JP2010256035A - Device for identifying position of inner wall of reactor primary system pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately identifying the position of an inner wall of a reactor primary system pipe by quantifying radiation from a radioactive nuclear species attached to the inner wall while avoiding the problem of an exposure dose. <P>SOLUTION: A device for identifying the position of an inner wall of a reactor primary system pipe includes: a pair of radiation detectors disposed substantially in a line with the primary system pipe therebetween and detecting a pair annihilation γ rays generated by a positron emitted from the radioactive nuclear species attached to the inner wall of the primary system pipe; a simultaneous counting device for counting the pair annihilation γ rays substantially at the same time; a detector moving device for moving the radiation detectors substantially in parallel along the cross-section of the primary system pipe; a pair annihilation γ ray intensity distribution calculation device for performing data processing on the total absorption peak counting rate of a radiation energy distribution obtained by the simultaneous counting device at the positions of the moved radiation detectors as an intensity distribution of the pair annihilation γ rays with respect the positions of the radiation detectors; and a positional relationship identifying device for calculating the correlation between the position of the primary system pipe in the cross-section and the positions of the radiation detectors based on the intensity distribution of the pair annihilation γ rays, and identifying the position of the primary system pipe in the cross-section from any positions of the radiation detectors. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In order to accurately identify the positional relationship between the inner wall portion of the piping and the radiation detector, which is required when monitoring the radiation in the primary piping performed during the operation of the reactor, The present invention relates to an inner wall position identification device for a reactor primary system pipe that quantifies the radiation emitted from a radionuclide attached to a pipe inner wall and identifies the inner wall position of the pipe from the radiation intensity distribution obtained by moving the position of the radiation detector.

  A monitoring device (hereinafter referred to as “radiation online monitor”) that monitors radiation within the reactor primary system piping (hereinafter referred to as “primary system piping”) performed during the operation of the reactor is provided in the reactor containment vessel. Since the radiation dose is very high compared to the periodic inspection, it is impossible to carry out measurement by the same method as the periodic inspection, and it is impossible to use the device used for the periodic inspection.

  The influence of background caused by interfering radionuclides (for example, N-13, N-16, F-18, etc.) contained in the reactor coolant flowing in the primary piping during reactor operation and reducing the measurement accuracy In order to minimize, the radiation online monitor needs to optimize the surface area and volume ratio of the primary piping expected by the collimator. For this purpose, it is necessary to accurately grasp the positional relationship between the inner wall portion of the primary system pipe and the radiation detector provided in the radiation online monitor.

  Currently, the positional relationship between the inner wall of the primary system pipe and the radiation detector is the actual thickness from the outside of the heat insulating material, or the actual thickness is measured from the outside of the primary system pipe by removing the heat insulating material. It is possible to estimate using the heat insulation thickness. However, even within the reactor containment vessel during regular inspection, the radiation dose is relatively high, leading to an increase in the exposure dose, and it is difficult to carry out actual measurements for a long time. Furthermore, the heat insulating material in an actual plant environment often does not have a uniform thickness as determined at the time of design due to deformation or the like. Therefore, it is difficult to grasp the positional relationship with high accuracy by the method using the actual size. Therefore, at present, it is extremely difficult to accurately measure the concentration on the inner wall of the primary pipe of the radionuclide obtained from the radiation online monitor.

  If the positional relationship between the inner wall of the reactor primary piping and the radiation detector can be identified, the measurement accuracy of the radiation monitoring device can be effectively improved, and the exposure dose can be effectively reduced. As a related art related to this, Patent Document 1 discloses that the radioactivity deposited almost uniformly on the inner surface of the pipe, the aqueous solution-like radioactivity almost uniformly distributed inside the pipe, and the uniform distribution inside the pipe. Two or more γ-ray measured values measured at two or more measurement points by changing the angle facing the piping of the detection system using a detection system for γ-rays emitted from gaseous radioactivity, A pipe internal radioactivity measurement method is disclosed in which the radioactivity is quantified using the inner diameter of the pipe, the outer diameter of the pipe, the distance from the axis of the pipe to the detector, etc. known from the previous stage of measurement.

  Further, Patent Document 2 discloses a method for accurately measuring the radioactivity of a positron (positron) emitting nuclide for a sample containing an interfering nuclide using a pair of scintillation detectors and a coincidence circuit, and covering a wide measurement range. An apparatus for detecting annihilation gamma rays is disclosed.

Japanese Patent Laid-Open No. Sho 62-223686 JP-A-8-285946

  As described above, the actual size work from the outside of the heat insulating material has a fundamental problem that the radiation dose in the reactor containment vessel is relatively high, leading to an increase in the exposure dose. In actual size work after peeling, the exposure dose will further increase.

  Patent Document 1 discloses one of the techniques for accurately quantifying the radioactivity inside the piping, but the actual actual size and design values are used for the positional relationship between the primary system piping and the radiation detector. However, there is no description of the positional relationship identification by radiation measurement, and the simultaneous counting method that can effectively reduce the contribution of interfering radiation as a radiation measurement technique. There is no description about it at all. And patent document 1 with respect to the subject of this invention of grasping | ascertaining correctly the positional relationship for optimizing the ratio of the primary system piping surface area and primary system piping volume which the radiation detector installed in a radiation online monitor anticipates. Nor does it provide a solution.

