JPS62134594A - Protective 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 [Industrial Application Field] The present invention relates to a nuclear reactor protection device, and particularly to a nuclear reactor protection device suitable for application to a nuclear reactor having an internal pump.

[Prior Art] A new type of boiling water reactor has been developed to replace the boiling water reactor in which the core flow rate is adjusted by a recirculation pump installed in the recirculation system piping. In this boiling water reactor, the core flow rate is adjusted by an internal pump provided within the reactor pressure vessel. As a protection device for a boiling water reactor having such an internal pump, Japanese Patent Application Laid-Open No. 59-84197 and Japanese Patent Application Laid-open No. 59-18859 are known.
9 and Japanese Unexamined Patent Publication No. 60-15599 are known.

FIG. 4 shows a boiling water reactor with a conventional internal pump. The internal pump 21 is installed within a reactor pressure vessel 23 containing a reactor core 22. The rotation shaft of the internal pump 21 is connected to a motor 24 installed outside the reactor pressure vessel 23. The motor 24 of the internal pump 21 is supplied with power from the stationary inverter 19. The restraint type inverter 19 is
The power frequency input from the bus bar 18 is adjusted based on the control signal output from the recirculation flow rate control device 20, and the rotational speed of the internal pump 21 is controlled.

[Problems to be solved by the invention] In a conventional nuclear reactor that includes multiple internal pumps, assuming that all the internal pumps trip, there is a possibility that the cooling capacity of the core will decrease transiently. I newly discovered that there is.

That is, the combined inertia of the internal pump 21 and the static inverter 19 in a nuclear reactor with an internal pump is the combined inertia of the recirculation pump and the MG upper set that controls its rotation speed in a nuclear reactor with recirculation system piping. becomes very small compared to . For this reason, nuclear reactors with internal pumps are superior in quick response to requests for changes in reactor output, etc. However, in the unlikely event that bus 1
If all the internal pumps 21 trip due to a loss of power to the internal pumps 8, the rotational speed of the internal pumps will sharply drop, and the core flow rate will drop sharply. Such a sudden decrease in the core flow rate leads to a sudden decrease in the core cooling capacity, which may lead to an unfavorable state from the viewpoint of the thermal margin of the fuel.

An object of the present invention is to provide a nuclear reactor protection device that can scram a nuclear reactor in a short time even when all internal pumps trip.

[Means for solving the problem] The above problem is such that when the reactor power detected by the 2M slave reactor power detection means is equal to or higher than the first predetermined level, cooling is supplied to the core as measured by the flow meter. This problem can be solved by providing a scram determination means that outputs a scram signal when the material flow rate is below a second predetermined level, and rapidly inserting the control rods into the reactor core based on the scram signal output from the scram determination means. Ru.

[Function] A scram determination device determines whether or not a reactor scram is necessary due to a sudden decrease in the core flow rate due to all trips of the internal pump, and if necessary, it is output to scram No. 48, and based on this scram signal, the atomic Furnace is scrammed.

[Example] An advantageous example of the present invention applied to a boiling water reactor is as follows.
This will be explained based on FIGS. 1 and 2.

Boiling water reactors with internal pumps have core 2
An internal pump 21 is installed in a reactor pressure vessel 23 containing a reactor pressure vessel 23. The ten internal pumps 21 are arranged in an annular gap between the reactor pressure vessel 23 and the core shroud 25 surrounding the reactor core 22 so as to surround the reactor core shroud 25 . Ten motors 24 are installed outside the reactor pressure vessel 23 and at the bottom of the reactor pressure vessel 23 . A rotating shaft of the internal pump 21 passes through the lower wall of the reactor pressure vessel 23 and is connected to the motor 24 . One motor 24 for one internal pump 21
are concatenated. A control rod 16 that adjusts the reactor output is installed so that it can be moved in and out of the reactor core 22. control rod 16
Is the control rod drive device! It is connected to i15. A large number of local power range monitors (hereinafter referred to as LPRMs) 26 are installed within the reactor core 22 to detect the reactor output. A flow meter 28 is provided to measure the core flow rate. The average power range monitor (hereinafter referred to as APRM) 27 receives the output signals of each LPRM 26 and calculates an average neutron flux signal corresponding to the average power of the reactor. Reference numeral 19 denotes a static inverter, which is connected to a bus bar 18 which is a power source. 20 is a recirculation flow rate control device.

