A post-accident high-range regional radiation monitoring ionization chamber

Abstract

The invention belongs to the technical field of nuclear protection, and specifically relates to an ionization chamber for post-accident high-range regional radiation monitoring, the ionization chamber comprising a protective shell and an ionization chamber body disposed in the protective shell, the ionization chamber body comprising a coaxially arranged outer high-voltage electrode, a collector and a central high-voltage electrode, and the outer high-voltage electrode, the collector and the central high-voltage electrode are fixed by insulators, the collector extends out of the insulator and is connected to a cable connector, a collector jacket is provided along the periphery of a connection portion between the collector and the cable connector, and a front end of the central high-voltage electrode is embedded in an inspection source; the invention has the advantages of small size, high sensitivity, wide range, radiation resistance, high temperature and high humidity resistance, and can adapt to the harsh environment in a containment vessel after an accident.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear protection, and in particular relates to an ionization chamber for post-accident high-range regional radiation monitoring. Background Art

[0002] When an accident occurs, the environment inside the containment of a nuclear power plant is extremely bad, which is specifically manifested in the following five aspects: (1) The temperature inside the containment reaches 218°C in a few tens of seconds and exceeds 100°C for a long time; (2) The pressure inside the containment reaches 408kPa in half an hour and exceeds 100kPa for a long time; (3) The relative humidity reaches 100%; (4) Within one year after the accident, the gamma radiation dose rate remains at 1.13×10 4 Gy / h, cumulative dose up to 2.53×10 5 Gy; the β radiation dose rate remained at 6.77×10 4 Gy / h, cumulative dose up to 2.58×10 6 Gy; (5) Within 23 hours after the accident, the concentration of boric acid in the containment atmosphere was 2428 ppm, and the concentration of trisodium phosphate was 7.53 g / l; the pH value was 7.80-7.85, which was weakly alkaline.

[0003] To sum up, after the accident, conventional detectors such as conventional NaI detectors and plastic scintillator detectors are not applicable, either in terms of adaptability to the harsh environment inside the containment or in terms of detection capabilities of radiation dose and energy range. Instead, it is necessary to use gamma-sensitive ionization chamber detectors that are resistant to high temperature, high pressure, corrosion, moisture, and radiation, have a wide detection range, and a high upper limit. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an ionization chamber for post-accident high-range regional radiation monitoring, which has small size, high sensitivity, wide range, radiation resistance, high temperature and high humidity resistance, and can adapt to the harsh environment inside the containment after the accident.

[0005] The technical solution adopted by the present invention is:

[0006] A post-accident high-range area radiation monitoring ionization chamber,

[0007] The ionization chamber comprises a protective shell and an ionization chamber body placed in the protective shell, an insulator is arranged at the front end of the ionization chamber body, a front insulator and a hard cable fixing seat are sleeved along the outer periphery of the insulator, the hard cable extending into the ionization chamber and the end of the hard cable protective shell are fixed on the hard cable fixing seat and connected with a cable connector, a rear end insulator is arranged at the rear end of the ionization chamber body, and two sets of disc springs are installed between the rear end insulator and the ionization chamber body;

[0008] The ionization chamber body includes a coaxially arranged outer high-voltage electrode, a collecting electrode and a central high-voltage electrode, and the outer high-voltage electrode, the collecting electrode and the central high-voltage electrode are fixed by insulators. The collecting electrode extends out of the insulator and is connected to the cable connector. A collecting electrode jacket is provided along the periphery of the connecting portion between the collecting electrode and the cable connector, and the front end of the central high-voltage electrode is embedded in the inspection source.

[0009] Furthermore, a high-voltage tail end is welded to the rear end of the outer high-voltage electrode, the tail end of the central high-voltage electrode is threadedly connected to the high-voltage tail end, and tail end insulators are provided on both sides of the tail end of the central high-voltage electrode. One end of the tail end insulator supports the high-voltage tail end, and a group of springs are provided between the other end and the collecting electrode; a head end insulator is provided at the front end of the central high-voltage electrode, and the inspection source is arranged between the front end of the central high-voltage electrode and the head end insulator.