Patent Document 2 discloses one technique for simultaneously counting pair annihilation gamma rays. However, Patent Document 2 has no description regarding the annihilation γ-ray intensity distribution due to the movement of the detector device, and further accuracy improvement is required for accurately measuring the inner wall position of the primary piping.
An object of the present invention is to provide an inner wall position identification device for a reactor primary system pipe that solves the above-described problems.

  In order to achieve the above-described object, the inner wall position identification device of the reactor primary system pipe of the present invention is i) a detector that is installed at a substantially linearly opposed position across the reactor primary system pipe. A pair of radiation detectors for detecting annihilation gamma rays by positrons radiated from radionuclides attached to the inner wall of the primary piping by operation of the reactor, and ii) counting the pair annihilation gamma rays at approximately the same time A coincidence device; iii) a detector moving device that moves the radiation detector substantially parallel along the cross-section of the primary piping; and iv) the simultaneous detection at the position of the radiation detector moved by the detector moving device. A pair annihilation γ-ray intensity distribution calculating device for processing the total absorption peak count rate of the radiation energy distribution obtained from the counting device as a pair annihilation γ-ray intensity distribution for the radiation detector position; and v) the pair annihilation γ-ray Intensity distribution Accordingly, the correlation between the position in the cross section of the primary pipe and the radiation detector position is calculated, and the positional relationship identification device that identifies the cross-sectional direction position of the primary pipe from an arbitrary position of the radiation detector, It is characterized by providing.

  Further, the inner wall position identification device of the reactor primary system pipe of the present invention is a detector i) installed at a substantially linearly opposed position across the reactor primary system pipe, and the above-mentioned by operation of the reactor A pair of radiation detectors for detecting annihilation gamma rays by positrons radiated from the radionuclide adhering to the inner wall of the primary pipe, and ii) radiating in the 4π direction at approximately the same time as the radionuclide emits the positron A radiation detector for detecting cascade γ rays, iii) a coincidence counting device for counting the pair annihilation γ rays and the cascade γ rays at substantially the same time, and iv) the radiation detector for the primary system. A detector moving device that moves substantially parallel along the cross section of the pipe; and v) the cascade γ-ray radiation so that the measurement region expected by the cascade γ-ray radiation detector and the measurement region expected by the radiation detector overlap. detection Vi) of the radiation energy distribution obtained from the coincidence counting device at the position of each radiation detector moved by the detector moving device and the cascade γ-ray detector moving device; A pair annihilation γ-ray intensity distribution calculating device for processing the total absorption peak count rate as a pair annihilation γ-ray intensity distribution with respect to the radiation detector position; vii) the primary piping based on the pair annihilation γ-ray intensity distribution; A positional relationship identification device that calculates a correlation between a position in the cross section of the radiation detector and a position of the radiation detector, and identifies a position in the sectional direction of the primary piping from an arbitrary position of the radiation detector. .

  Further, the positional relationship identification device of the inner wall position identification device of the reactor primary system pipe according to the present invention is configured such that the radiation detector position that is substantially the center of symmetry of the pair annihilation γ-ray intensity distribution is set to the axis portion of the primary system pipe. And when the distance from the detector position, which is substantially the center of symmetry of the intensity distribution, to the inflection point of the intensity distribution is translated from the axis of the primary piping in the direction of movement of the detector moving device. The correlation between the position in the cross section of the primary pipe and the position of the radiation detector is calculated by setting the distance of

According to the present invention, the radiation online monitor can be installed with high accuracy by identifying the position of the inner wall of the reactor primary system piping using the radionuclide adhering to the primary system piping. Moreover, compared with the conventional method, the exposure amount during work can be reduced. Furthermore, since not only a semiconductor detector such as a Ge semiconductor detector but also an inexpensive scintillator can be employed as the radiation detector, the cost can be reduced. Further, since the pair annihilation γ-rays have a characteristic of being emitted almost oppositely, high-precision measurement is possible without a collimator for ensuring the directivity of the radiation to be detected.
As described above, the present invention has a remarkable effect as compared with the prior art.

