Radioactive waste dose rate measuring method based on multimode measurement

Abstract

The invention discloses a radioactive waste dose rate measuring method based on multimode measurement. The method comprises the steps that radioactive waste is clamped into a shielding groove of a detection table; using a thallium-doped sodium iodide gamma spectrometer of the detector to perform dose rate measurement on the radioactive waste to obtain a first measurement value, and if the first measurement value is smaller than or equal to a preset dose rate switching threshold value, taking the first measurement value as a measurement result; and if the first measurement value is greater than a preset dose rate switching threshold value, performing dose rate measurement on the radioactive waste by adopting a GM tube detection unit of the detector to obtain a second measurement value, and taking the second measurement value as a measurement result. Wide-range measurement of the radioactive waste dose rate is realized based on multimode measurement, and dose rate measurement in a wide-range range of 0.01 [mu] Gy / h-100 mGy / h can be realized by adopting a double-detector working mode of the thallium-doped sodium iodide gamma spectrometer and the GM tube detection unit.

Description

Technical Field

[0001] The invention relates to the technical field of radioactive material processing, and in particular to a radioactive waste dose rate measurement method based on multi-mode measurement. Background Art

[0002] Minimizing radioactive waste is one of the key factors for the sustainable development of the nuclear industry. It can reduce the burden of radioactive waste treatment and disposal in nuclear power plants and ensure good human health and ecological environment. Radioactive waste sorting is a practical activity based on the characterization of radioactive waste sources (mainly achieved through measurement) to provide appropriate waste differentiation for subsequent management links according to the chemical, physical, biological and radioactive characteristics of radioactive waste. Radioactive waste sorting is a requirement and important means to achieve waste minimization, a need for classified treatment and disposal of radioactive materials, and an effective means to achieve classified treatment and disposal of radioactive waste generated in all links of waste generation based on radioactive waste measurement technology.

[0003] The measurement of specific activity of radioactive waste is crucial for radioactive waste management. Specific activity, that is, the radioactivity of a certain nuclide contained in a unit mass of product, is an important parameter for measuring radioactive waste. According to the measurement results of specific activity, radioactive waste can be divided into categories such as low-level waste, intermediate-level waste and high-level waste. Different types of waste require different management and disposal measures to ensure safety and minimize environmental impact. When the proportion of the main gamma nuclides and their specific activity concentrations in the waste is known, the control value of the specific activity concentration per unit surface of the waste gamma is calculated by the specific activity concentration limit of each nuclide, so that the radioactivity level of the waste can be determined by measuring the gamma surface contamination level. In theory, there should be a positive correlation between the gamma dose rate on the waste surface and the gamma surface specific activity concentration. The surface specific activity concentration can be inferred by measuring the surface dose rate, that is, the radioactivity level of the waste can be directly determined by measuring the surface dose rate of the waste, and preliminary screening can be performed before sorting the radioactive waste to improve the sorting efficiency. It is difficult to achieve a dose rate test range of 0.1 μSv / h to 100 mSv / h in the prior art. Therefore, providing a method for expanding the measurement of radioactive waste dose rate has become a technical problem that needs to be solved urgently in the relevant technical field. Summary of the invention

[0004] The object of the present invention is to provide a method for measuring radioactive waste dose rate based on multi-mode measurement, so as to at least solve some of the above technical problems.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A radioactive waste dose rate measurement method based on multi-mode measurement includes S1, clamping the radioactive waste into a shielding slot of a detection table;

[0007] S2. The detector under the shielding slot starts dose rate measurement: the thallium-doped sodium iodide gamma spectrometer of the detector is used to measure the dose rate of the radioactive waste to obtain a first measurement value. If the first measurement value is less than or equal to a preset dose rate switching threshold, the first measurement value is used as the measurement result; if the first measurement value is greater than the preset dose rate switching threshold, the GM tube detection unit of the detector is used to measure the dose rate of the radioactive waste to obtain a second measurement value, and the second measurement value is used as the measurement result.

[0008] In some embodiments of the present invention, the dose rate switching threshold is determined by measuring the dose rate linear range of the thallium-doped sodium iodide gamma spectrometer and the GM tube detection unit.

[0009] In some embodiments of the present invention, the thallium-doped sodium iodide gamma spectrometer is a thallium-doped sodium iodide crystal.

[0010] In some embodiments of the present invention, the crystal size of the thallium-doped sodium iodide crystal is φ50 mm×50 mm.

[0011] In some embodiments of the present invention, the GM tube detection unit includes a plurality of GM counter tubes.

[0012] In some embodiments of the present invention, the GM counter tube of the multi-segment GM counter tube adopts a metal cathode GM counter tube.

[0013] In some embodiments of the present invention, the multi-stage GM counter tube includes a high-range GM counter tube, a mid-range GM counter tube and a low-range GM counter tube.

