JP3274904B2 - Reactor power measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a boiling water reactor (BW).
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor power measurement device applied to power measurement of a large core such as R), and more particularly to a reactor power measurement device which simplifies the configuration of a power detector and improves measurement accuracy.

[0002]

2. Description of the Related Art Conventionally, as a power measurement technology of a nuclear reactor,
A method in which multiple power detectors are loaded in the core and the output of all cores is calculated from the average value of the output signal values, and a method in which multiple power detectors are installed outside the core and the core power is calculated from the average power Are known. Generally, the former is BW
It is used for measuring the power of large cores such as R, and the latter is used for measuring the power of small cores.

FIG. 4 illustrates a conventional power measuring device employed in a BWR core. A plurality of detector assemblies (only one is shown in the figure) 3 are installed in a core 2 of the reactor pressure vessel 1. The detector assembly 3 has a configuration in which a fixed neutron detector (hereinafter, referred to as LPRM) 5 composed of a nuclear fission chamber is provided in a protective tube 4 penetrating the core. This LPRM 5 is, for example, A,
As shown by B, C and D, four units are arranged at predetermined intervals along the axial direction, and their outputs are input to an output monitoring device 8 via a signal cable 7 to measure and control the reactor power. Is performed.

The fission ionization chamber used as the LPRM 5 has a configuration in which a fissile substance (usually uranium 235 is used) is housed in a cladding tube, and the fissile substance absorbs neutrons and causes fission. An output signal is obtained by utilizing the gas ionization effect at the time. Therefore,
Use in a furnace reduces the amount of fissile material and the sensitivity of the detector changes gradually.

In order to cope with this change in sensitivity, conventionally, L
Means for calibrating the sensitivity of the PRM 5 is provided. The most frequently used calibration means is that a hollow guide tube 6 is provided in the protective tube 4 adjacent to the LPRM 5, and a movable neutron detector (hereinafter, referred to as a “calibration device”) for calibrating the sensitivity of the LPRM 5 is provided in the guide tube 6. 9 (referred to as TIP).
The TIP 9 is composed of a fission ionization chamber like the LPRM 5, 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. Thus, the output calibration of the LPRM 5 is performed. By performing this operation periodically for all the detector assemblies 3, the outputs of all the LPRMs 5 installed in the core 2 can be normalized to the TIP 9.

[0006]

Problems to be Solved by the Invention 1.1 million KW
In a BWR of the class, 172 LPRMs are usually loaded, and the same number of electronic devices and signal cables as LPRMs for processing the detection signals are installed. In addition, a large number of parts attached to these components, such as a conduit for protecting signal cables, a connector for connecting cables, and a monitoring panel for storing electronic devices, are required.

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

On the other hand, in the above-described TIP, it is necessary to keep the sensitivity constant for the purpose of LPRM calibration.
Since it is constituted by a fission ionization chamber like the RM, the sensitivity changes when used in a furnace for a long time. For this reason, measures are taken to prevent the sensitivity from being pulled out of the reactor pressure vessel 1 except when used for calibration.

[0009] However, an apparatus for extracting a TIP from a high-temperature and high-pressure reactor is extremely complicated, and high mechanical accuracy is required to maintain the positional accuracy with respect to the LPRM to be calibrated. Therefore, the TIP and its driving device are expensive, and the maintenance work is complicated. In addition, since the calibration work requires insertion and removal of the TIP and a wide range of traveling operations, there is a certain restriction on the number of calibrations, and this is one factor that limits the improvement in output measurement accuracy.

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

According to such a technique, the calibration detector 1
Since the fixed type 1 is used, the configuration of the movable detector described above is complicated, and the difficulty of operation is eliminated. But,
Also in this technique, the measurement of the power distribution in the core axis direction is L
Due to the use of the PRM 5, improvement in the measurement accuracy could not always be expected, and the arrangement of the calibration detectors 11 was set to be substantially equally spaced corresponding to the arrangement of the LPRM 5, so that the measurement accuracy was reduced by about 20% at the maximum.

