JPH04208899A - Reactor scram device - Google Patents

Abstract

PURPOSE:To keep fuel integrity of a reactor by judging the power change of reactor due to the change in reactor recirculation drive flow and judging the abnormal state of the reactor by a predetermined judgment conditions. CONSTITUTION:By using a thermal power monitor signal 5, a power change rate is calculated at a thermal power monitor changing rate calculation part 2 and the positive thermal power monitor changing rate signal 6 is sent to a reactor abnormality judgment part 7. At the reactor abnormality judgment part 7, whether or not the reactor is abnormal is judged using both changing rate signals 4 and 6. In this case, the recirculation drive flow changing rate signal 4 is negative and the thermal power monitor changing rate signal 6 is positive, and so the reactor is judged to be abnormal and then reactor abnormality signal 8 is output to a load demand deviation signal production part 9. At the load demand deviation signal production part 9, a zero load demand deviation signal 18 upon inputting the reactor abnormality signal 8 is output to a recirculation system main controller 16 and at the same time a scram demand signal 10 is output to a reactor safeguard system.

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety protection system for a boiling water nuclear reactor, and more particularly to a scram device for a nuclear reactor. [0002]

[Prior Art] In general, in a boiling water reactor, the reactor output is determined by changing the reactivity of the control rods by inserting or withdrawing them into the reactor, or by changing the reactor recirculation flow rate. It is controlled by changing the so-called void reactivity of boiling water reactors. Therefore, if the control rods of a nuclear reactor are pulled out, the reactor output will be
If the reactor recirculation flow rate is increased, the reactor power will increase. Even in that case, the boiling in the reactor core is in a state of nucleate boiling within a certain normal operation control range. When the boiling is in the nucleate boiling state, the heat transfer coefficient is good, so the temperature difference between the fuel rod cladding tube and the coolant is small, the cladding tube temperature is sufficiently suppressed, and the integrity of the fuel rod is maintained. However, as the reactor power increases and the heat flux increases,
The state shifts from nucleate boiling to transition boiling, and the cladding temperature begins to rise. As the heat flux increases further, the process shifts to film boiling,
There is a possibility of damage to the cladding. In addition, even if the reactor coolant is constant, if the coolant flowing through the reactor core decreases or the coolant flow path is blocked, resulting in insufficient heat removal from the fuel rods, the relative As a result, the heat flux increases, and the boiling state changes from nucleate boiling to transition boiling and then to film boiling as described above. This raises the possibility of damage to the cladding. (0003) The minimum critical power ratio (hereinafter abbreviated as MCPR) is used as an index to express the thermal margin of a nuclear reactor in such cases.In the current boiling water reactor,
The safety limit MCPR (hereinafter abbreviated as SLMCPR) has been established as a safe limit value that can maintain the integrity of the fuel, and even when the reactor reaches an abnormal transient state, the operating MCPR can be maintained.
The system is such that the value does not fall below the SLMCPR. (Operating MCPR > S LMCP R is the condition for maintaining fuel integrity.) Among the abnormal transient changes during operation in current boiling water reactors capable of high-speed scram, MCPR deteriorates the most. The event that occurs is loss of feed water heating. Therefore, in conventional equipment, a scram set point is installed for the thermal output monitor that depends on the core flow rate, so that even if the output increases abnormally, the reactor can be shut down by scram without compromising the integrity of the fuel. It has become. [0004]

