JPH0225477B2 - - Google Patents

Description

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

(b) Prior art In general, for boiling water reactors, a reactor standard 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 standard water level is not exceeded. Deviations in reactor water level must be within permissible limits. In the event that the reactor water level deviates from this allowable range,
The reactor must be shut down by reactor scram, 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 constantly fluctuates 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, the flow rate of feed water sent to the reactor is must be controlled. A device provided for this purpose is a reactor feed water control device, which usually controls the rotation speed of the reactor feed water pump or the opening degree of the flow rate regulating valve provided at the outlet of the reactor feed water pump. , controls the flow rate of feed water sent to the reactor.

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 setter that provides a water level reference signal; 5 is a water level detector that detects the reactor water level; 6 is a water level reference signal _L1 from the water level setter 4 and a water level signal _L2 from the water level detector 5; water level controller that inputs and calculates the flow rate command signal _L3 , 7
8 is a flow rate detector that detects the flow rate of the pump, and 8 inputs the pump flow rate signal L ₄ from the flow rate detector 7 and the flow rate command signal L ₃ from the water level controller 6 to control the opening degree of the flow rate adjustment valve 3. It is a flow controller.

FIG. 2 is a block diagram showing the operation of the above configuration, where G ₁ (S) is a transfer function representing the water level controller 6, G ₂ (S) is a transfer function representing the flow rate controller 8,
G ₃ (S) is a transfer function representing the flow rate adjustment valve 3, G ₄
(S) is a transfer function representing the nuclear reactor 1. The deviation signal (water level deviation signal) L ₅ (S) of the water level reference signal L ₁ (S) and the water level signal L ₂ (S) is input to the transfer function G ₁ (S) of the water level controller, while the flow rate command signal L ₃
(S) and the deviation signal (flow rate deviation signal) L ₆ (S) of the pump flow rate signal L ₄ (S) is input to the transfer function G ₂ (S) of the flow rate controller. The output (opening command signal) L ₇ (S) of the transfer function G ₃ (S) of the flow controller is:
Input to the flow rate adjustment valve transfer function G ₃ (S), G ₃ (S)
The output (pump flow rate signal L ₄ (S)) is input to the reactor transfer function G ₄ (S). Reactor transfer function G ₄
The output of (S) is the water level signal L ₂ (S).
At this time, the transfer characteristic from the water level reference signal L ₁ (S) to the flow rate deviation signal L ₆ (S) can be expressed by the following equation.

L ₆ (S) = G ₁ (S) / 1 + G ₂ G ₃ (S) + G ₁ G ₂ G ₃
G ₄ (S) L ₁ (S)...(1) Normally, the water level controller 6 has a proportional gain, the flow rate adjustment valve 3 has an O type (i.e. lim S→0 G(S) = finite), and the reactor 1 has a proportional gain. It is expressed as an integral characteristic,
Since the flow rate controller 8 includes an integral element, G ₁ (S)=K...(2-a) lim S→0G ₂ (S)=∞...(2-b) lim S→0G ₃ (S ) = finite ... (2-c) G ₄ (S) = 1/T _R S (T _R : time constant of the reactor) ... (2-d), and the step-like change in L ₁ (S) By using the final value theorem of Laplace transform, the steady value of L ₆ becomes L ₆ =O (3). Therefore, the flow rate command L ₃ and the pump flow signal L ₄
match, and the flow rate of the water supply pump 2 is controlled by the water level controller 6.

However, when the water supply pump 2 is stopped, the pump flow rate signal L ₄ is zero, so the state is similar to G ₃ (S) = O, and equation (1) is L ₆ (S) = G ₁ (S) L ₁ (S) ...(4) is rewritten. Therefore, the valve opening command signal at this time
L ₇ becomes L ₇ (S) = G ₁ G ₂ (S) L ₁ (S) ...(5), and the final value theorem of Laplace transform and (2-
From equation b), it can be seen that the steady value of _L7 diverges to infinity in response to a slap-like change in _L1 . That is, when the water supply pump 2 is stopped, the valve opening command signal _L7 from the flow rate controller 8 is saturated, and the opening degree of the flow rate regulating valve 3 is always in a fully open state.

To simplify the explanation, the above is based on the water supply pump 2.
However, in a general nuclear power plant, a plurality of water supply pumps are installed, and normal water supply control is performed using some of these pumps (for example, 2 out of 4 pumps). The remaining feed water pumps are used for backup and are normally stopped; however, in the event of a failure of a constantly running water pump, etc., there is a possibility that the reactor water level may deviate from the permissible range and drop suddenly. It is designed to automatically start up and supply water. It goes without saying that the time required for automatic startup must be short in order to minimize fluctuations in the reactor water level, but flow control for automatically activated feedwater pumps must also begin promptly. .