The present invention has been made in view of the above circumstances, and eliminates the need for a traveling device, has a high reliability, is low in cost, and can accurately measure the power distribution in the axial direction of the reactor core. It is intended to provide a device.

[0013]

In order to achieve the above-mentioned object, a reactor power measuring apparatus according to the present invention comprises: a protective tube penetrating a reactor core along an axial direction; A plurality of fixed neutron detectors installed at predetermined intervals in the axial direction thereof, and the number of radial positions inside the protection tube is made different from that of the fixed neutron detector, so that the number is larger than that of the fixed neutron detector. The fixed neutron detector is installed, and the interval at the axial center position of the core portion is set coarsely, and the interval at the end portion in the same direction is set more densely than the central position in the same direction. And a γ-ray thermometer capable of performing the following.

[0014]

According to the present invention, not only a fixed neutron detector but also a γ-ray thermometer is used as the power detector for detecting the reactor power, thereby enriching the power detection data. Since multiple γ-ray detectors are fixed at predetermined intervals over the entire length of the core, the power distribution in the axial direction of the core is determined based on the output at each position of the γ-ray thermometer, and the range of power detection data collection is expanded. Can also be planned. Therefore, it is possible to measure the power distribution in the axial direction of the core with higher accuracy than before. In addition, since the traveling device is not required, the configuration can be simplified and the operation can be simplified, the reliability can be improved, and the cost can be reduced.

In particular, the arrangement of the γ-ray thermometers is set such that the intervals at the axial center of the core are set coarsely and the intervals at the end portions in the same direction are set closer than those in the same direction. In the core axial direction end portion having a large distribution, the power distribution measurement accuracy can be improved.

The γ-ray thermometer can be used simultaneously with the output detector for the calibration of a fixed neutron detector. Since the γ-ray thermometer hardly causes a change in sensitivity, the γ-ray thermometer has a relatively high sensitivity. High reliability for calibration is obtained.
Absolute calibration of the detector output with respect to the total heat output of the reactor may be performed by the heat balance of the reactor as in the past.

[0017]

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

FIG. 1 shows a schematic arrangement of a reactor power measuring apparatus, and FIG. 2 shows a detailed arrangement. Also, FIG.
An example of an output distribution obtained by the present embodiment is shown.

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

The LPRM 25 is shown in FIGS.
As shown by B, C, and D, 4
The body is arranged at a predetermined interval, and these outputs are input to a local output monitoring device 28 via a signal cable 27.

The gamma ray thermometer 26 is provided with L
LPRM2 with radial position different from PRM25
More than five are fixedly installed at predetermined intervals over the entire axial direction of the core 22. The γ-ray thermometer 26 measures the reactor power based on the calorific value generated by γ-rays in the reactor core 22. The γ-ray thermometer has little sensitivity deterioration and can be self-calibrated by having a calibration heater inside. Things. Therefore, the detector sensitivity calibration required for TIP is not required.

In this embodiment, FIGS. 1 and 2 show a
As shown by i, the γ-ray thermometers 26 are arranged at predetermined intervals, for example, at nine locations in one cladding tube 29 to constitute one γ-ray thermometer assembly 26A. And γ
The arrangement of the linear thermometer 26 is such that the interval at the axial center position of the reactor core 22 is set coarsely, and the interval at the end (upper end and lower end) side in the same direction is set closer than the center position in the same direction. is there. That is, as shown in FIG. 2, the distance from the bottom of the core is 364 mm at the upper end (the distance between i and h) and 309 mm at the lower end (the distance between a and b). Center-side interval (each interval between b to h (about 454 to 47
4 mm)).

The output of the γ-ray thermometer 26 is input to an axial power distribution measuring device 30, and a local power monitoring device 28
To be entered.

With respect to the operation of this embodiment having the above-described configuration, the function of each device at the time of rated output at a reactor power of 100% will be described below in comparison with the conventional device.

