Method for measuring body source dose rate under strong line source interference

Abstract

The invention discloses a method for measuring a body source dose rate under strong line source interference. The method comprises the following steps: step 1, measuring a gamma dose rate Dair at the same height in a nearby non-pipeline interference area through a gamma dose rate monitor; 2, calculating to obtain a gamma dose rate contribution ratio as a constant k; 3, measuring gamma dose rate measured values M1 and M2 at h1 and h2 positions on the central axis of the pipeline through a gamma dose rate monitor; 4, the gamma dosage rate caused by the air in the monitoring area is evaluated according to the value k, the M1 and the M2, and rapid early warning is carried out. The gamma dosage rate caused by the ambient air can be obtained by changing the position of one gamma dosage rate monitor; according to the method, the problem that ambient air radioactivity early warning cannot be realized through a gamma dose rate instrument in a part of strong radioactive pipeline passing areas in a plant is solved, the monitoring cost of radioactive gas leakage in the plant can be expected to be reduced, and the monitoring timeliness is improved.

Description

Technical Field

[0001] The invention relates to the technical field of radiation detection, in particular to a method for measuring body source dose rate under strong line source interference. Background Art

[0002] Reactor operation produces many fission products and corrosion activation products. Due to leakage or discharge, the air in the reactor building, nuclear auxiliary building and fuel building may be contaminated by radioactivity. Therefore, the radioactivity of the air in these areas must be monitored.

[0003] Conventional monitoring methods in factories include radioactive aerosol monitoring, radioactive iodine monitoring, inert gas radioactivity measurement, and gamma dose rate monitoring. Among them, radioactive aerosol monitoring and radioactive iodine monitoring both use sampling methods, filtering the target sample onto filter paper, and then using a detector to measure the filter paper to obtain the activity concentration of the target sample; inert gas radioactivity measurement generally uses a small chamber sampling method, using a vacuum pump and a pipe to draw air into a small chamber for measurement. Due to the existence of the sampling process and the measurement process, the time to obtain the results of the above methods is usually at the level of several minutes to several hours. Gamma dose rate monitoring can achieve real-time online monitoring, and the time to obtain monitoring results is usually in seconds. However, due to the presence of highly radioactive loop pipes in many areas of the factory, the gamma dose rate measurement results are greatly affected by the loop pipes and can only be used for external exposure evaluation of personnel. It is impossible to characterize the radioactivity level in the air in the factory and warn of the occurrence of radioactive leaks. Summary of the invention

[0004] The object of the present invention is to provide a method for measuring body source dose rate under strong line source interference to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for measuring body source dose rate under strong line source interference, the method steps are as follows:

[0007] Step 1: Use a gamma dose rate monitor to measure the gamma dose rate D at the same height in a nearby area without pipeline interference. air ;

[0008] Step 2: Calculate the gamma dose rate contribution ratio as a constant k;

[0009] Step 3: Measure h on the central axis of the pipeline using a gamma dose rate monitor 1 and h 2 The gamma dose rate measured at position M 1 and M 2 ;

[0010] Step 4: According to k value, M 1 and M2 The measured values ​​evaluate the gamma dose rate caused by the air in the monitoring area and provide a rapid warning.

[0011] As a further solution of the present invention: the gamma dose rate D at the same height measured in step 1 is air Take the average value through multiple measurements.

[0012] As a further solution of the present invention: the calculation of the two constants k in the step:

[0013] The height of the radiation source to the center is h 0 The gamma dose rate contributed by 0 According to the inverse square formula of ray attenuation, the gamma dose rate contribution of the micro-point source at point x to the monitor with the center position h is:

[0014]

[0015] The total gamma dose rate at the center of the entire line source pair at a height of h is:

[0016]

[0017] Then, the height of the line source to the center is h 1 and h 2 The gamma dose rate contribution ratio at is a constant:

[0018]

[0019] As a further solution of the present invention: the gamma dose rate measurement values ​​at positions h1 and h2 in step 3 are M1 and M2 respectively, then:

[0020] D air +D 1 =M 1

[0021] D air +D 2 =M 2 (4)

[0022] Combining formula (3), we can get:

[0023]

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention can obtain the gamma dose rate caused by ambient air by changing the position of a gamma dose rate monitor. This method solves the problem that some areas in the factory where highly radioactive pipelines pass cannot be warned of ambient air radioactivity by a gamma dose rate meter. It is expected to reduce the monitoring cost of radioactive gas leakage in the factory and improve the timeliness of monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a pipeline equivalent line source for a method of measuring body source dose rate under strong line source interference.

[0027] Figure 2 This is a three-dimensional schematic diagram of the pipeline axis arranged at an angle of 2π. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] See also Figures 1-2 In an embodiment of the present invention, a method for measuring body source dose rate under strong line source interference is provided, and the method steps are as follows:

[0030] Step 1: Use a gamma dose rate monitor to measure the gamma dose rate D at the same height in a nearby area without pipeline interference. air ;

[0031] Step 2: Calculate the gamma dose rate contribution ratio as a constant k;

[0032] Step 3: Measure h on the central axis of the pipeline using a gamma dose rate monitor 1 and h 2 The gamma dose rate measured at position M 1 and M 2 ;

[0033] Step 4: According to k value, M 1 and M 2 The measured values ​​evaluate the gamma dose rate due to the air in the monitoring area.

[0034] The gamma dose rate D at the same height measured in step 1 is air The average value is obtained through multiple measurements, and a quick warning is issued.