[Problem to be Solved by the Invention] As mentioned above, when the reactor recirculation flow rate is constant and the reactor output changes, the thermal output monitor detects an abnormality in the reactor output and scrams the reactor. However, when the recirculation flow control system is in automatic operation mode, the situation is slightly different. When a transient change occurs, such as loss of feedwater heating, the reactor power is injected with positive reactivity due to an increase in core inlet subcooling. As the reactor power increases thereby, the reactor pressure increases and the pressure control system, with a constant load setting, uses the reactor pressure to compensate for the increase in reactor pressure to the recirculation system. Outputs a recirculation flow rate reduction signal to suppress the furnace output. As a result, the reactor power is suppressed, the positive reactivity input due to the increase in the core inlet subcooling is compensated for, and the increase in the reactor power remains small. in this case,
The reason why the reactor output is not completely compensated is because the increase in the core inlet subcooling increases the reactor output due to the reactivity input, but the reactor steam flow rate does not increase, and the reactor pressure and reactor output do not increase. This is due to the fact that it does not rise. For this reason,
The reactor remains at some power increase without reaching the scram set point of the thermal power monitor. [0005] In particular, with recent advances in nuclear fuel and operation technology, it is possible to expand the operating range beyond the conventionally defined operating range, reduce the number of control rod operations, and reduce fuel cycle costs. As more and more people are trying to reap the benefits, thermal output monitor settings are being extended to low flow areas, making it even more difficult to reach scram set points. On the other hand, since the recirculation system is in automatic mode, the reactor recirculation flow rate decreases. Therefore, the core flow rate of the nuclear reactor becomes relatively low compared to the reactor output, the MCPR described above deteriorates, and there is a possibility that the fuel integrity of the reactor is impaired. This tendency is particularly strong for recent high-performance fuels in which the limit power of the fuel is highly sensitive to the reactor core flow rate. [00061 The present invention has been made in consideration of these points, and it is possible to expand the operating range while maintaining the soundness of the fuel,
The purpose of the present invention is to provide a recirculation flow rate control device for a nuclear reactor that can reliably scram. [0007]

[Means for Solving the Problems] As a means for achieving the above object, the present invention provides a recirculation drive flow rate change rate that determines the time change rate of the reactor recirculation drive flow rate and outputs a recirculation drive flow rate change signal. a calculation means; a thermal output monitor change rate calculation means for determining the time change rate of the thermal output monitor signal and outputting a thermal output monitor change rate signal; In addition to determining the reactor output change in response to the change, the abnormal state of the reactor is determined based on predetermined judgment conditions, and a signal is sent to the reactor recirculation system to maintain the output signal of the main controller of the reactor recirculation system constant. The present invention is characterized in that a reactor abnormality determination means is provided for outputting a reactor request signal to the system main controller and to the safety protection system. [0008]

