JPH07128481A - Transion relaxation system for reactor - Google Patents

Abstract

PURPOSE:To surely actuate a high pressure water injection system (HPCF) in the case of duplicated failure of a loss-of-feed water tansient event and a reactor isolation-time cooling system (RCIC) in the case of lowering of reactor water level to a specific level, by actuating HPCF timer and actuating HPCF after elapsing a specified time. CONSTITUTION:To a reactor 11, water level meter 23 is provided to measure the water level at a plurality of sections and the water level signal 25 is input in an actuation logic 10. Also, an HPCF timer 28 to input water level signals 25 from a water level meter is provided. The timer 28 is actuated in case of lowering of the reactor water level below a specific level and after elapsing a specific time, it inputs the HPCF time up signal 7 in an actuation logic 10. The RCIC system 26 supplies replenishing water from a condensate reservoir tank 22 or a suppression chamber 21 to the reactor 11 to prevent the lowering of the reactor water level in the case of water supply pump 18 stopping.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transient mitigation system suitable for a boiling water reactor (hereinafter referred to as BWR).

[0002]

2. Description of the Related Art The newest B among the latest BWRs
There is a WR (hereinafter referred to as ABWR). This ABWR emergency core cooling system (ECCS) is equipped with one system for reactor isolation cooling system (hereinafter referred to as RCIC) and two systems for high pressure water injection system (hereinafter referred to as HPCF). When it is detected that the reactor water level has dropped to a predetermined level, cooling water is supplied to the reactor to cool the core.

In ABWR, the safety of the nuclear reactor is maintained even if a water loss transient event occurs in which the water supply pump that constantly supplies water to the nuclear reactor stops for some reason. It is required to design.

Therefore, in the case of ABWR, although it is extremely rare in practice, the reactor water level is always restored to a safe water level even if a water supply loss transient event occurs. That is, as shown in FIG. 4, various devices are stopped or started according to the decrease in the reactor water level L. For example, the reactor water level gradually decreases due to the operation stop of the feed pump, When the water level drops to L4, the recirculation pump is stopped first, and when the reactor water level reaches L3, the reactor scram is automatically performed, and the reactor water level secures a safe water level. .

However, if the operation of the feed water pump is not restarted during this period, the reactor water level will start to drop again and L2
RCIC is activated, the make-up water is supplied from the condensate storage tank to the reactor. Therefore, the safe water level is restored without the reactor water level dropping to L1.5.

However, if the RCIC fails here and its startup fails, the reactor water level further drops to L1.5. In this case, the two HPCF systems are started, and the condensate tank water or the pressure suppression is suppressed. The pool water is supplied to the reactor, the main steam isolation valve (MSIV) is closed, and the main steam pipe that connects the reactor and the turbine and guides steam is shut off. As a result, it is possible to prevent the reactor water level from further lowering to L1 and starting the automatic depressurization system (ADS) and the low pressure ECCS.

[0007]

However, in such a conventional ABWR, when the HPCF is started at L1.5, the reactor water level immediately recovers, but the MSIV
Since it will be closed at the same time, the steam generated in the reactor cannot be cooled by the main condenser attached to the turbine. As a result, the reactor pressure rises in the short term, and the relief safety valve automatically operates.

After a long period of time thereafter, in the unlikely event that M
When the operator fails to restart the SIV, the operator manually opens the relief safety valve to decompress the reactor, and the reactor shutdown cooling system cools it.

Although such a series of manual operations is relatively easy for a well-trained operator, if the series of manual operations can be avoided, the burden on the operator will be reduced and, in turn, the operation will be reduced. It will also improve the safety of the nuclear reactor.

Therefore, the present invention has been made in consideration of such circumstances, and its purpose is to duplicate a transient event of loss of water supply and a failure of the RCIC for supplying cooling water to the reactor at that time. Even in such a case, the HPCF can be reliably started to restore the reactor water level to a predetermined water level, and at the same time the MSIV can be prevented from being closed, and the steam generated in the reactor is guided to the main condenser to be cooled. It is to provide a transient mitigation system for a nuclear reactor.

[0011]

The present invention is configured as follows in order to solve the above-mentioned problems.

The invention according to claim 1 of the present application (hereinafter, referred to as the first
Invention), the reactor water level is a predetermined level, for example L2
And a predetermined water level lower than the reactor water level at which the reactor isolation cooling system should be started, for example, L
A high-pressure water injection system that starts at 1.5 to inject cooling water into the reactor, a timer that starts when the reactor water level drops from a predetermined level, and a timer that starts when a predetermined time elapses. It has a starting logic for starting the high pressure cooling system.

The invention according to claim 2 of the present application (hereinafter referred to as the second invention) is characterized in that the activation start of the start-up timer and the start-up of the RCIC system occur at the reactor water level L2. .

