JPS6017078B2 - Reactor coolant recirculation flow control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coolant reshielding circulation flow rate control device for a boiling water nuclear reactor.

FIG. 1 shows a schematic configuration of a conventional coolant recirculation flow rate control device for a boiling water reactor.

In this figure, the nuclear reactor 1 is cooled by the coolant flowing back through the recirculation system piping 2A, 28. The recirculation speed of the coolant is regulated by recirculation pumps 4A, 4B driven by electric motors 3A, 381. The above electric motor 3A, 3
The rotation speed of B is variably controlled by changing the combined power supply frequency of variable frequency power supplies 5A and 5B. The variable frequency power supplies 5A and 5B are controllers 7A and 7B that operate based on frequency request signals RA and RB output from the main controller 6.
controlled by The main controller 6 operates based on a deviation signal SD from a deviation device 8 which obtains the deviation between the load setting signal SL and the main steam flow rate signal SF. In the conventional device with the above configuration, the variable frequency power supplies 5A and 5B are configured to control the degree of coupling between the fluid handles, so it is difficult to stabilize the degree of coupling for all frequency request signals.
It exhibits nonlinear characteristics in a certain frequency range and may induce periodic oscillations in the core coolant flow rate.

Examples of the above-mentioned nonlinear characteristic patterns include a step-like pattern shown in FIG. 2a and a hysteresis-like pattern shown in FIG. 2b. Figures 2a and 2b are frequency characteristic curve diagrams in which the horizontal axis represents the frequency request signal and the vertical axis represents the frequencies of the variable frequency power supplies 5A and 5B, and the point P in the figure represents the nonlinear region, that is, the nonlinear region. This is the lower limit frequency value of the stable region, and point P2 is the upper limit frequency value. Also, Q,,Q2 are the above P
, , shows the frequency values of the variable frequency power supplies 5A and 5B corresponding to P2. The recirculation flow characteristics of a conventional device having such nonlinear characteristics are as shown in FIGS. 3a and 3b. Figure 3a shows a frequency request signal line with time t on the horizontal axis and the variable frequency range 0 to 100% of frequency request signals RA and RB on the vertical axis, and Figure 3b shows time t on the horizontal axis. The axis shows a core flow rate curve in which the variable range of the coolant core flow rate from 0 to 100% is taken as the vertical axis. The points P, , P2 on the above-mentioned required frequency signal axis are the same as the points P, , P2 explained in FIG. 2. As is clear from Fig. 3a and b, when the frequency request signal R changes RB over time, the frequency of the variable frequency power supply becomes periodic in L~t2 and La~t4 corresponding to the unstable regions P, ~P2. oscillations, resulting in oscillations in the recirculation flow rate, resulting in unstable behavior such as oscillations in the core flow rate as shown in Figure 3b. This oscillation of the zero flow rate in the furnace may cause unexpected fluctuations in the output of the power plant. In order to deal with this problem, conventional methods have been to limit the control range of recirculation, and to have skilled operators perform output increases and decreases at power plant start-up. However, as the difference in electricity demand between day and night has increased as seen recently, the fluctuations in the output of nuclear power plants between day and night also become large.
The burden on the operator who operates it also increases, which has become a problem. The present invention has been made to solve the above problems, and provides cooling with stable characteristics that do not cause unstable behavior such as periodic oscillations in the core flow rate even for frequency request signals in the unstable region. An object of the present invention is to provide a material recirculation flow rate control device.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a block diagram of the pulse generation circuit 9 of the coolant recirculation flow rate control device according to the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals. In FIG. 4, the deviation signal SD is converted into a frequency request signal R by the main controller 6, and sent to the judgment command unit 10 and the pulse signal generator 11. The judgment command unit 10 compares the lower limit P and upper limit P2 of the frequency request signal indicating the unstable region with the frequency request signal R, and opens the switch 12 when P≦the frequency request signal R≦P2. , close switch 13.
For this reason, a pulse frequency request signal RP with the width of the unstable region P, ~P2 having the minimum value of the pulse peak value from the pulse signal generator 11 is sent to the controllers 7A, 7B via the closed switch 13. Sent. The following configuration is the same as that of the conventional device described above, so a description thereof will be omitted. In the above configuration, when the frequency request signal R is changed over time as shown in FIG. During the above period, the switches 12 and 13 are switched, and the pulsed frequency request signal RRB, which is varied at high speed, is sent from the pulse signal generator 11 to the controllers 7A and 7B through the closed switch 13. .

