Control rod design method and device and design method of air-cooled micro reactor

Abstract

The invention discloses a control rod design method and device and a design method of an air-cooled micro reactor, and the control rod design method comprises the following steps: determining an arrangement space and a control rod material of a control rod according to a reactor core geometric structure, temperature distribution and material compatibility data of the micro reactor; determining physical parameters of a control rod according to the shutdown margin limiting condition, the residual reactivity, the temperature reactivity and the iodine pit depth of the micro reactor; determining an adjusting band range of the control rod according to the rod bouncing accident safety constraint condition and the power adjusting requirement; and arranging the control rod in the arrangement space according to the physical parameters of the control rod and the adjustment band range. By adopting the method, the reactivity control capability of the control rod can be improved under the condition of ensuring the compactness of the reactor core.

Description

Technical Field

[0001] The present invention belongs to the technical field of reactors, and particularly relates to a control rod design method, a device, and a design method for a gas-cooled micro reactor. Background Art

[0002] Due to its wide range of uses, especially in specific scenarios such as remote areas and isolated islands, micro nuclear reactors have extremely high requirements for compactness and safety.

[0003] However, due to the compact arrangement of the micro reactor core and limited available space, it is difficult to provide sufficient drive mechanisms and control rod channels. The traditional control rod design cannot be effectively arranged within the limited space while maintaining sufficient reactivity control capabilities.

[0004] Therefore, the existing technology for the design of control rods for micro reactors cannot ensure the miniaturization and compact design of micro reactors while guaranteeing the reactivity control accuracy of control rods. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a control rod design method, a device, and a design method for a gas-cooled micro reactor in view of the above deficiencies existing in the prior art. Using this design method, the control accuracy of the control rod can be improved while ensuring the compactness of the reactor core.

[0006] In a first aspect, an embodiment of the present invention provides a control rod design method, the method

[0007] includes:

[0008] Determine the arrangement space and control rod material of the control rod according to the core geometry, temperature distribution, and material compatibility data of the micro reactor;

[0009] Determine the physical parameters of the control rod according to the shutdown margin limit conditions, residual reactivity, temperature reactivity, and iodine pit depth of the micro reactor;

[0010] Determine the adjustment band range of the control rod according to the ejection rod accident safety constraint conditions and power adjustment requirements, and the adjustment band range is the adjustable area of the control rod in the reactor core;

[0011] Set the control rod within the arrangement space according to the physical parameters of the control rod and the adjustment band range.

[0012] Optionally, the physical parameters include: the diameter, stroke, and number of the control rod;

[0013] The step of determining the physical parameters of the control rod according to the shutdown margin limit conditions, residual reactivity, temperature reactivity, and iodine pit depth of the micro reactor specifically includes:

[0014] S201. Determine the residual reactivity, temperature reactivity and iodine pit depth of the micro reactor core;

[0015] S202. Obtain the initial parameters of the control rod, where the initial parameters include the initial diameter, initial stroke and initial number;

[0016] S203. Determine the integral worth of the control rod according to the initial parameters;

[0017] S204. Determine the shutdown margin under different operating conditions according to the integral worth, residual reactivity, temperature reactivity and iodine pit depth;

[0018] S205. In the case where the shutdown margin under any operating condition does not meet the shutdown margin limit condition, adjust at least one of the initial diameter, initial stroke and initial number to obtain the adjusted initial parameters, and return to execute S202 to S205,

[0019] until the shutdown margin meets the shutdown margin limit condition, and determine the adjusted initial parameters as the physical parameters of the control rod.

[0020] Optionally, the determining the shutdown margin according to the integral worth, residual reactivity, temperature reactivity and iodine pit depth specifically includes:

[0021] Calculate the shutdown margin through the following formula (1):

[0022] ρ st = ρ CR × (1 - ω) - Δρ ex - Δρ T × (1 + ω) - Δρ I × (1 + ω)(1)

[0023] where ρ st is the shutdown margin, ρ CR is the sum of the integral worths of other control rods except the control rod with the largest integral worth, ω is the uncertainty factor, Δρ ex is the residual reactivity, Δρ T is the temperature reactivity, Δρ I is the iodine pit depth.

[0024] Optionally, the determining the adjustment band range of the control rod according to the control rod ejection accident safety constraint conditions and power regulation requirements specifically includes:

[0025] Determine the lower limit of the adjustment band of the control rod according to the control rod ejection accident safety constraint and the lower limit requirement of power regulation, where the lower limit requirement of power regulation is the control rod position corresponding to the lowest power level at which the reactor core is in the critical state;

[0026] Determine the upper limit of the adjustment band of the control rod according to the maximum power demand, where the maximum power demand is the control rod position corresponding to the core reaching the full power state.

[0027] The adjustment band range of the control rod includes the lower limit of the adjustment band and the upper limit of the adjustment band.

[0028] Optionally, the method further includes:

[0029] Determine the initial control parameters of the control rod according to the number of control rods, the dead zone range of the core state parameters, the limit value of the neutron flux change rate, and the limit time of the accident condition. The initial control parameters include the step size, speed range, and emergency insertion time of each control rod.

[0030] When the initial control parameters meet the simultaneous control constraint conditions, determine the initial control parameters as the control rod control parameters of the micro reactor to synchronously control the control rod through the initial control parameters.

[0031] When the initial control parameters do not meet the control constraint conditions, divide the control rods into N groups.

[0032] Determine the group control parameters of each group of control rods according to the number of control rods in each group, the dead zone range of the core state parameters, the limit value of the neutron flux change rate, and the limit time of the accident condition.

[0033] Control the control rods in groups according to the group control parameters corresponding to each group of control rods.

[0034] Optionally, the control constraint conditions include the following formula (2):

[0035]

[0036] Where VNmax is the maximum speed of the normal extraction and insertion of the control rod, VSmax is the maximum extraction speed of the control rod corresponding to the core alarm or safety signal, LS is the step size of the control rod, LDmax is the maximum step size of the control rod allowed by the dead zone range of the core state parameters, tmin is the time for the control rod to be inserted into the core emergently under the accident condition, and ts is the maximum insertion time of the control rod allowed for the core state parameters not to exceed the limit value under the accident condition.

[0037] In a second aspect, an embodiment of the present invention further provides a control rod design device, and the device includes:

[0038] A first determination module, configured to determine the arrangement space and control rod material of the control rod according to the core geometry structure, temperature distribution, and material compatibility data of the micro reactor.

[0039] A second determination module, configured to determine physical parameters of a control rod according to the shutdown margin limit condition, the remaining reactivity, the temperature reactivity, and the iodine pit depth of the micro reactor;

[0040] A third determination module, configured to determine an adjustment band range of the control rod according to the ejection accident safety constraint condition and the power adjustment requirement, where the adjustment band range is an adjustable area of the control rod in the reactor core;

[0041] A design module, respectively connected to the first determination module, the second determination module, and the third determination module, configured to arrange the control rod in the arrangement space according to the physical parameters of the control rod and the adjustment band range.

[0042] In a third aspect, an embodiment of the present invention further provides a design method for a gas-cooled micro reactor, where the method includes:

[0043] Using the control rod design method of the micro reactor in the first aspect, determining the arrangement space, material, physical parameters, and adjustment band range of the control rod;

[0044] According to the determined arrangement space, material, physical parameters, and adjustment band range of the control rod, forming a gas-cooled micro reactor.

