JPS60120285A - Preventive circuit for drawing of control rod - 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 Application of the Invention] The present invention relates to a control rod withdrawal prevention circuit that issues a prevention signal to prevent a nuclear reactor control rod from being excessively withdrawn from the reactor.

[Background of the invention]

Nuclear reactors automatically shut down nuclear reactors to prevent or suppress abnormal transients or malfunctions that could compromise safety, or if such events are expected to occur. A safety protection system is provided that performs reactor protection operations such as shutting down the reactor. 1 of this safety protection system
One method is to measure the neutron flux of a nuclear reactor, which is a typical parameter of reactor output, and automatically shut down the reactor if the neutron flux exceeds a specified value.

Factors that increase the neutron flux of a nuclear reactor depend on reactor-specific characteristics such as turbine load fluctuations, but usually control rods installed in the reactor are damaged due to erroneous operation or malfunction when withdrawing them from the reactor. In many cases, the reactor is automatically shut down when the neutron flux exceeds the specified value due to excessive withdrawal of neutrons.

Therefore, in order to improve reactor availability and provide deep protection for reactor safety, normally in nuclear reactors, withdrawal of control rods is monitored before the automatic protection operation for reactor shutdown due to high reactor neutron flux is activated. A control rod withdrawal prevention circuit is provided that prevents the control rods from being withdrawn if an abnormality in the reactor output is detected. An example of the configuration of this control rod withdrawal prevention circuit is shown in FIG.

The control rod withdrawal prevention circuit shown in FIG. 1 includes a plurality of local power detection devices 1a...1n such as nuclear fission chambers distributed in the reactor core, and these detection devices 1a.
An average neutron flux monitor device 2 that calculates the reactor average power by averaging the outputs of ~1n, and a local power detection device that selects the output of local power detection devices around the control rod to be operated selected by the control rod selection circuit 4. a device selection circuit 3; an average value circuit 5 for averaging the outputs of the local output detection devices selected by the selection circuit 3;
When the control rod selection circuit 4 changes the selection of control rods, the output of the average value circuit 5 automatically matches the output of the reactor average neutron flux monitor 2 before control rod withdrawal is started. The output of the gain adjustment circuit 6 is compared with the signal set by the control rod pull-out prevention level setting circuit 7, and the output of the gain adjustment circuit 6 is compared with the signal set by the control rod withdrawal prevention level setting circuit 7. A control rod withdrawal prevention signal is issued from the comparator circuit 8.

However, this conventional control rod withdrawal prevention circuit requires relatively complicated operations such as selecting the output of the local output detection device around the control rod to be operated using the aforementioned control rod selection circuit. Such a configuration is essential for boiling water reactors, which have the characteristic that the neutron flux in the vicinity of the control rods to be operated varies greatly; If the effects of neutron flux fluctuations occur not only in the vicinity of the control rods but over a wide range, a circuit for selecting a local power detection device around the control rods as described above is not necessarily required. Additionally, the gain of the gain adjustment circuit 6 is configured to be adjusted when the control rod selection is changed, but in the case of a reactor where the reactor output is automatically controlled by the control rods, there is a problem in when to perform the gain adjustment. It becomes.

[Purpose of the invention]

An object of the present invention is to simplify the conventional control rod withdrawal prevention circuit and provide a control rod withdrawal prevention circuit suitable for application to a heavy water-moderated light water boiling type nuclear reactor that automatically controls the way the reactor exits using the control rods. Our goal is to provide the following.

[Summary of the invention]

The basic purpose of the control rod withdrawal prevention circuit is to monitor the power distribution of the reactor core to prevent the power from increasing locally, and to limit the partial power increase of the reactor within a specified time. It is to be.

For this purpose, the present invention divides the core into several regions,
A control rod withdrawal level setting circuit is provided which calculates the average output of the region and applies a predetermined amount of bias to the average output, and the average output of the region and the output of the control rod withdrawal level setting circuit are set. It is designed to monitor the withdrawal of control rods by comparison, and specifically, it is configured to input a signal that is the sum of the average output and bias of each region to an integrator, and the input to the integrator is based on the control rod operation. When changing or periodically, the integrator is configured to hold a signal obtained by adding the average output of each area and a bias, and compare this held value with the average output of each area. This is what I did.

