JP2016194479A - Radioactivity measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radioactivity measuring device that can meet requirements for continuous monitoring in a broad concentration range from low to high and evade increases in the size and complexity of the monitoring equipment.SOLUTION: A radioactivity measuring device (1) is equipped with a chamber (2) forming a measurable space (S) of a prescribed volume, a low-range detector (3) that is so fitted to the chamber as to direct its detection face (3a) toward the measurable space and intended to measure a relatively low range of the radioactivity concentration of measurable gas (G), and a high-range detector (4) that is so fitted to the chamber as to direct its detection face (4a) to the measurable space and intended to measure a relatively high range of the radioactivity concentration of measurable gas.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a radioactivity measuring apparatus applicable to a radioactive gas monitor that monitors a radioactive concentration of a gaseous radioactive substance in exhaust gas flowing through an exhaust pipe, an exhaust pipe duct or an exhaust system process pipe of a nuclear facility.

  For example, in a nuclear reactor facility that is one of nuclear facilities, a radioactive gas monitor is installed to measure the radioactivity concentration in exhaust gas discharged from an exhaust stack that is the final discharge end of the facility. The radioactive gas monitor samples the exhaust gas from the exhaust pipe, guides it to the measurement container, detects the radiation emitted from the radioactive noble gas in the exhaust gas with the radioactivity measurement device attached to the measurement container, and sends the detection signal to the measuring instrument Input and measure radioactivity concentration.

  The radioactivity level to be measured by the radioactivity measuring device covers a wide measurement range from the normal background level to a high concentration level assuming an accident. To meet the demand for continuous monitoring over a wide range from low concentration level to high concentration level, low range monitor and high range monitor are installed corresponding to low range monitor and high range monitor. The structure which branches and introduces into the low range side measurement container and the high range side measurement container is proposed (for example, refer patent document 1 and patent document 2). Under normal conditions, the gas to be measured is allowed to flow from the sampling pipe into the low range side measurement vessel to measure the background level radioactivity concentration. It is controlled so that high concentration radioactivity can be measured by flowing into the range side measurement container.

Japanese Patent Laid-Open No. 2001-153958 JP 52-55585 A

  However, the radioactive gas monitors described in Patent Document 1 and Patent Document 2 require two sampling systems corresponding to the low range monitor and the high range monitor, and the low range side measurement container and the high range side measurement container are provided. Since it is necessary, there is a problem that the gas monitor facility is inevitably increased in size and complexity.

  The present invention has been made in view of such problems, and its object is to meet the demand for continuous monitoring over a wide range from a low concentration level to a high concentration level, and to increase the size and complexity of the monitor equipment. It is an object of the present invention to provide a radioactivity measuring apparatus that can avoid the above.

  The radioactivity measurement apparatus according to the present invention includes a chamber or a part of process piping that forms a measurement space having a predetermined volume, and a measurement unit through which the gas to be measured passes through the measurement space and a detection surface facing the measurement space. A first detector attached to the measurement unit and having a relatively low range of the radioactivity concentration of the gas to be measured as a measurement target, and attached to the measurement unit so that a detection surface faces the measurement space. And a second detector whose measurement target is a relatively high range of the radioactivity concentration of the gas to be measured. According to the present invention, since the detection surfaces of the first detector and the second detector are arranged to face the same measurement space, it is necessary to continuously monitor a wide range from a low concentration level to a high concentration level. In addition to being able to respond, there is no need to provide two gas flow paths corresponding to the low range monitor and the high range monitor, and the enlargement and complexity of the monitor equipment can be avoided.

  In the present invention, the first detector and the second detector may be disposed opposite to the measurement unit with the measurement space interposed therebetween. Moreover, in this invention, a said 1st detector and a said 2nd detector can be arrange | positioned in parallel along the direction through which the said to-be-measured gas flows with respect to the said measurement part.

