JPS62148895A - Emergency stop 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 a nuclear reactor emergency shutdown device that stops the operation of a nuclear reactor when the internal pressure, power, etc. of a nuclear reactor exceed emergency shutdown limit values. .

[Technical background of the invention and its problems]

Generally, in a boiling water type atomic steam turbine plant such as J5, a turbine generator is directly electrically connected to a power grid via a circuit breaker. therefore,
When frequency fluctuations occur in the power system, the rotational speed of the turbine generator is influenced by this and fluctuates.

In other words, in the event of a breakdown such as a transmission line accident in the power system, the balance between the total power generation amount of the generators connected to the power system and the power usage speed of the users will be disrupted, causing frequency fluctuations. Fluctuations occur, leading to fluctuations in the rotational speed of the turbine generator that is directly connected to the fluctuations. Accordingly, the turbine speed control device operates in accordance with this variation in rotational speed to control the opening degree of the steam control valve, thereby regulating the amount of steam flowing into the turbine. As a result, the steam generated in the reactor is not consumed smoothly, and the pressure in the reactor fluctuates.

By the way, pressure fluctuations in the reactor are undesirable for boiling water reactors because they cause fluctuations in the reactor output, and in particular, as the pressure increases, the reactor output increases and exceeds the limit value. The nuclear reactor will automatically shut down, and the power plant will shut down. Therefore, conventionally, a bypass conduit for guiding a part of the main steam to the condenser by bypassing the turbine is branched from the main steam 3g pipe from the middle of the main steam conduit.

FIG. 4 is a schematic system diagram of a nuclear turbine plant to explain this. Steam generated in the reactor 1 passes through the main steam J pipe 2, and its flow rate is controlled by the steam control valve 3. It is introduced into the steam turbine 4. The steam introduced into the steam turbine 4 performs work there,
A generator 5 directly connected to the steam turbine 4 is driven, and the electric power generated there is sent to the power grid via a breaker 6. On the other hand, the steam that has performed work in the steam turbine 4 is sent to the condenser 7, where it is condensed.

Further, a bypass conduit 9 having a bypass valve 8 is branched out from the main steam conduit 2, and a part of the main steam can be guided to the condenser 7 by bypassing the steam turbine 4 as necessary. be.

On the other hand, a frequency detector 10 for measuring the power system frequency is provided at the outlet of the breaker 6 to the power system, and the frequency signal detected by the frequency detector 10 is transmitted to the comparator 11.
, where it is compared with a preset frequency set value, and if the frequency signal exceeds the frequency set value, the recirculation pump 12 is decelerated to reduce the reactor output to reduce the occurrence of a nuclear reaction. It's Nishide.

Further, the opening degree of the steam control valve 3 is controlled by a turbine speed control device so that the deviation between the actual turbine speed and the set speed is within a certain range, and the steam inflow fil into the turbine is adjusted. Furthermore, in response to the control of the opening direction of the steam control valve 3, the bypass valve 8 is controlled in the opening direction, and excess air is guided to the condenser 7.

However, generally the steam capacity that can flow through the bypass valve 8 is the same as that of the steam control valve 3! i is about 25% compared to 100%. Therefore, when the frequency of the electric saw system increases significantly, when the opening degree of the steam control valve is significantly reduced to prevent the rotation speed from increasing, even if the reduction Q of the steam control valve 3 is within 25%. For example, m having a volume of 25% can be absorbed and an increase in reactor pressure can be prevented.

However, if a frequency shift occurs that causes the steam control valve 3 to be throttled down further, the steam control valve 3 will be switched to the bypass valve 8.
If the capacity of the reactor is exceeded, the reactor pressure will increase, causing problems such as the reactor automatically shutting down due to the increase in reactor output.

The frequency increase G and the restriction 61 of the steam control valve are determined by the speed regulation rate in the turbine speed control device, and currently the speed regulation rate is 5%.

In other words, if the actual turbine speed increases by 5%, the steam control valve is to be throttled down by 100%, and a 5% increase in the actual turbine speed is 52.51 when converted to 5011z.
Becomes 12. If we calculate the upper shift limit of the frequency that can be absorbed by the bypass valve, it will be 50.625 Hz. On the other hand, in general, in the case of a power system failure, it is necessary to consider n on the frequency of up to 1,511z. Therefore, the current capacity of the bypass valve is insufficient, but increasing the capacity of the bypass valve would require a significant increase in equipment and increase plant construction costs, which is not realistic.