However, as described above, in the conventional reactor water supply control system, the flow rate adjustment valve for the stopped water pump is fully open, and the pump flow rate immediately after startup is 100% flow rate. In addition, since the flow rate controller 8 itself is saturated, the saturation of the flow rate controller 8 must be eliminated in order to enable flow rate control, but the saturation occurs immediately after feedback of the pump flow rate signal _L4 is applied. is not eliminated, but is gradually eliminated by the integrator time constant in the flow rate controller 8. Therefore, in the conventional reactor feed water control system, after the feed water pump 2 is automatically started, the flow rate of the automatically started feed water pump is 100% or close to 100% without control for a certain period of time determined by the time constant of the integrator. As a result, the reactor water level would rise rapidly, and there was a possibility that the deviation from the reactor standard water level would exceed the permissible range.

(c) Purpose of the Invention The purpose of the present invention is to provide a stable reactor water supply control system by eliminating saturation of the flow rate controller and eliminating fluctuations in the reactor water level at the time of starting the feed water pump, which were caused by saturation of the flow rate controller. It's about doing.

(d) Structure of the Invention The present invention will be described below based on an embodiment shown in 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, and the difference from FIG. 1 is that the output of the flow rate controller 8 is fed back to the input of the flow rate controller 8 via the contact 9. .

FIG. 4 is a block diagram showing the operation of the above structure. In the diagram, the same reference numerals as in FIG. 2 indicate the same or equivalent parts as in FIG. 2, and the difference from the block diagram in _{FIG .} The point is that feedback is being provided to the The contact 9 is closed when the water supply pump 2 is stopped. Therefore, when the water supply pump 2 is in operation, the block diagram is exactly the same as shown in FIG. 2, and the operation of the control system is also the same.

On the other hand, when the water supply pump 2 is stopped, the flow rate command signal is
Since the flow rate signal L ₄ (S)=O, the transfer characteristic from L ₃ (S) to the valve opening command signal L ₇ (S) is L ₇ (S)=G ₂ (S)/1+G ₂ (S). )L ₃ (S)……(6
) becomes. Therefore, from the final value theorem of Laplace transform and equation (2-b), L ₇ =L ₃ ...(7) holds in steady state. Therefore, the flow rate command signal L ₃
Since the opening command signal L 7 and the opening command signal L ₇ match, the flow rate controller 8 is not saturated, and the flow rate control valve 3 is directly controlled by the water level controller 6 .

In the above explanation, it is assumed that the contact 9 is closed when the water supply pump 2 is stopped.
L ₄ may be input to the comparison circuit, and when the pump flow rate L ₄ becomes less than a certain value, the contact 9 may be closed. Furthermore, in order to simplify the explanation, the flow rate of the water supply pump is controlled by the flow rate adjustment valve 2 in the above description, but the present invention is equally applicable even if the flow rate is controlled by the rotational speed of the pump. It is possible.

(e) Effects of the Invention As explained above, according to the present invention, saturation of the flow rate controller 8 can be prevented even when the water supply pump 2 is stopped, and the opening degree of the flow rate regulating valve 3 can always control the water level. 6. Therefore, the flow rate control is effective immediately after starting the water supply pump, and since the opening degree of the flow rate regulating valve 3 is also controlled according to the state of the plant before starting up, the opening degree is appropriate even when the flow rate control is started. There is. Therefore, even if the backup water pump is automatically started due to a malfunction of the constantly operating water pump, superfeeding of water to the reactor will not occur and the reactor water level will be stably controlled within the allowable range. Is possible.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of a conventional reactor feed water control system, Figure 2 is a block diagram showing the operation of a conventional reactor water supply control system, and Figure 3 is a diagram showing the configuration of an embodiment of the present invention. Block Diagram FIG. 4 is a block diagram showing the operation of one embodiment of the present invention. 1... Nuclear reactor, 2... Water supply pump, 3... Flow rate adjustment valve, 4... Water level setter, 5... Water level detector,
6...Water level controller, 7...Flow rate detector, 8...Flow rate controller, 9...Contact.

Claims (1)

[Claims] 1. A water level controller that inputs a reactor water level reference signal and a reactor actual water level signal and calculates a flow rate command signal for a reactor feed water pump, and inputs said flow rate command signal and said reactor feed water pump's actual flow rate signal, a flow rate controller including an integral element that controls the flow rate of the reactor feed water pump; and a feedback loop that feeds back an output signal of the integral element to the flow rate command signal when the reactor feed water pump is stopped. A nuclear reactor water supply control device characterized by comprising: