JPH04215099A - Control device for atomic power plant - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a reactor water level rise turbine trip owing to the rise of a water level in a reactor during cutoff of a load, to prevent a minimum limit output ratio of fuel from exceeding an allowable limit, and to prevent the occurrence of a reactor scram owing to a rapid decrease in a core flow rate. CONSTITUTION:A re-circulating pump trip optimizing means operated in a manner described below is provided. During cutoff of a load, the optimum number of trips is evaluated and selected according to the input of a core flow rate signal and a re-circulating pump trip signal responding to the evaluating result is outputted. Through the input of an opening success and an opening failure signal, the optimum number of trips is re-evaluated, and a re-circulating pump trip correction signal responding to the re-evaluating result is inputted to a re-circulating pump trip means. During ordinary operation, the optimum number of trips is evaluated and selected through the input of a reactor output reduction signal, and a re-circulating pump trip signal responding to the evaluating result is outputted.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for a nuclear power plant, and more particularly to a system for controlling the number of trips of a recirculation pump.

0002

2. Description of the Related Art Steam generated in a nuclear reactor is guided through a turbine steam control valve to a turbine, which is connected coaxially with a generator to generate electricity. The steam is then guided to the main condenser, which is also connected to a bypass pipe that directs steam directly from the main steam pipe without going through the turbine. A bypass valve is installed in this bypass pipe, and this valve is normally closed. When the load on the generator is cut off due to an accident in the power transmission system, the turbine steam control valve is quickly closed to protect the turbine and generator, stopping the supply of steam to the turbine, and
The bypass valve suddenly opens and directs the steam generated in the reactor directly to the condenser. In a partial capacity bypass plant, the capacity of the bypass valve and condenser can only absorb a portion of the steam;
The pressure in the reactor increases. For this reason, in partial capacity bypass plants, the reactor is scrammed at the same time as load shedding to alleviate the rise in power and pressure.

On the other hand, in a full-capacity bypass plant, the bypass valve has the ability to absorb 100% of the steam flow rate during rated operation, so even if a load shedding occurs, the reactor can be operated independently without stopping the reactor. It is designed to be portable. In addition, in the unlikely event that the bypass valve does not open,
Upon receiving a signal that the bypass valve has failed to open, the reactor is scrammed to reduce the subsequent rise in output and pressure. In the current design, the time required for the bypass valve to open after a load shedding occurs is within 200 msec, and if the bypass valve does not open within this time, the reactor is immediately scrammed.

Next, the relationship between generator load shedding and recirculation pump trip will be explained. In the case of a partial capacity bypass plant or a full capacity bypass plant, if the bypass valve fails to open, the reactor is scrammed to suppress the rise in power and pressure, but normally reactor scram alone is not sufficient as a control measure. , the minimum critical power ratio exceeds the permissible limit value. For this reason, the recirculation pump is tripped by a load cutoff signal to reduce the core flow rate, and a negative reactivity is introduced due to the increase in voids, thereby reducing the output. In the improved BWR, a large number of recirculation pumps are installed in the pressure vessel, but their rotational inertia is small and the core flow rate drops rapidly during a trip, so if too many pumps are tripped at the same time, On the contrary, the coolant becomes insufficient, the minimum output ratio increases, and thermal conditions become severe. For this reason, partial capacity bypass plants are designed to scram the reactor with a load shedding signal and trip multiple recirculation pumps at once.

On the other hand, in a full capacity bypass plant, the following two methods have been considered for tripping the recirculation pump. (1) The load shedding signal immediately trips the five recirculation pumps. After approximately 200 mesc, it is confirmed whether the bypass valve is open or not. If it is open, the system shifts to in-station isolated operation, and if it fails to open, the reactor is scrammed. (2) When a load shedding signal is generated, no particular mitigation operation is taken for approximately 200 msec until the opening of the bypass valve is confirmed, and only when opening fails, the reactor is scrammed and the five recirculation pumps are tripped.

