JPH0449676B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a neutron detection device for a nuclear reactor, and particularly to a control rod withdrawal and shutdown device for a nuclear reactor that normally drives control rods during power operation.

[Background of the invention]

The first example of a control rod withdrawal and stop device for a conventional nuclear reactor is shown below.
This will be explained using figures. The maximum value LPM (MAX) of the signal of the neutron detector placed in the reactor core shown in FIG. 1 is selected by the maximum value selection circuit. Then this
The value of LPM (MAX) is transmitted to the control rod withdrawal stop judgment device, compared with the RSM set value V ₀ , and LPM
When (MAX) was greater than V ₀ , a control rod withdrawal stop signal was issued to stop the control rod drive device. The configuration of this conventional control rod withdrawal and stop device was effective for reactors with relatively small cores, but when the core becomes large, the power near the control rods increases when the control rods are withdrawn, but the Since the increase in overall output is delayed, if a neutron detector near the control rod has failed and is disconnected, it may not be possible to effectively generate a control rod withdrawal stop signal.

Another example of a conventional nuclear reactor control rod withdrawal and stop device will be described with reference to FIG.

The core of the nuclear reactor shown in FIG. 2 is divided into four regions in each 1/4 quadrant, and the neutron detector signals in the first region are added by an adding device to determine P ₁ (t). P in other areas can be found in the same way. Here t is time
P ₁ indicates the neutron detector addition result of the first region.
Assuming that the calibration time of the control rod withdrawal and stop device RSM is t ₀ , P ₁ (t ₀ ) at time t ₀ is transmitted to the RSM calibration device. Next, the RSM calibration device uses the core total power measurement value generated in the reactor core, which is determined from various flow rates such as the reactor's main steam flow rate and the temperature measurement results of each part, and the core radial power distribution calculated by the core process calculator. Based on this, the output of each region from the first region to the fourth region is determined. Taking the example of the first region, the calibration coefficient α ₁ is determined using the following equation using the determined region output PR ₁ (t ₀ ) of the first region.

α ₁ = PR ₁ (t ₀ )/P ₁ (t ₀ ) The α ₁ obtained here will remain in the first region until the next calibration.
Used as a calibration coefficient for RSM. Therefore, the conventional control rod withdrawal and stop device (RSM device) using a neutron detector in the first region is expressed by the following equation.

The RSM signal R ₁ (t) in the first region is R ₁ (t) = P ₁ (t) × α First, the RSM signal R ₁ ( _t ) to _{R 4} in the four regions in the core
The maximum value of (t) is R(t) _nax is selected by the maximum value selection circuit. Finally, this R(t) _nax was compared with the RSM set value _R0 , and when R(t) _nax was larger than _R0 , a control rod withdrawal stop signal was generated. This conventional RSM is a region output detection device RPM for each region.
This has the advantage that the RSM and RPM signals can be shared. However, with this conventional RSM, there was no problem with small cores such as 1/4 rotation target cores where the output differs little in each region, but when the core becomes larger or 1/4 rotation target core instead of 1/4 rotation core When the output of the quadrants is different, the range of output increase until the RSM signal is generated differs greatly depending on the area, and there is a problem that the generation of the RSM signal is delayed if the control rod is pulled out in the initial low output area. In particular, when the reactor core is divided into multiple regions and the output of each region is automatically and constantly controlled, it is conceivable that control rods in each region will be erroneously withdrawn at the same time.
In the RSM shown in the figure, there is undesirable variation in the amount of output rise until RSM occurs between regions.

As shown above, in the RSM of a nuclear reactor in which conventional control rods are driven under automatic control as shown in Figures 1 and 2, when the core becomes large and the control rod withdrawal is accompanied by a significant rise locally, or when the reactor is When the output of each region differs greatly under normal conditions, delays or variations in the RSM signal occur, which is undesirable.

Therefore, it has been desired to invent an RSM that can immediately stop control rod withdrawal in the event of an abnormal operation of a control rod in a nuclear reactor where the core is enlarged and the reactor core is divided into multiple regions and the output must be automatically controlled by control rods.

