimization unit; the position initialization unit is used to set the initial position of the detector; the count rate estimation unit is used to calculate the neutron count rate at the initial position based on the first layout parameters and the second layout parameters; the position optimization unit is used to adjust the circumferential, radial, and axial positions of the detector when the neutron count rate meets the preset requirements, thereby determining the third layout parameters.

[0016] Optionally, the position optimization unit is further configured to: optimize the detector position to reduce neutron irradiation damage to the detector during power operation, provided that a preset count rate is met; and ensure that the arrangement of the secondary source rods can provide a neutron count signal of the overall reactor status. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0018] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart illustrating a method for controlling the start-up source strength of a reactor antimony-beryllium neutron source, provided in an embodiment of this disclosure; Figure 2 A schematic diagram of a secondary source rod provided in an embodiment of this disclosure; Figure 3 A schematic diagram of a fuel assembly provided for an embodiment of this disclosure; Figure 4 This is an overall schematic diagram of a reactor provided in an embodiment of the present disclosure; Figure 5 A flowchart of another method for controlling the start-up source strength of a reactor antimony-beryllium neutron source provided in an embodiment of this disclosure; Figure 6 A flowchart illustrating another method for controlling the start-up source strength of a reactor antimony-beryllium neutron source, provided as an embodiment of this disclosure; Figure 7 A flowchart illustrating another method for controlling the start-up source strength of a reactor antimony-beryllium neutron source provided in this embodiment of the present disclosure; Figure 8 A flowchart illustrating another method for controlling the start-up source strength of a reactor antimony-beryllium neutron source, provided as an embodiment of this disclosure. Detailed Implementation

[0020] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0021] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0022] During reactor loading and startup, the subcritical state of the reactor core must be monitored in real time, and the rate of reactivity introduction must be strictly controlled. This monitoring is achieved by measuring the number of fission neutrons released from the core. Although nuclear fuel itself contains spontaneous fission neutrons, their yield is extremely low, and neutrons are slowed down and absorbed by coolant, reactor internals, and pressure vessels before being detected, resulting in extremely weak signals. Especially for external detectors, the neutron count rate is extremely low after penetrating the thick barriers, easily creating monitoring blind spots and posing potential risks to reactor safety.

[0023] To address this issue, the industry typically introduces a neutron source during the initial fuel loading phase to raise the neutron background level. This ensures that the detector can effectively record fission neutrons from the start of fuel loading, thereby monitoring the introduction of positive reactivity in real time and ensuring that the core's effective multiplication factor (Keff) remains within the expected control range. Based on their usage characteristics, start-up neutron sources can be categorized into primary and secondary neutron sources. Primary neutron sources are used only during the first full-core cycle, while secondary neutron sources, activated by initial irradiation during the first cycle, can be reused in subsequent cycles. Currently, the widely used secondary neutron source is the antimony-beryllium (Sb-Be). Its principle involves the Sb-123 isotope capturing neutrons within the reactor core and activating them into the unstable Sb-124. During decay, Sb-124 emits gamma rays, which bombard the beryllium-9 nucleus, causing a (γ, n) reaction and releasing neutrons.

[0024] However, the antimony-beryllium secondary source must first be irradiated for a sufficient period of time at a certain power level to activate it before its source intensity meets the lower limit requirement for activation monitoring. Therefore, designing the shape and structure of the source rod and selecting a suitable irradiation location within the reactor core to maximize its activation efficiency is the primary problem to be solved. Secondly, the activated source intensity needs to be effectively detected by an external neutron detector. Given a fixed source intensity and detector hardware performance, optimizing the relative positions of the source and detector in three-dimensional space to maximize the effective neutron count rate while considering the detector's lifespan is another problem that needs to be addressed.

[0025] Based on this, such as Figure 1 As shown, Figure 1 This disclosure provides a flowchart of a method for controlling the start-up source strength of an antimony-beryllium neutron source in a reactor, as an embodiment of the present disclosure. The reactor control method includes: S1. Based on the target neutron source strength, the structural parameters of the secondary source rod and the first layout parameters within the fuel assembly are determined through iterative optimization.

[0026] The structural parameters include diameter, length, and number of sections, and the first layout parameter includes the placement position in the fuel assembly guide tube.