[0045] The control rod design method of the present invention, first, optimizes the control rod arrangement space based on the reactor core geometry structure and temperature distribution to ensure the compactness of the reactor core; secondly, through the comprehensive compensation of the shutdown margin formula combined with the remaining reactivity, temperature reactivity, and iodine pit depth, it is ensured that the reactor core has sufficient shutdown margin under all working conditions to achieve safe shutdown; finally, determining the adjustment band range based on the ejection accident safety constraint and power demand can improve the accuracy of power adjustment. Thus, it is possible to improve the reactivity control ability of the control rod while ensuring the compactness of the reactor core. Description of the Drawings

[0046] Figure 1 : A flowchart of a control rod design method for a micro reactor according to Embodiment 1 of the present invention;

[0047] Figure 2 : A flowchart of another control rod design method for a micro reactor according to Embodiment 1 of the present invention;

[0048] Figure 3 : A reactor core model diagram of a gas-cooled micro reactor according to Embodiment 1 of the present invention;

[0049] Figure 4 : A burnup characteristic curve diagram of a gas-cooled micro reactor according to Embodiment 1 of the present invention;

[0050] Figure 5 : A structure diagram of a control rod design device for a micro reactor according to Embodiment 3 of the present invention.

[0051] The meanings of the marks in the figure are as follows:

[0052] 1. Pressure vessel; 2. Suspended basket; 3. Boron-containing carbon brick; 4. Reflector; 5. Fuel assembly; 6. Second group of control rods; 7. First group of control rods. Specific implementation manners

[0053] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0054] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, the elements defined by the statement "comprising..." do not exclude the existence of additional identical elements in the process, method, article or device comprising the said elements.

[0055] Portable micro nuclear energy devices applicable to specific scenarios such as remote areas and isolated islands have become a research hotspot at home and abroad. Micro nuclear energy devices have stringent requirements for the compactness of the system and the safety of operation. A reactivity control means that is easy to implement in engineering and meets the requirements of safe shutdown and power regulation is one of the key issues in the research and development of microreactors.

[0056] Common control means for reactors include solid burnable poisons, control rods, chemical shim poisons, movable reflectors, etc. Chemical shim poisons, such as boron-containing water in pressurized water reactors, are incompatible with in-core materials of various micro-reactor types. The absorber sphere method used in large high-temperature gas-cooled reactors has a complex system and is not suitable for being arranged on compact micro-reactors. The movement of the reflector can provide an additional means of reactivity safety shutdown, but the detachment of the reflector directly exposes the core active area, which may lead to a sharp increase in radioactive dose. Moreover, the above methods mainly provide additional shutdown means, require corresponding safety-class auxiliary systems, and it is also difficult to accurately control reactivity to achieve the purpose of power regulation. Control drums are designed in space reactors and new micro-reactors, but control drums with slightly larger sizes are difficult to meet the mechanical property requirements and are also difficult to implement in engineering. Moreover, the absorber of the control drum is always within the reflector, resulting in a large reactivity penalty. Control rod technology is mature, has a fast movement speed, reliable operation, and flexible use, and is very suitable as a means for emergency control of reactivity and power regulation in micro-reactors. However, the core layout of micro-reactors is compact, there are not enough control rod channels in the core, and it is also difficult to provide enough space for arranging drive mechanisms outside the reactor. A small number of control rods not only need to compensate for a large amount of reactivity to meet the shutdown requirements, but also need to accurately control reactivity to meet the power regulation requirements.

[0057] Embodiment 1:

[0058] Based on the above research, to solve the above technical problems, as Figure 1 shown, this embodiment provides a control rod design method that can be applied to nuclear power plants.

[0059] Specifically, it includes the following steps 101 to step 102.

[0060] Step 101, determine the arrangement space of the control rod and the control rod material according to the core geometry structure, temperature distribution, and material compatibility data of the micro-reactor.

[0061] Specifically, first, a core model can be established through three-dimensional modeling (such as the Monte Carlo code MCNP) to identify the layout of fuel assemblies, reflectors, and coolant channels, and determine the positions of the channels where the control rods can be inserted. Then, according to the core inlet temperature (such as 450 °C) and outlet temperature (such as 750 °C), avoid the high-temperature area (such as the outlet end), and arrange the control rods at the positions of the side reflector or the coolant inlet end.

[0062] For the selection of control rod materials, they need to be high-temperature resistant, have a large neutron absorption cross-section, and good compatibility. For example, the absorber material can be selected as B4C (boron carbide) because of its wide neutron energy spectrum absorption characteristics, low density, and mature technology. The cladding material can be selected as 800H alloy (nickel-based superalloy) that can withstand a high temperature of 760 °C to ensure structural stability.

[0063] Step 102: Determine the physical parameters of the control rod according to the shutdown margin limit conditions, residual reactivity, temperature reactivity, and iodine pit depth of the micro-reactor.

[0064] Among them, the residual reactivity is the residual reactivity that the control rod needs to compensate when the core runs from full power to the shutdown state. The calculation method of the residual reactivity: The maximum value of the sum of the residual reactivity of the zero-burnup full-power core (such as 2447 pcm) and the reactivity disappearance due to burnup + xenon poisoning can be taken.

[0065] The temperature reactivity is the negative reactivity introduced when the core cools down to the cold state during shutdown at full power. For example, the negative reactivity (such as 6651 pcm) introduced when the core cools down to the cold state (300K) during shutdown at full power.

[0066] The iodine pit depth is the depth of reactivity change caused by the dynamic characteristics of xenon poisoning during the shutdown process of the core.

[0067] Specifically, determine the physical parameters of the control rod through the comprehensive compensation of the shutdown margin limit conditions combined with the residual reactivity, temperature reactivity, and iodine pit depth. It can ensure that the physical parameters of the control rod have sufficient shutdown margin under all working conditions. Ensure that the micro-reactor can operate safely and reliably during shutdown, and avoid over-compensation of reactivity or insufficient reactivity.

[0068] Step 103: Determine the adjustment band range of the control rod according to the ejection accident safety constraint conditions and power adjustment requirements.

[0069] The adjustment band range is the adjustable area of the control rod in the core.

[0070] Specifically, it is necessary to balance the safety constraints and power adjustment requirements. The ejection of the control rod during an ejection accident may cause a sudden change in reactivity. Therefore, it is necessary to set reasonable upper and lower limits of the adjustment band to ensure safety and meet the flexibility of power adjustment. Ensure that during operation, the control rod can adjust the core power within an effective area without causing the reactor to get out of control or become unstable.

[0071] Step 104: Set the control rod in the layout space according to the physical parameters and adjustment band range of the control rod.

[0072] Finally, determine the specific design of the control rod according to the physical parameters and adjustment band range of the control rod obtained in the previous steps and arrange it in the core. Ensure that the control rod can efficiently adjust the power and meet safety requirements such as emergency shutdown.

[0073] In this embodiment, first, through comprehensive consideration of the core geometry, temperature distribution, and material compatibility, it is ensured that the control rods can be reasonably arranged in a compact space and can safely shut down the reactor under all operating and accident conditions. Secondly, based on factors such as the core's residual reactivity, temperature reactivity, and iodine pit depth, the physical parameters of the control rods are accurately calculated to ensure that the micro-reactor has sufficient reactivity compensation during the shutdown process and avoid the risks of insufficient or excessive reactivity. Finally, through the design of the adjustment band range, it is ensured that the control rods can operate within a reasonable adjustment range, thereby achieving precise power adjustment and meeting the engineering requirements of the micro-reactor in terms of compactness, safe shutdown, and power adjustment.

