JPH0690307B2 - Reactor protection method and device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for protecting a nuclear reactor, and more particularly to a method and a device for protecting a nuclear reactor which are suitable for application to a nuclear reactor having an internal pump. It is a thing.

[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 provided in the recirculation system piping. In this boiling water reactor, the core flow rate is adjusted by an internal pump provided in the reactor pressure vessel. As a protection device for a boiling water reactor having such an internal pump, there are JP-A-59-84197, JP-A-59-188599, and JP-A-6-88599.
The one disclosed in the publication 0-15599 is known.

FIG. 4 shows a boiling water nuclear reactor having a conventional internal pump. Internal pump 21, core 22
It is installed in the reactor pressure vessel 23 containing the. The rotary 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 static inverter 19. The stop inverter 19 is a recirculation flow controller 20.
The power supply frequency input from the bus 18 is adjusted based on the control signal output from the internal pump 21, and the rotation speed of the internal pump 21 is controlled.

[Problems to be Solved by the Invention] In a conventional nuclear reactor having a plurality of internal pumps, assuming that a hypothetical total number of internal pumps trips, the cooling capacity of the core may transiently decrease. It was newly found that there is.

That is, the inertia combined with the internal pump 21 and the static inverter 19 in the reactor having the internal pump is the inertia combined with the recirculation pump in the reactor having the recirculation system piping and the MG set for controlling the rotation speed thereof. Very small compared to. For this reason, the reactor having the internal pump is excellent in responsiveness to a request for changing the reactor output and the like. However, should all of the internal pumps 21 trip due to a loss of the power source of the bus 18, etc., the rotational speed of the internal pumps sharply decreases and the core flow rate sharply decreases. Such a rapid decrease in the core flow rate leads to a sharp decrease in the core cooling capacity, which may lead to an unfavorable state from the viewpoint of fuel thermal margin.

It is an object of the present invention to provide a reactor protection method and apparatus that can reliably and quickly scram the reactor even when all internal pumps trip.

[Means for Solving Problems] The above problem is conditioned on the coolant flow rate decreasing by the second predetermined value or more within the set time when the reactor power is operating at the first predetermined value or more. It is solved by doing a scrum.

[Operation] The scrum determination device determines whether or not reactor scram is required due to a sudden reduction in core flow rate due to 100% trips of internal pumps, and outputs a scrum signal when required, and the reactor is based on this scrum signal. To be scrum.

[Example] A preferred example of the present invention applied to a boiling water reactor,
A description will be given based on FIGS. 1 and 2. In a boiling water reactor having an internal pump, an internal pump 21 is installed in a reactor pressure vessel 23 containing a core 22. The 10 internal pumps 21 are the reactor pressure vessels 23
And a core shroud 25 surrounding the core 22 are arranged so as to surround the core shroud 25. The ten motors 24 are arranged outside the reactor pressure vessel 23.
Is installed at the bottom of the. The rotating shaft of the internal pump 21 penetrates the lower wall of the reactor pressure vessel 23 and is connected to the motor 24. One motor for one internal pump 21
24 are connected. A control rod 16 for adjusting the reactor power is installed so as to be able to move in and out of the core 22. The control rod 16 is
It is connected to the control rod drive unit 15. The local power range monitor (hereinafter referred to as LPRM) 26 that detects the reactor power is the core
Many will be installed within 22. A flow meter 28 for measuring the core flow rate is provided. An average power range monitor (hereinafter referred to as APRM) 27 inputs the output signal of each LPRM 26 and obtains an average neutron flux signal corresponding to the average output of the reactor. A static inverter 19 is connected to a bus line 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 device control device 3, a scrum determination device 17, an LPRM 26, and a flow meter 28. Details of the scrum determination device 17 will be described with reference to FIG. The scrum determination device 17 includes a reactor power determination unit 4,
It has a core flow rate determination unit 11 and an AND circuit 28. 7
Is a signal holding unit and is a kind of delay circuit. The reactor output determination unit 4 is connected to the APRM 27 via the filter 2. The core flow rate determination unit 11 uses the flow meter 28 through the filter 10.
Connected to. One input end of the AND circuit 28 is connected to the reactor output determination unit 4 via the signal holding unit 7, and the other input end of the AND circuit 28 is connected to the core flow rate determination unit 11.
The output terminal of the AND circuit 28 is connected to the control rod drive device control device 3. The control rod driving device control device 3 is disclosed in JP-A-51-1.
It is composed of a scrum inlet valve, a scrum outlet valve, and a pilot solenoid valve for scrum shown in Japanese Patent No. 37091. The output signal of the AND circuit 28 becomes an open signal of the pilot solenoid valve for scrum.

The reactor protection device of this example was installed in the reactor based on the results of the following examination. The results will be described below based on the characteristics shown in FIG.

The event targeted by the reactor protection device of the present embodiment is a virtual event such that all internal pumps trip due to power loss of the static inverter 19 or trip of the static inverter, and the core flow rate suddenly decreases. This is a phenomenon in which the core cooling capacity may suddenly drop suddenly. Therefore, when considering the protection device, the following 3
It is necessary to consider the points.

(1) The higher the reactor output (hereinafter referred to as the initial reactor output) when all the internal pumps have tripped, the greater the adverse effect on the reactor due to the rapid decrease in the core flow rate. On the other hand, if the initial reactor power is low, the decrease in core cooling capacity does not pose a problem even if the core flow rate decreases sharply. According to the analysis, the lower limit of the initial reactor power that causes adverse effects is considered to be 70% power.

