JPH03137598A - Output controlling device for natural circulating reactor - Google Patents

Abstract

PURPOSE:To decrease nuclear reactor output, and to keep integrity and a core cooling configuration of a nuclear reactor vessel by providing a control measure to make a feed water pump run-back and trip, and, at the same time, to open a plurality of pressing reducing valves with certain time delay. CONSTITUTION:When reactor output rises over a preset point A of a nuclear reactor output and also a nuclear reactor pressure rises higher than a higher high level of the nuclear reactor pressure, automatic pressure reducing valves 22a, 22b and 22c of which each group can release the maximum 40% of rated main steam flow, are made to open with time delaying interval of 30 second, utilizing time delaying circuit 47a and 47b, a feed water pump 16 is made to run-back and concentrated solution of sodium pentaborate is rapidly injected into a nuclear reactor vessel 2 by a high pressure liquid poison accumulator 31. By this procedure, sub-cooling degree at a reactor core inlet decreases and also reducing effect of natural circulating force of nuclear reactor works and therewith core flow rate decreases and nuclear power output also decreases.

Description

[Detailed description of the invention] [Objective of the invention] (Industrial application field) The present invention aims to reduce the amount of heat generated in a nuclear reactor in a natural circulation type nuclear reactor plant, especially when control rods cannot be inserted due to a transient event. This invention relates to an output control device for a natural circulation furnace.

(Prior Art) Generally, in a forced coolant circulation type boiling water nuclear reactor, a recirculation system is provided in the reactor pressure vessel. In this recirculation system, reactor water from the reactor pressure vessel is pressurized by a recirculation pump, and is jetted downward from multiple jet pumps via a collecting pipe as driving water. The reactor water inside the reactor pressure vessel is forcibly circulated.

In addition, in boiling water reactors, when control rods cannot be inserted, a scram signal is used to trip the recirculation pump and reduce the core flow rate. As a result, the amount of core voids increases and negative reactivity is added, so the neutron flux is controlled and the reactor output is reduced.

(Problem to be solved by the invention) However, since natural circulation reactors are not equipped with the recirculation pump, the recirculation pump used in forced coolant circulation reactor plants when control rods cannot be inserted is No measures can be taken to reduce reactor output due to trips. Therefore, in natural circulation reactors, there is a problem that the integrity of the reactor vessel cannot be maintained unless a new output reduction means is installed to replace the recirculation pump trip.

The present invention has been made to solve the above problems, and the output of the natural circulation reactor is capable of reducing the amount of heat generated in the reactor even when transient changes occur during operation in the natural circulation reactor and control rods cannot be inserted. The purpose is to provide a control device.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a reactor vessel containing a reactor core, a cylindrical body installed in the reactor vessel and surrounding the reactor core, and a cylindrical body and the above-described cylindrical body. A natural circulation flow path is formed between the reactor vessel and the reactor vessel to guide the coolant discharged from the upper part of the reactor core to the lower part of the reactor core along with the feed water flowing in from the feed water pump, and the steam generated in the reactor vessel is In an output control device for a natural circulation reactor having a discharge main steam pipe and a plurality of pressure reducing valves provided in the main steam pipe, the plurality of pressure reducing valves are simultaneously run back or tripped by the feed water pump. It is characterized in that it is provided with a control means for opening at a time lag. (Function) In the present invention, when a transient change occurs during reactor power operation and it becomes impossible to insert a control rod, the control means runs back or trips the feed water pump, and at the same time, the plurality of pressure reducing valves are operated at different times. to open it.

Here, when the feedwater pump is run back or tripped, the core entry loss subcooling degree decreases, and the natural circulation force reduction effect due to the lowering of the reactor water level comes into play, resulting in a decrease in the core flow rate. Therefore, the reactor output can be reduced as a result. Further, by opening the pressure reducing valve, the number of voids in the core increases, and negative reactivity is applied to the core. Therefore, the reactor output sharply decreases due to the effects of the water supply bomb back or trip. In this case, the plurality of pressure reducing valves are opened at different times. This prevents the reactor water level from flashing due to a sudden drop in reactor pressure, causing the two-phase flow to reach the main steam pipe and even the pressure reducing valve, thereby preventing the pressure reducing valve from choking.

(Example) The present invention will be described based on illustrated embodiments.

