JPH0350235B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recirculation pump control device for a boiling water nuclear reactor in which reactor output is controlled by a recirculation pump, and in particular, when a recirculation pump drive power source momentarily stops, This invention relates to a device equipped with functions suitable for protecting nuclear reactor operation.

Generally, in a boiling water reactor, the output of the reactor is controlled by controlling the core flow rate of coolant using a recirculation pump. In other words, coolant vapor bubbles (hereinafter referred to as voids) are normally generated in the reactor core, and increasing the core flow rate temporarily reduces the voids, thereby reducing the coolant (moderator) in the core. increases relatively. This increase in the relative amount of coolant slows down neutrons in the reactor core, accelerates nuclear reactions, and increases reactor power. When the reactor output increases to a certain point, the number of voids increases, and the output is stabilized when the relative relationship between the voids, the coolant, and the output is balanced.

However, when the core flow rate decreases, the number of voids increases temporarily, and the reactor output (neutron flux) may decrease. In this way, when the core flow rate increases or decreases in a relatively short period of time, the corresponding decrease or increase in voids increases, which causes the fluctuation range of neutron flux (corresponding to reactor power) to become abnormal. There have been cases where the reactor has become so large that it has led to a reactor scram.

For example, as shown in the graph of Figure 1, t=
If a momentary power failure occurs in the recirculation pump drive power supply at 0, the speed will be rapidly reduced due to the low inertia of the recirculation pump and drive motor. Next, when the momentary power failure is restored, the speed will be increased at the maximum speed increase rate. When the core flow rate is rapidly decreased or increased in accordance with this pump speed, the neutron flux once decreases as shown in FIG. 1, but as a reaction to this, it rapidly increases as the core flow rate increases. The neutron flux rise is due to the reactor's neutron flux high scram setpoint (e.g.
120%), a reactor scram is performed, including rapid insertion of control rods. When scramming, the neutron flux continues to rise somewhat until the control reactivity overcomes the void reactivity, but it is rapidly reduced to zero output by the effect of the scram reactivity.

As mentioned above, if there is a sudden voltage fluctuation in the recirculation pump drive power supply, such as a momentary power outage, there is a risk that the reactor will be scrammed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a recirculation pump control device that can prevent a nuclear reactor scram caused by sudden voltage fluctuations such as instantaneous power outage of the recirculation pump drive power source.

The present invention outputs a recirculation pump deceleration command signal to decelerate the recirculation pump in response to a power failure detection signal of the recirculation pump drive power supply, and then maintains a constant rate of increase after a predetermined period of time or when a normal return command is input. By configuring the recirculation pump control device with an instantaneous power failure speed control circuit that outputs a return speed command signal that increases the speed to a speed corresponding to the reactor output target value, it is possible to prevent sudden voltage fluctuations such as instantaneous power failures. The aim is to prevent reactor scrams caused by

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 2 shows an overall configuration diagram of a nuclear reactor and recirculation pump control device according to an embodiment of the present invention. As shown in FIG. 2, the boiling water reactor includes a reactor vessel 1, a reactor core 2 disposed in the center of the vessel 1, and a plurality of recirculation pumps 3 disposed at the bottom. A drive motor 4 engaged with the pump 3, a control rod 5 inserted into the reactor core 2, a drive device 6 for the control rod 5,
It consists of a steam separator 7 provided at the head of the reactor core 2 and a dryer 8 provided at the top of the vessel 1. Coolant 9 is allowed to flow out into the reactor vessel 1 to a predetermined level.
This coolant is heated and vaporized by the core 2,
The steam is sent through a steam separator 7 and a dryer 8 to a main steam line 10. Further, the coolant around the core 2 is caused to flow into the core 2 as indicated by an arrow 11 in the figure by a recirculation pump 3.

The drive motor 4 is connected to a motor control device 12, which is formed from a stationary frequency variable power supply device, and has a frequency that corresponds to a speed command signal S _N input from a speed command circuit 13. , which outputs motor drive power. In addition, the power input terminal 1 of the motor control device 12
A low voltage detector 15 is connected to 4, and this detector 1
The detection signal V _L of No. 5 is input to the speed command circuit 13. The block configuration of this speed command circuit 13 is shown in FIG.

As shown in Figure 3, the target output value of the reactor
An output deviation ΔP between P _O and the output inspection value P _A is calculated by a subtracter 21 and inputted to the normal speed command circuit 23 via the signal holding circuit 22 . From this normal speed command circuit 23, a speed command signal _SNA for the recirculation pump 2 required to make the output deviation ΔP "0" is generated, and is output to the low value passage gate circuit 24. There is. On the other hand, the instantaneous power failure speed command circuit is formed of a speed increase rate limiter 29, and a deceleration speed setter 25 and a return speed setter 26 connected to the speed increase rate limiter 29 via gates 27 and 28, respectively. has been done. The speed increase rate limiter 29 is configured to limit the rate of increase to a certain value when the input deceleration command signal S _L or return speed command signal S _H increases, and conversely decreases the rate of increase. It is designed so that there are no restrictions when doing so. This speed increase rate limiter 29
The speed command signal _SNB is the low value passing gate circuit 2.
4, and the speed command signal with the lower value of the speed command signal S _NA mentioned above is the speed command signal S _N
The output signal is output to the motor control device 12 as follows.

Furthermore, the low voltage detection signal V _L (logical signal) output from the low voltage detector 15 is transmitted to the signal holding circuit 30.
While the detection signal V _L is being held, the gate 27 is "open" and the gate 28 is "closed".
When the signal holding circuit 30 is reset by the return signal R, the gate 27 is "closed" and the gate 28 is "closed".
is formed to be "open". Note that if the low voltage detector 15 is provided with a signal self-holding circuit, this signal holding circuit 30 is not necessary.

