JPS5828689A - Method and device for controlling reactor power at load loss - 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 The present invention relates to a method and apparatus for controlling the reactor power of a nuclear coupler plant, particularly during load loss in a boiling water nuclear power plant having a full capacity turbine bypass system! The present invention relates to a nuclear reactor power control device used for transition to single load operation in 1-.

BACKGROUND OF THE INVENTION Conventionally, boiling water nuclear power plants have adopted a full capacity turbine bypass system so that the plant can continue operating under a single internal load without shutting down the reactor when generator load is lost. This system quickly closes the turbine steam control valve to prevent the turbine from running at full speed when the generator load is lost, and immediately opens the turbine bypass valve with sufficient capacity to direct excess steam to the condenser. By injecting the reactor, the pressure in the reactor will not increase, high neutron flux scrams will be prevented, and the station will be able to shift to single-load operation. However, in conventional full-capacity turbine bypass systems, the sudden opening of the bypass valve tends to be delayed slightly compared to the sudden opening of the regulating valve. For this reason,
Immediately after the regulator valve is suddenly closed, a temporary steam flow rate mismatch occurs and the reactor pressure rises transiently. Therefore, in the conventional system, there is a possibility that the neutron flux increases and reaches the neutron flux high scram setting value. ing.

Even with the conventional method described above, a high neutron flux scram does not occur, and it is possible to shift to in-house single load operation. However, since the insertion reactivity due to selective control rod insertion and the recirculation pump trip pattern are constant regardless of the reactor operating status, if a load loss occurs during low-power operating status, the reactor will be There is a possibility that the output will drop too much and the turbine-driven water pump will go out of its operating range and become uncontrollable. To prevent this, it is necessary to perform operations such as switching to a feed water pump with a different drive source, which causes unnecessary fluctuations in the reactor water level and, in turn, the risk of a low water level scram or a high water level turbine trip.

An object of the present invention is to provide a method and apparatus for controlling reactor output at the time of load loss, which can smoothly shift to in-station single load operation at the time of generator load loss in any reactor output state.

The above object of the present invention is to ensure that the setting value of the neutron flux high scram, which is a major factor in failure to shift to isolated load operation at the time of load loss, is always constant regardless of the reactor operating state. In low output operating conditions, there is a low possibility of scram occurring due to high neutron flux in the event of load loss, and therefore there is no need to input a large negative reactivity immediately after the regulator valve is suddenly closed, making it easy to operate with a single load within the station. In addition, if a load loss occurs during operation on a low-power control rod pattern, the reactor power will be sufficiently low if the core flow rate is lowered, and even if the reactor power increases due to subsequent loss of feedwater heating, the TPM will be maintained. Focusing on the low possibility of scrum occurrence,
A selective control rod insertion pattern and a recirculation pump operation pattern are prepared according to each reactor operating state so that the power drop rate is optimal even when the load is lost in a low-power state, and This is achieved by selecting and operating these patterns to shift to in-plant single load operation.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of a boiling water nuclear power plant to which an embodiment of the method and apparatus for controlling reactor output during load loss according to the present invention is applied.

Steam generated in the nuclear reactor 1 is sent to a steam turbine 3 via a steam control valve 2. The steam turbine 3 drives a generator 4 connected thereto, and the steam that has completed its work is returned to water in a condenser 5. This condenser 5 is connected to the nuclear reactor 1 via a turbine bypass valve 6 by piping.

Therefore, if the steam control valve 2 is closed and the turbine bypass valve 6 is opened, the steam generated in the evaporator furnace 1 will be directly sent to the condenser 5.

The steam generated in the reactor 1 is transferred to a control rod 8 driven by a control rod drive device 7, and a recirculation pump 1 directly connected to a motor 9.
The core flow rate is controlled by the core flow rate pumped into the reactor core via the jet pump 11 driven by zero. Note that the MG upper set 3 is connected to the recirculation pump drive motor 9 via a motor power supply circuit breaker 12.

During the above plant operation, if a load loss occurs in the generator 4, the load imbalance relay is activated to prevent the turbine 3 from accelerating, and the regulating valve 2 is suddenly closed.Normally, the capacity is sufficient. The turbine bypass valve 6 is closed, but when the regulating valve 2 is suddenly closed as described above, it is quickly opened to send surplus steam directly to the condenser 5. At this time,
The neutron flux transiently increases due to a temporary mismatch in the main steam flow rate caused by a slight difference in opening/closing time between the control valve 2 and the bypass valve 6.