[Purpose of the invention]

The present invention was made in consideration of the above circumstances, and is designed to enable continuous operation without stopping the reactor even if the frequency of the power system increases to a predetermined value that is considered to increase due to a system failure. The purpose is to provide a nuclear reactor emergency shutdown device.

[Summary of the invention]

The present invention provides a scram circuit that outputs a shutdown signal for the reactor when the internal pressure, output, etc. of a nuclear reactor exceeds an emergency shutdown limit value, and a method that prevents the scram circuit from outputting a shutdown signal. The scram avoidance circuit cooperates with a condition determination unit that avoids operating the scram avoidance circuit while the frequency J3 of the power system to which the turbine generator is connected and the bypass valve opening of the main steam are respectively under predetermined conditions. It is something.

[Embodiments of the invention]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention together with a power generation system, and the same reference numerals as in FIG. 4 indicate the same 12i elements. In this case, the scram circuit 11 inputs the signal of the reactor pressure detector 12 and the signal of the reactor power detector 13, and outputs a reactor stop signal when at least one of the reactor pressure and the reactor power increases abnormally. However, this Scrum circuit 11 has no way to avoid that operation! A scram circuit 15 is added that detects the grid frequency by inputting the signal from the frequency detector 10 that detects the system frequency and the signal from the opening degree detector 14 that detects the opening degree of the bypass valve 8. If the bypass valve opening degree has not increased even if the bypass valve opening has increased, it is provided with a condition determining section 16 that determines that there is an abnormality outside the power plant and operates the scram avoidance circuit 15.

FIG. 2 is an explanatory diagram of the configuration of the condition determination unit 15, and shows that when the system frequency reaches the first regulation 1aA [871 or higher, 1'°
The comparator 21 outputs a signal of
a comparator 22 that outputs a signal of "1" when the system frequency exceeds the specified value B [%]; an AND circuit 23 that takes the logical product of the outputs of these two comparators; a comparator 24 that outputs a signal of 1'' when the opening degree of the bypass valve falls below a second specified value C [%] lower than the first specified value; and a second specified value that is smaller than the first specified value. D [%]
Comparator 2 outputs a signal of “°1°” when the value falls below
5, and an AND circuit 26 which performs the logical product of the outputs of these two comparators.

The operation of this embodiment configured as described above will be explained below with reference to the time chart of FIG.

First, the scram circuit 11 determines that the reactor 1 has become abnormal when at least one of the output signal of the reactor pressure detector 12 and the output signal of the reactor power detector 13 exceeds a predetermined 1 shift. An attempt is made to output a reactor shutdown signal to urgently insert a power supply and shut down the reactor.

However, the situation where the system frequency rises abnormally is not caused by something inside the power plant, and therefore there is no necessity to shut down the reactor. The scram avoidance circuit 15 and the condition determination section 16 are provided to avoid outputting a reactor stop signal in such a case.

In other words, when the frequency of the power grid increases as shown in FIG. 3 (a), the maximum value is suppressed by the action of the power grid stabilizing device, and it gradually returns to normal.

In this case, although there are some differences in the maximum value and rate of change depending on the size of the power system, the change generally follows the change trend shown in FIG. 3(a).

FIG. 3(b) shows changes in the opening degree CV of the steam control valve 3 and the opening degree BV of the bypass valve 8 with respect to frequency fluctuations. Valve 8 is heard in reverse. However, bypass valve 8
When the opening reaches 25%, which is the upper limit of the equipment capacity, the throttle of the steam control valve 3 cannot be compensated for, and the furnace output and furnace pressure increase after time t1 as shown in Figure 3 (C). do. Then, when the reactor output reaches the first limit value S1 at point 14, the scram circuit 11 is activated to output a reactor stop signal. If a reactor stop signal is output at these 14 points, the reactor output and reactor pressure will quickly drop as shown by the broken line. However, in this embodiment, when the system frequency reaches the specified value A [tlz] at point 21, comparator 22 outputs a signal of ``1'' at point 21, and the opening degree of the bypass valve exceeds B [%]. is i+1
! Since a + signal is output, the AND circuit 23 activates the scram avoidance circuit 15 to prevent the scram circuit 11 from outputting a reactor stop signal.

Eventually, when the system frequency decreases to below the specified value 1ac [IIZ], which is lower than the specified value A[H2], the comparator 24 outputs a signal of "1", and the bypass valve opening becomes the specified value B[%].
], the comparator 25 also becomes 11.
Since the signal of 1 I+ is output, the AND circuit 26 resets the scram avoidance circuit 15. FIG. 3(d) shows the operating state of the scram avoidance circuit 15.

Here, a specific method for preventing the scram avoidance circuit 15 from issuing a reactor stop signal will be described below (△)
There are two methods: , (B).

