JPH04194782A - Recirculation flow controller - Google Patents

Abstract

PURPOSE:To prevent unnecessary low reactor water level/emergency plant stop and operation in the over limit region by running back the recirculation pump to an optimum runback speed according to the operational state in the case of lack of supply pump capacity. CONSTITUTION:An arithmetic circuit 41 calculates an optimum runback reaching speed signal 41c as a function of core flowrate signal 41a and flow force signal 41b and inputs 42c to a memory circuit 42. The output 42a of the circuit 42 varies in accordance with the input 42c when a switch 42b is closed, and maintains the value of the immediate previous input 42c when the switch 42b is opened. That means, a recirculation pump speed demand signal 45 and an output 42a are switched at switches 43a and 43b to be a recirculation pump speed command 44. If the water supply pump stops during operation by some reason and the startup of a backup pump also fails, a water supply pump capacity lacking signal 46a turns on and the switch 43a and 42b close and the switch 43b opens due to the recirculation runback signal 46. Then the signal 46a decreases to the speed of signal 41c calculated for the operation condition immediately before the signal 46a turns on. Therefore, in the case of a single pump trip, the region of emergency plant stop is minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to a recirculation flow rate control device in a boiling water atomic couplant.

(Prior Art) In general, in a boiling water nuclear coupler, there are control rods and a recirculation pump as means for controlling the reactor output. Its configuration is shown in Fig. 4, and the core flow rate can be changed by changing the position of the control rods 2 using the control rod drive device 1 or by changing the speed of the recirculation pump 3. 4, the amount of heat generated, that is, the furnace output changes.

In the plant, steam generated according to the furnace output is supplied to a turbine 6 by adjusting the opening of a steam control valve 5, and is converted into electrical energy by a generator 7. In addition, condenser 8
The steam that has passed through the turbine 6 becomes water, which is supplied into the reactor pressure vessel 10 by the water supply pump 9, thereby forming a total balance by keeping the reactor water level constant.

Incidentally, the control characteristics of the furnace output have characteristics as shown in FIG. That is, when the control rods are withdrawn while keeping the recirculation pump speed constant, the output increases according to curves 11a and llb (the pump speed is higher on curve 11b than on curve 11a), and if the control rod pattern is kept constant When the recirculation pump speed is increased and the core flow rate is increased, the output increases as shown by curves 12a and 12b. Among these methods, the latter method allows the output of the reactor to be changed simply by changing the pump speed, so it is characterized by the ability to change the output more quickly than the former method of changing the output using control rods.

In a typical nuclear coupler plant, this property is utilized to avoid a drop in the reactor water level/emergency shutdown of the plant in the event that the water supply pump fails or trips and the required water supply flow rate cannot be obtained. A system that rapidly reduces the recirculation pump speed to a preset speed (usually the minimum speed) when a water pump capacity shortage signal is issued, aiming to ensure that the furnace output is less than the maximum water supply flow rate at that time. (runback interlock) is installed.

For example, if two feed pumps are installed with a 55% rated water flow rate, if one trips and the backup feed pump (27.5% capacity) fails to start, the recirculation pump speed will be reduced to the minimum. The speed is then rapidly reduced so that the furnace pressure is below 55% rated. The movement of the operating point in this example is shown in FIG. 6(a). Note that the water supply pump capacity shortage signal in this case is obtained by the logic shown in FIG. 6(b), but it may also be set by other logic.

(Problem to be Solved by the Invention) In a boiling water nuclear coupler, in order to obtain 100% rated output, the core flow rate does not necessarily need to be 100%, and depending on the control rod pattern, the core flow rate may be even lower. However, 100% rated output can be obtained.

That is, taking FIG. 7 as an example, 100% rated output can be obtained not only at the operating point 31 but also at operating points 32, 33, 33, and 34.

On the other hand, in a boiling water reactor, the lower the core flow rate/blast core output, the worse the thermal hydraulic stability of the core becomes. Therefore, in order to perform operation with more reliable thermal-hydraulic stability, as shown in FIG.
A restriction line indicated by B may be provided to restrict driving in the upper left area of this line.

In such a case, if the recirculation pump speed is run back to the lowest speed in the event of a feed water pump trip and standby unit startup failure using a conventional runback interlock, the initial operating point will be 32.33. In the case of 34, the vehicle enters a region where driving is restricted.

As a way to avoid this, code 31. 32°33.3
4. A method of increasing the recirculation bomb runback attainment speed so as not to enter the operation restricted area after the runback from any of the operating points in 4. (In this case, the operating point after the runback is on the line 38A-38B. In this way, according to the traditional runback interlock,
Although the reactor water level drop/emergency shutdown of the plant could be avoided,
Since the recirculation pump speed after runback is high, a sufficient reduction in the reactor output cannot be achieved, resulting in the problem that an emergency shutdown of the plant due to low reactor water level cannot be avoided.