In order to suppress this, a plurality of predetermined control rods (selected control rods) among the control rods 8 are rapidly inserted into the reactor core, and the power circuit breaker 12 of the motor 9 is opened to open the recirculation pump 1.
Trip 0. This causes a sudden decrease in the core flow rate and a temporary increase in voids within the core, which injects negative reactivity and suppresses the increase in neutron flux. The above two neutron flux increase suppressing effects prevent the occurrence of a high neutron flux scram, and the plant can shift to in-house single load operation. Furthermore, since the flow rate of steam flowing into the turbine during single-load operation within the plant is about 8 inches, which is the rated value, the amount of steam extracted to the feed water heater also decreases, and the temperature of the feed water drops. However, the aforementioned selective control rods are inserted in order to prevent TPM scram that may occur due to the increase in reactor power.

Conventionally, the selective control rods mentioned above were inserted by quickly closing the control valve regardless of the operating state of the reactor, and the same number of control rods were always inserted, so when used in conjunction with a recirculation pump (IJ tube). Depending on the operating state of the reactor at the time of load loss, the reactor output during isolated load operation within the station may drop significantly.
There is a possibility that it will drop to 10% or less of the rating.

Usually two T/D-11'Ps are used for large-capacity atomic couplets.
Water is supplied to the reactor by a turbine-driven water pump (turbine-driven water supply pump), but since the T/D-RFP adjusts the water supply flow rate by controlling the turbine speed, if the pump's flow rate decreases, the turbine There is a possibility of entering a dangerous area or causing an unstable phenomenon. Therefore, if the reactor output during the above-mentioned in-house single load operation is significantly reduced and the water supply flow rate is also reduced, it will be difficult to stably control the reactor water level in the T/D-box 1'P.

Therefore, when the load is cut off, the water supply system is immediately turned off to 1゛/D-HJ.
□M allows stable flow control at low water supply flow rates from l'
/D-RFP (motor-driven water pump) may be considered. However, this method is undesirable for the following reasons. In other words, generally, the switching of the water supply pump is performed manually by three operating personnel, but switching the water pump within a few minutes after a load loss places an excessive burden on the operating personnel, making it difficult to operate smoothly. This poses a problem when performing single-load operation within a station. Further, since the water level continues to fluctuate for a while after the load loss occurs, switching the pump at this time will increase the water level fluctuation and may cause unnecessary scram or turbine trip. Furthermore, even in the process of rejoining the plant and increasing the output due to subsequent system restoration, it is necessary to switch back to the T/D-RFP, which makes the operation complicated. Therefore, the nuclear power plant shown in FIG. 1 uses the following method and device for controlling reactor output during load loss.

FIG. 2 is a diagram showing the relationship between reactor power and core flow rate of a boiling water nuclear power plant, illustrating an embodiment of the reactor power control method during load loss according to the present invention.

Normally, a nuclear reactor is operated within the general range shown in the diagram. This operating range includes flow control curve 14 on the 105% power control rod pattern, natural circulation flow line 15.4 (l flow control curve 16 on the power control rod pattern), recirculation pump minimum speed line (pump speed 20. % to 30%) 17, is limited by the rated reactor output line 18 and the rated core flow rate line 19. Therefore, the normal operating state is limited by the reactor power and core flow rate at that time within the above operating range. It will be represented as a single point.

In this example, the operating range is divided into a plurality of small regions by some straight lines or curves, and an optimal reactor output control method at the time of load loss is provided for each small region. Particularly, the present invention allows smooth transition to and continuation of single-load operation within the plant, regardless of the normal operating state of the plant.

Figure 2 shows the case where the reactor operating range is divided into three small areas by two straight lines and a curve.

The straight line 20 used for this division is the line for the reactor output of 80 inches, and the curve 21 shows the flow rate control curve on the 70 inch output control rod pattern. By means of the straight line 20 and the curve 21, the operating range of the nuclear reactor is divided into three small regions A, H and C as shown in FIG. These three small areas are defined as follows.

