JPS62187294A - Nuclear reactor output reducer - 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 Field of Industrial Application] The present invention is a boiling water reactor that detects the occurrence of an accident in the event of a loss of recirculation flow of reactor coolant and reduces the reactor output. Regarding a furnace output reduction device.

[Conventional technology]

In general, boiling water reactors have a large negative output reactivity coefficient and are self-regulating against reactivity disturbances caused by control rod operations and the like. That is, when the reactor power increases due to reactivity disturbance, the voids in the reactor core increase, so thermal neutrons are no longer decelerated, and the increase in the reactor power is suppressed.

From having such characteristics right? ill! In a rising water reactor, the reactor output is controlled by controlling the flow of coolant flowing through the reactor core. An example of this operating characteristic is shown in FIG. 5, and it is clear from this figure that as the core flow rate of the coolant increases, the reactor power also increases.

By the way, reactor cooling 7. for forcibly recirculating cold JJI material into the reactor core. If the power to the recirculation pumps in the JL material recirculation system is lost for some reason, or all the recirculation pumps stop, and the reactor coolant flow rate rapidly decreases.
When an S fault occurs, voids occur in the reactor core, and as mentioned above, the nuclear reaction within the reactor core is suppressed due to the generation of voids, but this decrease in power reduces the heat flow on the surface of the fuel rod cladding tube. Due to the characteristics of heat transfer within the fuel rods, a time of about 5 to 6 seconds is required for this to decrease. For this reason, in the event of an accident in which the reactor coolant recirculation capacity is lost,
For a few seconds after the accident occurred, the reactor output decreased.11. yl
fi decreases only slightly, and the cold II capacity of the fuel decreases.

However, even if power is lost to the recirculation pump, the pump will stop according to its inertia, so in reactors equipped with large recirculation pumps, the reactor coolant flow rate will depend on the total flow rate of the fuel. It does not decline so rapidly that it becomes a problem. In addition, voids that occur within the reactor due to a sudden decrease in the reactor coolant flow rate cause the water level within the reactor to rise, causing a turbine trip that increases the reactor water level, and the reactor to shut down safely.

[Problem that the invention seeks to solve]

On the other hand, in a nuclear reactor equipped with many small recirculation pumps, the inertia of these recirculation pumps is small, so when the power to the recirculation pumps is lost, the reactor coolant flow m rapidly decreases, and the fuel rods cooling may be reduced and the health of the fuel may be compromised.

Figure 6 shows a simulation of the reactor output, the reactor water level of the coolant, and the cladding temperature when all recirculation pump power is lost in a nuclear reactor that has a large number of built-in recirculation pumps. This is the result.

According to Fig. 6, as the core inlet drift shown by curve A rapidly decreases, voids rapidly increase in the reactor core, and as a result, the neutron flux in the reactor core, shown by curve B, decreases rapidly. The reactor water level will rise.

However, the decrease in the heat flux on the surface of the J combustion chamber shown by curve C is gradual compared to the decrease in the core flow rate described above, so the decrease in the heat flux within the core! The state transitions from a nucleate boiling state with a relatively large heat transfer coefficient to a film boiling state with a small heat transfer coefficient, the fuel rod cladding surface temperature shown by curve E increases, and the reactor water level eventually reaches the turbine trip setting. When the reactor emergency shutdown system was activated, the neutron flux J3 and heat flux decreased faster, and the surface temperature of the fuel rod Xl tube also decreased.

Start. Although this increase in fuel rod cladding surface temperature is not large enough to damage the fuel rod, such a rise in fuel rod cladding temperature is not desirable in order to maintain the integrity of the fuel. . Furthermore, if a turbine trip does not occur due to the high reactor water level, the surface temperature of the fuel rod cladding tube will continue to rise above t, and there is a possibility that the fuel will be damaged.

The present invention was made in consideration of the points J and B, and all recirculation pumps in the reactor coolant recirculation system are stopped.
It is an object of the present invention to provide a reactor power reduction device that quickly reduces the power of the reactor and maintains the health of the fuel when the core flow rapidly decreases.