The present invention has been made in consideration of these points, and is capable of automatically adjusting the runback reaching speed in a plant having an operation restriction area so that the operating point after the runback does not fall within the operation restriction area. By doing so and maintaining the range of reactor output reduction due to runback as much as possible, it is possible to avoid unnecessary low reactor water levels/plant emergency shutdowns and operation in restricted operation areas when the feed water pump capacity is insufficient. The purpose of the present invention is to provide a recirculation flow rate control device that can be used.

[Structure of the invention]

(Means for Solving the Problem) As a means for achieving the above object, the present invention grasps the reactor operating state based on a core flow rate signal and a reactor output signal,
It is characterized by being equipped with a calculation circuit that calculates the optimal runback speed according to the operating state, and an interlock that allows the recirculation pump to run back to the runback speed when the water supply pump capacity is insufficient. shall be.

(Function) In the recirculation flow rate control device according to the present invention, when the feed water pump capacity is insufficient, the lowest recirculation pump speed that does not enter the operation restriction area after runback is calculated from the reactor operating state, Rapidly run back to that speed.

Therefore, it is possible to avoid low reactor water level/plant emergency shutdown and operation in the restricted operation area.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of the recirculation flow rate control device according to the present invention. In the figure, reference numeral 41 is a calculation circuit for the optimum runback attainment speed, and this calculation circuit 41 is connected to the core flow rate signal 4.
1a and the reactor output signal 41b, the optimum runback attainment speed signal 4 is always
1c, and this optimum runback arrival speed signal 41c
is input to an analog signal storage circuit 42.

The output 42a of the memory circuit 42 changes in accordance with the human input signal 42c when the input contact 42b is closed, and maintains the value of the input signal 42c immediately before the input contact 42c was opened when the input contact 42b is open. It has become.

This output 42a then becomes a recirculation pump speed command 44 via a contact 43a.

On the other hand, the recirculation pump speed request signal 4 used in normal times
5 becomes a recirculation pump speed command 44 via a contact 43b, as shown in FIG.

That is, this recirculation pump speed request signal 45 and the output 42a of the memory circuit 42 are switched by contacts 43a and 43b to become a recirculation pump speed command 44.

Further, the contacts 43a, 43b, and 42b are configured to close, open, and close, respectively, when the recirculation bomb runback command signal 46 is established.

As shown in FIG. 1, this recirculation pump run back command signal 46 is output as a hold signal for the water pump capacity shortage signal 46a, and is released by a reset command 46b.

Next, the operation of this embodiment will be explained.

The calculation circuit 41 calculates 4.1 c-F (41a, 4 l
The optimal runback arrival speed signal 41c is calculated using a function given in advance in the form b). This function is given as shown in FIG.

That is, the reactor operating conditions are as shown in FIG.
In the case of 51a and 51b, the optimal runback attained speed signal 41c is set as a function of two variables so that the PLR pump constant speed change curve LR pump speed values indicated by symbols 56-56' are given. In addition, when the reactor operating conditions are 52 degrees 52a, 52b, the PLR pump constant speed change curve LR pump speed value indicated by 57-57' is given as the optimum runback attained speed signal 41C. , is set as a function of two variables. Furthermore, if the reactor operating conditions are 53 degrees 53a, 53b, the PLR pump constant speed change curve L indicated by 58-58' is used as the optimum runback attained speed signal 41c.
The R pump speed value is set as a function of two variables to be given.

In addition, the extension line of the PLR pump constant speed change curve 5l-51a-51b with reference numerals 56-56' is the operation limit curve 50.
-50', the PLR pump constant speed change curve passing through the intersection 51d, and the extension line of the PLR pump constant speed change curve 52-52a-52b with reference numerals 57-57' are the operation limit curve 50-50'. PLR passing through the intersection 52d
Pump constant speed variable speed curve. Furthermore, PLR pump constant speed change curve curve 5B-53; a-53 with reference numerals 58-58'
A PLR pump constant speed change curve passes through an intersection 53d where the extension line of b intersects with the operation limit curve 50-50'.

Here, the curve 5l-51a-51b is the locus of the operating point that changes by lowering the PLR pump speed when the reactor operating condition is at code 51, and the curve 5
2-52a-52b, 53-53a-53b, 54-5
The same applies to 4a-54b.

Also, curves 56-56', 57-57', 58-5
8' is a constant speed change curve of the PLR pump, which is a locus when the PLR pump speed is kept constant and the control rod is withdrawn and inserted to change the reactor output.

By the way, when the PLR pump constant speed change curve indicated by the symbol 58-58' is the lowest operating speed of the PLR pump, it is not possible to run back below this speed, so the operating point is indicated by the symbols 54-54a-54b. If the pump speed is at the point indicated by , the pump speeds indicated by numerals 58 to 58', that is, the lowest speeds, are given as the optimum runback attained speed signal 41c.

