JPH0535838B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a nuclear reactor water level control method, in which the condensate pump in the condensate system does not have a reserve capacity or the reserve capacity is small. Malfunctions such as trips in the pump (hereinafter referred to as trips)
The present invention relates to a reactor water level control method suitable for reducing the amount of decrease in the reactor water level due to a decrease in the reactor feed water flow rate after the occurrence of a nuclear reactor water flow rate.

[Background of the invention]

A conventional nuclear power plant is shown in FIGS. 1 and 2.

Figure 1 shows the main steam system, condensate water supply system, and reactor recirculation control system. The water is purified to an appropriate quality by the condensate purification device 3, and the pressure is increased by the high pressure condensate pump 4.
The water is heated by the low-pressure feedwater heater 5, boosted in pressure by the turbine-driven feedwater pump 7 or the motor-driven feedwater pump 6, heated by the high-pressure feedwater heater 8, and then supplied to the reactor pressure vessel 9.

The steam generated by the reactor pressure vessel 9 drives the steam turbine 11, rotates the transmitter G,
Generate electricity.

Next, in reactor water level control, single-element control is performed using the reactor water level detector 15 during low loads, and single element control is performed using the reactor water flow rate detector 14, reactor water level detector 15, and main steam flow rate detector during high loads. Three-element control including 16 is performed. For load fluctuations and transient events,
The water level in the reactor pressure vessel 9 is kept constant by controlling and following the feed water flow rate by the steam control valve 12 in the turbine-driven feed water pump 7 and by the feed water flow rate control valve 13 in the motor-driven feed water pump 6. keeping.

In addition to reactor output control using control rods, plant output is controlled by controlling the reactor core flow rate and reactor output using the reactor recirculation pump 10 during normal operation.

In addition, in Fig. 1, 17 is the reactor recirculation pump 1.
0, the steam control valve 12, and the water supply amount control valve 13 are shown.

In the conventional condensate water supply system, when the low-pressure condensate pump 2 or the high-pressure condensate pump 4 does not have a backup unit, or when the reserve capacity is small, the low-pressure condensate pump 2 or the high-pressure condensate pump 4 is tripped. In this case, the reactor water level will be controlled as follows.

That is, when the reactor water level is low and the turbine-driven feedwater pump 7 trip is activated, the reactor recirculation pump 10 is runback, the core flow rate is reduced, the reactor power is reduced, and the main steam flow rate is reduced. This prevents the reactor water level from dropping.
However, in this conventional technology, the low pressure condensate pump 2,
If the high pressure condensate pump 4 does not have a standby unit,
It is difficult to restore the reactor feed water flow rate, and the reactor water level is low and does not recover, resulting in a "low water level" situation and the reactor may scram.

Here, low pressure condensate pump 2, high pressure condensate pump 4
When the pump trips, the downstream pump is also tripped to ensure the pushing pressure of the downstream pump. That is, for example, if one of the low-pressure condensate pumps 2 trips, the pressure for pushing the water supply decreases, so one high-pressure condensate pump 4 and one turbine-driven water supply pump 7 are tripped. Trips in the low-pressure condensate pump 2 and high-pressure condensate pump 4 are detected by detecting trips in the turbine-driven water supply pump 7.

As described above, the conventional technology has a problem in that the reactor scrams every time the condensate water supply system pump trips.

Next, Fig. 2 shows the reactor spray system. In the case where there is only one electric motor-driven water supply pump 6, the electric motor-driven water supply pump 6 is used when the plant is started or stopped. If the feed water pump 6 trips, the reactor feed water is lost and a scram occurs with the "reactor water level low".

