JPS6060596A - Method of interrupting main steam of boiling-water type reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a main steam shutoff method for shutting off main steam when the main steam pipe of a boiling water nuclear reactor breaks.

[Background of the invention]

Figure 1 shows an overview of the main steam and water supply system of the Nateng water type nuclear power plant. In Figure 1, reactor 1
0 is housed in the containment vessel 12 (411), and the steam generated in the nuclear reactor 1o can be sent to the high-pressure turbine 16 by main steam (G14). The main steam that has entered the high-pressure turbine 16 is bound to the low-pressure turbine 20 via the moisture separator 18, drives the low-pressure turbine 2o, and is then sent to the condenser 22 where it is condensed. The condensate in the condenser 22 is sucked into the condensate pump 24 and sent to the purification system 2.
6 and is purified and returned to the second hot well of the condenser 22. The condensate in the second boiler is sucked by the feed water pump 28, heated by the feed water heater 3o, and then supplied to the reactor 10 again as feed water.

The main steam pipe 14 is provided with a plurality of main steam isolation valves 32, and a flow restrictor 34 is provided upstream of the main steam isolation valves 32. Moreover, on the upstream side of the flow restrictor 34, a distribution 38 is connected to a suppression pool 36 provided at the lower part of the containment vessel 12, and a relief safety valve 40 is provided in this piping 38. 38
The relief safety valve 4 is provided to prevent the reactor pressure from rising.
0 and drains the steam inside the reactor into the suppression pool 36.
It is designed to be able to be discharged.

The conventional main steam isolation valve 32 described above is shown in FIG. In FIG. 2, the valve box 42 has an upstream side 4
A valve seat 48 is provided which separates the valve seat 4 and the downstream side portion 46 .

A valve rod 52 is connected to the valve body 50 that comes into contact with and separates from the valve seat 48 . The upper end of the valve stem 52 is connected to the piston rod 54
It is fixed to a sliding part 56 provided in the. This sliding portion 56 moves up and down along the guide 60 by the air cylinder 58.

In addition, the reference numeral 62 shown in FIG. 2 is an oil cylinder for adjusting the opening/closing speed of the valve, and the reference numeral 64 is a spring for closing the valve. Further, reference numeral 66 is a limit switch section,
A limit switch is provided at the upper end to confirm that the valve is open, and a limit switch is provided at the lower end to confirm that the valve is closed.

Based on transient analysis, this valve is supposed to close in 3 seconds or more from the fully open state to the fully open state. It has become. Then, when the valve is closed by 1°,
A reactor scram signal is issued. For this reason, the steam and reactor water flowing out from the main steam pipe rupture part (2) is as shown in Figure 3.

In other words, in such a boiling water nuclear power plant, if the main steam pipe 14 breaks at the break point P, for example, a large amount of steam will flow out from the break point P since the inside of the reactor lo is at commercial pressure. leak. For this reason, the steam flow rate in the main steam pipe 14 increases significantly, and upon detecting this increase in flow rate, the main steam isolation valve 32 is closed to shut off the main steam. In other words, the flow restrictor 34, which normally functions as a flow meter, is configured to allow the main steam to flow only up to 200% of its maximum flow rate, and due to the rupture of the main steam g14, the When the flow rate reaches 200 cm, the flow restrictor 34 detects this change in flow rate, and a control device (not shown) issues a signal to close the main steam isolation valve 32, thereby shutting off the main steam. The amount of main steam and reactor water flowing out from the breakage of the main steam 1, 14 until the main steam is shut off by the main steam isolation valve 32 is as shown in Fig. β. That is, for about 2 seconds after the main steam pipe 14 breaks, the pressure inside the reactor gradually decreases due to the outflow of steam from the breakage portion P, and the outflow amount gradually decreases. However, as the pressure inside the nuclear reactor 10 decreases, reactor water begins to flow out, and the amount of steam and reactor water that flows out rapidly increases.

Approximately 3.5 seconds after the completion of the rupture accident, the effect of closing the main steam isolation valve appears, and the amount of steam and reactor water flowing out rapidly decreases.

It is undesirable that there is a risk that a large amount of reactor water, which is highly radioactive, may leak out. Therefore, a self-pressure type valve as shown in Fig. 4 was developed to prevent the live steam isolation valve from closing at high speed in the event of a rupture in the main steam pipe. In this self-pressure type valve, the valve body 50 is driven by a cylinder 70 housed within a guide 68. The driving force for the cylinder 70 is such that high-pressure steam within the reactor 10 is guided to a steam passage 72 that closes a valve communicating with the upstream side portion 44, and main steam is supplied to the upper part of the cylinder 70 via a solenoid valve 74. I'm trying to guide it and close the valve. Note that the reference numeral 76 shown in FIG. 4 is a direct opening gauge, and the opening switch 78
The opening/closing state of the lid can be determined by the opening switch 80 and opening switch 80.

