JPH02264886A - Apparatus for output control of reactor - Google Patents

Abstract

PURPOSE:To improve sharply the safety of a nuclear power plant by determining by a first determining element whether ATWS (Anticipated Transients Without Scram) is severe or gentle. CONSTITUTION:A scram operation request signal 8 is delivered from a detecting system on the occasion of full closure of a main steam isolating valve and the signal 8 is given a time delay by a time delay element 3 to be a corrected scram operation request signal 9. An ATWS signal control element 4 receiving the signal 9 and an average output monitor signal 10 determines whether ATWS is severe or gentle. Meanwhile, a reactor pressure signal 12 detected by a reactor pressure sensor is inputted to a reactor pressure high signal control element 7 and compared with a reactor pressure high set value set beforehand and a reactor pressure high signal 13 is outputted therefrom. An ATWS signal 11a and the signal 13 are inputted to an RPT/ARI operation signal control element 5 and an ARI operation request signal 14a and an RPT signal 15 are outputted therefrom. Receiving the signal 14a, ARI (Alternative Rod Insertion) operates, while RPT (Recirculation Pump Trip) operates on reception of the signal 15.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) RPT (Re-Circulation Pump
Trip System; recirculation pump trip)
, or A RI (Alternate Rod
This invention relates to a nuclear reactor power control device that outputs an operation request (Insertion of alternative control rods).

(Prior Art) In general, boiling water nuclear reactors are operated while keeping the reactor pressure constant under normal operating conditions. At this time, a transient change (transient event) such as a sudden increase in reactor pressure due to some cause 5, such as a turbine trip, etc.
When this happens, the voids (bubbles) generated inside the reactor are crushed due to the increased pressure, and as a result, the density of the moderator (light water) inside the reactor increases, causing the moderation of neutrons inside the reactor to increase. This increases the nuclear fission reaction rate and increases reactor power. This increase in power causes a sudden increase in the amount of steam generated within the reactor, which further increases the reactor pressure.

This indicates that in general the pressure coefficient of boiling water reactors is usually positive. Therefore, if a transient event such as a sudden rise in pressure occurs, and no measures are taken to suppress the pressure rise, the reactor pressure will rise and the pressure in the reactor containing the reactor core will increase. The pressure limit of the container may be exceeded.

For this reason, in boiling water reactors, the turbine main steam control valve suddenly closes, which causes transient changes such as sudden pressure increases.
If an event such as a sudden opening of the turbine main steam stop valve or a sudden shut-down of the main steam isolation valve occurs, the 90% stroke position of the response is detected and the reactor is scrammed and safely stopped.

However, although the probability of occurrence is very small and normally does not need to be considered, if the scram by the reactor safety protection system fails when a transient event occurs, so-called ATWS, in the worst case, the reactor pressure vessel may damage the soundness of

For example, a typical 1100 MWei B W R1 for the most severe cases such as main steam isolation valve fully closed ATWS.
5 will be explained as an example. If the main steam isolation valve is fully closed for some reason during reactor rated power operation, the steam generated in the reactor is shut off by the main steam isolation valve, and the reactor pressure begins to rise.

On the other hand, suppose that the main steam isolation valve is closed and a scram signal is generated at the 90% stroke position, but insertion of all control rods fails for some reason. Because there is no way to suppress the rise in power and pressure, the reactor pressure rises further until it reaches the set pressure of the main steam relief safety valve installed in the main steam pipe, which opens and the steam passes through the exhaust pipe. A part of the generated steam is released into the pressure suppression chamber. However, the capacity of the main steam relief safety valve is not sufficient to release all of the steam generated in the reactor into the suppression chamber, so the pressure may continue to rise, potentially damaging the integrity of the reactor pressure vessel. In addition, the pool water temperature in the pressure suppression chamber continues to rise due to the steam released from the main steam relief safety valve, and eventually the steam released from the main steam relief safety valve can no longer be condensed, causing the pressure of the water source for core cooling to rise. There is a risk of damaging the integrity of the suppression room.

Therefore, in order to avoid such a situation, the following measures have been considered. First, there is a so-called RPT in which two coolant recirculation pumps are tripped by a reactor pressure high signal in order to suppress the initial reactor pressure during ATWS. This reduces the core flow rate by tripping two coolant recirculation pumps, increases the void fraction in the core, reduces the moderator density, introduces negative reactivity, and reduces the reactor power. In this case, the reactor pressure is suppressed by reducing the amount of steam generated. However, as it is, the reactor will still maintain its nuclear output, especially if the reactor is isolated. All generated steam is discharged into the pressure suppression chamber. Therefore, the pool water temperature in the pressure valve control chamber continues to rise. For this reason, so-called ARI, which inserts control rods using signals and methods different from those of the reactor safety protection system, has been considered in order to completely shut down the reactor.

