A method and device for controlling axial flux deviation at the end of life of a nuclear power plant reactor

Abstract

Embodiments of the present invention disclose a method and apparatus for controlling axial flux deviation at the end of a nuclear power plant reactor's lifespan. The method includes determining the timing for adjusting a target axial flux deviation value based on the unit's average temperature deviation; if adjustment is required, modifying the axial flux deviation control band based on the adjusted target axial flux deviation value to maintain the target axial flux deviation value within the axial flux deviation control band. The technical solution of the present invention can minimize the likelihood of xenon oscillation in a nuclear power plant, improving the safety of the reactor core and the safety of extended unit operation.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of reactor control and protection technology, and in particular to a method and device for controlling axial flux deviation at the end of life of a nuclear power plant reactor. Background Art

[0002] To enhance economic efficiency and operational flexibility, nuclear power plants generally require the ability to operate for extended periods. This allows for greater flexibility in scheduling outages for major maintenance. Furthermore, it improves fuel efficiency, increases burnup depth, and enhances plant economics. Extended operation is typically performed at the end of a reactor's lifespan. When the primary boron concentration falls below 10 ppm and positive reactivity cannot be achieved through boron dilution, positive reactivity can be introduced by reducing core power or lowering coolant temperature to support continued reactor operation. During extended operation, positive reactivity can be released by reducing core power and raising control rods to support continued operation beyond the reactor's design lifespan. Whether extended operation is performed at reduced power or by raising control rods, the core power shifts toward the upper core, manifesting as a positive core axial power offset. Improper control can easily lead to xenon oscillations, which ultimately necessitate a major outage.

[0003] Axial flux difference (AFD) control in advanced third-generation nuclear power plants utilizes a constant axial offset control method, which uses specific axial offset control rods (AO rods) to control the core AFD and maintain a constant AFD. However, during extended operation in advanced third-generation nuclear power plants, the core power margin tilts toward the upper half of the core, manifesting as a positive AFD. Improper control can easily trigger xenon oscillations, which ultimately necessitate a shutdown and overhaul. During extended operation, the control rods are positioned relatively high, and the AO rods must be immobilized during extended operation at reduced power. Therefore, AFD control using only AO rods is not feasible, necessitating the development of specific methods for AFD control. Summary of the Invention

[0004] The present invention provides a method and device for controlling axial flux deviation at the end of the life of a nuclear power plant reactor, which can minimize the possibility of xenon oscillation in the nuclear power plant and improve the safety of the core and the safety of extended operation of the unit.

[0005] According to one aspect of the present invention, a method for controlling an axial flux deviation at the end of a nuclear power plant reactor life is provided. The method for controlling an axial flux deviation at the end of a nuclear power plant reactor life comprises:

[0006] Determine the adjustment timing of the target axial flux deviation value based on the average temperature deviation of the unit;

[0007] If adjustment is required, the axial flux deviation control band is modified based on the adjusted target axial flux deviation value so that the target axial flux deviation value is maintained within the range of the axial flux deviation control band.

[0008] Optionally, determining the adjustment timing of the target axial flux deviation value according to the average temperature deviation of the unit includes:

[0009] When the average temperature deviation of the unit meets the first preset condition, wait for the actual axial power deviation value of the unit to be greater than the target axial power deviation value, and adjust the target axial flux deviation;

[0010] When the average temperature deviation of the unit meets the second preset condition, the target axial power deviation value of the unit is adjusted to the target axial power deviation value of the day.

[0011] Optionally, before determining the adjustment timing of the target axial flux deviation value according to the average temperature deviation of the unit, the method further includes:

[0012] The daily axial flux deviation values ​​during the extended operation of the unit are simulated and predicted.

[0013] Optionally, after simulating and predicting the daily axial flux deviation value during the extended operation of the unit, the method further includes:

[0014] The target axial flux deviation value of the core on the day during the extended operation of the computer group.

[0015] Optionally, during the operation, the rod position of the axially offset control rod is maintained at 250 steps, and the movement is performed within 2 steps.

[0016] Optionally, the axial flux deviation control band is +1% to -1% of the target axial flux deviation value.

[0017] Optionally, the first preset condition is +0.56°C, and the second preset condition is -0.56°C.

[0018] According to another aspect of the present invention, a device for controlling an axial flux deviation at the end of the life of a nuclear power plant reactor is provided. The device comprises:

[0019] An adjustment module, used to determine an adjustment timing of a target axial flux deviation value according to an average temperature deviation of the unit;

[0020] The adjustment module is configured to modify the axial flux deviation control band based on the adjusted target axial flux deviation value if adjustment is required, so that the target axial flux deviation value is maintained within the range of the axial flux deviation control band.