  In the present invention, a first collimator provided between a detection surface of the first detector and the measurement space and having an opening corresponding to a measurement target range of the first detector, and the second And a second collimator provided between the detection surface of the detector and the measurement space and having an opening corresponding to the measurement target range of the second detector. By providing a first collimator and a second collimator corresponding to each measurement target range of the first detector and the second detector, the first collimator has a first collimator opening size. The range to be measured by the detector and the second detector can be set.

  When setting the ranges to be measured by the first detector and the second detector by the first collimator and the second collimator, the first detector and the second detector are the same. You may use what has a detection sensitivity.

  Moreover, in this invention, the said measurement part is comprised by the chamber which forms the said measurement space, and can be set as the structure provided in the middle of the sampling piping connected to the exhaust pipe or the exhaust pipe duct. In the present invention, the measurement unit may be configured by a part of an exhaust system process pipe.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to respond to the request | requirement which continuously monitors the wide range from a low concentration level to a high concentration level, the enlargement and complication of a monitor installation can be avoided.

It is a systematic diagram of a radioactive gas monitor system provided with the radioactivity measuring apparatus which concerns on this Embodiment. It is sectional drawing of the radioactivity measuring apparatus which concerns on this Embodiment. It is explanatory drawing of the detector provided in the radioactivity measuring apparatus of this Embodiment. It is a systematic diagram of the radioactive gas monitor system which samples gas from an exhaust pipe duct. It is explanatory drawing of the radioactivity measuring apparatus arrange | positioned in parallel with process piping. It is sectional drawing to which the part enclosed by A in FIG. 5 was expanded.

  Hereinafter, an embodiment of the present invention (hereinafter abbreviated as “embodiment”) will be described in detail. In the present embodiment, an example applied to a radioactive gas monitor system that monitors the radioactive concentration of a gaseous radioactive substance in exhaust gas discharged from an exhaust pipe of a nuclear facility will be described.

  FIG. 1 is a system diagram of a radioactive gas monitor system including a radioactivity measuring apparatus according to the present embodiment. In this example, an outline of a gaseous emission radioactive material sampling system in a nuclear facility of a boiling water reactor (BWR) is illustrated. The radioactivity measurement apparatus 1 includes a chamber 2 through which sampled exhaust gas is guided, and a low range detector as a first detector whose measurement target is a relatively low range of the radioactivity concentration to be measured. 3 and a high range detector 4 as a second detector whose measurement target is a relatively high range of the radioactivity concentration to be measured.

  As shown in FIG. 1, the radioactivity measurement apparatus 1 is connected in the middle of sampling pipes 21 and 22 connected to an exhaust cylinder 20 that is a final discharge end for exhausting exhaust gas in a nuclear facility. A sampling nozzle 20 a serving as a gas intake port on the upstream side of the sampling pipe 21 is inserted into the exhaust cylinder 20. The sampling pipe 21 is provided with a dust collecting portion 23 made of dust collecting filter paper and activated carbon cartridges for removing particulate matter contained in the exhaust gas. Part of the exhaust gas that passes through the exhaust cylinder 20 is taken in from the sampling nozzle 20a, and after removing particulates and the like by the dust collection unit 23, is supplied to the chamber 2 of the radioactivity measurement apparatus 1 as the measurement gas. In FIG. 1, the flow direction of the gas to be measured passing through the upstream sampling pipe 21 is indicated by an arrow B.

  The other end of the sampling pipe 22 is connected to the exhaust pipe 20 so that the gas to be measured that has passed through the chamber 2 of the radioactivity measuring apparatus 1 is returned to the exhaust pipe 20 through the downstream sampling pipe 22. In FIG. 1, the flow direction of the gas to be measured passing through the sampling pipe 22 on the downstream side is indicated by an arrow C. The sampling pipe 22 includes a pressure gauge 24 for measuring the pressure in the sampling pipe 22, a flow meter 25 for measuring the flow rate of the gas to be measured, and a flow control valve for controlling the flow rate of the gas to be measured. 26, a pump 27, and the like are provided. The direction in which the exhaust gas flows is controlled so that the gas to be measured taken from the sampling nozzle 20 a by the pump 27 returns to the exhaust pipe 20 via the chamber 2 of the radioactivity measuring apparatus 1.