The signals for activating this RPT and ARI are as follows:
A high reactor pressure signal and a low reactor water level signal are considered.

(Problem to be solved by the invention) The signal setting pressure considered in this way targets the most severe main steam isolation valve fully closed/fully controlled insertion loss ATWS, and is designed to prevent malfunctions from consideration for plant operation. In order to prevent
The number of valves that open is determined according to the set pressure, which is divided into several stages from the highest stage to the highest stage. All the main steam relief safety valves are open at the highest stage. ), and BWR plants in the United States that take ATWS measures are set this way.

When set in this way, in the most severe main steam isolation valve fully closed / fully control rod insertion failure ATWS, the initial reactor pressure rise rate is also severe to reach the signal setting pressure, so RPT, A
RI is activated, the reactor scrams, and can be safely shut down.

However, when the set pressure is high like this, events other than main steam isolation valve fully closed/full control rod insertion failure ATWS, such as when the initial output is low, and partial control rod failure ATWS (
During so-called partial ATWS, the ARI does not operate, and the steam released into the pressure suppression chamber via the main steam relief safety valve causes the pool water temperature in the pressure suppression chamber to rise, causing the operator to
The temperature limit set to deal with WS has been reached.

ARI, which was originally set up to contain the ATWS event, is not fully effective.

By the way, even during non-severe (gentle) ATWS, RP
If T and ARI are simply activated, malfunctions occur frequently and the reliability of the nuclear power plant cannot be maintained.Furthermore, in the case of less severe ATWS, activating RPT reduces core cooling by reducing the core flow rate. This is not desirable as it will not be possible to secure the

The purpose of the present invention is to provide A
To obtain a nuclear reactor power control device capable of operating ARI even during TWS, not operating RPT during less severe ATWS, and reducing malfunction of ARI during events other than ATWS.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, in the present invention, a reactor output signal and a scram operation request signal are input, and the state of transient fluctuation when scram is disabled is severe transient fluctuation. a first determination section that determines whether there is a moderate transient fluctuation; outputting a coolant recirculation pump trip signal and an alternative control rod insertion operation request signal when the transient fluctuation is a severe transient fluctuation; A second determination unit outputs an alternative control rod insertion operation request signal when the transient fluctuation determined in is a gentle transient fluctuation.

(Function) In the device configured in this way, the first determination section determines whether the ATWS is severe or mild, so ARI can be activated even during mild ATWS, and the ATWS In other events, ARI malfunctions can be reduced. In addition, in the second judgment section, the severe ATWS
At times, RPT and ARI are activated, and during mild ATWS, RPT is not activated and ART is activated, so that the core flow rate can be secured during mild ATWS.

(Embodiment) An embodiment of the nuclear reactor power control device according to the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram showing the configuration of one embodiment. The first determination section 1 includes a time delay section 3 and an ATWS signal control section 4.
It is composed of. The second determination unit 2 is a RPT/A
It is composed of an RI operation signal control section 5, an ARI operation signal control section 6, and a reactor pressure high signal control section 7. The scram operation request signal 8 is output from a detection system provided in a main steam isolation valve (not shown) and provided separately from the reactor safety protection system. This detection system is the main steam isolation valve 90%
It is configured to output a scram operation request signal 8 at the stroke position. The time delay section 3 inputs the scram operation request signal 8, provides a time delay of 1 to 2 seconds, and outputs a corrected scram operation request signal 9. The ATWS signal control unit 4 inputs the average output monitor signal 10 and the correction scram operation request signal 9, and selects either severe ATWS or mild ATWS.
It is determined whether it is WS, and if the ATWS is severe, the ATWS signal 11a is output, and if the ATWS is gentle, the ATWS signal 11b is output.

The reactor pressure signal 12 is output from a reactor pressure sensor (not shown) and input to the reactor pressure high signal control section 7. The reactor pressure high signal control section 7 is.

If the reactor pressure signal 12 is higher than the set value, a reactor pressure high signal 13 is output.

The RPT/ARI activation signal control unit 5 receives the ATWS signal 11
a and the reactor pressure high signal 13 are input, and if these two signals are established, the ARI operation request signal 14a and the RPT signal 15 are output. The ARI activation signal control unit 6 is an ATW
Input the S signal 11b and the reactor pressure high signal 13, and if these two signals are established, the ARI operation demand compensation signal 14b
Output.

