JPS61105496A - Automatic decompression device for nuclear 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 (Technical Field of the Invention) The present invention relates to an automatic reactor decompression device incorporated in an emergency core cooling system of a boiling water nuclear power plant, and in particular:
Automatic depressurization device with improved automatic startup method: full.

[Technical bluestone of invention and its problems]

In general, in nuclear power generation, an emergency core cooling system (Emergency Core Cooling System) is installed in case piping connected to the reactor pressure vessel ruptures during reactor operation and reactor coolant leaks or is lost. Core Cooli
ng 5yste+++ (hereinafter abbreviated as ECC8) is provided. This ECC 8 is composed of four systems, which are independent and based on different principles: a high pressure core spray system, an automatic depressurization system, a low pressure core spray system, and a low pressure injection system, and is designed to be activated automatically in response to a required activation signal.

FIG. 4 is a system diagram that does not show the configuration of the main parts of the reactor related to this ECC 8. A suppression pool 3 is formed at the bottom of the reactor containment vessel 2 that houses the reactor pressure vessel 1. The ECC 8 includes a high-pressure core spray system that sprays water from the suppression pool 3 or condensate storage tank 4 from a nozzle in the sparger header immediately above the core using a high-pressure core spray pump 5, and a low-pressure core spray pump 6 that sprays water from the suppression pool 3 from the nozzle of the sparger header immediately above the core. A low-pressure core spray system that sprays water from the nozzle of another sparger header, and a low-pressure water injection system that injects water from the suppression pool 3 into the reactor by low-pressure water injection pumps 7, 8 and 9, respectively, as backup for this low-pressure core spray system. and high pressure core spray pumps 5 for each of these cooling systems.
, low pressure core spray pump 6 and low pressure water injection pump 7.
8 and 9 are each driven by receiving power from the in-house mm1o or the emergency diesel power generator 8111.

On the other hand, a main steam pipe 12 and a water supply pipe 13 are connected to the reactor pressure vessel 1, and the main steam pipe 12 is equipped with a relief safety valve 14 for releasing steam to the bit sub-reactor thermal reactor steam pressure pool 3. Furthermore, this relief safety valve 14
is the reactor water level low signal and the containment volume! 5 1jaT reactor automatic depressurization system δ (＾uto Depressu
rization 5ysLe-hereinafter abbreviated as ADS) released by 15 and 1! It is configured to do this.

Jt, here the high pressure core spray system is high pressure FCC!
;、Low pressure core spray system and low pressure water injection system
As C8, an outline of the core cooling operation in the event of a loss of coolant accident will be explained below.

For example, if a breakage accident occurs in the recirculation system piping (not shown), the coolant flows out and a portion of it is lost.

If the reactor water level drops due to this coolant loss accident and the reactor core is exposed, there is a risk that the fuel cladding material will melt1.In order to prevent this melting, when the reactor water level drops, the high pressure ECC8 is activated. The reactor core inside the high-pressure reactor pressure vessel 1 is cooled down by 7 Jl, and the reactor water level is restored.

By the way, if the reactor water level continues to drop even after the high pressure ECC 8 is activated, the low pressure ECC 8 is created, but this low pressure ECC 8 will not operate if the pressure inside the reactor pressure vessel 1 is high. Therefore, under the conditions that the water level in the reactor is lower than a predetermined value (and the pressure in the reactor containment vessel is higher than a predetermined value), the ADS 15 opens the relief safety valve 14 and reduces the high pressure in the reactor pressure vessel 1. By releasing steam into the water in the suppression pool 3, the reactor pressure is actively lowered, allowing the low-pressure ECC 8 to inject coolant into the reactor pressure vessel 1.

That is, the ADS 15 has a function of prompting water injection by the low pressure ECC 8. The conventional AD815 is activated when the above-mentioned reactor water level is "low" and the Tj reactor containment vessel pressure water is high at the same time, but it also activates when a manual operation signal is output in addition to this. The configuration is such that the relief safety valve 14 is opened in the same manner as described above.

In this way, even if a loss of coolant accident occurs, sufficient core cooling is performed by the operation of the ^-pressure ECC 8, ADSI 5, and low-pressure ECC 8, so that fuel damage can be prevented.

In recent years, amidst the trend to improve the safety of nuclear couplants, the integrity of nuclear couplants in the event of failure of the nuclear reactor lip system (RTS) has become an issue.