[0035] The calculation of the constant k in the second step is:

[0036] When the reactor is in steady-state operation, the radioactivity level in the loop pipe is relatively stable. The pipes in the plant are equivalent to uniform line sources, which are composed of countless micro-point sources, such as Figure 1 As shown, the length of the pipeline is much larger than the diameter of the pipeline (more than 10 times), so it is equivalent to a line source.

[0037] The height h of the micro-point source at the origin to the center 0 The gamma dose rate contributed by 0 According to the inverse square formula of ray attenuation, the gamma dose rate contribution of the micro-point source at point x to the monitor with the center position h is:

[0038]

[0039] The total gamma dose rate at the center of the entire line source pair at a height of h is:

[0040]

[0041] Then, the height of the line source to the center is h 1 and h 2 The gamma dose rate contribution ratio at is a constant:

[0042]

[0043] The gamma dose rate measurement values ​​at positions h1 and h2 in step 3 are M1 and M2 respectively, then:

[0044] D air +D 1 =M 1

[0045] D air +D 2 =M 2 (4)

[0046] The factory corridor is approximately a cuboid. Assuming that the gaseous radioactive substances are evenly distributed in the cuboid, when the monitors are symmetrically located in the factory, the γ dose rates caused by the gaseous radioactive substances received by the monitors are the same, both D air Assume that h is the center axis of the pipeline. 1 and h 2 The gamma dose rate measurements at the locations are M1 and M2 respectively.

[0047] Combining formula (3), we can get:

[0048]

[0049] In the case of no leakage (for example, no radioactive leakage is found in other air radioactivity monitoring channels in the same area), the γ dose rate monitoring result at the same height in the nearby area without pipeline interference is taken as D air, we can calculate the value of k, and after multiple measurements, we can get the mean and standard deviation of k. 1 and M 2 The measured value evaluates the gamma dose rate caused by the air in the monitoring area, and the gamma dose rate meter is used to monitor the leakage of gaseous radioactive materials in the factory. By deducting the additional impact of the pipeline from the gamma dose rate monitoring results, the gamma dose rate intensity contributed by the air is directly obtained, thereby realizing the rapid identification of gaseous radioactive materials in the air.

[0050] Based on the above method, by changing the position of a gamma dose rate monitor (the gamma dose rate monitor is selected as much as possible on the central axis of the pipeline; the position of the gamma dose rate monitor is as symmetrical as possible inside the plant; a gamma dose rate monitor with high sensitivity is selected), the gamma dose rate caused by the ambient air can be obtained, thereby realizing a rapid early warning of radioactive leakage. The gamma dose rate monitor can continuously obtain the gamma dose rate caused by the ambient gas by cyclically measuring at two positions.

[0051] The implementation of this method is not limited to placing the gamma dose rate monitor on the central axis of the pipeline. In fact, the gamma dose rate ratio at different heights on the vertical axis at any point in the pipeline is a constant, such as Figure 2 As shown, the value of the constant can be obtained through formula (5). The derivation process of the formula is the same as Figure 1 The method shown is similar, but the calculation is more complicated, so Figure 1 The basic principle of this method is explained. Figure 2 In the figure, the circle formed by the dotted line indicates that the deployment range of the gamma dose rate monitor is 2π, and the plane where the circle formed by the dotted line is located is perpendicular to the axis. Taking the two solid arrows (pointing lines) corresponding to different deployment positions of the gamma dose rate monitor as an example, the two arrows respectively take the center of the circle formed by the dotted line as the starting point and point in the centrifugal direction. They are located in the plane where the circle formed by the dotted line is located and are perpendicular to the axis, but the angle between the two arrows is π / 2, which is equivalent to the deployment angle of the gamma dose rate monitor corresponding to one pointing line / arrow is 0, and the deployment angle of the gamma dose rate monitor corresponding to another pointing line / arrow is π / 2.

[0052] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring body source dose rate under strong line source interference, characterized in that: The method steps are as follows: Step 1: Use a gamma dose rate monitor to measure the gamma dose rate D at the same height in a nearby area without pipeline interference. air ; Step 2: Calculate the gamma dose rate contribution ratio as a constant k; Step 3: Measure the gamma dose rate values ​​M1 and M2 at the positions h1 and h2 on the central axis of the pipeline using a gamma dose rate monitor; Step 4: Evaluate the gamma dose rate caused by the air in the monitoring area based on the k value, M1 and M2 measurement values, and issue a rapid warning.

2. The method for measuring body source dose rate under strong line source interference according to claim 1, characterized in that: The gamma dose rate D at the same height measured in step 1 is air Take the average value through multiple measurements.

3. The method for measuring body source dose rate under strong line source interference according to claim 1, characterized in that: The calculation of the constant k in the second step is: The gamma dose rate contributed by the radiation source to the center height h0 is d0. According to the inverse square formula of ray attenuation, the gamma dose rate contribution of the micro-point source at point x to the monitor at the center position h is: The total gamma dose rate at the center of the entire line source pair at a height of h is: Then, the ratio of the gamma dose rate contribution of the line source to the center heights h1 and h2 is a constant:

4. The method for measuring body source dose rate under strong line source interference according to claim 1, characterized in that: The gamma dose rate measurement values ​​at positions h1 and h2 in step 3 are M1 and M2 respectively, then: D air +D1=M1 <h2 style=";text-align:left;direction:ltr">D<h2 style=";text-align:left;direction:ltr"> air <h2 style=";text-align:left;direction:ltr"> +D2=M2(4) Combining formula (3), we can get:

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