[0074] Optionally, the above physical parameters include: the diameter, stroke, and number of the control rods;

[0075] The above step 102 specifically includes the following steps:

[0076] S201. Determine the residual reactivity, temperature reactivity, and iodine pit depth of the micro-reactor core;

[0077] S202. Obtain the initial parameters of the control rods, where the initial parameters include the initial diameter, initial stroke, and initial number;

[0078] S203. Determine the integral worth of the control rods according to the initial parameters;

[0079] S204. Determine the shutdown margin under different conditions according to the integral worth, residual reactivity, temperature reactivity, and iodine pit depth;

[0080] S205. In the case where the shutdown margin under any condition does not meet the shutdown margin limit condition, adjust at least one of the initial diameter, initial stroke, and initial number to obtain the adjusted initial parameters, and return to execute S202 to S205,

[0081] until the shutdown margin meets the shutdown margin limit condition, and determine the adjusted initial parameters as the physical parameters of the control rods.

[0082] Specifically, for step S201, by determining the residual reactivity of the core during full-power operation, the reactivity change caused by temperature changes, and the impact of the dynamic characteristics of xenon poisoning (iodine pit depth) on reactivity, it is possible to determine the reactivity value that needs to be compensated during the process of the core from full power to shutdown.

[0083] For step S202, the initial parameters can be set based on engineering experience or a simplified model to provide a starting point for subsequent iterative optimization.

[0084] The initial diameter can be initially selected (e.g., 58 mm) based on the neutron absorption efficiency of the absorber material (such as B4C) and process limitations. The diameter affects the neutron absorption ability of the control rod. The larger the diameter, the larger the area for neutron absorption, and the higher the integral worth may be. However, too large a diameter may occupy too much core space and affect compactness.

[0085] The initial stroke can be initially selected (e.g., 130 cm) based on the core axial length (such as 195 cm) and high-temperature zone limitations. The stroke refers to the depth at which the control rod is inserted into the core. The longer the stroke, the greater the reactivity that the control rod can compensate for, but too long a stroke may lead to a complex mechanical structure and increase the risk of deflection deformation, especially in a high-temperature environment. Therefore, the stroke needs to be long enough to provide sufficient shutdown margin, while not being too long to avoid structural problems.

[0086] The initial number can be initially selected (e.g., 6) based on the core symmetry (such as hexagonal layout). The number of control rods needs to meet the symmetry requirements to prevent uneven power distribution. For example, in a gas-cooled microreactor, choosing 6 control rods may be to maintain radial symmetry. However, the more the number, the greater the space requirement for the drive mechanism, which may conflict with the compactness requirements. Therefore, the number needs to be optimized according to the core layout and space limitations.

[0087] For step S203, the integral worth reflects the total absorption ability of the control rod for reactivity and is the basis for calculating the shutdown margin. The MCNP can be used to establish a core model containing the control rod, simulate the neutron absorption effect when the control rod is fully inserted, and calculate the change of k eff variation.

[0088] For step S204, comprehensively consider the integral worth of the control rod, the residual reactivity, the temperature effect, and the xenon poison dynamics to quantify the shutdown safety.

[0089] For step S205, parameter adjustment and iterative optimization. Through parameter sensitivity analysis (such as the influence of diameter on the shutdown margin), by adjusting the combination of diameter, stroke, and number, balance compactness (such as reducing the number) and safety (such as increasing the diameter). The process of iterative analysis may require multiple adjustments of the diameter, stroke, and number until the shutdown margin requirement is met. For example, by adjusting the diameter and insertion depth of the control rod, calculate the corresponding integral worth, and then calculate and verify whether the shutdown margin meets the shutdown margin limit condition. If not, the parameters need to be readjusted until the condition is met.

[0090] In some embodiments, the shutdown margin limit condition can be that the shutdown margin is greater than 1%.

[0091] Optionally, S204 specifically includes the following steps:

[0092] The shutdown margin is calculated by the following formula (1):

[0093] ρ st = ρ CR × (1 - ω) - Δρ ex -Δρ T × (1 + ω) - Δρ I × (1 + ω)(1)

[0094] Where ρ st is the shutdown margin.

[0095] ρ CR is the sum of the integral worths of all control rods except the one with the largest integral worth.

[0096] ω is the uncertainty factor, used to cover uncertainties such as calculation errors and material property fluctuations, and can take 10%.

[0097] Δρ ex is the residual reactivity, and the determination method is as follows:

[0098] (1) Zero burnup condition: Calculate the effective multiplication factor (k e ff) of the unburned core through a Monte Carlo code (such as MCNP, RMC). For example, k e ff = 1.02477 corresponds to Δρ ex = 2447 pcm.

[0099] (2) Burnup + xenon poisoning condition: Combine burnup calculation (such as ORIGEN, RMC)

[0100] with xenon poisoning transient analysis, and take the maximum value (such as 2401 pcm) of the sum of the residual reactivity and the xenon poisoning disappearance reactivity at a certain burnup depth (such as 3 EFPD).

[0101] (3) Value-taking principle: Δρ ex takes the larger value of the above two conditions (such as 2447 pcm).

[0102] Δρ T is the temperature reactivity. Based on thermal-hydraulic analysis (such as CFD), calculate the influence of temperature changes on the fuel and moderator densities. For example, Δρ T = -6651 pcm.

[0103] Δρ I is the iodine pit depth. Through xenon poisoning transient simulation (such as CINDER90), calculate the reactivity change corresponding to the peak xenon concentration after shutdown. For example, Δρ I = -70 pcm.

[0104] The shutdown margin of the microreactor can be accurately calculated through the above formula (1).

[0105] Optionally, step S103 described above may specifically include the following steps:

[0106] Determine the lower limit of the control rod adjustment band according to the ejection accident safety constraint and the lower limit requirement of power regulation. The lower limit requirement of power regulation is the control rod position corresponding to the lowest power level at which the reactor core is in a critical state;

[0107] Determine the upper limit of the control rod adjustment band according to the upper limit requirement of power regulation. The upper limit requirement of power regulation is the control rod position corresponding to the highest power level at which the reactor core is in a critical state,

[0108] The adjustment band range of the control rod includes the lower limit and the upper limit of the adjustment band.

[0109] Specifically, the determination of the lower limit POSmin of the control rod adjustment band needs to consider the maximum value in two operating conditions:

[0110] (1) Reactivity introduced by the ejection accident: The ejection accident refers to the situation where the control rod accidentally pops out of the reactor core. When the control rod is inserted during an ejection accident, positive reactivity will be introduced, which may cause a sudden increase in reactor power. Therefore, the lower limit of the adjustment band needs to ensure that even in the event of an ejection accident, the introduced reactivity does not exceed the effective fraction of delayed neutrons, thereby ensuring the stability and safety of the reactor. The effective fraction of delayed neutrons refers to the contribution ratio of delayed neutrons to the total number of neutrons. If the reactivity introduced by the ejection accident multiplied by the uncertainty factor is still less than the effective fraction of delayed neutrons, it means that even in the event of an ejection accident, the reactor can still maintain stability through the delayed effect of delayed neutrons and avoid prompt critical accidents.

[0111] The safety constraint for the ejection accident is: Reactivity of ejection accident × (1 + ω) < Effective fraction of delayed neutrons. Where ω is the safety factor, used to consider errors and uncertainties, and the effective fraction of delayed neutrons represents the number of neutrons that can effectively control the reactor.

[0112] (2) Control rod position corresponding to the lowest power level: In the lowest power state of the micro-reactor, the reactor core is in a critical state. At this time, the insertion position of the control rod should ensure that the power of the reactor core will not be too low and can operate stably. The reactivity change of the control rod at this position will determine the lower limit. For example, at hot zero power, the control rod needs to be inserted to a certain position (such as 105 cm) so that the lowest power level (0% full power) at which the reactor core is in a critical state.

[0113] The upper limit POSmax of the control rod adjustment band is determined by the rod position corresponding to the highest power demand. For example: When the control rod is lifted to 130 cm, the reactor core can reach the 120% full power level. Therefore, POSmax = 130 cm.

