JP5034101B2 - Radiation monitoring apparatus and radiation monitoring system - Google Patents

Description

  The present invention relates to a radiation monitoring apparatus and a radiation monitoring system, and more particularly to a radiation monitoring apparatus and a radiation monitoring system provided in a primary piping of a nuclear power plant.

  A nuclear power plant stores nuclear reactor fuel in a reactor pressure vessel and generates thermal energy by fissioning the nuclear reactor fuel. Primary reactor piping is connected to the reactor pressure vessel, the reactor coolant is circulated inside and outside the reactor pressure vessel, the power plant is operated, and the reactor pressure vessel is controlled to a predetermined temperature range. Yes. As described above, the primary system piping for circulating the reactor coolant plays an important role in the nuclear power plant, and nuclides that generate radiation adhere to the inside of the primary system piping. In maintaining and managing a nuclear power plant, it is important to identify and quantify nuclides adhering to the inside of the primary piping.

  At present, radiation monitoring in the primary piping, that is, identification and quantification of the measurement target nuclide adhering to the primary piping is performed only at the time of periodic inspection using a general-purpose radiation detector. In order to effectively reduce work exposure during periodic inspections of nuclear power plants and control radionuclides adhering to primary piping, they adhere to primary piping not only during periodic inspections but also during operation of nuclear power plants. It is expected to identify and quantify the measurement target nuclide, and it is desired to realize a radiation monitoring apparatus and a radiation monitoring system that enable this.

  In Patent Document 1, an on-line germanium nuclide detector is installed on the side of the reactor primary system high-temperature pipe, and the amount of radioactivity attached to the pipe during the operation of the reactor plant is measured. A measurement method of a reactor primary system and a method of reducing reactor water radioactivity concentration, which are characterized by controlling the quality of water and feed water, are described.

  Patent Document 2 discloses, as a conventional example of a radiation monitor, an annihilation gamma ray radiated from a disturbing nuclide such as N-13 by configuring two opposed γ-ray detectors and a non-coincidence circuit or coincidence circuit. The radiation monitor which suppresses the influence of this and measures a measurement object nuclide accurately is described.

  Patent Document 3 describes a measurement method for measuring gamma rays emitted from deposited radioactivity, aqueous radioactivity, and gaseous radioactivity inside a pipe through a collimator from the outside of the pipe.

JP-A-8-304584 JP-A-8-101275 JP 62-223683 A

  As explained in the background section, in order to effectively reduce work exposure during periodic inspections of nuclear plants and control radioactive radionuclides attached to primary piping, nuclides attached to primary piping during operation of the nuclear plant Realization of a radiation monitoring device and a radiation monitoring system for measuring

  However, since the radiation dose in the reactor containment vessel during operation of the nuclear power plant is very high compared to the periodic inspection, there is a method for identifying and quantifying the measurement target nuclide adhering to the primary piping used during the periodic inspection. Radiation measurements could not be performed in the same way. In particular, background radiation generated from disturbing nuclides (N-16, O-19, etc.) contained in the reactor coolant flowing in the primary system piping becomes noise, and the primary system piping is selected from the background radiation noise. It was difficult to detect radiation generated from the target nuclide adhering to the inside.

  For example, in the radiation measurement method described in Patent Document 1, the influence of noise of background radiation generated from interfering nuclides contained in the reactor coolant flowing in the primary system piping is not considered, and the operation of the nuclear power plant is not performed. In addition, it was difficult to detect the radiation generated from the measurement target nuclide adhering to the primary system piping by suppressing the influence of background radiation noise at an arbitrary location of the primary system piping.

  As described above, in the conventional radiation monitoring apparatus and its radiation monitoring system, the influence of the interfering nuclides is suppressed, and the target nuclides are highly sensitive by discriminating the interfering nuclides adhering to the primary piping. It was difficult to measure with high accuracy. For this reason, the adhesion kinetics of the target nuclide in the primary piping during operation of the nuclear power plant has not been clarified, and there is a problem that the design, operation and maintenance of the nuclear power plant cannot be performed safely and efficiently. there were.

  An object of the present invention is to provide a radiation monitoring apparatus and a radiation monitoring system in a nuclear plant primary system pipe capable of measuring a measurement target nuclide adhering in the primary system pipe during operation of the nuclear plant with high accuracy and high sensitivity. .

  The radiation monitoring apparatus of the present invention that achieves the above-described object includes at least two radiation detectors that detect, via a collimator, radiation including cascaded γ-rays radiated by a measurement target nuclide attached to a pipe through which a radioactive fluid flows. A radiation measurement processing device that counts detection signals related to the cascade γ rays detected at approximately the same time by the radiation detector from among the detection signals of the radiation detected by the radiation detector, and the radiation detector The measurement target range expected by the collimator installed in the pipe is less than or equal to ½ of the pipe radial direction inner area existing in the same plane as the collimator central axis.

  Further, the radiation monitoring system of the present invention is a radiation monitoring system included in a primary piping of a nuclear power plant connected to a reactor pressure vessel in which nuclear reactor fuel is stored, wherein the reactor pressure vessel includes the atomic pressure vessel. Thermal energy is generated by the reactor fuel, and the primary system pipe circulates a reactor coolant inside and outside the reactor pressure vessel, and the primary system pipe passes the reactor coolant. Among the radiation detection signals detected by the radiation detector, at least two radiation detectors for detecting radiation including cascade γ-rays radiated from the measurement target nuclide attached to the pipe through the collimator, the radiation A radiation measurement processing device that counts detection signals related to the cascade γ-rays detected at approximately the same time by a detector, and the radiation detector A measurement target range expected by the collimator to be installed is ½ or less of a pipe radial direction inner area of the primary pipe existing in the same plane as the central axis of the collimator.

  According to the present invention, it is possible to provide a radiation monitoring apparatus and a radiation monitoring system in a nuclear plant primary system pipe capable of measuring a measurement target nuclide adhering in the primary system pipe during operation of the nuclear plant with high accuracy and high sensitivity. it can.