  The radiation detection signals output from the low range detector 3 and the high range detector 4 are output to the control unit 30 via the corresponding preamplifiers 28 and 29, respectively. The control unit 30 counts radiation detection signals, which are weak electrical signals amplified by the preamplifiers 28 and 29, converts them into monitoring parameters such as radioactivity concentration, and records them. In the control unit 30, the relational data between the count number and the radioactivity concentration (becquerel) based on the radiation detection signal is stored in advance, and the radiation detection signal sent from the low range detector 3 and the high range detector 4. The radioactivity concentration can be calculated based on the count number.

Next, a specific configuration of the radioactivity measurement apparatus 1 in the present embodiment will be described. FIG. 2 is a cross-sectional view of the radioactivity measurement apparatus 1. Chamber 2, a cylindrical through-passage penetrating the center portion is formed, the through passage forms the measurement space S _1. Measurements on the upstream side opening of the space S ₁ of the one side chamber 2 one end of the upstream sampling pipe 21 is connected downstream to the downstream opening of the chamber 2 as the other end of the measurement space S ₁ One end of the sampling pipe 22 is connected. Measurement space S ₁ forms a measuring space of a predetermined volume through which the measurement gas G. As shown in FIG. 2, the low range detector 3 and the high range detector 4 are attached to the chamber 2 so as to be opposed to each other with the measurement space S <b> ₁ interposed therebetween. Low range detector 3 is attached to the chamber 2 toward the detection surface 3a in measurement space S _1. As described above, the low range detector 3 uses a relatively low range of the radioactivity concentration of the gas G to be measured as a measurement target. Specifically, the low range detector 3 is set so that the radioactivity concentration at the background level is the measurement target. The high-range detector 4 is attached to the chamber 2 toward the detection surface 4a in measurement space S _1. The high range detector 4 uses a relatively high range of the radioactivity concentration of the gas G to be measured as a measurement target. Specifically, the high radioactivity concentration assumed in the event of an accident at a nuclear facility (a high range that exceeds the background level and cannot be measured by the low range detector 3) becomes a measurable range. Is set. Here, the range of activity concentrations the detector be measured can be set by the radiation on the detection surface of the detector as described later squeeze area in the measurement space S ₁ can be incident (collimated) However, it can also be set by selecting the detection sensitivity of the detector itself to be used. For example, a NaI (TI) scintillation counting device, an ionization chamber, a plastic scintillation counting device, and a GM counting device can be selected according to the radioactivity concentration range to be measured and the target nuclide because the detection sensitivity is different.

  As shown in FIG. 2, the chamber 2, the low range detector 3, and the high range detector 4 constituting the radioactivity measuring apparatus 1 are made of a shielding container 31 formed of a shielding material having a radiation shielding effect such as lead. Housed inside. The chamber 2 is disposed near the center of the inner space of the shielding container 31, and the upstream sampling pipe 21 is inserted into the shielding container 31 and connected to the upstream opening of the chamber 2. A downstream sampling pipe 22 is inserted into the shielding container 31 and connected to the downstream opening of the chamber 2. The front end flange portions of the detector cases 5 and 6 inserted from the outside of the shielding container 31 are fixed to the outer side surfaces on both sides of the chamber 2. The detector cases 5 and 6 can be made of a material such as SUS. As shown in FIG. 2, each of the detector cases 5 and 6 has an inner diameter slightly larger than the outer diameters of the low-range detector 3 and the high-range detector 4 and is located between the inner walls of the cases. A low-range detector 3 and a high-range detector 4 are accommodated with a gap therebetween. The low-range detector 3 is located on the detector body 11, the shielding base 13 formed of a shielding material against radiation such as lead, located on the rear end side of the detector body 11, and the rear end side of the shielding base 13. And a connector 14 configured to be configured. Among these, the detector main body 11 and the shielding base 13 are accommodated in the detector case 5. The shielding base 13 has substantially the same thickness as the side wall of the shielding container 31. The connector 14 is located outside the shielding container 31, and the flange portion of the connector 14 is fixed to the outer surface of the shielding container 31. Similarly, the high range detector 4 includes a detector main body 12, a shielding base 15 that is located on the rear end side of the detector main body 12 and is formed of a shielding material against radiation such as lead, and a rear end of the shielding base 15. And a connector 16 located on the side. The detector main body 12 and the shielding base 15 are accommodated in the detector case 6, the connector 16 is located outside the shielding container 31, and the flange portion of the connector 16 is fixed to the outer surface of the shielding container 31. Thus, by arranging the shielding bases 13 and 15 made of lead or the like of the detectors 3 and 4 at the same position as the side wall portion of the shielding container 31, the support mechanism of the radiation measuring apparatus 1 for the shielding container 31 is simplified. In addition, the shielding container 31 can be reduced in size.