[0027] For example, for a large nuclear reactor containing 157 fuel assemblies, a detection capability of no less than 1×10⁻⁶ is achieved at the external detector. 8  An equivalent source strength of n / s is required to ensure a sufficiently high neutron count rate during the initiation phase.

[0028] Designers input the target source strength, and the optimization program began iterative iterations, trying various combinations: Option A, 10mm diameter, 3.2m length, 4 tubes, arranged in the guide tube at the edge of the module. Option B, 12mm diameter, 3.6m length, 3 tubes, arranged in the guide tube near the center of the module. Neutronics calculations revealed that Option B, due to its larger diameter and superior center layout, had an initial source strength approximately 30% higher than Option A.

[0029] Through systematic parameter scanning and iteration, the optimal design scheme can be discovered, requiring fewer but thicker source rods. This not only meets physical objectives but also significantly saves on expensive Sb-Be materials, reduces manufacturing costs, and avoids under- or over-design.

[0030] S2. Based on core neutronics parameters and fuel management data, the second layout parameters of the secondary source rods at the target fuel assembly position are determined by screening from multiple fuel assemblies.

[0031] The fuel management data from the first cycle of the reactor core was retrieved to understand the three-dimensional power distribution. First, the positions occupied by all 20 control rod assemblies were automatically eliminated. Then, the neutron parameters of the remaining 137 fuel assembly positions were analyzed. The program identified the second layout parameters of the secondary source rod positions in the fuel assemblies, which are positions in the core that have both a high neutron flux rate and ensure that the emitted neutron signals have good global core representativeness.

[0032] Based on the selection of real physical environment, it is ensured that the secondary source rod is placed in the globally optimal position, thereby maximizing its activation efficiency and the spatial representativeness of the generated signal at the same time, providing a guarantee for the safe and stable start-up of the reactor.

[0033] S3. Based on the estimated neutron count rate, determine the third layout parameters of the detector and the target fuel assembly.

[0034] The third layout parameters include the detector's position in the circumferential, radial, and axial directions.

[0035] The detector is initially positioned 0.5 meters from the container. Based on the scheme determined in S1 and S2, if the count rate at this position is calculated to be too high and the radiation damage during power operation will far exceed the limit, the detector is automatically adjusted radially to 0.7 meters, and the circumferential angle is finely adjusted to align with the source component. This process is repeated until the count rate meets the requirements and the radiation damage is reduced to a safe range.

[0036] This step, through the linkage of source item design and detector positioning, resolves the contradiction between the need for a strong signal during startup and the need to avoid damage during operation. As a result, while ensuring monitoring functionality, it greatly extends the lifespan of the detector and reduces maintenance costs.

[0037] S4. Based on the first layout parameters, second layout parameters and third layout parameters determined in the above steps, calculate the secondary source intensity and neutron count rate after preset cyclic irradiation.

[0038] S5. Determine whether the neutron count rate meets the preset requirements; if not, iteratively adjust at least one of the first layout parameters, the second layout parameters, and the third layout parameters, and recalculate the secondary source strength and neutron count rate after the preset cyclic irradiation.

[0039] For all parameters in steps S1-S3 above, simulations are performed to calculate the final neutron count rate after one complete fuel cycle of irradiation, when the source intensity has changed due to Sb-124 decay. If the initial calculation shows that the count rate is only 90% of the target, the iterative control module is immediately activated, guiding the optimization process to adjust the number of source rods in step S1, which can be increased from 3 to 4, and steps S2-S4 are rerun; after multiple iterations, until all indicators of the final scheme meet the design requirements.

[0040] It should be noted that: Figure 2 The black area shown indicates the selectable location of the secondary source rod. Figure 2 Only the locations of 24 guide tubes are shown, with secondary source rods placed inside the guide tubes; the central area can be used to place a detector, which is an in-pile detector and is inserted for detection when in use.

[0041] Figure 3 The detector shown is located outside the reactor; it is an external detector that performs detection from the outside. There can be one or more detectors.

[0042] in, Figure 2 The whole is equivalent to a fuel assembly. Figure 3 One of the small cubes is a fuel assembly, which is... Figure 2 yes Figure 3 Part of it.

[0043] Figure 4 This is an overall schematic diagram, firstly through Figure 2 Determine the diameter, length, and number of secondary source rods, i.e., the first layout parameters; then... Figure 3 Determine the location of the fuel assembly, i.e., the second layout parameters; finally, through... Figure 4 Determine the specific location of the external detector, i.e., the third layout parameter.