  The present invention is based on new knowledge obtained by various studies on methods for distinguishing between the measurement target nuclide adhering in the primary system pipe and the interfering nuclide contained in the reactor coolant flowing in the primary system pipe. It was made. This finding focuses on the cascade γ-rays that the target nuclides adhering in the primary piping radiate in the 4π direction at approximately the same time, and when the cascade γ-rays radiated at approximately the same time are detected at the same time, By counting, the influence of the radiation emitted from the disturbing nuclides contained in the reactor coolant flowing in the primary piping is removed, and the measurement target nuclides adhering in the primary piping are measured. As described above, in the present invention, since counting is performed only when two or more cascaded γ-rays whose energy is known in advance are simultaneously measured, background γ-rays due to interfering nuclides can be greatly reduced.

  In addition, the radiation from the interfering nuclides contained in the reactor coolant flowing in the primary piping is very strong, so the SN ratio of the cascade γ rays emitted from the measurement target nuclides to the background γ rays by the interfering nuclides is improved. Therefore, the measurement target range expected by the collimator equipped in the radiation detector is set to ½ or less of the pipe radial direction inner area existing in the same plane as the collimator central axis. In this way, in the present invention, by optimizing the ratio of the primary pipe surface area and the primary pipe volume that the radiation measurement system expects, that is, the ratio of the measurement target nuclide to be measured and the disturbing nuclide It is possible to detect the cascade γ-rays emitted from the measurement target nuclide with high sensitivity and high accuracy while suppressing the influence of the background radiation generated from the nuclide.

  In the present invention, by combining the simultaneous detection of cascade γ rays from the measurement target nuclides adhering to the primary system piping and the selection of the measurement target range expected by the collimator equipped in the radiation detector, It is possible to realize a radiation monitoring apparatus and a radiation monitoring system capable of measuring a measurement target nuclide adhering in a plant primary system pipe with high sensitivity and high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same referential mark is attached | subjected to the same component and description is abbreviate | omitted.

  FIG. 1 shows a radiation monitoring device in the primary piping of the nuclear power plant according to the first embodiment. The radiation monitoring apparatus in the nuclear power plant primary system piping (hereinafter abbreviated as primary system piping) of the first embodiment includes radiation detectors 1A and 1B, a collimator 3, a coincidence counting circuit 13, and a multichannel wave height analyzer 15. And a radiation measurement processing device 60 connected to the radiation detectors 1A and 1B.

  In the first embodiment shown in FIG. 1, the signals detected by the radiation detector 1A and the radiation detector 1B are sent to the timing units 11A, 11B and the preamplifiers 8A, 8B and the main amplifiers 10A, 10B, respectively. Branches to the variable delay amplifiers 14A and 14B. The preamplifiers 8A and 8B are connected to high voltage power supplies 9A and 9B. The coincidence circuit 13 is connected to the timing units 11A and 11B.

  A delay unit 12 is provided between the timing unit 11B that receives the detection signal of the radiation detector 1B and the coincidence circuit 13. The delay unit 12 is installed for the energy discrimination type coincidence process, and matches the condition connected from the radiation detector 1A and the condition connected from the radiation detector 1B.

  The variable delay amplifiers 14A and 14B are connected to the peak hold circuits 45A and 45B, and the outputs of the radiation detector 1A and the radiation detector 1B are input to the multichannel wave height analyzer 15. The coincidence circuit 13 is connected to the multi-channel wave height analyzer 15 and the scaler 17 through the gate circuit 16. The multichannel wave height analyzer 15 is connected to a data processing device 18, and the data processing device 18 is connected to a display device 19. The radiation monitoring apparatus according to the first embodiment of the present invention includes a data processing device 18 and retains data detected by the radiation detectors 1A and 1B for a long period of several months to one year or more, Can be processed.

  FIG. 2 shows a radiation monitoring system using the radiation monitoring apparatus according to the first embodiment of the present invention. The reactor pressure vessel 51 stores the reactor fuel 56 therein. The main steam 52 containing the radionuclide flows from the reactor pressure vessel 51 to the main steam pipe 53. The main steam 52 becomes the reactor coolant 20 in a condenser (not shown) and is circulated to the reactor pressure vessel 51 through the primary system pipe 6A. Further, the reactor coolant 20 containing the radionuclide flows from the reactor pressure vessel 51 to the primary piping 6B. The reactor coolant 20 is circulated to the reactor pressure vessel 51 via the pump 55.

  Cascade γ-rays 5, 5 ′ emitted from the measurement target nuclide 4 adhering to the primary piping 6 A, 6 B are detected by the radiation detector 1 A and the radiation detector 1 B including the collimator 3 and measured by the radiation measuring device 54. Is done. The measurement result is sent to the data processing device 18, and the display device 19 displays the analysis result such as the amount of the measurement target nuclide 4 adhering to the primary pipes 6A and 6B.

  Based on FIG. 1 again, a radiation monitoring apparatus and a radiation monitoring system according to a first embodiment of the present invention will be described. The radiation detectors 1 </ b> A and 1 </ b> B are each provided with a collimator 3 and installed near the primary system pipe 6. A heat insulating material 7 surrounds the primary system pipe 6 to be inspected and is attached to the primary system pipe 6.

  For example, when the nuclear power plant is in operation, the reactor coolant 20 made of water or steam containing interfering nuclides 21 such as N-16 and O-19 flows in the primary piping 6. In the primary system pipe 6, for example, a measurement target nuclide 4 including a cascade γ-ray emitting nuclide containing Co-60, Mn-56, Co-58, and the like is attached. The radiation detectors 1 </ b> A and 1 </ b> B are provided with a collimator 3 having a solid angle that allows the attachment region of the measurement target nuclide 4 to overlap and are disposed so as to look at the inner wall of the primary system pipe 6.

  Due to the solid angle set by the collimator 3, the radiation detectors 1 </ b> A and 1 </ b> B cause the cascade γ-rays 5, 5 ′ emitted from the measurement target nuclide 4 adhering in the primary system pipe 6 to be measured and the primary system pipe 6. The background gamma rays 22 radiated from the interfering nuclides 21 included in the reactor coolant 20 are measured.

  Here, the cascade γ rays 5 and 5 ′ emitted from the measurement target nuclide 4 will be described. Cascade γ-rays 5 and 5 ′ are γ-rays emitted in the process of transition of the measurement target nuclide 4 to a stable nuclide, and a plurality of these γ-rays are emitted as γ-rays having different energies at substantially the same time. . Also, the radiation direction is randomly radiated in the 4π direction, and there is often no angular correlation.