Small area A has a reactor output of 80qI within the normal operating range of the reactor.
Subregion B indicates a reactor operating state in which the reactor output is 80% or less and the control rod pattern is 70% output control rod pattern or greater within the normal reactor operating range; indicates a reactor operating state (operating state other than the above A and H) in which the control rod pattern is equal to or less than the 704 control rod pattern within the normal operating range of the reactor. In addition, above 3
The different operating states are referred to as mode A1, mode B, and mode C, respectively.

Next, an optimal method for controlling the reactor output when the reactor operating state is in modes A, H, and C will be described. If the operating state at the time of load loss was Mode A, the reactor output was high and the main steam flow rate mismatched when the control valve was suddenly closed due to load loss, resulting in a temporary increase in neutron flux and a high neutron flux scram. High possibility of occurrence. To avoid this, the recirculation pump trips immediately upon load shedding to prevent the neutron flux from increasing. In addition, by inserting the selective control rod, the increase in neutron flux during the above-mentioned transient is suppressed, and the generation of 'l' PM scram due to loss of heating of the feed water after transition to in-station single load operation is prevented. In this case, the in-station single load operation continues on the natural circulation flow line 15 of FIG. 2, and the reactor power is between 20 and 40% of the rated power.

Next, the case where the operating state is mode B will be described.

In this mode, the reactor output is low at 80% or less, so even if the neutron flux increases due to the affected part of the control valve, there is no risk of a high neutron flux scram occurring. Therefore, the recirculation pump) +J
Although no tsubu is carried out, ゛l'PM due to loss of feed water heating
Recirculation bomb runback is performed by inserting a selective control rod to prevent scram occurrence. Accordingly, station single load operation continues on the recirculation pump minimum speed line 17 of FIG. 2, and the reactor power is between 15% and 25% of rated.

Furthermore, when the operating state is mode C, the recirculation pump is not tripped and runback is performed because the output is low as in mode B. In this case, the in-plant single load operation is performed on the recirculation pump minimum speed line 17, but as can be seen from FIG. 2, the reactor output becomes a lower value than in modes A and B due to the drop in the core flow rate. Therefore, even if the output increases due to loss of feed water heating, TPM scram will not occur, so there is no need to insert a selective control rod. In addition, if selective control rod insertion is performed, the output may further drop to 10% or less of the rated value, so control rod insertion is not desirable.

The operating state of the nuclear reactor is divided into the small regions A, B, and C described above, and each region is caused to perform an optimal transition to in-station single load operation at the time of load loss. However, the numerical values of the reactor output and power control rod pattern for dividing the small areas may vary slightly depending on the plant. Next, we will discuss the operations required to shift to in-house single load operation in the event of load loss in each mode. When operating in Mode A, insert recirculation pump trips and select control rods. During operation in mode B, recirculation bomb runback and selective control rod insertion are performed. Also, while operating in mode C, only the recirculation bomb runback is performed and the selective control rod is not inserted.

According to this embodiment, by predetermining a control method for each mode, it is possible to prevent the reactor output from dropping below 9, and also to prevent the occurrence of l' P M scram due to loss of feed water heating. . Therefore, the water supply flow rate is 'l'/DH,F
This has the effect of preventing the P operation range from being exceeded and decreasing to the point where it becomes necessary to switch to the M/D-RFP, and allowing for smooth in-house single load operation.

In addition, since it is possible to reduce the number of trips of the recirculation pump as much as possible, it is possible to continue the operation of 'l'/1)-14,l'P, and during the plant re-joining and output increase process after system accident recovery. This has the effect of making it possible to easily operate the nuclear power plant, and also has the effect of improving the reliability and availability of the nuclear power plant.

FIG. 3 is a diagram illustrating a main part of an embodiment of a control device that implements the method for controlling reactor output at the time of load loss according to the present invention. The main part of this device is the pattern logic circuit 22, which selects the optimal reactor output control method in response to the reactor operating state at the time of load loss and generates a control signal to do so. This will be explained according to the diagram.

