Water supply control device and water supply control method

Abstract

To provide a water supply controller capable of suppressing a water level fluctuation width during insertion or extraction of a control rod to realize stable nuclear reactor water level control, and a water supply control method.SOLUTION: A water supply controller receives input of speed information for extraction / insertion of a control rod 2 and information on the number of control rods 2 to be driven (speed information input step, number information input step); and when the extraction / insertion speed of the control rod 2 exceeds a specified value, or when the number of control rods 2 to be driven exceeds a specified value, instructs a water supply pump to change a water level setting value of a nuclear reactor (water level change instruction step).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a water supply control device and a water supply control method. [Background technology]

[0002] As an example of a water level control device that can indirectly detect abnormalities in the reactor feedwater system or reactor feedwater control system that result in a loss or abnormal reduction in reactor feedwater flow rate, and automatically operate when the reactor water level drops, regardless of whether the feedwater pump is operating or stopped, to prevent the reactor from scramming due to a drop in the water level, Patent Document 1 describes a device that monitors the deviation between the reactor main steam flow rate and the reactor feedwater flow rate, and forcibly reduces the core flow rate when the phenomenon in which the reactor feedwater flow rate is less than the reactor main steam flow rate by more than a specified value continues for more than a specified time and the reactor water level drops below a separately specified set value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 62-144098 Summary of the Invention [Problem to be solved by the invention]

[0004] In a boiling-type nuclear power plant, the insertion or withdrawal of control rods increases or decreases the voids in the cooling water in the reactor pressure vessel, causing an increase or decrease in the reactor water level.

[0005] In particular, when the control rod speed is high, the degree of increase in the void reduction becomes large, and the degree of rise or fall of the reactor water level becomes large.

[0006] In this case, if the reactor water level rises too much, it may lead to a turbine trip from the viewpoint of turbine protection. On the other hand, if it falls too low, it may lead to the reactor scram (emergency shutdown). Turbine trips and reactor scrams due to a rise or fall in the reactor water level are undesirable from the viewpoint of stable plant operation.

[0007] One of the measures to improve this problem is to monitor the mismatch (deviation) between the main steam flow rate flowing out of the reactor and the feedwater flow rate flowing in, and to proactively control the rise or fall of the reactor water level using the signal. Also, in the case of an excessive fall in the reactor water level, there is a method to detect the fall and forcibly reduce the core flow rate by running back the recirculation pump (reducing the rotation speed), thereby recovering the fall in the reactor water level. Specifically, the following process is used to avoid a scram due to a fall in the water level.

[0008] (1) Water level rise due to increase in voids By reducing the core flow rate, the number of voids in the cooling water increases, temporarily raising the reactor water level, mitigating the drop in water level caused by a reduction in the feedwater flow rate.

[0009] (2) Optimization of output balance When the core flow rate is reduced and the voids are increased, the nuclear fission reaction decreases and the reactor power decreases, so the main steam flow rate flowing out of the core decreases and the reactor water level is restored.

[0010] In the above-mentioned method, an excessive rise or fall in the reactor water level is detected by monitoring the mismatch (deviation) between the flow rate of main steam flowing out of the reactor and the flow rate of feedwater flowing in, as shown in Patent Document 1, for example.

[0011] Specifically, the mismatch between the main steam flow rate and the feedwater flow rate is calculated, and if a mismatch occurs and the reactor water level rises or falls excessively, the mismatch is converted into an equivalent reactor water level, and the feedwater flow rate is increased or decreased in advance. Furthermore, if the reactor water level falls, a runback signal to run back the recirculation pump is input to the recirculation flow control device of the reactor, thereby reducing the core flow rate. At this time, the reactor power also decreases with the decrease in the core flow rate.

