JPH0429083A - Sensitivity calibrator for radiation detector - Google Patents

Abstract

PURPOSE:To obtain an accurate measured value by setting the sensitivity of an arbitrary radiation detector calculated by performing the averaging processing of a detection signal outputted from the radiation detector as reference, and performing sensitivity correction setting the difference of a counting rate with that of another radiation detector as a calibration constant. CONSTITUTION:Plural gamma ray detectors 2(A1,A2)-(F1,F2) forming pairs in a depth direction are arranged on an inner wall forming cylindrical space. A used fuel rod 4 supported with a handling mechanism 3 is inserted from an aperture at the upper terminal of the cylindrical space to the space at an inspection board 1. The fuel rod 4 is inserted to the inspection board 1 while stepping at each of stopping positions A-F by the mechanism 3 in this configuration. When the tip of the fuel rod 4 arrives at the positions A-F, a signal detected by a detector 2 is inputted to a statistical processing circuit 6. The averaging processing is applied to a statistical processing result outputted from the circuit 6 at an averaging processing circuit 7. At a sensitive correction part 9, the sensitivity correction is performed setting the difference of the counting rate as the relative sensitivity calibration constant of each correspondent detector by setting, for example, a certain gamma ray detector as reference, and finding the difference between the counting rate of the gamma ray detector set as reference and that of another gamma ray detector.

Description

Detailed Description of the Invention [Objective of the Invention] [Field of Industrial Application] The present invention provides a plurality of radiation detectors used to measure the axial burnup distribution of spent fuel rods containing radioactivity. The present invention relates to a radiation detector sensitivity calibration device for calibrating the relative sensitivity of a radiation detector.

[Conventional technology]

Conventionally, multiple radiation detectors were installed along the insertion direction of the fuel rods on the inner wall of a cylindrical inspection table into which the spent fuel rods were inserted, and the spent fuel rods were inserted into the inspection table. ,
Radiation signals from each radiation detector located at various locations in the axial direction of the fuel rod are measured, and the burnup distribution of the spent fuel rod is measured from the correlation of the outputs of each radiation detector.

In such a radiation measurement device, measurement accuracy is determined by the relative sensitivity of a plurality of radiation detectors rather than the absolute sensitivity of each radiation detector.

On the other hand, since the detection sensitivity of radiation detectors decreases over time, the detectors are periodically transported to a radiation source calibration room with a pre-calibrated radiation source to calibrate the absolute sensitivity (absolute comparison).

Then, the burnup distribution was measured by determining the correlation between the outputs of each radiation detector based on the absolute sensitivity obtained during calibration.

However, since the above-mentioned periodic sensitivity calibration is generally performed at a cycle of six months or more, errors due to changes in detection sensitivity during that period are included in the measured values.

Furthermore, if the period of sensitivity calibration is shortened to the extent that it can accommodate changes in detection sensitivity, the operating efficiency of the apparatus itself will drop significantly.

Furthermore, the sensitivity calibration described above requires a radiation source with high radiation intensity as a radiation source for sensitivity calibration, and also requires complicated work such as transporting a radiation detector to a radiation source calibration room.

[Problems to be Solved by the Invention] Therefore, the conventional sensitivity calibration performed on the radiation detector in the radiation measuring device as described above requires a complicated work such as transporting the radiation detector to a radiation source calibration room. In addition, there were problems such as not being able to sufficiently respond to changes in detection sensitivity, resulting in errors being included in the measured values, making it impossible to obtain accurate measured values.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to obtain accurate measurement values that sufficiently correspond to changes in detection sensitivity without performing sensitivity calibration using a calibration facility such as a radiation source calibration room. The purpose of the present invention is to provide a radiation detector sensitivity calibration device that can perform the following steps.

C Configuration of the Invention] [Means for Solving the Problems] In order to solve the above problems, the present invention includes a plurality of spent fuel rods installed along the axial direction of the spent fuel rods on an inspection table into which the spent fuel rods are inserted. In a radiation detector sensitivity calibration device that calibrates the sensitivity of radiation detectors that have been used, when the spent fuel rod is moved in its axial direction and inserted into the inspection table, the radiation output from each radiation detector is Means for calculating each coefficient rate indicating the sensitivity characteristics of each radiation detector by averaging each detection signal, and using the sensitivity of an arbitrary radiation detector calculated by this means as a standard; The difference between the coefficient rate of the radiation detector and the coefficient rate of other radiation detectors is set as a relative sensitivity calibration constant, and each coefficient rate of the radiation detector with the above function is multiplied by each relative sensitivity calibration constant to calculate each radiation The configuration includes a sensitivity correction means for correcting the sensitivity of the detector.

[Effect]

By adopting the above-described measures, the present invention enables detection signals output from each radiation detector located at various locations in the axial direction of a used control rod inserted into an inspection table to Averaging processing is performed for each position, and a coefficient rate indicating the sensitivity characteristics of each radiation detector is calculated. In the sensitivity correction means, the sensitivity of an arbitrary radiation detector is used as a reference, each difference between the coefficient rate of the radiation detector used as the reference and the coefficient rate of other radiation detectors is used as a relative sensitivity calibration constant, and the other The sensitivity of each radiation detector is corrected by multiplying the coefficient rate of each radiation detector by each relative sensitivity calibration constant. As a result, the relative sensitivities of the plurality of radiation detectors are calibrated, and accurate measurement values can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a sensitivity calibration device that is an embodiment of the present invention. Reference numeral 1 shown in the figure is an examination table in which a cylindrical bottomed space is formed, and on the inner wall forming the cylindrical space, a plurality of γ-ray detectors 2 are arranged in pairs along the depth direction. (AI, A2).