[0006] In addition, rather than as a method for responding to transient events such as generator load shedding, it is necessary to avoid negative reactivity in the core as a method of output adjustment in the current design, considering the expansion of the core operating range in the future of the improved BWR. There are recirculation pump trips, runbacks, and selective control rod insertions that provide However, when considering the core flow rate adjustment range, because the recirculation pump trip is uniform, when comparing the low flow rate side and the high flow rate side, the rate of rapid decrease in the core flow rate is severer on the high flow rate side. .

[0007]

[Problem to be solved by the invention] By the way, improved BW
When R is a full-capacity bypass plant, the conventional nuclear power plant control described above has the following problems. (1) When a generator load cutoff occurs, the turbine steam control valve is rapidly closed and the turbine bypass valve is rapidly opened, so that the increase in output and pressure is suppressed within an allowable range, and the plant can continue to operate. However, when 5 out of 10 recirculation pumps trip due to the load shedding signal, the core flow rate decreases, voids increase, and the reactor water level rises, leading to a high reactor water level turbine trip. When a turbine trip occurs, a turbine stop valve provided in the main steam pipe closes and a reactor scram occurs, resulting in a plant shutdown. In other words, even though the bypass valve has successfully opened and continued operation is possible, the plant will be shut down due to another factor, such as a rise in the reactor water level. For this reason, even if the capacity of bypass valves and the like is increased as a full-capacity bypass plant, it will not be able to fulfill its function.

(2) When a generator load cutoff occurs and the turbine steam control valve closes rapidly, the turbine bypass valve only needs to open suddenly, but if it fails to open, the output and pressure increase. In order to suppress this, it is necessary to activate the mitigation function as soon as possible. However, this operation is suspended for about 200 msec until it is confirmed that the bypass valve has failed to open. During this period, the output and pressure continue to rise, but according to the evaluation results, even if the reactor scram and 5 out of 10 recirculation pumps are tripped after a 200 msec delay, the minimum output ratio still satisfies the allowable limit value. I can't.

(3) In the case of an improved BWR, in recirculation pump trips as a means of reducing reactor power, the rotational inertia of the recirculation pump is small, and if a large number of pump trips occur at once, a rapid core flow rate will occur. A decline occurs. In addition, in a plant with a constant power output and a core flow rate adjustment range, because the recirculation pump trip is uniform, when comparing low flow points and high flow points, the rate of sudden decrease in core flow rate becomes more severe at high flow points. A sudden decrease in core flow rate leads to reactor scram. In other words, attempts were made to reduce reactor power in order to continue operating the reactor, but it would be meaningless if the reactor scrammed and shut down due to a sudden decrease in core flow rate.

The present invention has been made in consideration of these points, and it is possible to avoid a high reactor water level turbine trip due to a rise in the reactor water level at the time of load shedding, and also to reduce the minimum fuel output ratio. To provide a control device for a nuclear power plant, which can prevent reactor scram from exceeding an allowable limit value, avoid reactor scram due to sudden decrease in core flow rate, and improve operability of core flow rate adjustment during normal operation. The purpose is to

[0011]

[Means for Solving the Problems] As a means for achieving the above object, the present invention provides a core flow rate measuring means for measuring the core flow rate and outputting a core flow rate signal; recirculation pump trip means for tripping a number of recirculation pumps according to the number of recirculation pumps; turbine bypass valve operation confirmation means for confirming the open state of the turbine bypass valve and outputting an opening success or opening failure signal; and measuring reactor output. reactor output measuring means for outputting a reactor output reduction signal; at load cutoff, evaluating and selecting the optimum number of trips based on the input of the reactor core flow rate signal, and outputting a recirculation pump trip signal in accordance with this; With,
By inputting the opening success or opening failure signal, the optimum number of trips is re-evaluated, and a corresponding recirculation pump trip correction signal is given to the recirculation pump trip means, and during normal operation, the reactor output reduction signal is and a recirculation pump trip optimization means for evaluating and selecting the optimum number of trips based on the input of and outputting a corresponding recirculation pump trip signal.