The reactor protection device of this embodiment includes a control rod drive control device 3, a scram determination device 17. LPRM26 and flow meter 2
It has 8. Details of the scrum judgment device 17 will be explained based on FIG. 2. The scram determination device 17 includes a reactor power determination section 4, a core flow rate determination section 11, and an AND circuit 28.
have.

7 is a signal holding section, which is a kind of delay circuit.

The reactor power determination unit 4 receives AP'RM via the filter 2.
27. Core flow rate determining section 11 is connected to flow meter 28 via filter 10 .

One input end of the AND circuit 28 is connected to the reactor power determination section 4 via the signal holding section 7, and the other input end of the AND circuit 28 is connected to the core flow rate determination section 11, respectively. The output end of the AND circuit 28 is connected to the control rod drive control device 3. The control rod drive device control device 3 is manufactured by Japanese Patent Application Laid-Open No. 51-13
It is composed of a scram population valve, a scram outlet valve, and a scram pilot solenoid valve as shown in Japanese Patent No. 7091.

The output signal of the AND circuit 28 becomes an opening signal for the scram pilot solenoid valve.

The reactor protection device of this example was installed in a nuclear reactor based on the following study results. The results will be explained below based on the characteristics shown in FIG.

The event targeted by the reactor protection system of this embodiment is a hypothetical event in which all internal pumps trip due to a loss of power to the stationary inverter 19 or a trip of the stationary inverter, and the reactor core flow rate suddenly decreases. This is an event that could result in a rapid and transient decrease in core cooling capacity. Therefore, when considering such a protection device, it is necessary to consider the following three points.

(1) The higher the reactor power at the time when all internal pumps trip (hereinafter referred to as initial reactor power), the greater the adverse effect on the reactor due to a sudden decrease in core flow rate. On the other hand, if the initial reactor power is low, the drop in core cooling capacity will not be a problem even if the core flow rate decreases rapidly. According to the analysis, the lower limit of initial reactor power at which adverse effects occur is considered to be 70% power.

(2) The larger and more rapid the fall in the core flow rate, the greater the negative impact, but fluctuations in the core flow rate within the normal operating range above the internal pump minimum speed operating point are not a problem, and all internal pumps trip. It is sufficient to protect against a hypothetical event in which the core flow rate suddenly and significantly decreases by more than 50%/sec.

(3) Care should be taken to avoid issuing unnecessary scram signals during normal operation or when starting and stopping.

The logic of reactor protection considering the above points is as follows.

(a) When the initial reactor power is about 70% or more, perform a reactor protection operation, that is, scram the reactor.

(b) The range up to the lowest pump speed line is the range in which operation is expected during normal operation, and a natural circulation state is reached when all recirculation pumps are tripped. Therefore, it is reasonable to scram between the natural circulation line and the lowest pump speed line. That is, the reactor protection operation is performed when the core flow rate is below about 35%, which is "abnormally low."

(c) If the core flow rate decreases faster than about 50%/sec, perform a reactor protection operation.

The nuclear reactor protection device shown in FIG. 1 has the functions (a) to (c) above.

The average neutron flux signal output from the APRM 26 is input to the filter 2 having a delay element.

Filter 2 removes noise from the average neutron signal and converts it into reactor power.

Such a filter 2 is a means for determining the reactor output.

The reactor output determination unit 4 compares the reactor output signal output from the filter 2 and the reactor output determination value (70% output) 5, and when the former level exceeds the latter level, the reactor output A signal 6 indicating that the value is greater than or equal to the judgment value is output. This signal 6 is held in the signal holding circuit 7 for a predetermined period of time (for example, about 2 seconds) and then outputted from the signal holding circuit 7 to the AND circuit 28 . Even if the reactor output signal once exceeds the reactor output determination value 5, the reactor power determination unit 11 is activated after 2 seconds or more have passed since the reactor output falls below the reactor output determination value 5.
When the signal output from the reactor indicates that the core flow rate is low, the rate of decrease in the core flow rate is sufficiently slow compared to 50%/sec, and does not pose a problem in terms of reactor protection measures.