Figures 5 and 6 show the operating characteristics of this self-pressure valve when it is opened.
The figure shows a comparison between the conventional valve and the conventional valve. FIG. 5 shows the performance during normal rated operation. In the conventional valve shown in Fig. 2, the dashed line 8
As shown in Figure 2, the closing time for closing the valve is 0.
The closing operation starts 5 seconds later, and the fully open state occurs 5 seconds after the closing signal is generated.

On the other hand, in the self-pressure type valve shown in Fig. 4, the solid line 8
As shown in Fig. 4, the operation starts 1.1 seconds after the closing signal is generated and becomes fully open 2.5 seconds later. As described above, self-pressure valves operate faster than conventional valves, and in particular, as shown in FIG. 6, their operation in the event of a main steam pipe rupture accident is extremely slow compared to conventional valves.

In other words, with conventional valves, even if a main steam pipe rupture accident occurs, the operating time until the valve is fully closed remains almost the same (as compared to the rated time). In contrast, self-pressure valves start operating 0.8 seconds after the accident occurs, and 0.1 seconds later in the event of a live steam pipe burst #IT accident where the main steam flow rate is 200% of the rated value. The valve becomes fully open 0.9 seconds after the accident occurs. As before, the valve is 10% from the fully open position.
In the closed state, the reactor is scrammed by a signal from the direct opening gauge 76.

In this way, since the operating time of the self-pressure valve is extremely short in the event of a breakage accident of the main steam v14, the amount of steam flowing out from the breakage portion P can be significantly reduced. However, because the valve is closed too quickly, the pressure in the reactor increases as shown in FIG. That is, in the conventional valve currently in use, the main steam v14 is broken as described above.
υ [Then, reactor water flows out of the system from the fracture P, so the main steam isolation valve 32 shuts off the main steam 1υ as shown by the broken line 86.
``Even if we do, we can keep the core pressure 9 degrees lower than the initial pressure.

On the other hand, when a self-pressure type main steam isolation valve is used, as shown by the solid line 88, the valve is closed and the core pressure rises rapidly, resulting in the currently expected reactor pressure take-up value. (Transient change when the load cutting turbine bypass system is not operating) There is a concern that the p1 fuel salary will be damaged, which will have an unfavorable effect on the reactor.

[Purpose of the invention]

The present invention provides a new method for main steam a that can prevent an abnormal increase in reactor pressure due to high-speed closure of the main steam isolation valve by using a self-pressure valve as the main steam isolation valve. With the goal.

[Summary of the invention]

The present invention detects the flow rate of main steam flowing through the main steam pipe when the main steam pipe breaks, closes the main steam isolation valve provided in the main steam pipe, and connects the suppression pool and the main steam pipe. Forcibly open the safety valve installed in the pipe that is
It is designed to prevent pressure rise within the reactor by diverting the steam within the reactor to a suppression pool and condensing it.

[Embodiments of the invention]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the main steam shutoff method for a boiling point Ii* water reactor according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 8 shows the flow of an embodiment of the main steam shutoff method for a boiling water reactor according to the present invention.

The main steam shutoff method of the original embodiment is that when the main steam pipe 14 shown in FIG. ” emanates from the cape device Gourd. The self-pressure type main steam isolation valve starts closing 0.8 seconds after the upper self-valve close signal is issued. Then, at the stage when the valve is closed for 10 days, a reactor scram signal is issued, the reactor is scrammed, and 0.1 seconds after the main steam isolation valve starts to close, the main steam is isolated. The monument design is the same as above.
In response to the stomach signal and the valve closing signal, the main steam relief safety valve 40 is opened, and the steam in the reactor 10 is released via the distribution line 38 to one portion of the cooling water in the suppression pool 36 .

The steam released into the cooling water of the suppression pool 36 is cooled by the cooling water and condensed. The cooling water in the suppression pool 36 is then fed to the residual heat removal system cylinder provided in the residual heat removal system tube 90 as shown in FIG.
After being cooled in a heat exchanger 102, it is returned to the re-breathing/gour 36.

By doing this, the core pressure can be adjusted by changing the self-pressure valve to the main steam isolation valve 32, as shown by the dashed line 104 in FIG.
Compared to the case where the main steam is simply shielded by VDr, it is much smaller and does not impair the safety of the reactor.

In addition, by using a self-pressure valve as the main steam isolation valve, the amount of steam flowing out is as shown by line 106 in Fig. 11.
Approximately 1/9 compared to the conventional valve shown in the dashed line 108
It is possible to reduce the amount of radiation to a certain degree, reduce the exposure dose, and improve environmental safety. In addition, the relief safety valve 40 is connected to the main steam pipe 14.
Since the valve is opened based on an increase in the flow rate of the main steam isolation valve 32 and a closing signal of the main steam isolation valve 32, malfunction of the relief safety valve 40 can be prevented.