Further, in the invention according to claim 3 of the present application (hereinafter referred to as the third invention), the startup logic is such that the reactor water level is set to a predetermined water level at which the reactor isolation cooling system should be started, for example, L2. At the same time, the water level non-recovery signal output when not recovering, the reactor isolation cooling system failure signal from the failure detection device, and the time-up signal output when the timer measures the elapse of a predetermined time And an AND logic signal that outputs an AND logic signal when received, and at least one of the AND logic signal and a water level signal that is output when the reactor water level drops below a predetermined water level at which the high-pressure water injection system should be activated. And an OR logic that outputs a start signal for starting the high-pressure water injection system when received.

Furthermore, in the invention according to claim 4 of the present application (hereinafter, referred to as a fourth invention), the failure detecting device is
Detects the flow rate of the reactor isolation cooling system pump at startup of the reactor isolation cooling system, and generates a reactor isolation cooling system failure signal when the detected flow rate does not reach the predetermined flow rate within the predetermined time. It is characterized in that it is configured as follows.

Further, in the invention according to claim 5 of the present application (hereinafter referred to as the fifth invention), the high-pressure water injection system is started even at a predetermined water level lower than the reactor water level when the timer is started. It is characterized in that it is configured as follows.

[0017]

[Action]

<First to Fifth Inventions> Should a water loss transient event occur, the reactor water level will drop, and if the water level drops to a predetermined water level for starting the reactor isolation cooling system, for example, L2, this atom The cooling system at the time of reactor isolation is activated, cooling water is supplied to the reactor, the core is cooled, and the timer for activating the high-pressure water injection system is activated. When this timer measures a predetermined time, the activation logic activates the high pressure water injection system.

Therefore, according to the present invention, even in the unlikely event of a water supply loss transient event and a failure of the reactor isolation cooling system, the high-pressure water injection system is surely activated by the timer to set the reactor water level. Since the water level can be restored to the predetermined level, the safety of the nuclear power plant can be improved.

<Third invention> The startup logic satisfies the AND condition when the water level non-recovery signal, the reactor isolation cooling system failure signal, and the timer time-up signal are simultaneously input to the AND logic. Let's say "1" A
The ND logic signal is output.

When this AND logic signal or at least one of the water level signals output when the reactor water level drops below the water level at which the high pressure injection system should be started, for example, below L1.5, is given to the OR logic. The OR signal can be surely activated by the activation signal from the OR logic by satisfying the OR condition.

Therefore, the safety of the nuclear power plant can be improved.

<Fourth Invention> A failure detecting device detects a flow rate of a reactor isolation cooling system pump at the time of startup of a reactor isolation cooling system, and the detected flow rate does not reach a predetermined flow rate within a predetermined time. At this time, since it is configured to generate a failure signal for the reactor isolation cooling system, it is possible to reliably detect a failure in starting the reactor isolation cooling system, that is, a failure.

<Fifth Invention> Since the high-pressure water injection system is configured to start at a predetermined water level lower than the reactor water level when the timer starts, for example, L1.5, the timer should fail. Even in such a case, the high pressure water injection system can be surely activated.

[0024]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a block diagram of an embodiment of a transient mitigation system for a nuclear reactor according to the present invention. The steam generated by the nuclear heating of the core 12 housed in the reactor 11 is
It is guided to the turbine 15 by the main steam pipe 14 via 13 and drives the turbine 15 to rotate a generator (not shown) for power generation. Then steam is turbine 1
The water is guided to a condenser 16 attached to the fuel cell 5, cooled to be condensed water, and is again guided to the nuclear reactor 11 by a water supply pipe 17 via a water supply pump 18.

The reactor 11 includes L4, L3, L2, L1.
A water level gauge 23 for measuring the water level of L5 and L1 is provided, and the water level signal 25 is input to the activation logic 10. In addition, the water level signal 25 from the water level gauge 23 is input.
A PCF timer 28 is provided. The HPCF timer 28 is started when the reactor water level drops to L2, and the HPC timer 28 is activated when a predetermined time, for example, 120 seconds has elapsed.
The CF timer time-up signal 7 is input to the activation logic 10.