Here, the reactor trip system refers to the emergency insertion (scram) of control rods for reactor shutdown when an abnormal state or malfunction occurs during the operation of the reactor, or during a transition period before transitioning to an abnormal state. This is a system that protects the reactor and power plant, but if a failure occurs, such as when some control rods are not inserted during a scram during the transition period to an abnormal state, the reactor will continue to output power due to continued nuclear fission. Therefore, at this time, an abnormal drop in the reactor water level and a sudden rise in the reactor containment vessel pressure are expected.

In response to such a situation, the high pressure ECC8 and ADS1 described above are used.
5 and the low-pressure E CCS will operate, and Oma's cold water will be supplied to the core.

By the way, among the above-mentioned nuclear couplers, especially in boiling water reactors (13WR), increases and decreases in steam bubbles (hereinafter referred to as voids) present in the reactor core have a large effect on the reactor output.

In other words, boiling water reactors generally have a negative reactivity coefficient, so if the voids decrease, positive reactivity will be added to the reactor, and conversely, if the voids increase, negative reactivity will be added to the reactor. . Therefore, in the event of a reactor trip system failure, A
If DS15 were activated and a large amount of cold water was injected into the reactor core, the reactor output would rapidly increase due to the sudden decrease in voids due to cooling, resulting in an unfavorable situation in terms of core health.

As described above, the conventional ADS 15 was not necessarily configured to operate under optimal conditions from the viewpoint of the health of the device.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an automatic reactor decompression device that can reliably maintain the integrity of a nuclear reactor core.

[Summary of the invention]

To achieve this objective, the present invention is designed to reduce reactor pressure by opening a safety valve that releases reactor steam to a subledge: 1 pool in order to encourage water injection by a low-pressure non-low B emergency core cooling system. In the reactor automatic depressurization system, the reactor water level low signal is output when the water level in the reactor pressure vessel drops to a level that requires caution, and the reactor water level low signal is output when the pressure in the reactor containment wX rises to a level that requires caution. At least simultaneously with the output containment vessel high signal, the reactor output low signal that is output when the nuclear power output drops below the critical output is input at 1rJ1, or when the reactor output is above When the output is above the critical output and the low-pressure ECC8 operation signal that is output when at least one of the low-pressure emergency core cooling W systems is activated is input at the same time, The present invention is characterized in that it includes a logic operation section that outputs a valve opening operation signal for opening the safety valve.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 31. In addition, Figures 1 and 2, middle,
The same parts as in FIG. 4 are designated by the same reference numerals, and the explanation thereof will be omitted.

FIG. 1 is a block diagram showing the main parts of the logic operation section incorporated in an embodiment of the automatic decompression device according to the present invention, including first and second AND gates 20, 21, OR gate 22,
It has a NOT gate 23.

The first AND gate 20 inputs the reactor water level low signal S24, the containment vessel high signal 825, and the reactor output low signal 326, and when this AND condition is satisfied, the OR gate 20
2, the valve opening operation signal S27 is output. The reactor water level low signal S24 is output when the water level in the reactor pressure vessel 1 has decreased to a level that requires caution,
The containment vessel pressure high signal 825 is output when the pressure within the reactor containment vessel 2 rises to a pressure that requires caution. Further, the reactor power low signal 826 is output when the reactor power output has decreased to a value lower than the critical power, for example, to about several percent or less.

Further, the second AND gate 21 is connected to the reactor water level low signal 8.
24 and the containment vessel pressure high signal S25 are input, and the reactor output low signal 826 is input to NOT gate 2.
3, and low pressure 'E CCS
The I unit operation signal 828 is input. Therefore, the valve opening operation signal 827 is output when the AND condition of either the first AND gate 20 or the second AND gate 21 is satisfied, and the relief safety valve 14 to which this valve opening operation signal 827 is input is opened. The high-pressure steam in the reactor pressure vessel 1 is released to the suppression pool 3, reducing the pressure inside the reactor.

As shown in FIG. 2, the low pressure ECC 3I operation signal 828 is transmitted to each pump 6.7.8 of the plurality of low pressure ECCs 8.
9 is output from a logic operation circuit for selectively operating only one unit.

