JPH03213603A - Controller for turbine steam governing valve - Google Patents

Abstract

PURPOSE:To moderate a transient phenomenon in a nuclear reactor at the time of closure of a turbine steam governing valve, in a controller where a valve position control circuit controls the position of the steam governing valve, by providing a change rate restricting device for restricting a closing speed of the steam governing valve, and varying a preset value according to the output of the reactor. CONSTITUTION:In a controller for a turbine steam governing value, the position of a steam governing valve 3 is determined according to an opening degree requiring signal 10 output from a pressure controller 9 on the basis of a nuclear reactor pressure signal 8 from a reactor pressure vessel 1, via a valve position control circuit 11. A power load unbalance relay 14 for inputting a turbine first-stage steam chamber pressure signal 12 and a current signal 13 from an electric line 7 is adapted to give an output to a rapid operational mode start circuit 15 when an output deviation exceeds a predetermined value, to rapidly close the steam governing valve 3 as well as to operate an emergency reactor shutdown system 16. In this case, the valve position control circuit 11 is provided therein with a change rate restricting device 18, a preset value of which can be varied according to a reactor output equivalent signal 19 by means of a change rate setting control circuit 20.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a turbine steam control valve control device in a nuclear power plant equipped with a boiling water type light water reactor, and particularly relates to a pressure control device during rated power operation. It is possible to alleviate transient events in the reactor when the turbine steam control valve is closed due to a failure of equipment, etc., and to reduce the rotational speed of the turbine main shaft in the event of generator load shedding while the reactor output is low. The present invention relates to a turbine steam control valve control device that can prevent the rise from exceeding a design target value and alleviate transient events in a nuclear reactor.

(Prior art) In a nuclear power plant equipped with a boiling water reactor, when a turbine steam control valve closure request signal is output due to a failure in a pressure control device, etc., a circuit that specifically limits the closure time is installed. Because it is not provided, the turbine steam control valve closes at a very rapid rate. The shutdown time is generally less than a few seconds in a typical nuclear power plant with a boiling water reactor.

(Problem to be Solved by the Invention) However, when the turbine steam control valve is closed at such a high speed, the outflow of the steam generated in the reactor is restricted, and the pressure in the reactor increases, resulting in This collapses the voids in the reactor core, injecting positive reactivity and increasing the reactor's output. According to the results of the dynamic characteristic analysis, it is known that there is a possibility that the margin in terms of fuel integrity will decrease as the output of the reactor increases.

One possible way to alleviate this problem is to make the turbine steam control valve close more slowly than it currently does.

According to the results of dynamic characteristic analysis, it has been found that fuel integrity can be ensured when a transient event occurs if the turbine steam control valve is closed for 6 to 8 seconds or more from fully open to fully closed.

For this purpose, it can be said that it is an effective measure to slow down the closing time by providing a closing speed change rate limiter in the valve position control circuit of the turbine steam control valve.

On the other hand, in a nuclear power plant equipped with a boiling water reactor, if the power grid is interrupted during plant operation,
In order to promptly stop the steam supply to the turbine generator and prevent the rotational speed of the turbine main shaft from increasing, a circuit is provided for rapidly closing the turbine steam control valve. The design goal of this nuclear power plant is that the rotational speed of the turbine main shaft does not exceed approximately 110% of the rated value when the generator load is cut off, and from this point of view, the closing time of the turbine steam control valve is required to be fast. .

For this purpose, nuclear power plants have a protection relay called a power load unbalance relay, which constantly compares the reactor output calculated from the turbine's first stage steam chamber pressure and the generator load calculated from the transmission line current. When the difference exceeds 40%, the turbine steam control valve is closed in a rapid operation mode. At this time, the output of the reactor increases due to a sudden pressure rise, and the margin for fuel integrity decreases, but the nucleate boiling state is maintained due to the reactor scram, etc. that occurs at the same time as the start of the rapid operation mode, which is particularly problematic. It is designed to prevent this from happening. The closing time of the turbine steam control valve in the rapid operation mode is extremely fast, usually less than about 100 m5ec, and even if a generator load shedding occurs, the rotation speed of the turbine main shaft will not exceed the design target value.