[Means for solving problems]

The present invention is a nuclear reactor power reduction device for avoiding a reduction in reactor power, which includes a function generator to which a reactor thermal output signal is input and outputs a neutron flux setting signal based on the reactor thermal output signal, and a function generator for outputting a neutron flux setting signal based on the reactor thermal output signal. A comparator that compares the neutron flux setting signal from the generator and the measured neutron flux signal and outputs a reactor power reduction request signal or reactor shutdown signal when the neutron flux signal is lower than the neutron flux setting signal by a certain value. It is characterized by having the following.

(Function) According to the present invention, the neutron flux signal is compared with the neutron flux setting signal by a comparator, and if the neutron flux signal is lower than the neutron flux setting signal by a certain value, a reactor power reduction request signal or reactor shutdown is issued. Since it outputs a signal, it is possible to keep the humidity rise in the surface temperature of the fuel rod cladding to a low level and ensure the integrity of the fuel.Also, the reactor output is kept below the cooling capacity of the coolant, further improving the safety of the reactor. You can do it.

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings and examples.

FIG. 1 shows a first embodiment of the reactor power reduction device according to the present invention, in which a neutron flux signal 1 measured by a system (not shown) is input to a filter 2 to filter only a specific frequency range. The neutron flux signal f31' is input to the comparator 33. On the other hand, by passing the neutron flux signal 1 through an appropriate 1.1-minute torrent circuit, it is possible to simulate the heat flux, or to simulate the reactor heat flux derived from equivalent reactor steam flow, reactor pressure, etc. The output signal 4 is input to a function generator 5, which outputs a neutron flux setting signal 6 to a comparator 3. The neutron flux signal 1'J3 and the neutron flux setting signal 6 described above are compared in the comparator 3, and if the neutron flux signal 1' is lower than the neutron flux setting signal 6, the reactor output reduction request signal 7 is output from the comparator 3. It is designed to be output to the control rod drive system or reactor emergency shutdown system.

The neutron flux setting signal 6 output from the function generator 5 to the comparator 3 is a function of the reactor heat output signal 4, as shown by curve F in FIG. In addition to taking into consideration the integrity of the salmon, the system is designed to ensure that it does not interfere with the operation of the nuclear reactor.

According to the above-described configuration, the neutron flux signal 1', which is a part of the neutron flux signal 1 measured by the cutting system, and the reactor heat output signal 4 are input to the function generator 5, and the neutron flux generated by The comparator 3 compares the neutron flux signal q6 with the neutron flux setting signal q6, and if the neutron flux signal 1' exceeds the neutron flux setting signal 6, no signal is output from the comparator 3, but the neutron flux signal 1' If the flux is below the bundle setting signal 6, the comparator 3 outputs a reactor output reduction request signal 7' to the control rod drive system or the reactor emergency shutdown system. When the reactor power reduction request signal 7 is manually input to the control rod drive system, the control rod drive system inserts the control rods into the reactor to reduce the reactor power, and also activates the reactor emergency shutdown system. When the reactor power reduction request signal 7 is input, the reactor is shut down.

Figures 3(a) and 3(b) show the reactor output J3 when all recirculation pump power supplies are lost in J3 in this embodiment.
The reactor heat output signal 4 is a pseudo heat flux signal obtained by inputting the neutron flux signal 1 to a time delay circuit (not shown) with a time constant of 6 seconds. When this pseudo heat flux signal is above the rated value and the neutron flux is below 50%, the reactor is shut down by the reactor emergency shutdown system.

Figures 3(a) and 3(b) show the simulation results of the conventional method described above.Compared with Figure 6, curves B and C'C-show 1-inside the core. Since the neutron flux and the heat flux on the fuel rod surface rapidly decrease, curve E
The rise in the surface temperature of the J-fuel cladding tube is slower than in the conventional case, and the healthy fi of the fuel can be maintained.

Thus, according to this embodiment, when the neutron flux signal 1' falls below the neutron east setting signal 06, the reactor power reduction request signal 7
is output from the comparator 3 and input to the control rod drive system or reactor emergency shutdown system, and the reactor output is reduced or the reactor is shut down, so the integrity of the fuel can be ensured.

Furthermore, it becomes possible to reduce the reactor output below the cooling capacity of the cold 'fJI material flow suspension, thereby improving the safety of the reactor.

