JPH0446323B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a nuclear reactor water supply control system, and more specifically, to a nuclear reactor water supply control system, and more specifically, a system for controlling water supply water in a boiling water type nuclear power plant when a relief safety valve and a turbine bypass valve are accidentally opened. , relates to a reactor water supply control device that controls the rise in reactor water level.

[Background of the invention]

FIG. 1 is a diagram showing the overall configuration of a boiling water nuclear power plant and the configuration of a water supply control system. The reactor vessel 1 is housed inside a containment vessel 2, and boiling occurs in the reactor core 3, which is separated into steam and saturated water in a steam separator 4. The separated saturated water is sent to water supply pipe 6
The water is mixed with the feed water supplied through the recirculation pump 5 and enters the core 3 again via the jet pump 7. On the other hand, the separated steam flows out from the reactor vessel 1 via the main steam pipe 8 and enters the high pressure turbine 11 via the control valve 9. High pressure turbine 11
The steam that exits enters a moisture separator 12 to separate moisture, and then enters a low pressure turbine 13. A generator 14 is directly connected to the low pressure turbine 13, and energy is given to the generator 14. low pressure turbine 1
The steam that exits the steam generator 3 enters the condenser 15 and is returned to water. Condensate from the condenser 15 is sent out by a condensate pump 16, passed through a low-pressure feedwater heater 17, boosted in pressure by a feedwater pump 18, and supplied to the reactor vessel 1 via a high-pressure feedwater heater 19. be done.

As shown in the figure, the main steam pipe 8 is equipped with a relief safety valve 20 that detects the reactor pressure and releases steam to the suppression pool when an abnormal transient change occurs in the reactor. There is. Also, main steam pipe 8
A turbine bypass valve 10 is arranged to release steam directly to the condenser 15 in the event of an abnormality or startup of the reactor.

The feed water control system consists of a reactor water level detector 22, a main steam flow rate converter 23, a feed water flow rate converter 24, and a feed water flow rate control device 25, and the water level detection signal output from the reactor water level detector 22 and the main steam flow rate are converter 2
The main steam flow rate signal outputted from 4 and the feedwater flow rate signal outputted from the feedwater flow rate converter 25 are respectively input to the feedwater flow rate control device 25, and control calculations are performed. Based on the control calculation, the low pressure steam control valve 2
6, controls the flow rate of steam to the feed water pump drive turbine 27, controls the rotation speed of the feed water pump 18, controls the flow rate of water feed to the reactor, and as a result controls the reactor water level. .

The water supply control system controls the reactor water level in order to always ensure a constant flow rate of the most important amount of cooling water for cooling the reactor core 3. Even if the reactor water level slightly fluctuates transiently from the normal operating water level (eg ±15 cm), an alarm will be generated. This means that if the reactor water level falls, a reactor scram will occur,
On the contrary, if it rises, a turbine trip will occur, and in both cases, the blunt will have to be stopped.

There are two main types of water supply control systems. The first water supply control method is a three-element water supply control method in which the water level detection signal, the main steam flow rate signal, and the water supply flow rate signal described above are controlled by a single controller. The second water supply control method is a two-loop water supply control method in which a main control loop that controls the reactor water level and a sub-control loop that controls each pump flow rate in a minor loop are configured in a cascade.

Each of these control methods has the following configuration. That is, FIG. 2 is a diagram showing a conventional example of a water supply control device 25 that realizes a three-element water supply control system. As shown in the figure, an adder 31 adds the water level setting signal S1 output from the water level setting device 30 and the negative water level detection signal S2 output from the reactor water level detector 22 to obtain a deviation signal S3. On the other hand, an adder 32 adds the main steam flow rate signal S4 output from the main steam flow rate converter 23 and the negative feed water flow rate signal output from the feed water flow rate converter 24 to obtain a deviation signal S6. This deviation signal S6 is multiplied by a mismatch gain in an amplifier 33 to obtain a signal S7, and the above deviation signal S3 and signal S7 are added together in an adder 34.
A water supply control signal S8 is formed. Water supply control signal S8
is input to the water supply controller 35, and the water supply controller 35
PI calculation (proportional/integral calculation) is performed. The output of the water supply controller 35 is input to the turbine pump device 37 via the function generator 36, and the pump flow rate signal S
9 is formed. Here, the turbine pump device 3
7 corresponds to the low pressure steam control valve 26 and the feed water pump driving turbine 27 shown in FIG.
Note that the output of the water supply controller 35 is also given to other water supply pump systems (not shown), and the output is provided to the motor-driven water supply pump system (first
Not shown. ) is the opening control signal for the discharge side flow rate control valve.

