WO2011102625A2

WO2011102625A2 - Method for searching for a reference radioactive waste drum to verify effectiveness of indirect calibration of a gamma scanner and method for verifying a calibration to extend life of standard radioactive material

Info

Publication number: WO2011102625A2
Application number: PCT/KR2011/000967
Authority: WO
Inventors: 정성엽
Original assignee: (주)성우이앤티
Priority date: 2010-02-19
Filing date: 2011-02-14
Publication date: 2011-08-25
Also published as: KR100979559B1; WO2011102625A3

Abstract

The present invention relates to a method for searching for a reference radioactive waste drum to verify the effectiveness of indirect calibration of a gamma scanner, and to a method for verifying a calibration. According to the present invention, calibration of a gamma scanner can be performed in a shortest time period to thereby prevent workers working in the relevant industrial fields from being exposed to radiation, and carry out calibration and calibration verifying work with minimum cost.

Description

Retrieval of reference radioactive waste drums for indirect calibration effectiveness of drum nuclide analysis device and calibration verification test method to maximize service life of standard radioactive materials

The present invention relates to a method for detecting and calibrating a reference radioactive waste drum. More specifically, the drum nuclide analysis device can be calibrated in the shortest time, thereby minimizing radiation exposure of workers and reducing costs. The present invention relates to a method for retrieval of reference radioactive waste drums for the indirect calibration validity of drum nuclide analysis equipment and to verify the calibration of the radionuclide.

In general, in order to measure an object to be measured using a precision measurement system, a valid measurement result that maintains traceability with a national standard representative body can be obtained by calibrating the system with a standard material representative of the measurement range. In general, when the measurement range is wide, the standard material having several representative values is calibrated, and the standard material approaching the upper limit or the lower limit of the measurement range is inevitably increased due to technical difficulty in manufacturing.

In the case of radioactive materials, not only technical difficulty but also the cost of safety management of manufactured standard materials (hereinafter referred to as standard radiation source) adds to the cost of use. In particular, in the case of highly radioactive standard radiation sources, it is inevitable to increase the safety management costs such as storage and handling of the produced isotopes along with technical problems such as the limitation of production facilities (required more than a certain size of experimental reactor), neutron beam control technology, and manufacturing time. Do. In addition, in the case of more than a certain quantity and concentration, the use of standard radioactive sources such as management by licensee and license or report of isotope is very strict and it is not easy to use. Calibration techniques are being developed recently.

Radionuclear drum nuclide analysis device (hereinafter referred to as drum nuclide analysis device) is a device that analyzes the radioactive amount of radioactive waste present in the drum in a non-destructive way to permanently dispose of radioactive waste generated from nuclear power plant. The radioactivity of radioactive waste drums is classified into low and high level radioactive wastes according to their contents, and the permanent disposal of low and low level wastes currently under construction in Gyeongju is limited to low and low level wastes. The measurement results of the drum nucleus analyzer are the basic data to confirm that the total radioactivity of the drum to be permanently disposed does not exceed the storage limit of the disposal facility. Therefore, a high degree of accuracy is required.

The analysis range of the drum nucleus analyzer in Korea is designed to measure all of them with a single detector for drums with a wide range of radiation dose from 0 to 100 mSv / hr based on surface dose in consideration of the radioactive level of wastes generated from nuclear power plants. . In the case of this device, a measurement range of 0 to 2 mSv / hr can be calibrated with a low-radiation standard radiation source, and a range of 2 mSv / hr to 100 mSv / hr can be calibrated using a high-radiation standard radiation source. In consideration of the safety of the use, a calibration technique that avoids high radiation standard radioactive sources is used.

In general, the problem with the measurement technique to extend the analysis range to the mid-level waste drum is the dead time correction of the detector. That is, the higher the radiation level of the object under test, the more accurate the dead time correction is, and the problem that the measurement accuracy deteriorates occurs. Techniques for overcoming this problem include a method of controlling the radioactivity concentration of the object under measurement, such as a partial sampling or dilution of the object, and a method of controlling the number of radiation incident into the detector, such as an aperture, a measurement distance, or a shield. It is distinguished by. In the case of the drum nucleus analyzer, the latter method of changing the measurement structure is used because the object to be measured cannot be processed.