The block configuration of the inner wall position identification apparatus of the reactor primary system piping of Example 1 of this invention is shown. An example of the detector installation of Example 1 is shown. An explanatory view of an energy spectrum obtained by the coincidence circuit system of Example 1 is shown. A mode that a pair of radiation detector of Example 1 moves, and primary system piping area distribution which a detector expects are shown. A mode that the detector moving apparatus of Example 1 moves to the circumference direction of primary system piping is shown. The pair annihilation γ-ray intensity distribution 34 is shown when the pipe thickness of the primary system pipe 3 is such that the pair annihilation γ-rays are not substantially attenuated. The pair annihilation γ-ray intensity distribution 34 when the pair annihilation γ-rays are attenuated by the pipe thickness of the primary pipe 3 is shown. A correlation diagram between the position of the radiation detector and the position in the direction along the cross section of the primary pipe 3 is shown. The block structure of the inner wall position identification apparatus of the reactor primary system piping of Example 2 of this invention is shown. As an example of the measurement target nuclide, the decay process by Co-58 is shown. The detection surface at the time of making the shape of the collimator of the radiation detector with which the inner wall position identification apparatus of the reactor primary system piping of Example 3 of this invention is provided is a cylinder is shown. The detection surface at the time of making the shape of the collimator of the radiation detector with which the inner wall position identification apparatus of the reactor primary system piping of Example 3 of this invention is equipped with a prism is shown. In the apparatus for identifying the inner wall position of the reactor primary system piping according to the fourth embodiment of the present invention, a state in which three pairs of radiation detectors are installed in the detector moving device 7 is shown as an example. In the inner wall position identification device of the reactor primary system piping according to the fourth embodiment of the present invention, as an example, a state in which three pairs of detector moving devices 7 are arranged without being connected to the adjacent detector moving devices 7 is shown. The mode that the pair of array type radiation detector was arrange | positioned in the inner wall position identification apparatus of the reactor primary system piping of Example 5 of this invention is shown.

  In the present invention, the present inventors use the radionuclide adhering in the primary system piping to measure the outside of the heat insulating material, or peel off the heat insulating material to make the primary system piping actual size. This is based on new knowledge obtained through various studies on methods for accurately identifying the positional relationship between the pipe inner wall portion and the radiation detector.

This finding is a pair of radiation detectors that are installed at positions that are almost linearly opposite to the primary system piping, and detect annihilation gamma rays emitted by radionuclides attached to the inner wall of the primary system piping due to the operation of the reactor. And
A simultaneous counting device that counts the pair annihilation gamma rays at approximately the same time;
A detector moving device that moves a pair of radiation detectors substantially parallel to the cross-sectional direction of the primary piping;
Paired annihilation γ-rays that process the total absorption peak count rate of the radiation energy distribution obtained from the coincidence counting device for each radiation detector position moved by the detector moving device as a paired annihilation γ-ray intensity distribution for the radiation detector position An intensity distribution calculating device;
The position of the radiation detector at the center of symmetry of the annihilation γ-ray intensity distribution is taken as the position of the axis of the primary piping, and the radiation at the inflection point from the position of the radiation detector at the center of symmetry of the annihilation γ-ray intensity distribution. By calculating the correlation between the radiation detector position and the cross-sectional direction position of the primary system pipe, the distance to the detector position is the distance moved in parallel to the radiation detector movement direction from the axis of the primary system pipe. By providing a positional relationship identification device that identifies the position in the cross-sectional direction of the primary system pipe from the position of the radiation detector, the inner wall position of the reactor primary system pipe can be identified. The contents of the new knowledge will be specifically described below.

A general γ-ray detector is used as a radiation detector for annihilation γ-rays. For example, in the case of a scintillation detector, there are NaI (Tl), CsI (Ce), LaBr ₃ (Ce), BGO, GSO (Ce), LuAG (Pr), and in the case of a semiconductor detector, There are Ge, CdTe, CZT, etc., all of which are applicable to the present invention.

  Examples of the radionuclide that adheres to the primary piping by the operation of the nuclear reactor include Co-60, Co-58, Mn-54, and Fe-59. Examples of the radionuclide contained in the reactor water of the primary piping include N-13, N-16, F-18, and O-19. Here, Co-60 is a radionuclide produced by the (n, γ) reaction of Co-59 contained in the reactor structural material. Hereinafter, Co-58 is also (n, p) of Ni-58. In the reaction, Mn-54 is an (n, p) reaction of Fe-54, Fe-59 is an (n, γ) reaction of Fe-58, and N-13 is an O-16 (p, α) of a water molecule. ), N-16 is the (n, γ) reaction of O-16, F-18 is the (p, n) reaction of O-18, and O-19 is the (n, γ) reaction of O-18. As a result, it is a produced radionuclide.

Among these radionuclides, Co-58, N-13, and F-18 emit pair annihilation gamma rays. In either case, the positron generated by β ⁺ decay interacts with nearby electrons, and radiates two gamma rays of the same energy in both directions of approximately 180 degrees at the same time. Since the mass energy of electrons and positrons is 1.022 MeV, the energy of the two γ rays is 511 keV. Here, the half-lives of Co-58, N-13, and F-18 are about 70.86 days, about 9.965 minutes, and about 109.8 minutes, respectively. F-18 is greatly attenuated during regular inspections compared to when the reactor is in operation, and it is easily expected that F-18 will be significantly less than the annihilation γ-ray intensity contributing to Co-58. Therefore, most of the pair annihilation γ-rays measured at the regular inspection are derived from Co-58.