The signal necessary to perform optimal reactor power control for modes A, H, and C described above is the selected control rod insertion signal 2.
3. Recirculation Pump) There are three signals: IJ knob signal 24 and recirculation pump back signal 25. In addition, in generating the above three signals according to the reactor operating status,
It is necessary to constantly input the reactor output signal and the core flow rate signal into the pattern logic circuit 22. However, in consideration of measurement accuracy and reliability, the turbine first stage post-pressure signal 26 is used as the reactor output signal, and the recirculation loop flow rate signal 27 is used as the core flow rate signal. The turbine first stage post-pressure signal 26 inputted to the comparator 28 is compared with a set value 29 determined in advance corresponding to the reactor output of 80 inches. If the turbine first stage post-pressure signal 26 is smaller than the set value 29, the comparator 28 generates a signal that prevents the recirculation bomb trip signal 24 from being generated by the regulating valve quick-closing signal 3o. The recirculation loop flow rate signal 27 is also input to a function generator 31 having the characteristics shown in FIG.

This function generator 31 outputs a conversion signal 32 equivalent to the reactor power value corresponding to the value of the recirculation loop flow rate signal 27 on the 70% output control rod pattern. This conversion signal 3
2 is input to a comparator 33 and compared with the turbine first stage post-pressure signal 26. If the conversion signal 32 is small, the comparator 33 prevents generation of the selective control rod insertion signal 23 by the regulating valve quick closing signal 30. Generates a signal to

According to this embodiment, mode A control method is selected when comparators 28 and 33 are not generating a blocking signal, and mode B control method is selected when only comparator 28 is generating a blocking signal. is carried out, and when both the comparator 28 and the comparator 33 are generating a blocking signal, the control method of mode C is selected, so that the reactor output at the time of load shedding is optimal for modes A, H, and C. No matter which control method is selected and the reactor is operated at any point within the normal operating range shown in FIG. 2, there is an effect that smooth transition and continuation of in-station single load operation can be achieved in the event of load loss.

Note that in this embodiment, the reactor operating range is divided into three small regions along the straight line 20 and the curved line 21, but the operating range is further divided into a large number of curves to reduce the number of selected control rods to be inserted. By predetermining a plurality of different patterns, it is also possible to perform reactor output control at the time of load loss more precisely than in this embodiment.

As is clear from the above description, according to the present invention, by performing control operations by selecting the optimal selection control rod insertion pattern and recirculation pump operation pattern according to the reactor operating state, what kind of atoms can be controlled? It is possible to provide a method and apparatus for controlling reactor output at the time of load loss, which can smoothly shift to in-station single load operation at the time of generator load loss even in the reactor output state.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the configuration of a boiling water nuclear power plant to which an embodiment of the reactor output control method and apparatus at the time of load loss according to the present invention is applied, and FIG. A flow rate control curve diagram showing the relationship between the reactor output and the core flow rate of a boiling water nuclear power plant to explain an embodiment of the reactor output control method, and FIG. 3 shows the reactor output control at the time of load loss according to the present invention. FIG. 4 is a block diagram illustrating the essential parts of an embodiment of the apparatus, and is a diagram showing the relationship between the recirculation loop flow rate signal and the conversion signal showing the characteristics of the function generator shown in FIG. 3. 1... Nuclear reactor, 2... Steam control valve, 3... Turbine, 4... Generator, 5... Condenser, 6... Turbine bypass valve, 7... Control rod Drive device, 8...Control rod, 10...Recirculation pump, 11...Jet pump, 28.33...Ratio

Claims (1)

[Scope of Claims] ■4 In a reactor output control method at the time of load loss for shifting to in-station isolated load operation at the time of generator load loss, the reactor operating state given by the reactor core flow rate and reactor output is The operating states are classified into multiple operating states based on the flow rate value and reactor output value, and the selected control rod insertion pattern and recirculation pump operating pattern, which are the operating patterns to be adopted when generator load loss occurs, are classified into the classified operating states. A nuclear reactor output control method at the time of load loss, characterized in that the operation pattern is determined for each time, and the operation pattern corresponding to the operating state at the time of load loss is selected and executed to shift to in-station single load operation. 2. In the reactor power control system, which performs selective control rod insertion and recirculation bomb trip based on the turbine steam control valve rapid closing signal when generator load is lost, the reactor power is classified in advance by reactor power and core flow rate. A logic circuit is provided that selects the control rod insertion pattern and recirculation pump operation pattern according to the reactor operating state at the time of load loss from the reactor output signal and core flow rate signal. ,
A nuclear reactor output control device at the time of load loss, characterized in that a transition to in-plant single load operation is performed by controlling the reactor output according to the reactor state at the time of load loss.