JPS62112902A - Feedwater controller for nuclear reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a nuclear reactor feed water control system, particularly when the recirculation pump speed (or equivalent recirculation pump flow rate or core flow rate) changes suddenly. The present invention relates to a water supply control device suitable for suppressing fluctuations in reactor water level.

[Background of the invention]

FIG. 2 shows a conventional BWR type nuclear power plant water supply and recirculation flow control system. The steam generated in the reactor 1 passes through the main steam pipe 2, through the control valve 3, and enters the main turbine 4, where it generates mechanical energy and is condensed in the condenser 5 and returned to water. This water is supplied by water pumps 6A, 6B, 6G,
The water is returned to the reactor 1 via a water supply pipe 7 by a water supply pump 6 made of 6D.

A reactor feed water flow control system is provided. BWR type 1'
The main purpose of the feed water flow rate control system, which is one of the most important control systems in a nuclear power plant, is to keep the reactor water level 8 constant at a predetermined optimum value. The difference signal between the main steam flow rate signal 10 and the feed water flow rate signal 11 is multiplied by the mismatch gain 12, and the sum signal of the nine mismatch flow rate signal 13 and the reactor water level detected by the detector 9 is determined as the reactor water level setting value (Ref). A difference signal 14 is obtained. This difference signal 14 is subjected to a proportional-integral (PI) control calculation in the feedwater main controller 15 , and the signal corrected by the function generator 17 is input to the feedwater pump turbine controller 18 . The turbine controller output controls the rotational speed of the water supply turbine 19 using the regulating valve 20, and the flow rate of the water supply pump 6 is adjusted. Two water supply pumps are normally driven by turbines (6A, 6B), each having a capacity of about 55%, and two pumps are always operated. Furthermore, motor-driven water supply pumps (6G, 6D) are installed as a standby system. The capacity of motor-driven pump is 27.5% per unit.
It has a capacity of

On the other hand, a reactor recirculation flow control system is provided to continuously control reactor power by varying the reactor recirculation flow rate. An example of recirculation flow rate control is to use a drive motor 21.1 as shown in FIG. A fluid coupling 22 constitutes an M/G set with an alternator 23, and the generator speed, ie, frequency, is controlled by controlling the position of the scoop pipe (not shown) of the fluid coupling. The load on the generator is the motor 26 of the recirculation pump 25, and the frequency of the motor is continuously controlled to change the core flow rate. The control system includes a speed requestor 28 from a recirculation main controller 27 and a generator speed signal 24.
The deviation signal is subjected to PI calculation by the speed controller 29, and the signal corrected by the function generator 30 is configured to become the scoop pipe position signal of the fluid coupling 22. Recirculation pump 25. M/
The G set and the speed controller 29 are usually composed of two systems.

By the way, in general, in automatic frequency control (AFC) operation, an automatic frequency control signal, which is a load request signal with a variation width of about ±5% at intervals of 1 to 5 minutes, is used as a load request signal in the reactor recirculation flow control system. is input, which changes the recirculation flow, core flow, and main steam flow signals, causing the turbine generator output to follow the automatic frequency control signal.

At this time, as the main steam flow rate signal 13 increases or decreases, the water supply flow rate signal 14 also increases or decreases in a manner that follows, but the detection mechanism and Since there is a delay in the reactor water supply control system, the response of the water supply flow rate is delayed, and the reactor water level ξ3 oscillates as shown by curve a in FIG. 3.

In other words, in Fig. 3, the horizontal axis shows time and the vertical axis shows the reactor water level, and when the rectangular automatic frequency control signal shown in the curve is input, the reactor water level will change as shown in curve a. Changes to

According to the analysis, this reactor water level fluctuation range is approximately ±6G for a load request fluctuation range of approximately ±5%, but considering the measurement error of the reactor water level gauge 9 of at least 2 to 3 cm, There is a risk of a low water level alarm occurring at water level L4, which is set approximately 11G below the reference water level, or a high water level alarm occurring at water level L7, which is set approximately 9" below the reference water level. In this case, There is a risk that an alarm will occur every time the automatic frequency control signal is input.

On the other hand, when the automatic frequency control signal is input, the rotation speed of the recirculation hopper 25.32 increases or decreases, the core flow rate increases or decreases, the turbine generator output increases or decreases, and at this time, the feed water flow rate also increases or decreases as the main steam flow rate increases or decreases. Although it increases and decreases in a following manner, there is a problem that the reactor water level fluctuation range becomes large because the response of the feed water flow rate is slow.

As a method of suppressing fluctuations in the reactor water level, for example, as shown in Japanese Patent Laid-Open No. 59-40200, a differential signal of the turbine steam flow rate is added to the main water supply controller output signal 16 in the reactor feed water control system. It is known that the opening degree of the water supply control valve is controlled using this signal. This method can suppress fluctuations in the reactor water level to some extent, but since the control signal is a differential signal of the turbine steam flow rate,
The response may be delayed and it may not always be possible to control the reactor water level in a sufficiently stable manner.

[Purpose of the invention]

- An object of the present invention is to provide a reactor water supply control device that minimizes the range of unnecessary fluctuations in the reactor water level during automatic frequency control operation.

