JPH05119189A - Nuclear reactor injection water flow automatic controller - Google Patents

Abstract

PURPOSE:To obtain the controller for maintaining the integrity of a reactor and a reactor container by automatically regulating the setting of a main steam release safety valve for the purpose of proper actuation, stabilizing a reactor water level with reactor pressure and injection water flow controlled and making easy the control of the reactor output even in the case where the actuation of a high pressure water injection system has been failed at the time of ATWS. CONSTITUTION:The reactor injection water floe automatic controller is provided with an ATWS judging part 1 for outputting an ATWS signal, a high pressure water injection system non-actuation discrimination part 2 for outputting a high pressure water injection system non-actuation signal, a high pressure water injection system non-actuation judging part 3 at the time of ATWS for outputting a high pressure water injection system non-actuation signal at the time of ATWS, a main steam release safety valve opening and closing pressure changing part 4 for outputting the open setting pressure changing signal and the close setting pressure changing signal of a main steam release safety valve and a main steam release safety valve opening and closing setting pressure control part 5 for controlling the open and close setting pressure of the main steam release safety valve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-scram transient change in a nuclear power plant.
The present invention relates to an automatic reactor water injection flow rate control device that maintains the soundness of a nuclear reactor when a so-called severe accident is assumed when the high pressure water injection system fails, at the time of With outScram (hereinafter abbreviated as ATWS).

[0002]

2. Description of the Related Art Generally, in operation control of a boiling water reactor,
When the reactor water is lost or the water supply volume decreases due to some malfunction in normal operating conditions, the water level of the reactor decreases, but this water level is constantly monitored at each level and the water level is Due to "Low (L-3)", the reactor is brought to an emergency stop (Scram, hereinafter referred to as "scram") by rapid automatic insertion of all control rods. As a result, the flow rate of steam flowing out from the reactor through the main steam pipe is suppressed, and the decrease in reactor water level becomes slower. However, since the decay heat is generated in the core of the nuclear reactor even if it is scrammed, generally about 5% of the rated steam flow will continue to be generated. Therefore, if at least this feed water flow rate cannot be secured, the reactor water level will further decrease and reach the “reactor water level low (L-2)” due to the mismatch between the inflow amount and the outflow amount. When the reactor water level reaches “Reactor water level low (L-2)”, the main steam isolation valve closes and the reactor isolation cooling system (Reactor CoreIsolatio)
(n Cooling System, RCIC) and high pressure emergency core cooling system (Emergency Core Cooling System, ECCS) are automatically started, and cooling water is injected into the reactor to prevent the reactor water level from dropping below this level.

On the other hand, since the main steam isolation valve is closed, steam generated by decay heat from the core increases the reactor pressure and finally reaches the open set pressure of the main steam relief safety valve provided in the main steam pipe. After that, the main steam relief safety valve is opened. As a result, a part of the generated steam is discharged to the suppression pool of the pressure suppression chamber through the exhaust pipe of the main steam relief safety valve, cooled and condensed, and the rise of the reactor pressure is suppressed. In this way, the reactor water level and reactor pressure are controlled safely. However, in the event of a transient change (ATWS) that is impossible to scrum,
Assuming more severe conditions, the following can be considered, for example. When the water supply is lost from normal operating conditions, the reactor water level will drop and the "Reactor water level low (L-
3) ”causes a reactor scrum signal to be emitted, but it is assumed that the rapid insertion of all control rods accompanying this has failed for some reason. As a result, the reactor water level continues to drop and reaches "low reactor water level (L-2)".

When the reactor water level reaches "(L-2)", the main steam isolation valve closes. In addition, an automatic start signal for the reactor isolation cooling system and the high-pressure emergency core cooling system is issued, but if these also become unable to be started for some reason, the reactor water level will further drop and the core exposure Reach potential,
It will progress to what is called a severe accident. Therefore, in order to avoid such a situation, the following means have been conventionally considered. (1) The reactor recirculation pump is tripped when an ATWS is detected in order to reduce the reactor power output and suppress the steam generation amount in the reactor as much as possible at the initial stage of the abnormality. (2) When the high pressure water injection system does not operate because the reactor is isolated when an ATWS occurs, the main steam relief safety valve is operated to reduce the pressure inside the reactor to a reactor pressure that can be injected by the low pressure water injection system, Cooling water is injected into the reactor from the low-pressure injection system to secure the reactor water level.