  The coincidence counting method is a radiation measurement circuit device that counts only when two radiations resulting from one decay are incident on two radiation detectors at almost the same time and become γ-ray detection signals. This measurement method is based on, for example, cascade γ-rays (γ-ray energy 1.173 MeV, 1.332 MeV) radiated from Co-60 adhering to the primary system piping and disturbing nuclides present everywhere in the reactor containment vessel. Since background γ rays are not counted, a high S / N ratio of the total absorption peak can be obtained. Since the energy of the pair annihilation γ-ray is only 511 keV, the output of the coincidence circuit device is processed as data of the wave height distribution by the multichannel wave height analyzer, and the obtained energy spectrum becomes a single peak. From the net count value and measurement time of this peak, the count value by simultaneous counting, that is, the annihilation γ-ray intensity can be obtained.

  The pair of radiation detectors are respectively installed in the detector moving device, and the count value by the coincidence circuit device, that is, the annihilation γ-ray intensity can be obtained at an arbitrary position of the radiation detector. Furthermore, a device is provided for processing data from the obtained pair annihilation γ-ray intensity data as a pair annihilation γ-ray intensity distribution at each radiation detector position. In the acquired pair annihilation γ-ray intensity distribution, it is possible to confirm one position of the radiation detector position and the two positions of the radiation detector positions at the inflection point, which are almost symmetrical centers of the distribution. Here, the radiation detector position at which the distribution is almost symmetrical means the position where the detection surface central axis of the radiation detector intersects with the primary system piping axis. The radiation detector position at the inflection point means the position where the measurement area of the pair of radiation detectors looks at the edge of the primary piping, that is, the position where the inner wall area of the primary piping expected by the pair of radiation detectors is the maximum. is doing.

  The distance from the radiation detector position, which is the center of symmetry of the distribution, to the radiation detector position at the inflection point is from the primary piping axis to the edge of the primary piping in the direction of movement of the detector (in a direction parallel to the detector). It corresponds to the distance. Thus, the correlation between the radiation detector position and the position from the tube axis in the cross section of the primary system pipe is calculated, and from this, from the arbitrary radiation detector position, from the tube axis in the cross section of the primary system pipe By identifying the position, it becomes possible to identify the position of the inner wall of the reactor primary piping. As described above, a positional relationship identification device is provided as a device for processing data. The output of the multi-channel wave height analyzer, the annihilation γ-ray intensity distribution, and the positional relationship identification device is made visible by a display device.

As described above, a pair of radiation detectors are installed at positions that are almost linearly opposed to the primary piping and detect annihilation gamma rays emitted by radionuclides attached to the inner wall of the primary piping by the operation of the reactor. , A coincidence counting device that counts paired annihilation gamma rays at substantially the same time, a detector moving device that moves the pair of radiation detectors substantially in parallel across the section of the primary piping, and a detector moving device A annihilation γ-ray intensity distribution calculating device for processing the data of the total absorption peak count rate of the radiation energy distribution obtained from the coincidence device for each radiation detector position moved by the as a annihilation γ-ray intensity distribution for the radiation detector position; The position of the inflection point from the radiation detector position, which is the center of symmetry of the pair annihilation γ-ray intensity distribution, with the position of the radiation detector position, which is approximately the center of symmetry of the pair annihilation γ-ray intensity distribution, as the axial portion By making the distance to the radiation detector position the distance moved in parallel to the radiation detector movement direction from the axis of the primary system pipe, the position of the radiation detector and the position from the pipe axis in the cross section of the primary system pipe It is equipped with a positional relationship identification device that calculates the correlation and identifies the position from the tube axis in the cross section of the primary system piping from an arbitrary radiation detector position. The inner wall position can be identified.
Preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a basic configuration of Embodiment 1 of the present invention. The device 24 for identifying the inner wall position of the reactor primary system pipe according to the first embodiment includes a radiation detector 1A, a radiation detector 1B, a radiation measurement device 22A, a data processing device 23, and a display device 20. Here, the radiation measuring device 22A includes a preamplifier 8, a high-voltage power supply 9, a main amplifier 10, a timing unit 11, a delay unit 12, a coincidence circuit device 13, a gate circuit system 14, a variable delay circuit system 15, and a peak hold circuit. System 16 is provided. The data processing device 23 includes a multi-channel wave height analyzer 17, a pair annihilation γ-ray intensity distribution calculating device 18, and a positional relationship identifying device 19. The radiation detector 1A and the radiation detector 1B are branched to the timing unit 11 and the variable delay circuit system 15 via the preamplifier 8 and the main amplifier 10. The high voltage power supply 9 is connected to the preamplifier 8. The timing unit 11 is connected to the coincidence counting circuit device 13.

  In the example shown in FIG. 1, as an example, the delay unit 12 is provided between the timing unit 11 connected from the radiation detector 1B and the coincidence counting circuit device 13, but it is installed by this energy discrimination type coincidence processing. Even if the delay unit 12 is provided between the timing unit 11 connected from the radiation detector 1A and the coincidence circuit device 13, it has the same meaning. The variable delay circuit system 15 is connected to the peak hold circuit system 16, and its output line is connected to the multichannel wave height analyzer 17. The coincidence circuit device 13 is connected to the gate circuit system 14, and its output line is connected to the multichannel wave height analyzer 17.