0012

[Operation] In the nuclear power plant control device according to the present invention, when a generator load shedding occurs, the bypass valve is immediately expected to open successfully, evaluates the optimal number of trip units according to the current core flow rate, and trips the valve. At the same time, when a bypass valve opening success or opening failure signal is received, the number of tripped units is re-evaluated, and the excess or deficiency is processed for the recirculation pump with respect to the number of units previously tripped. Therefore, it is possible to avoid a high reactor water level turbine trip due to a rise in the reactor water level, and to prevent the minimum fuel output ratio from exceeding the allowable limit value.
It becomes possible to avoid a reactor scram caused by a sudden decrease in core flow rate. On the other hand, during normal operation, the optimum number of trip units is evaluated and tripped by inputting a reactor output reduction signal. Therefore, it is possible to improve the operability of core flow rate adjustment even when the core operating range is expanded.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a reactor pressure vessel. Inside this reactor pressure vessel 1, a reactor core 2 containing nuclear fuel is stored, and the heat generated by the nuclear reaction is given to the coolant. There is. A plurality of recirculation pumps 3 are installed in the lower part of the reactor pressure vessel 1 according to the thermal output of the reactor, and the coolant efficiently removes heat, and the flow rate of the coolant is changed to control the reactor. It is designed to control output. The steam generated in the reactor pressure vessel 1 is guided to the turbine 5 through the main steam pipe 4 connected to the upper part of the reactor pressure vessel 1, and the rotational force generated in the turbine 5 is transferred to the turbine main shaft. 6, the signal is transmitted to the generator to generate electricity. After doing work in the turbine 5, the steam is cooled in a condenser 7 and becomes condensed water.

A bypass pipe 8 is also connected to the condenser 7, which directly leads steam from the main steam pipe 4 without going through the turbine 5. Each pipe 8 is provided with a turbine bypass valve 10 . The turbine steam control valve 9 is normally controlled by a required signal to control the pressure of the nuclear reactor, while the turbine bypass valve 10 is normally closed.

As shown in the figure, a motor 11 is connected to the recirculation pump 3 for providing rotational driving force.
This motor 11 receives electric power from a power supply device 12 to rotate. Further, a control rod 13 for output control is provided at the lower part of the reactor pressure vessel 1, and this control rod 13 is driven by a control rod drive mechanism 14.

[0016] This plant also includes, as shown in the figure,
A generator load cutoff detection circuit 15 that detects that the load of the generator is cut off, a core flow rate measurement circuit 16 that detects the core flow rate, and a turbine bypass valve operation confirmation circuit that detects whether the turbine bypass valve 10 opens successfully or fails. 17, a recirculation pump trip circuit 18 that controls the number of trips of the recirculation pump, and a recirculation pump trip optimization circuit 19
The recirculation pump trip optimization circuit 19 evaluates and selects the optimal number of trips based on the core state, and outputs a recirculation pump trip signal according to the number of trips.
The recirculation pump trip circuit 18 is adapted to be fed to the recirculation pump trip circuit 18.

Next, the operation of this embodiment will be explained. When the load of the generator is cut off due to an accident in the power transmission system of the power plant, etc., the generator load cutoff detection circuit 15 detects this and outputs a load cutoff signal. Then, the turbine steam control valve 9 is quickly closed, the supply of steam to the turbine 5 is stopped, and the rotation of the turbine 5 is stopped. At the same time, the turbine bypass valve 10 is opened by the sudden opening signal,
Steam generated in the nuclear reactor is sent directly to the condenser 7 to suppress pressure rise in the reactor. Here, in a partial capacity bypass plant, the control rod drive mechanism 14 is
A reactor scram signal is given to shut down the reactor.

On the other hand, in a full capacity bypass plant, the reactor is scrammed only when the turbine bypass valve operation confirmation circuit 17 generates a signal indicating that the turbine bypass valve 10 has failed to open. However, in the conventional full-capacity bypass plant, the number of trips of the recirculation pump is fixed, which causes the above-mentioned problems.