Similarly, the drum nuclide analysis device installed in Korea changes the measurement distance (Near / Far) and the number of shields used (O: 0, A: 1, B: 2, C: 3), and the opening area of the aperture ( The combination of Wide / Narrow allows for a wide range of measurements with a single detector by altering the geometry. There are five types of geometric measurement structures: NOW (Drum Proximity), FON (Drum Spacer), FAN (Additional Measurement of Drum Spacer 1), FBN (Additional Measurement of Drum Spacer 2), FCN (Drum Spacer) 3 Additional measurements) can be performed in sequence from low level radioactive waste drums to medium level radioactive waste drums. For reference, the measurement structure of NOW means the use of proximity measurement-no shield window-wide aperture.

Since it is impossible to directly calibrate all five measurement structures with only a low-radiation standard radiation source, the direct and indirect calibration methods are performed in parallel. To explain this in more detail, the low level measurement structure (NOW) uses direct calibration using a standard radiation source (uniform radiation source) and a calibration drum (homogeneous medium), and then uses a direct calibration method to determine the efficiency of the detector. The structure is a combination of direct and indirect calibration methods that calculate the efficiency of the detector using some direct measurements and density correction factors and shield plate correction factors. Both direct and indirect calibration methods perform calibration checks to complete calibration. As the scope of indirect calibration increases, the technical difficulty and procedures of calibration checks increase.

The calibration verification test is a test to verify the validity of the calibration. It is the final procedure and a necessary condition of the calibration. In the case of the direct calibration method, the calibration can be completed only by the absolute calibration check which directly compares the certified radioactivity of the standard radiation source with the measurement result, and no technical problem occurs. On the other hand, in the case of direct and indirect calibration, the validity of the calculated efficiency should be verified by combining the absolute calibration check and the relative calibration check, and the reference radioactive waste drum to replace the high radioactive standard radiation source should be selected in advance. . The reference radioactive waste drum must meet three conditions: first, homogeneity of radioactive material, second, suitable radioactive concentration for the comparative group of measurement targets, and third, homogeneous medium of drum contents. . In addition, these verification tests should be confirmed in a short time using non-destructive methods using simple tools. The problem is described in more detail below.

In general, the distribution and medium of the radiation source of a radioactive waste drum is non-uniform and heterogeneous. In addition, because the object to be measured is relatively large compared to the detector, the analysis cannot be completed in a single measurement. In order to overcome this problem, it adopts a method of dividing and measuring the measured object in the vertical direction, and minimizes the non-uniformity and inhomogeneity by measuring by rotating the object to be measured in the circumferential direction. However, in order to calibrate a device or perform a calibration check, a calibration tool with uniformity of a radiation source and homogeneity of a medium is required as described above. Detailed conditions of reference radioactive waste are as follows: First, the distribution of reference nuclides (Cs-137 and Co-60) in the drum should be uniform. Second, it should be confirmed that the concentration of the reference nuclide is a measurable radiation concentration for all the groups of measurement structures to be compared. Third, the drum medium should be homogeneous so that the radiation generated inside the drum is uniformly attenuated so that the count rate of gamma rays observed from outside the drum should be kept constant. In addition, since radioactive waste drums are stored densely in limited spaces, the radioactive waste drums must be selected quickly with a simple tool to minimize the radiation exposure of the operator, and the drum itself is the first barrier against the release of radioactive materials. As a result, non-destructive methods that do not damage the drum are required. Therefore, continuous research is required to ensure that the reference radioactive waste drum is searched and verified through a safe and efficient method.

The present invention has been made to solve the above problems of the prior art, by minimizing the exposure of the radiation exposure to the worker by inspecting the calibration of the drum nuclide analysis device in the shortest time, while reducing the cost of the test progress The aim of the present invention is to provide a method for screening the reference radioactive waste drum for the indirect calibration validity test of the drum nuclide analysis device and to provide a calibration and verification method for maximizing the service life of the standard radioactive material.