The chamber 2 is provided with a first collimator 7 having an opening communicating with the measurement space S ₁ between the detection surface 3 a of the low range detector 3 and the measurement space S ₁ . The first collimator 7 is set to have an opening width corresponding to the range of radioactivity concentration that the low range detector 3 is to be measured. A second collimator 8 having an opening communicating with the measurement space S ₁ is provided between the detection surface 4 a of the high-range detector 4 and the measurement space S ₁ . The second collimator 8 is set to an opening width corresponding to the range of the radioactivity concentration that is measured by the high-range detector 4. For example, depending on the volume of the measurement space _{S 1,} the opening width of the first collimator 7 is set to 10 mm, to set the opening width of the second collimator 8 to 1.5 mm. As shown in FIG. 2, a sealing film 9 is provided on the inner wall surface of the chamber 2. Sealing film 9, the opening of the first collimator 7 and the second collimator 8 optionally closed hermetically, the measured gas through the measurement space S ₁ is to prevent from entering into the apparatus case 5, 6 Yes. Sealing film 9, the rubber sheet, the resin film from the measurement space S ₁ side, and can be constructed by sequentially stacking a stainless steel plate, having a thickness of about 1mm across. By making the sealing film 9 have the above-described laminated structure (thickness of about 1 mm), it is possible to adopt a configuration that allows the radiation (β rays, γ rays, etc.) to be detected to pass but does not allow other air components to pass. . Therefore, β-rays and γ-rays emitted from the nuclide contained in the gas G to be measured pass through the sealing film 9 and are narrowed down by the collimators 7 and 8 before being detected by the low range detector 3 and the high range detector 4. Each of the detection surfaces 3a and 4a can be reached. Here, a specific configuration of the detector used in the present embodiment will be described.

  FIG. 3 is a diagram schematically showing a configuration of a detector provided in the radioactivity measuring apparatus 1 of the present embodiment. FIG. 3A is a cross-sectional view of a scintillation detector mainly suitable for detecting β rays that can be used as the low range detector 3 and the high range detector 4. FIG. 3B is a scintillation detector mainly suitable for detecting γ rays that can be used as the low range detector 3 and the high range detector 4, and is a cross-sectional view thereof. In FIG. 3, the internal configuration of the scintillation detector will be described using the high range detector 4 illustrated in the same direction as in FIG. 2. The low range detector has the same configuration and detection sensitivity.