However, when generator load shedding occurs when the initial output of the reactor is lower than the rated output, there are cases where the operation set value of the power load imbalance relay is not reached. Typically, this occurs when the reactor output is 40% or less and generator load shedding occurs, but in reality, the reactor output is 60 to 7%.
Even in the case of 5%, the power load unbalance relay may not operate.

This is the case when the power system frequency increases slightly when the reactor power is initially operating at 60-75%, and then the generator load is cut off.

Generally, when the system frequency increases, the pressure control device detects this and instructs the turbine steam control valve to be slightly throttled in order to reduce the rotational speed of the turbine main shaft.

For this reason, the amount of steam supplied from the reactor to the turbine generator decreases, the pressure in the turbine first stage steam chamber decreases, and as a result, the reactor output equivalent signal input to the power load imbalance relay decreases by 40%. If the following conditions occur, the power load unbalance relay will not operate even if a generator load shedding occurs. If the power load unbalance relay is not activated, the quick-actuation mode of the turbine steam control valve is not activated, and the turbine steam control valve closes in a normal closing mode, which is slower than the rapid-actuation mode, according to the commands of the pressure control device.

According to the analysis results, it is known that the increase in the rotation speed of the turbine main shaft becomes the most severe in such cases, and in order to maintain the design target of approximately 110% or less of the rated value, it is necessary to increase the turbine steam control valve. The closing time in the normal closing mode is required to be approximately 6 to 8 seconds or less from fully open to fully closed.

Now, during rated power operation, the minimum allowable closing time of the turbine steam regulator is set to α seconds, power low The maximum allowable closing time of the turbine steam control valve to suppress the increase in rotation speed of the turbine main shaft to approximately 110% or less in the event of a generator load shedding in which the imbalance relay does not operate is assumed to be β seconds, and each power generation plant If you evaluate this for each case, it will be found that β < α or even if α < β, the difference is small, and it is necessary to actually install a rate of change controller in the valve position control circuit of the turbine steam control valve to limit the closing time. The results show that it is difficult.

In addition, in current nuclear power plants, the setting value of the power rotor unbalance relay is 40%, and even if this setting value is lowered and the generator load is cut off, the turbine steam control valve will be rapidly turned on by the rapid operation mode. If it is closed, the upper part of the turbine shaft rotational speed will not be a problem, but
In this case, there is a disadvantage that the reactor will be shut down due to reactor scram occurring in parallel, so it is not a realistic plan.

The present invention has been made in consideration of the above circumstances, and is intended to alleviate transient events in a nuclear reactor when the turbine steam regulating valve is closed due to a failure of the pressure control device. Due to the requirement that the closing time needs to be slowed down, the rotation of the turbine main shaft occurs when there is a generator load shedding, such as when the power load unbalance relay does not operate and the rapid operation mode of the turbine steam control valve does not operate. It is an object of the present invention to provide a turbine steam control valve control device that can satisfy two requirements: the need to shorten the closing time in order to suppress the increase in the number of steam regulators to below a design target value.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a turbine steam control valve provided in a main steam pipe that guides steam from a boiling water reactor to a turbine generator, and a turbine steam control valve provided in a main steam pipe that guides steam from a boiling water reactor to a turbine generator. A turbine steam regulator control device comprising a valve position control circuit that controls the valve position of a regulator valve, a rate of change limiter that limits the closing speed of the turbine steam regulator, and a set value of the rate of change limiter. It is equipped with a rate-of-change setting control circuit that changes the output according to the reactor output.

(Function) When the reactor output is as high as the rated output, this function is used to alleviate transient events when a turbine steam control valve closing request signal is generated due to a failure in the rate of change setting control circuit or pressure control device, etc. The setting value of the rate of change limiter is varied so that the closing speed is slower than the minimum allowable closing time of the turbine steam control valve.

The rate of change limiter limits the closing speed of the turbine steam control valve to be slower than the minimum allowable closing time based on its set value. Therefore, it is possible to alleviate a transient event in the reactor in which the margin in terms of fuel integrity decreases due to an increase in the output of the reactor.