FIG. 3 is a diagram showing a conventional example of the water supply control device 25 (see FIG. 1) that realizes a two-loop water supply control system, and the same parts as the specific example of the three-element water supply control system shown in FIG. The same symbols are attached. As shown in the figure, a deviation signal S3 between the water level setting signal S1 and the water level detection signal S2 is directly input to the water supply controller 35. Then, the output signal S1 of the water supply controller 35
and a signal S obtained by multiplying the deviation signal S6 between the main steam flow rate signal S4 and the feed water flow rate signal S5 by a mismatch gain.
7 is added by the adder 34 to form the water supply request signal S11 to the sub-flow rate control loop 40. This sub-flow rate control loop 40 has a pump flow rate signal S9
The adder 39 takes the deviation signal S12 between the and the water supply request signal S11, the subloop controller 37 performs PI calculation (proportional/integral calculation), and the function generator 35 performs nonlinear compensation for the water supply pump 18 (see Fig. 1). The turbine pump device 36 is provided with the following information.

The differences between the three-element water supply control system and the two-loop water supply control system described above can be summarized in the following two points.

(1) In the three-element water supply control system, the sub-flow control loop 40 is not provided, but in the two-loop water supply control system, it is provided.

(2) In the three-element water supply control system, the main steam flow rate signal S
The water supply controller 3 outputs a signal S7 obtained by multiplying the deviation signal S6 between 4 and the water supply flow rate signal S5 by the mismatch gain.
However, in the two-loop water supply control system, it is applied after the water supply controller 35.

In other words, based on the difference in (1), the two-loop water supply control system has the following characteristics: (a) the flow rate balance between each water supply pump is good, and (b) changes in flow rate caused by the water supply pump system can be absorbed by the minor loop. There is. In particular, (b)
Regarding this, in order to ensure the minimum flow rate of the water supply pump 18, it is effective to absorb flow rate fluctuations in the recirculation system which is bypassed to the water supply pump suction side.

Also, from the difference in (2), in the two-loop water supply control system, (c) controllability of the reactor water level against core flow rate fluctuations is good, and when changing output due to recirculation flow rate,
It is known that this system has superior responsiveness when the reactor water level rises when the recirculation pump trips, compared to the three-element water supply control system.

However, not only the three-element water supply control system but also the two-loop water supply control system having the above characteristics have the following drawbacks. That is, the relief safety valve 20 shown in FIG. 1 has a capacity of 1100 MWe.
In the case of boiling water type nuclear power plants, there are about 18 of them installed, and although they will not open under reactor pressure during normal operation, it is assumed that they open accidentally for some reason.

When the relief safety valve 20 opens erroneously, the reactor pressure decreases, depressurized boiling occurs in the reactor core 3, the number of voids in the core increases, and the reactor water level increases. On the other hand, the main steam flow rate detected by the main steam flow rate converter 23 is the same as that of the main steam flow rate detected by the main steam flow rate converter 23 because the relief safety valve 20 is located upstream of the main steam flow rate converter 23 (see Figure 1). The steam flow rate decreases by the same amount as the steam flow rate. Therefore, in FIGS. 2 and 3, the main steam flow rate signal S
4 becomes a small value, the deviation signal S6 also becomes a small value, and the signal S7 also becomes a small value. Therefore,
The water supply control signal S8 in FIG. 2 and the water supply request signal S10 in FIG. 3 have small values, and act to lower the reactor water level in both the three-element water supply control system and the two-loop water supply control system. This is preferable in response to a rise in the reactor water level caused by the accidental opening of the relief safety valve 20, but generally the water supply controller 35 sets the proportional gain to around 1.0 in order to stabilize the response of the reactor water level. , the integration time is set to about 1 minute. Therefore, it has the disadvantage of not being able to cope with a sudden rise in the reactor water level.

Further, assuming that the turbine bypass valve 10 shown in FIG. 1 is accidentally opened, reduced pressure boiling occurs in the reactor, similar to when the relief safety valve 10 is accidentally opened, and the reactor water level rises rapidly. On the other hand, since the turbine bypass valve 10 is provided downstream of the main steam flow rate converter 23, the main steam flow rate detected by the main steam flow rate converter 23 increases by the amount of steam flowing into the turbine bypass valve 10. do. Therefore, in FIGS. 2 and 3, the main steam flow rate signal S4 has a large value, and as a result, the signal S7 has a large value. Therefore, the water supply control signal S8 in FIG. 2 and the water supply request signal S10 in FIG. 3 have large values, and act to raise the reactor water level in both the three-element water supply control system and the two-loop water supply control system. As a result, the reactor water level that has risen due to reduced pressure boiling will continue to rise. In particular, in the two-loop water supply control system, since the water level detection signal S2 passes through the water supply controller 35, the decrease in the water supply request signal S10 due to the rise in the reactor water level is delayed, and the atomic The reactor water level will rise.

