JPS60120289A - Neutron detector - 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 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]

An example of a conventional control rod withdrawal/stop device for a nuclear reactor will be described with reference to FIG. The signal of the neutron detector placed in the reactor core shown in Fig. 1 is selected by the maximum value selection circuit, L P M
(MAX) is selected. Next, this L P M (MA
The value of X) is transmitted to the control rod withdrawal stop determination device, and R8M
Set value V. When LPM (MAX) is larger than Vo, a control rod withdrawal stop signal is 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small cores, but when the core becomes large, the power near the control rods increases when the control rods are withdrawn, but the Since the increase in overall output is delayed, if a neutron detector near the control rod has failed and is disconnected, it may not be possible to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.

In addition, other examples of conventional control rod withdrawal and stop devices for nuclear reactors are shown in the second section.
This will be explained with a diagram.

The core of the reactor shown in Figure 2 is divided into four regions in each quarter quadrant, and the neutron detector signals in the first region are added by an adding device to determine Px(ri). Here, t is time and Pi indicates the neutron detector addition result in the first region.

The calibration time of the control rod withdrawal stop device R8M is t. Then, P+(to) at time to is transmitted to the R8M calibration device. Next, the R8M calibration device uses the core total power measurement value generated in the reactor core, which is determined from various flow rates such as the main steam flow rate of the reactor, and the temperature measurement results of each part, and the core radial power distribution calculated by the core process computer. from the first area to the fourth area
Calculate the output of each area up to the area. Taking the example of the first area, the area output PRI (to
), calculate the calibration coefficient α using the following formula.

αs = PRt (to)/Pt ('a) αs determined here is used as a calibration coefficient for the first region R8M until the next calibration. Therefore, the conventional control rod withdrawal stop device t (R8M device) using a neutron detector in the first region is expressed by the following equation.

R8M signal Rt (R = Pt (t)
The maximum value of R(')m-t is selected by the maximum value selection circuit. Finally, this R (S, fi, 8 is RAM
Compared with the set value Ro, R(') m a xO is Ro
When the control rod became a dog, a control rod withdrawal stop signal was generated. This conventional RAM has a region output detection device RPM for each region.
Since they are the same signal, there is an advantage that the R8M and RPM signals can be shared. However, this conventional R8M
There was no problem with small cores such as 1/4 rotation target cores where the output in each region was almost the same, but when the core became larger or the output in the 1/4 quadrant instead of the 1/4 rotation target core differed. In this case, the range of increase in output until the R8M signal is generated differs greatly depending on the region, and there is a problem in that if a control rod is pulled out in the initial low output region, the generation of the R8M signal is delayed. 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 may be accidentally withdrawn at the same time.
In M, there are variations in the output rise range until LSM occurs (between regions), which is undesirable.

As mentioned above, in the RAM 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 control rod withdrawal is accompanied by a significant rise locally, or when the reactor is enlarged. If the output of each region is significantly different under normal conditions, the R8M signal may be delayed or varied, which is undesirable.

Therefore, in a nuclear reactor where the reactor core is enlarged and the output needs to be automatically controlled by control rods in multiple regions, there has been a desire for an R8M invention that can immediately stop withdrawal of control rods in the event of abnormal drive of the control rods.

[Embodiment 1 of the invention] An embodiment of the present invention will be described below with reference to FIG.

FIG. 3 is a diagram showing a control rod withdrawal and stop device for a large-scale pressure tube nuclear reactor having 600 or more fuel assemblies in the reactor. 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 FIG. 3, the control rod withdrawal and stop device is configured to detect neutrons in a total of five regions: four regions in each 1/4 quadrant in the radial direction and a region in the center of the reactor core. The signals of the neutron detectors in region 1 of FIG. is sent to the R8M calibration device.
Calibration of M is performed using the value TPM (t
This is carried out by calculating the R8M calibration coefficient α using OL.

Calibration coefficient α can be calculated using the following formula.

α+=TPM(fol/Pt' (to) where α: R8M calibration coefficient 1: Region number T PM: Signal to 2 of core total power measuring device Calibration time Pt: Neutron detector addition signal by region Next, each region's The calibration coefficient αI is sent to the R8M calculation device for each region, and the R8M signal for each region is calculated.

The RAM value for each area, R1, is determined by the following formula.

R'(t)=P t'(S×α1) Specifically, in this method, if the total core power is 8 (l), the RAM
If calibration is performed, all R8M values will be set to 80 even if there is a difference in output between regions. In other words, if the control rod withdrawal stop signal generation setting value for R8M is set to 105, a fair output increase limit will be set for all regions, and for a rating of 100, each region will not be able to withdraw the control rod with an output increase of about 5 inches. A stop signal will be generated. When using the conventional area output itself, there is a difference of about 4 inches between the areas, and in the rated output area, the output increases by 3 inches in the 102 area, and in the 98 area, the output increases by 7 inches. In this example, the issue has been resolved.

In the embodiment shown in FIG. 3, the R8M value for each area is selected by the maximum value selection circuit, and the control rod withdrawal signal setting value R
o to R (If the worker is a dog, the control rod withdrawal stop signal is generated.

〔Effect of the 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 for each region after the calibration time. A neutron system that uses a signal multiplied by the average output and compares and judges it with a control rod withdrawal stop setting value common to all areas of the reactor core, and generates a control rod withdrawal stop signal if the set value is exceeded. Detection device. 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 overlapped in a plurality of divided regions. By using a signal obtained by multiplying the ratio at an arbitrary 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 possible to determine whether the set value has been exceeded. A neutron detection device characterized in that it generates 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 based on the total core power determined from the heat balance of one core at any calibration time and the neutron detection in the area at that time. By multiplying the average value of the neutron detector values in the region after the calibration time by the ratio of the average value of the neutron detector values, the control rod withdrawal stop signal is determined to be the control rod withdrawal stop setting value common to all areas of the reactor core. A neutron detection device characterized by generating a control rod withdrawal stop signal when the neutron exceeds the limit.