[0044] Based on the above scheme, this application provides a method for controlling the start-up source strength of an antimony-beryllium neutron source in a reactor. This control method improves the neutron count rate by systematically integrating the structural parameters of the secondary source rods, the core layout parameters, and the position of the external detectors, thereby optimizing the relative position between the neutron source and the detectors. First, by iteratively optimizing the structural parameters (diameter, length, number of rods) of the secondary source rods and their first layout parameters within the fuel assembly, the optimal balance between material cost and source term efficiency is achieved while meeting the target source strength. Second, based on the core neutronics parameters and fuel management data, the second layout parameters of the source rods in the core are determined, ensuring that the secondary source is placed in the correct position. The optimal position, which has a high subflux rate and enables the detector signal to truly reflect the global state of the reactor core, simultaneously improves the activation efficiency of the source and the accuracy of the monitoring signal. Furthermore, by determining the third layout parameters of the detector and the target fuel assembly based on the pre-estimated flux rate, the contradiction between the signal strength during startup and the irradiation damage to the detector during power operation is balanced, significantly extending the detector's lifespan. Finally, by integrating all parameters and simulating and verifying the actual performance of the system after a complete irradiation cycle, and by introducing an iterative adjustment mechanism, the reliability and safety of the design scheme under long-term operating conditions are fundamentally ensured, overcoming the performance limitations caused by traditional step-by-step design and reliance on experience.

[0045] like Figure 5 As shown, in some embodiments, S1, determining the structural parameters of the secondary source rod and the first layout parameters within the fuel assembly through iterative optimization based on the target neutron source strength includes: S11. Set the initial values ​​of the diameter, length, number of rods, and placement position of the secondary source rods (first layout parameters).

[0046] For example, designers set initial parameters: the secondary source rods have a diameter of 10mm, a length of 3.0m, a number of 4, and are arranged on the edge guide tube of the fuel assembly.

[0047] S12. Calculate the initial neutron source intensity based on historical neutron parameters; analyze the influence of structural parameters and first layout parameters on the initial neutron source intensity, and identify the parameters that affect the initial neutron source intensity; adjust the values ​​of structural parameters and first layout parameters based on the analysis results of the influence.

[0048] For example, the reactor design needs to meet a target source strength of 1.2 × 10⁻⁶. 8 For a secondary source rod with n / s, the initial source strength calculated in step S11 above based on typical component neutronics parameters is 8.5 × 10⁻⁶. 7 n / s, and then analyze the influence of structural parameters and first layout parameters on the initial neutron source strength.

[0049] Increasing the diameter of the secondary source rod from 10mm to 11mm can increase the source strength by 5%. Moving the placement of the secondary source rod from the edge to near the center can increase the source strength by 2%. Increasing the length of the secondary source rod to 3.6m can increase the source strength by 3%.

[0050] Analysis revealed that the first layout parameter was the most sensitive parameter, the diameter was the second most sensitive parameter, and the length was an insensitive parameter.

[0051] Based on the analysis of the impact, the source rod position was adjusted to be closer to the center guide tube of the module, with its diameter optimized to 11mm while its length remained unchanged at 3.6m. Calculations showed that this optimized scheme achieved a source strength of 1.25 × 10⁻⁶. 8 n / s, fully meets the target requirements.

[0052] By combining steps S11 and S12, the limitations of relying on a single empirical scheme in traditional design are avoided. By analyzing the influence of the initial neutron source strength, the key parameter with the greatest impact on the source strength, namely the layout position, is identified; thus, the optimal setting is achieved, which can further improve the optimization efficiency.

[0053] like Figure 6 As shown, in some embodiments, S2, based on core neutronics parameters and fuel management data, determines the second layout parameters for the secondary source rod at the target fuel assembly location from multiple fuel assemblies, including: S21. Based on the fuel management data, analyze the neutron parameters of each fuel assembly position after excluding the control rod assembly position.

[0054] For example, an optimal location is determined for a reactor core with 157 fuel assemblies to arrange secondary source rods, with the goal of simultaneously ensuring high activation efficiency and high off-core detector count rate.