[0005]

When the high pressure water injection system does not operate during ATWS, the main steam relief safety valve is opened and closed by the operator's operation while monitoring the reactor pressure. Due to the depressurization of the reactor, the major parameters of the reactor vibrate greatly, which makes it quite difficult to understand the behavior of the reactor.In some cases, the core may be exposed and core damage may occur. It Also, even if the reactor water level is secured, it is desirable to suppress the reactor output as much as possible in order to reduce the heat load for steam release to the suppression pool in the pressure suppression chamber.
There is a method of keeping the reactor water level low and reducing the natural circulation force of the reactor to suppress the core inlet flow rate. However, when the reactor power could not be controlled sufficiently, the reactor pressure fluctuated due to the continuous opening and closing of the main steam relief safety valve, and the reactor water level also fluctuated. It becomes very difficult to control the water level, and it becomes difficult to control the reactor power. Therefore, it is conceivable that the amount of steam released to the pressure suppression chamber increases and the soundness of the reactor containment vessel is hindered.

The object of the present invention is to automatically adjust the opening / closing pressure setting of the main steam relief safety valve even when the operation of the high-pressure water injection system fails during ATWS to operate the reactor pressure properly. In addition to controlling the reactor water injection flow rate, the reactor water injection flow rate is stabilized, the reactor water level is stabilized, the control of the reactor power is facilitated, and the soundness of the reactor and the containment vessel is maintained. To provide.

[0007]

ATWS for outputting an ATWS signal from a reactor output signal and a scrum operation request signal
A determination unit, a high-pressure water injection system inactivation determination unit that outputs a high-pressure water injection system inactivation signal from a high-pressure water injection system flow signal and a high-pressure water injection system start signal, and the ATWS signal and the high-pressure water injection system inactivation signal are input to input ATWS A high pressure water injection system inoperative determination unit for ATWS that outputs a high pressure water injection system inoperative signal at the time of AT
The high pressure water injection system inactivation signal during ATWS and the reactor output signal from the high pressure water injection system inactivity determination unit during WS are input and the open set pressure change signal and the close set pressure change signal of the main steam relief safety valve are output. Main steam relief safety valve opening / closing set pressure control section, and main steam relief safety valve opening / closing set pressure control that receives the opening setting pressure change signal and the closing setting pressure change signal of the main steam relief safety valve Parts.

[0008]

[Operation] If the high pressure injection system does not operate during ATWS, AT
The WS determination unit determines the ATWS event occurrence from the reactor output signal and the scrum request signal and outputs the ATWS signal, and the high pressure water injection system inactivity determination unit detects the high pressure water injection system flow rate signal and the high pressure water injection system start signal from the high pressure water injection system. Detects inactivity and outputs high pressure water injection system inactivity signal. Input these two signals and
The TWS / high pressure water injection system inactivation determination unit determines that the high pressure water injection system is inactive during ATWS, and outputs a high pressure water injection system inactivation signal during ATWS. In the main steam relief safety valve opening / closing pressure changing unit from this signal and the reactor output signal, the reactor pressure at which the required flow rate of the reactor can be injected from the low-pressure water injection system, and the opening / closing set pressure of the main steam relief safety valve corresponding to this can be changed. The signal is calculated and output to the main steam relief safety valve opening / closing set pressure control unit. In the main steam relief safety valve opening / closing set pressure control unit, the main steam relief safety valve is automatically operated according to the opening / closing set pressure. By opening and closing this main steam relief safety valve, the reactor pressure is appropriately controlled and water is injected from the low-pressure water injection system, so stable reactor water level and output control is automatically performed, and the reactor pressure vessel and The integrity of the containment vessel can be ensured.

[0009]

An embodiment of the present invention will be described with reference to the drawings.
As shown in the block diagram of FIG.
Inputs the reactor output signal S1 obtained from the reactor and the scrum request signal S2 to determine that an ATWS event has occurred, and outputs an ATWS signal S3. The high-pressure water injection system inactivation determination unit 2 inputs the high-pressure water injection system flow rate signal S4 and the high-pressure water injection system start signal S5, detects the inactivity of the high-pressure water injection system, and outputs the high-pressure water injection system inoperative signal S6. Also AT
In the WS / high-pressure water injection system inactivation determination unit 3, the ATWS signal S3 from the ATWS determination unit 1 and the high-pressure water injection system inactivation signal S6 from the high-pressure water injection system inactivation determination unit 2 are input, and the ATW
At S, it is determined that the high pressure water injection system is inoperative, and the high pressure water injection system inactivation signal S7 at ATWS is output. Further, the main steam relief safety valve opening / closing pressure changing unit 4 includes the reactor output signal S1 and the ATWS / high pressure water injection system inactivation determining unit 3
The high pressure water injection system inactivation signal S7 at the time of ATWS from is input to the main steam relief safety valve opening / closing set pressure control unit 5 to output the main steam relief safety valve open set pressure change signal S8 and closed set pressure change signal S9. It is configured to output.