[0012] Conventional water level control devices could mitigate the drop in the reactor water level by forcibly reducing the flow rate of the cooling water to the core, increasing voids, suppressing nuclear fission, and reducing power output. However, natural circulation reactors without recirculation pumps cannot rely on functions to adjust the circulation force, such as the runback function of the recirculation pump. This means that there is a possibility that the amount of water level drop when the control rod is inserted cannot be appropriately adjusted. This water level fluctuation is particularly noticeable in natural circulation reactors, where the control rod speed increases and the water level fluctuation becomes large.

[0013] An object of the present invention is to provide a feedwater control device and a feedwater control method capable of suppressing the range of water level fluctuations when inserting and withdrawing control rods, thereby realizing stable reactor water level control. [Means for solving the problem]

[0014] The present invention includes multiple means for solving the above problems. One example is a feedwater control device that controls the water level of a nuclear reactor, which receives input information on the speed of control rod withdrawal / insertion and information on the number of control rods to be driven, and instructs a feedwater pump to change the water level setting value of the nuclear reactor. Effect of the Invention

[0015] According to the present invention, it is possible to suppress the fluctuation range of the water level when the control rod is inserted or withdrawn, and to realize stable reactor water level control. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing an example of an overall schematic configuration of a nuclear reactor including a feedwater control device according to an embodiment. [Diagram 2] FIG. 1 is a diagram of a feedwater control device and a control rod operation monitoring device of the reference technology. [Diagram 3] A feedwater control device and a control rod operation monitoring device including the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment of the water supply control device and water supply control method of the present invention will be described with reference to Figures 1 to 3. In the drawings used in this specification, the same or corresponding components are denoted by the same or similar reference numerals, and repeated explanations of these components may be omitted.

[0018] First, the overall configuration of the reactor including the control rod operation monitoring device will be explained using Figure 1. Figure 1 shows the configuration of the reactor including the feedwater control device.

[0019] As shown in Figure 1, nuclear fission of atomic nuclei is promoted or suppressed by inserting and withdrawing control rods 2 inside a reactor pressure vessel 1. Nuclear fission causes the coolant inside the reactor to boil, generating steam. The steam generated in the reactor core is sent to a steam turbine 6 through a main steam pipe 3. The steam rotates the steam turbine 6, drives a generator (not shown in the figure), and is then condensed in a condenser 7, becoming cooled water, which is supplied to a feedwater pump 5 and fed back into the reactor pressure vessel 1 through a feedwater pipe 4.

[0020] The nuclear reactor to which the present invention is applied is a boiling water reactor, and more preferably a natural circulation boiling water reactor.

[0021] The reactor water level in the reactor pressure vessel 1 is detected by a reactor water level gauge 10. In addition, steam generated in the reactor pressure vessel 1 passes through a main steam pipe 3, and the amount of this steam is detected by a main steam flow meter 8. Water is supplied to the reactor pressure vessel 1 through a feedwater pipe 4, and the amount of this feedwater is detected by a feedwater flow meter 9.

[0022] During normal constant operation, the main steam flow detection signal S2 detected by the main steam flow meter 8 and the feedwater flow detection signal S3 detected by the feedwater flow meter 9 are constant, and the amount of water injected into and discharged from the reactor pressure vessel 1 are the same, so the reactor water level is maintained constant.

[0023] When the control rod 2 is inserted or withdrawn, a command signal from a control rod operation monitoring device 12 is sent to a drive inverter motor 13 .

[0024] The command signals from this control rod operation monitoring device 12 include a control rod insertion signal S5, a control rod withdrawal signal S6, a control rod drive speed command signal S7, and a drive control rod number command signal S8, and each command signal changes depending on the plant state.

[0025] The drive inverter motor 13 receives a signal from the control rod operation monitoring device 12 and outputs a control rod drive command S9, whereby the control rod 2 is inserted or withdrawn.

[0026] In existing reactors, the reactor water level fluctuates when the control rod 2 is inserted and withdrawn as described above. When the control rod 2 is withdrawn, nuclear fission is promoted, the coolant in the reactor boils, and voids increase. At this time, the reactor water level rises as the voids increase. On the other hand, when the control rod 2 is inserted, nuclear fission is suppressed, and the boiling of the coolant in the reactor is suppressed, so the voids decrease. At this time, the reactor water level falls as the voids decrease.