[0021] Optionally, the nuclear power plant reactor end-of-life axial flux deviation control device further includes:

[0022] a first adjusting unit, configured to adjust the target axial flux deviation when the average temperature deviation of the unit satisfies a first preset condition and when the actual axial power deviation value of the unit is greater than the target axial power deviation value;

[0023] The second adjustment unit is used to adjust the target axial power deviation value of the unit to the target axial power deviation value of the day when the average temperature deviation of the unit meets the second preset condition.

[0024] Optionally, the nuclear power plant reactor end-of-life axial flux deviation control device further includes:

[0025] The prediction module is used to simulate and predict the daily axial flux deviation value during the extended operation of the unit;

[0026] The calculation module is used to calculate the target axial flux deviation value of the core on the day during the extended operation of the computer group.

[0027] The technical solution of this embodiment adjusts the target axial flux deviation control band by adjusting the target axial flux deviation value when the AO rod cannot be used in the core to control the axial flux deviation, ensuring that the axial flux deviation value of the unit always remains within the target axial flux deviation control band, and slowly increases in a stable and controllable manner to prevent the initiation of divergent xenon oscillations, thereby improving the safety of the extended operation of the unit. At the same time, the impact of the axial flux deviation control on the average temperature deviation is comprehensively considered. While effectively controlling the axial flux deviation of the core, it also plays a positive role in the control of the average temperature deviation, which helps to stabilize the state of the unit. The technical solution of this embodiment solves the problem in the prior art that during the extended operation of a nuclear power plant, the core power margin will tilt toward the upper half of the core, and improper control will easily cause xenon oscillations, which will eventually cause the unit to be shut down for overhaul.

[0028] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1This is a flow chart of a method for controlling axial flux deviation at the end of reactor life in a nuclear power plant provided by an embodiment of the present invention;

[0031] Figure 2 This is a flow chart of another method for controlling axial flux deviation at the end of reactor life in a nuclear power plant provided by an embodiment of the present invention;

[0032] Figure 3 This is a flow chart of another method for controlling axial flux deviation at the end of reactor life in a nuclear power plant provided by an embodiment of the present invention;

[0033] Figure 4 1 is a schematic structural diagram of an axial flux deviation control device for a nuclear power plant reactor at the end of its life provided by an embodiment of the present invention;

[0034] Figure 5 It is a structural schematic diagram of another device for controlling axial flux deviation at the end of reactor life in a nuclear power plant provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0036] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0037] Figure 1 This is a flow chart of a method for controlling axial flux deviation at the end of reactor life in a nuclear power plant according to an embodiment of the present invention. Figure 1 The embodiment of the present invention provides a method for controlling an axial flux deviation at the end of a nuclear power plant reactor life cycle. The method for controlling an axial flux deviation at the end of a nuclear power plant reactor life cycle includes the following steps:

[0038] S110. Determine the adjustment timing of the target axial flux deviation value according to the average temperature deviation of the unit.

[0039] Specifically, when the unit's average temperature deviation is high, the target axial flux deviation value must be adjusted only after the unit's actual axial flux deviation value is more positive than the target axial flux deviation value. This prevents the AO rod from lifting due to adjustment of the target axial flux deviation value, further increasing the average temperature deviation. When the unit's average temperature deviation is negative, the unit's target axial flux deviation value can be adjusted in a positive direction, causing the AO rod to lift while controlling the core axial flux deviation, thereby increasing the average temperature deviation.

[0040] S120 . If adjustment is required, modify the axial flux deviation control band based on the adjusted target axial flux deviation value, so that the target axial flux deviation value is maintained within the range of the axial flux deviation control band.

[0041] Optionally, the axial flux deviation control band is between +1% and -1% of the target axial flux deviation value. Specifically, during routine operation of a nuclear power plant, the axial flux deviation control band is set between +1% and -1% of the target axial flux deviation value. Modifying the target axial flux deviation value will change the axial flux deviation control band accordingly, ensuring that the core axial flux deviation remains within the control band and increases slowly in a stable and controllable manner when the AO rod is not in operation.

[0042] Optionally, during operation, the axial offset control rod position is maintained at 250 steps, with movements within 2 steps. Specifically, the AO rod position is maintained at 250 steps, with movements within 2 steps, throughout the entire extended operation to ensure control of the AFD during normal fluctuations and prevent divergent xenon oscillations.

