JPS588905A - Method of controlling feedwater for steam generator - 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 water supply control method for a steam generator, and in particular,
The present invention relates to a water supply control method for a steam generator that can stably supply cooling water even during a pump trip.

Steam generated in the reactor pressure vessel of a boiling water reactor is supplied to a turbine through a main steam pipe and rotates one turbine. Steam exhausted from the turbine is condensed in a condenser and returned to cooling water. After that, the cooling water is transferred to the condensate pump,
It is returned to the reactor pressure vessel through a desalter, low pressure feedwater heater, feedwater pump and high pressure feedwater heater. A total of three condensate pumps (capacity 50% per unit) are installed, two in constant operation and one in reserve. The water supply pumps are two constantly driven turbine-driven water pumps (capacity 50% per unit).
Spare motor-driven water pump (capacity 25% per unit)
Two of the four machines are installed.

Water supply control for a boiling water reactor is controlled so that the level of cooling water in the reactor pressure vessel remains constant.

Therefore, three-element control is performed based on measured values of the cooling water level in the reactor pressure vessel, the main steam flow rate, and the feed water flow rate, and the rotation speed of the turbine-driven feed water pump is adjusted. Feed water means cooling water supplied to the reactor pressure vessel.

An object of the present invention is to prevent a steam generator from shutting down during a pump trip.

A feature of the present invention is that when each one of the plurality of first pumps arranged downstream and the plurality of second pumps arranged upstream thereof trips, the flow rate of water supplied from the first pump is increased. It's about letting people know.

The present invention was achieved through detailed study of water supply control for conventional boiling water reactors.

The results of this study will be explained in detail below.

During operation of a boiling water reactor, two condensate pumps and two turbine-driven feed water pumps are operated to supply cooling water into the reactor pressure vessel. Even if one of the turbine-driven water pumps in operation trips, the remaining turbine-driven water pump will ensure the required amount of water to the reactor during the transition period until the spare motor-driven water pump reaches its rated state. To achieve this, turbine-driven water pumps are capable of operating up to approximately 125% of their rated flow rate. That is,
In the turbine-driven water pump rated characteristic curve 1 shown in FIG. 1, the Bonplan outflow limit f[ii (%) is approximately 125% of the rated flow rate of the turbine-driven water pump.

The rated operating conditions of the turbine-driven water pump are defined by the head curve 3 based on the flow rate characteristic 10 in FIG. 2 when two condensate pumps are in operation. This rated operating condition is for a case where two turbine-driven water supply pumps are operated. In a transient state in which one turbine-driven water pump trips, the operating conditions of the turbine-driven water pump shift to head curve 4. Therefore, it is necessary to limit the runout flow of the turbine-driven water supply pump, and as a condition of pump water supply control, an upper limit is placed on the pump rotation speed, and the rotation speed of the turbine-driven water supply pump must be kept at the Bonn runout flow limit rotation speed. The rotational speed can be suppressed to the speed of pump characteristic curve 2 at the same time.

1 turbine-driven feedwater pump and 1 condensate pump each
If the condensate pump in FIG. 2 is tripped, one of the condensate pumps in FIG. 2 cannot be operated, so the operating conditions of the turbine-driven water pump shift to head curve 5 in FIG. 1. Since the rotation speed is limited by the pump characteristic curve @2, the operating state of one turbine-driven water pump in operation is point 8, and the condensate pump 1
The flow rate is limited to 7 during platform operation. Therefore, the water supply capacity of the turbine-driven feedwater pump during operation is less than the flow rate of 125% of the pump rated flow rate required by the reactor during the transient state until the motor-driven feedwater pump is activated.

The problems caused by this will be explained based on FIGS. 3 and 4. If one of the turbine-driven feed water pumps and condensate pumps in operation trips, the flow rate of feed water supplied to the reactor pressure vessel decreases, and the rotation speed of the recirculation pump is runback, causing the water inside the reactor pressure vessel to The flow rate of cooling water passing through the reactor core decreases. The output of boiling water reactors will also decrease. As a result, the amount of steam generated by the nuclear reactor decreases as shown by characteristic 12 in FIG. However, since the feed water flow rate decreases rapidly as shown in characteristic 13, the water level in the reactor pressure vessel decreases from the reference water level 16 as shown in FIG. 4 and changes as shown in characteristic 18, and the scram water level 17 It will drop to. When the scram level 17 is reached, the reactor is scrammed.

The present invention provides that when one turbine-driven feedwater pump and one condensate pump trip, the reason why the reactor is scrammed is because the operating state of the remaining turbine-driven feedwater pumps is 8.
This was done by paying attention to the fact that the water supply flow rate higher than the limit flow rate of 7 cannot be obtained due to the situation. The present invention, which was made with attention to such a phenomenon, changes the runout 70-limit rotation speed of the water supply pump to suppress a decrease in the water supply flow rate when one water supply pump trips.