[0055] First, the fuel management data from the first cycle of the reactor core is retrieved, including the three-dimensional power and neutron flux distribution. Then, the program automatically identifies and excludes the remaining 20 grid positions occupied by control rod assemblies (because these positions are already occupied and source rods cannot be installed). Next, the system begins to analyze the neutronics parameters of the remaining 137 fuel assembly positions, especially the average thermal neutron flux and fast neutron flux of each position during the operating cycle.

[0056] S22. Based on neutron parameters, select the fuel assembly position that can simultaneously improve the secondary source activation efficiency and the final neutron count rate from multiple fuel assembly positions as the target fuel assembly.

[0057] Based on the neutron parameters analyzed by S21, the system comprehensively evaluates and selects candidate sites: Location A, in the central region, has an extremely high neutron flux level, which is beneficial for improving the activation efficiency of the secondary source.

[0058] Location B, in the outer region, has a low neutron flux level, but neutrons are prone to leaking out of the core, which may help improve the initial count rate; Location C, between the center and the periphery, has a high neutron flux level. At the same time, due to its relatively close position to the periphery, the neutrons produced can better represent the global state of the reactor core and effectively reach the detector.

[0059] In summary, location C can be selected as the target fuel assembly location. Through the synergistic effect of steps S21 and S22, by introducing fuel management data and eliminating unusable locations, it is ensured that the secondary source can be efficiently activated and provide a sufficiently strong signal to the external detector that accurately reflects the overall critical state of the reactor core.

[0060] like Figure 7 As shown, in some embodiments, S3, determining the third layout parameters of the detector and target fuel assembly based on the estimated neutron count rate includes: S31. Set the initial position of the detector.

[0061] S32. Calculate the neutron count rate at the initial position based on the first layout parameters and the second layout parameters.

[0062] S33. When the neutron count rate meets the preset requirements, adjust the circumferential, radial, and axial positions of the detector to determine the third layout parameters.

[0063] After determining the secondary source rod parameters (first layout parameters) and their positions in the reactor core (second layout parameters), it is necessary to find an optimal installation location for the detector, which is the third layout parameter. The final requirements are: the neutron count rate must be no less than 2 cps, and the radiation damage to the detector during power operation must be within the annual limit.

[0064] First, based on step S31, the initial position of the detector is set near the outer wall of the container, at a radial distance of 0.5 meters, to ensure sufficient signal strength.

[0065] Then, based on step S32, the neutron count rate of the detector at the initial position is calculated according to the determined first and second layout parameters. At the initial position of 0.5 meters, the detector count rate is as high as 10 cps, far exceeding the minimum requirement of 2 cps. However, further calculations show that this position will be subjected to an extremely high neutron flux rate when the reactor is operating at full power, and the annual cumulative radiation damage will reach 180% of the design limit, which means that the detector will fail in a short period of time.

[0066] Therefore, based on step S33, the detector position is automatically adjusted, and the detector is gradually moved outward along the radial direction to calculate the neutron count rate. If it is at 0.6 meters: the count rate drops to 8 cps, and the radiation damage is 90% of the limit. If it is at 0.7 meters: the count rate drops to 3 cps, and the radiation damage is 45% of the limit. The radial position of 0.7 meters can be used as the radial position in the final third layout parameters. Based on the above steps S31-S33, the circumferential and axial positions are further determined, which will not be elaborated further here.

[0067] Through the synergistic effect of steps S31 to S33, the direction of optimization is clarified, and the optimal position of the detector is achieved. While ensuring that the monitoring signal is sufficiently sensitive during reactor start-up and shutdown, the service life of the detector is extended to the maximum extent, thereby significantly reducing operation and maintenance costs and improving the economic efficiency and safety of reactor operation.

[0068] like Figure 8 As shown, in some embodiments, S33, when the neutron count rate meets the preset count rate, adjusting the circumferential, radial, and axial positions of the detector to determine the third layout parameters includes: S331. Reduce neutron irradiation damage to the detector during power operation while meeting the preset count rate.

[0069] In other words, while ensuring that the detector has a sufficiently strong signal (high count rate) in the early stages of startup, we must minimize the damage it suffers when the reactor is operating at high power.

