JPS636837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recirculation flow control system for a nuclear reactor,
In particular, the present invention relates to a device that maintains the integrity of the fuel by holding the recirculation flow rate when the neutron flux changes to exceed a predetermined allowable upper limit value.

In conventional nuclear power plants, when plant load demands increase, it is considered that there is no problem if the neutron flux is below the high neutron flux scram level (approximately 120% rating), but recent experiments have shown that the neutron flux is lower than the rated value. It has been found that if the value is exceeded, the possibility of fuel damage increases, and so-called
PCIOML operation is required, but no fundamental countermeasures have been taken in the control system to deal with this.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above, control the main controller output when the recirculation flow rate changes, suppress the neutron flux below a certain value, maintain the health of the fuel, and enable high neutron flux scram. It is an object of the present invention to provide a control device that can reduce the noise.

The main part of the present invention is to detect the neutron flux of the nuclear reactor with a neutron flux detector, set the allowable upper limit value of the neutron flux for the reactor core conditions such as reactor output, core flow rate, control rod pattern, etc. exceeds the allowable upper limit, the main controller output of the recirculation flow rate control system is held to prevent an increase in neutron flux.

This device can be applied to any of the following methods: recirculation flow control using a variable frequency MG set, flow control using valve opening, or flow control using an internal pump inserted within the reactor core. An embodiment of the present invention will be described below with reference to the drawings, taking the MG set system as an example. FIG. 1 shows a recirculation flow rate control system, and the area surrounded by a dashed line is an example of the use of the present invention. Reference numeral 15 denotes a neutron flux upper limit setting device for manually setting a neutron flux upper limit value determined in accordance with reactor core conditions such as reactor output, core flow rate, and control rod pattern. This signal and the signal from the neutron flux detector 16 are input to the adder 17, and the hold circuit 12, which can hold the output of the main controller 13 depending on the positive/negative of the output, is operated by the signal 103, and the main controller 1
The output of the adder 17 is inputted to a logic circuit 14 which tracks the output of the adder 3 to the same value as the hold value using a signal 104.

Note that 101 is a control signal from the pressure control system, and 10
2 is an input signal to the adder 10. signal 102
is branched off and used for flow control of other same systems.

The output signal 102 of the hold circuit 12 and the feedback signal of the rotational speed of the alternator 6 obtained from the tachometer 9 are input to an adder 10. The deviation signal is input to the speed controller 11, and the output converted by the speed controller 11 is input to the flow joint 7. As a result, the drive induction motor 8, which is operated at a constant speed, Via the fluid coupling 7 the alternator 6 is speed controlled.

By controlling the speed of the alternator 6, the generator output frequency can be controlled and, as a result, the speed of the pump motor 5 can be controlled.

A pump 4 is mechanically connected to the pump motor 5 and controls the recirculation flow rate. The flow rate of the jet pump pumped out from the jet pump 2 in the pressure vessel 3 is controlled by this recirculation flow rate. As a result, the core flow rate flowing through the reactor core 1 is controlled, and the output can be controlled by changing the void reactivity.

FIG. 2 shows an embodiment in which the core flow rate is detected instead of the neutron flux signal and the hold circuit 12 is operated using this signal. In the figure, 22 is a core flow rate detector, 21 is a core flow rate upper limit setter, and an adder 18
and outputs the difference signal to the logic circuit 14. As another embodiment of the hold circuit 12, as shown in FIG.
1 can also be connected in series to the output side of the main controller 13. Note that the output gain converter 31 and the main controller 13 receive signals 105 and 10 from the logic circuit 14.
It is connected to receive 6. Further, as shown in FIG. 4, a tracking circuit 41 and a hold circuit 12 may be connected in series to the output side of the main controller 13. In this case as well, the main controller 13 tracking circuit 41 and hold circuit 12 each have a logic circuit 1.
4 to receive signals 107, 108, and 109. In FIGS. 2 to 4, 102 is connected to the adder 10, and 101 is connected to the pressure control system.

Note that the present invention can also be implemented using other signals corresponding to reactor power (for example, pseudo heat flux, main steam flow rate, etc.) instead of neutron flux or core flow rate.

Next, the operation of the present invention will be explained. When the plant load demand increases while the reactor is operating near its rated power, the reactor recirculation control system operates, causing the core flow rate to increase and the neutron flux to temporarily significantly exceed the rated value. do. The neutron flux upper limit setter 15 is
Since the output of the adder 17 is set to almost the rated value, the output of the adder 17 becomes positive and it is necessary to hold the recirculation control system.
2 is operated and the output of the main controller 13 is tracked to the hold value. This tracking functions to maintain the output signal of the main controller 13 at the value at the time of operation of the hold circuit so that the main controller 13 can be smoothly switched when the hold circuit 12 is released.