  The multichannel wave height analyzer 17 and the detector moving device 7 are connected to a pair annihilation γ-ray intensity distribution calculating device 18. The pair annihilation γ-ray intensity distribution calculating device 18 is connected to the positional relationship identifying device 19. The multi-channel wave height analyzer 17, the pair annihilation γ-ray intensity distribution calculation device 18, and the positional relationship identification device 19 are all connected to the display device 20.

  The coincidence circuit system configuration shown in FIG. 1 is an example. As another example, when a photomultiplier tube with a scintillation crystal bonded to the radiation detectors 1A and 1B is used, the photomultiplier tube dynode output is placed in front. It is also possible to connect the amplifier 8, the main amplifier 10, and the variable delay circuit system 15 in this order, and connect the photomultiplier tube anode output in this order to the timing unit 11 and the coincidence circuit device.

  FIG. 2 shows an example of detector installation according to the first embodiment. The reactor coolant 21 is a coolant contained in the reactor pressure vessel. The radiation detector 1A and the radiation detector 1B are installed in the detector moving device 7, have a function of moving in the direction of the arrow in the figure, and transmitting radiation detector position information to the data processing device 23.

  The heat insulating material 4 is attached so as to surround the reactor primary system piping 3 to be inspected. In FIG. 1, as an example, the case where the reactor coolant 21 is included in the primary piping 3 is shown, but the reactor coolant 21 may not be included during the periodic inspection. Radionuclide 2 (for example, Co-58, Co-60, Mn-54, Fe-59) is attached to the inner wall of the primary piping 3. The radiation detector 1A and the radiation detector 1B are installed at substantially opposite positions on a straight line, and installed on the detector moving device 7 so as to look at the primary system pipe 3.

  The pair annihilation γ-rays 5 due to the positrons radiated from the radionuclide 2 are emitted in the direction of approximately 180 degrees at the same time, and are detected by the radiation detector 1A and the radiation detector 1B. The radiation detection signals obtained by the radiation detector 1A and the radiation detector 1B are amplified by the preamplifier 8 and the main amplifier 10, and sent to the coincidence circuit device 13 via the timing unit 11. However, in the radiation measuring apparatus 22A shown in FIG. 1, the delay unit 12 is provided between the timing unit 11 connected from the radiation detector 1B and the coincidence circuit apparatus 13, and the timing for coincidence counting is adjusted. It has become.

  The coincidence circuit device 13 is connected to the gate circuit system 14, and a gate signal is sent from the gate circuit system 14 to the multichannel wave height analyzer 17. With this gate signal, the radiation detection signal obtained via the radiation detector 1A and the radiation detector 1B, the preamplifier 8, the main amplifier 10, the variable delay circuit system 15, and the peak hold circuit system 16 It is taken into the analyzer 17.

  FIG. 3 is an explanatory diagram of an energy spectrum obtained by the coincidence circuit system according to the first embodiment. Here, the simultaneous counting circuit device 13 effectively measures the single total absorption peak 25 derived from the pair annihilation γ-ray 5, and obtains the count rate from the net count value and measurement time of the total absorption peak 25. Can do. The count rate obtained here is handled as the pair annihilation γ-ray intensity, and the information is sent from the multichannel wave height analyzer 17 to the pair annihilation γ-ray intensity distribution calculating device 18. Further, the position information of the radiation detector that has obtained the pair annihilation γ-ray intensity is also sent from the detector moving device 7 to the pair annihilation γ-ray intensity distribution calculating device 18.

  FIG. 4 shows the movement of the pair of radiation detectors of Example 1 and the distribution of the area in the primary system piping expected by the detectors. The detector moving device 7 has a function of moving in a direction along the cross section of the primary system pipe 3 while maintaining a condition that the pair of radiation detectors 1A and 1B are located on a substantially straight line across the primary system pipe 3. , And position information based on an arbitrary position of the radiation detector is transmitted to the pair annihilation γ-ray intensity distribution calculating device 18. FIG. 4 shows, as an example, the movement of the measurement region 6 when the radiation detector 1A and the radiation detector 1B looking into the primary piping 3 are installed on the detector moving device 7 and moved, and the detector movement. An area distribution 33 in the primary system piping that is expected from the device 7 is shown.

  When the radiation detector 1A is moved from the left position shown in FIG. 4 to the right, the area in the primary system pipe reaches a maximum value 29 when the edge of the primary system pipe 3 is viewed. When moved from the edge of the primary pipe toward the primary pipe axis 27, the area of the primary pipe expected by the detector shows a minimum point 28 when the detection surface center axis 26 and the primary pipe axis 27 intersect. If the detector is further moved outward in the direction of the primary system piping axis 27, the above-mentioned area is maximized again when the edge portion of the primary system piping 3 is expected. This tendency does not change even if the diameter of the detection surface and the diameter of the primary system pipe change. FIG. 4 shows a state in which the detector moving device 7 moves in parallel along the cross section of the primary system pipe 3, but as shown in FIG. In this case, the same effect can be obtained.