In other words, each pump 6.7.8.9 of the low pressure ECC 8 of multiple systems is activated by the output of the reactor water level low signal 824 and the containment vessel pressure high signal S25, and at this time, the low pressure ECC 8 of each system is activated. A confirmation signal 829 is output. However, in this state, since the pressure inside the reactor pressure vessel 1 is still high, the low-pressure ECC 8 is not injecting or spraying water into the reactor and is in a standby state. One of the low voltage ECC8 operation confirmation signals 829 is input to the NOT gate 30a of the feedback circuit 30, inverted there and input to the AND gate 30b. Since this AND gate 30b has one input as the output signal of the NOT gate 23 which receives the reactor output low signal S26, it is in a state where the reactor output low signal 826 is not output, that is, the reactor output is higher than the critical output. Moreover, each pump of the low pressure ECCS of multiple systems is 6.7°8
．． Selection signal 831 when none of 9 are activated.
Output. This selection signal 831 is fed back to each low pressure ECC 8, and the selected low pressure ECCS pump, for example 6.1
Start only the unit and inject coolant into the reactor pressure vessel 1.
Or wait to spray. At the same time, the low-pressure ECC 8 on standby outputs a low-pressure ECC 8 operation confirmation signal S29, which is output to the first AND gate 21 as a low-pressure ECC 3I operation signal S24. Therefore, conventional AI)81
5, the reactor water level is low and the reactor containment vessel pressure is high! When the li state occurred at the same time, the relief safety valve was opened, but here the condition is that the reactor output is below a predetermined value close to the buttock, that is, it has fallen below the critical output, or in the critical output state, the low-pressure ECC3I unit is in the injection standby state. The relief safety valve is opened only when certain conditions are met. This means that even if an abnormal condition occurs due to a failure in the reactor trip system, the critical output is maintained.
In this state, a large amount of cold water is prevented from being injected, suppressing a sudden increase in reactor output, and if the reactor trip system operates normally, a large amount of cold water is injected without delay to prevent overheating or melting of the core. This shows that it can be prevented.

In this way, safe core cooling u1 is possible without adding significant positive reactivity to the reactor.

Figures 3 (a) to (C) show changes in reactor pressure, ECC8 flow rate, and reactor power during an abnormal transient state due to a failure in the reactor trip system, when using the conventional ADS15. The case where the ADS of the present invention is used is shown by the dashed line, and the solid line shows the case where the ADS of the present invention is used. In Figure 3, when the reactor water level is low and the containment vessel pressure is high at time t1, the conventional ADS
15 operates at this point, the reactor pressure then decreases as shown by curve p and ECC3i! ! Since l increases significantly as shown in curve 1a, the reactor power increases sharply as shown in curve r.However, in the ADS of the present invention, even if the reactor water level is low at time t1,
Even if the containment vessel pressure becomes high and the ADS is activated, the low pressure ECC
8, the number of units in the injection standby state is suppressed, so there is no sudden injection of cold water as shown by curve q, and a sudden increase in the reactor output is prevented.

〔Effect of the invention〕

As is clear from the above explanation, the automatic reactor depressurization system of the present invention can function reliably in the same manner as conventional systems in the event of a loss of coolant accident, and can also function automatically in the event of a reactor trip system failure. In situations where the operation of the depressurizer is unfavorable, only the low-pressure ECC8 necessary and sufficient to secure the water level is put on standby, so even if the automatic reactor depressurizer operates, the health of the reactor core can be maintained reliably. Effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of the logic operation section incorporated in an embodiment of the automatic reactor depressurization system according to the present invention, and FIG. 2 is a block diagram showing the overall configuration of the logic operation section of this embodiment. 3(a) to 3(C) are time charts for explaining the operation of this embodiment, and FIG. 4 is a dimensional system diagram showing the general configuration of the automatic pressure reduction system. 1... Reactor pressure vessel, 2... Reactor containment vessel, 3
...Pressure pool, 5...8 pressure core spray pump, 6...Low pressure core spray pump, 7,8゜9...Low pressure water injection pump, 12...Main steam pipe, 13.
... Water supply pipe, 14 ... Relief safety valve, '15 ... Reactor automatic decompression device, 20 ... 1st AND gate, 21 ...
・・2nd AND gate, 22-OR gate, 23-・
・-N OT K-]・, S27... Valve opening operation signal,
828... Low pressure ECC3I unit operation signal, 30...
feedback circuit.

Claims (1)

[Claims] In the automatic reactor depressurization system, which lowers the reactor pressure by opening the safety valve that releases reactor steam to the suppression pool to encourage water injection by the low-pressure emergency core cooling system,
The reactor water level low signal is output when the water level in the reactor pressure vessel drops to a level that requires caution, and the containment vessel high signal is output when the pressure in the reactor containment vessel rises to a level that requires caution. and the reactor output low signal, which is output when the reactor output drops below the critical output, is input at the same time, or when the reactor output is above the critical output. and when the low-pressure ECCS activation signal that is output when at least one system of the low-pressure emergency core cooling system is activated is input at the same time, a valve opening operation signal that opens the safety valve is generated. An automatic nuclear reactor decompression device characterized by being provided with a logic operation section that outputs output.