JPH0368360B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a nuclear reactor feed water control device that controls a reactor feed water pump and maintains a constant water level in the reactor.

(b) Prior art In general, for boiling water reactors, a reactor reference water level is determined that is necessary for stable operation of the reactor, and no matter what operating state the reactor is in, the reactor reference water level is Deviations in reactor water level must be within permissible limits. In the event that the reactor water level deviates from this allowable range,
Due to reactor scram, the reactor must be shut down, and maintaining the reactor water level at a reference value is extremely important in boiling water reactors. On the other hand, the reactor water level tends to constantly fluctuate due to changes in the flow rate of steam flowing out from the reactor to the turbine depending on the reactor output, so in order to maintain the reactor water level at the standard value, it is necessary to Flow rate must be controlled. The device provided for this purpose is the reactor water supply control device.
Normally, the flow rate of feed water sent to the reactor is controlled by changing the rotational speed of the reactor feed water pump or the opening degree of a flow rate regulating valve provided at the outlet of the reactor feed water pump.

Figure 1 shows an example. 1 is a nuclear reactor, 2 is a water supply pump for sending water into the reactor, and 3 is a flow rate adjustment device installed at the outlet of the water supply pump 2 to adjust the water supply flow rate. 4 is a water level setting device that provides a reactor reference water level; 5 is a water level detector that detects the reactor water level; 6 is a water level setting signal L ₁ from the water level setting device 4 and a water level signal L ₂ from the water level detector 5; A water level controller that inputs and calculates the water supply flow rate command signal _L4 ,
7 is a flow rate controller that controls the opening degree of the flow rate adjustment valve 3 based on the water supply flow rate command signal _L4 .

FIG. 2 is a block diagram showing the operation of the above configuration, where G ₁ (S) represents the transfer function representing the water level controller 6, and G ₂ (S) represents the water supply flow rate controller 7 and the flow rate regulating valve 3. The transfer function G ₃ (S) is a transfer function representing the reactor 1. The deviation signal (water level deviation signal) L ₃ (S) of the water level setting signal L ₁ (S) is input to the water level controller transfer function G ₁ (S), and the water supply flow rate command signal L ₄
(S) is the transfer function G ₂ of the flow controller and flow adjustment valve
(S) is input. The output of the transfer function G ₂ (S) of the flow rate controller and flow regulating valve becomes the feed water flow rate L ₅ (S), which is subtracted from the steam flow rate L ₆ (S), and then becomes the reactor transfer function G ₃ (S). is input. reactor transfer function
The output of G ₃ (S) is the water level signal L ₂ (S). The reason why the steam flow rate L ₆ (S) is shown in FIG. 2 is that the steam flow rate acts as a disturbance signal on the reactor feed water control system. At this time, the water level deviation signal L ₃ (S) can be expressed by the following equation.

L ₃ (S) = 1/1 + G ₁ G ₂ G ₃ (S) L ₁ (S) + 1/
1+G ₁ G ₂ (S) L ₆ (S)...(1) Normally, the water level controller 6 has a proportional gain, and the combined flow rate controller 7 and flow rate adjustment valve 3 has an O type (i.e. lim S→0G( S)=α), reactor 1 is expressed by an integral element, so G ₁ (S)=K ...(2-A) lim S→0G ₂ (S)=α ...(2-B) G ₃ (S)=1/T _R S (T _R : reactor time constant)
...(2-C) Therefore, equation (1) is transformed as follows.

L ₃ (S) = T _R S / T _R S + KG ₂ (S) L ₁ (S) +
1/1+KG ₂ (S) L ₆ (S)...(3) Therefore, for step-like changes in L ₁ (S) and L ₆ (S), by using the final value theorem of Laplace return, L It can be seen that the steady value of ₃ is L ₃ = 1/1 + KαL ₆ ... (4). Therefore, by making K sufficiently large, L ₃ ≒ 0 can be achieved without being affected by L ₆ , that is, the steam flow rate that becomes a disturbance signal, and the water level setting signal
It becomes possible to keep the deviation of the water level signal L ₂ from L ₁ within an allowable range.