FIG. 3 shows the decay process of Co-60 as an example of the decay process that emits cascade gamma rays of the target nuclide. As shown in FIG. 3, Co-60 is, beta ^- decays to Ni-60 in an excited state by decay. Generally, it takes a very short time to reach a ground state through a decay process that emits cascade γ rays.

As a measurement target nuclide that adheres in the primary piping and emits cascade γ rays, for example, Co-60 is given. Co-60 is a radionuclide generated by the (n, γ) reaction of Co-59 contained in the nuclear reactor structural material, and causes β ^- decay with a half-life of 5.27 years. This decay causes Co-60 to decay to Ni-60 in an excited state. And since Ni-60 of an excited state will be in a ground state, it discharge | releases the energy as a gamma ray.

  This γ-ray has two or more energies and radiates in the 4π direction at almost the same time. For example, the time difference between the γ-ray having the energy of 1.173 MeV and the γ-ray having the energy of 1.332 MeV is about 0.413 ps. Since it is difficult to measure this time difference in an ordinary radiation measurement system circuit, it is assumed that the actual measurement is detected at substantially the same time.

  In the present invention, Co-60 γ-rays are detected by using two or more radiation measurement systems having a solid angle such that the inner surface portion of a primary system pipe is superposed. That is, in the radiation measurement system, the solid angle is a collimator formed of a material having a high γ-ray shielding effect such as lead, and various scintillators such as NaI (Tl), GSO (Ce), BGO, LSO (Ce) It is measured using various semiconductor detectors such as Ge, CdTe, CZT, and GaAs. The case of measuring using a scintillator will be described separately in the second embodiment.

  In the radiation measurement by the coincidence method, for example, γ-rays having energy of 1.173 MeV derived from Co-60 are measured by the radiation measurement system, and γ-rays having energy of 1.332 MeV derived from Co-60 at approximately the same time. Is counted only when measured by other radiation measurement systems. It is possible to suppress background radiation caused by interfering nuclides (N-16, O-19, etc.) contained in the reactor water by assuming that Co-60 has been measured when this counting is performed. It becomes. This energy discrimination type coincidence processing means that when 1.332 MeV γ-rays are measured, the measurement conditions are exactly the same as when 1.173 MeV γ-rays are measured at approximately the same time. .

  When the cascade γ-rays 5 and 5 ′ are detected by the radiation detectors 1A and 1B at substantially the same time, the radiation detection signals obtained by the radiation detectors 1A and 1B are converted into preamplifiers 8A and 8B and a main amplifier, respectively. The signals are amplified by 10A and 10B and output to the coincidence counting circuit 13 via the timing units 11A and 11B. However, in the radiation measurement system shown in FIG. 1, the delay unit 12 is provided between the timing units 11A and 11B connected from the radiation detector 1B and the coincidence circuit 13, and the coincidence timing is adjusted.

  The coincidence circuit 13 is connected to the gate circuit 16, and a gate signal is sent from the gate circuit 16 to the multichannel wave height analyzer 15. With this gate signal, the radiation detection signals obtained via the radiation detectors 1A and 1B, the preamplifiers 8A and 8B, the main amplifiers 10A and 10B, the variable delay circuits 14A and 14B, and the peak hold circuits 45A and 45B, The data is taken into the multichannel wave height analyzer 15 and displayed on the display device 19 via the data processing device 18. Further, the count value of the measurement target nuclide 4 can be obtained by counting the gate signal with the scaler 17.

  The installation of the collimator 3 installed in the radiation detectors 1A and 1B and the measurement geometric conditions will be described. 4 and 5 show the internal surface area (S) in the primary pipe 6 and the primary pipe 6 that the radiation detector expects from the solid angle of the collimator 3 installed in the radiation detector 1A and the radiation detector 1B. The relationship of the ratio (S / V) of the volume (V) in the pipe is shown. FIG. 4A shows an example of installation of the collimator 3 in which the collimator central axis 23 is in contact with the primary pipe. FIG. 4B shows an example of installation of the collimator 3 in which the collimator central axis 23 does not intersect with the primary system pipe. FIG. 4C shows the measurement geometric condition. FIG. 5A shows the installation of the collimator 3 in which the collimator central axis 23 intersects the primary system piping, and FIG. 5B shows the measurement geometric conditions.

  Lead or the like having a high γ-ray shielding effect is used for a collimator installed in the radiation measurement system. Then, a geometrical arrangement in which the central axis directions of the two collimators 3 are opposed to the primary piping 6 is set. The measurement range expected by the collimator based on this geometrical arrangement is the volume of the primary piping in the reactor cooling system including the surface area of the piping to which Co-60 is attached and the disturbing nuclides (N-16, O-19, etc.). When these ratios are (surface area in the pipe: S) / (volume in the pipe: V), the larger the ratio (S / V), the greater the radiation from the primary system pipe volume (reactor coolant). Background radiation can be reduced, and cascade gamma rays derived from Co-60 on the inner surface of the primary piping can be measured with high sensitivity and high accuracy.

4 and 5, when the solid angle of the collimator 3 is expanded with the radiation detector installation position fixed, the ratio (S / V) expected by the collimator 3 is the same as that of the primary piping. The maximum value of the ratio (S / V) is shown in the region where the edge portion is expected. When the solid angle of the collimator 3 is further expanded, the ratio (S / V) decreases monotonously and shows a minimum value at a certain solid angle. As the solid angle of the collimator 3 is further expanded, this ratio (S / V) monotonously increases until the solid angle of the collimator 3 allows for the entire primary piping. When the ratio at which the solid angle of the collimator 3 is expected to total primary system pipe and _{S M} / _V M, there is the solid angle Θ58 as the _{S / V ≒ S M / V} M.

There is a region where the solid angle Θ58 where S / V≈S _M / V _M , that is, the area in the pipe radial direction existing in the same plane as the collimator central axis 23 is approximately ½. Therefore, measurement is performed in the measurement target region 25 where S / V> S _M / V _M , that is, the area in the pipe radial direction existing in the same plane as the collimator central axis 23 is approximately ½ or less. Thus, the ratio of the nuclide to be measured and the interfering nuclide can be optimized, and the influence of the interfering nuclide 21 can be effectively suppressed.