If such a rise in the reactor water level occurs, it will lead to a turbine trip and the plant will be forced to shut down. The purpose of this turbine trip caused by the rise in the reactor water level is to prevent the moisture content of the steam from increasing due to a decrease in the efficiency of the steam-water separator 4 due to the rise in the reactor water level, which would adversely affect the turbine. However, if a turbine trip occurs and the plant is forced to shut down, this is undesirable from the standpoint of plant availability, and new technology is needed to prevent the reactor water level from rising even if the safety relief valve or turbine bypass valve opens accidentally. development was desired.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and aims to prevent the reactor water level from rising and to avoid plant shutdown even if the safety relief valve or turbine bypass valve is accidentally opened. The purpose is to provide a reactor water supply control system that can perform

[Summary of the invention]

The reactor feed water control device of the present invention includes a first means for obtaining a deviation signal between the main steam flow rate flowing through the main steam pipe and the feed water flow rate to the reactor, and the steam flow rate flowing to the relief safety valve of the reactor and the turbine bypass valve. and a third means for subtracting the correction signal from the deviation signal to correct the control signal of the water supply control system. It is said that

[Embodiments of the invention]

The present invention will be described in more detail below with reference to embodiments shown in the accompanying drawings.

FIG. 4 is a diagram showing a first embodiment of the present invention, in which the reactor water supply control device of the present invention is applied to a three-element water supply control system. In the same figure, V
1 to VN are opening signals of the N safety relief valves, which have a logical value of "1" when the corresponding safety relief valve opens. Each opening signal V1 to Vn
are added by an adder 50, and a signal S100 indicating the number of open safety relief valves is calculated. Piece count signal S
100 is input to the flow rate calculator 51, and the total amount of steam flowing into the open relief safety valve is determined as the relief safety valve flow rate signal S101. The flow rate calculator 51 multiplies the amount of steam flowing to one relief safety valve during steady operation by a number signal S100 corresponding to the number of open relief safety valves to obtain the total amount of steam flowing to the open relief safety valves. It is something. This safety relief valve flow signal S101 is input to the adder 34 as a negative signal. As a result, unlike the prior art shown in FIG. 2, the difference signal S3 between the water level setting signal S1 and the water level detection signal S2 and the main steam flow rate signal S
From the added value of the signal S7 obtained by multiplying the deviation signal S6 between 4 and the water supply flow rate signal S5 by the mismatch gain,
A water supply control signal S8 is formed and output by subtracting the relief safety valve flow rate signal S101. By this,
The water supply control signal is corrected to correspond to the total amount of steam flowing to the relief safety valve, and the water supply flow rate is reduced by the amount of correction compared to the conventional technology shown in Figure 2, suppressing the rise in the reactor water level. Ru.

FIG. 5 is a diagram showing a second embodiment of the present invention, in which the reactor water supply control device of the present invention is applied to a two-loop water supply control system. Just like the first embodiment shown in FIG. 4, by forming a relief safety valve flow signal S101 corresponding to the total amount of steam flowing into the open relief safety valve and adding this to the adder 34 as a negative signal, The sum of the output signal S10 of the water supply controller 35 and the output signal S7 of the amplifier 33 is corrected to form a water supply request signal S11. As a result, a signal correction corresponding to the total amount of steam flowing into the relief safety valve is applied, and the feed water flow rate is reduced by the correction amount compared to the case of the conventional technology shown in Figure 3, suppressing the rise in the reactor water level. Ru. In particular, in the case of the two-loop water supply control system, the relief safety valve flow rate signal S101 is added as a negative signal on the output side of the water supply controller 35, so that only the transmission delay of the sub-flow rate control loop 40 occurs. Therefore, the water supply flow rate decreases rapidly,
A rise in reactor water level due to reduced pressure boiling is effectively prevented.

