JPH06289182A - Nuclear reactor output measuring device - Google Patents

Abstract

PURPOSE:To provide a nuclear reactor output measuring device which does not require a traveling device, secures high reliability, can be manufactured at a low cost, and can carry out the measurement of the reactor core axial direction output distribution having high precision. CONSTITUTION:A protecting pipe 24 which penetrates through along the axial direction in the reactor core 22 part of a nuclear reactor is installed. Inside the protecting pipe 24, a plurality of fixed neutron detectors 25 as the first output detector are arranged in a certain interval in the axial direction of the protecting pipe 24. Inside the protecting pipe 24, at the different position in the radial direction of the fixation type neutron detector 25, gamma-beam thermometers 26 which serve as calibrating means for the fixation type neutron detector 25 and the second output detector in the number larger than the quantity of the fixation type neutron detectors 25 are fixedly installed in a certain interval over the whole in the axial direction of the reactor core 22. The gamma-beam thermometers 26 are arranged, in the rough interval at the center position in the axial direction of the reactor core 22, and in the close interval in the edge part side in the same direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a boiling water reactor (BW).
The present invention relates to a reactor power measuring device applied to the power measurement of a large core such as R), and more particularly to a reactor power measuring device in which the structure of the power detector is simplified and the measurement accuracy is improved.

[0002]

2. Description of the Related Art Conventionally, as a technique for measuring the output of a nuclear reactor,
A method in which multiple output detectors are loaded inside the core and the output of the entire core is obtained from the average value of the output signal values, and a method in which multiple output detectors are installed outside the core and the core output is obtained from the average output There are two known methods. Generally the former is BW
It is used to measure the output of large cores such as R, and the latter is used to measure the output of small cores.

FIG. 4 exemplifies a conventional power measuring device used in a BWR core. A plurality of detector assemblies (only one body is shown in the figure) 3 are installed in a core 2 of a reactor pressure vessel 1. The detector assembly 3 has a structure in which a fixed neutron detector (hereinafter referred to as LPRM) 5 including a fission ionization chamber is provided in a protective tube 4 penetrating the core. This LPRM5 is, for example, A,
As shown by B, C, and D, four bodies are arranged at intervals along the axial direction, and the outputs of these are input to the output monitoring device 8 via the signal cable 7 to perform reactor power measurement and control. Done.

By the way, the fission ionization chamber used as the LPRM5 is constructed such that a fissile material (usually uranium 235 is used) is housed in a cladding tube, and this fissile material absorbs neutrons to cause fission. An output signal is obtained by utilizing the gas ionization action at the time. Therefore,
The use in the reactor reduces the amount of fissile material and gradually changes the sensitivity of the detector.

In order to deal with this change in sensitivity, the conventional L
Means are provided to calibrate the sensitivity of PRM5. The most frequently used calibration means is to provide a hollow guide tube 6 in the protection tube 4 adjacent to the LPRM 5, and to the guide tube 6 a mobile neutron detector for sensitivity calibration of the LPRM 5 (hereinafter, (TIP) 9 is inserted.
Like the LPRM 5, the TIP 9 is composed of a fission ionization chamber, and is driven in the axial direction of the hollow guide tube 6 by the driving device 10 and the TIP monitoring device 11, and its position signal and output signal are input to the output monitoring device 8. The output of LPRM5 is calibrated. By periodically performing this operation for all the detector assemblies 3, the outputs of all LPRMs 5 installed in the core 2 can be normalized with respect to TIP9.

[0006]

By the way, in a 1.1 million KW class BWR, 172 LPRMs are usually loaded, and an electronic device or a signal cable for processing the detection signal is L
The same number as PRM is installed. In addition, a large number of parts are attached to them, such as a conduit for protecting the signal cable, a connector for connecting the cable, and a monitoring panel for housing the electronic device.

As described above, when the number of detectors increases, the scale of the apparatus increases in proportion to the increase in the number of detectors, and the plant construction cost and maintenance cost increase. Therefore, it is desirable to reduce the number of LPRMs from an economical point of view, but if the number of detectors is simply reduced, the output increase cannot be accurately grasped when the output partially increases at a position where there is no detector. , You cannot simply reduce the number of detectors.

On the other hand, the above-mentioned TIP needs to keep the sensitivity constant for the purpose of LPRP calibration.
Since it is composed of a fission ionization chamber like RM, the sensitivity changes when it is used for a long time in the reactor. Therefore, except when used for calibration, measures are taken to prevent the sensitivity from being pulled out from the reactor pressure vessel 1.

However, the apparatus for pulling out the TIP from the high temperature and high pressure reactor is extremely complicated, and high mechanical accuracy is required to maintain the positional accuracy between the TIP and the LPRM to be calibrated. Therefore, the TIP and its driving device are expensive and the maintenance work is complicated. Further, since the calibration work requires insertion / removal of the TIP and a wide range of traveling operation, there is a certain limitation on the number of calibrations, which is one factor limiting the improvement in output measurement accuracy.