On the other hand, the core flow rate signal 9 measured by the flow meter 28 is input to the filter 10 to remove noise, and then input to the core flow rate determination section 11. The core flow rate determination unit 11 uses the core flow rate signal and the core flow rate abnormality determination value (approximately 35% flow rate) 1
2, and if the former level becomes smaller than the latter level, a "core flow rate low" signal 13 is output.

This “core flow low” signal 13 is input to the AND circuit 28.

The AND circuit 28 determines that the reactor output is a predetermined value (judgment value near 0).
%) or more, indicating that the reactor output is at least 35%, and signal 13, indicating that the core flow rate is below the predetermined value (judgment value of 35%), are input. A flow rate rapid scram signal 14 is output.

The core flow rate sudden scram signal 14 is input to the scram pilot solenoid valve of the control rod drive device control device 3. The scram pilot electromagnetic valve operates as shown in Japanese Patent Laid-Open No. 51-137091 by inputting the scram signal 14 to open the scram inlet valve and the scram outlet valve. Therefore, high-pressure driving water is supplied from the accumulator to the control rod drive device 15, and the control rod 16 is rapidly inserted into the reactor core 22 by driving the control rod drive device 15.

Therefore, the reactor is scrammed.

In the system currently being considered, if we hypothetically assume that all the internal pumps 21 trip, the amount of voids in the core 22 will increase rapidly due to a sudden decrease in the core flow rate, and the reactor water level will rise. leading to a turbine trip. If a turbine trip occurs, the reactor will scram and shut down safely. However, this embodiment can scram the reactor in a shorter time than such a reactor protection device.

In this embodiment, in order to obtain the reactor output signal, A P
Although the average neutron flux signal from RM 27 is filtered, this can also be achieved by taking in the main steam flow rate, turbine inlet pressure, etc. and performing similar filter processing.

Further, the determination values and signal holding times shown in this embodiment are representative examples, and are appropriately set for each plant.

In the embodiment shown in FIG. 1, the output signal 6 of the reactor output determination unit 4 is input to the AND circuit via the signal holding circuit (signal delay circuit) 7, but the output signal 6 is not passed through the signal holding circuit 7. Alternatively, it may be directly input to the AND circuit 28. but,
When the core flow rate decreases, the reactor output also decreases, so if the signal holding circuit 7 is provided, it is possible to more accurately detect a sudden decrease in the core flow rate due to all trips of the internal pumps.

[Effects of the Invention] According to the present invention, even if all internal pumps trip, the reactor can be scrammed in a short time, and the safety of the reactor is significantly improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a nuclear reactor protection device that is a preferred embodiment of the present invention, Fig. 2 is a detailed block diagram of the scram judgment device shown in Fig. 1, and Fig. 1 is a block diagram of a nuclear reactor protection device shown in Fig. 1. FIG. 4 is a diagram of the reactor core flow rate curve explaining the logic of the device, and is a configuration diagram of a nuclear reactor having an internal pump. 2.10...Filter, 4...Reactor output determination section, 7
... Signal holding section, 11... Core flow rate determination section, 15.
... Control rod drive device, 16 ... Control rod, 17 ... Scram judgment device, 21 ... Internal pump, 22
...Reactor core, 24...Motor, 28...AND circuit.

Claims (1)

[Scope of Claims] 1. A reactor vessel containing a reactor core, a plurality of internal pumps provided in the reactor vessel and supplying coolant into the reactor core, and a control device inserted into the reactor core. A protection device for a nuclear reactor having a control rod and a means for driving the control rod, a means for detecting reactor power, a flow meter for detecting a flow rate of coolant supplied to the reactor core, and a means for detecting the reactor power. scram determination means for outputting a scram signal when the reactor output detected by the detection means is above a first predetermined level and the coolant flow rate measured by the flow meter is below a second predetermined level; and means for controlling the control rod drive device to rapidly insert the control rods based on the scram signal output from the scram determination means. 2. Claim 1, wherein the first predetermined level is 70% output and the second predetermined level is 35% flow rate.
Reactor protection device as described in Section 1.