After the reactor scram, there is no cooling water to cool the inside of the reactor, so the water level detector 15 detects "low and low reactor water level" and starts the cooling water pump 22 shown in FIG. 2. This cooling water pump 22 injects condensate in the condensate storage tank 21 into the reactor pressure vessel 9 to remove heat. At the same time,
The high-pressure core spray pump 23 is activated in response to "low or low reactor water level" and the condensate in the sublet pool 26 is injected into the reactor pressure vessel 9. After the pressure in the reactor pressure vessel 9 is reduced by the cooling water pump 22 and the high-pressure core spray pump 23, the condensate in the suppression pool 26 is injected into the reactor pressure vessel 9 by the low-pressure core spray pump 24, and the pressure is further reduced.
Reduce the temperature and shut down the reactor. In addition, in Figure 2,
25 indicates a reactor containment vessel.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a nuclear reactor water level control method that solves the problems of the prior art and can prevent reactor scram when a pump of a condensate system is tripped during normal operation.

[Summary of the invention]

The present invention detects when a pump in a condensate system trips, and compares the number of operating pumps in the condensate system with the plant load,
When the number of operating pumps is insufficient, the reactor recirculation pump is runback to reduce the core flow rate,
The feature is that the reactor output is reduced, and with this configuration, it is possible to prevent reactor scram when the pump of the condensate system is tripped during normal operation.

[Embodiments of the invention]

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

3 to 5 show an example of a water level control device for carrying out the present invention and its functions.

Figure 3 shows the main steam system, condensate water supply system, and reactor recirculation control system. The water is purified to an appropriate quality by the condensate purification device 3, and the pressure is increased by the high pressure condensate pump 4.
The water is heated by the low-pressure feedwater heater 5, boosted in pressure by the turbine-driven feedwater pump 7 or the motor-driven feedwater pump 6, heated by the high-pressure feedwater heater 8, and then supplied to the reactor pressure vessel 9.

The steam generated by the reactor pressure vessel 9 drives the steam turbine 11, rotates the generator G,
Generate electricity.

Next, in reactor water level control, single-element control is performed using the reactor water level detector 15 during low loads, and single element control is performed using the reactor water flow rate detector 14, reactor water level detector 15, and main steam flow rate detector during high loads. Three-element control including 16 is performed. In addition, in response to load fluctuations and transient events, the water supply flow rate is controlled by the steam control valve 12 in the turbine-driven water supply pump 7 and by the water supply control valve 13 in the motor-driven water supply pump 6. The water level in the reactor pressure vessel 9 is kept constant.

Furthermore, in addition to the reactor output control using the control rods, the plant output is controlled by controlling the reactor core flow rate using the reactor recirculation pump 10 during normal operation, thereby controlling the reactor output.

The capacity and number of pumps in the condensate water supply system in this example are as follows: Low pressure condensate pump 2...33% x 3 High pressure condensate pump 4...33% x 3 Turbine driven water supply pump 7...50% x 2 Base electric motor driven water supply pump 6... 25% x 1 unit.

In FIG. 3, reference numeral 17 indicates a controller for the reactor recirculation pump 10, steam control valve 12, and water supply amount control valve 13 during normal operation.

The present invention is characterized in that the apparatus is provided with a runback determiner 31. Then, a pump trip is detected based on the number of operating low-pressure condensate pumps 2, high-pressure condensate pumps 4, turbine-driven water supply pumps 7, and motor-driven water supply pumps 6, and the water supply flow rate signal from the water supply flow rate detector 14,
It is configured to determine whether or not a runback of the reactor recirculation pump 10 is necessary, and to run back the reactor recirculation pump 10 when necessary.

Next, FIG. 4 shows the determination logic of the runback determiner 31, and an example of the method of the present invention will be explained with reference to FIGS. 3 and 4.

During 100% load operation of the plant, all three low pressure condensate pumps 2 are operated. At this time, the water supply flow rate detector 14 sends to the runback determiner 31 that water is being supplied at the 100% load water supply flow rate.

In this operating state, the low pressure condensate pump 2 is
When the machine trips, a trip signal is sent to the runback judger 31, which judges that the water supply capacity of the pump is insufficient to the operating load of 100%, as shown in FIG. The reactor recirculation pump 10 is run back and reactor power is reduced. Thereby, the amount of water level drop in the reactor pressure vessel 9 can be reduced and reactor scram can be prevented.