FIG. 12 shows another embodiment of the main steam shutoff method according to the present invention. In the embodiment shown in FIG. 12, when an increase in the flow rate of the main steam pipe is detected, the main steam isolation valve close signal and the safety relief valve open signal are simultaneously issued. As a result, the self-pressure main steam isolation valve starts closing operation 0.5 seconds after the closing signal is issued, and when the valve is 10% quiet, it issues a reactor scram signal and the reactor scrams. do. Then, 0.6 seconds after the close signal is issued, the main steam isolation valve 32 is fully closed. On the other hand, the relief safety valve 40 starts its opening operation 0.3 seconds after the opening signal is issued, and the relief safety valve 40 is fully opened 0.1 seconds after this. When it is detected that the relief safety valve 40 is fully opened, a timer is automatically activated to generate a signal to close the relief safety valve 40 after 10 seconds. However, the close signal for the safety relief valve 4° is such that the safety relief valve 40 remains fully open when the pressure in the reactor 10 is higher than the safety relief valve setting pressure of the safety relief valve 40.

According to this embodiment, as shown by QillO in FIG. 13, the specific yield is equal to the broken line 111 when a self-pressure valve is simply used as the main steam isolation valve 32, and the reactor pressure can be made very low. Nuclear reactors can be kept safe. In addition, the minimum value of the ratio between the limit output and the actual output (ΔMCPR) does not fall below the initial value as shown by the solid line 112 in the case of this embodiment, which prevents damage from occurring due to temperature rise of the fuel rods. It can be prevented. On the other hand, when this embodiment is not used, the value of ΔMCPH becomes as shown by the broken line 114, and it can be seen that the main steam cutoff according to this embodiment takes a value on the very safe side.

FIG. 14 shows changes in the flow rate of the relief safety valve 40 when the main steam is shut off according to the embodiment shown in FIG. 12. Note that the broken line shown in FIG. 14 indicates that the main steam isolation valve 32 is a self-pressure type valve, and that the relief safety valve 40
This shows the case where the In this case, the reactor pressure increases as indicated by the broken line 111 shown in FIG. 13, and this pressure increase causes the relief safety valve 40 to open.

〔Effect of the invention〕

As explained above, according to the present invention, when a self-pressure valve is used as a main steam isolation valve, by forcibly opening the relief safety valve when the main steam isolation valve is blocked, the main steam isolation valve can be rapidly blocked. It is possible to prevent an abnormal increase in reactor pressure due to this.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the main steam and feedwater type system of a submerged reactor, Figure 2 is a cross-sectional view of a conventionally used main steam isolation tank, and Figure 3 is a main steam pipe rupture accident. Fig. 4 is a ljT view of the main steam isolation valve of the self-pressure valve, and Fig. 5 is the operating state of the main steam isolation tank during rated operation. Figure 6 shows the operating status of the main steam isolation box in the event of a main steam pipe rupture accident. A diagram showing changes in core pressure when using a steam isolation valve and an eye-pressure main steam isolation cell; FIG. A diagram showing the circulation of cooling water in the two-pressure pool, Figure 10 is the main steam according to the present invention; JS
Figure 11 is a diagram showing the change in core pressure between the main steam shutdown method and the conventional main steam shutdown method, Figure 11 is a diagram showing the difference in the steam and reactor water outflow area between the above embodiment and the conventional method, and Figure 12 is the main steam shutdown method. FIG. 13 is a diagram showing another embodiment of the main steam shutoff method for a boiling water reactor according to the invention; FIG. 13 is a diagram showing an example of a transient change in the reactor according to the embodiment shown in FIG. 12; FIG. 12 is a diagram showing the relief safety valve flow rate in the embodiment shown in FIG. 12. FIG. DESCRIPTION OF SYMBOLS 10... Nuclear reactor, 12... Containment vessel, 14... Main steam pipe, 16... High pressure turbine, 32... 1 [valve in main illumination air gap, 34... Flow restrictor, 36... Suppression pool, 38... Piping, 40... Safety relief valve. Agent Patent Attorney Tatsuyuki Unuma $3 3rd X/) 3 For fr after car emblem (utility υ Figure 4% 5th HsrVFM48f occurrence reed e+ RIIQ (5e C
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Claims (1)

[Claims] 1. A main steam pipe that guides the steam generated in the reactor to the turbine, a main steam V5 valve installed in this main steam pipe, and a cooling water installed at the bottom of the containment vessel in which the reactor is housed. The main steam in a boiling water nuclear reactor is equipped with a suppression pool serving as a reservoir, and a safety valve provided in a pipe connecting the upstream side of the main steam isolation valve of the main steam pipe and the sub-reduction pool. In a main steam shutoff method for a boiling water reactor, which operates a main steam isolation valve to block a main steam pipe when a pipe is ruptured, the flow rate of steam flowing through the main steam pipe when the main steam pipe is ruptured. 1. A method for shutting off main steam in a boiling water nuclear reactor, characterized in that the main steam pipe is blocked by the main steam isolation valve upon detecting this, and the safety valve is forcibly opened.