Further, an RCIC system 26 for pouring water into the reactor 11 by the RCIC pump 19 using the suppression chamber 21 and the condensate storage tank 22 as water sources is provided. The RCIC system 26, in order to prevent the water level of the reactor 11 from decreasing when the feed pump 18 is stopped,
Condensate storage tank 22 or suppression chamber 2
The supply water is supplied from 1 to the reactor 11. RC
A flow meter 24 is provided on the downstream side of the IC pump 19 as an example of an RCIC failure detection device. This flow meter 24
If the flow rate of the RCIC pump 19 measured by does not reach the predetermined flow rate within a predetermined time, eg, 30 seconds, the RCIC fault signal 6 is input to the activation logic 10. During this predetermined time, the flow meter 24 is activated by inputting the water level signal 25 of the reactor water level L2 generated by the water level meter 23 to the flow meter 24. In this embodiment, the flowmeter 2 is used as an example of the RCIC failure detection device.
4 is shown, but since the RCIC failure detection device confirms that the RCIC pump 19 is not activated,
It may be one that detects the number of revolutions of the RCIC pump 19 or the like. Further, in the present embodiment, the water level signal 29 of L2 is branched and input from the water level meter 23 to the flow meter 24 to activate the flow meter 24, and for example, 30 seconds are timed, and when the predetermined flow rate is not detected, the RCIC The fault signal 6 is transmitted to the activation logic 10. However, the L2 water level signal 29 is not branched and input to the flow meter 24, the flow meter 24 is always operated, the flow rate signal is transmitted to the activation logic 10, and the L2 water level signal 25 is transmitted from the water level meter 23 to the activation logic. From the time when 10 receives the RCI
The C fault signal 6 may be generated.

Further, as in the RCIC system 26, the suppression chamber 21 and the condensate storage tank 22 are used as water sources to inject water into the reactor 11 by the HPCF pump 20.
A PCF system 27 is provided. The HPCF system 27 backs up the RCIC system 26 when it fails. The HPCF pump 20 receives the HPCF activation signal 4 from the activation logic 10 and activates it.

The start-up logic 10 in the embodiment of the present invention having such a configuration will be described with reference to FIG.

FIG. 2 is a block diagram of the start-up logic 10 of the high-pressure water injection system 27 in one embodiment of the present invention. In the figure, the start-up logic 10 indicates a water supply loss event due to, for example, a failure of a water supply pump, and a reactor isolation time. Cooling system (hereinafter RCI
When a failure of (C) overlaps, it outputs a start signal for starting a high pressure water injection system (hereinafter referred to as HPCF), and has an AND logic 2 and an OR logic 3.
The HPCF activation signal 4 is output from the OR logic 3.

The AND logic 2 has a water level of L2.
Water level L2 non-recovery signal 5 generated at lower times, RCIC failure signal 6 and HPCF generated from flow meter 24
When the timer time-up signal 7 satisfies the AND condition, for example, an AND logic signal 8 of "1" is output. The AND logic signal 8 and the water level L1.
When at least one of the signals 5 and less than 5 is applied to the OR logic 3, the HPCF activation signal 4 is applied from the OR logic 3 to the HPCF pump 20 to activate it.

In the transient mitigation system for a nuclear reactor of the present invention configured as described above, in the unlikely event that the cooling water is constantly supplied to the nuclear reactor, for example, the water supply pump is stopped for some reason and a water supply loss event occurs. However, if the reactor water level falls below the normal operating water level, appropriate measures will be taken depending on the water level drop. Therefore, as shown in FIG. 3, the water level L below the normal operating water level is received from the upper level to the lower level, and L
4, L3, L2, L1.5, and L1 are sequentially set.

That is, when the reactor water level L drops to L4, the recirculation pump trips, and when it further drops to L3, the reactor is automatically scrammed. As a result, the reactor water level temporarily recovers, but if the failure of the feedwater pump is still not recovered, the reactor water level will start to drop again.

For this reason, when the reactor water level further drops to L2, the RCIC system 26, the flow meter 24 and the HPC
Each of the F timers 28 is activated. Where by any chance,
When the RCIC pump 19 fails and fails to start, the reactor water level further decreases. At this time, if the flow meter 24 does not detect the predetermined flow rate within a predetermined time, for example, 30 seconds, it sends the RCIC failure signal 6 to the start-up logic.

The RCIC failure signal 6 is ANDed.
Given to logic.

The HPCF timer 28 generates the HPCF timer time-up signal 7 when a predetermined time, for example 120 seconds, is measured. The HPCF timer 28 of the present embodiment has the sensitivity shown by the curve A in FIG. 4, and when 120 seconds is set, the design target water level obtained by adding the design margin water level to the reactor water level L1.5 (indicated by the broken line in FIG. 4). )
This figure shows that a slightly higher water level can be secured. That is, if 120 seconds is set, L1.5 will be
The HPCF pump 20 recovers the reactor water level with some margin.

On the other hand, the water level L2 non-recovery signal is also given to the AND logic 2 when the reactor water level is lower than L2.
Therefore, the AND logic 8 signal is given to the OR logic 3 while satisfying the AND condition of the AND logic 2.
When the OR condition is satisfied, the HPCF activation signal 4 is given to the two HPCF systems to activate them.

As a result, a large amount of cooling water is supplied from the HPCF system 27 into the high pressure reactor 11 and the reactor water level is rapidly restored. As a result, it is possible to automatically prevent the reactor water level from dropping to L1.5 and closing the main steam isolation valve 13.