In order to achieve the above object, the present invention includes a first step of measuring the dead time or dose rate by inserting a low-radiation standard radiation source in the calibration drum through one or more portable measuring instruments; A second step of selecting one of the plurality of portable measuring instruments as a reference portable measuring instrument and calculating a sensitivity correction factor CF _Ri therefrom; A third step of calculating a position correction factor (CF _Si ) by measuring a dead time or a dose rate according to the position of the equally divided section of the calibration drum through the portable measuring device; Measurement group dead time or dose rate correction factor of the calibration drum by using the average dose rate of the optimized drum surface in the group that performed the absolute calibration test and the average dose rate of the drum surface in the group that performed the relative calibration test ( Calculating a CF _Gi ); A fifth step of calculating a dead time or a dose rate τ _Oi of the relative calibration check group through the dead time or dose rate correction factor and selecting a corresponding radioactive waste drum; The dead time or dose rate was measured using the portable measuring device for the entire equal division section of the drum selected in the fifth step, and then the positional correction factor was applied to each section to normalize the measured dead time or dose rate. A sixth step of selecting a drum having a relative ratio of 1 for the entire divided section by calculating a relative ratio based on a measurement result of one section of the standardized dead time; And performing a spectroscopic analysis on the selected drum using the portable measuring instrument or the drum nuclide analysis device to determine whether a reference nuclide is present and to select the reference radioactive waste drum.

In another aspect, the present invention, the method for checking the calibration confirmation of the standard radioactive source and the reference radioactive waste drum exceeding the recommended period of use, the first step of reducing the scope of performing the absolute calibration check to only the low-level measurement structure; A second step of performing a relative calibration check on the measurement structure group of the absolute calibration check and the measurement structure group of the relative calibration check performed when the scope of the relative calibration check test does not exceed the recommended period of use; In the second step, the configuration of the measurement structure corresponding to performing the relative calibration check may include some measurement structures that pass the absolute calibration check or some measurement structures that pass the previous relative calibration check.

As described above, the calibration check test method for maximizing the use period of the reference radioactive waste drum and the standard radioactive material for indirect calibration validation of the drum nuclide analysis device according to the present invention is a low radioactivity standard used for the absolute calibration check test. Using the radiation source and the calibration drum, measure the dead time or radiation dose rate of the portable measuring instrument, and measure the measurement result of the portable measuring instrument through the sensitivity correction factor of the portable measuring instrument, the position correction factor of the drum division, and the dead time correction factor of the measuring structure. Using the results of calculating the optimum dead time or the radiation dose of the relative calibration check measurement group, the drum with the optimal radioactivity concentration is selected, and the uniformity and medium of the radiation source using the relative ratio to the drum division section. By providing a method for selecting a reference radioactive waste drum with homogeneity of It does not require a separate calibration of the surrogate, it can be checked in a short time with less than a few minutes of measurement time per drum, and can quickly determine the state of the waste drum without the permeation test using the conventional radioisotope used to check the homogeneity of the medium. Make the decision.

1 is a view schematically showing a dead time measuring structure using a portable measuring device in the present invention.

2 is a view schematically showing a dead time measurement structure for the position of the drum equal division section in the present invention.

Hereinafter, with reference to the drawings will be described the calibration check test method for maximizing the use of the reference radioactive waste retrieval and standard radioactive material for the drum nuclide analysis device indirect calibration validation test according to the present invention.

The reference radioactive waste drum search method for indirect calibration validity checking of the drum nuclide analysis device according to the present invention basically includes a first step of measuring a dead time (dose rate) after inserting a low radioactive standard radiation source into a calibration drum, and a plurality of The second step of calculating the sensitivity correction factor (CF _Ri ) from the reference portable meter of the portable measuring device, and calculates the position correction factor (CF _Si ) by measuring the dead time (dose rate) according to the position of the equally divided section of the calibration drum Dead time (dose rate) correction factor of the calibration drum measurement group using the third step and the average drum surface dose rate in the group that performed the absolute calibration check and the average drum surface dose rate in the group that performed the relative calibration test (CF _Gi) for calculating a fourth step, a dead time (dose rate), correction factor (CF _Gi) by using the calculated dead time (dose rate) of the relative correction check test group (τ _Oi) how to The fifth step of screening the dead waste drums and the dead time (dose rate) were measured for the entire equal division section of the sorted drums, and then standardized them using the position correction factor, and the measurement results of the 1 section of the standardized dead time. The sixth step of selecting a drum having a relative ratio of 1 for all divided sections by calculating the relative ratio, and determining the presence of the reference nuclide through the spectroscopic analysis of the selected drum to select the reference radioactive waste drum The seventh step is made.