FIG. 1 shows a schematic configuration of a natural circulation boiling water reactor (BWR) to which a power control device according to an embodiment of the present invention is applied. In the figure, reference numeral 1 indicates a reactor containment vessel, and this reactor containment vessel 1 is installed in a reactor building (not shown). A reactor pressure vessel 2 is housed within the reactor containment vessel 1, and this reactor pressure vessel 2 is installed on a pedestal (not shown). This reactor pressure vessel 2
A reactor core 3 is disposed inside, and a coolant 4 for cooling the reactor core 3 is housed therein.

The reactor core 3 includes a plurality of fuel assemblies and control rods 3a (not shown).
It consists of The temperature of the coolant 4 rises due to the heat of the nuclear reaction in the core 3, and it becomes a two-phase state of water and steam.The coolant 4 is heated up by the heat of the nuclear reaction in the core 3, and becomes a two-phase state of water and steam. Chimney) 5 is distributed. The steam flows into a steam dryer (not shown), becomes dry steam, and is fed to the turbine 7 via a main steam pipe 6 connected to the upper part of the reactor pressure vessel 2.

On the other hand, the water separated within the reactor pressure vessel 2 flows down to the lower part of the reactor core 3 via the downcomer section, is guided to the lower part of the reactor core 3 again, and is made to flow within the reactor core 3. Main steam isolation valves (hereinafter referred to as M
(referred to as SIV) 8 and 9 are interposed. This MS
A main steam stop valve 10 and a main steam control valve 11 are successively interposed between the IV9 and the turbine 7.

The steam fed to the turbine 7 drives the turbine 7 and rotates the generator 12. The steam that drove the turbine 7 is stored in a condenser 13 installed below the turbine 7, and is condensed to become condensed water. This condensate is again introduced into the reactor pressure vessel 2 via the condensate pump 14, the feed water heater 15, and the motor-driven feed water pump 16, and is supplied to the lower part of the reactor core 3.

A natural circulation passage 2a is formed between the reactor pressure vessel 2 and a cylindrical body 5 serving as a shroud, and the natural circulation passage 2a allows the coolant 4 in the upper part of the reactor core 3 to be transferred from the water supply pump 16. It is led to the lower part of the reactor core 3 together with the water supply.

On the other hand, a turbine bypass pipe 17 is disposed between the main steam pipe 6 and the condenser 13 between the MSIV 9 and the main steam stop valve 10 . A turbine bypass valve 18 is interposed in this turbine bypass pipe 17 . Here, when a load cutoff occurs, the main steam control valve 11 is closed, and at the same time, the turbine bypass valve 18 is opened. Thereby,
Steam is introduced directly into the condenser 13 via the turbine bypass pipe 17.

A main steam relief safety valve (SRV) 19 is connected to the MS IV 8 entrance side of the main steam pipe 6, and a main steam relief pipe 20 is connected to the main steam relief safety valve 19. The lower end of this main steam relief pipe 20 is immersed in water 21a of a pressure control chamber 21 that serves as a suppression pool provided at the bottom of the reactor pressure vessel 2. For example, M
When SIVs 8 and 9 close and the main steam pressure rises transiently, the main steam relief safety valve 19 opens and the main steam inside the reactor pressure vessel 2 opens the main steam relief pipe 20 to suppress the pressure. The water is released into the water 21a in the chamber 21, thereby suppressing the pressure rise in the reactor pressure vessel 2.

Furthermore, on the entrance side of the MSIV 8 of the main steam pipe 6,
Automatic pressure reducing valves 22as 22b and 22c are connected. When it is necessary to reduce the reactor pressure in a short time, the automatic pressure reducing valves 22a, 22b, 22c are opened at predetermined time intervals.

By the way, a high-pressure liquid poison accumulator (SLC) 31 is connected to the reactor pressure vessel 2 via an injection valve 32, and by opening this injection valve 32, a concentrated solution of sodium pentaphosphate, which is a liquid poison, is transferred to 5LC31. is injected into the reactor pressure vessel 2 at high speed. Inside the reactor core 3 is an average power monitor (APRM) 4 that monitors the reactor output.
2 is installed, and a reactor pressure detector (P) 43 is installed at the upper part of the reactor pressure vessel 2 to detect the pressure. A reactor water level detector (L) 44 is provided.

The output signals of the average output monitor 42, pressure detector 43, and water level detector 44 are transmitted to the output control device 4 as a control means.
1, and this output control device 41 controls a runback signal (or trip signal) of the water supply pump 16 and an automatic pressure reducing valve 20 consisting of three groups based on the output signal.
A signal for releasing the injection valve 32 and a signal for releasing the injection valve 32 are respectively sent out with a time difference.