  Next, the pair annihilation γ-ray intensity distribution obtained by the apparatus according to the present invention will be described. FIG. 6 shows that the concentration of the radionuclide 2 adhering to the inner wall of the primary pipe 3 is almost uniform, and the pipe thickness of the primary pipe 3 is such that the annihilation gamma rays are not substantially attenuated. The simulation result of the pair annihilation γ-ray intensity distribution 34 is shown. The tendency of this distribution is the same as in FIG. Also in FIG. 6, there exists an inflection point corresponding to the minimum point 28 at the position where the detection surface central axis 26 and the primary piping axis 27 in FIG. Similarly, in FIG. 6, an inflection point 31 corresponding to the inflection point at a position where the inner area expected by the detector of FIG.

  FIG. 7 shows the annihilation γ-ray intensity distribution when the concentration of the radionuclide 2 adhering to the inner wall of the primary pipe 3 is almost uniform and the annihilation γ-ray 5 is attenuated by the pipe thickness of the primary pipe 3. 34 simulation results are shown. In FIG. 7, since the effective attenuation rate of the pair annihilation γ-ray 5 increases as the edge of the primary system pipe 3 is estimated, the intensity of the pair annihilation γ-ray at the position where the radiation detector 1A has a maximum inner area 29 is expected. However, the distribution symmetry center position 30 does not change, and an inflection point 31 exists at a position where the maximum inner area value 29 expected by the detector is present. There is no change.

  Based on the above simulation results, by measuring three inflection points without considering the effective attenuation rate due to the thickness of the reactor primary system piping 3, the primary system piping 3, the radiation detector 1A, and the radiation detector It is possible to obtain a positional correlation with 1B.

  FIG. 8 shows a correlation diagram between the position of the radiation detector and the position in the direction along the cross section of the primary system pipe 3. Here, as an example, the radiation detector position at the distribution symmetry center position 30 is the position of the primary system piping shaft 27 and the origin of the position along the cross section of the primary system piping 3. Since the position of the inflection point 31 corresponds to the position moved from the primary system piping shaft 27 in parallel to the direction in which the detector moving device 7 has moved, the distance from the distribution symmetrical center position 30 to the inflection point 31 is expressed as X , Y, the positions along the cross section of the primary piping 3 are X and Y from the primary piping shaft 27, respectively. The approximate curve 35 is assumed to be approximated by a linear function as an example using the above three points of the distribution symmetry center position and two inflection points. Then, from this approximate curve 35, it is possible to identify the position along the cross section of the primary system pipe 3 from any radiation detector position, and from the result, it is possible to identify the inner wall position of the primary system pipe 3 at the radiation detector position. Become.

  FIG. 9 shows an inner wall position identification device for a reactor primary system pipe according to embodiment 2, which is another embodiment of the present invention. In the second embodiment, the inner wall position identification device 36 of the reactor primary system piping includes a radiation detector 1A, a radiation detector 1B, a cascade γ-ray radiation detector 37, a radiation measurement device 22B, a data processing device 23, and a display device 20. Except for the cascade γ-ray radiation detector 37 and the radiation measuring device 22B. Here, the radiation measuring device 22B includes a preamplifier 8, a high voltage power source 9, a main amplifier 10, a timing unit 11, a delay unit 12, a coincidence circuit device 13, a gate circuit system 14, a variable delay circuit system 15, and a peak hold circuit. System 16 is provided.

The radiation detector 37 for the cascade γ-ray detects the cascade γ-ray 40 emitted in the process in which the radionuclide 2 adhering to the primary system pipe 3 is excited by β ⁺ decay and transitions from the excited state to the ground state. In addition, the measurement region is installed in the cascade γ-ray detector moving device (not shown in FIG. 9) so as to overlap the measurement region expected by the radiation detector. Cascade gamma rays 40 are emitted in the 4π direction and often have no angular correlation. FIG. 9 shows one cascade γ-ray radiation detector 37, but the number of cascade γ-ray radiation detectors may be one or more.

FIG. 10 shows a decay process by Co-58 as an example of a measurement target nuclide. Co-58 decays into excited Fe-58 due to β ⁺ decay. The time required to reach the ground state is generally an extremely short time, and is a time that can be ignored in the measurement by a general radiation measurement system. Therefore, in actual measurement, the pair annihilation γ-ray 5 and the cascade γ-ray 40 are detected at almost the same time. When the detection of the pair annihilation γ-ray 5 by the radiation detector 1A and the radiation detector 1B and the detection of the cascade γ-ray 40 by the radiation detector 37 for the cascade γ-ray are almost the same time, the radiation detector 1A and the radiation detector The radiation detection signals obtained by 1B and the cascade γ-ray radiation detector 37 are amplified by the preamplifier 8 and the main amplifier 10 and sent to the coincidence circuit system 13 via the timing unit 11. Then, when the coincidence circuit system 13 sends the signal to the gate circuit system 14, the gate circuit system 14 sends a gate signal to the multichannel wave height analyzer 17.