  As shown in FIG. 3A, the high range detector 4 is arranged in the order of a plastic scintillator 41, a light guide 42, and a photomultiplier tube 43 from the detection surface 4a side. Optical coupling layers 44 a and 44 b are interposed between the plastic scintillator 41 and the light guide 42 and between the light guide 42 and the photomultiplier tube 43. The detector body 12 includes a plastic scintillator 41, a light guide 42, a photomultiplier tube 43, optical coupling layers 44a and 44b, and the like. The detector body 12 forms an outer wall by the storage cylinder 17. As shown in FIG. 3A, a shielding base 15 made of lead or the like is inserted from an opening on the rear end side of the storage cylinder 17. Thereby, the shielding base 15 is disposed on the rear end side of the detector main body 12. As shown in FIG. 3A, a plate 45 is disposed at the front end of the shielding base 15, and the shielding base 15 is in contact with the plate 45. A connector 16 is provided at the rear end of the shielding base 15 and outside the storage cylinder 17. The storage cylinder 17 provided with the detector main body 12 and the shielding base 15 inside is accommodated in the detector case 6 shown in FIG. 2, but the connector 16 is located outside the detector case 6, and in FIG. As shown, the flange portion of the connector 16 is fixed on the outer surface of the shielding container 31. As shown in FIG. 3A, the elastic portion 47 is arranged between the photomultiplier tube 43 and the shielding base portion 15 in the storage cylinder 17. The plate 45 and the light guide 42 positioned at the front end of the shielding base 15 are supported so as to be movable in the direction of the detection surface 4a, and the shielding base 15 is inserted from the rear end, so that the photomultiplier tube 43 The base end is pressed in the direction of the detection surface 4a. At this time, the photomultiplier tube 43, the light guide 42, and the optical coupling layers 44a and 44b are pressed in the direction of the detection surface 4a, and each member is positioned.

  When radiation (β rays or the like) is incident on the plastic scintillator 41, the plastic scintillator 41 reacts with a scintillation substance constituting the plastic scintillator 41 to emit scintillation light. The scintillation light is efficiently guided to the photomultiplier tube 43 via the light guide 42 and the optical coupling layer 44, and is converted into a radiation detection signal (pulsed electronic signal) which is a current pulse by the photomultiplier tube 43. Converted. The radiation detection signal is sent to the connector 16 via the electric cable 46. The radiation detection signal is sent to the control unit 30 via the connector 16.

  The detector 4 shown in FIG. 3B is a scintillation detector mainly suitable for detecting γ-rays, and the other basic configuration is the same as that of FIG. 3A except that the plastic scintillator 41 shown in FIG. 3A is replaced with a NaI scintillator 48. It is. 3B, the same reference numerals as those in FIG. 3A indicate the same members as in FIG. 3A. In the configuration of FIG. 3B, when radiation (mainly γ rays) is incident on the NaI scintillator 48, the NaI layer reacts with the radiation and emits scintillation light. The scintillation light is efficiently guided to the photomultiplier tube 43 through the light guide 42 and the optical coupling layers 44a and 44b, and the photomultiplier tube 43 converts the scintillation light into a radiation detection signal that is a current pulse. The radiation detection signal is sent to the connector 16 via the electric cable 46. The radiation detection signal is sent to the control unit 30 via the connector 16.

The radioactivity measurement operation in radioactivity measurement apparatus 1 of the present embodiment will be described. A part of the exhaust gas passing through the exhaust pipe 20 shown in FIG. 1 is sucked into the sampling pipe 21, and the measurement gas G passes through the measurement space S ₁ of the chamber 2 of the radioactivity measurement apparatus 1. At this time, the radiation emitted from the nuclide contained in the gas G to be measured with respect to the detection surfaces 3a and 4a of the low range detector 3 and the high range detector 4 attached to the chamber 2 is the first and first. It is incident through two collimators 7 and 8.

