JP2921923B2 - Radiation detector sensitivity calibration device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] [Industrial Application Field] The present invention relates to a plurality of radiation detectors used for measuring 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, a plurality of radiation detectors are provided on the inner wall of a cylindrical inspection table into which spent fuel rods are inserted along the fuel rod insertion direction, and the spent fuel rods are inserted into the inspection table. The radiation signals from the radiation detectors located at various positions in the axial direction of the fuel rod are measured, and the burnup distribution of the spent fuel rod is measured from the correlation between the outputs of the radiation detectors.

In such a radiation measuring apparatus, the measurement accuracy is determined by the relative sensitivities of a plurality of radiation detectors rather than the absolute sensitivities of the individual radiation detectors.

On the other hand, since the detection sensitivity of the radiation detector decreases with the passage of time, the radiation detector is periodically carried into a radiation source calibration room having a radiation source calibrated in advance, and the absolute sensitivity is calibrated (absolute comparison). Then, based on the absolute sensitivity obtained at the time of calibration, the correlation between the outputs of the radiation detectors was obtained to measure the burnup distribution.

However, since the periodic sensitivity calibration described above generally has a period of six months or more, an error due to a change in detection sensitivity during that period is included in the measured value. Also, if the sensitivity calibration cycle is made short enough to cope with changes in detection sensitivity,
The operating efficiency of the device itself is significantly reduced.

Furthermore, the above-described sensitivity calibration requires a high-intensity source as a source for sensitivity calibration, and also requires a complicated operation such as carrying a radiation detector into a source calibration room.

[Problems to be solved by the invention]

Therefore, the conventional sensitivity calibration performed on the radiation detector in the radiation measurement device as described above,
Complicated work such as loading the radiation detector into the radiation source calibration room is required, and it is not possible to respond sufficiently to changes in detection sensitivity, resulting in errors in the measurement values and accurate measurement values. There was a problem that it could not be done.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a radiation detector sensitivity calibration device capable of obtaining accurate measurement values sufficiently corresponding to changes in detection sensitivity without performing sensitivity calibration using a calibration facility such as a source calibration room. I do.

[Constitution of the Invention] [Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for installing a plurality of spent fuel rods along an axial direction of a spent fuel rod on an inspection table into which the spent fuel rods are inserted. In the radiation detector sensitivity calibration device that performs the sensitivity calibration of the detected radiation detector, when the spent fuel rod is moved in the axial direction and inserted into the inspection table, each detection output from each radiation detector Means for calculating the count rate indicating the sensitivity characteristic of each radiation detector by averaging each signal, and the radiation characteristic which is based on the sensitivity characteristic of any radiation detector calculated by this means. The difference between the counting rate of the detector and the counting rate of the other radiation detectors is defined as a relative sensitivity calibration constant, and the counting rate of each of the other radiation detectors is multiplied by each relative sensitivity calibration constant to calculate the relative sensitivity of each radiation detector. Correcting relative sensitivity Is obtained by and a sensitivity correction unit.

[Action]

Therefore, in the sensitivity calibration apparatus for a radiation detector of the present invention, by taking the above measures, the output from each radiation detector located at various positions in the axial direction of the spent fuel rod inserted into the inspection table is obtained. The detected signal is averaged for each position of the fuel rod in the axial direction, and the count rate indicating the sensitivity characteristic of each radiation detector is calculated. In the sensitivity correction means, with the sensitivity of any radiation detector as a reference, each difference between the reference rate of the radiation detector and the count rate of the other radiation detectors as relative sensitivity calibration constants,
The sensitivity correction of each radiation detector is performed by multiplying the count rate of each of the other radiation detectors 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〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a sensitivity calibration device according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an inspection table in which a cylindrical bottomed space is formed, and a plurality of γ-ray detectors 2 each forming a pair along the depth direction are provided on an inner wall forming the cylindrical space. (A1, A2), (B1, B2), (C1, C2), (D1, D2),
(E1, E2) and (F1, F2) are installed. This inspection table 1
A used fuel rod 4 supported by the handling mechanism 3 is inserted into the cylindrical space through an upper end opening. In addition, A to F shown in the figure are preset stop positions where the handling mechanism 3 stops when the spent fuel rod 4 is inserted.

Each γ-ray detector 2 is connected to the calculation unit 5. The arithmetic unit 5 includes a plurality of statistical processing circuits 6 to which the detection signals of the respective γ-ray detectors 2 are respectively input, and a pair of γ-ray detectors installed at the same depth position among the statistical processing circuits 6. A plurality of averaging circuits 7 for averaging the outputs corresponding to the respective 2 and calculating respective sensitivity characteristics indicated by the count rate; a recorder 8 for recording the output of each of the averaging circuits 7; The difference between the count rate of the γ-ray detector and the count rate of each of the other γ-ray detectors is determined based on the count rate of an arbitrary γ-ray detector from the output of each averaging processing circuit 7. It comprises a sensitivity correction unit 9 for multiplying the count rate of another γ-ray detector by each relative sensitivity calibration constant as a relative sensitivity calibration constant to calibrate the whole relative sensitivity.