That is, as shown in FIG.
It has an ND circuit 45 as 45 bs and an OR circuit 46, and the AND circuit 45a receives a pressure signal indicating that the pressure detector 43 has detected a high reactor pressure and a reactor output that has detected a preset value a or more. An AND circuit 45b performs a logical product with the output signal of the APRM 42, and an AND circuit 45b performs a logical product between the output signal of the APRM 42 which has detected a value higher than the set value and the water level signal which has detected a low or low reactor water level by the water level detector 44. ,
Based on the output signals of these AND circuits 45a and 45b, an OR circuit 46 performs a logical sum, and the AND circuit 45a or 45b sends out an output signal.

Therefore, one group is equipped with automatic pressure reducing valves 22a, 22b and 122c that can release up to 40% of the rated main steam flow rate.
The tDelB circuits 47a and 47b are opened at 30 second intervals.

A signal to run back or trip the water supply pump 16 is sent out 1, and a signal to actuate the injection valve 32 is outputted.

Next, the operation of this embodiment will be explained.

First, the operation of the output control device 41 when the full insertion of the control rod 3a, that is, the scram, fails despite the MSIV 8.9 being fully closed in the above configuration will be described. In the natural circulation boiling water reactor in this embodiment, as shown in FIG. This detected value is given to the output control device 41 as an input value. Normally, MSIV8.9 is fully closed,
When the valve stroke position becomes 90% or less, the reactor scrams and the reactor output is suppressed to about 200% or less. In this case, the reactor pressure rises and the pressure detector 43 detects the high reactor pressure, which opens the relief safety valve (SRV) 19 that can release approximately 50% of the rated main steam flow rate. The amount of pressure increase is suppressed to 10 kg/cnf or less.

On the other hand, if the scram fails as shown in Figure 4 (A), the reactor output will temporarily exceed 300% (or the APRM42 will be upscaled), and the reactor pressure will exceed the reactor pressure bulk. shows. Then, as shown in FIGS. 3 and 4, the power control device 41 controls when the reactor power exceeds the preset reactor power set point a and the reactor pressure exceeds the reactor pressure bulk. In addition, each group is equipped with automatic pressure reducing valves 22a, 22b, and 22c that can release up to 40% of the rated main steam flow rate.
A7 circuits 47a and 47b are used to open the water supply pump 16 at 30 second intervals, run back (or trip) the water supply pump 16, and then open the high pressure liquid poison accumulator 3.
For example, about 7 m' of sodium pentaphosphate concentrated solution
, a signal is issued to open the injection valve 32 to cause high-speed injection into the reactor pressure vessel 2 in 5 minutes.

Therefore, when the feed water pump 16 is runback (or tripped), the degree of subcooling entering the reactor core decreases, and the natural circulation force reduction effect works due to the lowering of the reactor water level, and the reactor core flow rate decreases, so the reactor output decreases. Decrease.

And automatic pressure reducing valve 22 a s 22 b s 22
By opening c, the voids in the core increase and negative reactivity is applied to the core, so the reactor output sharply decreases due to the synergistic effects of the water supply bomb back or trip.

In this case, in the present invention, three groups of natural pressure reducing valves 22a122b
, 22c to Til1le Dela1 circuits 47a, 47
By releasing the pressure at intervals of 30 seconds using b, the reactor water level will cause flushing, and the two-phase flow will reach the main steam piping and eventually the automatic pressure reducing valve, making it possible to prevent the automatic pressure reducing valve from choking. It is. Furthermore, combined with the poison effect of the concentrated sodium pentaborate solution, the reactor becomes subcritical in a short period of time.

In addition, the rise in reactor pressure due to the full closure of MSIV8.9 will cause the reactor pressure to rise and the safety valve 19 and automatic pressure reducing valve 22a1 will be released.
Since 22b and 22c are open, the integrity of the reactor pressure vessel 2 is ensured.

As mentioned above, when using the output control device 41 of the natural circulation reactor according to this embodiment, even if there is no recirculation pump trip (RPT) function adopted in forced circulation type BWR, MSIV8.9 can be completely closed. Even when a scram failure occurs, the reactor can be rendered subcritical in a short time while maintaining the integrity of the reactor pressure vessel 2 and maintaining the cooling shape of the reactor core 3.

Next, in the natural circulation BWR having the above configuration, the operation of the output control device 41 will be described when the full insertion (ie, scram) of the control rod 3a fails despite the water supply pump 16 tripping. Normally, water supply pump 1
6 trips and the reactor water level falls below the reactor water level low, the reactor will scram and the reactor power will not rise above the initial value. In addition, MSI is increasing due to the drop in reactor water level.
V8.9 is fully closed, but the safety relief valve 19 is closed due to high reactor pressure.
Since the reactor pressure is released, the amount of increase in reactor pressure is also small.