[0010] Furthermore, two groups of insulating support rings are provided between the protective shell and the ionization chamber body; and four groups of disc springs are provided between the central high-voltage electrode and the insulator.

[0011] Furthermore, an inflation nozzle is provided on the rear end of the protective shell, and the inflation nozzle inflates air into the interior of the ionization chamber through an opening on the rear end of the ionization chamber body. The rear end of the protective shell is connected to the rear cover through threads, and the front end of the protective shell is welded to the front cover.

[0012] Furthermore, the hard cable protective sleeve and the protective shell are welded by argon arc welding, and the hard cable and the hard cable protective sleeve are welded by copper or silver brazing.

[0013] Furthermore, the ionization chamber body is connected to the protective shell, and the ionization chamber body and the protective shell are isolated by insulating materials, and the outer high-voltage electrode and the central high-voltage electrode are isolated from the collecting electrode respectively by insulating materials.

[0014] Furthermore, the outer end surface of the insulator is in a convex stepped shape, the collecting electrode passes through the insulator and extends outward, and the outer high-voltage electrode is fixed on the insulator and retracted inward.

[0015] Furthermore, the protective shell is made of 316L corrosion-resistant stainless steel, and its wall thickness is 1.6 mm.

[0016] Furthermore, the outer high-voltage electrode, the collecting electrode and the central high-voltage electrode are all made of 6063 light aluminum material, and the wall thickness of the outer high-voltage electrode, the collecting electrode and the central high-voltage electrode is 1.5 mm.

[0017] Furthermore, the distances between the outer high-voltage electrode and the central high-voltage electrode and the collector are 3.5 mm to 5 mm.

[0018] Beneficial effects of the present invention:

[0019] 1. The outer high-voltage electrode, the collecting electrode and the central high-voltage electrode of the present invention are all hollow coaxial cylinders, and the working gas of a certain pressure is filled in the middle. This structure can make the electric field in the sensitive volume evenly distributed, avoiding the existence of abnormal areas of too strong or too weak electric field in the ionization chamber, thereby ensuring the uniformity of ionization of the working gas in the ionization chamber;

[0020] 2. The distance between the electrodes in the ionization chamber body of the present invention is very small, only 3.5 to 5 mm, which can effectively increase the electric field strength and the drift speed, so the working gas pressure does not need to be too high, which is conducive to improving the performance stability under a large-varying working environment;

[0021] 3. In the present invention, the outer end faces of the insulators fixing the outer high-voltage electrode and the collector are designed to be not in the same plane. The collector extends outward through the insulator, and the outer high-voltage electrode retracts inward, so that the outer high-voltage electrode and the collector are relatively staggered to form a high-voltage protection ring of the ionization chamber, which not only ensures the high insulation resistance of the insulator and prevents high-voltage breakdown between the high-voltage electrode and the collector, but also meets the gas sealing requirements of the ionization chamber.

[0022] 4. The present invention arranges two groups of butterfly springs between the ionization chamber and the insulating material at the rear end of the shell, and welds the shell to fix the ionization chamber under a certain pre-compression force to prevent the ionization chamber from axially displacing with the shell when vibrated; two groups of polyimide insulating support rings are arranged in the middle of the gap between the ionization chamber and the shell, and an interference fit is adopted to prevent the ionization chamber from radially displacing with the shell when vibrated; four groups of butterfly springs are arranged between the central high-voltage electrode and the insulator, and a group of springs is arranged between the collecting electrode and the rear end insulator, and a certain pre-compression force is given to them during welding and packaging, so that the three coaxial electrodes are reliably connected to prevent mutual displacement when vibrated. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the present invention;

[0024] Figure 2a , 2b This is a structural diagram of the ionization chamber body of the present invention;

[0025] Figure 3 This is the welding process flow chart for the ionization chamber body packaging;

[0026] Figure 4 Flow chart of the welding process for ionization chamber detector packaging.