[0043] The core's axial flux deviation is maintained within a relatively narrow control band. Therefore, during normal core operation, the core's AFD is controlled within the control band by raising and lowering the AO rods. However, during power reduction and rod extension operations, the AO rods must remain stationary, while the core's AFD is controlled within the operating band. This allows the AFD to increase slowly and in a stable and controllable manner, always remaining within the control band to ensure unit safety. This control method minimizes the possibility of xenon oscillations in the nuclear power plant and improves core safety.

[0044] This solution is based on the extended operation mode of power reduction and control rod lifting at the end of the service life of third-generation nuclear power plants. When the AO rods are not in operation, the core AFD control can be performed by modifying the target AFD value of the unit and then modifying the AFD control band. This solution also comprehensively considers the impact of AFD control on the average temperature deviation. The result of the entire control strategy is that while effectively controlling the core AFD, it also plays a positive role in controlling the average temperature deviation, which helps stabilize the unit state. Currently, there are only four third-generation nuclear power plants in operation worldwide. Currently, there is no research on AFD control during the extended operation process of third-generation nuclear power plants at the end of their service life. This solution can fill the industry gap in AFD control for extended operation at the end of the service life of third-generation nuclear power plants.

[0045] The technical solution of this embodiment adjusts the target axial flux deviation control band by adjusting the target axial flux deviation value when the AO rod cannot be used in the core to control the axial flux deviation, ensuring that the axial flux deviation value of the unit always remains within the target axial flux deviation control band, and slowly increases in a stable and controllable manner to prevent the initiation of divergent xenon oscillations, thereby improving the safety of the extended operation of the unit. At the same time, the impact of the axial flux deviation control on the average temperature deviation is comprehensively considered. While effectively controlling the axial flux deviation of the core, it also plays a positive role in the control of the average temperature deviation, which helps to stabilize the state of the unit. The technical solution of this embodiment solves the problem in the prior art that during the extended operation of a nuclear power plant, the core power margin will tilt toward the upper half of the core, and improper control will easily cause xenon oscillations, which will eventually cause the unit to be shut down for overhaul.

[0046] Figure 2 This is a flow chart of another method for controlling axial flux deviation at the end of reactor life in a nuclear power plant according to an embodiment of the present invention. Figure 2 Optionally, S110, determining the adjustment timing of the target axial flux deviation value according to the average temperature deviation of the unit specifically includes the following steps:

[0047] S111. When the average temperature deviation of the unit meets the first preset condition, wait for the actual axial power deviation value of the unit to be greater than the target axial power deviation value, and adjust the target axial flux deviation;

[0048] S112. When the average temperature deviation of the unit meets the second preset condition, adjust the target axial power deviation value of the unit to the target axial power deviation value of the day.

[0049] Specifically, optionally, the first preset condition is +0.56°C, and the second preset condition is -0.56°C. The timing for adjusting the target axial flux deviation value is determined by judging the average temperature deviation of the unit. When the average temperature deviation of the unit is high, that is, close to +0.56°C, it is necessary to wait until the actual axial power deviation value of the unit is more positive than the target axial power deviation value before adjusting the target axial power deviation value, so as to avoid the AO rod being lifted up due to the adjustment of the target axial power deviation value, thereby further increasing the average temperature deviation. When the average temperature deviation of the unit is negative, that is, close to -0.56°C, the target axial power deviation value of the unit can be adjusted in a positive direction, so that the AO rod can be lifted up to increase the average temperature deviation in the process of controlling the core axial flux deviation.

[0050] Figure 3 This is a flow chart of another method for controlling axial flux deviation at the end of reactor life in a nuclear power plant according to an embodiment of the present invention. Figure 3 Optionally, the method for controlling axial flux deviation at the end of life of a nuclear power plant reactor further includes:

[0051] S210. Simulate and predict the daily axial flux deviation value during the extended operation of the unit.

[0052] Specifically, relying on the online core monitoring system of the third-generation nuclear power plant, a simulation and predictive analysis of the daily axial flux deviation values ​​during the extended operation process was carried out. The analysis results showed that the axial flux deviation values ​​of the core increased by an order of 0.5%-1% per day during the unit's power reduction and rod extension operation.

[0053] S220. Calculate the target axial flux deviation value of the core on the day during the extended operation of the computer group.

[0054] Specifically, during the extended operation of the unit, the online core monitoring system is used to calculate the target axial flux deviation value of the core every day.

[0055] S230. Determine the adjustment timing of the target axial flux deviation value according to the average temperature deviation of the unit.

[0056] S240: If adjustment is required, modify the axial flux deviation control band based on the adjusted target axial flux deviation value, so that the target axial flux deviation value is maintained within the range of the axial flux deviation control band.

[0057] Specifically, the specific processes of S230 and S240 are detailed in the above embodiment and will not be repeated here.

