JPH0528800B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a new type of boiling water reactor (hereinafter referred to as A-BWR).
The present invention relates to a nuclear reactor protection device that has the function of protecting a nuclear reactor even when, for example, a coolant circulation pump that forcibly circulates coolant into the reactor core stops and the reactor core flow rate suddenly decreases.

[Prior Art] A conventional example will be explained with reference to FIG. FIG. 3 is a sectional view showing a schematic configuration of the A-BWR, and reference numeral 1 in the figure is a reactor pressure vessel. A coolant 2 and a reactor core 3 are housed within the reactor pressure vessel 1 . This core 3 includes a plurality of fuel assemblies (not shown) and control rods 4 (only one is shown in the figure).
It is composed of etc. The coolant 2 flows upward through the reactor core 3, and its temperature increases due to the heat of nuclear reaction in the reactor core 3. The heated coolant 2 enters a two-phase flow state of water and steam. The coolant 2 in this two-phase flow state is introduced into a steam-water separator 5 installed above the reactor core 3 and is separated from steam and water. The separated internal steam is introduced into a steam dryer 6 installed above the steam separator 5 and dried to become dry steam. This dry steam is transferred to the main steam pipe 12 connected to the reactor pressure vessel 1.
The fuel is transferred to a turbine system (not shown) via the system and used for power generation. On the other hand, the separated internal water flows down the downcomer section 8 between the reactor pressure vessel 1 and the shroud 7, joins with the supply water flowing in through the water supply piping 13 and the water supply spurgeer 9, and flows into the recirculation pump (hereinafter referred to as "interchanger"). (referred to as a null pump) 11.
It is pressurized by this internal pump 11 and supplied to the lower part of the reactor core 3 again. A plurality of internal pumps 11 are installed in the circumferential direction, and each is driven by a motor.

A safety protection device 21 is installed in the A-BWR having such a configuration. For example, reactor pressure vessel 1
When an abnormality occurs such as an increase in internal pressure or a decrease in the water level, the occurrence of the abnormal situation is detected and an abnormality occurrence signal S22 is output to the safety protection device 21. Thus, the safety protection device 21 outputs a control signal S24 to the control rod drive mechanism 23, and
is urgently inserted into the reactor core 3, and the reactor output is rapidly reduced. This is the so-called scrum operation.

[Problems with the background art] In the above configuration, the internal pump 11 is
When two recirculation pumps are installed outside the reactor pressure vessel 1 (BWR type), they are smaller than the recirculation pumps, and if the pump power is lost, the inertia of the small failed pump is small. It is expected that the flow rate will drop rapidly and the core flow rate will decrease rapidly. In such a case, there is a possibility that the heat generated within the reactor core 3 will not be removed sufficiently. This also applies when the internal pump 11 is further downsized as the plant becomes smaller. Therefore, in order to prevent this kind of situation from occurring in the past, the motor power supply for the internal pump 11 is made sufficiently reliable, and the power supply system is divided into multiple parts, so that the motor power supply for all internal pumps 11 is This ensures that power is not lost at the same time.

However, in order to further improve safety, it is necessary to maintain the integrity of the reactor core 3 even in the event that the motor power of all internal pumps 11 is lost, and this is required. It had been.

[Objective of the Invention] The present invention has been made based on the above points, and its purpose is to prevent the core flow rate from suddenly decreasing in the event that the motor power of all internal pumps is lost. Even if a situation occurs,
It is an object of the present invention to provide a nuclear reactor protection device that can maintain the integrity of fuel and, in turn, the integrity of the reactor core.

[Summary of the Invention] That is, a nuclear reactor protection device according to the present invention is a nuclear reactor protection device for a nuclear reactor in which a coolant recirculation pump is disposed in a reactor pressure vessel. a filter means for removing minute fluctuations and signal noise during normal reactor operation from a coolant flow rate signal; and a reduction rate calculation means for calculating a flow rate reduction rate from the flow rate signal from which minute fluctuations and noise have been removed by the filter means. and comparison means for comparing the flow rate reduction rate calculated by the reduction rate calculation means with a set value and outputting a scram signal for emergency shutdown of the reactor when the flow rate change rate exceeds the set value. It is characterized by the fact that