[Embodiments of the invention]

An embodiment of the present invention will be described below using FIG. FIG. 3 is a diagram showing a control rod withdrawal and stop device for a large-scale pressure tube nuclear reactor in which the number of fuel polymers in the raw paper reactor is 600 or more. In pressure tube reactors, in order to control xenon oscillations, it is necessary to divide the core into multiple regions and control the output of each region. In addition, in order to prevent the control rods from being withdrawn accidentally, if the core becomes large, it is necessary to divide the core into multiple regions and stop the withdrawal of control rods by monitoring the output of each region.

In Figure 3, the control rod withdrawal and stop device is configured to detect neutrons in a total of five areas: four areas in each 1/4 quadrant in the radial direction and the area in the center of the reactor core. The signals of the neutron detector in region 1 of FIG. 3 are added by an adding device,
P _t '(t) is found. Here, P _t ' is a signal from the adder, and t indicates time. This P _t ′(t)
is sent to the RSM calibration device. The RSM is calibrated using the value TPM (t ₀ ) of the core total power measuring device TPM.
This is done by finding the calibration coefficient α. Calibration coefficient α is calculated using the following formula.

α ₁ = TPM (t ₀ )/P _t ⁱ (t ₀ ) where α: RSM calibration coefficient i: Region number TPM: Signal of core total power measurement device t ₀ : Calibration time R _t : Neutron detector addition by region Signal Next, the calibration coefficient α _i of each region is sent to an RSM calculation device for each region to obtain an RSM signal for each region.
R ⁱ (t), which is the RSM value for each region, is determined by the following equation.

R ⁱ (t) = P _t ⁱ (t) × α _iThis method specifically applies when the total core power is 80%.
If RSM calibration is performed, all RSM values will be set to 80 even if there is a difference in output between regions. In other words, if the RSM control rod withdrawal stop signal generation setting value is set to 105, a fair limit on output increase will be set for all areas, and the rated
100, a control rod withdrawal stop signal will be generated when the output increases by approximately 5% in each region. This example solves the problem that when using the conventional area output itself, there is a deviation of about 4% between the areas, and at the rated output, the output increases by 3% in the area of 102, and the output increases by 7% in the area of 98. This means that it has been resolved. In the embodiment shown in Fig. 3, the RSM value for each region is R(t) _nax selected by the maximum value selection circuit, and control rod withdrawal is stopped if R(t) _nax is greater than the control rod withdrawal signal set value _R0 . It is configured to generate a signal.

〔Effect of the invention〕

According to the present invention, in a nuclear reactor where the reactor core is divided into multiple regions and the output of each region needs to be automatically controlled, when a control rod is accidentally withdrawn, the output increase in each region is detected fairly and the control rod can be withdrawn safely. At the same time as stopping the control rod, it is possible to prevent the generation of an erroneous control rod withdrawal stop signal, thereby improving the operating rate of the reactor.

[Brief explanation of the drawing]

1 and 2 are block diagrams of a conventional control rod withdrawal stop device, and FIG. 3 is a block diagram of a control rod withdrawal stop device according to an embodiment of the present invention.

Claims (1)

[Claims] 1. In a neutron detection device for a nuclear reactor, the reactor core is divided into a plurality of regions, and the ratio of the average power of each region to the core power at a given calibration time is calculated as the average of each region after the calibration time. Using the signal multiplied by the output, compare it with the control rod withdrawal stop setting value common to all areas of the reactor core.
A neutron detection device characterized in that it generates a control rod withdrawal stop signal when a set value is exceeded by making a determination. 2. In the neutron detection device according to claim 1, when control rods are arranged at the boundaries of regions, the average power and core power of the region around the region boundary control rods overlap in a plurality of divided regions. By using a signal obtained by multiplying the ratio at any calibration time by the average output of the area surrounding the boundary control rod, and comparing it with the control rod withdrawal stop setting value common to all areas of the reactor core, it is determined that the set value is exceeded. is a neutron detection device characterized by generating a control rod withdrawal stop signal. 3 In the neutron detection device according to claims 1 and 2, the signal of the neutron device is the total power of the reactor obtained from the heat balance of the core at any calibration time and the neutron detectors in the area at that time. Calculated by multiplying the average value of the neutron detector in the area after the calibration time by the ratio of the value of
A neutron detection device that generates a control rod withdrawal stop signal when the control rod withdrawal stop signal exceeds a control rod withdrawal stop setting value common to all regions of the reactor core.