Furthermore, the speed command signals S _NA and S _NB are sent to the comparator 3.
2, and this comparator 32 satisfies S _NA > S _NB
When this happens, a signal is output to the signal holding circuit 22. When this signal is input, the signal holding circuit 22 outputs the output deviation ΔP at that time.
It is designed to hold and output. This holding is then released when S _NA <S _NB .

Regarding the operation of the embodiment configured in this way,
The operation will be explained below with reference to the flowchart of the operation shown in FIG.

Under normal conditions, the speed command signal S _NA (for example, 100% rotational speed command) according to the deviation between the output target value P _O and the output detected value P _A is the speed command signal S _N
Based on this, the recirculation pump 3 is driven by the power of the frequency output from the motor control device 12 to control the core flow rate.

When a voltage drop in the power supply for driving the recirculation pump 3 due to an instantaneous power outage is detected by the low voltage detector 15 (step 41 in FIG. 4), the voltage drop occurs in step 42.
, the gate 28 is "closed" and the gate 27 is "opened", and the signal input to the speed increase rate limiter 29 is determined from the return speed command signal S _H (set to 105%, for example). Command signal S _L (e.g. 40%
is set to . ), and this limiter 29 outputs S _L , whose rate of change is not limited in any way, as the speed command signal _SNB . Since this S _L is a sufficiently low value compared to the normal speed command signal S _NA , the low value passage gate circuit 24 outputs the deceleration command signal S _L as the speed command signal S _N instead of S _NA . Output. At the same time, in step 43, the comparator 32 operates, and the output deviation ΔP of the signal holding circuit 22 is fixed at the value at that time.

As a result, as shown in Fig. 5, the speed of the recirculation pump 3 is temporarily reduced rapidly according to the time constant of the pump system (for example, 0.7 seconds) at the same time as the instantaneous power failure occurs. is recovered, the deceleration command signal
The deceleration speed is controlled to a constant value based on S _L , and the core flow rate is accordingly controlled to a constant low flow rate.
Therefore, since the fluctuation range of the core flow rate is small, the fluctuation range of the neutron flux is also suppressed as shown in FIG. 5.

In this way, when the change in neutron flux becomes stable (it settles down in about 5 minutes), after a predetermined period of time has elapsed, or when a return command is given by the operator (step 44), gate 27,
28 is switched between "open" and "closed", and the input of the speed increase rate limiter 29 changes from the deceleration command signal S _L to the return speed command S _H. This change is in the direction of increasing speed, so the rate of increase is a constant rate (e.g.
A speed command signal S _NB limited at 10%/min, for example increased from 40% to 105%, is output (step 45). As a result, as shown in FIG. 5, the pump speed of the recirculation pump 3 is gradually increased, and the core flow rate and neutron flux are also stably increased accordingly.

When S _NB gradually increases and reaches S _NA or higher, the speed command signal is output from the low value passage gate circuit 24.
S _N is switched to S _NA , and at the same time, the fixation of the signal holding circuit 22 is released (step 46), and from then on, the recirculation pump 3 is controlled by the normal speed command circuit 23.
is now controlled (step 47).

Therefore, according to the above-mentioned embodiment, it is possible to effectively suppress the range of fluctuations in the core flow rate caused by power supply voltage fluctuations such as instantaneous power outages, and therefore it is possible to suppress abnormal increases in neutron flux. As a result, high neutron flux scrams can be prevented, unnecessary reactor scrams can be prevented,
This has the effect of reducing unnecessary reactor scrams and improving operating efficiency.

In the above example, the output deviation ΔP was fixed because the detected output value P _A G was naturally significantly reduced during control using the instantaneous power failure speed command, so the control was switched to the normal speed command. This is because there is a risk that an abnormally large ΔP may be input. However, if the rate of increase in the recovery process is made to sufficiently correspond to the reactor output response, it does not necessarily need to be fixed.

Further, the present invention is not limited to the above-mentioned embodiment, and it is easily possible to construct the same thing by applying a microprocessor or the like.

As explained above, according to the present invention, it is possible to prevent reactor scrams caused by sudden voltage fluctuations such as instantaneous power outage of the recirculation pump drive power supply, and to improve the operating rate. There is an effect.

[Brief explanation of drawings]

Fig. 1 is a diagram showing changes in recirculation pump speed, core flow rate, and neutron flux due to instantaneous power failure in the conventional example, Fig. 2 is an overall configuration diagram of an embodiment to which the present invention is applied, and Fig. 3 2 is a main part control block diagram of the illustrated embodiment, FIG. 4 is a flow chart explaining the operation, and FIG. FIG. 3... Recirculation pump, 4... Drive motor, 12
...Motor control device, 13...Speed command device, 1
5...Low voltage detector, 23...Normal speed command circuit, 24...Low value passing gate, 25...Deceleration speed setter, 26...Return speed setter, 27, 28...
...Gate, 29...Speed increase rate limiter, 30...
Signal holding circuit, 31...NOT circuit, 32...Comparator.

Claims (1)

[Claims] 1. A normal speed command circuit that outputs a speed command signal for a coolant recirculation pump according to a deviation between a target output value and a detected output value of the reactor; an instantaneous power outage speed command circuit that outputs a deceleration command signal set by the deceleration command signal, and outputs a return speed command signal that increases the deceleration command signal at a predetermined rate after a predetermined period of time or in response to a given normal return command; A speed command device comprising: a low value passing gate circuit that compares the output signals of the instantaneous power failure speed command circuit and the normal speed command circuit and outputs a speed command signal of a lower value; Furnace recirculation pump control device.