[0114] In some embodiments, as the fuel burnup deepens, the core's residual reactivity gradually decreases, and the adjustment band range needs to be dynamically adjusted. For example: at 3 EFPD (equivalent full power days), the core's residual reactivity decreases, and the lower limit of the adjustment band may need to be increased to ensure that the rod ejection accident still meets the safety criteria. This can be achieved through burnup calculations (such as Figure 4 the fuel characteristic curve) and dynamic analysis of xenon poisoning to update the adjustment band parameters at different burnup stages.

[0115] In this embodiment, by accurately determining the adjustment band range of the control rods, it can be ensured that the control rods can effectively adjust the core power under different operating conditions and operate within a safe range. By considering the reactivity introduced by the rod ejection accident, the minimum and maximum power requirements, it can be ensured that the control rods can achieve the purpose of safe adjustment under any operating conditions.

[0116] Optionally, the above method may further include the following steps:

[0117] Determine the initial control parameters of the control rods according to the number of control rods, the dead zone range of the core state parameters, the limit value of the neutron flux change rate, and the time limit of the accident condition. The initial control parameters include the step size, speed range, and emergency insertion time of each control rod;

[0118] When the initial control parameters meet the simultaneous control constraint conditions, determine the control rod control parameters of the micro reactor with the initial control parameters to synchronously control the control rods through the initial control parameters;

[0119] When the initial control parameters do not meet the control constraint conditions, divide the control rods into N groups;

[0120] Determine the group control parameters of each group of control rods according to the number of control rods in each group, the dead zone range of the core state parameters, the limit value of the neutron flux change rate, and the time limit of the accident condition;

[0121] Control the control rods in groups according to the group control parameters corresponding to each group of control rods.

[0122] Among them, the dead zone range of the core state parameters: The dead zone range refers to a small range that the control system cannot accurately perceive during the change of the core state. The determination of the dead zone range is to ensure that the insertion and withdrawal of the control rods within this range will not cause misoperation or out-of-control situations.

[0123] The limit value of the neutron flux change rate: The limit value of the neutron flux change rate means that the withdrawal rate of the control rods cannot exceed this limit, otherwise it may lead to stability problems and safety problems of the reactor system. The step size and speed range of the control rods need to meet the physical limitations of the neutron flux change.

[0124] Accident condition time limit: The accident condition time limit refers to the time limit for inserting the control rods into the core. In case of an accident, the control rods need to be quickly inserted to rapidly reduce the reactivity of the core. The emergency insertion time needs to meet this requirement.

[0125] In this embodiment, first, synchronous control of the control rods is performed using the initial control parameters. However, if all the control rods move simultaneously (single-group control), it may cause system instability due to excessive or too fast reactivity changes, or exceed the safety limits. Therefore, before performing synchronous control, it is necessary to determine whether the preliminary control parameters meet the control constraint conditions. If the control constraint conditions are not met, group control needs to be performed to re-determine the control parameters of each control rod. This can disperse the influence of reactivity changes, reduce the amplitude of single adjustment, thereby more precisely control the power, and at the same time avoid triggering the safety protection mechanism.

[0126] Specifically, the first step is to determine the initial control parameters:

[0127] (1) Determine the initial step size. First, considering synchronous control, all the control rods move as a whole, and the step size may need to be determined according to the reactivity requirements of the overall system. A larger step size may lead to insufficiently fine adjustment, while a smaller step size may increase the complexity of the operation and is also difficult to achieve in engineering.

[0128] The step size of the control rods can be preliminarily determined according to the reactivity change amount (such as 30 pcm) corresponding to the dead zone range of the core state parameters (such as power, temperature) (such as power ±2%, temperature ±5°C).

[0129] (2) Normal insertion and extraction speed range (VNmin~VNmax).

[0130] The maximum normal insertion and extraction speed of the control rods can be determined according to the reactivity change rate (such as 100 pcm / s) corresponding to the safety signal limit (such as neutron flux change rate ≤3% / s). The overall movement speed needs to balance the requirements of rapid adjustment and the bearing capacity of the mechanical system. Excessive speed may lead to mechanical wear or out-of-control risks, and too small speed may make it difficult for the mechanical structure to achieve precise drive.

[0131] The emergency insertion time (tmin) is the time required for the control rods to be fully inserted into the core in case of an accident. In an emergency, the insertion time of the entire control rod group needs to be fast enough to ensure safety, but also consider the limitations of the mechanical and power systems.

[0132] The second step is to determine whether group control is required.

[0133] When the preliminary control parameters determined in the first step meet the control constraint conditions, synchronous control is directly performed using the initial parameters, and all the control rods move uniformly.

[0134] When the preliminary control parameters determined in the first step do not meet the control constraint conditions, it is necessary to consider grouped control of the control rods. In the case of grouping, each group of control rods may have different control parameter settings to adapt to different adjustment requirements. By formulating constraint conditions, it is ensured that the movement of the control rods will not cause the core state parameters to exceed the safe range (such as excessive power fluctuations or temperature overlimits).

[0135] The grouped control strategy is as follows:

[0136] (1) Grouping method: Adopt a symmetric grouping method. According to the geometric symmetry of the core (such as a hexagonal layout), the control rods are divided into N groups (for example, 6 rods are divided into 2 groups, with 3 rods in each group symmetrically distributed).

[0137] In some embodiments, a set of standby control rods can also be reserved to act when the main control group fails.

[0138] (2) Redesign the control parameters of the subgroups:

[0139] Optimize the control parameters of each group of control rods to ensure that each group can accurately adjust the core power under corresponding working conditions. Grouped control not only improves the adjustment accuracy of the microreactor but also ensures that in the event of an accident, multiple control groups can work together to achieve the safe shutdown of the reactor.

[0140] In one example, after grouping, the control strategy can be that when each group of control rods moves, it should be carried out step by step in sequence, and the difference in the rod positions of any two groups does not exceed the specified step difference, for example, not exceeding 1 step.

[0141] For example: 6 rods are divided into 6 subgroups, with each subgroup having 1 rod, numbered 1 - 6. When moving, it is required to move in sequence, step by step, and in order as 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6... Thus, not only can the worth of the control rods during single-step movement be reduced, improving the control accuracy of power adjustment, but also it can be avoided that the rod positions of each group differ too much, resulting in a serious radial deviation of the core power and other characteristics, causing potential safety hazards.

[0142] In one example, after iterative analysis and considering the process maturity of the drive mechanism, the 6 groups of rods of the first set of control rods adopt a grouped control strategy. The maximum normal extraction and insertion speed VNmax of the control rods is conservatively selected as 2 cm / s, the control rod step size LS is conservatively selected as 1 cm / step, and the time tmin for the control rods to be emergently inserted into the core under accident conditions is conservatively selected as 30 s.

[0143] In this embodiment, by precisely designing the initial control parameters of the control rods and considering factors such as core state parameters, accident conditions, and neutron flux changes, it is ensured that the micro-reactor can safely and stably regulate power under all operating and accident conditions. By dividing the control rods into multiple groups and performing grouped control, even when the initial control parameters do not meet the conditions, the reactivity regulation of the core can still be guaranteed not to be affected, thereby improving the safety and reliability of the system.

[0144] Furthermore, when the number of control rods is small, a synchronous control method can be adopted, and when the number of control rods is large, a control strategy of grouped control can be adopted. Thus, according to the core state parameter limits and the number of control rods, single-group or grouped control can be automatically selected to optimize the regulation efficiency.