Further, the main steam relief safety valve opening / closing pressure changing unit 4 inputs the reactor output signal S1 and the high pressure water injection system inactivation signal S7 at ATWS, as shown in detail in the block diagram of FIG. , A reactor output-to-injection flow rate conversion unit 10 which outputs a low-pressure system injection flow rate signal S10, this injection flow rate signal S10, and the pressure from the low-pressure injection system pressure-injection flow rate characteristic unit 11 illustrated in the characteristic diagram of FIG. Input the signal S11 to calculate the optimum pressure of the low-pressure water injection system for the reactor,
The optimum pressure calculating unit 12 for the low-pressure water injection system that outputs the pressure setting signal S12 and the main steam relief safety valve opening / closing setting pressure control unit 5 shown in FIG. It is composed of a main steam relief safety valve open / close set pressure setting unit 13 which outputs an open set pressure change signal S8 and a close set pressure change signal S9 of the relief safety valve. The main steam relief safety valve opening set pressure is automatically set to a pressure lower than the injection start pressure of the low-pressure water injection system within the pressure range shown in Fig. 3, and the main steam relief safety valve closing set pressure is adjusted to a pressure commensurate with the output during decompression. Set. It should be noted that FIG. 3 is a characteristic diagram showing an example of the function of the low-pressure water injection system pressure vs. injection flow rate characteristic section 11 in which the horizontal axis is the injection flow rate and the vertical axis is the reactor pressure. A pressure signal S11 is obtained by means of the characteristic curve 14.

Next, the operation of the above configuration will be described. If the total feedwater flow rate loss occurs for some reason during the rated output operation of the reactor, the reactor water level will drop, and the scrum request signal S2 will be issued at "reactor water level low (L-3)". This separately commands the rapid insertion of all control rods, but it is assumed that the insertion of all control rods failed for some reason. At this time, the ATWS determination unit 1 that has received the reactor output signal S1 and the scrum request signal S2 receives the reactor output signal S2 even though the scrum request signal S2 is issued.
Since the reactor output of No. 1 has not decreased, it is determined that an ATWS event has occurred, and the ATWS signal S3 is output. On the other hand, the reactor water level further decreased, and the reactor water level was low (L-2).
And the main steam isolation valve is closed, the cooling system for reactor isolation and the high pressure core spray
y, HPCS) high pressure emergency core cooling system activation signal is issued. However, if it is also impossible to start due to some reason, the high-pressure water injection system inactivation determination unit 2 that has input the high-pressure water injection system activation signal S5 and the high-pressure water injection system flow rate signal S4 generated thereby causes the high-pressure water injection system activation signal to be high. If the high-pressure water injection system flow rate signal S4 is zero or an extremely low flow rate while S5 is being input, it is determined that the high-pressure water injection system is inoperative, and the high pressure injection system 3 for ATWS / high-pressure water injection system inoperative determination unit 3 The water system inactivation signal S6 is output. This high-pressure water injection system inactivation signal S6 and the ATWS signal S from the ATWS determination unit 1
The ATWS / high pressure water injection system non-operation determination unit 3 that received 3
It is judged by TWS that the high pressure water injection system is inoperative.
The high pressure water injection system inoperative signal S7 at the time of TWS is output.

In the main steam relief safety valve opening / closing pressure changing unit 4, the high pressure water injection system inactivation signal S7 at the time of ATWS,
The reactor output signal S1 is input to the main steam relief safety valve opening / closing set pressure control unit 5 to change the main steam relief safety valve opening / closing set pressure. The change signal S9 is output. Upon receiving this signal, the main steam relief safety valve opening / closing set pressure control unit 5
Change the opening / closing set pressure of the main steam relief safety valve. As shown in FIG. 2, the set pressure of the main steam relief safety valve at this time is set by the reactor output-to-injection flow rate conversion unit 10 in the main steam relief safety valve opening / closing pressure changing unit 4 to the reactor output signal S1 and the high-pressure injection system failure. The operation signal S7 is input, this reactor output is converted into the required water injection flow rate, and the water injection flow rate signal S10 is output. Next, in the low pressure water injection system optimum pressure calculation unit 12, this pressure water injection flow rate signal S10 and the pressure signal S11 from the low pressure water injection system pressure vs. injection flow rate characteristic section 11 illustrated in FIG. The setting signal S12 is output to the main steam relief safety valve opening / closing pressure setting unit 13. In the main steam relief safety valve opening / closing pressure setting unit 13, the calculated setting pressure of the pressure setting signal S12 is added with an operation width for obtaining a reliable and stable operation during repeated opening / closing operations of the main steam relief safety valve. Calculate the open / close set pressure of the relief safety valve ± 10% of the set pressure (Open set pressure: + 10% of the calculated set pressure, Close set pressure: − of the calculated set pressure
10%) to output the open set pressure change signal S8 and the close set pressure change signal S9 of the main steam relief safety valve.