In this way, during reactor operation, if the feedwater pump stops for some reason and the standby unit also fails to start, the feedwater pump capacity shortage signal 46a turns ONt, and the recirculation bomb back command signal 46 is output. At this time, the runback decreases to the speed given by the optimum runback attainment speed signal 41c determined by a function from the reactor operating conditions immediately before the feed water pump capacity shortage signal 46a turns ON.

The effect varies depending on the capacity and number of water pumps, how the operation restriction area is set, etc., but an example of the effect will be described below with reference to FIG. 2.

Regarding water supply pumps, there are many cases where two 55% capacity pumps are installed, and if one of these pumps stops, the remaining one can supply approximately 65% of the water due to the Q/H characteristics of the pump. be.

Therefore, in the case of one water pump, the furnace output is
If it is set below the line 60-60' in FIG. 2, it is possible to avoid a drop in reactor water level/emergency shutdown of the plant due to insufficient water supply.

When the recirculation flow rate control device according to this embodiment is applied to such a plant, even if only one water pump is used when operating below the curve 55-55d-53d,
Recirculation Bonn Run Back achieves a reduction to the furnace power below curve 60-60' and avoids an emergency plant shutdown.

However, if only one water pump is operated during operation in the area surrounded by curve 55-55d-51d-51-55, the output will not fall below curve 60-60' even after runback, causing a plant emergency. It will be stopped.

However, if the conventional interlock is maintained and the operation is not entered into the restricted operation area after runback, runback will only be possible to the PLR speed shown by curve 56-56', and one water pump will be stopped. The area where emergency plant shutdown cannot be avoided is curve 5l-52-
The area is surrounded by 52d-55d-51d-51,
The range becomes wider.

Therefore, according to this embodiment, it is possible to reduce the area where a plant emergency shutdown occurs when one water pump trips.

In the above-mentioned embodiment, as described above, there is still an operating region in which an emergency stop of the plant cannot be avoided due to tripping of one water pump.

By the way, in boiling water reactors, in addition to reducing reactor power by recirculating bomb back, selective control rod insertion (SR
There is also a method of reducing the furnace output using I).

Therefore, if there is an operating region where there is a possibility of emergency shutdown of the plant, as in the above embodiment, in addition to the method of the above embodiment, it is possible to prevent the water supply pump capacity from being insufficient in such an operating region. On the other hand, by simultaneously operating the SRI, it is possible to reduce the furnace output when one feed water pump is operated to below the curve 60-60' shown in FIG.

FIG. 3 shows another embodiment of the present invention applied to such a case. In the figure, reference numeral 61 is an SRI required area determination circuit, and this SRI required area determination circuit 61 includes:
A core flow rate signal 41'a and a reactor output signal 41b are respectively input.

This SRI necessary area determination circuit 61 processes both the signals 41a and 41a.
, 41b, the operating region changes to curve 5 shown in FIG.
5-55d-51d-51-55, and if it is within the range, the SRI request signal 61
It is designed to output a. Then, the SRI insertion signal 62 is outputted by ANDing the SRI request signal 61a and the recirculation Bonn run back command signal 46.

In this way, by operating the SRI simultaneously, it is possible to completely avoid an emergency stop of the plant even when one water pump trips.

〔Effect of the invention〕

As explained above, according to the present invention, recirculation bomb runback to avoid emergency shutdown of the reactor due to insufficient capacity of the feedwater pump can be performed without entering the operation restriction region, and moreover, can effectively avoid emergency shutdown of the reactor. This makes it possible to improve the operation rate of the atomic couplant.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a recirculation flow rate control device according to an embodiment of the present invention, and FIG. 2 is a graph showing its control characteristics.
FIG. 3 is a block diagram showing another embodiment of the present invention, FIG. 4 is a configuration diagram showing reactor power control means in a boiling water reactor plant, and FIG. 5 is a graph showing an example of reactor power control characteristics. FIG. 6(a) is a graph showing an example of runback.
FIG. 7B is an explanatory diagram showing an example of the logic of the water pump capacity shortage signal in this case, and FIG. 7 is a graph showing the relationship between the operation restriction region and runback. 41... Calculation circuit, 41a... Core flow rate signal, 41
b...Furnace output signal, 41c...Optimum runback attained speed signal, 44...Recirculation pump speed command, 45...
- Recirculation pump speed request signal, 46... Recirculation pump run back command signal, 46a... Water pump capacity shortage signal. Applicant's representative: Kiyoshi Sato - Kiyoshi Yushin Figure 2 Figure 3 Figure 4 (a) (b) Figure 6

Claims (1)

[Claims] A calculation circuit that grasps the operating state of a nuclear reactor based on a core flow rate signal and a reactor output signal, and calculates an optimal runback speed according to the operating state; A recirculation flow control device comprising: an interlock for causing a recirculation pump to run back to a back speed;