[0145] Optionally, the above control constraint conditions include the following formula (2):

[0146]

[0147] Wherein, VNmax is the maximum speed of normal insertion and extraction of the control rod, VSmax is the maximum extraction speed of the control rod corresponding to the core alarm or safety signal, LS is the control rod step size, LDmax is the maximum control rod step size allowed by the core state parameter dead zone range, tmin is the time for the control rod to be inserted into the core emergently under accident conditions, and ts is the maximum insertion time of the control rod allowed for the core state parameters not to exceed the limit under accident conditions.

[0148] In this embodiment, by formulating the constraint conditions, it is ensured that the movement of the control rod will not cause the core state parameters to exceed the safe range (such as excessive power fluctuations or temperature overlimit).

[0149] Optionally, for grouped control, an alternating movement method can be adopted. For example, after group A moves 1 step, group B moves 1 step, which can avoid power distribution deviation. When necessary, all groups can also move synchronously for rapid regulation (such as emergency power reduction).

[0150] Embodiment 2:

[0151] This embodiment provides a design method for a gas-cooled micro-reactor, and the method includes:

[0152] Adopt the control rod design method of the micro-reactor provided in any of the above embodiments to determine the arrangement space, material, physical parameters, and adjustment band range of the control rod;

[0153] According to the determined arrangement space, material, physical parameters, and adjustment band range of the control rod, a gas-cooled micro-reactor is formed.

[0154] In this embodiment, by adopting the control rod design method of the micro reactor provided in any of the above embodiments, the compactness, safety, and power regulation accuracy of the gas-cooled micro reactor are ensured. By determining the arrangement space, material, physical parameters, and regulation band range of the control rod, it is ensured that the control rod can provide sufficient shutdown margin under all operating and accident conditions and can accurately regulate the operating state of the reactor core. This method effectively solves the problem of insufficient reactivity control means in the new micro reactor and improves the overall safety and operating efficiency of the micro reactor.

[0155] For the convenience of understanding the control rod design method provided in this embodiment, the practical application description of the above method is provided here, such as Figure 2 shown, specifically referring to the following example:

[0156] Taking the design analysis process of the control rod of a typical gas-cooled micro reactor as an example, the present application is further described in detail. The core model of a typical gas-cooled micro reactor is as Figure 3 shown. The reactor core is composed of hexagonal fuel assemblies 5 with the same geometric structure in the active zone and a reflector 4. Outside the reactor core, there are boron-containing carbon bricks 3, a basket 2, a pressure vessel 1, a first set of control rods 7, a second set of control rods 6, etc. There are 30 fuel assembly columns in the radial direction of the reactor core, and each column of assemblies has 3 layers of fuel assemblies axially. Therefore, there are 90 fuel assemblies in the whole reactor. The radial opposite side distance of the fuel assembly is 19 cm, and the axial length is 50 cm. The total diameter of the reactor core is 180 cm, and the total length is 195 cm. The fuel loading of the reactor core can meet the design requirements of a thermal power of 5 MW and a service life of 3 years.

[0157] The specific implementation steps are as follows:

[0158] Step 1: Obtain the core loading scheme of the micro reactor.

[0159] According to the core loading scheme of a typical gas-cooled micro reactor, an advanced general Monte Carlo program is used to establish a real and detailed three-dimensional model of the reactor core.

[0160] Step 2: Determine the space where the control rod can be arranged (i.e., determine the arrangement space of the control rod) and the in-core service environment.

[0161] Use a Monte Carlo program (such as MCNP) to establish a detailed three-dimensional model of the micro reactor core, and combine the core geometric structure (such as Figure 3 the hexagonal fuel assembly 5 and reflector 4 of the gas-cooled micro reactor shown) to determine the positions of the channels where the control rod can be inserted.

[0162] In this embodiment, the gas-cooled micro-reactor is a horizontal small modular prismatic high-temperature gas-cooled reactor. The inlet temperature of the reactor core is about 450 °C, and the outlet temperature is about 750 °C. The fuel assembly has dense fuel rod channels, coolant channels, burnable poison channels, etc. Considering that the control rod absorber material and structural material generally cannot withstand high temperatures for a long time, the control rods should be arranged radially on the side reflector of the reactor core and axially inserted from the coolant inlet end.

[0163] Step 3: Screen the control rod material.

[0164] The control rod absorber materials mainly include B4C, Cd, Gd2O3, Sm2O3, HfO2, Eu2O3, etc. Considering the high temperature in the reactor and the relatively hard neutron energy spectrum of the micro-reactor, B4C with a relatively wide neutron absorption energy spectrum, a large absorption cross-section, a small material density, good compatibility with other materials in the reactor, and mature technology can be selected. The control rod cladding material is selected as the 800H alloy that can withstand a high temperature of 760 °C for a long time and has mature technology.

[0165] As Figure 3 shown in the reactor core structure, the control rods can be arranged in the side reflector to avoid direct contact with the high-temperature fuel assembly.

[0166] Step 4: Determine the diameter, stroke, and number of control rods (i.e., determine the physical parameters of the control rods).

[0167] To avoid serious radial power shift in the reactor core, the control rods should be symmetrically arranged radially. Therefore, for Figure 3 the gas-cooled micro-reactor core, the number of the first set of control rods 7 may be 3, 6, 9, or 12. Each control rod needs to be equipped with a driving mechanism, and the radial space diameter required for the driving mechanism is about 30 cm, that is, the interval between every two control rods should be at least greater than 30 cm. Six control rods are initially selected.

[0168] The diameter of the control rod has a great influence on its integral worth. The stroke should be as small as possible on the premise of meeting the shutdown margin requirement to avoid the control rod inserting into the high-temperature area at the outlet end of the reactor core, and also to avoid the horizontally placed control rod having too large a deflection and deforming.

[0169] The diameter, stroke, and number of control rods are determined by the following formula (1):

[0170] ρ st =ρ CR ×(1 - ω)-Δρ ex -Δρ T ×(1 + ω)-Δρ I ×(1 + ω) (1)

[0172] In the formula, ρ st is the shutdown margin, and it is required that ρ st > 1%;

[0173] ρ CR is the integral worth of all control rods except the one with the maximum worth, that is, the integral worth when 5 groups of control rods are fully inserted into the core;

[0174] ω is the uncertainty factor, taking 10%;

[0175] Δρ ex is the residual reactivity that the control rods need to compensate for when the core goes from full power operation to shutdown state, determined by the larger value of the following two conditions:

[0176] (1) The residual reactivity of the zero burnup full power core. From Figure 4 it can be known that at this time, the core keff = 1.02477, corresponding to 2447 pcm reactivity;

[0177] (2) The maximum value of the sum of the residual reactivity of the full power core with a certain burnup depth and the reactivity introduced by the disappearance of xenon poison. After calculation and analysis, at 3 EFPD, the core keff = 1.01259, the positive reactivity introduced by the disappearance of xenon poison is 1150 pcm, and the maximum sum is 2401 pcm. Therefore, Δρ ex takes 2447 pcm.

[0178] As Figure 4 shown by the change of the core residual reactivity with burnup, Δρ ex can be determined.

[0179] Δρ T is the reactivity introduced by the temperature decrease when the core shuts down from full power. During cold shutdown, the average core temperature is about 300 K, and the reactivity introduced by the temperature decrease is 6651 pcm;

[0180] Δρ I is the depth of the "iodine pit" generated by the dynamic characteristics of xenon poison when the core shuts down from full power. It is calculated to be 70 pcm.

[0181] Specifically, by adjusting the diameter and insertion depth (or quantity) of the control rods, calculate the corresponding integral worth ρ CR , and then substitute it into formula (1) to verify whether the shutdown margin ρ st is greater than 1%. If not, the parameters need to be readjusted until the conditions are met. By balancing the geometric parameters of the control rods (diameter, stroke, quantity) with the physical characteristics of the core (reactivity compensation, temperature effect, xenon poison dynamics), combined with uncertainty analysis, iterative optimization design is carried out to ensure the control rod diameter, stroke, and quantity that meet the shutdown margin and compactness requirements.