During 66% load operation, if three low pressure condensate pumps 2 are in operation, the initial load is 66% even if one trip, so it is possible to supply water to the reactor with two low pressure condensate pumps. Since the reactor water level does not decrease,
The runback determiner 31 is the reactor recirculation pump 1
Do not run back 0. The low pressure condensate pump 2
If one of the reactor recirculation pumps trips while two of them are in operation, the runback determiner 31 runs back the reactor recirculation pump 10 to reduce the amount of water level drop in the reactor pressure vessel 9 because the water supply capacity is insufficient. As a result, it becomes possible to prevent reactor scrams.

As can be seen from FIG. 4, the runback determiner 31 operates in the same manner even when the high-pressure condensate pump 4 and the turbine-driven water supply pump 7 trip.

In this way, the runback determiner 3 of this embodiment
1, when the pumps in the condensate water supply system trip, the number of operating pumps is compared with the water supply flow rate as the plant load, and when the number of operating pumps is insufficient, the reactor recirculation pump 10 is activated. Runback is performed to reduce the amount of water level drop in the reactor pressure vessel 9 and prevent reactor scram.

As mentioned above, the runback determination device 31 of this embodiment uses the feed water flow rate as the plant load determination element, but other factors such as generator output, pressure after the first stage of the high pressure turbine, etc. It is also possible to adopt a method that can detect the load of the plant.

Next, FIG. 5 shows water level control characteristics according to the prior art and the embodiment of the present invention. In FIG. 5, the conventional technique is shown by a dashed line, and the change according to the embodiment of the present invention is shown by a solid line, which shows the change when the low pressure condensate pump 2 trips during 100% load operation.

As can be seen from Fig. 5, in the conventional technology, the water level in the reactor pressure vessel 9 becomes low in about 50 seconds after the low-pressure condensate pump 2 trips, and there is a possibility that a reactor scram may occur. However, in the embodiment of the present invention described above, the amount of water level drop is small and the recovery is quick, making it possible to avoid reactor scram.

Figure 6 shows a condensate injection system that injects condensate into the reactor pressure vessel after a reactor scram, and a suppression pool water injection system that injects condensate from the suppression pool. This shows the case where the electric motor-driven water supply pump does not have a standby unit.

The water level control device shown in FIG. 6 injects condensate in a condensate storage tank 21 into a reactor pressure vessel 9 using a cooling water pump 22. On the other hand, the high pressure core spray pump 23 and the low pressure core spray pump 2
4, the condensate in the suppression pool 26 is injected into the reactor pressure vessel 9.

In the present embodiment, the apparatus is configured such that when the motor-driven water supply pump 6 which is operated at the time of starting and stopping the plant trips, the trip is detected by the runback determiner 31 and the cooling water pump 22 is started. .

Next, FIG. 7 shows the determination logic of the runback determiner 31, and an example of the runback determination method will be explained with reference to FIGS. 6 and 7.

When the plant starts or stops, electric motor-driven water supply pump 6
If the reactor trips during operation, the runback determiner 31 starts the cooling water pump 22, immediately injects the condensate in the condensate storage tank 21 into the reactor pressure vessel 9, and suppresses the amount of water level drop. The high-pressure core spray pump 23 and the low-pressure core spray pump 24 are prevented from starting, and the inside of the reactor power vessel 9 is prevented from being contaminated with condensate in the suppression pool 26.

Here, as can be seen from FIG. 7, if the motor-driven water supply pump 6 trips while operating in parallel with the turbine-driven water supply pump 7, plant operation can be continued and there is no need to start the cooling water pump 22. The runback determiner 31 starts the cooling water pump 22 only when the load of the plant is within the operating range of only one motor-driven water supply pump, that is, in this embodiment, when the load is less than 25%. The load is detected by the water supply flow rate detector 14.

In this embodiment, the load of the plant is set at the upper limit of the operating range of the motor-driven water supply pump 6, and the upper limit is set at 25%, but the load is not limited to this value. Furthermore, the reactor water level drop signal can be extracted and used as a starting condition for the cooling water pump 22.