[0027] Among them, 1. Protective shell; 2. Outer high-voltage electrode; 3. Collector; 4. Central high-voltage electrode; 5. Inspection source; 6. Insulator; 7. Collector jacket; 8. Hard cable; 9. Hard cable protective cover; 10. Front cover; 11. Hard cable fixing seat; 12. Front insulator; 13. Insulating support; 14. Rear insulator; 15. Rear cover; 16. Inflator nozzle; 17. Disc spring; 18. Spring; 19. Tail insulator; 20. Head insulator. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The exemplary embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0029] like Figure 1 As shown in FIG. 2 , the present invention specifically discloses a post-accident high-range area radiation monitoring ionization chamber, the ionization chamber comprises a protective shell and an ionization chamber body placed in the protective shell 1, an insulator is arranged at the front end of the ionization chamber body, a front end insulator 12 and a hard cable fixing seat are sleeved along the outer periphery of the insulator, the hard cable 8 and the hard cable protective sleeve 9 extending into the ionization chamber end are fixed on the hard cable fixing seat, and a cable connector is connected, a rear end insulator 14 is arranged at the rear end of the ionization chamber body, and two sets of disc springs 17 are installed between the rear end insulator 14 and the ionization chamber body; the ionization chamber body comprises a coaxially arranged outer high-voltage electrode 2, a collecting electrode 3 and a central high-voltage electrode 4, and the outer The high-voltage electrode 2, the collector 3 and the central high-voltage electrode 4 are fixed by insulators. The collector 3 extends out of the insulator and is connected to the cable connector. A collector jacket 7 is provided along the periphery of the connection part between the collector 3 and the cable connector. A high-voltage tail end is welded to the rear end of the outer high-voltage electrode 2. The tail end of the central high-voltage electrode 4 is threadedly connected to the high-voltage tail end. Tail end insulators 19 are provided on both sides of the tail end of the central high-voltage electrode 4. One end of the tail end insulator 19 supports the high-voltage tail end, and a group of springs 18 are provided between the other end and the collector 3. A head end insulator 20 is provided at the front end of the central high-voltage electrode 4, and an inspection source 5 is provided between the front end of the central high-voltage electrode 4 and the head end insulator 20.

[0030] In the present invention, the ionization chamber adopts a three-coaxial design structure, namely: a coaxially arranged outer high-voltage electrode 2, a collecting electrode 3 and a central high-voltage electrode 4. This structure can make the electric field in the sensitive volume evenly distributed, avoiding the existence of abnormal electric field areas that are too strong or too weak in the ionization chamber, thereby ensuring the uniformity of ionization of the working gas in the ionization chamber. A hole is opened at the bottom of the ionization chamber, and the working gas is filled into the ionization chamber through the inflation nozzle 16. In order to reduce the weight of the ionization chamber as much as possible and to inflate the ionization chamber, the central high-voltage electrode 4 is hollow.

[0031] At the same time, when detecting gamma rays, the ionization chamber electrodes also play the role of solid radiators. The incident gamma rays first ionize the gas near the outer high-voltage electrode 2 to produce electron-ion pairs. Due to the effect of the electric field, positive ions drift toward the outer high-voltage electrode 2, and electrons drift toward the collector 3. In this way, the distance that positive ions need to drift before drifting to the outer high-voltage electrode 2 and being collected is significantly shorter than when the outer high-voltage electrode 2 is applied with positive high voltage. This reduces the probability of recombination between positive ions and electrons, thereby improving the saturation plateau characteristics of the ionization chamber and increasing the charge collection efficiency.

[0032] The ionization chamber in the present invention is an isobaric ionization chamber, so the insulator does not need to be sealed, the interior of the ionization chamber and the ionization chamber and the stainless steel protective shell are connected, and only the outer stainless steel protective shell is used for sealing, which reduces the sealing requirements for the ionization chamber. In addition, a working gas (dry inert gas) is also filled between the ionization chamber and the stainless steel protective shell as a protective gas for the ionization chamber. Therefore, the insulator is made of polyimide material.

[0033] In order to prevent high voltage breakdown at the end edges of the outer high-voltage electrode 2 and the collector 3, at the output end of the ionization chamber, the outer end faces of the insulators fixing the outer high-voltage electrode and the collector 3 are designed not to be in the same plane, that is, the collector extends outward and the outer high-voltage electrode retracts inward, so that the outer high-voltage electrode and the collector are relatively staggered to form a high-voltage protection ring for the ionization chamber.