[Operation] In the nuclear reactor scram device according to the present invention, an abnormal state of the reactor is detected and the reactor is Since the core flow rate is kept constant and the reactor is scrammed, a sufficient thermal margin of the reactor can be maintained and the fuel integrity of the reactor can be ensured. [0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a scram device for a nuclear reactor according to the present invention, and in the figure, reference numeral 1 indicates a recirculation drive flow rate change rate calculation section, and reference numeral 2 indicates a heat output monitor change rate calculation section.
The recirculation drive flow rate change rate calculation unit 1 receives the recirculation drive flow rate signal 3, calculates its time change rate, and outputs a recirculation drive flow rate change signal 4. Also,
The thermal output monitor rate of change calculating section 2 receives the thermal output monitor signal 5, calculates its temporal rate of change, and outputs a thermal output monitor rate of change signal 6. [00101 Both rate-of-change signals 4 and 6 are input to the reactor abnormality determination section 7, and when the reactor abnormality determination section 7 determines that the reactor is abnormal, A reactor abnormality signal 8 is outputted to a load request deviation signal generation section 9, and a scram request signal 10 is outputted to a safety protection system. That is, the reactor abnormality determination unit 7 determines the reactor output change from both rate-of-change signals 4 and 6, and also determines the abnormal state of the reactor based on predetermined determination conditions. [00111 FIG. 2 shows the conditions for determining whether or not the reactor is abnormal in this reactor abnormality determination unit 7, and the driving flow rate change rate positive/negative determination unit determines whether the recirculation drive flow rate change rate signal 4 is positive or negative. 11, a thermal output monitor change rate positive/negative determining section 12 that determines whether the thermal output monitor change rate signal 6 is positive or negative, and an AND gate 13 which receives the outputs of both of these determining sections 11 and 12 as input. The output of the gate 13 is used to determine whether there is an abnormality in the reactor. That is,
If the recirculation drive flow rate change signal 4 is negative and the thermal output monitor change rate signal 6 is positive, the reactor is determined to be abnormal;
In other cases, the reactor is judged to be normal, or even if it is abnormal, the current equipment is sufficient to handle the situation. [0012] The negative load demand deviation bone preparation section 9 is also configured to receive a load demand deviation signal 14 from the pressure control system, and in normal times, the main controller input corresponding to this load demand deviation signal 14 is input. A signal 15 is input to a recirculation system main controller 16, and a main controller output signal 17 is output from the recirculation system main controller 16. Further, in the event of a reactor abnormality, the load request deviation signal 14 is bypassed and the zero load request deviation signal 18 is output to the recirculation system main controller 16. [00131]Next, the operation of this embodiment will be explained by taking as an example a case where the recirculation flow rate control system is in automatic operation mode and a transient change in feed water heating loss occurs. When feedwater heating loss occurs, reactor power is injected with positive reactivity due to an increase in core inlet subcooling. As the reactor power increases, the reactor pressure increases, and since the load setting is constant, the pressure control system increases the reactor output to compensate for the increase in reactor pressure to the recirculation system. In order to suppress this, a negative load demand deviation signal 14 is output to reduce the recirculation flow rate. As a result, the reactor power is suppressed, the positive reactivity input due to the increase in the core inlet subcooling is compensated for, and the increase in the reactor power remains small. The recirculation drive flow rate change rate calculation unit 1 calculates the time change rate of the recirculation drive flow rate signal 3, and the negative recirculation drive flow rate signal 3 is sent to the reactor abnormality determination unit 7. [0014] On the other hand, the thermal output monitor change rate calculation unit 2 calculates the temporal change rate of the thermal output monitor signal 5, and outputs a positive thermal output monitor change rate signal 6 to the reactor abnormality determination unit 7.
will be sent. [0015]] The child reactor abnormality determination unit 7 determines whether or not the reactor is abnormal from both of these rate-of-change signals 4 and 6. In this case, since the recirculation drive flow rate change signal 4 is negative and the thermal output monitor change rate signal 6 is positive, the reactor is determined to be abnormal, and the reactor abnormality signal 8 is sent to the load request deviation signal generator 9. Output. In response to the input of this reactor abnormality signal 8, the load demand deviation signal generation unit 9 bypasses the load demand deviation signal 14 from the pressure control system and outputs the zero load demand deviation signal 18 to the recirculation system main controller 16. At the same time, a scram request signal 10 is output to the reactor safety protection system. [0016] In this way, even when the recirculation flow fine control system is operated in automatic mode, when the reactor falls into an abnormal state, the recirculation system can be accurately controlled and the reactor can be safely shut down. can. [0017]

[Effects of the Invention] As explained above, according to the present invention, even when the recirculation flow rate control system is operated in automatic mode,
When operating within the defined range, even if abnormal transient changes occur during operation, the operating MCPR will remain within the SLM.
The reactor can be reliably scrammed without falling below CPR. In particular, when the operating range has been expanded as recently, it is difficult for operators to recognize the abnormality of the reactor because the above event is within the normal operating range. According to this method, a nuclear reactor can be safely shut down without special precautions, greatly reducing the burden on operators.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a scram device for a nuclear reactor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing reactor abnormality determination conditions.

[Explanation of symbols]

1 Recirculation drive flow rate change calculation section 2 Thermal output monitor rate of change calculation section 3 Recirculation drive flow signal 4 Recirculation drive flow rate change signal 5 Heat output monitor signal 6 Thermal output monitor change rate signal 7 Reactor abnormality determination section 8 Reactor abnormality signal 9 Load request deviation signal creation section 10 Scrum request signal 16 Recirculation system main controller 18 Zero load request deviation signal

Claims (1)

[Claims] 1. Recirculation drive flow rate change calculation means for determining the time change rate of a reactor recirculation drive flow rate and outputting a recirculation drive flow rate change signal; Thermal output monitor change rate calculation means outputs an output monitor change rate signal, and by inputting both of the change rate signals, determines the reactor output change with respect to the reactor recirculation drive flow rate change, and according to predetermined judgment conditions. Determines the abnormal state of the reactor, outputs a signal to the reactor recirculation system main controller to keep the output signal of the reactor recirculation system main controller constant, and sends a reactor request signal to the safety protection system. A scram device for a nuclear reactor, comprising: a reactor abnormality determination means for outputting an output.