  The radiation detection signals obtained via the radiation detector 1A, radiation detector 1B, cascade γ-ray radiation detector 37, preamplifier 8, main amplifier 10, variable delay circuit system 15 and peak hold circuit system 16 are Then, it is taken into the multichannel wave height analyzer 17 and further displayed on the display device 20 via the pair annihilation gamma ray intensity distribution calculating device 18 and the positional relationship identifying device 19.

  In the embodiment shown in FIG. 9, as an example, the delay unit 12 is provided between the timing unit 11 connected from the radiation detector 1B and the coincidence circuit device 13, but in this energy discrimination type coincidence process, The delay unit 12 to be installed may be provided between the timing unit 11 connected from the radiation detector 1A and the coincidence circuit device 13.

  Note that a circuit system for transmitting a radiation detection signal obtained from the cascade γ-ray radiation detector 37 using the high-voltage power supply 9, the preamplifier 8, and the main amplifier 10 is transmitted as a variable delay circuit system 15 and a peak hold circuit. The system connected to the multi-channel wave height analyzer 17 via the system 16 and the system connected to the coincidence counting circuit device 13 via the timing unit 11 are replaced with the system connected via the timing unit 11 instead. Only the system connected to the counting circuit device 13 may be used.

  In Example 2, since the cascaded γ-ray radiation detector 37 is provided, accidental coincidence due to background γ-rays incident on the radiation detector 1A and the radiation detector 1B can be effectively suppressed. Thus, counting with higher accuracy becomes possible.

  An inner wall position identification device for a reactor primary system pipe according to Embodiment 3 of the present invention will be described with reference to FIGS. 11 and 12. Here, in the radiation detector 1A, the radiation detector 1B, and the cascade γ-ray radiation detector 37, a collimator 43 that defines a measurement region expected by each detector and an attached collimator 42 that can be attached to the collimator 43 are provided. Is the same as in either Example 1 or Example 2.

  In the third embodiment, the collimator shape of the attached collimator 42 is a cylinder (see FIG. 11) or a prism (see FIG. 12), and the detection surface 44 is the radiation detector 1A, the radiation detector 1B, or the cascaded γ-ray radiation detector 37. It is a detection part. The collimator 43 has a shape that looks at the edge 41 of the detection surface.

  In the third embodiment, the detection portions of the radiation detector 1A, the radiation detector 1B, and the cascade γ-ray radiation detector 37 can be arbitrarily changed by the attached collimator 42 without replacing each detector. High position detection accuracy can be expected by reducing the shape of the collimator.

  An inner wall position identifying device for a reactor primary system pipe according to Embodiment 4 of the present invention will be described with reference to FIGS. 13 and 14. In the fourth embodiment, there are N pairs of radiation detectors when N is a natural number of 1 or more, and the N pairs of radiation detectors are installed in parallel to the detector moving device. 1 to any one of Example 3.

  FIG. 13 shows, as an example, three pairs of radiation detectors from the radiation detector 1A to the radiation detector 1F, and these radiation detectors are installed in the detector moving device 7, and this detector moving device 7 Shows the inner wall position identification device of the reactor primary system piping, which has a structure connected to the adjacent detector moving device 7, and these three pairs of radiation detectors are placed so as to face each other. ing.

FIG. 14 shows an inner wall position identification device of a reactor primary system pipe in which the detector moving device 7 is not connected to the adjacent detector moving device 7 as an example.
In Example 4 described above, since the movement time of the radiation detector can be shortened, the measurement time can be shortened.

  In the first to fourth embodiments described above, the operation of the detector moving device for moving the radiation detector and the cascade γ-ray radiation detector is preferably programmed in advance and automatically.

  The inner wall position identifying device for the reactor primary system piping according to the fifth embodiment of the present invention will be described with reference to FIG. The fifth embodiment is the same as any one of the first to fourth embodiments except that the detector moving device 7 includes an array type radiation detector 45A and an array type radiation detector 45B.

  In the fifth embodiment, as an example, an array type radiation detector 45A and an array type radiation detector 45B are provided along the cross section of the primary system pipe 3. By measuring the coincidence signal in a pair of arrays installed almost opposite to each other and shortening the array width 46, the position identification accuracy can be improved, and the movement of the radiation detector can be omitted. Measurement time can also be shortened.

