JPS623920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to water level control in a nuclear reactor during transient events, and more particularly, to the control of water level in a nuclear reactor during transient events, and in particular to the temporary control of pressure regulator set points during generator load shedding, with a suitable delay time. The present invention relates to a reactor pressure control device for stably controlling the reactor water level by making changes to avoid high water level scrams.

Next, transient changes at the time of generator load cut-off when using the conventional control device will be explained.

Plants (hereinafter referred to as
Compared to partial-capacity bypass plants, full-capacity bypass plants (called full-capacity bypass plants) do not require the reactor to be scrammed because all main steam can be processed by bypass even if full-load shedding is the main operation. is a major feature.

By the way, when a load cutoff of the generator occurs due to lightning damage or the like in the external power system, the turbine generator acceleration protection device is activated to quickly close the turbine control valve. In a plant equipped with a total main steam relief device, the device operates at the same time as the control valve closes, processing all the main steam, running the recirculation system or tripping the recirculation pump, reducing the core flow rate, and performing selective control. By inserting rods, the reactor power can be increased by approximately 30
Reduce to -50% rating. The behavior of the reactor water level during this transient phenomenon process is that it temporarily decreases due to the pressure increase due to the closure of the turbine control valve immediately after load shedding, but by inserting selective control rods and reducing the core flow rate, the reactor output As the reactor pressure decreases, the reactor pressure also decreases and the water level rises, but after reaching its peak value, it decreases, and as the reactor pressure is stabilized by the control of all main steam relief devices, the reactor water level increases. In order to stabilize the reactor, the reactor can transition to isolated operation without scramming. However, in the water level change during load shedding mentioned above, when reactor pressure is controlled by conventional control equipment, the reactor pressure starts to drop quickly as the reactor power decreases, and as a result, the reactor water level rises significantly. In some cases, the high water level could reach the turbine trip level and cause the reactor to scram.

Originally, a major feature of the above-mentioned full-capacity bypass plant was that it could avoid a scram even if the entire load was cut off, but if the reactor were to scram due to the above reasons, the external power system would be restored. After that, it takes a lot of time and effort to restart the plant, which completely negates the benefit of providing a full-capacity bypass.

The purpose of the present invention is to eliminate the drawbacks of the conventional control devices described above, and to provide a reactor pressure control device that suppresses the peak of the reactor water level at the time of generator load interruption and stably controls the water level. The aim is to avoid unnecessary scrams in the plant. According to the device of the present invention, the reactor water level is stably controlled by controlling the reactor pressure at the time of load shedding using the pressure set point changing circuit that is activated by detecting a signal indicating the occurrence of load shedding.

The present invention is applicable regardless of whether a turbine bypass valve or a safety relief valve is used as the total main steam relief device. Here, a plant having a turbine bypass valve will be explained as an example.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram when the pressure control device of the present invention is applied to a BWR plant. What is entirely surrounded by a broken line 21 in FIG. 1 is a pressure set point changing circuit which is a feature of the present invention. In FIG. 1, a nuclear reactor 1 generates main steam, and the main steam flows through a main steam pipe 2, passes through a turbine control valve 4, is sent to a main turbine 5, and then becomes condensate. In addition, the main steam that cannot be processed by the turbine control valve 4 passes through the turbine bypass piping 8 to the turbine bypass valve 3.
The water is sent directly to a condenser (not shown) and becomes condensate. This condensate is supplied to the reactor 1 again through the water supply pipe 7 via the water supply pump 6. Also,
When the main steam cannot be processed by the control valve 4 and the bypass valve 3, it is sent to a sub-reduction chamber (not shown) through a relief safety valve 17. The reactor pressure is determined by a control valve 4 installed in the middle of the main steam pipe 2.
Pressure sensor 9 installed on the upstream side (reactor side) of
and is input to the pressure regulator 10 as a reactor pressure signal 18. This pressure regulator 10
inputs two signals, the pressure signal 18 and the pressure setting signal 11, and outputs a turbine control valve opening request signal 15 and a turbine bypass valve opening request signal 16.
The reactor pressure is controlled by controlling the opening degrees of the regulating valve 15 and the bypass valve 16 using the output. On the other hand, the signal output from the function generator 13 passes through the pressure setting regulator 14 and is input to the signal adder 20. This adder 20 adds the signal from the function generator 13 and the signal from the pressure setting device 12, which outputs the pressure setting point during normal operation of the reactor, to set the pressure to the pressure regulator 10. A point signal 11 is output. The function generator 13 starts operating in response to a signal 22 from a power load unbalance relay (not shown) which operates when the load is interrupted, and outputs a predetermined function.

The pressure set point regulator 14 also includes a numerical value generator 1.
It controls the signal output from 3, and has gain adjustment and limiter functions. Note that the signal 22 may be input to the regulator 14 to prevent the function generator 13 from malfunctioning.

Next, the operation of the present invention will be explained.