[0070] During reactor startup after shutdown, the core contains very few fission neutrons, requiring neutrons from the secondary source to provide a signal. At this stage, the detector needs to be as close as possible to the neutron source (secondary source) to obtain a sufficiently strong signal to reliably monitor the reactor startup process. Once the reactor reaches criticality and increases power, the core itself produces a massive amount of fission neutrons. If the detector is too close to the core at this point, it will be exposed to an extremely high neutron flux, leading to rapid aging.

[0071] Neutron irradiation damage can significantly reduce the lifespan of detectors. This can be mitigated by optimizing their installation location and placing them at a sufficient distance from the reactor core, while still meeting the startup signal requirements.

[0072] S332. Ensure that the placement of the secondary source rods provides a neutron count signal indicating the overall state of the reactor.

[0073] In other words, the signal generated when the neutrons emitted from the secondary source reach the detector after being modulated by the reactor core must accurately reflect the macroscopic state of the entire reactor core, rather than the state of a certain local area.

[0074] By arranging secondary source rods in the middle region of the reactor core or using a multi-source symmetrical arrangement, it is ensured that the neutron signals they generate can perceive the physical state of the entire reactor core, rather than local effects.

[0075] This disclosure also provides a start-up source strength control system for a reactor antimony-beryllium neutron source, the control system comprising: a source rod parameter optimization module, a component position screening module, a detector positioning module, a simulation calculation module, and an iterative control module.

[0076] The source rod parameter optimization module is used to determine the structural parameters of the secondary source rod and the first layout parameters within the fuel assembly through iterative optimization based on the target neutron source strength. The structural parameters include diameter, length, and number of rods, and the first layout parameters include the placement position in the fuel assembly guide tube.

[0077] The component location filtering module is used to filter and determine the second layout parameters of the secondary source rods at the target fuel assembly location from multiple fuel assemblies based on core neutronics parameters and fuel management data.

[0078] The detector positioning module is used to determine the third layout parameters of the detector and the target fuel assembly based on the estimated neutron count rate; the third layout parameters include the detector's position in the circumferential, radial, and axial directions.

[0079] The simulation calculation module is used to calculate the secondary source intensity and neutron count rate after preset cyclic irradiation based on the first layout parameters, second layout parameters, and third layout parameters determined by the source rod parameter optimization module, component position screening module, and detector positioning module.

[0080] The iterative control module is used to determine whether the neutron count rate meets the preset requirements; if not, it triggers at least one of the source rod parameter optimization module, component position filtering module and detector positioning module to adjust its parameters and starts the simulation calculation module to recalculate.

[0081] The reactor control system provided in this application is implemented through the coordinated operation and closed-loop iteration of its five modules. Taking the design of a reactor's secondary source system as an example: First, the source rod parameter optimization module started the design process based on the target source strength. Through sensitivity analysis, it was found that adjusting the source rod from the edge of the component to be closer to the central guide tube could increase the source strength by 4%. Based on this, the diameter was optimized to 8mm, while increasing the number of rods and shortening the length. This saved 20% of Sb-Be material while meeting the performance requirements.

[0082] Next, the component location screening module calls the fuel management data, automatically excludes 20 control rod positions, and then accurately selects two specific components with high neutron flux and good signal representativeness at half the core radius from the remaining 137 positions, so that the secondary source can obtain an excellent activation environment at the same time.

[0083] Subsequently, the detector positioning module initially set the detector at 0.5 meters. Calculations showed that although the count rate met the standard, the radiation damage exceeded the limit. Therefore, it automatically adjusted the detector to the optimal position of 0.7 meters, successfully balancing the count rate requirement and the detector lifespan.

[0084] Subsequently, the simulation calculation module integrates all the aforementioned parameters to simulate the irradiation process of the entire fuel cycle and accurately predict the true source intensity and count rate after decay. When the initial calculation result does not fully meet the standard, the iterative control module immediately triggers a new round of optimization, adjusts the number of source rods, and re-executes the entire process, ultimately outputting an optimal design scheme under long-term operation.

[0085] In some embodiments, the source bar parameter optimization module includes: a parameter initialization unit, an initial calculation unit, a sensitivity analysis unit, and a parameter adjustment unit.

[0086] The parameter initialization unit is used to set the initial values ​​of the diameter, length, number of rods, and placement position of the secondary source rods.

[0087] The initial calculation unit is used to calculate the initial neutron source intensity based on historical neutronics parameters.