[0182] In an example, through iterative analysis, when the outer diameter of the control rod absorber is 58 mm and it is inserted deepest into the active zone to an axial depth of 130 cm, ρCR = 12170 pcm. At this time, ρ st = 1113 pcm, meeting the shutdown margin requirement of at least 1%.

[0183] Step 5. Determine the adjustment band range [POSmin, POSmax] for operation control.

[0184] (1). Lower limit POSmin of the control rod adjustment band.

[0185] The lower limit POSmin of the control rod adjustment band is determined by the larger value of the following two conditions:

[0186] (1) Reactivity introduced by the rod ejection accident × (1 + ω) < delayed neutron effective fraction; The rod ejection accident refers to the situation where the control rod accidentally pops out of the core, which introduces positive reactivity and may cause a sudden increase in reactor power. Therefore, the lower limit of the adjustment band needs to ensure that even in the event of a rod ejection accident, the introduced reactivity does not exceed the delayed neutron effective fraction, thus ensuring the stability and safety of the reactor. The delayed neutron effective fraction refers to the contribution ratio of delayed neutrons to the total number of neutrons. If the reactivity introduced by the rod ejection accident multiplied by the uncertainty factor is still less than the delayed neutron effective fraction, it means that even in the event of a rod ejection accident, the reactor can still maintain stability through the delayed effect of delayed neutrons and avoid prompt critical accidents.

[0187] (2) The rod position corresponding to the lowest power level that needs to be adjusted.

[0188] At different burnup levels, the lower limit of the adjustment band is different. Taking the zero burnup point as an example, when the core is in a hot zero-power state, the control rod needs to be inserted to a certain position so that the core is at the lowest power level in the critical state.

[0189] For example, the rod positions of 6 groups of the first set of control rods are 105 cm (the distance between the control rod and the rear end of the active zone). At this time, the positive reactivity introduced by ejecting one rod is 520 pcm. Considering a 10% calculation uncertainty, it is still less than the delayed neutron effective fraction (about 0.007). Therefore, at the zero burnup point, the lower limit of the adjustment band can be selected as 105 cm, and the lower limit of power adjustment is 0% full power.

[0190] (2). Upper limit POSmax of the control rod adjustment band.

[0191] The upper limit POSmax of the control rod adjustment band is determined by the rod position corresponding to the highest power level that needs to be adjusted. The higher the control rod is lifted, the larger the area where the absorber is removed from the core, the more positive reactivity is introduced, and the power increases accordingly.

[0192] Set the upper limit of power adjustment as 120% full power, and the corresponding control rod position is 130 cm, that is, the upper limit of the adjustment band is 130 cm.

[0193] Therefore, at zero burnup, the adjustment band range for control rod operation control is 105 cm to 130 cm, and the power adjustment range is from 0% to 120% of the full power level in the hot state.

[0194] (III). Dynamic adjustment and burnup impact.

[0195] Burnup effect: As the fuel burnup deepens, the core's residual reactivity gradually decreases, and the adjustment band range needs to be dynamically adjusted. For example, at 3 EFPD (equivalent full power days), the core's residual reactivity decreases, and the lower limit of the adjustment band may need to be increased to ensure that the rod ejection accident still meets the safety criteria.

[0196] Monte Carlo simulation: Update the adjustment band parameters at different burnup stages through burnup calculation (refer to Figure 4 the fuel characteristic curve) and dynamic analysis of xenon poisoning.

[0197] Step 6. Determine the control rod step size, normal speed range, and emergency insertion time (shortest insertion time) for power adjustment.

[0198] The specific steps are as follows:

[0199] Under the control rod non-grouping control strategy, determine the step size, normal speed, and emergency insertion time according to the following formula (2); if not satisfied, move the control rods in a symmetric grouping manner and determine the step size, normal speed, and emergency insertion time according to the following formula (2).

[0200] (I). Control rod non-grouping control strategy

[0201] Determine the step size, normal speed, and emergency insertion time through formula (2):

[0202]

[0203] In formula (1),

[0204] VNmax is the maximum speed of normal extraction and insertion of the control rod, that is, the upper limit of the movement speed of the control rod during normal operation.

[0205] VSmax is the maximum extraction speed of the control rod corresponding to the core alarm or safety signal. It is necessary to avoid a sharp change in reactivity caused by too high a speed, triggering a safety signal or alarm. The reactivity change rate can be deduced based on the set value of the neutron flux change rate or temperature change rate; combined with the differential worth of the control rod, the speed limit can be inversely deduced.

[0206] Based on the setpoint signal of 3% / s for the positive change rate of neutron flux, the reactor period is calculated to be approximately 33.8 s, corresponding to a reactivity of 100 pcm; according to the differential worth curve of the control rods, the maximum total differential worth of 6 rods is 160 pcm / cm; therefore, if 6 control rods have the same rod position and move together, VSmax = 0.625 cm / s.

[0207] LS is the control rod step size;

[0208] LDmax is the maximum control rod step size allowed by the dead zone range of the core state parameters. The key core state parameters mainly include the power level and the outlet temperature. If a dead zone interval of ±2% is considered for the power level and a dead zone interval of ±5 °C is considered for the outlet temperature, through calculation and analysis, it can be known that the corresponding reactivity is about 30 pcm; according to the differential worth of the control rods, when 6 rods have the same rod position and move together, LDmax = 0.19 cm / step.

[0209] tmin is the time for the control rod to be inserted into the core emergently under accident conditions, that is, the time required for the control rod to be fully inserted into the core from the current position under accident conditions, which should be less than the allowed time ts for the core state parameters (such as fuel temperature) to exceed the limit;

[0210] ts is the maximum insertion time of the control rod allowed for the core state parameters not to exceed the limit under accident conditions. Based on the core thermal-hydraulic transient analysis (such as loss of flow accident, ejection rod accident), the time ts for the fuel temperature to rise to the limit (such as 1600 °C) can be determined. In conservative design, if the gas-cooled reactor has strong inherent safety (ts is longer), tmin can be relaxed to 30 s.

[0211] The gas-cooled microreactor has excellent inherent safety. Under accident conditions, it can automatically shut down only relying on the negative temperature feedback, ensuring that the fuel temperature does not exceed the limit and avoiding core melting and a large release of radioactive substances. Therefore, a very large value can be taken for ts.

[0212] (2) Control rod grouped control strategy

[0213] If the single-group control rod movement cannot meet the constraint conditions (such as formula 3), the control rods need to be grouped and moved, and the reactivity perturbation of a single movement is reduced by symmetric grouping.

[0214] Grouping method:

[0215] Symmetric grouping: For example, divide 6 control rods into two groups (3 rods in each group), symmetrically distributed around the core center to avoid power distribution deviation.

[0216] Movement coordination: Each group moves alternately or synchronously to ensure uniform reactivity change.

[0217] After grouping, the step length and speed limits for single-group actions are relaxed (for example, if divided into two groups, VSmax is increased from 0.625 cm / s to 1.25 cm / s; if divided into six groups, it is increased to 3.75 cm / s), while keeping the total reactivity change controllable.

[0218] In one example, through iterative analysis and considering the process maturity of the drive mechanism, a grouped control strategy is adopted for the 6 groups of rods in the first set of control rods. The maximum normal insertion / withdrawal speed VNmax of the control rods is conservatively selected as 2 cm / s, the step length LS of the control rods is conservatively selected as 1 cm / step, and the time tmin for the control rods to be emergently inserted into the core under accident conditions is conservatively selected as 30 s.