[0027] An example of reactor water level suppression during normal operation when control rod 2 is withdrawn and inserted is shown below.

[0028] Figure 2 shows the configuration of the existing control rod operation monitoring device and feedwater control device and the flow of their control signals.

[0029] 2, in the control rod operation monitoring device 12, an operator manually or automatically presses a pull / insert PB 14 for the control rod 2. According to this signal and the plant status, a control rod selection unit 15 selects one or more control rods 2 to be driven.

[0030] Thereafter, the drive speed is determined in the control rod drive speed command unit 16 (in existing boiling water nuclear power plants, the control rod drive speed is constant: (existing is a constant speed)) and transmitted to the drive inverter motor 13. Based on the transmitted control rod drive speed command signal S7, the control rod 2 is pulled out and inserted.

[0031] The withdrawal and insertion of the control rod 2 causes the reactor water level to fluctuate as described above.

[0032] Specifically, the steam flow rate generated in the core increases during the withdrawal operation. If the steam flow rate increases from a state in which the feedwater flow rate and steam flow rate of the reactor pressure vessel 1 are constant, the feedwater flow rate will eventually become less than the steam flow rate, and the reactor water level will decrease.

[0033] On the other hand, the steam flow rate generated in the core decreases during the insertion operation. If the steam flow rate decreases, the feedwater flow rate will eventually exceed the steam flow rate, and the reactor water level will rise.

[0034] In other words, by observing the deviation (mismatch) between the feedwater flow rate and the steam flow rate, it is possible to predict whether the future reactor water level will rise or fall, and this mismatch signal can be used as a leading control signal for reactor water level control. Based on the above principle, the following control is performed within the feedwater control device 111 in Figure 2 of the reference technology.

[0035] The feedwater control device 111 includes a water level setting 17 for setting the reactor water level to a preset value.

[0036] The feedwater control device 111 has two methods (1) to control the reactor water level by generating a feedwater flow rate command signal S4 depending only on the deviation (subtractor 31) between the reactor water level detection signal S1 and the water level setting 17 (connection 33, single element control), and (2) to add the deviation (subtractor 32, mismatch) between the main steam flow rate detection signal S2 from the reactor and the feedwater flow rate detection signal S3 supplied by the feedwater pump 5 to the deviation between the reactor water level detection signal S1 and the water level setting 17 (adder 34), to generate the feedwater flow rate command signal S4 and control the reactor water level in advance (connection 35, three element control).Then, the water level change instruction signal S13 obtained by performing proportional integral calculation processing on the feedwater flow rate command signal S4 by the proportional integral calculator 18 is output to the feedwater pump 5.

[0037] When the control rod 2 is withdrawn, the reactor water level detection signal S1 increases due to an increase in voids. After a short time, the main steam flow detection signal S2 also increases. When the control rod 2 is inserted, the reactor water level detection signal S1 decreases due to a decrease in voids. After a short time, the main steam flow detection signal S2 also decreases. Based on these signals, if the reactor water level decreases, the feedwater flow command signal S4 is increased and a feedwater flow increase signal is output to the feedwater pump 5.

[0038] When the reactor water level increases, the feedwater flow rate command signal S4 is decreased and a feedwater flow rate decrease signal is output to the feedwater pump 5. As a result, the reactor water level recovers and the water level transitions to a stable state.

[0039] In this manner, when using the feedwater control device 111 as shown in FIG. 2, the control rod operation monitoring device 12 will drive the control rod 2 simultaneously with or shortly after the water level is changed in accordance with the instruction to change the water level.