For this reason, the main steam from the reactor 11 is continuously introduced into the main condenser 16 and cooled, so that the reactor pressure rapidly rises and a relief safety valve (not shown) is activated. The state can be avoided in advance.

Then, the flow meter 24 and the HPCF timer 2
If a failure occurs in 8 and the HPCF startup fails, the reactor water level continues to drop and reaches L1.5.

In this case, the main steam isolation valve 13 is automatically closed, but the signal 9 below the water level L1.5 is OR logic 3
Since the OR logic 3 supplies the HPCF activation signal 4 to the HPCF pump 20, the HPCF activation signal 4 is started. Therefore, although the main steam isolation valve 13 has already been closed, the reactor water level recovers rapidly.

In such a case, in addition to the occurrence of the water supply loss event and the RCIC failure, the RCIC failure occurs further.
It is assumed that an IC failure detection device, for example, the failure of the flowmeter 24 and the failure of the HPCF timer 28 occur in a duplicated manner, and such an occurrence is extremely low.

That is, according to the present invention, the reactor water level is L
It is possible to sufficiently reduce the probability that the MSIV will be closed and the MSIV will be closed, and the safety of the nuclear power plant can be secured.

[0044]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, even when the transient event of loss of water supply and the failure of RCIC occur in duplicate, the HP of the HP is ensured while ensuring a sufficiently safe reactor water level.
The CF can be reliably activated.

For this reason, the reactor water level can be rapidly restored to avoid the automatic closing of the main steam isolation valve, and the subsequent change in transient events can be significantly mitigated.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a transient mitigation system for a nuclear reactor according to the present invention.

FIG. 2 is a block diagram of HPCF startup logic in one embodiment of a transient mitigation system for a nuclear reactor according to the present invention.

FIG. 3 is a diagram showing the reactor water level of the embodiment shown in FIG. 1 and the start or stop of various equipment in association with each other.

FIG. 4 is a diagram showing an analysis of the relative relationship between the set time of the HPCF timer of the embodiment shown in FIG. 1 and the minimum reactor water level.

FIG. 5 is a view showing a conventional reactor water level and the start or stop of various devices in association with each other.

[Explanation of symbols]

 1 Transient Mitigation System 2 AND Logic 3 OR Logic 4 HPCF Activation Signal 5 Water Level L2 Non-Recovery Signal 6 RCIC Failure Signal 7 HPCF Timer Time Up Signal 8 AND Logic Signal 9 Water Level L1.5 or Less Signal 10 Startup Logic 11 Reactor 13 MSIV 19 Water supply pump 19 RCIC pump 20 HPCF pump 21 Suppression chamber 22 Condensate storage tank 23 Water level meter 24 Flow meter 28 HPCF timer L1, L1.5, L2, L3, L4 Reactor water level

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shin Naito 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefectural Yokohama Office, Toshiba Corporation

Claims (5)

[Claims] Claim: What is claimed is: 1. A reactor isolation cooling system that starts when the reactor water level drops to a predetermined level and replenishes cooling water to the reactor, and the reactor isolation cooling system that should be started. A high-pressure injection system that starts at a predetermined water level lower than the water level and injects cooling water into the reactor, a timer that starts when the reactor water level drops from a predetermined water level, and this timer measures the elapse of a predetermined time. A transient mitigation system for a nuclear reactor, comprising a start-up logic for starting the high-pressure cooling system in the event of a failure. 2. Start-up of the start-up timer and RC
The transient mitigation system for a nuclear reactor according to claim 1, wherein the start-up of the IC system occurs at the reactor water level L2. 3. The start-up logic comprises a water level non-recovery signal output when the reactor water level does not recover to a predetermined water level for activating the reactor isolation cooling system, and a reactor isolation cooling from a failure detection device. AND logic that outputs an AND logic signal when simultaneously receiving a system failure signal and a time-up signal that is output when the timer measures the elapse of a predetermined time, and the AND logic signal and the high-pressure water injection system And an OR logic which outputs a start signal for starting the high pressure water injection system when receiving at least one of the water level signals output when the reactor water level drops below a predetermined water level to be started. The transient mitigation system for a nuclear reactor according to claim 1 or 2, characterized in that: 4. The failure detection device detects the flow rate of the reactor isolation cooling system pump at the time of startup of the reactor isolation cooling system, and when the detected flow rate does not reach the predetermined flow rate within a predetermined time, The transient mitigation system for a nuclear reactor according to claim 3, wherein the transient mitigation system is configured to generate a reactor isolation cooling system failure signal. 5. The high-pressure water injection system is configured to be activated even at a predetermined water level lower than a reactor water level when the timer is activated.
A transient mitigation system for a nuclear reactor according to any one of 1.