[0058] Figure 4 Schematic diagram of the structure of an axial flux deviation control device for a nuclear power plant reactor at the end of its life provided by an embodiment of the present invention, with reference to Figure 4The embodiment of the present invention further provides a device for controlling an axial flux deviation at the end of the life of a nuclear power plant reactor. The device comprises:

[0059] An adjustment module 30 is configured to determine an adjustment timing for a target axial flux deviation value based on an average temperature deviation of the unit;

[0060] The adjustment module 40 is configured to modify the axial flux deviation control band based on the adjusted target axial flux deviation value if adjustment is required, so that the target axial flux deviation value is maintained within the range of the axial flux deviation control band.

[0061] The above-mentioned nuclear power plant reactor end-of-life axial flux deviation control device can execute the nuclear power plant reactor end-of-life axial flux deviation control method provided by any embodiment of the present invention, and has the corresponding functional modules and beneficial effects for executing the nuclear power plant reactor end-of-life axial flux deviation control method.

[0062] Figure 5 Schematic diagram of the structure of another nuclear power plant reactor end-of-life axial flux deviation control device provided by an embodiment of the present invention, with reference to Figure 5 Optionally, the nuclear power plant reactor end-of-life axial flux deviation control device further includes: a first adjustment unit 301, used to wait for the actual axial power deviation value of the unit to be greater than the target axial power deviation value when the average temperature deviation of the unit meets the first preset condition, and adjust the target axial flux deviation; a second adjustment unit 302, used to adjust the target axial power deviation value of the unit to the target axial power deviation value of the day when the average temperature deviation of the unit meets the second preset condition.

[0063] Continue to refer Figure 5 Optionally, the axial flux deviation control device for the end of the life of a nuclear power plant reactor further includes: a prediction module 10, used to simulate and predict the daily axial flux deviation value during the extended operation of the unit; and a calculation module 20, used to calculate the target axial flux deviation value of the core on that day during the extended operation of the unit.

[0064] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for controlling axial flux deviation at the end of life of a nuclear power plant reactor, characterized in that: include: Determine the adjustment timing of the target axial flux deviation value based on the average temperature deviation of the unit; If adjustment is required, the axial flux deviation control band is modified based on the adjusted target axial flux deviation value so that the target axial flux deviation value is maintained within the range of the axial flux deviation control band.

2. The method according to claim 1, characterized in that The adjustment timing of determining the target axial flux deviation value according to the average temperature deviation of the unit includes: When the average temperature deviation of the unit meets the first preset condition, wait for the actual axial power deviation value of the unit to be greater than the target axial power deviation value, and adjust the target axial flux deviation; When the average temperature deviation of the unit meets the second preset condition, the target axial power deviation value of the unit is adjusted to the target axial power deviation value of the day.

3. The method according to claim 1, characterized in that Before determining the adjustment timing of the target axial flux deviation value according to the average temperature deviation of the unit, the method further includes: The daily axial flux deviation values ​​during the extended operation of the unit are simulated and predicted.

4. The method according to claim 3, characterized in that After simulating and predicting the daily axial flux deviation value during the extended operation of the unit, the method further includes: The target axial flux deviation value of the core on that day during the extended operation of the computer group.

5. The method according to any one of claims 3-4, characterized in that: During the above operation, the position of the axial deflection control rod was maintained at 250 steps, and the operation was performed within 2 steps.

6. The method according to claim 1, characterized in that The axial flux deviation control band is +1% to -1% of the target axial flux deviation value.

7. The method according to claim 2, characterized in that The first preset condition is +0.56°C, and the second preset condition is -0.56°C.

8. A device for controlling axial flux deviation at the end of reactor life in a nuclear power plant, characterized in that: include: An adjustment module, used to determine an adjustment timing of a target axial flux deviation value according to an average temperature deviation of the unit; The adjustment module is configured to modify the axial flux deviation control band based on the adjusted target axial flux deviation value if adjustment is required, so that the target axial flux deviation value is maintained within the range of the axial flux deviation control band.

9. The device according to claim 8, characterized in that Also includes: a first adjusting unit, configured to adjust the target axial flux deviation by waiting for the actual axial power deviation value of the unit to be greater than the target axial power deviation value when the average temperature deviation of the unit satisfies a first preset condition; The second adjustment unit is used to adjust the target axial power deviation value of the unit to the target axial power deviation value of the day when the average temperature deviation of the unit meets the second preset condition.

10. The device according to claim 8, characterized in that Also includes: The prediction module is used to simulate and predict the daily axial flux deviation value during the extended operation of the unit; The calculation module is used to calculate the target axial flux deviation value of the core on the day during the extended operation of the computer group.

Images