In this embodiment, as described above, the opening width of the first collimator 7 provided between the detection surface 3a of the detector 3 for the low range and the measurement space S _1, the detector 4 for detection the high range It is set larger than the opening width of the second collimator 8 provided between the surface 4a and the measurement space S _1. Thus, by changing the opening width of each collimator, a detector having the same detection sensitivity can be used for the low range detector 3 and the high range detector 4. By making the opening width of the first collimator 7 larger than the opening width of the second collimator 8, the radiation amount incident on the detection surface 3a of the low-range detector 3 through the first collimator 7 can be reduced. This is larger than the radiation dose incident on the detection surface 4a of the high range detector 4 through the second collimator 8. Therefore, the radiation dose count (detection pulse) detected by the low range detector 3 is larger than the radiation dose count (detection pulse) detected by the high range detector 4. For the same radioactivity concentration, the high range detector 4 has a smaller number of counts for the radiation dose than the low range detector 3, so even if the low range detector 3 reaches the count limit of the detection limit, The range detector 4 has not yet reached the count number of the detection limit, and can measure a higher radioactivity concentration than the low range detector 3.

In this embodiment, since the chamber 2 is one, low range detector 3 and the high-range detector 4 is in the same gas to be measured G passing through the measurement space S ₁ and the measurement object. As described above, in the present embodiment, the low-range detector 3 and the high-range detector 4 have the same detection sensitivity, but the opening widths of the collimators 7 and 8 that connect the measurement space S1 are changed. Therefore, even when the same gas to be measured G is used as a measurement target, the count number of radiation (for example, β rays) measured by the low-range detector 3 is the radiation measured by the high-range detector 4 ( It is larger than the count number of β rays. The control unit 30 shown in FIG. 1 includes a count number of radiation (β rays) measured by the low range detector 3 and a count number of radiation (β rays) measured by the high range detector 4. Both have been sent. At this time, the control unit 30 calculates the radiation concentration by using the count number measured by the low range detector 3 for the low background radioactivity level at the normal time. Detection can be performed with higher sensitivity. On the other hand, when an accident or the like occurs and the radioactivity concentration contained in the gas G to be measured increases significantly, the low range detector 3 exceeds the measurement range, but the high range detector 4 is incident on the collimator 7. Since the radiation dose is reduced, it can be kept within the measurement range. At this time, the control unit 30 determines that the radioactivity concentration has exceeded the range to be measured by the low range detector 3. Then, the radiation concentration is calculated using the count number using the radiation detection signal measured by the high range detector 4 in which the current radioactive concentration is in the measurement range. As described above, the control unit 30 appropriately calculates the radioactivity at the high concentration level by calculating the radioactivity concentration using the count number obtained from the high range detection unit 4 in the event of an abnormality such as an accident. Can do. As a result, it is possible to meet the demand for continuous monitoring over a wide range from a low concentration level to a high concentration level.

  As described above, in the radioactivity measuring apparatus 1 of the present embodiment described in detail, the gas flow path system for taking in the sampling gas is made one system as compared with the structure of the radiation gas monitor disclosed in Patent Document 1 or Patent Document 2. It is possible to perform continuous monitoring over a wide area by providing only one chamber 2. As a result, an increase in size and complexity of the monitor facility can be avoided.

  Further, when comparing the effects of the case where the range parallel switching type is adopted as the radiation gas monitor, in the configuration of the radiation gas monitor disclosed in Patent Document 1 or Patent Document 2, the gas flow between the low range monitor and the high range monitor is described. Although switching of the path is required, a predetermined time is required until the gas to be measured is filled in the switching destination chamber, and there is a problem that accurate measurement cannot be performed during that time. Further, in the configuration in which one radiation detector is used for both the low range monitor and the high range monitor as in the radiation gas monitor shown in Patent Document 2, when the measurement target range is switched from the low range to the high range (or vice versa). There is a problem that it takes time until a normal measurement state is obtained corresponding to the measurement range of the switching destination. According to the radioactivity measuring apparatus 1 of the present embodiment, the low range detector 3 and the high range detector 4 maintain the normal measurement state in parallel at the same time regardless of whether it is normal or abnormal. Even if the measurement range is switched between normal and abnormal times, continuous measurement is possible without causing missing measurements.