[0014] In some embodiments of the present invention, the multi-segment GM counter tubes of the detector are used to measure the dose rate of radioactive waste to obtain the second measurement value, which includes: a high-range GM counter tube, a medium-range GM counter tube and a low-range GM counter tube perform multi-channel counting capture respectively, and then adaptively weight the multi-channel captured count values ​​to obtain the second measurement value.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention realizes wide-range measurement of radioactive waste dose rate based on multi-mode measurement, specifically adopts a dual-detector working mode of a thallium-doped sodium iodide gamma spectrometer plus a GM tube detection unit, obtains dose rate data through the thallium-doped sodium iodide gamma spectrometer in low-level radioactivity measurement, and obtains dose rate data through the GM tube detection unit in high-level radioactivity measurement, thereby realizing dose rate measurement in a wide range of 0.01 μGy / h to 100 mGy / h, and widening the dose rate range. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a flow chart of the method of the present invention.

[0018] Figure 2 The dose rate response curve of the thallium-doped sodium iodide gamma spectrometer of the present invention is shown in FIG.

[0019] Figure 3 This is the dose rate response curve of the GM tube detection unit of the present invention.

[0020] Figure 4 It is a counting weighting schematic diagram of the multi-segment GM counter tube of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0022] like Figure 1 As shown, the present invention provides a method for measuring radioactive waste dose rate based on multi-mode measurement, comprising the following steps:

[0023] S1. Clamp the radioactive waste into the shielding slot of the detection table;

[0024] S2. The detector under the shielding slot starts dose rate measurement: the thallium-doped sodium iodide gamma spectrometer of the detector is used to measure the dose rate of the radioactive waste to obtain a first measurement value. If the first measurement value is less than or equal to a preset dose rate switching threshold, the first measurement value is used as the measurement result; if the first measurement value is greater than the preset dose rate switching threshold, the GM tube detection unit of the detector is used to measure the dose rate of the radioactive waste to obtain a second measurement value, and the second measurement value is used as the measurement result.

[0025] The present invention realizes wide-range measurement of radioactive waste dose rate based on multi-mode measurement, specifically adopts a dual-detector working mode of a thallium-doped sodium iodide gamma spectrometer plus a GM tube detection unit, obtains dose rate data through the thallium-doped sodium iodide gamma spectrometer in low-level radioactivity measurement, and obtains dose rate data through the GM tube detection unit in high-level radioactivity measurement, thereby realizing dose rate measurement in a wide range of 0.01 μGy / h to 100 mGy / h, and widening the dose rate range.

[0026] In one embodiment, the dose rate switching threshold is determined by measuring the dose rate linear range of the thallium-doped sodium iodide gamma spectrometer and the GM tube detection unit, and is specifically determined according to the actual models or parameters of the thallium-doped sodium iodide gamma spectrometer and the GM tube detection unit.

[0027] In one embodiment, the thallium-doped sodium iodide gamma spectrometer is a thallium-doped sodium iodide crystal, that is, a NaI(Tl) crystal. Preferably, the crystal size of the thallium-doped sodium iodide crystal is φ50 mm×50 mm.

[0028] In one embodiment, the GM tube detection unit includes a multi-segment GM counter tube. The GM counter tube has the advantages of high sensitivity, fast response speed, and simple structure, and is suitable for detecting various types of radiation, such as alpha particles, beta particles, gamma rays, etc. A dose rate measurement component with GM counting as the core is constructed, which is mainly composed of a radiation detection sensor element GM counter tube, a back-end signal processing circuit and a high-voltage power supply. The inside of the GM counter tube is filled with inert gas, such as helium, neon or argon, and a DC high voltage generated by a high-voltage power supply is applied during detection, usually 400-900 volts. When the incident radiation particles or photons make the gas conductive by ionization, the GM counter tube will briefly conduct electric charge. The Townsend discharge effect makes the ionization phenomenon in the tube significant, thereby generating an easily measurable electrical pulse signal, which is processed by the back-end circuit. Preferably, the GM counter tube of the multi-segment GM counter tube adopts a metal cathode GM counter tube.

[0029] When the crystal size of the thallium-doped sodium iodide crystal is φ50mm×50mm and the GM counter of the multi-segment GM counter uses a metal cathode GM counter, the dose rate response curves of the thallium-doped sodium iodide gamma spectrometer and the GM tube detection unit are as follows: Figure 2 and Figure 3 As shown. Figure 2 It can be seen that the thallium-doped sodium iodide gamma spectrometer with a crystal size of φ50mm×50mm has a good linear relationship in the range of 0.01~200μGy / h; Figure 3 It can be seen that the metal cathode GM counter has a good linear relationship in the range above 100 μGy / h. Taking all factors into consideration, the dose rate switching threshold is set at 100 μGy / h.