[Summary of the invention]

The present invention adds a differential signal of the recirculation pump speed (or the equivalent recirculation pump flow rate or core flow rate) to the feed water main controller output signal of the reactor feed water control system as a correction signal, thereby increasing the main steam flow rate. Prior to the change, the reactor water level control signal was controlled in advance to minimize fluctuations in the yX child reactor water level.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the invention. The same symbols as in the conventional example in FIG. 2 indicate the same contents. This embodiment is implemented by attaching a reactor water level setting regulator 100 surrounded by a broken line to the conventional reactor water supply control system shown in FIG. The main part is that the reactor water level setting request signal 35 is used to correct the water supply main controller output signal 16 of the reactor water supply control system. This is determined by the recirculation pump speed 33 by the recirculation pump speed detector.
．． 34 is detected, and the reactor water level setting regulator 100 calculates and outputs the rate of change of the sum of the recirculation pump speeds.

It is known that the rate of decrease in recirculation pump speed is approximately proportional to the rate of decrease in recirculation pump flow rate, and that the amount of increase in voids in the core during transient periods is approximately proportional to the rate of decrease in recirculation flow rate. The output 35 of the water level setting regulator 100 is a value that estimates the amount of change in the reactor water level that occurs when the recirculation pump speed fluctuates, and the output signal as a result of comparing it with the water supply main controller output signal 16 is the value that indicates the amount of change in the reactor water level that occurs when the recirculation pump speed fluctuates. This is an actual reactor water level setting request signal that is modified to take into account and compensate for the disturbance that occurs.

FIG. 4 is a more specific embodiment of the present invention, and shows a configuration diagram of a reactor water level setting regulator 100. This regulator 100
consists of a differential calculator 110 and a signal limiter 120. The differential calculator 110 takes in the sum of the A-system recirculation pump speed signal 33 and the B-system recirculation pump speed signal 34, performs an incomplete differential calculation, and outputs the sum. In addition to cutting the signal, upper and lower signal limits are applied to cut excessive signals, and the signal is output. Here, appropriate values can be obtained for the time constant T and gain K of the differential calculator 110 and the signal cut setting value of the signal limiter 120 through simulation analysis or actual machine testing. The output 35 of the signal limiter 120 is added to the water supply main controller output signal 16 in an adder, and the result is input to the function generator 17 as a modified reactor water level setting request signal.

FIG. 5 shows the response during automatic frequency control operation according to the embodiment described above. Due to the rectangular reduction request of the recirculation flow rate request signal, the recirculation pump speed and recirculation pump flow rate follow and decrease with a slight delay, but due to the advance correction water level request compensation number 35 calculated from the rate of change of the recirculation pump speed, A rapid and large reduction in the feed water flow rate is realized, and therefore the rise in the reactor water level is significantly reduced. In addition, a good reactor water level can be maintained even in the case of a rectangular increase request, ramp-like decrease request, ramp-like increase request of the recirculation flow rate request signal, or disturbances that cause large fluctuations in the recirculation flow rate, such as a recirculation pump trip. Control characteristics can be achieved.

FIG. 6 shows another embodiment of the reactor water level setting regulator 100. This regulator 100 consists of a differential calculator 130 and a function generator 150. The differential calculator 130 takes in the sum of the A-system recirculation pump speed signal 33 and the B-system recirculation pump speed signal 34, performs an incomplete differential calculation, and outputs it.
At 50, the signal is converted and output as shown in FIG. Here, appropriate values for the specific number T and gain of the differential calculator 130 and the function shape of the function generator 150 can be obtained through simulation analysis or actual machine testing. The output 35 of the function generator 150 is summed with the feed water main controller output signal 16 in an adder to form a corrected reactor water level setting request signal.
It is input to the function generator 17.

FIG. 7 shows an embodiment of the function generator 150.

The reactor water level setting regulator 100 described above is one example, and the time constant T can be set by using a computer program, for example.

The gain K is optimally changed depending on the reactor output state.

Alternatively, it is also possible to continuously set the function shapes of the signal limiter and function generator.

Further, in this embodiment, the input signal of the reactor water level setting regulator 100 is the recirculation pump speed, but the number of drops of the recirculation pump and the reactor core flow rate may also be used as parameters.

〔Effect of the invention〕

According to the present invention, it is possible to significantly suppress fluctuations in the reactor water level due to automatic frequency control operation, and it is possible to realize rotation.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is a system diagram of a conventional example, and FIG. 3 is a graph showing changes in reactor water level when controlled by the water supply control device shown in FIG. Figure 4 is the first
Figure 5 is a diagram showing the response of the main parameters when controlled by the water supply control device shown in Figure 1. Figure 6 is a reactor water level setting different from Figure 4. FIG. 7 is a diagram showing an example of the function shape of the function generator attached in FIG. 6. 1... Nuclear reactor, 15... Water supply main controller, 100...
・Reactor water level setting regulator.

Claims (1)

[Claims] 1. In a reactor water supply control system equipped with a water level regulator that constantly controls the water level in the reactor pressure vessel to a target value, means for acquiring the recirculation pump speed of the reactor and detecting its rate of change over time; A nuclear reactor water supply control device characterized in that a cutoff for receiving a water level request signal according to the rate of change is added as a preliminary control element of the water level regulator.