On the other hand, when the reactor output is low enough that the power load unbalance relay does not operate, the rate of change setting control circuit or the power load unbalance relay does not operate. The setting value of the rate of change limiter is changed so that it becomes faster than the maximum allowable closing time of the turbine steam control valve in order to suppress the increase in the rotational speed of the turbine to below the design target value.

The rate of change limiter limits the closing speed of the turbine steam control valve to be faster than the maximum allowable closing time based on its set value. Therefore, the increase in the rotational speed of the turbine main shaft can be suppressed to below the design target value. In this case, since the reactor power is low, transient events in the reactor can be alleviated even if the closing speed of the turbine steam control valve is increased.

(Example) Hereinafter, an example of a turbine steam control valve control device according to the present invention will be described with reference to the accompanying drawings.

In FIG. 1, a main steam pipe 2 is connected to a reactor pressure vessel 1, and this main steam pipe 2 is connected to a turbine 4 after a turbine steam control valve 3 is inserted downstream. The turbine 4 is connected to a generator 6 via a turbine main shaft 5, and the power generated by the generator 6 is transmitted to the power grid via a power transmission line 7.

On the other hand, a reactor pressure signal 8 from the reactor pressure vessel 1 is input to a pressure control device 9, and this pressure control device 9 outputs an opening request signal 10 for the turbine steam control valve 3. . This opening request signal 10 is input to a turbine steam regulating valve position control circuit 11, and this turbine steam regulating valve position control circuit 11 determines the valve position of the tapin steam regulating valve 3 according to the opening request signal 10. It has become.

Further, a turbine first stage steam chamber pressure signal 12 from the turbine 4 and a current signal 13 from the power transmission line 7 are input to a power load unbalance relay 14, and this power load unbalance relay 14 detects the output deviation. is 40
% or more, a signal is sent to the rapid operation mode starting circuit 15 that starts the rapid operation mode of the turbine steam control valve to rapidly close the turbine steam control valve 3, and a signal is sent to the reactor emergency shutdown system 16. immediately scram the reactor.

If the pressure control device 9 malfunctions and the opening request signal 10 that closes the turbine steam control valve 3 is output, the turbine steam control valve 3 will be fully closed in a few seconds, and the reactor pressure will rise. As a result, fuel integrity becomes a problem. Further, when the frequency of the power system temporarily increases or generator load cutoff occurs, and the rotation speed of the turbine main shaft 5 increases, a turbine rotation speed increase signal 17 is transmitted to the pressure control device 9.
A command is issued to close the turbine steam control valve 3.

Figure 2 shows the minimum allowable value α for the closing time of the turbine steam regulator 3 based on the results of a dynamic characteristic analysis conducted assuming that a failure occurred in the pressure control device 9 and the turbine steam regulator 3 was closed for a certain period of time. is determined for each reactor output, and in the rated output operating state, the value α is about 6 to 8 seconds. Further, in a state where the reactor power is reduced, α gradually decreases, and even if the reactor is shut down fairly quickly in a state of 50 to 60% power, for example, the fuel integrity of the reactor can be sufficiently maintained.

On the other hand, the reactor output at which generator load shedding occurs such that the power load unbalance relay 14 does not operate varies depending on the individual boiling water type light water reactor, but is approximately 60 to 75%. In such a case, the maximum allowable closing time β of the turbine steam control valve 3 is approximately 5 to 7 seconds, although this also varies depending on the individual boiling water reactor.

Therefore, constraint conditions from this viewpoint are also shown in FIG. 2. The conventional turbine steam regulator valve position control circuit 11 of a boiling water type light water reactor is not provided with a circuit that limits the closing time of the turbine steam regulator valve 3. The closing time γ is determined by the structure of the turbine steam control valve 3 body,
Generally less than a few seconds.