  In addition, since the present embodiment includes the first collimator 7 and the second collimator 8 corresponding to the measurement target ranges of the low range detector 3 and the high range detector 4, the low range detector 3 and the high range detector 4 can be detectors having the same detection sensitivity (same specifications). The first collimator 7 and the second collimator 8 are set to have the same opening width (or the collimator is removed), and detectors having different detection sensitivities are used as the low range detector 3 and the high range detector 4. May be.

In FIG. 1, the measurement unit is configured by a chamber 2 having a measurement space S ₁ (see FIG. 2), and the radioactivity measurement device 1 is provided in the middle of sampling pipes 21 and 22 connected to the exhaust pipe 20. It has been. However, in this Embodiment, the sampling point or installation place of the radioactivity measuring apparatus 1 is not limited, It can be set as the following sampling points or installation places.

  FIG. 4 is a system diagram of a radioactive gas monitor system that samples gas from the exhaust duct. FIG. 4 shows a radioactive gas monitor system applied to a gaseous emission radioactive material sampling system in a nuclear facility of a pressurized water reactor (PWR). 4, the same reference numerals as those in FIG. 1 denote the same parts as those in FIG. In FIG. 4, the radioactivity measurement apparatus 1 is provided in the middle of sampling pipes 51 and 52 connected to an exhaust pipe duct 50 that is a final duct connected to the exhaust pipe 20. The radioactivity measurement apparatus 1 shown in FIG. 4 includes a chamber 2 as a measurement unit, a low range detector 3 and a high range detector 4 as in FIG. 1 and FIG. Yes. As shown in FIG. 4, a dust collection unit 23, a pump 27, a flow control valve 26, a flow meter 25, and the like are connected to the upstream sampling pipe 51, but this is merely an example.

In the above description, only the structure and the detector 3 for the low range to high range detector 4 has been described for the case where the opposing sandwiching the measurement space S _1, the present invention is that opposed pair of detectors Not.

  FIG. 5 is an explanatory diagram of a radioactivity measuring apparatus arranged in parallel with the process piping. FIG. 6 is an enlarged cross-sectional view of a portion surrounded by A shown in FIG. The radioactivity measurement apparatus shown in FIG. 5 shows a modification in which a low range detector and a high range detector are arranged in parallel. In addition, this modification is an example in which the installation location of the radioactivity measurement apparatus 1 is a process pipe.

In the radioactivity measurement apparatus 60 shown in FIG. 5, detectors 66 and 67 are attached to a measurement unit 61 configured by a part of an exhaust system process pipe 62. The process pipe 62 is a pipe on the way to guide exhaust gas to the exhaust pipe 20. Process piping 62, the measurement unit 61 to form a measurement space S ₂ of a predetermined volume part of the pipe is provided. The measuring unit 61 is connected between the downstream process pipe 63 and the upstream process pipe 64 to constitute the process pipe 62 as a unit. The measurement unit 61 is configured so that both ends thereof have the same diameter as the process pipe 62, and the flanges 65 a formed at both ends of the measurement unit 61 are joined and fixed to the flanges 65 b of the opposing process pipes 63 and 64. ing. Thereby, the measurement part 61 which can attach the detectors 66 and 67 to a part of process piping 62 can be integrated. The exhaust gas passes through the process pipe 62 in the direction of the arrow shown in FIG.

As shown in FIGS. 5 and 6, a low range detector (first detector) 66 having a detection surface 66 a facing the measurement space S ₂ is attached to the measurement unit 61. The measurement space S high range detector with its detection surface 67a in ₂ (second detector) 67 is attached to the measuring unit 61. In the embodiment shown in FIGS. 5 and 6, the low range detector 66 and the high range detector 67 differ from FIG. 2 in the direction in which the gas to be measured flows with respect to the measurement unit 61 (the arrow in FIG. 5). Direction).