[0219] Considering the redundancy requirements of the reactor design, a second set of control rods is designed. The second set of control rods is used as a backup means and there is only one, located at the center of the core. Under power operation conditions, the second set of control rods remains withdrawn from the core (indicating that this set of control rods is in an unused state), and only when the first set of control rods fails to achieve the shutdown function, the second set of control rods is inserted into the core to achieve shutdown.

[0220] In this embodiment, the available space for arranging the control rods and the in-core service environment are determined through the micro-reactor loading scheme to ensure the compactness of the core system and the process feasibility of the control rods; by considering the reactivity to be compensated for shutdown under all normal and accident conditions to ensure sufficient shutdown margin and the safe shutdown function of the reactor; the adjustment band interval is determined by the rod ejection reactivity and power adjustment range to ensure the safety of core power adjustment; the normal operating speed of the control rods is limited by the safety signal limit value, the step length accuracy of the control rods is limited by the dead zone range of the core state parameters, and the emergency insertion time of the control rods is limited by the design limit value of the core parameters under accident conditions to ensure the precise power adjustment of the control rods.

[0221] It solves the problem of the lack of effective reactivity control means for the new advanced micro-reactor. On the basis of meeting the in-core service environment and the layout space of the out-core drive mechanism, it ensures that the new micro-reactor has sufficient shutdown margin under all operating and accident conditions, and the control rods are within a reasonable adjustment band and can precisely adjust the core operating state, meeting the engineering requirements of the new micro-reactor in terms of compactness, safe shutdown, power adjustment, etc.

[0222] The embodiment of the present application also provides a micro-reactor control rod system, which includes control rods, drive mechanisms, rod position measurement sensors, rod position recording and display systems, as well as supporting auxiliary circuits, signal processors, and computer memories.

[0223] Embodiment 3:

[0224] Such as Figure 5As shown in the figure, this embodiment provides a control rod design device 500 for a microreactor, which is used to implement the steps of the control rod design of the above microreactor. The device includes:

[0225] A first determination module 501, configured to determine the arrangement space and control rod material of the control rod according to the core geometry, temperature distribution, and material compatibility data of the microreactor;

[0226] A second determination module 502, configured to determine the physical parameters of the control rod according to the shutdown margin limit condition, residual reactivity, temperature reactivity, and iodine pit depth of the microreactor. The residual reactivity is the residual reactivity that the control rod needs to compensate when the core runs from full power to the shutdown state. The temperature reactivity is the negative reactivity introduced when the core cools to the cold state during shutdown at full power. The iodine pit depth is the depth of reactivity change caused by the dynamic characteristics of xenon poisoning during the shutdown process of the core;

[0227] A third determination module 503, configured to determine the adjustment band range of the control rod according to the ejection rod accident safety constraint condition and power adjustment requirement. The adjustment band range is the adjustable area of the control rod in the core;

[0228] A design module 504, connected to the first determination module 501, the second determination module 502, and the third determination module 503 respectively, and is configured to set the control rod in the arrangement space according to the physical parameters and adjustment band range of the control rod.

[0229] Optionally, the physical parameters include: the diameter, stroke, and quantity of the control rod;

[0230] The second determination module 502 is specifically configured to:

[0231] S201. Determine the residual reactivity, temperature reactivity, and iodine pit depth of the microreactor core;

[0232] S202. Obtain the initial parameters of the control rod. The initial parameters include the initial diameter, initial stroke, and initial quantity;

[0233] S203. Determine the integral worth of the control rod according to the initial parameters;

[0234] S204. Determine the shutdown margin according to the integral worth, residual reactivity, temperature reactivity, and iodine pit depth;

[0235] S205. In the case that the shutdown margin does not meet the shutdown margin limit condition, adjust at least one of the initial diameter, initial stroke, and initial quantity to obtain the adjusted initial parameters, and return to execute S202 to S205,

[0236] Until the shutdown margin meets the shutdown margin limit condition, determine the adjusted initial parameters as the physical parameters of the control rod.

[0237] Optionally, determining the shutdown margin according to the integral worth, the remaining reactivity, the temperature reactivity, and the iodine pit depth specifically includes:

[0238] Calculating the shutdown margin through the following formula (1):

[0239] ρ st = ρ CR ×(1 - ω) - Δρ ex -Δρ T ×(1 + ω) - Δρ I ×(1 + ω)(1)

[0240] Wherein, ρ st is the shutdown margin, ρ CR is the sum of the integral worths of other control rods except the control rod with the largest integral worth, ω is the uncertainty factor, Δρ ex is the remaining reactivity, Δρ T is the temperature reactivity, Δρ I is the iodine pit depth.

[0241] Optionally, the third determination module 503 includes:

[0242] The first determination unit is configured to determine the lower limit of the adjustment band of the control rod according to the ejection accident safety constraint and the lower limit requirement of power regulation, and the lower limit requirement of power regulation is the control rod position corresponding to the lowest power level at which the reactor core is in a critical state;

[0243] The second determination unit is configured to determine the upper limit of the adjustment band of the control rod according to the highest power requirement, and the highest power requirement is the control rod position corresponding to the reactor core reaching the full power state,

[0244] The adjustment band range of the control rod includes the lower limit of the adjustment band and the upper limit of the adjustment band.

[0245] Optionally, the device further includes:

[0246] The fourth determination module is configured to determine the initial control parameters of the control rod according to the number of control rods, the dead zone range of the reactor core state parameters, the neutron flux change rate limit value, and the accident condition time limit value, and the initial control parameters include the step size, the speed range, and the emergency insertion time of each control rod;

[0247] The fifth determination module is configured to determine the initial control parameters as the control rod control parameters of the micro reactor when the initial control parameters meet the simultaneous control constraint conditions, so as to synchronously control the control rod through the initial control parameters;

[0248] The partitioning module is configured to partition the control rods into N groups when the initial control parameters do not meet the control constraint conditions;

[0249] A sixth determination module determines the subgroup control parameters of each group of control rods according to the number of control rods in each group, the dead zone range of the core state parameters, the limit value of the neutron flux change rate, and the limit value of the accident condition time.

[0250] A control module is used to perform grouped control on the control rods according to the subgroup control parameters corresponding to each group of control rods.

[0251] In the control rod design device of the micro reactor in this embodiment, first, the control rod arrangement space is optimized based on the core geometry structure and temperature distribution to ensure the compactness of the core; second, the shutdown margin formula is combined with the comprehensive compensation of the residual reactivity, temperature reactivity, and iodine pit depth to ensure sufficient shutdown margin under all conditions and achieve safe shutdown; finally, the adjustment band range is determined based on the safety constraints of the rod ejection accident and the power demand to improve the accuracy of power regulation. Thus, it is possible to improve the reactivity control ability of the control rods while ensuring the compactness of the core.

[0252] It should be clear that the present application is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, the detailed description of known methods is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present application is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order between the steps after understanding the spirit of the present application.

[0253] It should also be noted that the functional blocks shown in the above structural block diagrams can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, it can be, for example, an electronic circuit, an application-specific integrated circuit (ASIC), appropriate firmware, a plug-in, a functional card, etc. When implemented in software, the elements of the present application are programs or code segments used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted via a data signal carried in a carrier wave on a transmission medium or a communication link. A "machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROMs, flash memories, erasable ROMs (EROMs), floppy disks, CD-ROMs, optical discs, hard disks, fiber optic media, radio frequency (RF) links, etc. The code segment can be downloaded via a computer network such as the Internet, an intranet, etc.