FIG. 6 shows a third embodiment of the present invention, which is an improvement on the first and second embodiments shown in FIGS. 4 and 5. That is, as in the first and second embodiments, the number signal S100 is calculated by summing the opening degree signals V1 to Vn of the relief safety valves. However, in this third embodiment, the reactor pressure signal S1 output from the reactor pressure detection device 61
20 is input to the function generator 62, and a function value S121 corresponding to the reactor pressure is output. This function value S121 is determined by the safety relief valve 1 under the reactor pressure.
It indicates the amount of steam flowing per unit, and when the reactor pressure is low, the value is small, and when the reactor pressure is high, the value is large. Then, this function value S121 and the number signal S101 are multiplied by a multiplier 63 to form a relief safety valve flow rate signal S101. Therefore, according to the third embodiment, it is possible to perform accurate correction corresponding to the reactor pressure, and it is possible to more effectively prevent the reactor water level from rising due to reduced pressure boiling. The first and second embodiments shown in FIGS. 4 and 5 are based on the assumption that the nuclear reactor is in steady operation.

FIG. 7 is a diagram showing a fourth embodiment of the present invention, which takes into consideration the case where a turbine bypass valve is opened erroneously in addition to the safety relief valve. This fourth embodiment is provided with means for forming a bypass valve flow signal S111 in addition to means for forming a relief safety valve flow signal S101. That is, the bypass valve opening transmitter 7
1 outputs an output signal S110 representing the amount of steam flowing through the turbine bypass valve. This output signal S
110 is input to the calculator 72, where a bypass valve flow rate signal S111 indicating a steam flow rate twice the bypass valve flow rate is obtained. This bypass valve flow signal S
111 is the relief safety valve flow signal S1 in the adder 52.
01, and the added value S113 is input to the adder 34 (see FIGS. 4 and 5) as a negative signal.

That is, when the turbine bypass valve opens, the main steam flow rate signal S4 increases by the amount of steam flowing into the turbine bypass valve. Therefore, the output signal S7 of the amplifier 33 also increases at this rate. As a result, in the three-element water supply control system, the water supply control signal S8, which is the sum of the deviation signal S3 and the output signal S7, increases, and the water supply amount functions to increase. Similarly, in the two-loop water supply control system, the output signal S1 of the water supply controller 35
0 and the output signal S7 of the amplifier 33 increases, and the amount of water supplied increases. However, according to this fourth embodiment, the bypass valve flow rate signal S111 corresponding to twice the steam flow rate of the turbine bypass valve is inputted as a negative signal as the output signal S113 of the adder 52, so that the water supply control signal S8 Or the water supply request signal S11 decreases. Therefore, a signal corresponding to the amount of steam flowing to the bypass valve is added to the water supply control signal S8 or the water supply request signal S111, and the water supply amount is reduced by that amount. Therefore, a rise in the reactor water level due to reduced pressure boiling is effectively suppressed. Although the fourth embodiment has been described on the assumption that the computing unit 72 outputs a bypass valve flow rate signal indicating a steam flow rate twice the bypass valve flow rate, the bypass valve flow rate signal is not necessarily limited to twice the bypass valve flow rate. It is sufficient to provide an appropriate gain for the water supply control system.

FIG. 8 is a diagram showing a fifth embodiment of the present invention, in which the fourth embodiment shown in FIG. 7 is provided with a correction means based on a time differential signal of the reactor pressure when the reactor pressure changes, This provides greater controllability.
That is, when the safety relief valve or turbine bypass valve opens, the reactor pressure decreases. This reactor pressure change is detected by the reactor pressure detection device 61 as a reactor pressure signal S1.
20, the first-order delay circuit 81 and the adder 8
Enter 2. Output signal S2 of the first-order delay circuit 81
01 coincides with the reactor pressure signal S120 when the reactor pressure is constant and does not change, and this output signal S2
01 is input to the adder 82 as a negative signal.
Therefore, when the reactor pressure is constant and does not change, the output signal S202 of the adder 82 becomes zero,
The output signal S203 of the proportional calculator 83 also becomes zero.
On the other hand, when the reactor pressure is constant and does not change, it means that the relief safety valve and the turbine bypass valve are closed, so the output signal S113 of the adder 52 also becomes zero. Therefore, the output signal S204 of the adder 84, which inputs the output signal S203 as a positive signal and the output signal S113 as a negative signal, becomes zero.