The pulse wave of the frequency request signal described above is in the unstable region P, ~P
2, it is possible to avoid the nonlinear characteristics of the variable frequency power supplies 5A and 5B as shown in Figures 2a and 2b, and the core flow rate as shown in Figure 3b, which is seen in conventional equipment, can be avoided. vibration does not occur. Furthermore, due to the large inertia of the electric motor and recirculation pump, the above-mentioned time t2 and t4
A rapidly fluctuating pulsed frequency request signal R output to
The flow rates also change smoothly for A and RB. especially,
In FIG. 5a, the time t when entering the unstable region. Then, output a pulse with a long time to output the P2 signal as shown in Fig. 6a, and as the frequency request signal R decreases, the width of P2 decreases as shown in Fig. 6 from a → b → c. On the other hand, at time t3 when it enters the unstable region again, a pulse is output for a short period of time to output the P2 signal like c, and as the frequency request signal R increases, P like c → b → a
If the pulse width and pulse interval are adjusted to increase the width, which is 2, stable core flow characteristics as shown in FIG. 5b can be obtained. In addition, the basic period of the pulse is the electric motor 3A, 3B.
It needs to be faster than the inertia constant of the recirculation system including recirculation pumps 4A, 4B, etc. (for example, 7 to 10 seconds in the case of the recirculation system MG set), and if you aim for a temperature of about 1/1 good. In this example, the pulse width and pulse interval of the frequency request signal were changed as shown in Fig. 6 a→b→c and c→b→a. The core flow rate characteristics shown in b are even more defined.

Note that the present invention is not limited to the above-described embodiment. For example, in the above embodiment, the main controller operates based on the deviation signal SD between the load setting signal SL and the main steam flow rate signal SF, and sends out the frequency request signal R, but the point is that the thermal output of the reactor is Any device that can send out a frequency request signal corresponding to the above may be used. It goes without saying that various other modifications can be made without departing from the gist of the present invention. As explained above, in the device according to the present invention, when a frequency request signal corresponding to the unstable region of the variable frequency power supply device arrives, the signal is detected by the determiner, and the changeover switch replaces the signal with a pulse. Since a pulsed frequency request signal having a peak value that avoids the above-mentioned unstable region from the signal generator is given to the controller for controlling the variable frequency power supply, the above-mentioned variable frequency The power supply does not exhibit unstable behavior.

As a result, the recirculation system including electric motors, recirculation pumps, etc. does not exhibit unstable behavior, and accordingly, the flow rate of the reactor core does not exhibit unstable behavior and exhibits stable characteristics. Furthermore, by appropriately adjusting the pulse width, pulse interval, and peak value of the pulsed frequency request signal, the flow rate characteristics of the furnace can be made extremely stable. Therefore, according to the present invention, it is possible to provide a coolant recirculation flow rate control device in which the core flow rate of the coolant exhibits stable change characteristics over the entire change range of the frequency request signal.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the secondary coolant recirculation flow rate control device, Fig. 2 a and b are curve diagrams showing the frequency characteristics of the conventional device, and Fig. 3 a and b are the recirculation device of the conventional device. 4 is a block diagram showing the configuration of a pulse circuit according to an embodiment of the present invention. FIGS. 5a and 5b are recirculation flow characteristics of the same embodiment. FIGS. c is a waveform diagram of a pulsed frequency request signal of the same embodiment. 1... Nuclear reactor, 3A, 3B... Electric motor, 4A, 4B... Recirculation pump, 5A, 5B...
...Variable frequency power supply, 6...Main controller,
10... Judgment command device, 11... Pulse signal generator. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. A recirculation pump that forcibly circulates coolant in a nuclear reactor core, an electric motor that drives this recirculation pump, a variable frequency power supply that controls the speed of this electric motor, and a a main controller that outputs a frequency request signal corresponding to the output; and a determiner that determines whether the frequency request signal output from the main controller is a frequency request signal corresponding to an unstable region of the variable frequency power supply. and a changeover switch that operates when the determiner determines that the frequency request signal corresponds to the unstable region; a pulse signal generator that sends out pulses that fluctuate at high speed with an amplitude larger than the variation width of the frequency request signal corresponding to the unstable region; A coolant recirculation flow rate control device for a nuclear reactor, comprising a controller that controls the frequency power supply device accordingly. 2. The coolant recirculation flow rate control device for a nuclear reactor according to claim 1, wherein the pulse signal generator is a rectangular pulse generator whose on/off ratio can be variably controlled.