[0040] In the conventional feedwater control device 111 shown in Fig. 2, the core flow rate of the cooling water can be forcibly reduced to mitigate the drop in the reactor water level. However, in a natural circulation reactor without a recirculation pump, the runback function of the recirculation pump cannot be relied upon. For this reason, there is a possibility that the water level drop becomes large when the control rod 2 is inserted, making it impossible to appropriately adjust the water level. This water level fluctuation is particularly noticeable in a natural circulation reactor where the speed of the control rod 2 increases and the water level fluctuation becomes large.

[0041] The present invention relates to a feedwater control device that can suppress the fluctuation range of the water level when inserting or withdrawing a control rod 2 in a natural circulation reactor and realize stable reactor water level control. Next, the configuration of the feedwater control device of the present invention will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of the schematic configuration of the feedwater control device of the embodiment.

[0042] The feedwater control device 11 shown in Figure 3 is a device for controlling the water level in a nuclear reactor, and is the same as the feedwater control device 111 of the reference technology shown in Figure 2 in that it has the above-mentioned (1) single-element control and (2) three-element control.

[0043] The feedwater control device 11 further includes a corrected water level signal generator 24 that instructs the feedwater pump 5 to change the reactor water level setting value, and an adder 25 adds a control rod speed / number-dependent water level correction signal S10 generated by the corrected water level signal generator 24 to a feedwater flow rate command signal S4 to generate an instruction signal S14. Thereafter, a proportional-integral calculation process is performed on the instruction signal S14 by the proportional-integral calculator 18, and a water level change instruction signal S13A is output to the feedwater pump 5 (water level change instruction step).

[0044] This corrected water level signal generator 24 is characterized by detecting a control rod drive speed command signal S7 (speed information for the withdrawal / insertion of control rod 2) and a drive control rod number command signal S8 (information on the number of control rods 2 to be driven) when inserting and withdrawing control rod 2, which cause fluctuations in the reactor water level (speed information input step, number information input step), and generating a control rod speed / number-dependent water level correction signal S10, thereby proactively adjusting the reactor water level, and has proportional units 19, 20, an adder 21, a sign inverter 22, and a multiplier 23.

[0045] When the number of control rods 2 to be driven in the driving control rod number command signal S8 exceeds a predetermined value, the proportionality factor (K1) is multiplied by the driving control rod number command signal S8 to generate a second water level correction signal S12.

[0046] When the withdrawal / insertion speed of the control rod 2 in the control rod drive speed command signal S7 exceeds a predetermined value, the proportionality controller 20 generates a first water level correction signal S11 by multiplying the control rod drive speed command signal S7 by a proportionality coefficient (K2).

[0047] The specific values ​​of the proportionality coefficient K1 used in the proportional controller 19 and the proportionality coefficient K2 used in the proportional controller 20 are based on the test results in an actual plant, but for example, the outline is as follows.

[0048] Proportional coefficient K1 (cm / number of drive control rods): Water level fluctuation range per control rod 2 Example: 1 piece gives a 1cm fluctuation, 26 pieces give a 5cm fluctuation → calculate K1.

[0049] Proportional coefficient K2 (cm / control rod drive speed): Actual water level fluctuation range at control rod drive speed Example: 5cm fluctuation at 33mm / sec, 10cm fluctuation at 66mm / sec → calculate K2.

[0050] Although the configuration has been described in which the proportional controller 19 generates the second water level correction signal S12 when the number of control rods 2 being driven exceeds a predetermined value, and the proportional controller 20 generates the first water level correction signal S11 when the withdrawal / insertion speed of the control rods 2 exceeds a predetermined value, the proportional controllers 19 and 20 are not limited to a configuration in which they each instruct the feedwater pump to change the set value of the water level of the reactor when the withdrawal / insertion speed of the control rods 2 exceeds a predetermined value or when the number of control rods 2 being driven exceeds a predetermined value, the configuration may be such that the proportional controller 19 generates the second water level correction signal S12 by multiplying the number of driven control rods command signal S8 by a proportionality coefficient (K1), and / or the proportional controller 20 generates the first water level correction signal S11 by multiplying the control rod drive speed command signal S7 by a proportionality coefficient (K2).