A preferred embodiment of the present invention applied to a boiling water reactor will be described below with reference to FIGS. 5 and 6. Steam generated in the reactor pressure vessel 21 is sent to the turbine 22 through the main steam pipe 32 and drives the turbine 22. The reactor pressure vessel 21 of such a boiling water reactor is a kind of steam generator. The generator 23 rotates together with the turbine 22. Steam exhausted from the turbine 22 is condensed in a condenser 24 and becomes cooling water. This cooling water is returned to the reactor pressure vessel 21 through the water supply pipe 33. Condensate pumps 25A, 25B and 25C1 demineralizer 38, low-pressure feed water heater 26, turbine-driven feed water pumps 27A and 27B, motor-driven feed water pumps 29A and 29B, and high-pressure feed water heater 30 are installed in water supply piping 33. ing. During operation of a boiling water reactor, condensate pumps 25A and 25B1 turbine-driven feed water pumps 27A and 27B
is in operation. The turbine-driven water supply pumps 27A and 27B are connected to a bleed pipe (not shown) from the main steam pipe 32.
is rotated by directing steam flowing into the drive turbines 28A and 28B. The condensate pump 25C and the motor-driven water supply pumps 29A and 29B are standby machines and are on standby.

The cooling water in the condenser 24 is supplied to the condensate pumps 25A and 25.
The water is pressurized in B, purified in a demineralizer 38, and then heated in a low-pressure feed water heater 26. The cooling water is further pressurized by the turbine-driven feedwater pumps 27A and 27B, passes through the high-pressure feedwater heater 30, and reaches the reactor pressure vessel l.

Water supply control to the reactor is the same as before, from reactor pressure vessel 1.
The water level of the cooling water inside the tank is controlled to be constant. The water level in the reactor pressure vessel is detected by the water level detector 28 and input to the control device 37 .

Normally, in order to improve controllability, the main steam flow rate measured by the flow meter 31 and the feed water flow rate measured by the flow meter 36 are input to the control device 37 to perform three-element control.

The output of the control device 17 is the turbine-driven water supply pump 27A.
and 27B, drive turbines 28A and 2
8B rotation speed control signal, motor-driven water supply pump 2
In the case of 9A and 29B, the rotation speed is constant and the water supply adjustment valve 3
The opening control signals 5A and 35B are used to control the amount of water supplied to the reactor pressure vessel 1.

Pressure detectors 39A, 39B and 39C are installed to detect the discharge pressures of condensate pumps 25A, 25B and 25C. Pressure detectors 39A to 39C monitor the operating status of the condensate pumps, including turbine-driven water pumps 27A and 27B and motor-driven water pumps 29A and 29.
Pressure detectors 4OA and 40B that detect the pressure on the discharge side of B
.

40C and 40D are provided. These pressure detectors monitor the operating status of the water pump.

Pressure detectors 39A-39C and pressure detectors 40A-4
The measured value of 0D is input to the runout flow restriction control device 41. The output of the runout 70-limit controller '41 is input to the controller 37.

The operation of this embodiment will be explained by taking as an example a case where the condensate pump 25A trips. A trip of the condensate pump 25A is detected by a decrease in the measured value of the pressure detector 39A. When trouble occurs in one condensate pump 25A and the condensate pump 25A trips, it is automatically activated. However, the downstream turbine-driven water pumps 27A and 2
Since pump 7B is in operation, the remaining continuously operating condensate pump 25B sends water at an excessive flow rate. For this reason, the discharge pressure of the condensate pump 25B decreases, and as a result, the downstream turbine-driven water supply pump 27A
The suction pressure of pumps 27A and 27B decreases, causing cavitation, and normal operation of turbine-driven water pumps 27A and 27B becomes impossible. Therefore, if one condensate pump 25A on the upstream side trips, the pressure detector 39A
One downstream turbine-driven water pump 27A is forcibly tripped by a control device (not shown) that inputs the measured value. The measured value of the pressure detector 39A is input to the runout flow restriction control device 41. The sequence of the runout flow restriction control device 41 is shown in FIG. Runout 70-limit control device 41 is pressure detector 39A
If the measured value satisfies the trip conditions for the turbine-driven water pump due to condensate pump trip, run-out protection is performed for the turbine-driven water pump 27B that is not tripped. That is, the Bonplung outflow limit rotation speed of the turbine-driven water supply pump 27B is selected from the relationship between the head curve 5 and the Bonplung outflow limit value 6 shown in FIG. Therefore, the operating condition of the turbine-driven water supply pump 27B shifts from the conventional point 8 to the point 9 condition. The conditions at point 9 are input to the control device 37, and the turbine-driven water supply pump 27B is operated under the operating conditions at point 9 under the action of the control device 37. The water supply flow rate due to the operation of the turbine-driven water supply pump 27B increases from the restricted flow rate 7 to the restricted flow rate 6. In this embodiment, the water supply flow rate increases as shown in characteristics 1 and 4 in FIG. 83, and the amount of mismatch with the steam generation amount shown as characteristic 38 can be reduced. As a result, as shown in characteristic 15, the time required for the amount of steam generation and the flow rate of water supply to be balanced can be significantly shortened. Since the water level in the reactor pressure vessel 21 changes as shown in characteristic 19 in FIG. 4, a scram of the reactor can be avoided. This will improve the operating rate of the reactor. In particular, this embodiment functions effectively when the backup condensate pump 25C is not activated when the condensate pump 25A trips.