[0030] In one embodiment, the multi-stage GM counter tube includes a high-range GM counter tube, a mid-range GM counter tube and a low-range GM counter tube. Figure 4As shown, the high-range GM counter tube, the medium-range GM counter tube and the low-range GM counter tube respectively perform multi-channel counting capture on the radioactive source, i.e., radioactive waste, and then adaptively weight the multi-channel captured count values ​​to obtain the second measurement value, wherein the adaptive weighting is an electrical signal, and the electrical signal is then converted into a digital signal by the back-end signal processing circuit in the GM tube detection unit, i.e., the second measurement value, which is also the measured dose rate. The GM counter tube has a dead time after recording an incident particle and cannot record a new incident particle. The larger the volume of the counter of the GM counter tube, the higher the sensitivity, but the longer the dead time. A single GM counter tube is difficult to meet the technical requirements of high sensitivity and wide range. Therefore, a dose rate measurement component is formed by using multiple GM counter tubes of different volumes, and the counts of the multi-channel GM counters are captured by the back-end signal processing circuit, and the current dose rate value is calculated using an adaptive weighting algorithm. When the counter of the GM counter tube works in a limited proportional region, due to the influence of photon feedback, ion feedback and space charge, the gas amplification coefficient in the avalanche process rises sharply with the working voltage, and the output signal amplitude is no longer proportional to the energy of the incident particle. As the voltage rises further, the output signal (amplitude and shape) of the counter has nothing to do with the properties of the incident particles (such as energy, type, etc.). The incident particles only play a role in triggering self-sustaining discharge. This working state is called the GM region. The counter works in this region, so the back-end signal processing circuit can count the electrical pulse signal and calculate the count value per unit time to obtain the radiation count rate. By calibrating the count rate, the conversion factor of the count rate-dose rate can be obtained, and the dose size can be obtained in sieverts (Sv), completing the measurement of the radiation dose rate.

[0031] The thallium-doped sodium iodide gamma spectrometer and the GM tube detection unit of the present invention can also be arranged on different detection structures. For example, the GM tube detection unit is arranged on a sorting robot that performs rapid dose rate initial screening. The radioactive waste with a high dose rate can be collected separately by the sorting robot for subsequent treatment, and the radioactive waste with a low dose rate can be transported to the measuring robot for further measurement. The thallium-doped sodium iodide gamma spectrometer is arranged on the measuring robot that performs further measurement, thereby improving the sorting efficiency of the radioactive waste and shortening the sorting time.

[0032] Finally, it should be noted that the above embodiments are only preferred embodiments of the present invention to illustrate the technical solutions of the present invention, rather than limiting them, and certainly not limiting the patent scope of the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. In other words, any changes or modifications made to the main design concept and spirit of the present invention that have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention in other related technical fields is also included in the patent protection scope of the present invention.

Claims

1. A method for measuring radioactive waste dose rate based on multi-mode measurement, characterized in that: The following steps are involved: S1. Clamp the radioactive waste into the shielding slot of the detection table; S2. The detector under the shielding slot starts dose rate measurement: the dose rate of the radioactive waste is measured by using the thallium-doped sodium iodide gamma spectrometer of the detector to obtain a first measurement value. If the first measurement value is less than or equal to a preset dose rate switching threshold, the first measurement value is used as the measurement result; If the first measurement value is greater than a preset dose rate switching threshold, the GM tube detection unit of the detector is used to measure the dose rate of the radioactive waste to obtain a second measurement value, and the second measurement value is used as the measurement result.

2. The method for measuring radioactive waste dose rate based on multi-mode measurement according to claim 1, characterized in that: The dose rate switching threshold is determined by measuring the dose rate linear range of the thallium-doped sodium iodide gamma spectrometer and the GM tube detection unit.

3. The method for measuring radioactive waste dose rate based on multi-mode measurement according to claim 1, characterized in that: The thallium-doped sodium iodide gamma spectrometer is a thallium-doped sodium iodide crystal.

4. The method for measuring radioactive waste dose rate based on multi-mode measurement according to claim 3, characterized in that: The crystal size of the thallium-doped sodium iodide crystal is φ50 mm×50 mm.

5. The method for measuring radioactive waste dose rate based on multi-mode measurement according to claim 1, characterized in that: The GM tube detection unit includes multiple sections of GM counter tubes.

6. The method for measuring radioactive waste dose rate based on multi-mode measurement according to claim 5, characterized in that: The GM counter tube of the multi-segment GM counter tube adopts a metal cathode GM counter tube.

7. The method for measuring radioactive waste dose rate based on multi-mode measurement according to claim 5, characterized in that: The multi-stage GM counter tube includes a high-range GM counter tube, a middle-range GM counter tube and a low-range GM counter tube.

8. The method for measuring radioactive waste dose rate based on multi-mode measurement according to claim 7, characterized in that: The method of measuring the dose rate of radioactive waste using a multi-segment GM counter tube of the detector to obtain a second measurement value includes: performing multi-channel counting capture by a high-range GM counter tube, a mid-range GM counter tube and a low-range GM counter tube respectively, and then adaptively weighting the multi-channel captured count values ​​to obtain the second measurement value.

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