Next, FIG. 8 shows water level control characteristics according to the prior art and the embodiments shown in FIGS. 6 and 7. In FIG. 8, the conventional technique is shown by a dashed line, and the changes according to this embodiment are shown by a solid line. Furthermore, FIG. 8 shows changes in the reactor water level when the motor-driven water supply pump 6 trips during operation when the plant is operated at 25% load.

As can be seen from FIG. 8, in the conventional technology, the reactor water level reaches the starting water level for the high-pressure core spray pump 23 after about 60 seconds, but according to this embodiment, the amount of water level decrease is small, and the water level also increases. It becomes possible to recover and avoid starting the high-pressure core spray pump 23.

As a result, contamination of the reactor pressure vessel 9 due to injection of condensate into the suppression pool 26 that has not been purified can be prevented.

〔Effect of the invention〕

According to the present invention, when a pump in the condensate system trips, the trip is detected, and the number of pumps in operation in the condensate water supply system is compared with the load of the plant, and if the number of pumps in operation is insufficient, the trip is detected. At times, the reactor recirculation pump is run back to lower the core flow rate and reactor output, which has the effect of preventing reactor scrams caused by tripping of the condensate system pumps.

[Brief explanation of drawings]

Figure 1 is a diagram showing each system of a nuclear power plant to explain the conventional reactor water level control method, Figure 2 is a diagram also showing the reactor spray system, and Figure 3 is a diagram showing each system of a nuclear power plant to explain the conventional reactor water level control method.
The figure shows an embodiment of a reactor water level control device for carrying out the present invention, and shows the connection relationship between the runback determiner that constitutes the reactor water level control device and each system of a nuclear power plant. Figure shown, 4th
The figure shows the judgment logic of the runback judger shown in Fig. 3, Fig. 5 shows a comparison of the water level control characteristics of the conventional technology and the reactor water level control system shown in Fig. 3, and Fig. 6 shows the judgment logic of the runback judger shown in Fig. 3. This is a diagram showing one embodiment of the reactor water level control system, and shows the connection relationship between the runback determiner and the reactor spray system that constitute the reactor water level control system, and FIG. 7 is similar to FIG. FIG. 8 is a diagram showing a comparison of the water level control characteristics of the conventional technology and the reactor water level control system shown in FIG. 6. 1... Condenser, 2... Low pressure condensate pump forming the condensate water supply system, 4... High pressure condensate pump,
6...Electric motor-driven water supply pump, 7...Turbine-driven water supply pump, 9...Reactor pressure vessel, 10
... Reactor recirculation pump constituting the reactor recirculation system, 11 ... Steam turbine, 14 ... Feed water flow rate detector, 15 ... Reactor water level detector, 16
... Steam flow rate detector, 21 ... Condensate storage tank forming the reactor spray system, 22 ... Cooling water pump, 23 ... High pressure core spray pump, 24 ... Low pressure core spray pump, 25...
... Reactor containment vessel, 26 ... Suppression pool, 31 ... Runback determiner forming the reactor water level control device.

Claims (1)

[Claims] 1 Pressurize the condensate in the condenser using multiple condensate pumps, then supply water to the reactor using multiple water supply pumps.
The reactor water level is controlled to a normal water level by controlling the water supply flow rate and the core flow rate by the reactor recirculation pump according to each detected value of the reactor water level, the water supply flow rate to the reactor, and the main steam flow rate from the reactor. In addition, when one of the water supply pumps trips and the water supply flow rate to the reactor is insufficient for the plant load, the reactor recirculation pump is runback to reduce the core flow rate and control the reactor water level to the normal water level. In the reactor water level control method, the number of the condensate pumps in operation is compared with the plant load, and when the number of pumps in operation is insufficient for the plant load, the reactor recirculation pump is run back to reduce the core flow rate. A nuclear reactor water level control method, comprising controlling the reactor water level to the normal water level.