  By providing this measurement geometric condition, high-sensitivity and high-precision count rate measurement and energy spectrum measurement of the measurement target nuclide 4 in the primary system pipe 6 using the radiation detectors 1A and 1B are realized. The inner area in the pipe radial direction means the inner area of the cross section of the pipe existing in the same plane as the collimator central axis 23.

  Therefore, the simultaneous counting method of cascade γ rays radiating in the 4π direction of Co-60 and the measurement target range expected by the collimator installed in the radiation measurement system are the same as the cross-sectional area in the pipe radial direction existing on the same plane as the collimator central axis. The radiation monitoring in the primary piping of the nuclear power plant during operation of the nuclear power plant, which is almost impossible to measure with the prior art, becomes possible.

  FIG. 6 shows an example of a γ-ray spectrum when the measurement target nuclide 4 attached in the nuclear power plant primary system pipe 6 measured by the apparatus of the present invention is, for example, Co-60. FIG. 6 shows a raw spectrum 31 and a spectrum 32 according to the invention. In the spectrum 32 according to the present invention, the photoelectric peak 29 of 6.1 MeV γ rays radiated from N-16, which is one of the disturbing nuclides 21 included in the unprocessed spectrum 31, and the scattering component 30 due to Compton scattering are not measured. Further, in the spectrum 32 according to the present invention, the 1.357 MeV γ-ray photoelectric peak 28 emitted from O-19 which is one of the disturbing nuclides 21 is not measured.

  For this reason, the spectrum 32 according to the present invention can remove noise components (interfering nuclides 21) of the photoelectric peaks 26 and 27 of the cascade γ-rays radiated from the Co-60 included in the unprocessed spectrum 31. The photoelectric peaks 26 and 27 of the cascade γ rays emitted from Co-60 included in the spectrum 32 according to the invention are all components derived from Co-60.

  According to the present invention, a radiation monitoring apparatus and a radiation monitoring system in a nuclear plant primary system pipe capable of continuously measuring a measurement target nuclide adhering in the primary system pipe during operation for a long time with high accuracy and high sensitivity. Can be realized.

  Regarding the measurement geometric condition of the collimator 3 described above, the first embodiment of the present invention has been described by taking the geometric arrangement condition in which the direction of the collimator central axis 23 of the collimator 3 and the primary piping central axis 24 are perpendicular to each other as an example. This geometrical arrangement can achieve the same effect even when the collimator 3 looks at the primary piping 6 obliquely. FIG. 7 shows the pipe radial direction cross section 47 and the pipe radial direction inner area when the collimator 3 looks at the primary system pipe 6 obliquely. In the case shown in FIG. 7, the pipe radial direction cross section 47 is elliptical, but the same effect as the preferred measurement target condition of the present invention shown in FIGS. 4 and 5 can be obtained.

  FIG. 8 shows a radiation monitoring apparatus and a radiation monitoring system in the nuclear power plant primary system piping of the second embodiment of the present invention. The radiation monitoring apparatus and radiation monitoring system 34 in the primary system piping of the second embodiment have the same configuration as that of the first embodiment, but the radiation detector 1C and the radiation detector 1D having a phoswich structure, and waveform discrimination. The circuit 46 is different from the first embodiment.

  In the second embodiment, the background γ-rays 22 emitted from the reactor coolant in the primary piping including the interfering nuclides 21, particularly the cascade γ-rays 5 emitted from the measurement target nuclide 4 (for example, from Co-60). The object is to suppress the influence of γ rays having higher energy than the radiated 1.332 MeV γ rays (for example, 6.1 MeV γ rays emitted from N-16).

  FIG. 9 shows the configuration of a radiation detector 1C and a radiation detector 1D having a phoswich structure. The phoswich structure means a structure in which two or more scintillators having different materials or different characteristics are combined. The scintillators used in the phoswich structure are NaI (Tl), CsI (Ce), BGO, GSO (Ce), LSO (Ce), and the like.

  FIG. 9 shows, as an example of a radiation detector having a phoswich structure, a cylindrical radiation detector 1E and a radiation detector 1F having the same diameter, and radiation that detects light emitted by these scintillators using a photodetector 36. The detection system is shown. In this radiation detection system, light emission by only the radiation detector 1E, light emission by only the radiation detector 1F, and light emission at approximately the same time by both radiation detectors can be considered for one γ-ray. As the photodetector 36, for example, a photomultiplier tube is used.

  Here, light emission at substantially the same time in both radiation detectors means that light emitted by cascade γ rays 5 or background γ rays 22 entering the radiation detector 1E and Compton scattering and Compton scattered γ rays 35. The light emission due to the incident on the radiation detector 1F is the same time in the pulse measurement processing time of the conventional radiation measurement system, and the time difference due to the light emission is negligible, so it is described as the light emission at almost the same time.

  In order to discriminate between these three types of light emission, the difference in the rise time of the radiation detection signal due to the light emission of each radiation detector is used. Here, FIG. 10 shows the difference in the rise time of the radiation detection signal, with the horizontal axis representing time and the vertical axis representing pulse height. Here, as an example, a radiation detection signal 48 by emission of the radiation detector 1E, a radiation detection signal 49 by emission of the radiation detector 1F, and a radiation detection signal 50 by emission of both the radiation detector 1E and the radiation detector 1F are shown. . Assume that the rising time of the radiation detection signal 48 is Δt1, the rising time of the radiation detection signal 49 is Δt2, and the rising time of the radiation detection signal 50 is Δt3.

  In the second embodiment, for example, when only the radiation detection signal 48 due to light emission of the radiation detector 1E is detected, the waveform discrimination circuit performs waveform discrimination setting so that the radiation detection signal whose rise time 33 is later than Δt1 is not captured. . At this time, since the radiation detection signal 50 due to light emission by both the radiation detector 1E and the radiation detector 1F is not detected, measurement of the count value and energy spectrum in which the influence by the Compton scattered γ-ray 35 is suppressed can be realized.

  This waveform discrimination is performed for measurement of the radiation detection signal 49 by light emission of the radiation detector 1F, so that a waveform discrimination setting in which the radiation detection signal whose rise time 33 is earlier than Δt2 is not taken in. Further, both the radiation detector 1E and the radiation detector 1F are used. For the measurement of the radiation detection signal 50 by the light emission at, when the rising time 33 is t, the same is true for the waveform discrimination setting condition in which the radiation detection signal that does not satisfy Δt1 <t <Δt2 is not taken.