In the first step, when the analysis formats of the drum nuclide analysis apparatus are various (the domestic drum nuclide analysis apparatus supports the TGS (Tomographic Gamma Scanner) and the SGS (Segment Gamma Scanner) analysis formats) density suitable for all analysis formats (about 0.5 g) After inserting a low-radiation standard radiation source into a calibration drum having a / cc) and measuring a dead time or dose rate using a portable measuring instrument while maintaining a predetermined separation distance at the middle height of the drum as shown in FIG. If multiple handheld meters are used, the dead time is measured after placing the handheld meter in the symmetrical direction at the same height and separation distance. Rotating the drum during the measurement can further increase the uniformity of the source. The portable measuring instrument may be a conventional radiation dose rate measuring instrument, portable scintillation detector, and the like.

In the second step, when the measurement of the first step is completed, one of the plurality of portable measuring instruments is selected as a reference portable measuring instrument, and the sensitivity correction factor CF _Ri of the portable measuring instrument is calculated using the following equation. If you are using a single handheld meter, you can skip this step.

(Where CF _Ri is the sensitivity correction factor for the i-th handheld meter, τ _i is the dead time or dose rate of the i-th handheld meter, and τ _r means the dead time or dose rate of the reference handheld meter.)

The third stage, since, depending on the location of evenly divided sections of the drum different from the exposed section of the radiation source, which is incident to a portable meter this standardization (Normalization) two euros required position correction factor (CF _Si) in order to, used in the first step as it is shown in FIG using orthodontic drum and the low radiation standard radiation source 2 to measure the dead time or the dose rate according to the position of the drum evenly divided section calculates a position correction factor (CF _Si) using the following equation. At this time, the drum and the portable measuring instrument measure each stage while maintaining a predetermined distance (same as step 1), and the standard radiation source and the calibration drum here are only homogeneous and homogeneous drums, so they measure only 1 ~ 4 stages of symmetrical structure. Position correction factors for the remaining 5 ~ 8 steps input the measurement results for 4 ~ 1 step in order.

Where CF _Si is the position correction factor for stage i, τ _Si is the dead time or dose rate of the handheld instrument for stage i, and τ _s4 is the dead time or dose rate of the handheld instrument for four stages (drum center height). it means.)

In the fourth step, a correction factor of the measurement structure group (CF _Gi) is obtained by using the average of the drum surface dose rates optimized for the group performing the absolute calibration check and the average of the drum surface dose rates optimized for the group performing the relative calibration check. ) Is calculated according to the following equation. In addition, since the intensity of the standard radiation source decreases when the standard radiation source with one half-life is used due to the physical half-life of the low-radiation standard radiation source, the scope of the absolute calibration check may be reduced and the relative calibration check group may be changed to two or more. . Therefore, this correction factor CF _Gi is calculated for the number of relative calibration check groups. Using this correction factor CF _Gi , it is possible to calculate the optimal dead time or dose rate of the group performing the relative calibration check.

Where CF _Gi is the dead time or dose rate correction factor of the ith relative calibration test group,

Is the average of the drum surface dose rate optimized for the absolute calibration test group,

Is the average of the drum surface dose rate optimized for the i-th relative verification test group.)

In the fifth step, after the preparation process from the first to the fourth step is completed, the dead time or the dose rate τ _Oi suitable for the relative calibration check group is calculated using the following equation. The same condition as the position measured in step 1 (middle drum height and separation distance), limited to radioactive waste drums similar to the density of the calibration drum (approximately 0.5 g / cc; drum weight approx. 100 kg for 200 liter drums). By measuring the dead time or dose rate of the drum in the drum and select a drum having a dead time or dose rate suitable for the relative calibration check. At this time, the calculated dead time or dose rate is determined by considering the range of measurement uncertainty. If there are two or more groups of relative calibration checks, the optimal dead time corresponding to the number of groups is calculated and the drums are sorted. Through this process, the selected drum can be confirmed that the radiation concentration suitable for the group.