The judgment conditions of the ATVS signal control unit 4 are shown in FIG. 2, as shown in FIG. If it is 80% or more of the output (21
), is determined to be a severe ATWS (22), and is a correction scram operation request signal person (23).

If the average output monitor signal is between 2% and 80% of the rated output (24), a mild ATWS is determined (25).

If the corrected scram operation request signal is (26) and the average output monitor signal is less than 2% of the rated output (27)
, the scrum is determined to be successful (2g).

Here, the meaning of setting the threshold at 80% of the rated output is to set the output with a margin in the capacity of the main steam relief safety valve for the rated main steam flow rate, and at an output of about 80% or less, there is a sudden increase in reactor pressure. This is because it can be determined that there will be no increase. 2% takes into account the error of the average output monitor, and if it is less than 2%, it can be determined that the scram by the reactor safety protection system was successful.

The set values of the reactor pressure high signal control unit 7 are shown in FIG. 3. In FIG. 3, the vertical axis shows the reactor pressure, and the conventional RPT/ARI reactor pressure high reactor pressure is shown by the dotted line in the figure. High setting value 3
The main steam relief safety valve highest stage setting pressure 31 is shown by the 0 line, the main steam relief safety valve first stage constant pressure 32 is shown by the two-dot broken line in the figure,
and the reactor pressure height setting value 33 of this example shown by the solid line in the figure.
are shown side by side. The conventional reactor pressure high setting value 30 for RPT/ARI was set higher than the safety valve highest stage setting pressure 31, but the reactor pressure high setting value 33 in this embodiment is higher than the main steam relief safety valve stage setting value 31. 1st stage setting pressure 3
It is set approximately 0.5 Icg/J lower than 2, considering the error and margin.

Next, the operation of this embodiment will be explained with reference to FIG.

This shows the case of main steam isolation valve fully closed/all control rod insertion failure ATWS.When the main steam isolation valve is fully open, a scram is detected from the detection system installed separately from the reactor safety protection system at the main steam isolation valve 90% stroke position. An actuation request signal 8 is issued. Taking into account the delay in inserting the control rods, a time delay unit 3 adds a time delay (1 to 2 seconds) to the scram operation request signal 8 to generate a corrected scram operation request signal 9. The ATWS signal control unit 4, which receives the corrected scram operation request signal 9 and the average output monitor signal 10, determines whether it is a severe ATWS or a gentle ATWS. In this case, all control rods have failed to be inserted into the ATWS, so the output is at least 100% or more. Therefore, it is determined that the ATWS is severe (reference numeral 22 in FIG. 2), and an ATVS signal 11a indicating the severe ATWS is output.

Meanwhile, the reactor pressure rises rapidly due to the main steam isolation valve being fully opened. Reactor pressure signal 12 detected by reactor pressure sensor
is input to the reactor pressure high signal control unit 7, and a preset reactor pressure high stage high signal 13 shown in FIG. 3 is output.

ATWS signal 11a and reactor pressure high signal 13 are RPT/
Since the two input signals are input to the ARI activation signal control section 5 and established, the ARI activation request signal 14b and the RPT signal 15 are output. In response to this ARI operation request signal 14a, ARI receives RPT signal 15 and performs RP.
T respectively operate. As a result, the sudden rise in initial pressure due to the full closure of the main steam isolation valve is completely suppressed by RPT, and the rise in pool water temperature in the pressure suppression chamber is completely suppressed by ARI, and the reactor is safely shut down.

Next, a case will be described in which the main steam isolation valve is fully closed for some reason in a boiling water reactor operating at rated power, and only half of the control rods are inserted. In this case, conventional RPT/A
With the RI set pressure, the pressure rise is not so severe that the reactor pressure is set at 30, which is the high reactor pressure for RPT/ARI shown in Figure 3. Therefore, the reactor pressure can be operated with a certain level of output. can continue. However, the reactor pressure rises above the set pressure of the main steam relief safety valve. At this time, since the reactor is in an isolated state, the generated steam is released into the pressure suppression chamber via the main steam relief safety valve.

Then, the temperature of the pool water in the pressure suppression chamber rises, reaching a temperature that forces the campaigners to take some sort of response.

In this embodiment, when the main steam isolation valve is fully closed, the scram operation request signal 8 is output from the detection system provided in the main steam isolation valve at the 90% stroke position of the main steam isolation valve. In consideration of the delay in inserting the control rods, a time delay circuit 2 adds a time delay (1 to 2 seconds) to the scram operation request signal 8 to generate a corrected scram operation request signal 9. The ATWS signal control unit 4, which receives the corrected scram operation request signal 9 and the average output monitor signal 10, determines whether it is a severe ATWS or a gentle ATWS.