These signals are input to the main steam relief safety valve opening / closing set pressure control unit 5 to automatically change the opening / closing set pressure of the main steam relief safety valve (not shown). As a result, the open / close set pressure in the main steam relief safety valve is always set to the operating pressure at which the low-pressure water injection system can be injected, so the reactor pressure that was high until now is suddenly reduced to the set pressure by the opening operation of the main steam relief safety valve. Therefore, the low-pressure water injection system operates properly to inject the cooling water into the furnace. After that, the reactor pressure and hence the reactor water level are automatically controlled by the operation of the main steam relief safety valve with the opening / closing set pressure controlled by the present invention. Therefore,
Since the reactor water level is properly secured, the reactor core can be fully submerged and the integrity of the reactor pressure vessel can be maintained. Also, since the reactor water level is kept low, the reactor output is also suppressed, so the heat load to the suppression pool in the reactor suppression chamber can be kept small, and the soundness of the reactor containment vessel is also ensured in good condition. .. This suppresses the reactor pressure and automatically controls the water injection flow rate of the low-pressure water injection system, so that the reactor water level can also be automatically controlled.

[0014]

As described above, according to the present invention, in the event of scram due to loss of reactor water or the like, even if the scram cannot be inserted due to failure of insertion of all control rods and the high pressure injection system does not operate, the reactor The pressure and the reactor water level are automatically controlled, and water is injected from the low-pressure water injection system without any problems, suppressing the reactor output and maintaining the soundness of the reactor pressure vessel and the reactor containment vessel. For this, existing equipment can be used to adequately control and respond. Further, since the operation is automatically performed and the reactor can be safely controlled, the reliability is improved and the burden on the operator is reduced.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a reactor water injection flow rate automatic control device according to the present invention.

FIG. 2 is a block configuration diagram of a main steam relief safety valve opening / closing pressure changing unit of the present invention.

FIG. 3 is a characteristic diagram of low-pressure water injection system pressure versus injection flow rate.

[Explanation of symbols]

1 ... ATWS determination unit, 2 ... High pressure water injection system inactivity determination unit, 3
… ATWS / high pressure water injection system inactivity judgment unit, 4… Main steam relief safety valve opening / closing pressure changing unit, 5… Main steam relief safety valve opening / closing set pressure control unit, 10… Reactor output versus water injection flow rate conversion unit, 11… Low pressure water injection system Pressure vs. injection flow rate characteristic part, 12 ... Low pressure injection system optimum pressure calculation part, 13 ... Main steam relief safety valve opening / closing setting pressure setting part, 14
... Characteristic curve, S1 ... Reactor output signal, S2 ... Scrum request signal, S3 ... ATWS signal, S4 ... High pressure water injection system flow signal, S5 ... High pressure water injection system start signal, S6 ... High pressure water injection system inoperative signal, S7 ... ATWS High pressure water injection system inactive signal, S
8 ... Main steam release safety valve open set pressure change signal, S9 ... Main steam release safety valve close set pressure change signal, S10 ... Water injection flow rate signal, S11 ... Pressure signal, S12 ... Pressure set signal.

Claims (1)

[Claims] 1. A transient change determination unit that cannot output a scrum signal from a reactor output signal and a scrum operation request signal, and a high pressure water injection system non-operation signal from a high pressure water injection system flow rate signal and a high pressure water injection system start signal High pressure water injection system inactivity determination unit, and the high pressure water injection system inactivity signal when the scrum is unavailable and the high pressure water injection system inactivity signal is input, and the high pressure water injection system inactivity determination unit is output when the scrum is unavailable And the high pressure water injection system inactivation signal when the scrum is disabled and the reactor output signal are input to output the main steam relief safety valve open set pressure change signal and the closed set pressure change signal. Section and the main steam relief safety valve opening / closing set pressure for controlling the opening / closing set pressure of the main steam relief safety valve in response to the opening setting pressure change signal and the closing setting pressure change signal of the main steam relief safety valve. A reactor water injection flow rate automatic control device comprising a control unit.