[0088] The sensitivity analysis unit is used to analyze the influence of structural parameters and first layout parameters on the initial neutron source intensity and identify the parameters that affect the initial neutron source intensity.

[0089] The parameter adjustment unit is used to adjust the values ​​of structural parameters and the first layout parameters based on the analysis results of the degree of influence.

[0090] In the example of the secondary source rod design for a large nuclear reactor, the source rod parameter optimization module starts working: First, the parameter initialization unit sets initial values ​​(diameter 10mm, length 3.6m, 4 rods, arranged in the guide tube at the edge of the assembly), avoiding the randomness and uncertainty brought about by relying entirely on personal experience in traditional design.

[0091] Next, the initial calculation unit used historical neutronics parameters to perform calculations, obtaining a source strength of 8.5 × 10⁻⁶ for this initial scheme. 7 Then, the sensitivity analysis unit starts operating, revealing the degree of influence of each parameter through precise quantitative analysis. Adjusting the source rod position from the edge to the center can increase the source strength by 4%, while increasing the diameter to 11mm can also bring a 5% improvement, but changing the length has a smaller impact. Thus, the layout position is identified as the most critical driving parameter, the diameter as the second most critical parameter, and the length as an insensitive parameter. Finally, based on this analysis result, the parameter adjustment unit focuses on improving the source rod position closer to the center, appropriately reducing the diameter, shortening the length, and increasing the number of rods to simplify the problem.

[0092] This modular closed-loop process enables the final solution to far exceed the initial design and meet the target requirements through precise optimization of key parameters. It also significantly improves optimization efficiency, shortens the design cycle, avoids the ineffective use of materials, and saves Sb-Be materials by identifying and ignoring insensitive parameters and adjusting minor parameters.

[0093] In some embodiments, the component location filtering module is further configured to: analyze the neutron parameters of each fuel component location after excluding the control rod component location based on fuel management data; and select, based on the neutron parameters, the fuel component location that can simultaneously improve the secondary source activation efficiency and the final neutron count rate from multiple fuel component locations as the target fuel component.

[0094] For example, the component location screening module optimizes the secondary source arrangement of a reactor core with 157 fuel assemblies.

[0095] The component location filtering module first calls the fuel management database to obtain the three-dimensional power and neutron flux distribution data of the first core cycle. Then it automatically identifies and excludes 20 grid locations that are permanently occupied by control rod assemblies, ensuring that subsequent analysis focuses on the 137 actually usable fuel assemblies.

[0096] Next, the component location screening module analyzes the neutron parameters of each candidate location: Although the components in the core center region have the highest thermal neutron flux, which is very conducive to the activation of Sb-Be, the neutron signals they generate need to pass through the entire core before reaching the external detector and are strongly absorbed by the fuel itself, resulting in a low count rate and mainly reflecting local characteristics; while the outermost components can generate a high initial count rate due to the high neutron leakage rate, but their low neutron flux rate will lead to insufficient activation of the secondary source and long-term source strength decay.

[0097] After multi-objective trade-offs and adjustments, the component location screening module finally selected two components at half the radius of the core as target fuel assemblies. This location has a sufficiently high thermal neutron flux rate to ensure excellent activation efficiency, and a moderate neutron leakage rate to ensure that the neutrons generated can effectively penetrate to the outside of the core and be captured by the detector, and the signal can represent the global state of the core.

[0098] This approach avoids the risk of monitoring signal distortion caused by selecting a central location in pursuit of excessive activation efficiency, and also prevents the potential for insufficient source strength caused by selecting a peripheral location in pursuit of an initial high count rate. This significantly improves the overall safety, reliability, and accuracy of reactor startup monitoring.

[0099] In some embodiments, the detector positioning module includes: a position initialization unit, a count rate estimation unit, and a position optimization unit.

[0100] The position initialization unit is used to set the initial position of the detector.

[0101] The count rate estimation unit is used to calculate the neutron count rate at the initial position based on the first layout parameters and the second layout parameters.

[0102] The position optimization unit is used to adjust the circumferential, radial, and axial positions of the detector when the neutron count rate meets the preset requirements, thereby determining the third layout parameters.