Then, as shown in FIGS. 2 and 5, when the reactor output is higher than the preset reactor output and the reactor water level is below the reactor water level, the output control device 41 Automatic pressure reducing valve 22a, 22b122c
The elB circuits 45a and 45b are used to open the circuits at 30 second intervals, and the sodium pentaborate solution is added, for example, to about 7rI.
! A signal is output to open the injection valve 32 so that the injection valve 32 is injected into the reactor pressure vessel 2 at high speed in about 5 minutes. Therefore, as shown in Fig. 6, the effect of lowering the subcooling level of the core inlet by the trip of the water supply pump 16 and lowering the natural circulation force, and the effect of lowering the natural circulation force of the automatic pressure reducing valve 22 CN
The effect of increasing the void rate in the core due to opening, combined with the poisoning effect of the concentrated sodium pentaphosphate solution, causes the reactor to become subcritical in a short period of time. In addition, MS at low and low reactor water levels
When the reactor pressure rises when IV8.9 is fully closed, the reactor pressure is high and the relief safety valve 19 opens, and the automatic pressure reducing valve 22
Since the depressurizing effect by aq 22b and 22c is also obtained, the integrity of the reactor pressure vessel 2 is not impaired. Note that the set value is preferably set to less than about 50% of the rated output, and in this embodiment is set to 50%.

In this way, if the output control device of the natural circulation reactor in this embodiment is used, it is possible to prevent the scram from failing at the time of the feed water pump trip even when the recirculation pump trip (RPT) function adopted in the forced circulation type BWR is not provided. In the event of an emergency, the integrity of the reactor pressure vessel 2 is maintained and the reactor core 3
It is possible to bring a nuclear reactor to subcriticality in a short time while maintaining its cooling configuration.

Note that the automatic pressure reducing valves 22a, 22b, and 22c1 of this embodiment are configured to release main steam and reactor into the containment vessel 1, but the main steam relief pipe is connected to the underwater 21a in the pressure suppression chamber 21. You can also let it escape.

[Effects of the Invention] According to the present invention, by selectively tripping and running back the feedwater pump and simultaneously opening the automatic pressure reducing valve, the reactor power is reduced and the integrity of the reactor vessel and core cooling profile are improved. can be retained.

Furthermore, by opening the automatic pressure reducing valve at different times, it is possible to prevent the automatic pressure reducing valve from choking when the reactor water level is flushed.

[Brief explanation of the drawing]

Fig. 1 is a schematic system diagram showing a natural circulation furnace equipped with an output control device according to an embodiment of the present invention, Fig. 2 is a block diagram showing the output control device in Fig. 1, and Fig. 3 is a main steam isolation Flowchart when the output control device of Fig. 1 is applied when the scram fails when the valve is fully open, Figs. 4 (A) and (B)
), (C) is a graph showing the transient changes of each event in Fig. 3, Fig. 5 is a flowchart in which the output control device of Fig. 1 is applied when the scram fails when the total water supply flow rate is lost,
FIGS. 6A, 6B, and 6C are graphs showing transient changes of each event in FIG. ■...Output control device (control means) 2...Average power monitor (APRM) 3...Reactor pressure detector (P) 4...Reactor water level detector (L) 1...Atom Reactor containment vessel 2...Reactor pressure vessel 3...Reactor core 3a...Control rods 4...Coolant 5...Cylinder 6...Main steam pipe 8.9...Main steam isolation Valve (MSIV) 16... Water supply pump 19... Main steam relief safety valve (SRV) 22... Automatic pressure reducing valve 31... High pressure liquid poison accumulator (SLC) 32... Injection valve (8733) agent Patent attorney Yoshiaki Inomata (and others)
1 person) Fuck 3 Flash

Claims (1)

[Claims] A reactor vessel containing a reactor core, a cylindrical body installed in the reactor vessel and surrounding the reactor core, and a cylindrical body formed between the cylindrical body and the reactor vessel and discharged from the upper part of the reactor core. A natural circulation flow path that guides the coolant to the lower part of the reactor core together with the feed water flowing in from the feed water pump, a main steam pipe that discharges steam generated in the reactor vessel, and a plurality of pipes provided in the main steam pipe. An output control device for a natural circulation reactor having a pressure reducing valve comprising: a control means for opening the plurality of pressure reducing valves with a time difference at the same time as running back or tripping the water pump; Furnace output control device.