However, in practice, it is not possible to increase the value of K due to the stability of the control system, so the water level deviation signal
_L3 cannot be made zero, and a deviation that cannot be ignored in terms of control occurs between the water level setting signal _L1 and the water level signal _L2 . Furthermore, as is clear from equation (4), the deviation increases in proportion to the steam flow rate signal L ₆ , so the larger the reactor output, the more the water level deviation from the reference water level will increase even with a slight disturbance to the control system. The possibility of deviating from the allowable range required for safe driving increases.

Normally, in order to make such a deviation signal completely zero, it is sufficient to use a controller that includes an integral element such as a PID, but in the reactor feed water control system, since the reactor 1 itself has integral characteristics, If a transfer function including a PID equal integral element is adopted as the water level controller 6, the control system will inevitably become unstable, and a controller including a PID equal integral element cannot be used.

In addition, in FIGS. 1 and 2, only one reactor feed water pump 2 is used to simplify the explanation, but in an actual plant, there are motor-driven water pumps, turbine-driven water pumps, etc. Multiple pumps with different characteristics are arranged, and the number of pumps in operation is switched depending on the operating status of the reactor, so α in equation (4) changes as the number of pumps in operation changes, resulting in fluctuations in the water level.

The above explanation is for the case where the feedback signal to the water level controller 6 is only the water level signal ₂ (this case is generally referred to as single-element control).
As a feedback signal, there is a control system that uses a steam flow rate signal and a water supply flow rate signal in addition to the water level signal L ₂ (this case is called three-element control). It has both control functions, and either control method can be selected. During three-element control, since the main steam flow rate signal is used as a feedback signal, it is possible to reduce the water level deviation signal _L3 to zero, but
In practice, the steam flow rate signal and the feed water flow rate signal cannot be used for control because the accuracy of each detector is inaccurate in the low flow region, and three-element control can only be used in a region where the reactor output is large. Therefore, even if the water level controller has a three-element control function, single-element control must be selected in the low power region of the reactor, and the above-mentioned problems cannot be solved. Furthermore, when the water level controller 6 is switched from single-element control to three-element control, or from three-element control to single-element control, the water level always fluctuates, which is unfavorable for operation.

(c) Purpose of the Invention The purpose of the present invention is to construct a control system that is stable under any operating state of the reactor, and to eliminate the difference between the water level of the reactor and the set water level, which could not be eliminated with the prior art. An object of the present invention is to provide a reactor water supply control device that can eliminate deviations in control accuracy caused by water level deviations.

(d) Structure of the Invention Hereinafter, as an embodiment of the present invention, a nuclear reactor feed water control system employing a PID controller as a water level controller including an integral element will be described with reference to FIGS. 3 and 4. FIG. 3 is a configuration diagram of a nuclear reactor feed water control system showing one embodiment of the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same or equivalent parts. The difference from the configuration in Fig. 1 is that the water level signal _L1 is controlled by a stabilizer 8 which has control characteristics including a proportional gain (comparison element).
The two points are that a stabilizing loop is provided to combine the correction signal outputted through the water level controller 6 with the water level deviation control signal L7 outputted from the water level controller 6, and that a RID controller is adopted as the water level controller 6.

FIG. 4 is a block diagram showing the operation of the above structure. In the diagram, the same symbols as in Figure 1 indicate the same or equivalent parts as in Figure 2, and the difference from the block diagram in Figure 3 is that the transfer function G ₄ (S) of the stabilizer 8 is inserted at the relevant location. and that the transfer function G ₁ (S) of the water level controller is a PID controller as shown below.

G ₁ (S)=K _P +K _I /S+K _P S (5) At this time, the water level deviation signal L ₃ (S) is expressed by the following equation.