In addition, as another embodiment of the present control device, as shown in FIG. 2, a core flow rate detector 2 is installed, similar to the neutron flux detector 16 and neutron flux upper limit setting device 15 in FIG.
2. By providing a core flow rate upper limit set value 21, it is possible to suppress neutron flux overshoot and exceeding the rated value not only by the neutron flux signal but also by the core flow rate signal.

As another embodiment of the hold circuit 12, an output gain converter 31 as shown in FIG.
3 and is operated by a signal from the logic circuit 14. In this case, the output gain converter 31
has a function of reducing the rate of change in the output of the main controller 13, so this output can reduce the rate of change in the flow rate of the reactor recirculation system. Therefore, operations such as changing the flow rate of the reactor recirculation system can be made smoother than when using the hold circuit 12.

As another embodiment of the circuit configuration including the main controller 13 and the hold circuit 12, as shown in FIG. Hold circuit 12
Even when the main controller 13 is released, the main controller 13
control becomes possible.

Since the reactor recirculation flow rate control device of the present invention is configured as explained above, in the conventional technology, when the reactor takes load countermeasures, the neutron flux reaches the allowable upper limit value (100% rating when near the rated output). However, this device holds the recirculation flow rate and suppresses the increase in neutron flux, which is effective both in terms of fuel protection and in avoiding high neutron flux scrams. An example of this is shown in Fig. 5. In the conventional technology, the neutron flux response to the step load request signal A (dotted chain line) was as shown by curve C (dashed line), and a large neutron flux overshoot occurred. When this device is used, it exhibits a response as shown in curve B (solid line), and this overshoot can be effectively suppressed and the high neutron flux scram can be kept below the set level D, resulting in good stability even during high-output operation. I can drive.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the reactor recirculation flow rate control device of the present invention, and FIGS. 2 to 4 are
A block diagram showing another embodiment of the reactor recirculation flow rate control device of the present invention, FIG. 5 is a graph showing the effects of the present invention, where the horizontal axis is time and the vertical axis is a graph showing changes in neutron flux or load requirements. It is. 12... Hold circuit, 13... Main controller, 14...
Logic circuit, 15... Neutron flux upper limit setter, 16... Neutron flux detector, 10, 17, 18... Adder, 21
...core flow rate upper limit setter, 22...core flow rate detector,
31...Output gain converter, 41...Tracking circuit.

Claims (1)

[Scope of Claims] 1. In a recirculation flow rate control system that controls the output of the reactor by adjusting the core flow rate circulating within the reactor core, an allowable upper limit of neutron flux is set in accordance with the output within the reactor core. a first means of setting a value;
a neutron flux detector for detecting the neutron flux of the nuclear reactor corresponding to the output of the first means; a comparator for comparing the output of the neutron flux detector with the output of the first means; When it is determined that the detected value exceeds the allowable upper limit value, one of the second means and the third means is activated, and the second means is configured to control the reactor recirculation system driving flow rate. 1. A nuclear reactor recirculation flow rate control device comprising means for holding a flow rate of the reactor recirculation system, and said third means comprising means for reducing a rate of change in flow rate of said reactor recirculation system. 2. The second means is comprised of a hold circuit that holds the output of the recirculation system controller, and a tracking circuit that causes the output of the controller to match the output of the hold circuit. A nuclear reactor recirculation flow control device according to scope 1. 3. In the recirculation flow rate control system that controls the output of the reactor by adjusting the core flow rate circulating in the reactor core, a fourth part sets an allowable upper limit value of the core flow rate in accordance with the output in the reactor core. means and this fourth
a core flow rate detector for detecting a core flow rate of the reactor corresponding to the output of the fourth means; a comparator for comparing the output of the core flow rate detector with the output of the fourth means; When it is determined that the detected value exceeds the allowable upper limit, one of the fifth means and the sixth means is activated, and the fifth means is configured to control the reactor recirculation system driving flow rate. 2. A nuclear reactor recirculation flow rate control device, characterized in that said sixth means comprises means for reducing a flow rate change rate of said reactor recirculation system. 4. The fifth means is comprised of a hold circuit that holds the output of the recirculation system controller, and a tracking circuit that causes the output of the controller to match the output of the hold circuit. A nuclear reactor recirculation flow control device according to scope 3.