Next, the operation of the present embodiment configured as described above will be described.

The spent fuel rod 4 for measuring the burnup distribution is inserted into the inspection table 1 while being stopped at the respective stop positions A to F by the handling mechanism 3. When the tip of the spent fuel rod 4 reaches each of the stop positions A to F, a detection signal detected by each γ-ray detector 2 is input to the statistical processing circuit 6. Performs statistical processing by the following equation in each of the statistical processing circuit 6 (1), and outputs the statistical processing results O _i.

O _i = n _i (1−e− ^τ ) (1) where n _i is a detection signal of each γ-ray detector 2, τ is a time constant (= 5000 / niσ ² ), and σ is a statistical variation. ing.

The statistical processing result O _i output from each statistical processing circuit 6 is:
It is input to the averaging processing circuit 7, where the average was treated by the following equation (2), and outputs the average value O _n of the statistical processing result.

O _n = (O _i1 + O _i2 ) / 2 (2) O _i1 and O _i2 indicate the results of statistical processing of the detection signals of the paired γ-ray detectors.

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

In the sensitivity correction unit 9, based on the sensitivity characteristics of each γ-ray detector shown in FIG. 2, for example, the γ-ray detectors (C1, C2) are used as a reference.
The difference L1 to L4 between the count rate of this γ-ray detector (C1, C2) and the count rate of another γ-ray detector is determined, and these L1 to L4 are used as relative sensitivity calibration constants of the corresponding detectors, respectively. The sensitivity is corrected by multiplying the γ-ray detector having a different sensitivity characteristic from the reference sensitivity characteristic by a relative sensitivity calibration constant.

Then, the burnup distribution of the spent fuel rod 4 is measured based on the data on which the sensitivity has been calibrated in this manner.

As described above, according to the present embodiment, when the spent fuel rod 4 is inserted while being stopped at each stop position, the difference in the counting rate measured by each of the γ-ray detectors 2 indicates that each of the γ-ray detectors is different. The sensitivity characteristics of the other γ-ray detectors are obtained by multiplying the difference of the count rate as a relative sensitivity calibration constant by multiplying this relative sensitivity calibration constant by using the sensitivity characteristic of an arbitrary γ-ray detector as a reference. Is calibrated, the relative sensitivity of a plurality of γ-ray detectors can be easily calibrated, and no special equipment such as a radiation source calibration room is required.

In addition, since such a sensitivity calibration can be performed in a very short time as compared with the absolute sensitivity calibration, the sensitivity can be sequentially calibrated in response to the sensitivity change without lowering the operation efficiency of the apparatus, and therefore, the sensitivity change can be performed. Preventing an error from being included in a measured value can improve measurement accuracy.

In the above embodiment, an example in which the sensitivity is automatically calibrated by the sensitivity calibrator 9 has been described. However, the operator manually performs the same sensitivity calibration as in the above embodiment based on the sensitivity characteristics displayed on the recorder 8. You can also.

[Effects of the Invention] As described in detail above, according to the present invention, accurate measurement values sufficiently corresponding to changes in detection sensitivity can be obtained without performing sensitivity calibration using a calibration facility such as a radiation source calibration room. And a sensitivity calibration device for the radiation detector capable of performing the above.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 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 rods, 5 ... Calculator, 6 ... Statistical processing circuit, 7 ... Averaging processing circuit, 8 ... ... recorder, 9 ...
... Sensitivity calibration unit.

Claims (1)

(57) [Claims] 1. A radiation detector sensitivity calibration device for calibrating the sensitivity of a plurality of radiation detectors installed along an axial direction of a spent fuel rod on an inspection table into which the spent fuel rod is inserted, When the spent fuel rod is moved in the axial direction and inserted into the inspection table, each detection signal output from each radiation detector is averaged to indicate the sensitivity characteristic of each radiation detector. Means for calculating the counting rate, based on the sensitivity characteristics of any radiation detector calculated by the means, the difference between the counting rate of the radiation detector and the counting rate of other radiation detectors as the reference, respectively A relative sensitivity calibration constant, sensitivity correction means for correcting the relative sensitivity of each radiation detector by multiplying each count rate of each of the other radiation detectors by each relative sensitivity calibration constant, and radiation. detection Sensitivity calibration device.