[0034] The rear end of the protective shell 1 is provided with an inflation nozzle 16, and the inflation nozzle 16 fills the mixed gas of Ar and N2 into the interior through the opening on the rear end of the ionization chamber body. The rear end of the protective shell 1 is connected to the rear cover through threads, and the front end of the protective shell is welded to the front cover.

[0035] As shown in Figure 2, the outer high-voltage electrode 2, the collecting electrode 3, and the central high-voltage electrode 4 are hollow coaxial cylinders, the outermost layer is the protective shell 1; the second layer is the outer high-voltage electrode 2; the third layer is the collecting electrode 3; the central high-voltage electrode; and the ionization chamber body and the protective shell 1 are connected, and the ionization chamber body and the connecting parts between the ionization chamber body and the protective shell 1 are filled with working gas at a certain pressure.

[0036] Two groups of insulating support rings 13 are arranged between the protective shell 1 and the ionization chamber body, and interference fit is adopted to prevent radial displacement between the ionization chamber body and the shell when the ionization chamber body is vibrated; four groups of disc springs are arranged between the central high-voltage electrode 4 and the insulator 6, and a group of springs is arranged between the collecting electrode 3 and the rear end insulator 14, which are given a certain pre-compression force during welding and packaging, so that the three coaxial electrodes are reliably connected to prevent mutual displacement during vibration; two groups of disc springs 17 arranged between the ionization chamber body and the rear end insulator 14 are welded to the shell to fix the ionization chamber under the condition of giving the ionization chamber a certain pre-compression force, so as to prevent axial displacement between the ionization chamber and the shell when the ionization chamber is vibrated.

[0037] The ionization chamber body is isolated from the protective shell 1 by insulating materials, and the outer high-voltage electrode 2 and the central high-voltage electrode 4 are isolated from the collector 3 by insulating materials respectively; the rear insulator 14, the front insulator 12, the insulator 6 and the insulating material are all made of radiation-resistant polyimide, which has a high temperature resistance of more than 400°C and a long-term use temperature range of -200°C to 300°C; polyimide also has good dielectric properties, with a dielectric constant of about 3.4 and a dielectric loss of only 0.004 to 0.007; the polyimide film is 5×10 9 The strength retention rate after rad fast electron irradiation is 90%, and it has high radiation resistance; its thermal expansion coefficient is 2×10 -5 m / ℃~3×10 -5 m / ℃, has good thermal stability.

[0038] At the connection between the hard cable and the front cover 10, a longer stainless steel hard cable protective sheath 9 is designed. The sheath and the back cover are welded by argon arc welding, and the hard cable 8 and the hard cable protective sheath 9 are welded by copper or silver brazing, which plays a role in protecting the hard cable and the welding weld during an earthquake; the hard cable 8 and the hard cable protective sheath 9 extending into the ionization chamber are fixed on the hard cable fixing seat, and then the cable connector is connected to ensure that when the front cover 10 is welded or vibrated, the force on the hard cable 8 will not be transmitted to the cable connector, so as to prevent the cable connector from being connected or disconnected due to force; the outer end face of the insulator is convex stepped, the collector 3 extends outward through the insulator and is connected to the cable connector, and the outer periphery of the connecting part is provided with a collector jacket 7, and the outer high-voltage electrode 2 is fixed on the insulator and retracted inward.

[0039] 316L corrosion-resistant stainless steel is selected as the protective shell 1 of the ionization chamber, so that the ionization chamber has sufficient shock resistance and shock absorption capabilities, withstands a certain air pressure, seals the working gas in the container, and prevents the internal high-voltage electrode, collector, working gas, etc. from being affected by the external temperature, humidity, and air pressure; secondly, in order to allow the gamma rays to smoothly pass through the stainless steel shell into the sensitive area of ​​the ionization chamber, interact with the working gas, and ionize the gas, the wall thickness of the outer shell of the ionization chamber is selected to be 1.6mm, which can ensure that the gamma ionization chamber detector of the containment high-range regional radiation monitor can fully adapt to the harsh environment of high temperature, high pressure, and high humidity in the atmospheric containment after the accident under the premise of meeting the measurement requirements; the outer high-voltage electrode 2, the collector 3, and the central high-voltage electrode 4 are all made of 6063 light aluminum, and the wall thickness of the outer high-voltage electrode 2, the collector 3, and the central high-voltage electrode 4 is 1.5mm.