[0254] It also needs to be noted that the exemplary embodiments mentioned in the present application describe some methods or systems based on a series of steps or devices. However, the present application is not limited to the order of the above steps, that is, the steps can be executed in the order mentioned in the embodiments, or different from the order in the embodiments, or several steps can be executed simultaneously.

[0255] Aspects of the present disclosure have been described above with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present disclosure. It should be understood that each block in the flowchart and / or block diagram, and the combinations of blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable scheduling device to produce a machine, such that the instructions executed by the processor of the computer or other programmable scheduling device enable the implementation of the functions / actions specified in one or more blocks of the flowchart and / or block diagram. Such a processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor, or a field-programmable logic circuit. It is also understood that each block in the block diagram and / or flowchart, and the combinations of blocks in the block diagram and / or flowchart, can also be implemented by dedicated hardware that performs the specified functions or actions, or can be implemented by a combination of dedicated hardware and computer instructions.

[0256] The above is only the specific implementation manner of this application. Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described systems, modules, and units can refer to the corresponding processes in the foregoing method embodiments, which will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered by the protection scope of this application.

Claims

1. A control rod design method, characterized in that, The method includes: Determining the arrangement space and material of the control rod according to the core geometry, temperature distribution and material compatibility data of the micro reactor; Determining the physical parameters of the control rod according to the shutdown margin limit condition, residual reactivity, temperature reactivity and iodine pit depth of the micro reactor; Determining the adjustment band range of the control rod according to the ejection accident safety constraint condition and power adjustment requirement, where the adjustment band range is the adjustable area of the control rod in the core; Setting the control rod in the arrangement space according to the physical parameters and the adjustment band range of the control rod.

2. The method according to claim 1, characterized in that, The physical parameters include: the diameter, stroke and number of the control rod; The determining the physical parameters of the control rod according to the shutdown margin limit condition, residual reactivity, temperature reactivity and iodine pit depth of the micro reactor specifically includes: S201. Determining the residual reactivity, temperature reactivity and iodine pit depth of the core of the micro reactor; S202. Obtaining the initial parameters of the control rod, where the initial parameters include the initial diameter, initial stroke and initial number; S203. Determining the integral worth of the control rod according to the initial parameters; S204. Determining the shutdown margin under different working conditions according to the integral worth, residual reactivity, temperature reactivity and iodine pit depth; S205. In the case that the shutdown margin under any working condition does not meet the shutdown margin limit condition, adjusting at least one of the initial diameter, initial stroke and initial number to obtain the adjusted initial parameters, and returning to execute S202 to S205, until the shutdown margin meets the shutdown margin limit condition, and determining the adjusted initial parameters as the physical parameters of the control rod.

3. The method according to claim 2, wherein The determining the shutdown margin according to the integral worth, residual reactivity, temperature reactivity and iodine pit depth specifically includes: Calculating the shutdown margin through the following formula (1): ρ st = ρ CR × (1 - ω) - Δρ ex -Δρ T × (1 + ω) - Δρ I × (1 + ω)(1) Among them, ρ st is the shutdown margin, ρ CR is the sum of the integral worths of the control rods other than the control rod with the largest integral worth, ω is the uncertainty factor, Δρ ex is the residual reactivity, Δρ T is the temperature reactivity, Δρ I is the iodine pit depth.

4. The method according to claim 1, wherein The determining the adjustment band range of the control rod according to the ejection accident safety constraint condition and power adjustment requirement specifically includes: Determining the lower limit of the adjustment band of the control rod according to the ejection accident safety constraint and the lower limit requirement of power adjustment, where the lower limit requirement of power adjustment is the control rod position corresponding to the lowest power level when the core is in the critical state; Determining the upper limit of the adjustment band of the control rod according to the upper limit requirement of power adjustment, where the upper limit requirement of power adjustment is the control rod position corresponding to the highest power level when the core is in the critical state, The adjustment band range of the control rod includes the lower limit of the adjustment band and the upper limit of the adjustment band.

5. The method according to claim 1, wherein The method further includes: Determining the initial control parameters of the control rod according to the number of control rods, the dead zone range of the core state parameters, the neutron flux change rate limit value and the accident working condition time limit value, where the initial control parameters include the step size, speed range and emergency insertion time of each control rod; In the case that the initial control parameters meet the simultaneous control constraint condition, determining the initial control parameters as the control rod control parameters of the micro reactor to synchronously control the control rod through the initial control parameters; In the case that the initial control parameters do not meet the control constraint condition, symmetrically dividing the control rods into N groups; Determine the subgroup control parameters of each group of control rods according to the number of control rods in each group, the dead zone range of the core state parameters, the limit value of the neutron flux change rate, and the time limit for accident conditions. Perform grouped control of the control rods according to the subgroup control parameters corresponding to each group of control rods.

6. The method according to claim 5, characterized in that, The control constraint conditions include the following formula (2): Where, VNmax is the maximum speed of normal insertion and extraction of the control rod, VSmax is the maximum extraction speed of the control rod corresponding to the core alarm or safety signal, LS is the control rod step size, LDmax is the maximum control rod step size allowed by the dead zone range of the core state parameters, tmin is the time for the control rod to be inserted into the core emergently under accident conditions, and ts is the maximum insertion time of the control rod allowed for the core state parameters not to exceed the limit value under accident conditions.

7. A control rod design device, characterized in that, The device includes: A first determination module, configured to determine the arrangement space and control rod material of the control rod according to the core geometry structure, temperature distribution, and material compatibility data of the micro reactor. A second determination module, configured to determine the physical parameters of the control rod according to the shutdown margin limit condition, residual reactivity, temperature reactivity, and iodine pit depth of the micro reactor. A third determination module, configured to determine the adjustment band range of the control rod according to the ejection accident safety constraint condition and power regulation requirement, and the adjustment band range is the adjustable area of the control rod in the core. A design module, connected to the first determination module, the second determination module, and the third determination module respectively, and configured to set the control rod in the arrangement space according to the physical parameters and the adjustment band range of the control rod.

8. The device according to claim 7, characterized in that, The physical parameters include: the diameter, stroke, and number of the control rod. The second determination module is specifically configured to: S201. Determine the residual reactivity, temperature reactivity, and iodine pit depth of the core of the micro reactor. S202. Obtain the initial parameters of the control rod, and the initial parameters include the initial diameter, initial stroke, and initial number. S203. Determine the integral worth of the control rod according to the initial parameters. S204. Determine the shutdown margin under different working conditions according to the integral worth, residual reactivity, temperature reactivity, and iodine pit depth. S205. In the case that the shutdown margin under any working condition does not meet the shutdown margin limit condition, adjust at least one of the initial diameter, initial stroke, and initial number to obtain the adjusted initial parameters, and return to execute S202 to S205. Until the shutdown margin meets the shutdown margin limit condition, determine the adjusted initial parameters as the physical parameters of the control rod.

9. The device according to claim 8, characterized in that The third determination module includes: A first determination unit, configured to determine the lower limit of the adjustment band of the control rod according to the ejection accident safety constraint and the lower limit requirement of power regulation, and the lower limit requirement of power regulation is the control rod position corresponding to the lowest power level when the core is in the critical state. A second determination unit, configured to determine the upper limit of the adjustment band of the control rod according to the upper limit requirement of power regulation, and the upper limit requirement of power regulation is the control rod position corresponding to the highest power level when the core is in the critical state. The adjustment band range of the control rod includes the lower limit of the adjustment band and the upper limit of the adjustment band.

10. A design method for an air-cooled micro reactor, characterized in that, The method includes: Using the control rod design method according to any one of claims 1-6, determine the arrangement space, material, physical parameters and regulation band range of the control rod; Form a gas-cooled micro reactor according to the determined arrangement space, material, physical parameters and regulation band range of the control rod.

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