[0051] The adder 21 is a part that adds a water level correction signal that depends on the withdrawal / insertion speed of the control rod 2 and the number of control rods 2 to be driven to the difference value between the feedwater flow rate by the feedwater pump 5 and the main steam flow rate, and specifically, adds the second water level correction signal S12 to the first water level correction signal S11 to generate a control rod speed / number dependent water level correction signal S10.

[0052] The sign inverter 22 and the multiplier 23 are components for making the water level correction signal positive when the control rod 2 is inserted, which reduces the water level in the reactor, and making the water level correction signal negative when the control rod 2 is withdrawn, which increases the water level in the reactor.

[0053] The sign inverter 22 inverts the sign of the control rod speed / number dependent water level correction signal S10 when the control rod 2 is inserted, which reduces the reactor water level, and the sign of the control rod speed / number dependent water level correction signal S10 is negative when the control rod 2 is withdrawn, which increases the reactor water level. In this way, the sign inverter 22 inverts the sign of the control rod speed / number dependent water level correction signal S10 when the control rod withdrawal signal S6 is generated.

[0054] The multiplier 23 multiplies the output of the sign inverter 22 by the control rod speed / number dependent water level correction signal S10.

[0055] Next, the effects of this embodiment will be described.

[0056] The feedwater control device 11, which controls the water level of the reactor in the above-mentioned embodiment, receives input of information on the withdrawal / insertion speed of the control rods 2 and information on the number of control rods 2 to be driven (speed information input step, number information input step), and instructs the feedwater pump to change the set value of the reactor's water level (water level change instruction step).

[0057] According to the present invention, by proactively adjusting the reactor feedwater flow rate, it is possible to suppress unnecessary increases or decreases in the reactor water level and realize stable reactor water level control, thereby providing a feedwater control device / method that is particularly suitable for natural circulation reactors that do not have a recirculation pump and cannot rely on the runback function of the recirculation pump.

[0058] In addition, when the withdrawal / insertion speed of the control rods 2 exceeds a predetermined value, or when the number of driven control rods 2 exceeds a predetermined value, an instruction is given to the feedwater pump to change the reactor water level setting value, thereby reducing the frequency with which proactive reactor feedwater flow rate adjustments are made and achieving stable water level control.

[0059] Furthermore, a water level correction signal that depends on the withdrawal / insertion speed of the control rod 2 and the number of control rods 2 being driven is added to the difference between the feedwater flow rate by the feedwater pump and the main steam flow rate. More specifically, the water level correction signal is generated by multiplying the number of control rods 2 being driven by information on the actual water level fluctuation range at the driving speed of the control rod 2, or by multiplying the withdrawal / insertion speed of the control rod 2 by information on the water level fluctuation range per control rod 2, thereby making it possible to generate a water level change instruction signal S13A that corresponds to the predicted amount of actual water level fluctuation.

[0060] Furthermore, by making the water level correction signal positive when the control rod 2 is inserted, which reduces the water level in the reactor, and making the water level correction signal negative when the control rod 2 is withdrawn, which increases the water level in the reactor, it is possible to generate a water level correction signal in response to the insertion / removal of the control rod 2 simply by providing a configuration for reversing the sign, thereby simplifying the configuration of the control system.

[0061] <Other> The present invention is not limited to the above-mentioned embodiment, and various modifications and applications are possible. The above-mentioned embodiment has been described in detail to explain the present invention in an easily understandable manner, and the present invention is not necessarily limited to having all of the described configurations. [Explanation of symbols]