[0040] The internal structural parameters of the ionization chamber of the containment high-range area radiation monitor are shown in Table 1-1:

[0041] Table 1-2 Internal structural parameters of the ionization chamber

[0042]

[0043]

[0044] For the ionization chamber in which the outer high-voltage electrode 2, the collector 3 and the central high-voltage electrode 4 are coaxially arranged, the electric field intensity at the distance r from the center within the sensitive volume for the central high-voltage electrode and the collector is:

[0045]

[0046] Where: V is the inter-electrode working voltage;

[0047] a is the radius of the central high voltage pole;

[0048] b is the radius of the collector.

[0049] For the outer high-voltage electrode 2 and the collecting electrode 3 , the formula for the electric field strength at a distance r from the center is the same as above, except that a becomes the radius of the collecting electrode 3 , and b is the radius of the outer high-voltage electrode 2 .

[0050] When the working voltage is constant, the smaller the distance between the high-voltage electrode and the collecting electrode, the greater the electric field strength between the electrodes, the faster the ion drift speed, and the smaller the transit time of the ionization chamber.

[0051] In order to ensure sufficient sensitive volume, the distance between the electrodes of the ionization chamber cannot be too small. At the same time, when the working voltage is relatively high, too small distance between the electrodes will cause high voltage discharge between the electrodes, making the ionization chamber lose its detection function. The distance between the outer high voltage electrode 2 and the central high voltage electrode 4 and the collecting electrode 3 is 3.5mm to 5mm.

[0052] The performance indicators of the developed containment high-range area radiation monitor gamma ionization chamber detector are shown in Table 1-2:

[0053] Table 1-2 Ionization chamber detector performance indicators

[0054]

[0055]

[0056] like Figure 3 , 4As shown, the welding of the ionization chamber is completed on a special welding fixture of a lathe. The welding fixture has a top on each side, three coaxial centering frames in the middle, and a micrometer for checking coaxiality is set on the slide rail. The two tops provide the required pre-tightening force for the two weldments, and the three centering frames are used to ensure the coaxiality of the two weldments. The welding of the ionization chamber body is carried out in two processes at the same time. One process: the outer high-voltage electrode and the high-voltage tail end are welded by argon arc welding, the central high-voltage electrode is threaded with the high-voltage tail end, and the two tail end insulators are installed, followed by the collector spring, and fixed on the welding fixture; the other process: the collector is threaded with the insulator, the head end insulator is installed, and then the inspection source is installed. The inspection source contacts the front end of the central high-voltage electrode, and then 4 sets of disc springs are installed and fixed on the welding fixture. Finally, the pre-tightening force is applied to adjust the semi-finished products of the two processes to coaxiality, and then welded by argon arc welding.

[0057] like Figure 4 As shown in the figure, the packaging process of the entire ionization chamber detector is divided into three simultaneous processes. The first process: the stainless steel protective shell is welded with the hard cable fixing seat by argon arc welding, the front insulator is installed, and the ionization chamber body is installed. Two insulating support rings are installed on the periphery of the ionization chamber body and fixed on the welding tool; the second process: the stainless steel protective shell is covered with the rear end gas nozzle core, and then the gas nozzle joint is installed, and the rear end insulator and two sets of disc springs are fixed on the welding tool in turn; the semi-finished products of the first process and the second process are pre-pressed to tighten the two The welded parts are adjusted to be coaxial and welded into an airtight cavity of the ionization chamber by argon arc welding; three working procedures: the hard cable and the hard cable sheath arranged outside the hard cable are welded to the hard cable bracket, the hard cable bracket is bolted to the hard cable fixing seat, and then the collector is welded, the collector jacket is installed along the outer periphery of the collector, the outer high-voltage electrode is welded to the insulator, and a stainless steel protective shell is installed, the above-mentioned workpieces are welded to the airtight cavity of the ionization chamber, and the working gas is injected into the entire device through the inflation nozzle, and the rear cover is installed to form an ionization chamber detector.