1A, 1B: Radiation detector, 2 ... Radionuclide, 3 ... Primary reactor piping, 4 ... Insulation, 5 ... Anti-annihilation gamma ray, 6 ... Measurement area, 7 ... Detector moving device, 8 ... Preamplifier , 9 ... High-voltage power supply, 10 ... Main amplifier, 11 ... Timing unit, 12 ... Delay unit, 13 ... Simultaneous counting circuit device, 14 ... Gate circuit system, 15 ... Variable delay circuit system, 16 ... Peak hold circuit system, 17 ... Multi-channel wave height analyzer, 18 ... Counter annihilation gamma ray intensity distribution calculation device, 19 ... Position relation identification device, 20 ... Display device, 21 ... Reactor coolant, 22A, 22B ... Radiation measurement device, 23 ... Data processing device, 24 ... Inner wall position identification device for reactor primary system piping, 25 ... Total absorption peak, 26 ... Detection surface central axis, 27 ... Primary system piping axis, 28 ... Minimum point, 29 ... Maximum inner area, 30 ... Distribution symmetry center Position, 31 ... Inflection point, 32 ... Count distribution, 33 ... Area distribution in primary piping, 34 ... Anti-annihilation gamma ray intensity distribution, 35 ... Approximate curve, 36 ... Reactor Primary wall inner wall position identification device, 37 ... Radiation detector for cascade γ-ray, 38 ... Collimator, 39 ... Radiation detector measurement area for cascade γ-ray, 40 ... Cascade γ-ray, 41 ... Edge part of detection surface, 42 ... attached collimator, 43 ... collimator, 44 ... detection surface, 45A, 45B ... array type radiation detector, 46 ... array width

Claims (7)

A detector installed at an almost linear position across the reactor primary system piping, and a pair of annihilation gamma rays by positrons emitted by radionuclides attached to the inner wall of the primary system piping due to the operation of the reactor A pair of radiation detectors for detecting
A coincidence device for counting the pair annihilation gamma rays at approximately the same time;
A detector moving device for moving the radiation detector substantially parallel along the cross-section of the primary piping;
The total absorption peak count rate of the radiation energy distribution obtained from the coincidence device at the position of the radiation detector moved by the detector moving device is subjected to data processing as a pair annihilation γ-ray intensity distribution with respect to the radiation detector position. Annihilation γ-ray intensity distribution calculation device,
Based on the pair annihilation γ-ray intensity distribution, the correlation between the position in the cross-section of the primary pipe and the position of the radiation detector is calculated, and the position in the cross-sectional direction of the primary pipe is calculated from an arbitrary position of the radiation detector. A positional relationship identification device to identify;
An inner wall position identification device for a reactor primary system pipe characterized by comprising: A detector installed at an almost linear position across the reactor primary system piping, and a pair of annihilation gamma rays by positrons emitted by radionuclides attached to the inner wall of the primary system piping due to the operation of the reactor A pair of radiation detectors for detecting
A radiation detector for cascade γ-rays that detects cascade γ-rays radiating in the 4π direction at approximately the same time that the radionuclide emits the positrons;
A coincidence device for counting the pair annihilation gamma rays and the cascade gamma rays at approximately the same time;
A detector moving device for moving the radiation detector substantially parallel along the cross-section of the primary piping;
A cascade γ-ray detector moving device for moving the cascade γ-ray radiation detector so that a measurement region expected by the cascade γ-ray radiation detector and a measurement region expected by the radiation detector overlap;
The total absorption peak count rate of the radiation energy distribution obtained from the coincidence counting device at the position of each radiation detector moved by the detector moving device and the cascade γ-ray detector moving device is compared with the radiation detector position. A pair annihilation γ-ray intensity distribution calculating device for processing data as an annihilation γ-ray intensity distribution;
Based on the pair annihilation γ-ray intensity distribution, the correlation between the position in the cross-section of the primary pipe and the position of the radiation detector is calculated, and the position in the cross-sectional direction of the primary pipe is calculated from an arbitrary position of the radiation detector. A positional relationship identification device to identify;
An inner wall position identification device for a reactor primary system pipe characterized by comprising: In the positional relationship identification device according to claim 1 or 2,
The position of the radiation detector, which is substantially the center of symmetry of the pair annihilation γ-ray intensity distribution, is the position of the axial portion of the primary piping, and the inflection of the intensity distribution from the detector position, which is the center of symmetry of the intensity distribution. By setting the distance to the point to be the distance when translated from the axis of the primary system pipe in the direction of movement of the detector moving device, the position in the cross section of the primary system pipe and the radiation detector position An inner wall position identification device for a reactor primary system pipe characterized in that the correlation is calculated. In the inner wall position identification device for a reactor primary system pipe according to any one of claims 1 to 3,
Reactor primary piping characterized in that it has a collimator smaller than the detection surface of the radiation detector, and the position identification accuracy of the primary piping can be changed by arbitrarily changing the collimator diameter. Inner wall position identification device. In the inner wall position identification device for a reactor primary system pipe according to any one of claims 1 to 4,
When N is a natural number of 2 or more, the pair of radiation detectors has N pairs, and each pair of the radiation detectors is installed in parallel on the detector moving device. An apparatus for identifying the position of the inner wall of the primary piping of the nuclear reactor. In the inner wall position identification device for a reactor primary system pipe according to any one of claims 1 to 4,
When N is a natural number of 2 or more, the pair of radiation detectors has N pairs, and the N pairs of radiation detectors are arranged in parallel on the detector moving device in an array. A device for identifying the position of the inner wall of the reactor primary piping.   The inner wall position identification device for a reactor primary system pipe according to any one of claims 1 to 6, wherein the detector moving device is automatically operated. apparatus.

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