Where τ _Oi is the optimized dead time or dose rate of the i th relative calibration test group, τ _r is the dead time or dose rate measured using a low-radiation standard radiation source and calibration drum, and CF _Gi is the i th relative calibration Dead time or dose rate correction factor of the confirmatory test group.)

In the sixth step, only the drum selected in the fifth step, the dead time or dose rate is measured with respect to the drum equalization section using a portable measuring instrument at the same separation distance as the first step. In this measurement, however, all divisions from the first to eighth stages of the drum are measured. Standardize the measured dead time or dose rate by applying the position correction factor (CF _Si ) to each stage using the following equation. Standardized dead time is calculated as relative ratio based on the result of 1st stage measurement, and drums with a relative ratio of 1 for all divided sections are selected. The selection criteria then determine that a drum having a relative ratio within this interval, including the uncertainty of measurement, is suitable. Through this process it is possible to check the uniformity of the radiation source of the drum and the homogeneity of the medium at the same time.

(Where τ _Ci is the dead time or dose rate of the standardized stage i, τ _r is the dead time measurement result of the handheld meter for stage i, and CF _Si is the position correction factor for stage i).

(Where R _i is the relative ratio of the standardized dead time or dose rate at stage i, τ _Ci is the standardized dead time or dose rate at stage i, and τ _C1 is the standardized dead time or dose rate at stage 1).

In the seventh step, the presence or absence of reference species Cs-137 and Co-60 may be determined by performing simple spectroscopic analysis on the drum selected through the first to sixth steps using a portable measuring instrument or a drum nuclide analysis device. And, consequently, the final reference radioactive waste drum.

When the dead time or dose rate is simultaneously measured for the drum equal division using a plurality of portable measuring instruments, the measurement time for this search can be shortened by adding the sensitivity correction factor of the portable measuring apparatus as shown in the following equation.

(Where τ _Ci is the dead time or dose rate of standardized stage i, CF _Si is the positional correction factor for stage i, and CF _Ri is the sensitivity calibration factor of the portable measuring instrument used to measure dead time or dose rate of stage i).

Drum radionuclide analysis device according to the present invention can be selected by the reference radioactive waste drum search method for the indirect calibration validity test very easily to perform the calibration and calibration verification according to the present invention described below The use of inspection methods can extend the service life of low-radiation standard radioactive sources, thereby reducing the cost of screening and verifying the reference radioactive waste drums.

The duration of use of standard radioactive sources for calibration is finite because they naturally decrease due to the inherent half-life of radionuclides. The general recommended service life is up to one half-life of the nuclides included in the source. If the recommended service life is exceeded, repurchase it. In particular, the reference source of the drum nucleus analyzer was Cs-137 and Co-60, and the shortest half-life was 5 years. For this reason, the standard radiation source used to calibrate the drum nucleus analyzer should be purchased and calibrated every five years. However, by using the calibration check test method according to the present invention, even if the service period of the standard radiation source is exceeded, it is possible to reduce the absolute calibration check test and extend the relative calibration check test to increase the service life while maintaining the same calibration accuracy. Can be. Table 1 shows the calibration verification test methods that change according to the recommended period of use.

Hereinafter, with reference to Table 1 will be described in more detail with respect to the calibration confirmation test method (two expressions) of the present invention.

Table 1-Calibration verification method for extending the service life of standard radiation sources

In the first step, an absolute calibration check is performed on a low level measurement structure using a low radiation standard radiation source and a calibration drum. At this time, because the recommended period of use of standard radioactive material, which is a standard radioactive material, is exceeded, the measurement structure (TGS-NOW, SGS-NOW) of the absolute calibration check is limited to low level use only. The acceptance criteria of this test shall be the same as the one used in the same accuracy criteria (deviation less than 10%).

In the second step, the two types of relative calibration checks are performed by the measurement structure group (TGS-NOW, SGS-NOW, TGS-FON, and SGS-) which performs the first absolute calibration check in one meal (before the recommended period of use). FON) and 1st group relative calibration check and 2nd group relative calibration for the measurement structure group (TGS-FON, SGS-FON, SGS-FAN, SGS-FBN and SGS-FCN). Perform a relative calibration confirmation test consisting of a confirmation test. The structure of the measurement structure for performing the relative calibration check may be a part of the measurement structure (TGS-NOW, SGS-NOW) that passed the first absolute calibration check or a part of the measurement structure (TGS-NO that passed the first relative calibration check). FON, SGS-FON, SGS-FAN, SGS-FBN, and SGS-FCN) must be included, and the same reference radioactive waste drum is repeatedly measured against the group's measurement structure so that the deviations of all measurement structures meet the following criteria: If satisfied, complete the calibration.