Therefore, in this embodiment, a recirculation pump trip optimization circuit 19 is used to control the number of trips according to the core state. That is, the recirculation pump trip optimization circuit 19 receives the core flow rate signal from the core flow rate measurement circuit 16 at the time of load cutoff, and on the premise that the turbine bypass valve 10 is successfully opened, the recirculation pump trip optimization circuit 19 operates the total recirculation pump 3.
The optimum number of trips is evaluated and selected from among these, and the signal thereof is given to the recirculation pump trip circuit 18 to trip the required number of recirculation pumps 3.

After that, when a signal indicating that the turbine bypass valve 10 has failed to open is received from the turbine bypass valve operation confirmation circuit 17, the number of trips is re-evaluated based on the core state at that time, and the number of trips that are excessive or insufficient is re-evaluated. A circulation pump trip signal is additionally commanded to the recirculation pump trip circuit 18. Further, even when a reactor power reduction signal is received during normal operation, an appropriate recirculation pump trip signal is provided to the recirculation pump trip circuit 18 to select an optimal recirculation pump trip.

As described above, by controlling the number of trips using the recirculation pump trip optimization circuit 19, the following effects can be obtained. (i) When generator load shedding occurs and the turbine steam control valve 9 is closed, the necessary number of recirculation pumps 3 are tripped depending on the core flow rate at that time. This makes it possible to avoid a high reactor water level turbine trip due to a rise in the reactor water level. (ii) Furthermore, when the turbine bypass valve 10 fails to open, the number of units to be tripped is reevaluated based on the state of the core at that time, an additional command is issued to those that were previously tripped, and the minimum fuel output ratio is can be prevented from exceeding the permissible limit value. Moreover, this action prevents an unnecessary number of recirculation pumps 3 from being tripped, and as a result, it is possible to avoid a reactor scram due to a sudden decrease in core flow rate. By the way, when the turbine bypass valve 10 fails to open, there are other methods to alleviate the increase in output due to the delay in reactor scram, such as expanding the volume of the main steam pipe 4, Significant design changes, such as enlarging the pressure vessel 1, are required. for example,
The volume of the main steam pipe 4 is approximately 2 in the partial capacity bypass plant.
twice as necessary. Therefore, it is necessary to enlarge the large structure, which is not practical. (iii) Even with the expansion of the core operating range, the number of recirculation pump trips can be evaluated and selected on a one-by-one basis to the optimum number depending on the situation, improving the operability of core flow rate adjustment.

[0022]

[Effects of the Invention] As explained above, the present invention controls the number of trips according to the reactor core condition, so that it is possible to avoid a high reactor water level turbine trip due to a rise in the reactor water level during load shedding. It also prevents the minimum fuel output ratio from exceeding the permissible limit value.
Reactor scram due to sudden decrease in core flow rate can be avoided. Moreover, the operability of core flow rate adjustment during normal operation can be improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a control device for a nuclear power plant according to an embodiment of the present invention.

[Explanation of symbols]

2 Core 3 Recirculation pump 5 Turbine 7 Condenser 9 Turbine steam control valve 10 Turbine bypass valve 15 Generator load cutoff detection circuit 16 Core flow rate measurement circuit 17 Turbine bypass valve operation confirmation circuit 18 Recirculation pump trip circuit

Claims (1)

[Claims] 1. Core flow rate measuring means for measuring the core flow rate and outputting a core flow rate signal; and recirculation pump tripping means for tripping a number of recirculation pumps according to the input of a recirculation pump trip signal. a turbine bypass valve operation confirmation means for confirming the open state of the turbine bypass valve and outputting an opening success or opening failure signal; and a reactor output measuring means for measuring the reactor output and outputting a reactor output reduction signal. During load shedding, the optimum number of trips is evaluated and selected by inputting the core flow rate signal, and a corresponding recirculation pump trip signal is output, and the optimum number of trips is determined by inputting the opening success or failure signal. A recirculation pump trip correction signal is given to the recirculation pump trip means in accordance with this re-evaluation, and during normal operation, the optimum number of trips is evaluated and selected by inputting the reactor output reduction signal. A control device for a nuclear power plant, comprising: recirculation pump trip optimization means for outputting a recirculation pump trip signal according to the recirculation pump trip signal.