(Bl, B2), (CI, C2), (DI, D2) (E
l, F2), (Fl, F2) are installed. A spent fuel rod 4 supported by a handling mechanism 3 is inserted into the cylindrical space of the inspection table 1 through its upper end opening. Note that A-F shown in the figure is a preset stopping position at which the handling mechanism 3 stops when inserting the spent fuel rod 4.

Each gamma ray detector 2 is connected to a calculation section 5. The calculation unit 5 includes a plurality of statistical processing circuits 6 into which the detection signals of the respective γ-ray detectors 2 are input, and γ-ray detection circuits installed at the same depth position among these statistical processing circuits 6 and forming a pair. Vessel 2
A plurality of averaging processing circuits 7 that calculate respective sensitivity characteristics expressed by coefficient rates by averaging the outputs corresponding to the respective outputs.
and a recorder 8 that records the output of each of these averaging processing circuits 7, and from the output of each averaging processing circuit 7, the counting rate of any γ-ray detector is determined based on the counting rate of that γ-ray detector. Sensitivity in which the overall relative sensitivity is calibrated by multiplying the counting rate of the other γ-ray detectors by each relative sensitivity calibration constant, using each difference from the counting rate of each other γ-ray detector as a relative sensitivity calibration constant. It is composed of a correction section 9.

Next, the operation of this embodiment configured in this manner will be explained.

A spent fuel rod 4 whose burnup distribution is to be measured is inserted into the inspection table 1 while being stopped at each stop position A to F by the handle mechanism 3. When the tip of the spent fuel rod 4 reaches each stop position A to F, a detection signal detected by each gamma ray detector 2 is inputted to the statistical processing circuit 6, respectively. Each statistical processing circuit 6 performs statistical processing using the following equation (1) and outputs the statistical processing result 01.

0 -n, (1-e-') ... (1
) Note that nl is the detection signal of each γ-ray detector 2, τ is the time constant (-5000/njσ2), and σ is the statistical fluctuation, respectively.

The statistical processing result O1 output from each statistical processing circuit 6 is
The signals are input to the averaging processing circuit 7, where they are averaged according to the following equation (2), and the average value Ofi of the statistical processing result is output.

0,, -(Oz+01□)/2 (2) Note that Oz, 0+□ indicates the result of statistical processing of the detection signal of the paired γ-ray detector.

In the recorder 8, based on the output from the averaging circuit 7,
The sensitivity characteristics of each γ-ray detector 2 as shown in FIG. 2 are recorded. That is, by detecting the radiation dose at the same location of the same spent fuel rod 4, the difference in detection sensitivity of each gamma ray detector is displayed as the difference in the counting rate.

The sensitivity correction unit 9 calculates the count rate and other values of the γ-ray detector (CI, C2) using the γ-ray detector (CI, C2) as a reference from the sensitivity characteristics of each γ-ray detector shown in FIG. Find the difference 1 to L4 in the counting rate with the gamma ray detector, and calculate the difference 1 to L4 in the counting rate
is the relative sensitivity calibration constant of each corresponding detector, and sensitivity correction is performed by multiplying the relative sensitivity calibration constant for γ-ray detectors whose characteristics differ from the sensitivity characteristics based on the above standard.

Then, the burnup distribution of the spent fuel rods 4 is measured based on the data whose sensitivity has been calibrated in this way.

As described above, according to this embodiment, when the spent fuel rods 4 are inserted while being stopped at each stop position, each gamma ray detector 2
The sensitivity characteristics of each γ-ray detector 2 are detected from the difference in the counting rate measured at Since the relative sensitivity of other gamma ray detectors is calibrated by multiplying by the calibration constant, relative sensitivity calibration of multiple gamma ray detectors can be easily performed, and special equipment such as a radiation source calibration room can be used. does not require.

In addition, since this type of sensitivity calibration can be performed in a much shorter time than absolute sensitivity calibration, it is possible to calibrate the sensitivity sequentially in response to sensitivity changes without reducing the operating efficiency of the device. Preventing errors from being included in measured values can improve measurement accuracy.

Although the above embodiment describes an example in which the sensitivity is automatically calibrated by the sensitivity calibration section 9, the configuration is such that the operator manually performs the sensitivity calibration similar to the above embodiment based on the sensitivity characteristics displayed on the recorder 8. You can also do that.

[Effects of the Invention] As detailed above, according to the present invention, accurate measurement values that sufficiently correspond to changes in detection sensitivity can be obtained without performing sensitivity calibration using a calibration facility such as a radiation source calibration room. It is possible to provide a sensitivity calibration device for a radiation detector that can perform the following steps.

FIG. 3 is a diagram showing sensitivity characteristics of each γ-ray detector.

DESCRIPTION OF SYMBOLS 1... Inspection table, 2... γ-ray detector, 3... Handling mechanism, 4... Spent fuel rod, 5... Arithmetic unit, 6... Statistical processing circuit, 7...・Average processing circuit, 8・
... Recorder, 9... Sensitivity calibration section.

Claims (1)

[Scope of Claims] A radiation detector sensitivity calibration device that calibrates the sensitivity of a plurality of radiation detectors installed along the axial direction of the spent fuel rods on an inspection table into which the spent fuel rods are inserted, When the spent fuel rod is moved in its axial direction and inserted into the inspection table, each detection signal output from each radiation detector is averaged and the sensitivity characteristics of each radiation detector are shown. A means for calculating the coefficient rate of a radiation detector, and a sensitivity characteristic of an arbitrary radiation detector calculated by this means as a standard, and the difference between the coefficient rate of the radiation detector used as the standard and the coefficient rate of other radiation detectors. and a sensitivity correction means for correcting the relative sensitivity of each radiation detector by multiplying the coefficient rate of each of the other radiation detectors by each relative sensitivity calibration constant. Radiation detector sensitivity calibration device.