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Note that the same parts as in the prior art will be described with the same reference numerals. FIG. 1 is a diagram showing the configuration of a nuclear reactor protection device 121 according to this embodiment, and reference numeral 131 in the figure is a filter circuit. A core flow rate signal S132 is input to this filter circuit 131. The filter circuit 131 removes minute fluctuations and signal noise during normal operation from the core flow rate signal S132. Generally, the period of minute fluctuations and signal noise during normal operation is relatively short, for example, about 0.1 to 0.5 seconds, and therefore, the present embodiment also uses a filter circuit 131 having a time constant of that order. The flow rate signal S132 from which minute fluctuations during normal operation and signal noise have been removed by the filter circuit 131 is input to the differentiation circuit 133. This differentiation circuit 133 calculates the rate of decrease in flow rate. The core flow rate signal S134 is then input to a comparison circuit 135. On the other hand, this comparison circuit 135 receives a preset core flow rate reduction rate setting signal S13.
6 is input. At this time, the rate of decrease in the core flow rate at which the integrity of the fuel is a problem is 30%/sec or more, and therefore, this value is used as the core flow rate setting signal S136. When the core flow rate reduction rate signal S134 of the comparison circuit 135 exceeds the core flow rate decrease rate setting signal S136, it outputs a scram signal S138 to the scram system 137.
As a result, the scram system 137 is activated, the control rods 4 are urgently inserted into the reactor core 3, and the core power is rapidly reduced.

As described above, according to this embodiment, even if, for example, a situation occurs in which the motor power of all internal pumps 11 is lost and the core flow rate suddenly decreases, this is detected and the reactor is scrammed to reduce the core output. Since it can be rapidly reduced, it is possible to reliably maintain the health of not only the fuel and the reactor core, but also the health of the entire reactor, making it possible to significantly improve stability. This will be shown in comparison with the conventional method. FIG. 2 is a diagram showing time changes in the cladding temperature with time on the horizontal axis and fuel rod cladding temperature on the vertical axis, where the broken line represents the conventional case and the solid line represents the present example. Indicate the case. As is clear from FIG. 2, in the case of this example, the temperature rise in the cladding tube of the fuel rod is effectively suppressed.

Note that the present invention is not limited to the above-mentioned embodiments, and various embodiments are possible. For example, in the embodiment described above, a differential circuit is used to calculate the rate of decrease in core flow rate, but the present invention is not limited to this, and any other circuit may be used as long as it can detect the rate of decrease in core flow rate. Furthermore, in the above embodiment, the problem was the rate of decrease in the core flow rate, but if the core flow rate signal and the core output signal are extracted and the difference between the two is calculated, and the difference exceeds a set value (the core flow rate is A configuration may also be used in which the scram signal is output when the signal is too small. In addition to this, a configuration may be adopted in which a core flow rate signal is extracted, a percentage of the rated value is calculated, and a scram signal is output when the value is less than a set value.

[Effects of the Invention] As detailed above, according to the nuclear reactor protection device according to the present invention, even if the internal pump motor power is lost and the coolant flow rate in the reactor core suddenly decreases, the reactor can be stopped in an emergency. The integrity of the fuel rods loaded in the reactor core can be ensured.

Furthermore, the present invention calculates the rate of decrease in the flow rate of the coolant flowing in the core of a nuclear reactor, and outputs a scram signal when this rate of decrease in flow rate exceeds a preset value. Compared to systems that output a scram signal when the flow rate of coolant flowing through the reactor core falls below a predetermined flow rate, the reactor can be brought to an emergency shutdown more quickly.

Furthermore, the reactor protection device of the present invention is equipped with a filter means that removes minute fluctuations and signal noise during normal operation, so scram judgment can be made quickly based only on the flow rate reduction rate without issuing unnecessary scram signals. Moreover, the reactor can be brought to an emergency shutdown with certainty.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing one embodiment of the present invention, and FIG. 1 is a diagram showing the configuration of a nuclear reactor protection device.
FIG. 2 is a diagram showing the temporal change in temperature of the fuel rod cladding tube in comparison with a conventional one, and FIG. 3 is a diagram showing the configuration of a conventional boiling water reactor. 1... Reactor pressure vessel, 2... Coolant, 3...
Reactor core, 4...control rod, 121 ...reactor protection device.

Claims (1)

[Claims] 1. In a reactor protection system for a nuclear reactor that includes a coolant recirculation pump installed in the reactor pressure vessel, minute fluctuations during normal reactor operation are detected from the flow rate signal of the coolant flowing in the reactor core. and a filter means for removing signal noise, a reduction rate calculation means for calculating a flow rate reduction rate from the flow rate signal from which minute fluctuations and noise have been removed by the filter means, and a flow rate reduction rate calculated by the reduction rate calculation means. 1. A nuclear reactor protection device, comprising comparing means for comparing with a set value and outputting a scram signal for emergency shutdown of the reactor when the flow rate change rate exceeds the set value.