A technique for eliminating the need for such a traveling calibration detector has been developed (Japanese Patent Laid-Open No. 3-6569).
No. 6). In this technique, for example, as shown in FIG.
A plurality of fixed calibration detectors 11 are provided in the protective tube 4 at substantially equal intervals (a, b, c, d) corresponding to the PRM 5 arrangement (A, B, C, D). . Each of the calibration detectors 11 is composed of a γ-ray thermometer, and the LPRM calibration value is obtained from the temperature value based on the γ-ray intensity.

According to such a technique, the calibration detector 1
Since 1 is a fixed type, the complicated structure of the movable detector and the difficulty of operation are eliminated. But,
Even with this technique, the power distribution in the axial direction of the core can be measured by L
Since the PRM5 is used, improvement in measurement accuracy cannot always be expected, and the calibration detectors 11 are arranged at substantially equal intervals corresponding to the arrangement of LPRM5, and the measurement accuracy deteriorates by about 20% at the maximum.

The present invention has been made in view of the above circumstances, and requires no traveling device, is highly reliable, is low in cost, and is capable of highly accurately measuring the power distribution in the axial direction of the reactor core. The purpose is to provide a device.

[0013]

In order to achieve the above-mentioned object, a reactor power measuring apparatus according to the present invention is provided with a protective pipe penetrating along an axial direction in a core portion of a nuclear reactor, and A plurality of fixed-type neutron detectors as first output detectors are installed inside the protective tube at intervals in the axial direction, and inside the protective tube, if the radial position is different from the fixed-type neutron detector. Then, a larger number of γ-ray thermometers that also serve as the calibration means of the fixed type neutron detector and the second output detector than the fixed type neutron detector are provided at intervals over the entire axial direction of the core. It is characterized by fixed installation.

In the present invention, preferably, the γ-ray thermometers are arranged such that the intervals at the center position in the axial direction of the core are coarse and the intervals at the end portions in the same direction are closer than those at the center position in the same direction. It is a thing.

[0015]

According to the present invention, the output detector for detecting the reactor output is constituted not only by the fixed neutron detector but also by the γ-ray thermometer, so that the output detection data can be enriched and Since multiple γ-ray detectors were fixed at intervals over the entire length of the core, the power distribution in the core axis direction was obtained based on the output at each position of the γ-ray thermometer, and the range of output detection data collection could be expanded. Can be achieved. Therefore, the power distribution in the axial direction of the core can be measured with higher accuracy than in the conventional case. Further, since the traveling device is not required, the structure can be simplified, the operation can be facilitated, the reliability can be improved, and the cost can be further reduced.

In particular, in the case where the γ-ray thermometer is arranged such that the interval at the axial center position of the core is coarse and the interval at the end portion side in the same direction is set closer than the central position in the same direction, The accuracy of power distribution measurement can be improved at the axial end portion of the core where the power distribution is large.

The γ-ray thermometer is also used as a calibration for the fixed neutron detector simultaneously with the output detector. Since this γ-ray thermometer hardly changes the sensitivity, the relative neutron detector High reliability for calibration is obtained.
The absolute calibration of the detector output with respect to the total heat output of the nuclear reactor may be performed by the thermal balance of the nuclear reactor as in the conventional case.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic arrangement of the reactor power measuring device, and FIG. 2 shows a detailed arrangement. Also, in FIG.
An example of the output distribution obtained by this example is shown.

As shown in FIG. 1, in the reactor power measuring apparatus of this embodiment, a plurality of detector assemblies (only one body is shown in the figure) 23 are installed in a core 22 of a reactor pressure vessel 21. Has been done. In this detector assembly 23, a fixed neutron detector (LPRM) 25 composed of a fission ionization chamber is provided as a first output detector in a protective tube 24 penetrating the core, and a calibration means for this LPRM 25 is provided. A γ-ray thermometer 26 that also serves as a second output detector is provided.

The LPRM 25 is shown in FIGS.
4 along the axial direction of the protective tube 24 as shown by B, C, D
They are arranged at intervals in the body, and their outputs are input to the local output monitoring device 28 via the signal cable 27.

The γ-ray thermometer 26 has an L inside the protective tube.
Radial position is different from PRM25, and LPRM2
More than five, fixedly installed at intervals over the entire axial direction of the core 22. This γ-ray thermometer 26 is used for the core 22
The reactor output is measured based on the amount of heat generated by the γ-rays inside, and there is little sensitivity deterioration, and it is possible to perform self-calibration by having a calibration heater inside.
Therefore, the detector sensitivity calibration required in TIP is not required.

In this embodiment, a is shown in FIGS.
As indicated by i, the γ-ray thermometers 26 are arranged, for example, at 9 positions in one cladding tube 29 at intervals so as to constitute one γ-ray thermometer assembly 26A. And, the arrangement of the γ-ray thermometer 26 is such that the interval at the axial center position of the core 22 is rough, and the interval at the end portion (upper end portion and lower end portion) in the same direction is closer than that in the same direction. It is set. That is, as shown in FIG. 2 showing the distance from the bottom of the core, the interval on the upper end side (the interval between i and h) is 364 mm and the interval on the lower end side (the interval between a and b) is 309 mm. Space on the central side (Each space between b and h (about 454 to 474 mm))
Is set smaller than.