[0103] For example, the detector positioning module optimizes the arrangement of external detectors for the reactor. The specific workflow is as follows: The position initialization unit first sets the initial position of the detector at 0.5 meters outside the pressure vessel. Then, the count rate prediction unit performs high-fidelity neutron transport calculations based on the determined first and second layout parameters. Although the count rate at this position is as high as 10 cps, far exceeding the minimum requirement of 2 cps, the radiation damage during power operation will reach 180% of the detector's annual tolerance limit. At this time, the position optimization unit starts a multi-objective optimization algorithm with the goal of meeting the count rate requirement and minimizing radiation damage. It automatically searches in three-dimensional space and finally determines a globally optimal third layout parameter by adjusting the detector radially to 0.7 meters and optimizing its circumferential angle, while the count rate still reaches 3 cps and the radiation damage drops sharply to the limit of 45%.

[0104] Through the closed-loop collaboration of the three units, not only is the reliability of the monitoring signals during the startup phase ensured, but the lifespan problem is also fundamentally solved by removing the detector from the high-irradiation area. It is expected to extend the lifespan of the detector by more than double, significantly reducing operation and maintenance costs and improving the reactor's continuous operation capability.

[0105] In some embodiments, the position optimization unit is further configured to: optimize the detector position to reduce neutron irradiation damage to the detector during power operation, provided that a preset count rate is met; and ensure that the arrangement of the secondary source rods can provide a neutron count signal of the overall reactor status.

[0106] For example, when the location optimization unit is started, the optimal secondary source rod parameters (such as three source rods with a diameter of 12 mm and a length of 3.8 m) and its core layout have been determined. At this time, the count rate prediction unit calculates that the neutron count rate is as high as 10 cps at 0.5 meters outside the container, far exceeding the minimum requirement of 2 cps. However, simulation shows that the neutron irradiation damage at this location during power operation will reach 180% of the detector design limit.

[0107] The location optimization unit uses a count rate ≥ 2 cps as a hard constraint and minimizes irradiation damage as the core objective to initiate the optimization algorithm. By adjusting the secondary source rod parameters (e.g., 12 source rods with a diameter of 8 mm and a length of 2.0 m), the detector is gradually moved outward along the radial direction and supplemented with circumferential and axial fine adjustments. It was found that when the detector is positioned at 0.7 meters, the count rate is 3 cps, while the irradiation damage index drops sharply to 45% of the limit. This fundamentally prevents the safety risk of misjudging the core status due to signal distortion, thereby achieving a synergistic improvement in safety, reliability, and economy at the system level.

[0108] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0109] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the start-up source strength of an antimony-beryllium neutron source in a reactor, characterized in that, include: Based on the target neutron source intensity, the structural parameters of the secondary source rods and the first layout parameters within the fuel assembly are determined through iterative optimization; the structural parameters include diameter, length, and number of rods, and the first layout parameters include the placement position within the fuel assembly guide tube; Based on core neutronics parameters and fuel management data, a second layout parameter for the secondary source rod at the target fuel assembly position is determined by screening from multiple fuel assemblies. Based on the estimated neutron count rate, a third layout parameter is determined between the detector and the target fuel assembly; the third layout parameter includes the position of the detector in the circumferential, radial, and axial directions. Based on the determined first layout parameters, second layout parameters, and third layout parameters, calculate the secondary source intensity and neutron count rate after preset cyclic irradiation; Determine whether the neutron count rate meets the preset requirements; if not, iteratively adjust at least one of the first layout parameters, the second layout parameters, and the third layout parameters, and recalculate the secondary source intensity and the neutron count rate after the preset cyclic irradiation.

2. The method for controlling the start-up source strength of the antimony-beryllium neutron source in a reactor according to claim 1, characterized in that, The determination of the structural parameters of the secondary source rod and the first layout parameters within the fuel assembly through iterative optimization based on the target neutron source intensity includes: Set the initial values ​​for the diameter, length, number of rods, and placement position of the secondary source rods; Calculate the initial neutron source intensity based on historical neutronographic parameters; Analyze the degree of influence of the structural parameters and the first layout parameters on the initial neutron source intensity, and identify the parameters that affect the initial neutron source intensity; Based on the analysis results of the degree of influence, the values ​​of the structural parameters and the first layout parameters are adjusted.