[Embodiments of the invention]

FIG. 2 is a schematic diagram showing the core configuration of a heavy water-moderated light water boiling reactor. In the figure, the number 11 indicates the location where the pressure pipes housing the fuel assemblies are arranged in a grid pattern. The neutron flux within the reactor with such a configuration is detected by three types of detectors. In other words, the starting detector assembly 14 (indicated by the Δ mark) measures the region where the neutron flux is extremely low at the time of starting the reactor.The output measures the neutron flux in the rising process from the starting region to the output region. Climbing detector assembly 13 (
) and the output region detector assembly 12 (indicated by a circle) that measures the neutron flux in the output region
The detectors are distributed as shown in the figure, and the neutron flux is detected by these detectors. Here, although not particularly shown, a necessary number of control rods are installed between the pressure pipe and the detector assembly.

The power range detector assembly 12 accommodates four local power detectors each consisting of a nuclear fission ionization chamber in the axial direction of the reactor core.

By the way, in a heavy water-moderated light water boiling reactor, the negative reactivity coefficient is small, so as the reactor becomes larger, Zenon spatial vibrations are likely to occur due to fluctuations in reactor output. Therefore, in order to suppress the spatial vibration of Zenon and operate the reactor stably, it is necessary to divide the reactor into several regions and perform region control. However, in terms of neutron flux behavior, since the mean free path of neutrons is large, changes in neutron flux due to movement of control rods do not affect only the vicinity of the control rods being operated, but also over a relatively wide range, and the characteristics There is. Although not described in detail here, in the case of the core configuration shown in Figure 2, the core is divided into four regions, 1st region 1 to 4th region ■, as shown in the figure, and the output of each region is monitored and the Zenon vibration is suppressed. The explanation will be based on the premise that it is appropriate to perform control.

FIG. 3 is a configuration diagram of a circuit block that calculates the average output of one of the first to fourth regions I to IV shown in FIG. 2. A local power detector 21a, such as a nuclear fission chamber, is installed in one area.

......, the output signal of 21n (in the case of Fig. 2, the number of detectors installed in one area is 44, so n is 44 or less) is amplified by the local output signal, which amplifies the signal and adjusts the gain. It is input to the area average neutron flux monitor circuit 23 via the width filters 22a, . . . , 22n.

The region average neutron flux monitor circuit 23 averages the output signals from the local output detectors 218 to 21n within the region and adjusts the gain to match the thermal output.

FIG. 4 is a diagram showing the overall configuration of a control rod withdrawal prevention circuit according to the present invention. The output signal ■ of the area average neutron flux monitor circuit 23 is added to the output signal ■ of the bias setting device 24 to become a signal 0, and the added signal 0 is subtracted from the output signal [F] of the integrator 26 to become a signal 0. The signal is then input to the integrator 26 via the switching circuit 25. The switching circuit 25 connects the subtraction signal 0 to the integrator 26 when changing the control rod withdrawal setting level, and normally the subtraction signal 0 is connected to the integrator 26.
is disconnected, and the output (2) of the integrator 26 holds the output value when the above [F] is connected and integrated.

The comparator 27 compares the output [F] of the integrator 26 and the output ■ of the area average neutron flux monitor circuit 23, and the signal ■ is the signal [F].
F], a control rod withdrawal prevention signal (on/off signal) [F] is issued.

FIG. 5 is a time chart of the output signals of each part in FIG. Enter. Therefore, the integrator output signal [F
] rises to a level equal to the output of the area average neutron flux monitor circuit 23 plus the bias amount ○ from the bias setter 24. After that, even if the control rod is withdrawn during the period indicated by symbol H and the area average neutron flux increases, the switch 25 is switched to the side that does not input the signal to the integrator 26.
The output (2) of the integrator 26 maintains a constant value.

If the output ■ of the area average neutron flux monitor circuit 23 is lower than the output ■ of the integrator 26 due to the control rod withdrawal operation, the control rod withdrawal prevention signal [F] is not generated.
When the output ■ of the area average neutron flux monitor circuit 23 becomes larger than the output [F] of the integrator 26 due to the control rod withdrawal operation, the comparator 27 operates and the period T during which this relationship is established
During this period, the control rod withdrawal prevention signal [F] is issued, and even if the control rod withdrawal operation is continued thereafter, the control rod withdrawal is stopped and the neutron flux does not increase thereafter.