[0058] The technical solutions disclosed in the embodiments of the present invention are introduced in detail above. The principles and implementation methods of the embodiments of the present invention are explained in this article using specific embodiments. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A post-accident high-range area radiation monitoring ionization chamber, characterized in that: It comprises a protective shell and an ionization chamber body placed in the protective shell, an insulator is arranged at the front end of the ionization chamber body, a front insulator and a hard cable fixing seat are sleeved along the outer periphery of the insulator, the hard cable extending into the ionization chamber and the end of the hard cable protective shell are fixed on the hard cable fixing seat and connected with a cable connector, a rear end insulator is arranged at the rear end of the ionization chamber body, and two sets of disc springs are installed between the rear end insulator and the ionization chamber body; The ionization chamber body includes a coaxially arranged outer high-voltage electrode, a collecting electrode and a central high-voltage electrode, and the outer high-voltage electrode, the collecting electrode and the central high-voltage electrode are fixed by insulators. The collecting electrode extends out of the insulator and is connected to the cable connector. A collecting electrode jacket is provided along the outer periphery of the connecting part between the collecting electrode and the cable connector, and the front end of the central high-voltage electrode is embedded in the inspection source.

2. The post-accident high-range regional radiation monitoring ionization chamber according to claim 1, characterized in that: A high-voltage tail end is welded to the rear end of the outer high-voltage electrode, and the tail end of the central high-voltage electrode is threadedly connected to the high-voltage tail end. Tail end insulators are provided on both sides of the tail end of the central high-voltage electrode, one end of the tail end insulator contacts the high-voltage tail end, and a group of springs are provided between the other end and the collecting electrode; a head end insulator is provided at the front end of the central high-voltage electrode, and the inspection source is arranged between the front end of the central high-voltage electrode and the head end insulator.

3. The post-accident high-range regional radiation monitoring ionization chamber according to claim 1, characterized in that: Two groups of insulating support rings are arranged between the protective shell and the ionization chamber body; and four groups of disc springs are arranged between the central high-voltage electrode and the insulator.

4. The post-accident high-range regional radiation monitoring ionization chamber according to claim 1, characterized in that: The rear end of the protective shell is provided with an air filling nozzle, which fills air into the interior of the ionization chamber through an opening on the rear end of the ionization chamber body. The rear end of the protective shell is connected to the rear cover through threads, and the front end of the protective shell is welded to the front cover.

5. The post-accident high-range regional radiation monitoring ionization chamber according to claim 1, characterized in that: The hard cable protective sleeve and the protective shell are welded by argon arc welding, and the hard cable and the hard cable protective sleeve are welded by copper or silver brazing.

6. The post-accident high-range regional radiation monitoring ionization chamber according to claim 1, characterized in that: The ionization chamber body is connected to the protective shell, and the ionization chamber body and the protective shell are isolated by insulating materials. The outer high-voltage electrode and the central high-voltage electrode are isolated from the collecting electrode respectively by insulating materials.

7. The post-accident high-range regional radiation monitoring ionization chamber according to claim 6, characterized in that: The outer end surface of the insulator is in a convex stepped shape, the collecting electrode passes through the insulator and extends outward, and the outer high-voltage electrode is fixed on the insulator and retracted inward.

8. The post-accident high-range regional radiation monitoring ionization chamber according to claim 6, characterized in that: The protective shell is made of 316L corrosion-resistant stainless steel, and its wall thickness is 1.6 mm.

9. The post-accident high-range regional radiation monitoring ionization chamber according to claim 6, characterized in that: The outer high-voltage electrode, the collecting electrode and the central high-voltage electrode are all made of 6063 light aluminum material, and the wall thickness of the outer high-voltage electrode, the collecting electrode and the central high-voltage electrode is 1.5 mm.

10. The post-accident high-range regional radiation monitoring ionization chamber according to claim 9, characterized in that: The distances between the outer high-voltage electrode and the central high-voltage electrode and the collecting electrode are 3.5 mm to 5 mm.

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