3. The method for controlling the start-up source strength of the antimony-beryllium neutron source in a reactor according to claim 2, characterized in that, The second layout parameters for determining the location of the secondary source rod in the target fuel assembly by screening from multiple fuel assemblies based on core neutronics parameters and fuel management data include: Based on the fuel management data, analyze the neutron parameters of each fuel assembly position after excluding the control rod assembly position; Based on the neutronics parameters, the fuel assembly position that can simultaneously improve the secondary source activation efficiency and the final neutron count rate is selected from the multiple fuel assembly positions as the target fuel assembly.

4. The method for controlling the start-up source strength of the antimony-beryllium neutron source in a reactor according to claim 1, characterized in that, The third layout parameters for determining the detector and the target fuel assembly based on the estimated neutron count rate include: Set the initial position of the detector; Based on the first layout parameters and the second layout parameters, the neutron count rate at the initial position is calculated; When the neutron count rate meets the preset requirements, the circumferential, radial, and axial positions of the detector are adjusted to determine the third layout parameters.

5. The method for controlling the start-up source strength of the antimony-beryllium neutron source in a reactor according to claim 4, characterized in that, When the neutron count rate meets the preset count rate, adjusting the circumferential, radial, and axial positions of the detector to determine the third layout parameters includes: While meeting the preset count rate, reduce neutron irradiation damage to the detector during power operation; Ensure that the arrangement of the secondary source rods can provide a neutron count signal for the overall state of the reactor.

6. A start-up source strength control system for an antimony-beryllium neutron source in a reactor, characterized in that, include: The source rod parameter optimization module is used to determine the structural parameters of the secondary source rod and the first layout parameters within the fuel assembly through iterative optimization based on the target neutron source strength; the structural parameters include diameter, length and number of rods, and the first layout parameters include the placement position in the fuel assembly guide tube; The component location filtering module is used to filter and determine the second layout parameters of the secondary source rod at the target fuel assembly location from multiple fuel assemblies based on core neutronics parameters and fuel management data. The detector positioning module is used to determine a third layout parameter between the detector and the target fuel assembly based on an estimated neutron count rate; the third layout parameter includes the position of the detector in the circumferential, radial, and axial directions. The simulation calculation module is used to calculate the secondary source intensity and neutron count rate after preset cyclic irradiation based on the first layout parameters, the second layout parameters and the third layout parameters determined by the source rod parameter optimization module, the component position filtering module and the detector positioning module. The iterative control module is used to determine whether the neutron count rate meets the preset requirements; if not, it triggers at least one of the source rod parameter optimization module, component position filtering module and detector positioning module to adjust its parameters, and starts the simulation calculation module to recalculate.

7. The start-up source strength control system for the reactor antimony-beryllium neutron source according to claim 6, characterized in that, The source rod parameter optimization module includes: The parameter initialization unit is used to set the initial values ​​of the diameter, length, number of rods, and placement position of the secondary source rods. The initial calculation unit is used to calculate the initial neutron source intensity based on historical neutronics parameters; A sensitivity analysis unit is used to analyze the degree of influence of the structural parameters and the first layout parameters on the initial neutron source intensity, and to identify the parameters that affect the initial neutron source intensity. The parameter adjustment unit is used to adjust the values ​​of the structural parameters and the first layout parameters based on the analysis results of the degree of influence.

8. The start-up source strength control system for the antimony-beryllium neutron source in a reactor according to claim 6, characterized in that, The component location filtering module is also configured to: Based on the fuel management data, analyze the neutron parameters of each fuel assembly position after excluding the control rod assembly position; Based on the neutronics parameters, the fuel assembly position that can simultaneously improve the secondary source activation efficiency and the final neutron count rate is selected from the multiple fuel assembly positions as the target fuel assembly.

9. The start-up source strength control system for the reactor antimony-beryllium neutron source according to claim 6, characterized in that, The detector positioning module includes: A position initialization unit is used to set the initial position of the detector; A count rate estimation unit is used to calculate the neutron count rate at the initial position based on the first layout parameters and the second layout parameters. The position optimization unit is used to adjust the circumferential, radial, and axial positions of the detector when the neutron count rate meets the preset requirements, thereby determining the third layout parameters.

10. The start-up source strength control system for the reactor antimony-beryllium neutron source according to claim 9, characterized in that, The position optimization unit is further configured to: While meeting the preset count rate, the detector position is optimized to reduce neutron irradiation damage to the detector during power operation; At the same time, it ensures that the arrangement of the secondary source rods can provide a neutron counting signal for the overall state of the reactor.

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