Taking these things into consideration, in order to maintain the fuel integrity of the reactor, the intersection point P of line α and line γ in FIG. At outputs above , the closing time of the turbine steam control valve 3 is set by the line
It can be seen that it is necessary to control so that the above is achieved. When α is larger than β in the rated power operating state, it is impossible to limit the closing time of the turbine steam control valve 3 using a constant value over the entire power range, but this is shown in Fig. 2. As shown by the broken line A, by making it variable according to the reactor output, it is possible to create a configuration that satisfies the initial requirements. Note that the broken line A may be curved, stepped, etc. as long as it envelops the line α.

Therefore, in this embodiment, a change rate limiter 18 is provided in the turbine steam regulator valve position control circuit 11 to limit the closing speed of the turbine steam regulator valve 3. Then, in order to change the closing time of the turbine steam control valve 3 as shown by the broken line A in FIG. A rate-of-change setting control circuit 20 is provided to change the rate of change according to the output of the reactor.

In this embodiment, when the reactor power is as high as the rated power, the rate of change setting control circuit 20 controls the pressure control device 9.
When a closure request signal for the turbine steam regulator 3 is generated due to a failure such as, the closing speed is slower than the minimum allowable closing time α of the turbine steam regulator 3 for mitigating the transient event. The setting value of the rate limiter 18 is changed.

The rate of change limiter 18 controls the turbine steam control valve 3 so that the rate of change limiter 18 is later than the minimum allowable closing time α based on its set value.
limit the closing speed. Therefore, it is possible to alleviate a transient event in a nuclear reactor where an increase in the reactor's output causes a decrease in the margin for the soundness of the fuel.

On the other hand, reactor output or power load unbalance relay 1
When the rate of change setting control circuit 20 is low to a certain extent, such as when the power load imbalance relay 14 does not operate, the design target is set to increase the rotation speed of the turbine main shaft 5 when a generator load cutoff occurs such that the power load imbalance relay 14 does not operate. The setting value of the rate of change limiter 18 is changed so that it becomes faster than the maximum allowable closing time β of the turbine steam control valve 3 for suppressing the closing time to below the value.

Based on the set value, the change rate limiter 18 controls the turbine steam control valve 3 so that the rate of change is faster than the maximum allowable closing time β.
limit the closing speed. Therefore, the increase in the rotational speed of the turbine main shaft 5 can be suppressed to below the design target value. In this case, since the reactor output is low, the turbine steam control valve 3
Faster closure speeds can also mitigate reactor transients.

〔Effect of the invention〕

As explained above, the present invention includes a rate-of-change limiter that limits the closing speed of a turbine steam control valve, and a rate-of-change setting control circuit that changes the set value of this rate-of-change limiter in accordance with the output of the reactor. By preparing for this, it is possible to alleviate transient events in the reactor when the turbine steam control valve is closed due to a failure of the pressure control device, etc., and to reduce the increase in the rotation speed of the turbine main shaft to the design target value when the generator load is cut off. It can be kept below.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a nuclear power plant equipped with a turbine steam control valve control device according to the present invention, and FIG. 2 is an example of the results of dynamic characteristic analysis regarding failure of the pressure control device in the above embodiment and turbine steam control device. FIG. 3 is a characteristic diagram showing a relationship between set values of valve closing time. 1 - Reactor pressure vessel, 2... Main steam pipe, 3... Turbine steam control valve, 4... Turbine, 5... Turbine main shaft, 6... Generator, 7... Power transmission line, 9 ... Pressure control device, 11 ... Turbine steam control valve position control circuit, I2 ... Turbine first stage steam chamber pressure signal, 15 ...
- Rapid operation mode starting circuit, 16... Nuclear reactor emergency shutdown system, 18... Rate of change limiter, 19... Nuclear reactor output equivalent signal, 20... Rate of change setting control circuit.

Claims (1)

[Claims] A turbine steam control valve control that includes a turbine steam control valve installed in a main steam pipe that guides steam from a boiling water light water reactor to a turbine generator, and a valve position control circuit that controls the valve position of this turbine steam control valve. The apparatus is characterized by comprising a rate-of-change limiter that limits the closing speed of the turbine steam control valve, and a rate-of-change setting control circuit that changes the set value of the rate-of-change limiter in accordance with the output of the reactor. Turbine steam control valve control device.