When the measured value of the pressure detector 40A decreases, the runout flow restriction control device 41 satisfies the turbine-driven water pump trip condition for the turbine-driven water pump alone,
Perform run-out protection for the turbine-driven water supply pump 27B. Naturally, the turbine-driven water pump 27A is tripped. Since the condensate pumps 25A and 25B are being driven, from the relationship between the head curve 4 and the limit value 6, the Bonplan outflow limit rotation speed of the turbine-driven feed water pump 27B is set to the pump characteristic curve 20 rotation speed. The operating conditions of the turbine-driven water supply pump 27B are determined by the control device 3.
7 becomes the condition for point 42.

Even in this case, the water supply flow rate is large, the water level in the reactor pressure vessel 21 decreases little, and the reactor does not scram.

1 of motor-driven water supply pumps 29A and 29B in operation
A case where the stand trips will be explained based on FIG. 7.

Characteristic 43 is motor driven water pump 29A and 29B
This is the pump characteristic curve.

44 is a rated flow rate, and 28 is a Bonplan outflow limit value. Characteristic 46 shows the rated system head, characteristic 47 shows the limiting system head when two condensate pumps are operated, and characteristic 48 shows the limiting system head when one condensate pump is operating.

If the motor-driven water supply pump 29A and condensate pump 25B trip, the runout flow restriction control device 4
16, the opening degree of the water supply regulating valve 35B on the discharge side of the motor-driven water supply pump 29B during operation is changed from point 49 to point 51.
The opening degree corresponding to the throttle amount is increased from point 49 to point 50 corresponding to the throttle amount. This allows for an increase in the water supply flow rate and avoids reactor scrams.

The present invention can be applied not only to water supply control to a reactor pressure vessel of a boiling water reactor, but also to water supply control to a steam generator of a pressurized water reactor and a fast breeder reactor. Also,
It can also be applied to water supply control to boilers, which are steam generators in thermal power plants.

According to the present invention, even if one condensate pump trips, the flow rate of water supplied to the steam generator can be increased without other water supply pumps that do not trip exceeding runout 70-. As a result, shutdown of the steam generation plant can be avoided, and the operating rate of the steam generation plant can be improved.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between the feed water flow rate and the head of the turbine-driven water feed pump, Figure 2 is a characteristic diagram showing the relationship between the feed water flow rate and the head of the condensate pump, and Figure 3 is the steam flow rate and the feed water flow rate. 4 is a characteristic diagram showing changes in reactor water level, FIG. 5 is a system diagram of a preferred embodiment of the present invention applied to a boiling water reactor, and FIG. 6 is a characteristic diagram showing changes in reactor water level. FIG. 5 is an explanatory diagram showing the sequence of the runout flow restriction control device, and FIG. 7 is a characteristic diagram showing the relationship between the water supply flow rate and the head of the motor-driven water supply pump. 21... Reactor pressure vessel, 24... Condenser, 25A
. 25B, 25C... Condensate pump, 27A, 27B...
・Turbine-driven water pump, 29A, 29B...%
- Evening drive water supply pump, 33... Water supply piping, 37...
Control device, 39A to 39B, 40A to 40B...Pressure test Figure 1 Rice feeding flow rate - 1g2 Figure 6 Figure 7 Clam* - Flow rate 1

Claims (1)

[Claims] 1. In a control method for supplying water to a steam generator using a plurality of first pumps arranged in parallel and a plurality of second pumps arranged in parallel on the upstream side of the first pump, the first
and when each one of the W12 pumps trips,
A water supply control method for a steam generator, characterized in that the water supply flow rate discharged from the first pump that is being driven without tripping is increased.