  Therefore, in the second embodiment, since the coincidence counting method using two or more radiation detectors having a phoswich structure is used, the cascade γ-ray 5 and the back are further provided as compared with the radiation measurement system installed in the first embodiment. It is possible to suppress the influence of Compton scattered γ-rays caused by the ground γ-rays 22 and realize high-sensitivity and high-accuracy counting values and energy spectrum measurements.

11 and 12 show a radiation monitoring apparatus and a radiation monitoring system in the primary piping of the third embodiment of the present invention. The third embodiment has the same configuration as the first embodiment or the second embodiment, but the cascade γ-rays 5 and 5 ′ and the background γ detected by the radiation detector 1A or the radiation detector 1B, respectively. Cascade γ-rays 5 detected by the radiation detector 1A or the radiation detector 1B when the combined γ-ray count rate of the lines 22 exceeds 10 ⁵ cps under the measurement geometric condition where S / V> S _M / V _M The measurement geometric condition of the collimator 3 is provided so that the γ-ray count rate obtained by adding 5 ′ and the background γ-ray 22 is 10 ⁵ cps or less. 10 ⁵ cps is a count rate limit for the multi-channel wave height analyzer 15 to measure a highly accurate energy spectrum.

11 and 12 show that the primary piping 6 according to the measurement geometric condition of the collimator 3 is used in order to install the collimator 3 so that the γ-ray counting rate of the radiation detector 1A or the radiation detector 1B is 10 ⁵ cps or less. This indicates that the measurement target range is less than the dotted line portion 25. A dotted line 37 is an example of S and V under the condition that the γ-ray count rate of the radiation detector 1A or the radiation detector 1B is 10 ⁵ cps or less. According to the third embodiment, it is possible to realize measurement of the counting rate and energy spectrum with higher sensitivity and accuracy.

  FIG. 13 shows a radiation monitoring apparatus and a radiation monitoring system in the primary piping of the fourth embodiment of the present invention. FIG. 13A shows a pipe radial direction cross-sectional view of the primary system pipe 6 and each radiation detector arrangement and a primary system pipe inner surface portion 39 where a solid angle by the collimator 3 is expected. FIG. 13B shows the state of installation of each radiation detector with respect to the reactor coolant flow direction 38 in the primary system pipe 6. Here, the measurement geometric condition of each radiation detector, that is, S / V is the same.

  The fourth embodiment has the same configuration as that of the first embodiment, the second embodiment, or the third embodiment, and the radiation detectors 1A and 1B are installed adjacent to each other, and the primary piping. 6 is parallel to and parallel to the reactor coolant flow direction 38, and the one side portion 3 'of the collimator 3 is shared by the radiation detectors 1A and 1B. Since the collimators 3 and 3 ′ have the same measurement geometric condition S / V, the radiation detectors 1A and 1B have the same solid angle. The measurement target region 40 in the primary pipe inner surface portion 39 where the solid angle by the measurement geometric condition S / V is expected is indicated by a dotted region.

  The advantage of the installation method of the radiation detectors 1A and 1B according to the fourth embodiment is that the collimators 3 of the radiation detectors 1A and 1B are installed adjacent to each other and parallel to the pipe length direction of the primary system pipe 6. In addition, since it is installed in parallel, the measurement geometric relationship of the radiation monitoring device is simplified, and the installation itself is facilitated. Furthermore, since the collimator 3 'is shared, the cost of the shield (collimator) can be reduced. Further, the radiation detectors 1A and 1B are installed in parallel and in parallel with the reactor coolant flow direction 38, so that the installation cost itself can be reduced.

  The advantage of the installation method of the radiation detectors 1A and 1B according to the fourth embodiment is that the measurement geometric relationship of the radiation monitoring device is simplified and the installation itself is facilitated. This is because the collimators 3 of the radiation detectors 1 </ b> A and 1 </ b> B are installed so as to be adjacent to each other, and are installed in parallel and in parallel with the pipe length direction of the primary system pipe 6. Furthermore, since the collimator 3 'is shared, the cost of the shield (collimator) can be reduced. Further, the radiation detectors 1A and 1B are installed in parallel and in parallel with the reactor coolant flow direction 38, so that the installation cost itself can be reduced.

  FIG. 14 shows a modification of the radiation monitoring apparatus and the radiation monitoring system in the primary piping of the fourth embodiment of the present invention. In the fourth embodiment of the present invention, the collimator 3 ′ is provided as a partition for each radiation detector. However, in the modification of the fourth embodiment of the present invention, a collimator 3 ′ to be a partition is installed. First, the effect of further expanding the measurement target range of each radiation detector can be expected. FIG. 14 shows an example of a radiation monitoring apparatus and a radiation monitoring system that include a collimator 42 that does not include a collimator 3 ′ as a partition. Each radiation detector with respect to the pipe radial direction cross section of the primary system pipe 6 is installed in the same manner as in FIG. A measurement target range 40 of the inner surface portion 39 of the primary system pipe that the collimator 42 expects is indicated by a dotted area.

  The advantage of the modification of the radiation monitoring apparatus and the radiation monitoring system of the fourth embodiment of the present invention is that the measurement target range can be made wider, and the collimator 42 can be shared by the radiation detectors 1A and 1B. The cost of the shield (collimator) can be reduced.

  FIG. 15 shows a radiation monitoring apparatus and a radiation monitoring system in the primary piping of the fifth embodiment of the present invention. In the fifth embodiment, as shown in FIG. 15, each radiation detector is installed in parallel and in parallel with the reactor coolant flow direction 38 in the primary pipe 6, and each radiation detector is Similarly to FIG. 13A, it is installed with respect to the pipe radial direction cross section of the primary system pipe 6. Here, the measurement geometric condition of each radiation detector, that is, S / V is the same.

  The fifth embodiment has the same configuration as that of the fourth embodiment, except that N radiation detectors and accompanying collimators 3 and 3 ′ (N ≧ 2) are installed, and two cascaded γ-rays are simultaneously used. Fourth Embodiment Regarding a radiation measurement processing apparatus that identifies a range in which a measurement target nuclide 4 exists from solid angles of N radiation detectors to be counted, and a radiation measurement processing apparatus that processes radiation detection signals from the N radiation detectors Is different.