-Group 1 relative calibration confirmation test: measurement deviation ± 20% or less (average of the accuracy of the first absolute calibration confirmation test of the formula 1 and the accuracy of the first relative calibration confirmation test)

-Group 2 relative calibration confirmation test: measurement deviation ± 30% or less (same as the accuracy of the first relative calibration confirmation test of Formula 1)

Calibration method for the detection of the reference radioactive waste drum and the use of standard radioactive material for maximizing the use period of the standard radioactive material for the indirect calibration validity of the drum nucleus analysis device according to the present invention. The dead time or radiation dose rate of the portable measuring instrument is measured by using the sensor, and the measurement result of the portable measuring instrument is standardized through the sensitivity correction factor of the portable measuring instrument, the position correction factor of the drum division, and the dead time correction factor of the measuring structure. Using the result of calculating the optimal dead time or radiation dose of the calibration check measurement group, the drum having the optimal radioactivity concentration is selected, and the standard having the uniformity of the radiation source and the homogeneity of the medium by using the relative ratio to the drum division section. By providing a method for selecting radioactive waste drums, It does not require calibration, and it can be checked in a short time with less than a few minutes per drum measurement, and it is possible to quickly determine the condition of the waste drum without permeation test using the existing radioisotope used for the homogeneity of the medium. do.

Claims

Inserting a low-radiation standard radiation source into a calibration drum and measuring a dead time or dose rate through one or more portable measuring instruments;

A second step of selecting one of the plurality of portable measuring instruments as a reference portable measuring instrument and calculating a sensitivity correction factor CF Ri therefrom;

A third step of calculating a position correction factor (CF Si ) by measuring a dead time or a dose rate according to the position of the equally divided section of the calibration drum through the portable measuring device;

Using the mean of the drum surface dose rate in the group performing the absolute calibration check and the mean of the drum surface dose rate in the group performing the relative calibration test, the dead time or dose rate correction factor CF Gi of the measuring drum was determined. A fourth step of calculating;

A fifth step of selecting a radioactive waste drum corresponding to the dead time or the dose rate τ Oi of the relative calibration test group by using the dead time or the dose rate correction factor CF Gi ;

The dead time or the dose rate was measured using the portable measuring device for the entire equal division section of the drum selected in the fifth step, and then the dead time or the measured dead time was applied by applying the position correction factor (CF Si ) to each section. A sixth step of standardizing the dose rate, calculating a relative ratio based on the measurement result of one section of the standardized dead time, and selecting drums having a relative ratio of 1 for the entire divided section;

A seventh step of determining whether a reference nuclide is present by performing a spectroscopic analysis on the selected drum using the portable measuring instrument or the drum nuclide analysis device. How to find a waste drum.
The method according to claim 1,

When using a plurality of the portable meter, the standardized dead time (τ Ci ),

Where τ Ci is the dead time or dose rate of the standardized stage i, CF Si is the positional correction factor for stage i, CF Ri is the sensitivity correction factor of the portable measuring instrument used to measure the dead time or dose rate of stage i , τ i Is the dead time or dose rate of the i th meter

A reference radioactive waste drum retrieval method for drum nuclide analysis device indirect calibration validity check, characterized in that taken by.
In the inspection method for confirming the calibration using a standard radioactive source to the reference radioactive waste drum retrieved according to claim 1 or 2,

A first step of reducing the scope of the absolute calibration check using only a standard radiation source whose recommended period of use has been exceeded to only a low level measurement structure;

A second step of performing a relative calibration check on the measurement structure group of the absolute calibration check test and the measurement structure group of the relative calibration check test performed when the scope of the relative calibration check test does not exceed the recommended period of use; Understand,

In the second step, the configuration of the measurement structure corresponding to performing the relative calibration check may include some measurement structures that pass the absolute calibration check of the first step or some measurement structures that pass the previous relative calibration check. Calibration check method to maximize the use period of standard radioactive material.