L ₃ (S) = (1 + G ₂ G ₃ G ₄ ) L ₁ + G ₃ + L ₆ /1 + G ₁ G ₂ G ₃ (S
)+G ₂ G ₃ G ₄ (S)...(6) Here, the transfer function of the water level controller 6 is expressed by the equation (5), and the transfer function of the reactor 1 is expressed by the equation (2-C), and is simple. For the purpose of calculation, if the transfer function of the stabilizer 8 is a proportional gain of G ₄ (S)=K _F , equation (6) can be transformed as follows.

L ₃ (S) = S (T _R S + K _F G ₂ ) L ₁ (S) + SL ₆ (S) / S _R S ²
+(K _I +K _P S+K _D S ² G ₂ +K _F G ₂
...(7) Therefore, since the linear term of S appears in the denominator of the transfer function in equation (7), it is difficult to By using the final value theorem of Laplace transform and equation (2-B), L ₃ =0 (8). Therefore, it is not affected by the steam flow rate,
The water level deviation signal _L3 is made completely zero, enabling a stable control system.

In order to simplify the explanation above, the feedback signal to the water level controller 6 is only the water level signal _L2 , but a three-element control method using the water level signal _L2 , steam flow rate signal _L6 , and feed water flow rate signal is used. It doesn't matter if it is. In addition, although the flow rate controller 7 was assumed to control the flow rate adjustment valve 3, as is clear from the fact that the only assumption for deriving equation (8) is equation (2-B),
It is sufficient if it simply satisfies equation (2-B).
Therefore, the present invention is equally applicable to a system in which the flow rate controller 7 controls the rotational speed of the water supply pump 2, for example. Further, the transfer function G4(S) of the stabilizer 8 only needs to include a proportional gain element, and is not limited to one having control characteristics only with the proportional element.

(e) Effects of the Invention As explained above, according to the present invention, even during single-element control in which only the water level signal _L2 is used as a feedback signal to the water level controller 6, it is theoretically independent of the steam flow rate. The water level deviation can be reduced to zero.
Therefore, it is possible to make the water level match the reference water level no matter what operating state the reactor is in, and compared to conventional methods, water level deviations due to disturbances to the control system are less than the tolerance required for safe operation of the reactor. The possibility of going out of range is reduced. In addition, since water level deviation does not normally occur, water level fluctuations that would otherwise occur due to water level deviation occur when changing the number of pumps in operation, when switching from three-element control to single-element control, or when switching from single-element control to three-element control. can be removed.
Furthermore, since no water level deviation occurs during single-element control, the feedback of the steam flow rate signal and feedwater flow rate signal, which were conventionally used to reduce the water level deviation to zero, can be used for other purposes, such as improving the speed response of water supply example control,
It can be used for purposes such as improving stability, and since an integral element such as a PID controller is adopted in the water level controller 6, and the transfer function of the stabilizer 8 can be selected from a wide range, control performance is significantly improved compared to conventional methods. .

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a conventional reactor feed water control system, Fig. 2 is a block diagram showing the operation of conventional reactor feed water control steam, and Fig. 3 is a block diagram showing an embodiment of the present invention. , FIG. 4 is a block diagram showing the operation of one embodiment of the present invention. 1... Nuclear reactor, 2... Nuclear reactor feed water pump, 3...
...Flow rate adjustment valve, 4...Water level setter, 5...Water level detector, 6...Water level controller, 7...Flow rate controller, 8
...Stabilizer.

Claims (1)

[Claims] 1. A water level setting device that outputs a water level setting signal for setting the water level of the reactor, a water level detector that detects the water level of the reactor and outputs a water level signal, and inputs the water level setting signal and the water level signal. , these 2
A water level controller that outputs a water level deviation control signal according to a control characteristic including an integral element in response to a water level deviation signal of the signal, and a control system that inputs the water level signal and controls the water level deviation signal so that it becomes zero as a result of the control. A stabilizer outputs a correction signal according to control characteristics including a proportional element for stabilization, and a feed water flow rate command signal synthesized from the water level deviation control signal and the correction signal controls the flow rate of the feed water pump of the reactor. A reactor water supply control device consisting of a flow rate controller.