Based on FIG. 15, the fifth embodiment of the present invention is a case where N radiation detectors D ₁ , D ₂ , D ₃ ,..., D _N and accompanying collimators 3 and 3 ′ are arranged. This will be described as an example. However, the solid angles of the first and Nth radiation detectors have a common measurement target area in the primary pipe 6, and when the (N + 1) th radiation detector is installed, the first and N + 1th radiation detectors. The solid angle of the radiation detector does not have a common measurement target range in the primary system pipe 6. When two cascaded γ-rays are simultaneously counted by N radiation detectors, there are {(N−1) · N / 2} combinations of the radiation detectors.

Therefore, {(N-1) · N / 2} sets of measurement target ranges exist. The measuring object range _A 2 when the measuring object range _A 1, _{D 1} and _{D 3} in the case of a combination of radiation detectors _{D 1} and _{D 2,} · · ·, measured when the _{D 1} and _{D N} range _{a N-1,} ···, a measuring object range when the _{D N-1} and _{D N} and _{a (N-1) · N} / 2. In FIG. 12, the measurement target ranges A ₁ and A ₂ are indicated by a dotted region 40, and the measurement target region A _N-1 is indicated by a horizontal line region 41.

  In the fifth embodiment, it is possible to identify a range in which the measurement target nuclide 4 exists from a combination of radiation detectors that simultaneously count. Further, by installing N radiation detectors and a collimator associated therewith, the measurement target area in the primary system pipe 6 is expanded, and the cascade γ-ray counting rate can be increased. That is, the advantage of the fifth embodiment is that radiation monitoring can be performed in a wide range, with high sensitivity and high accuracy.

  FIG. 16 shows a modification of the fifth embodiment. Although the case where the collimator 3 'is provided as a partition between the radiation detectors has been described as the fifth embodiment, FIG. 16 illustrates a radiation monitoring apparatus and a radiation including a collimator 42 that does not include the collimator 3' serving as a partition. Indicates a monitoring system. By not installing the collimator 3 'as a partition, it is possible to expect an effect of further expanding the measurement target range of each radiation detector. In the modified example of the fifth embodiment, the measurement target range of each radiation detector can be set in a wider range, and further, a single collimator 42 serves as a collimator for N radiation detectors, so that a shield (collimator) is installed. There is an advantage that the cost can be reduced.

  FIG. 17 shows a radiation monitoring apparatus and a radiation monitoring system in the primary piping of the sixth embodiment of the present invention. FIG. 17 shows a configuration in which each radiation detector is dispersedly arranged on one plane of the reactor coolant flow direction 38 in the primary system pipe 6. In FIG. 17, each radiation detector is installed as shown in FIG. 13A with respect to the pipe radial direction cross section of the primary system pipe 6.

  The sixth embodiment has the same configuration as the first embodiment, the second embodiment, or the third embodiment, except that N radiation detectors (N ≧ 2) are installed, and the measurement target The range 40 is estimated by the solid angles of all N radiation detectors, and the range where the measurement target nuclide 4 exists is identified from the solid angles of the N radiation detectors that simultaneously count two cascaded γ-rays. And a radiation measurement processing device for processing radiation detection signals by N radiation detectors.

  18 and 19 show a radiation monitoring apparatus and a radiation monitoring system in the primary piping of the seventh embodiment of the present invention. 18 and 19 show a configuration in which the radiation detectors are dispersedly arranged on one plane of the reactor coolant flow direction 38 in the primary system pipe 6. 18 and FIG. 19, each radiation detector is installed as shown in FIG. 13A with respect to the pipe radial direction cross section of the primary system pipe 6. The seventh embodiment has the same configuration as that of the first embodiment, the second embodiment, or the third embodiment, and the fourth embodiment, the sixth embodiment, the fifth embodiment, and It is characterized by combining the sixth embodiment. FIG. 18 shows an example of a system in which four radiation detectors 1A, 1B, 1A ′ and 1B ′ and collimators 3 and 3 ′ are arranged. Due to the solid angle by the collimators 3 and 3 ′, the measurement target range 40 is expected from the radiation detector 1A or 1B or 1A ′ or 1B ′.

  As also shown in the fifth embodiment, in the seventh embodiment, the measurement target range is determined by the combination of radiation detectors that perform simultaneous counting. FIG. 19 shows an example of a system in which four radiation detectors 1A, 1B, 1A ′ and 1B ′ and a collimator 42 are arranged. Due to the solid angle by the collimator 42, the measurement target range 40 is expected from the radiation detector 1A or 1B or 1A ′ or 1B ′. As shown in the fifth embodiment, in the seventh embodiment, the measurement target range is determined by the combination of radiation detectors that perform simultaneous counting.

  The radiation measurement system in which N (N = 2) radiation detectors among N (N ≧ 2) radiation detectors have been described with reference to FIGS. 18 and 19, but N (N ≧ 3). The same explanation can be made for the radiation measurement system in which the radiation detector is installed. The advantage of the seventh embodiment is that radiation monitoring with a wide range, high sensitivity, and high accuracy can be realized.

  FIG. 20 shows a radiation monitoring apparatus and a radiation monitoring system in the primary piping of the eighth embodiment of the present invention. FIG. 20 shows a radiation monitoring device and a radiation monitoring system in the primary system pipe of the eighth embodiment of the present invention based on the cross section of the primary system pipe 6. Here, the measurement geometric condition of each radiation detector, that is, S / V is the same. The eighth embodiment is the same as the first embodiment, the second embodiment, the third embodiment, the fourth embodiment, the fifth embodiment, the sixth embodiment, or the seventh embodiment. However, the radiation measurement system is installed in the circumferential direction of the primary pipe 6 or in a spiral shape.

  FIG. 20 shows an example in which five sets of combinations of the radiation detector 1A, the radiation detector 1B, and the collimator 3 are installed in the circumferential direction of the primary pipe 6 as an example of the eighth embodiment. According to the eighth embodiment, the distribution of the measurement target nuclide 4 in the circumferential direction of the primary pipe 6 can be easily measured, and the entire circumferential direction of the inner wall of the primary pipe 6 can be monitored.