Note that by setting an appropriate function in the function generator 5, the reactor can be stopped more quickly. In addition, if the reactor output is not controlled by control rods, the reactor output can be controlled by the reactor coolant recirculation system or the core flow m of the straw coolant, as explained in Figure 5. Therefore, it is also possible to use control signals such as the main controller output signal of the reactor coolant recirculation system, the rotation speed of the recirculation pump, or the pump rotation speed request signal as the reactor heat output signal 4.

FIG. 4 shows a second embodiment of the present invention. In this embodiment, the neutron flux signal 1' is not simply lower than the neutron flux setting signal 6, but is lower by a certain value by 1. There is a real IMplI'C that can be applied when it is only necessary to reduce the reactor power for the first time.

In this embodiment, a neutron flux signal 1 measured by an instrumentation system (not shown) is manually inputted to a filter 2 to become a neutron flux signal 1' only in a specific frequency range, and this neutron flux signal 1' is now manually input to the deviation circuit 8.

On the other hand, a reactor heat output signal 4b formed by one of various corresponding signals is input to a deviation circuit 8. This deviation circuit 8 is a neutron flux signal 1'11
3 and the reactor heat output signal 4 are calculated, and the deviation value signal 9 is outputted to the comparator 3. and,
This comparator 3 receives a set value 10 and outputs a reactor power reduction request No. 13 7 when the deviation value signal 9 exceeds the set value 10. Similar to the first embodiment described above, this reactor power reduction request signal 7 is input to the control rod operation system or the reactor emergency shutdown system, and is used to reduce the reactor power or shut down the reactor. There is.

〔Effect of the invention〕

As explained above, according to the present invention, even if the reactor cools down
Even if an accident occurs in which power is lost to all of the material recirculation pumps, the temperature rise in the surface temperature of the fuel rod cladding tubes can be suppressed to a low level and the integrity of the fuel can be ensured.

Moreover, the safety of the nuclear reactor can be further improved by reducing the reactor output to less than the cooling capacity of the coolant.

[Brief explanation of drawings]

Figure S1 is a block diagram showing an embodiment of the reactor power reduction device according to the present invention, Figure 2 is a graph showing the relationship between the reactor thermal output signal and the neutron flux setting signal, and Figures 3(a) and 3 FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. FIG. 6 is a graph showing the relationship between the IIPA core flow rate and the Bat sub-furnace output power, and FIG. 6 is a graph showing simulation results for a conventional device. 1.1'...neutron flux signal, 2...filter, 3.
... Comparator, 4... Reactor heat output signal, 5... Function generator, [5... Neutron flux setting signal, 7... Reactor output reduction request signal, 8... Deviation circuit , 9... Deviation value signal, 10... Setting value. Applicant's agent Mr. Sato Figure 2 Time (collar) (b) Figure 3 Leap Figure 4 Cold open furnace/J Biyoku Figure 5 Figure 6

Claims (1)

[Claims] 1. A function generator to which a reactor heat output signal is input and outputs a neutron flux setting signal based on the reactor heat output signal;
The neutron flux setting signal from this function generator and the measured neutron flux signal are compared, and when the neutron flux signal falls below the neutron flux setting signal by a certain value, a reactor power reduction request signal or a reactor shutdown signal is output. A nuclear reactor power reduction device comprising a comparator for reducing the output of a nuclear reactor. 2. The reactor power reduction device according to claim 1, wherein the neutron flux signal is input to the comparator via a filter. 3. The reactor power reduction device according to claim 1 or 2, wherein a signal from a deviation circuit is input to the comparator. 4. The reactor power reduction device according to any one of claims 1 to 3, wherein the reactor thermal output signal is formed by passing the neutron flux signal through a time delay circuit. . 5. The reactor power reduction device according to any one of claims 1 to 3, wherein the reactor thermal output signal is formed by a reactor steam flow rate. 6. The reactor power reduction device according to any one of claims 1 to 3, wherein the reactor heat output signal is formed based on reactor pressure. 7. The reactor power output according to any one of claims 1 to 3, wherein the reactor heat output signal is formed by a main controller output signal of a reactor coolant recirculation system. Lowering device. 8. The nuclear reactor according to any one of claims 1 to 3, wherein the reactor heat output signal is formed by the rotation speed or rotation speed request signal of a reactor coolant recirculation pump. Furnace power reduction device.