On the other hand, when the relief safety valve or the turbine bypass valve opens erroneously and the reactor pressure decreases, the reactor pressure signal S120 changes to a small value accordingly. However, the primary delay circuit 81 processes the reactor pressure signal S120 with a predetermined time delay, and forms and outputs the output signal S201. Therefore, the output signal S201 does not drop as sharply as the reactor pressure signal S120, and therefore the output signal of the adder 82 becomes a negative signal. Therefore, the output signal S203 of the proportional calculator 83 also becomes a negative signal and is input to the adder 84. On the other hand, the output signal S11 of the adder 52
3 is a positive signal because the relief safety valve or turbine bypass valve is erroneously opened. Here, as described above, the output signal S203 input to the adder 84
is a negative signal, and the output signal S113 is also input to the adder 84 as a negative signal. Therefore, adder 84
The output signal S204 also becomes a negative signal. For this reason,
The adder 32 adds the output signal S204, which is the negative signal, to the sum of the output signal S7 of the amplifier 33 and the deviation signal S3 (or the output signal of the water supply controller 35). The water supply control signal S8 (or water supply request signal S11) thus formed has a value smaller than that of the fourth embodiment shown in FIG.
By appropriately setting the time constant of 1 and the proportional constant of the proportional calculator 83, it becomes possible to control the feed water flow rate more accurately, and it is possible to prevent a rise in the reactor water level due to reduced pressure boiling.

Next, a comparison of the responses of the present invention and the conventional device is shown in FIGS. 9a and 9b. Figure 9a shows the water supply flow rate;
Figure b shows the time response of the reactor water level, and the dashed line is the conventional 2
This is a loop water supply control type device, and the solid line shows the case of a two-loop water supply control type device in which the fourth embodiment shown in FIG. 7 is applied. When the safety relief valve opens at time t ₀ , the reactor water level reaches a high water level turbine trip in the conventional system shown by the broken line, but in the system of the present invention, shown by the solid line, the plant shuts down without reaching the same trip level. can be avoided.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, even if the relief safety valve or the turbine bypass valve opens for some reason and the reactor pressure decreases, it is possible to effectively prevent the reactor water level from rising, thereby shutting down the plant. This can be avoided and the plant operation rate can be improved.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the overall configuration of a boiling water nuclear power plant and the configuration of the water supply control system, Figure 2 is a block diagram showing the reactor water supply control system with a three-element water supply control system, and Figure 3 is a two-loop diagram. FIG. 4 is a block diagram showing a reactor water supply control system using a water supply control method; FIG. 4 is a block diagram showing a first embodiment of the present invention; FIG. 5 is a block diagram showing a second embodiment of the present invention; FIG. 7 is a block diagram showing a fourth embodiment of the invention, FIG. 8 is a block diagram showing a fifth embodiment of the invention, and FIG. Figures 9a and 9b are characteristic diagrams comparing the control responsiveness between the feed water flow rate and the reactor water level between the conventional technology and the present invention. 10... Turbine bypass valve, 18... Feed water pump, 20... Relief safety valve, 22... Reactor water level detector, 23... Main steam flow rate converter, 24... Feed water flow rate converter, 25... Feed water flow rate control device, 26
...Low pressure steam control valve, 27 ... Water supply pump drive turbine, 30 ... Water level setting device, 31, 32, 3
4, 39, 50, 82, 84...Adder, 33...
... Amplifier, 35 ... Water supply controller, 36 ... Function generator, 37 ... Turbine pump device, 38 ... Sub-loop controller, 40 ... Sub-flow control loop,
51... Flow rate calculator, 61... Reactor pressure detection device, 62... Function generator, 63... Multiplier, 71
...Bypass valve opening transmitter, 72...Arithmetic unit, 8
1...First-order delay circuit, 83...Proportional calculator, S1
...Water level setting signal, S2...Water level detection signal, S
3, S6...Deviation signal, S4...Main steam flow rate signal, S5...Water supply flow rate signal, S7, S10...Output signal, S8...Water supply control signal, S9...Pump flow rate signal, S11...Water supply request Signal, V1~Vn
...Opening degree signal, S100...Number signal, S101
...Relief safety valve flow signal, S110, S113...
...output signal, S111...bypass valve flow rate signal.

Claims (1)

[Scope of Claims] 1. A first means for obtaining a deviation signal between the main steam flow rate flowing through the main steam pipe and the water supply flow rate to the reactor, and the steam flow rate flowing to the safety relief valve of the reactor and the steam flowing to the turbine bypass valve. a second means for forming a correction signal based on the flow rate; and a correction signal output from the second means is subtracted from a deviation signal output from the first means to correct the control signal of the water supply control system. A nuclear reactor water supply control device, characterized in that it is equipped with a third means for controlling. 2. The reactor feed water control system according to claim 1, wherein the second means includes means for calculating the flow rate of steam flowing to the relief safety valve in accordance with the reactor pressure signal. 3. The reactor water supply control according to claim 1, wherein the second means includes a device that calculates the flow rate of steam flowing into the safety relief valve in accordance with the opening signal of the safety relief valve. Device. 4. Claim 1, wherein the second means includes means for forming a time differential signal of a reactor pressure signal, and outputs a correction signal according to the magnitude of a change in reactor pressure. The reactor feed water control device described.