  FIG. 21 shows a radiation monitoring apparatus and a radiation monitoring system in the primary piping of the ninth embodiment of the present invention. FIG. 21A shows an example of the arrangement of each radiation detector based on a cross-sectional view of the primary system pipe 6. FIG. 21B shows an example of installation of each radiation detector that anticipates the primary system pipe surface portion 39. The ninth embodiment has the same configuration as the first to eighth embodiments, and two or more sets of radiation measurement systems having the same collimator width are installed. It is characterized in that it is installed at a position translated in one direction with respect to the radiation measurement system, and fixed at the time of measurement by each radiation measurement system.

  FIG. 22 shows the ratio of the pipe internal surface area (S) to the pipe internal volume (V) at the position where the radiation measurement system having a constant collimator width is translated so as to cross the primary pipe 6 (S / V). The zero point of the radiation detector moving position is based on the solid angle and when the radiation detector is arranged at the tangent portion of the circumference of the primary system pipe 6. When the collimator center axis 23 overlaps the primary piping center axis 24 at a position where the radiation detectors having the same collimator width are translated, the ratio (S / V) is minimized.

  In the radiation monitoring apparatus and radiation monitoring system shown in FIG. 21A, as an example, two sets of radiation detectors are installed. In this case, the radiation detector 1A and the radiation detector 1B expect the primary piping surface portion 39, and the radiation detector 1A 'and the radiation detector 1B' expect the primary piping surface portion 39 '. Under these radiation detector installation conditions, the ratio (S / V) between the surface area in the primary system pipe and the volume in the pipe is the dotted line portion 43 shown in FIG. 22 and the radiation detector 1A for the radiation detector 1A and the radiation detector 1B. If it is 'and radiation detector 1B', it will become the shaded part 44 shown in FIG.

  Deriving the unit surface area and the γ-ray count rate per unit volume from the γ-ray count rate measured by each radiation measurement system using the ratio (S / V) of the pipe internal surface area to the pipe internal volume of the primary pipe 6 And it becomes possible to identify the trace amount measurement object nuclide 4 adhering to the inner wall of the primary system piping 6 by those difference calculations. According to the ninth embodiment, by using the fact that the ratio (S / V) of the surface area in the pipe and the volume in the pipe is different, the measurement target nuclide 4 attached to the primary pipe 6 is relatively radiation-monitored. It becomes possible.

  The radiation monitoring apparatus and the radiation monitoring system described above are examples of the ninth embodiment, and the radiation measurement system is arranged in an array by combining with the fourth embodiment, the fifth embodiment, or the eighth embodiment. It is possible to perform wide-area, high-sensitivity, and high-accuracy radiation monitoring by making use of the characteristics of each embodiment.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to measure the radiation generated from the measurement object nuclide adhering in the nuclear power plant primary system piping that was impossible at present for a long time online. Further, not only a semiconductor detection system such as a Ge semiconductor detector as a radiation measurement system but also a detection system employing an inexpensive scintillator can be easily measured. In addition, the present invention has been described by taking as an example the case of measuring the measurement target nuclide adhering to the nuclear power plant primary system piping, but the present invention is a measurement that adheres to the piping under the condition in which radiation from interfering nuclides exists. It can be generally applied when measuring the target nuclide.

It is a figure which shows the structure of the radiation monitoring apparatus in the nuclear power plant primary system piping of the 1st Embodiment of this invention, and a radiation monitoring system. It is a figure which shows the whole structure of the radiation monitoring apparatus in a nuclear power plant primary system piping, and a radiation monitoring system. It is a figure explaining the decay | disintegration process of the cascade gamma ray of a measuring object nuclide. It is an explanatory diagram of the ratio (S / V) of the solid angle of the collimator and the surface area (S) of the nuclear power plant primary system pipe and the volume (V) of the primary system pipe in a range where the central axis of the collimator is in contact with or does not intersect with the primary system pipe. is there. It is explanatory drawing of the ratio (S / V) of the solid angle of the collimator in the range which a collimator central axis crosses with primary system piping, and the nuclear plant primary system piping surface area (S), and primary system piping internal volume (V). It is a figure which shows the unprocessed energy spectrum containing the energy spectrum obtained by embodiment of this invention, and the noise from interference nuclide. The cross section in the pipe radial direction and the area in the pipe radial direction when the collimator looks at the primary system pipe obliquely are shown. It is a figure which shows the structure of the radiation monitoring apparatus and the radiation monitoring system in the nuclear power plant primary system piping of the 2nd Embodiment of this invention. It is a figure which shows the structure of the radiation detector which has a phoswich structure, and the behavior of the incident gamma ray. It is a figure which shows the difference in the rise time of the radiation detection signal by light emission in the radiation detector which has a phoswich structure. In the third embodiment of the present invention, the collimator solid angle, the nuclear plant primary system pipe surface area (S) and the primary system pipe internal volume (V) in the range where the collimator central axis is in contact with or does not intersect with the primary system pipe. It is a figure which shows ratio (S / V). In the third embodiment of the present invention, the ratio of the solid angle of the collimator in the range where the central axis of the collimator intersects with the primary piping, the surface area (S) of the nuclear power plant primary piping, and the volume (V) of the primary piping (S / It is a figure which shows V). It is a figure which shows the structure of the radiation monitoring apparatus and the radiation monitoring system in the nuclear power plant primary system piping of the 4th Embodiment of this invention. It is a block diagram of the radiation monitoring apparatus and the radiation monitoring system in the nuclear power plant primary system piping of the 4th Embodiment of this invention. It is a figure which shows the structure of the radiation monitoring apparatus and the radiation monitoring system in the nuclear power plant primary system piping of the 5th Embodiment of this invention. It is a figure which shows the structure of the radiation monitoring apparatus in the nuclear power plant primary system piping of the modification of the 5th Embodiment of this invention, and a radiation monitoring system. It is a figure which shows the structure of the radiation monitoring apparatus and the radiation monitoring system in the nuclear power plant primary system piping of the 6th Embodiment of this invention. It is a figure which shows the structure of the radiation monitoring apparatus and the radiation monitoring system in the nuclear power plant primary system piping of the 7th Embodiment of this invention. It is a figure which shows the structure of the radiation monitoring apparatus and the radiation monitoring system in the nuclear power plant primary system piping of the 7th Embodiment of this invention. It is a figure which shows the structure of the radiation monitoring apparatus in the nuclear power plant primary system piping of the 8th Embodiment of this invention, and its system. It is a figure which shows the structure of the radiation monitoring apparatus and the radiation monitoring system in the nuclear power plant primary system piping of the 9th Embodiment of this invention. The ratio (S / V) of the parallel movement distance of the radiation detector with a certain collimator width used in the ninth embodiment, the nuclear plant primary system pipe surface area (S), and the primary system pipe volume (V) is shown. FIG.