(2) The larger the rate of decrease in core flow rate and the more rapid it is, the greater the adverse effect becomes. However, there is no problem with fluctuations in core flow rate within the normal operating range above the internal pump minimum speed operating point, and all internal pumps trip. It is sufficient to protect against a hypothetical event in which the core flow rate drops sharply at 50% / sec or more and drops drastically.

(3) Care should be taken not to output an unnecessary scrum signal during normal operation or 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, the protective operation of the reactor is performed, that is, the reactor is scrammed.

(B) The region up to the lowest pump speed line is the region where operation is expected during normal operation, and the natural circulation state is reached when the total number of recirculation pumps trips. Therefore, it is reasonable to scram between the natural circulation line and the lowest pump speed line. That is, the core flow rate is "abnormally low" about 35
% Protects the reactor.

(C) When the rate of decrease in core flow rate is faster than about 50% / sec, the reactor protection operation is performed.

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

The average neutron flux signal output from APRM26 is input to the filter 2 having a delay element. The filter 2 removes noise of the average neutron flux signal and converts it into a reactor output.

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

The reactor output determination unit 4 compares the reactor output signal output from the filter 2 with 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 equal to or greater than the determination value is output. The signal 6 is held in the signal holding circuit 7 for a predetermined time (for example, about 2 seconds) and then output from the signal holding circuit 7 to the AND circuit 28. Even if the reactor output signal exceeds the reactor output judgment value 5 once, the reactor output remains the reactor output judgment value 5
When the signal output from the core output determination unit 11 becomes low after 2 seconds or more after the decrease, the decrease rate of the core flow rate is sufficiently slower than 50% / second, and This is not a problem for 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 unit 11. The core flow rate determination unit 11 compares the core flow rate signal with the core flow rate abnormality determination value (about 35% flow rate) 12, and when the former level becomes smaller than the latter level, the signal "core flow rate is low". Output 13 This “core flow rate low” signal 13 is input to the AND circuit 28.

The AND circuit 28 has a predetermined reactor output (decision value: 70%)
When the signal 6 of "reactor power judgment value or more" indicating that it is above and the signal 13 of "core flow rate low" indicating that the core flow rate is below a predetermined value (decision value 35%) are input, the core flow rate suddenly increases. The scrum signal 14 is output.

In this way, the scrum signal 14 is output.
The signal holding unit 7 holds that the average neutron flux signal (reactor average output) detected by the average output region monitor 27 is 70% or more for 2 seconds after it becomes 70% or less. When the core flow rate decreases, the average reactor power also decreases in proportion to the core flow rate. In the above description, the scram signal 14 is calculated by the decrease rate of the core flow rate (for example, 50% / second) that the average reactor power has decreased to 35% within the unit time (setting time) of 2 seconds.
Is occurring.

The rapid core flow rate scram signal 14 is input to the scrum pilot solenoid valve of the control rod drive system controller 3. The pilot solenoid valve for scrum operates by the input of the scrum signal 14 as shown in JP-A-51-137091 to open the scrum inlet valve and the scrum outlet valve. Therefore, high-pressure drive water is supplied from the accumulator to the control rod drive unit 15, and the control rod drive unit 15 drives the control rod drive unit 15.
16 is rapidly inserted into the core 22. Therefore, the reactor is scrammed.

In the currently considered system, if it is assumed that all internal pumps 21 are to be tripped, the amount of voids in the core 22 will rapidly increase due to a sudden decrease in core flow rate, and the reactor water level will rise and It leads to a turbine trip. When a turbine trip occurs, the reactor scrams and shuts down safely. However, the present embodiment can scram the reactor in a shorter time than such a reactor protection device.

In this embodiment, the APRM27 is used to obtain the reactor output signal.
Although the average neutron flux signal by is filtered, it can be realized by taking in the main steam flow rate, turbine inlet pressure, etc. and performing similar filtering.

Further, the determination value and the signal holding time shown in this embodiment are representative examples, and are set appropriately 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. However, when the core flow rate decreases, the reactor output also decreases. By providing the signal holding circuit 7, it is possible to accurately detect a sudden decrease in the core flow rate due to a trip of all internal pumps.

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

[Brief description of drawings]

FIG. 1 is a block diagram of a reactor protection device according to a preferred embodiment of the present invention, FIG. 2 is a detailed block diagram of the scrum determination device of FIG. 1, and FIG. 3 is a reactor protection of FIG. A reactor power-core flow rate curve diagram for explaining the logic of the apparatus, and FIG. 4 is a configuration diagram of a reactor having an internal pump. 2, 10 ... Filter, 4 ... Reactor output determination unit, 7 ...
Signal holding unit, 11 ... Core flow rate determination unit, 15 ... Control rod drive device, 16 ... Control rod, 17 ... Scrum determination device, 21 ...
Internal pump, 22 ... Core, 24 ... Motor, 28 ...
… And circuit.

Claims (2)

[Claims] 1. A nuclear reactor in which a coolant is supplied into a reactor core by a plurality of internal pumps provided in a lower portion of a reactor vessel, the reactor output and the coolant flow rate are detected to detect the reactor. An atom characterized in that scram of the nuclear reactor is performed when the coolant flow rate decreases by a second predetermined value or more within a set time when the output is operating at a first predetermined value or more. Furnace protection method. 2. A reactor vessel containing a core, a plurality of internal pumps provided below the reactor vessel for supplying a coolant into the core, and a control rod inserted into the core. A control rod driving device, an output detecting means for detecting a reactor output, a flow meter for detecting a flow rate of the coolant supplied to the core, and a reactor output detected by the output detecting means. From a scrum determination means for outputting a scrum signal when the coolant flow rate measured by the flowmeter is equal to or higher than a first predetermined value and drops below a second predetermined value within a set time, And a control rod control device for rapidly inserting the control rod based on the output scrum signal.