When a generator load cutoff occurs during high-output operation, the main steam control valve 14 is suddenly closed, causing the reactor pressure to rise and the neutron flux to rise as well. However, due to the effect of the recirculation pump trip and the selective control rod insertion, the reactor power decreases, so the reactor pressure decreases and the reactor water level begins to rise. As a result, if the water level in the reactor rises too much, a turbine trip or reactor shutdown may occur. Therefore, the present invention is comprised of a program function generator 13 and a reactor pressure set point regulator 14 for creating a program for changing the set point predicted in advance, as shown in FIG. A reactor pressure set point change circuit 21 is provided at load cutoff, and is linked to a power load unbalance relay that operates when a mismatch between the turbine steam flow rate and the generator load occurs, and a signal 2 that operates when the load unbalance relay operates.
2 starts the function generator 13, and the signal from this circuit is added to the output signal of the pressure setting device 12 to control the reactor pressure. An example of this program is shown in FIG. According to this program, after the load unbalance relay is activated due to load shedding, the pressure set point is ramped up to keep the rise in water level low after a predictable period of time, and then ramped down again. After returning to the original set point, the conventional pressure set point signal returns. The reason why the pressure set point is increased in a ramp-like manner is that when the set point is increased in a step-like manner, the bypass valve 3, which had been open until now, suddenly closes. This neutron flux peak may cause a high neutron flux scram, so the lamp shape is designed to prevent this. As a result, the reactor water level peak is kept low, increasing the margin for high water scram levels. FIG. 3 shows the water level behavior when the generator load is cut off when the present invention is implemented. The dotted line shows the water level change when using the conventional control method. In Fig. 3 _{, L1} indicates the high water turbine trip level.
Furthermore, Figure 4 shows how the reactor pressure changes when the generator load is cut off. The dotted line shows the pressure change when the conventional control method is used, and the solid line shows an example of the pressure change when the present invention is implemented. As can be seen from Figures 3 and 4, when the present invention is implemented, the reactor pressure after a load shedding occurs starts to decrease more slowly than before, and due to this effect, the rise in the reactor water level is also suppressed to a much lower level than before. It can be seen that the situation of turbine trip scram due to this can be completely avoided. Thus, the reactor pressure control device of the present invention stably controls the water level during generator load cutoff, and is particularly suitable for plants with a reactor full main steam relief device (full capacity bypass, etc.). Even if a generator load shedding occurs, the reactor can be shifted to isolated operation without causing a scram.

Therefore, when the external power system is restored, the output can be increased immediately compared to the isolated operation within the station and the power system can be connected to the external power system, thereby increasing the reliability of the entire system, which has a great effect.
Furthermore, if the device of the present invention is not used, the pressure setting point may be changed manually, but unnecessary scrams due to operator errors can be prevented, so the effect of the device of the present invention is Very large.

[Brief explanation of the drawing]

Figure 1 shows the reactor pressure control system of the present invention in a BWR.
1 shows a block diagram showing an embodiment of the present invention when applied to a plant 1, and an embodiment of the present invention. FIG. 2 is a fold line diagram showing an example of a pressure adjustment program in a pressure set point adjustment device according to the present invention, and FIGS. 3 and 4 are
It is a diagram showing transient changes in the reactor water level and reactor dome pressure during generator load shedding, where the solid line shows the transient changes when the present invention is implemented, and the broken line shows the transient changes when using the conventional control device. 1... Nuclear reactor, 2... Main steam piping, 3... Turbine control valve, 4... Turbine bypass valve, 5...
Main turbine, 6... Water supply pump, 7... Water supply piping, 8... Bypass piping, 9... Pressure sensor,
10...Pressure regulator, 11...Pressure setting signal, 1
2...Pressure setting device, 13...Pressure set point adjustment function generator, 14...Pressure set point regulator, 15...
Turbine adjustment valve opening request signal, 16... Turbine bypass valve opening request signal, 17... Relief safety valve,
18... Turbine inlet pressure signal, 20... Signal adder, 21... Pressure set point change circuit.

Claims (1)

[Scope of Claims] 1. In a nuclear power plant having a total main steam relief device, a measuring device for detecting reactor pressure, a pressure setting device for outputting a reactor pressure set point, and a measuring device for detecting the reactor pressure, a pressure setting device for outputting the reactor pressure set point, and In addition to the reactor pressure control system, which is composed of a pressure regulator that receives the pressure setting signal as input and outputs a turbine control valve opening request signal and a turbine bypass valve opening request signal, the reactor pressure control system A nuclear reactor pressure control device characterized by being provided with a pressure setting change circuit that temporarily changes a reactor pressure set point. 2. The pressure set point changing circuit includes a function generator that generates a predetermined function, a pressure set point regulator,
2. The reactor pressure control system according to claim 1, further comprising an adder for adding and outputting signals from a pressure setting device and a pressure set point regulator.