That is, the average value of the reactor is measured using the average value of the LPRM 25 in the same manner as in the prior art, and is used as a safety protection system that requires a fast response. The total is 26. In this case, as shown in an example of the core axial power distribution in FIG. 3, the shape of the core 22 is greatly reduced at the upper and lower ends thereof. In this embodiment, the γ-ray thermometer 26 is located at the axial center position of the core 22. In the conventional example (four or eight at equal intervals), the distances at the upper end and the lower end were set to be coarser than the center position in the same direction. Compared with the installation), the root-mean-square error by the core three-dimensional simulation calculation 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 according to the present embodiment.

According to the above embodiment, the system configuration,
Maintenance and configuration work are simplified, labor saving and reduction of exposure can be realized, and highly accurate measurement of core axial power distribution can be performed.

In the conventional apparatus shown in FIG. 4, when calibrating the output of four LPRMs, it is necessary to insert and withdraw the TIP into the furnace, and the calibration work cannot be performed frequently. According to the embodiment, the use of the fixed-in-furnace γ-ray thermometer 26 enables the calibration of the LPRM 25 at any time, eliminates the need for a moving device, reduces the number of signal transmission cables, and reduces the system configuration. Is simplified, and the maintenance of the entire system becomes easy.

The present invention is not limited to the above embodiment, but can be variously modified or applied. For example, in order to improve the accuracy of core axial power distribution measurement, a γ-ray thermometer 2
5 may be increased in the number in the axial direction.

It is also possible to use the TIP guide tube in the conventional device. However, in this case, the number of the TIP guide tubes that can be installed is limited by the outer diameter of the TIP guide tube.
The inner diameter of the protection tube 24 that houses the PRM 25 and the γ-ray thermometer 26 may be effectively used. Thereby, the installation of ten or more γ-ray thermometers 26 is sufficiently possible. Further, if the accuracy of the core three-dimensional simulation calculation is improved, the same function can be realized with a total of six γ-ray thermometers arranged at four LPRM positions and the upper and lower ends of the core.

[0030]

As described above, according to the present invention, not only a fixed neutron detector but also a γ-ray thermometer is used as an output detector for detecting a reactor output, so that output detection data can be obtained. Along with enrichment, the gamma-ray detectors were fixed at a predetermined interval over the entire length of the core,
The power distribution in the core axis direction is obtained based on the power at each position of the γ-ray thermometer, and the power detection data collection range can be expanded. Therefore, it is possible to measure the power distribution in the axial direction of the core with higher accuracy than before. Further, since the traveling device is not required, the configuration can be simplified, the operation can be simplified, the reliability can be improved, and the cost can be reduced.

Further, the arrangement of the γ-ray thermometers is set such that the interval at the axial center of the core is set to be coarse and the interval at the end portion in the same direction is set to be denser than the center in the same direction, so that the power distribution is improved. The power distribution measurement accuracy can be improved at the core axial end portion having a large power distribution.

Further, the γ-ray thermometer can be used simultaneously with the output detector for the calibration of the fixed neutron detector, and since the γ-ray thermometer hardly causes a change in sensitivity, the γ-ray thermometer has a relatively low sensitivity. High reliability for calibration is obtained.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an example of an 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 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 protection tube 25 LPRM (fixed neutron detector (first output detector)) 26 γ-ray thermometer (second output detector)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G21C 17/10

Claims (1)

(57) [Claims] 1. A protective tube penetrating in a core portion of a nuclear reactor along an axial direction, a plurality of fixed neutron detectors installed inside the protective tube at predetermined intervals in the axial direction, and the protective tube The radial position of the core is different from that of the fixed neutron detector and the number of the neutron detectors is larger than that of the fixed neutron detector, and the interval at the axial center position of the core is coarse and in the same direction. A reactor power measurement device, comprising: a γ-ray thermometer capable of calibrating the fixed-type neutron detector, wherein a gap at an end position is set more densely than a center position in the same direction.