The emergency shutdown limit value of the method reactor output of (A) is set to S1! as shown in FIG. 3(C). :S2 is set, and when the scram avoidance circuit 15 is activated, the emergency stop limit value S2 is compared with the furnace output, and when the scram avoidance circuit 15 is reset, the emergency stop limit value S1 is compared with the furnace output. Make it. and,
When the reactor output exceeds these emergency shutdown limit values S, , s2, a reactor shutdown signal is output. Furthermore, by setting the emergency shutdown limit value S to 120E%] and S2 to 130[%], even if the reactor output exceeds the emergency shutdown limit value S1 due to an increase in frequency, the emergency shutdown limit value S2 can be set to 130[%]. This will prevent the reactor from automatically shutting down.

Incidentally, cases in which a nuclear reactor must be automatically shut down include an abnormal rise in reactor pressure, in addition to the above-mentioned normal rise in reactor output. Therefore, in the same way as described above, two types of emergency shutdown limit values with different levels are set for the reactor pressure, and a reactor shutdown signal is issued when at least one of the reactor output and reactor pressure exceeds the emergency shutdown limit value. All you have to do is configure it to output.

Method (B) The emergency stop limit value of the scram circuit 11 is fixed at one level as before, a relay is provided in the reactor stop signal circuit, and the scram avoidance circuit 15 prevents the operation of this relay. Even so, automatic shutdown of the reactor can be avoided. In addition, when adopting this method, a relay is provided in the scram avoidance circuit 15, and the output signal of the condition determination unit 16 causes this relay to skip operation, and the reactor stop signal of the scram circuit 11 is transmitted to the normally open contact of this relay. It may also be output via .

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a scram avoidance circuit that prevents the scram circuit from outputting an operation stop signal, and the frequency and bypass valve opening of the power system to which the turbine generator is connected, respectively. Since the system is equipped with a condition determination unit that operates the scram avoidance circuit while the predetermined conditions are met, the frequency increase that occurs when an accident occurs in the power system will not cause the plant to stop, and the frequency will be increased even when the bypass valve is fully open. The plant can be operated continuously while waiting for recovery.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an embodiment of the present invention together with the power generation system, Fig. 2 is a detailed configuration explanatory diagram of the main elements of the embodiment, and Fig. 3 is the operation of the embodiment. FIG. 4 is a block diagram showing the configuration of a conventional nuclear reactor emergency shutdown system together with a power generation system. 1... Nuclear reactor, 3... Steam control valve, 4... Steam turbine, 5... Generator, 7... Condenser, 8... Bypass valve, 10... Frequency detection 11... Scram circuit, 12... Furnace pressure detector, 13... Furnace output detector, 14... Opening degree detector, 15... Scram avoidance circuit, 16... Condition determination Department. Applicant's agent Sato - Yusan Figure 1

Claims (1)

[Claims] 1. The main steam generated from the nuclear reactor is controlled in flow rate by a steam control valve and introduced into the steam turbine, and a portion of the main steam is controlled in flow rate by a bypass valve linked to the steam control valve. In a nuclear power plant in which the reactor is controlled and introduced into a condenser, there is a scram circuit that outputs a nuclear reactor shutdown signal when the reactor internal pressure, output, etc. exceed emergency shutdown limit values, and this scram circuit A scram avoidance circuit that avoids outputting an operation stop signal, and a condition for operating the scram avoidance circuit while the frequency of the power system to which the turbine generator is connected and the opening degree of the bypass valve are respectively under predetermined conditions. A nuclear reactor emergency shutdown device characterized by comprising a determination section. 2. A patent characterized in that the scram circuit has two emergency stop limit values of different levels, and the scram avoidance circuit switches from a lower level emergency stop limit value to a higher level emergency stop limit value during operation. A nuclear reactor emergency shutdown device according to claim 1. 3. The reactor emergency shutdown system according to claim 1, wherein the scram circuit includes a relay that generates an operation stop signal, and the scram avoidance circuit suppresses the operation of the relay when the scram avoidance circuit operates. . 4. The condition determination unit operates the scram avoidance circuit when the frequency of the power system increases to a first specified value or more and the opening degree of the bypass valve becomes a first specified value or more. , the frequency of the power system has recovered to a second specified value or less that is lower than the first specified value, and the opening degree of the bypass valve is equal to or less than a second specified value that is smaller than the first specified value. The nuclear reactor emergency shutdown system according to any one of claims 1 to 3, wherein the operation of the scram avoidance circuit is canceled when the scram avoidance circuit recovers.