As shown in FIG. 6, between the measurement space S ₂ and the low-range detector 66, a first collimator 68 having an opening corresponding to the measured range of the low-range detector 66 is provided . Between the high range for the detector 67 and the measurement space S _2, the second collimator 69 is provided with an opening corresponding to the measured range of the high-range detector 67. Note that the low-range detector 66 and the high-range detector 67 shown in FIGS. 5 and 6 can have the same configuration as the detector shown in FIGS. 3A and 3B.

  As in this modification, by incorporating the measurement unit 61 in the process pipe 62 and including the radioactivity measurement device 60, it is not necessary to guide the sample gas to the measurement container through the sampling pipe, and the configuration can be simplified.

Even in the configuration in which a part of the process pipe 62 is the measurement unit 61 as in the above modification, the low range detector 66 and the high range detector 67 are connected to the measurement unit 61 as in FIG. across the measurement space S ₂ may be opposed. Further, even in the configuration using the chamber 2 shown in FIG. 2, the low range detector 3 and the high range detector 4 are placed in the direction in which the gas G to be measured flows with respect to the chamber 2 as in the above modification. Can be arranged in parallel along.

  According to the radioactivity measuring apparatus of the present invention, it is possible to detect a change in radioactivity concentration with high accuracy without missing during normal times and when there is an abnormality such as an accident, and the radioactivity measuring device can be used appropriately in a nuclear reactor facility or the like. At this time, the radioactivity measuring device of the present invention can be arranged in the middle of the sampling pipe branched from the exhaust pipe or the exhaust pipe duct, or can be configured by using a part of the process pipe, in addition to the radioactivity measurement. Miniaturization of the device can be realized, and a radioactivity measuring device can be appropriately installed in a place where a radioactivity measuring device is required according to inspection standards, examination guidelines, and the like.

1, 60 Radioactivity measuring device 2 Chamber (measurement part)
S ₁ , S ₂ Measurement space 3, 66 Low range detector (first detector)
3a, 4a, 66a, 67a Detection surface 4, 67 High range detector (second detector)
5, 6 Detector case 7, 8, 68, 69 Collimator 9 Sealed membrane 11, 12 Detector body 13, 15 Shield base 14, 16 Connector 17 Storage cylinder 20 Exhaust cylinder 21, 22, 51, 52 Sampling piping 30 Control section 31 Shielding container 41 Plastic scintillator 43 Photomultiplier tube 48 NaI scintillator 50 Exhaust pipe duct 61 Measuring section 62, 63, 64 Process piping

Claims (7)

A measurement unit comprising a part of a chamber or process piping forming a measurement space of a predetermined volume, and a measurement gas passing through the measurement space;
A first detector which is attached to the measurement unit so as to direct the detection surface toward the measurement space, and has a relatively low range of the radioactivity concentration of the gas to be measured;
A second detector that is attached to the measurement unit so as to direct the detection surface toward the measurement space, and has a relatively high range of the radioactivity concentration of the gas to be measured;
A radioactivity measuring apparatus comprising:   The radioactivity measurement apparatus according to claim 1, wherein the first detector and the second detector are disposed to face the measurement unit with the measurement space interposed therebetween.   The radioactivity measurement apparatus according to claim 1, wherein the first detector and the second detector are arranged in parallel along a direction in which the gas to be measured flows with respect to the measurement unit. . A first collimator provided between a detection surface of the first detector and the measurement space, and having an opening corresponding to a measurement target range of the first detector;
A second collimator provided between a detection surface of the second detector and the measurement space, and having an opening corresponding to a measurement target range of the second detector;
The radioactivity measurement apparatus according to claim 2 or 3, characterized by comprising:   The radioactivity measuring apparatus according to claim 4, wherein the first detector and the second detector have the same detection sensitivity.   The said measurement part is comprised in the chamber which forms the said measurement space, and is provided in the middle of the sampling piping connected to the exhaust pipe or the exhaust pipe duct, The claim 1 characterized by the above-mentioned. Radioactivity measuring device. The radioactivity measurement apparatus according to claim 1, wherein the measurement unit is configured by a part of a process pipe of an exhaust system.

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