By the way, it is appropriate to determine the prescribed time t during which the control rod withdrawal setting level change command G is issued and the switch 25 connects the signal 0 to the integrator 26 as follows.

In other words, if the time constant of the integrator 26 is TI, the transfer function of the integrator with a feedback loop is equivalent to a first-order lag circuit, so the integrator output is saturated in a time of approximately 2 to 3 TI. becomes. Therefore, the regular time meal may be about 2 to 3 TI during this time.

In addition, when the control rod is manually operated, the control rod withdrawal setting level change command G can be given instead of the selection change signal of the control rod to be operated, as is adopted in the prior art. However, if the control rods are operated automatically, it would be cumbersome for the operator to issue a command to change the control rod withdrawal setting level each time, so it would be troublesome to issue a command to change the control rod withdrawal setting level every time. This will make it easier to operate.

Although an integrator is used in FIG. 4, a storage element that stores and holds the sum of the average output of each region and the bias value may be used instead of the integrator.

〔Effect of the invention〕

As is clear from the above, according to the present invention, there is no need to operate to select the output of the local output detection device around the control rod, and when changing control rod selection, it is possible to match the output of the average neutron flux monitor device. There is no need for an automatic gain/adjustment circuit for comparison and adjustment, and a very simple control rod withdrawal prevention circuit can be realized.

In a light water boiling reactor, the average neutron flux is captured as the average neutron flux of the entire core, but in a heavy water-moderated light water boiling reactor, as mentioned above, it is necessary to capture the average neutron flux in each region, so the control rod withdrawal prevention circuit is also calculated in each region. It will be necessary to install it in Therefore, in a heavy water-moderated light water boiling reactor, the economic effect of simplifying the control rod withdrawal prevention circuit is extremely large.

[Brief explanation of the drawings] Figure 1 is a block diagram showing the configuration of a conventional control rod withdrawal prevention circuit, Figure 2 is a schematic diagram showing the core configuration of a heavy water-moderated light water boiling reactor, and Figure 3 is a block diagram showing the configuration of a conventional control rod withdrawal prevention circuit. FIG. 4 is a block diagram of a circuit for calculating the average output of one region shown in the figure, FIG. 4 is a block diagram of a control rod withdrawal prevention circuit according to the present invention, and FIG. 5 is a time chart of output signals of each part in FIG. 4. DESCRIPTION OF SYMBOLS 1... Local output detection device, 2... Average neutron flux monitor device, 3... Local output detection device selection circuit, 4...
Control rod selection circuit, 5... Average value circuit, 6... Gain adjustment circuit, 7... Control rod withdrawal prevention level setting circuit,
8... Comparison circuit, 11... Pressure pipe arrangement location, 12.
... Output area detector assembly, 13... Output increase detector assembly, 14... Start-up detector assembly, 21...
Local output detector, 22...Local output amplifier, 23...
・Area average neutron flux monitor circuit, 24...Bias setting device, 25...Switching circuit, 26...Integrator, 27.
...Comparator. Agent Patent Attorney Tatsuyuki Unuma

Claims (1)

[Claims] 1. Control rods that control the output of a nuclear reactor, a control rod drive circuit that controls the control rods, and a method that measures the neutron flux of the reactor to prevent the control rods from being excessively withdrawn from the inside of the reactor. a control rod withdrawal prevention circuit that monitors the control rod withdrawal, the signal holding means holding an average neutron flux signal of the nuclear reactor and a signal obtained by adding a predetermined amount of bias to the average neutron flux signal; When the average neutron flux signal deviates from the control rod withdrawal prevention level held by the signal holding means by comparing the signal with the output of the signal holding means, control rod withdrawal prevention 1Fj
and a comparison circuit for issuing a signal to the control rod drive circuit. 2. The control rod withdrawal prevention circuit according to claim 1, wherein the signal held by the signal holding means is changed periodically or periodically when the control rod is manually selected.