Explanation of symbols

1A, 1B, 1C, 1D, 1E, 1F, 1A ′, 1B ′, D ₁ ,..., D _N ... radiation detector, 2 ... radiation monitoring apparatus in the primary system pipe in the first embodiment, and Radiation monitoring system 3, 3 '... collimator, 4 ... measurement nuclide, 5, 5' ... cascade gamma ray, 6, 6A, 6B ... nuclear plant primary system piping, 7 ... heat insulation, 8A, 8B, 8C, 8D ... preamplifier, 9A, 9B, 9C, 9D ... high voltage source, 10A, 10B, 10C, 10D ... main amplifier, 11A, 11B, 11C, 11D ... timing unit, 12 ... delay unit, 13 ... coincidence counting circuit, 14A, 14B, 14C, 14D ... variable delay amplifier, 15 ... multichannel wave height analyzer, 16 ... gate circuit, 17 ... scaler, 18 ... data processing device, 19 ... display device, 20 ... reactor cooling 21 ... Interfering nuclides, 22 ... Background gamma rays, 23 ... Collimator central axis, 24 ... Primary piping central axis, 25 ... Distribution of conditions to be measured region, 26, 27 ... Photoelectric peak by cascade gamma rays, 28 , 29 ... Photoelectric peak due to interfering nuclides, 30, Scatter distribution due to Compton scattered γ rays due to interfering nuclides, 31 ... Unprocessed spectrum, 32 ... Spectrum according to the present invention, 33 ... Radiation detection signal rise time, 34 ... Second embodiment Radiation monitoring device and radiation monitoring system in the primary system pipe, 35 ... Compton scattered γ-ray, 36 ... photodetector, 37 ... inner area in the pipe radial direction when the count rate of one radiation detector is 10 ⁵ cps , 38 ... Flow direction of the reactor coolant, 39, 39 '... Inner surface portion of the primary piping, 40, 41 ... Measurements expected by a certain radiation detector Fixed range, 42... Collimator, 43, 44... Ratio (S / V) of primary system pipe internal surface area (S) to primary system pipe internal volume (V) expected from a radiation detector having a certain collimator width, 45A, 45B, 45C, 45D ... Peak hold circuit, 46C, 46D ... Waveform discriminating circuit, 47 ... Pipe radial inner area when primary system pipe 6 is viewed obliquely, 48 ... Radiation detection signal by emission of radiation detector 1E, 49 ... Radiation detection signal by emission of radiation detector 1F, 50 ... Radiation detection signal by emission of both radiation detector 1E and radiation detector 1F, 51 ... Reactor pressure vessel, 52 ... Main steam, 53 ... Main steam pipe, 54 ... Radiation measurement device, 55 ... Pump, 56 ... Reactor fuel, 57 ... Minimum point, 58 ... Solid angle, 60 ... Radiation measurement processing device, 61 ... Radiation measurement processing device

Claims (8)

At least two radiation detectors that detect, via a collimator, radiation including cascade γ-rays radiated by a measurement target nuclide attached to a pipe through which a radioactive fluid flows;
Among the radiation detection signals detected by the radiation detector, a radiation measurement processing device that counts detection signals related to the cascade γ-rays detected at approximately the same time by the radiation detector,
With
The radiation measurement target range expected of the collimator installed in the detector, co Rimeta central axis radiation monitoring device which is characterized in that less than half of the pipe diameter direction in the area that are in the same plane. The radiation monitoring apparatus according to claim 1, wherein the collimator and the radiation detector are arranged, and the measurement target range in which a count rate of the radiation measurement processing apparatus is 10 ⁵ cps or less is set.   By sharing an adjacent part of each collimator included in at least two radiation detectors installed adjacent to each other, the at least two radiation detectors are integrally arranged without being independent of each other, The radiation monitoring apparatus according to claim 1 or 2, wherein a measurement target range is set in parallel and parallel to a reactor coolant flow direction in the pipe.   The radiation monitoring apparatus according to claim 1, wherein the N (N ≧ 2) radiation detectors are distributed and arranged on a plane in the flow direction of the radioactive fluid in the pipe.   The radiation according to claim 1, wherein N (N ≧ 2) radiation detectors are installed in a circumferential direction or a spiral direction of the pipe, and a distribution of measurement target nuclides on an inner wall of the pipe is measured. Monitoring device. The ratio of the radiation detector, distribution pipe volumes and expected no distribution pipe the surface area of the solid angle of the collimator of N (N ≧ 2) having substantially the same solid angle by substantially the same opening width of the collimator values are arranged in each different translatable position, and count rate of the N of the radiation measurement apparatus, the primary system by the difference calculation from the ratio of the distribution pipe volume as expected no distribution pipe the surface area of the solid angle The radiation monitoring apparatus of any one of Claims 1-5 which measures the trace amount of said measurement object nuclide adhering to the inner wall of piping.   The radiation detector has a phoswich structure including at least two scintillators having different materials or different characteristics and a photodetector, and the radiation measurement processing device is detected by emission of radiation by the detector. The radiation monitoring apparatus according to claim 1, further comprising a waveform discrimination circuit that discriminates a difference between rise times of signals. A radiation monitoring system included in a primary piping of a nuclear power plant connected to a reactor pressure vessel in which nuclear reactor fuel is stored,
The reactor pressure vessel generates thermal energy from the reactor fuel,
The primary piping is for circulating a reactor coolant inside and outside the reactor pressure vessel,
The primary piping is
At least two radiation detectors for detecting, via a collimator, radiation including a cascade γ-ray radiated from a measurement target nuclide adhering to the primary system pipe through which the reactor coolant flows;
A radiation measurement processing device that counts detection signals related to the cascade γ-rays detected at approximately the same time by the radiation detector from among the detection signals of the radiation detected by the radiation detector, and
Radiation monitoring system, wherein the measuring object range expecting the collimator installed in the radiation detector, co Rimeta central axis is below half pipe diameter direction in the area that are in the same plane.

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