In this case, since the average output monitor signal is, for example, about 70%, it is determined that it is a mild ATWS (reference numeral 25 in Figure 2).
), an ATWS signal 11b indicating a mild ATWS is output.

On the other hand, the reactor pressure rises (it does not rise suddenly) because the main steam isolation valve is fully closed and the steam is suddenly cut off.
, reactor pressure signal 12 detected by the reactor pressure sensor
is input to the yX child reactor pressure high signal control section 7. Here, the reactor pressure high setting value 33 and the reactor pressure signal 1 in FIG. 3, which are set in advance to deal with such a partial ATWS, are
2 are compared.

Since the reactor pressure signal 12 is higher than the reactor pressure high set value 33, the reactor pressure high signal 13 is output. ATWS
The signal 11b and the reactor pressure high signal 12 are input to the ARI activation signal control unit 6, and since the two input signals are established, the ARI activation request signal 14b is output. This AR
In response to the I-operation request signal 14b, the ARI is activated and the reactor is safely shut down.

Next, the effects of this embodiment will be explained with reference to FIG. Fourth
The figure is a graph in which the horizontal axis represents the time since the occurrence of ATWS, and the vertical axis represents the pressure suppression chamber pool water temperature. Compared to conventional equipment, the reactor pressure high setting value is set lower,
It can be seen that the rise in pool water temperature in the pressure suppression chamber can be suppressed for mild ATWS.

As described above, according to this embodiment, events other than main steam isolation valve pre-closing/full control rod insertion failure ATWS during the most severe rated output operation, such as ATWS events with low initial output, and partial control rod failure ATWS (so-called partial The reactor pressure high set value is set lower than the first stage set pressure of the main steam relief safety valve even during ATWS, where the reactor pressure does not rise as much as during ATWS), and an ATWS signal control section is provided.

The ARI can be operated reliably without malfunction, the temperature of the pool water in the pressure suppression chamber can be kept low, the original ARI effect can be fully demonstrated, and the ATWS can be easily used by operators.
It is possible to safely shut down the reactor without placing an excessive burden on the reactor.

〔Effect of the invention〕

According to the present invention, the initial reactor pressure rise is not severe A
ARI can be activated even during TWS, and RPT can be activated or not activated during less severe ATWS.
Since ARI malfunctions can be reduced in other events, the safety of nuclear power plants can be greatly improved.

[Brief explanation of drawings]

1 to 4 show one embodiment of the present invention. Figure 1 is a block diagram showing the configuration, Figure 2 is a diagram showing ATVS judgment conditions in the ATWS signal control unit, Figure 3 is a diagram showing the reactor pressure high setting value in the reactor pressure high signal control unit, and Figure 4 is a diagram showing the reactor pressure high setting value in the reactor pressure high signal control unit. The figure is a graph showing changes in the temperature of pool water in the pressure suppression chamber. DESCRIPTION OF SYMBOLS 1... First judgment part, 2... Second judgment part, 8... Scram operation request signal, 10... Average output monitor signal, 11a, 1lb-ATWS signal, 12. ...Reactor pressure signal, 14a, 14b-A RI operation request signal, 15...
RPT signal. 32...Main steam relief safety valve first stage set pressure, 33...
・Reactor pressure high setting value. Agent Patent Attorney Nori Ken Yudo Daishimaru Ken

Claims (3)

[Claims] (1) a first determination unit that inputs a reactor output signal and a scram operation request signal and determines whether the state of transient fluctuation when scram is disabled is severe transient fluctuation or gentle transient fluctuation; A reactor pressure signal is input, and when this reactor pressure signal is equal to or higher than a set value and the transient fluctuation determined by the first determining section is a severe transient fluctuation, a coolant recirculation pump trip signal is determined. An alternative control rod insertion operation request signal is output, and when the reactor output signal is equal to or higher than a set value and the transient fluctuation determined by the first determining section is a gentle transient fluctuation, the alternative control rod is inserted. A nuclear reactor power control device comprising: a second determination unit that outputs an insertion operation request signal. (2) The reactor power control device according to claim 1, wherein the output signal of the nuclear reactor is an average power monitor signal. (3) the first determination unit determines that there is a severe transient fluctuation when the scram operation request signal is in a state where the scram operation request is “present” and the average output monitor signal is about 80% or more; 3. A mild transient fluctuation is determined when the scram operation request signal is in the scram operation request state and the average output monitor signal is approximately 2% to 80%. nuclear reactor power control device. 4. The reactor power control device according to claim 1, wherein the set value of the reactor pressure signal is set lower than the first stage set pressure of the main steam relief safety valve.