[0062] 1: Reactor pressure vessel 2: Control rod 3: Main steam piping 4: Water supply piping 5: Water supply pump 6: Steam turbine 7: Condenser 8: Main steam flow meter 9: Water supply flow meter 10:Reactor water level gauge 11,111: Water supply control device 12: Control rod operation monitoring device 13: Drive inverter / motor 14: Insertion and removal PB 15: Control rod selection section 16: Control rod drive speed command unit 17: Water level setting 18: Proportional integral calculator 19:Proportionalizer (K1) 20:Proportionalizer (K2) 21: Adder 22: Sign inverter 23: Multiplier 24: Compensated water level signal generator 25: Adder 31: Subtractor 32: Subtractor 33: Connection 34: Adder 35: Connection K1, K2: proportionality coefficients S1: Reactor water level detection signal S2: Main steam flow detection signal S3: Water supply flow rate detection signal S4: Water supply flow rate command signal S5: Control rod insertion signal S6: Control rod withdrawal signal S7: Control rod drive speed command signal S8: Drive control rod number command signal S9: Control rod drive command S10: Control rod speed / number dependent water level correction signal S11: 1st water level correction signal S12: 2nd water level correction signal S13, S13A: Water level change instruction signal S14: Instruction signal

Claims

1. A feedwater control device for controlling the water level of a nuclear reactor, In response to input of information on the speed of control rod withdrawal / insertion and the number of control rods to be driven, the system instructs the feedwater pump to change the water level setting of the reactor. Water supply control device.

2. The water supply control device according to claim 1, The feedwater control device instructs the feedwater pump to change the water level setting value of the reactor when the withdrawal / insertion speed of the control rod exceeds a predetermined value or when the number of the control rods being driven exceeds a predetermined value. Water supply control device.

3. The water supply control device according to claim 2, A water level correction signal that depends on the withdrawal / insertion speed of the control rod and the number of the control rods to be driven is added to the difference between the feedwater flow rate by the feedwater pump and the main steam flow rate. Water supply control device.

4. The water supply control device according to claim 3, As the water level correction signal, the number of the control rods to be driven is multiplied by information on the water level fluctuation range at the drive speed of the control rods. Water supply control device.

5. The water supply control device according to claim 3, As the water level correction signal, the withdrawal / insertion speed of the control rod is multiplied by information on the water level fluctuation range per one of the control rods. Water supply control device.

6. The water supply control device according to claim 3, When the control rod is inserted, the water level of the reactor decreases, and when the control rod is withdrawn, the water level correction signal is made negative. Water supply control device.

7. The water supply control device according to claim 1, The reactor is a natural circulation reactor. Water supply control device.

8. A method for controlling a water level in a nuclear reactor, comprising: a speed information input step of receiving input of speed information of withdrawal / insertion of the control rod; A number information input step of receiving input of information on the number of control rods to be driven; and a water level change instruction step of instructing a feedwater pump to change the water level setting value of the reactor. Water supply control method.

9. 9. The water supply control method according to claim 8, In the water level change instruction step, when the withdrawal / insertion speed of the control rods received in the speed information input step exceeds a predetermined value, or when the number of the control rods to be driven received in the number information input step exceeds a predetermined value, an instruction is given to a feedwater pump to change a water level setting value of the reactor. Water supply control method.

10. 10. The water supply control method according to claim 9, In the water level change instruction step, a water level correction signal depending on the withdrawal / insertion speed of the control rod and the number of the control rods to be driven is added to a difference value between the feedwater flow rate by the feedwater pump and the main steam flow rate. Water supply control method.

11. The water supply control method according to claim 10, In the water level change instruction step, the number of the control rods to be driven, which is received in the speed information input step, is multiplied with information on the water level fluctuation range results at the drive speed of the control rods, to obtain the water level correction signal. Water supply control method.

12. The water supply control method according to claim 10, In the water level change instruction step, the water level correction signal is obtained by multiplying the withdrawal / insertion speed of the control rod received in the number information input step by information on the water level fluctuation range per one of the control rods. Water supply control method.

13. The water supply control method according to claim 10, In the water level change instruction step, the water level correction signal is set to be positive when the control rod is inserted, which reduces the water level of the reactor, and the water level correction signal is set to be negative when the control rod is withdrawn, which increases the water level of the reactor. Water supply control method.

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