The output of the γ-ray thermometer 26 is input to the axial power distribution measuring device 30 and further the local power monitoring device 28.
It is designed to be input to.

The operation of this embodiment thus constructed will be described below by comparing the functions of the respective devices when the rated output of the reactor power is 100% in comparison with the conventional device.

That is, the average value of LPRM25 is used as in the conventional case for the measurement of the average output of the reactor, and it is used as a safety protection system that requires a fast response. 26 in total. In this case, as shown in FIG. 3 as an example of the core axial power distribution, the core 22 has a shape in which it is greatly lowered at the upper and lower ends. Since 9 intervals were set by setting the intervals at the rough position and the intervals at the upper end and the lower end closer than the center position in the same direction, the conventional example (4 or 8 at equal intervals) Compared with (installation), the root mean square error by the three-dimensional simulation calculation of the core is improved by about 20%, and the measurement can be performed with sufficient accuracy. This was confirmed by experiments. FIG. 3 shows an example of the axial power distribution of the reactor power obtained by this example.

According to the present embodiment described above, the system configuration,
Maintenance and configuration work can be simplified, labor can be saved and radiation exposure can be reduced, and highly accurate core axial power distribution can be measured.

Further, in the conventional apparatus shown in FIG. 4, when calibrating the outputs of LPRMs at four locations, the TIP is inserted into and removed from the furnace, and the calibration work cannot be performed frequently. According to the embodiment, by using the fixed γ-ray thermometer 26 in the reactor, the LPRM 25 can be calibrated at any time, and the moving device is not necessary, and the signal transmission cable is reduced. Is simplified and maintenance of the entire system is facilitated.

The present invention is not limited to the above embodiments, and various modifications and applications are possible. For example, in order to improve the accuracy of core axial power distribution measurement, a γ-ray thermometer 2
The number of 5 in the axial direction may be increased.

It is also possible to use the TIP guide tube in the conventional device. However, in that case, the number that can be installed is limited by the outer diameter of the TIP guide tube. Therefore, in order to increase the number of γ-ray thermometers 26 in the axial direction,
The inner diameter of the protective tube 24 accommodating the PRM 25 and the γ-ray thermometer 26 may be effectively used. As a result, it is possible to sufficiently install ten or more γ-ray thermometers 26. Further, if the accuracy of the three-dimensional simulation calculation of the core is improved, the same function can be realized even with a total of six γ-ray thermometers arranged at the four LPRM positions and the core upper and lower ends.

[0031]

As described above, according to the present invention, since the output detector for detecting the reactor output is constituted not only by the fixed neutron detector but also by the γ-ray thermometer, the output detection data Along with the enrichment, multiple γ-ray detectors were fixed at intervals over the entire length of the core, so the output distribution in the core axis direction was calculated based on the output at each position of the γ-ray thermometer. The detection data collection range can be expanded. Therefore, the power distribution in the axial direction of the core can be measured with higher accuracy than before. Further, since the traveling device is not required, the structure can be simplified, the operation can be facilitated, and the reliability can be improved, and the cost can be further reduced.

Further, when the γ-ray thermometer is arranged such that the interval at the axial center position of the core is set roughly and the interval on the end side in the same direction is set denser than the center position in the same direction, the output The power distribution measurement accuracy can be improved at the axial end portion of the core having a large distribution.

Further, the γ-ray thermometer also serves as a calibration of the fixed type neutron detector simultaneously with the output detector, and since this γ-ray thermometer hardly changes the sensitivity, the relative neutron detector High reliability for calibration is obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of axial arrangement of the γ-ray thermometer of FIG.

FIG. 3 is a diagram showing an example of a core axial power distribution according to the present embodiment.

FIG. 4 is a diagram showing a conventional example.

FIG. 5 is a diagram showing another conventional example.

[Explanation of symbols]

22 Core 24 Protective Tube 25 LPRM (Fixed Neutron Detector (First Output Detector)) 26 γ-Ray Thermometer (Second Output Detector)

Claims (2)

[Claims] 1. A protective tube penetrating along an axial direction in a core portion of a nuclear reactor, and a plurality of fixed neutron detectors as a first output detector are provided inside the protective tube, and the protective tube has an axial direction. The fixed neutron detector and the second output detector are used as the calibration means of the fixed neutron detector by making the radial position different from the fixed neutron detector inside the protective tube. A reactor output measuring device characterized in that a larger number of γ-ray thermometers than the fixed type neutron detector are fixedly installed at intervals over the entire axial direction of the core. 2. The arrangement of the γ-ray thermometer is characterized in that the interval at the axial center position of the core is set roughly and the interval at the end portion side in the same direction is set denser than the center position in the same direction. The reactor power measuring device according to claim 1.