JP5245173B2 - Radioactive gas measuring device and damaged fuel inspection device - Google Patents

Description

  The present invention relates to a radioactive gas measurement apparatus, and in particular, positron annihilation that measures radiation generated from a measurement target nuclide by significantly suppressing the influence of annihilation γ rays from a radio gas including the measurement target nuclide and a positron emission nuclide. The present invention relates to a γ-ray suppression type radioactive gas measuring device (hereinafter also referred to as “radioactive gas measuring device”) and a damaged fuel inspection device.

  Conventionally, nuclear power plants have always monitored the amount of fission products contained in reactor coolant (reactor water) and main steam for the purpose of confirming the soundness of reactor fuel. In particular, the reactor water and main steam often contain a lot of N-13 (nitrogen-13). For this reason, in the measurement of the index nuclides (I-131 (iodine-131), Xe-133 (xenon-133)) for monitoring the soundness of this fuel failure, the background generated by the annihilation gamma rays emitted by N-13 Measurement technology that suppresses the effects of radiation is essential.

  A conventional radioactive gas measuring device and damaged fuel inspection device will be described. Patent Document 1 (Japanese Patent Laid-Open No. 7-218638) discloses a damaged fuel inspection apparatus that detects the concentration of I-131 in reactor water using a conventional measurement method for suppressing positron annihilation γ-rays. In the apparatus described in Patent Document 1, by using two radiation detectors, the reverse coincidence processing is performed on positron annihilation γ-rays to reduce the influence of annihilation γ-ray emitting nuclides contained in the reactor water, and fuel breakage I-131 which is an index of detection is measured.

  Patent Document 2 (Japanese Patent Laid-Open No. 2001-235546) discloses a radioactive gas measuring device and a damaged fuel inspection device that detect a radiation concentration in a radioactive gas using a measurement method that suppresses positron annihilation γ-rays. . In the apparatus described in Patent Document 2, the annihilation γ-ray emission nuclide contained in the radioactive gas is obtained by performing reverse coincidence processing on the positron annihilation γ-ray using two radiation detectors for the radioactive gas. The influence is reduced, and Xe-133, which is an index for detecting fuel breakage, is measured.

  FIG. 17 shows an example of the configuration of a radioactive gas measuring apparatus provided with a conventional inverse coincidence processing apparatus. In the conventional radioactive gas measuring device shown in FIG. 17, a radioactive gas measuring cell 42 is provided in the inlet / outlet pipes 40a and 40b of the radioactive gas (mainly extracted from the reactor condensate system and called off-gas). Detect the fuel damage by performing the reverse coincidence processing with the two detectors of the main detector 43 and the sub-detector 44 provided in the gas detector to reduce the influence of the annihilation gamma ray emission nuclide (N-13) contained in the gas. Is effectively measured.

  These are measurements of the index nuclide (I-131, Xe-133) for detecting fuel breakage during normal operation of the reactor. By examining the effects of annihilation gamma rays reduced by about 50% to 20%, The presence or absence is detected.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 2005-9890) discloses a conventional radioactive gas measuring device having a mechanism for automatically changing the position of a collimator. The gas radioactivity concentration measuring apparatus described in Patent Document 3 includes a collimator capable of automatically changing the position between a radioactive gas measurement container (measurement cell) and a radiation detector, and the measurement radioactive gas in the measurement cell. Radiation measurement is possible corresponding to the concentration range from low to high.

  Furthermore, Patent Document 4 (Japanese Patent Application Laid-Open No. 2001-141829) discloses a fluid in a pipe and a pipe inner wall using a radioactivity measuring apparatus including a measurement system in which a collimator and a radiation detector move integrally with a pipe through which a radioactive fluid flows. A conventional distribution measuring method for measuring the distribution of radioactivity is disclosed. In the method described in Patent Document 4, the amount of radioactivity adhering to the pipe inner wall area is calculated from two or more measured values having different measurement ranges of the pipe inner wall area and the pipe measured fluid volume along the pipe through which the measurement fluid flows. Calculate the measured fluid radioactivity.

JP 7-218638 A JP 2001-235546 A Japanese Patent Laid-Open No. 2005-9890 JP 2001-141829 A

  In order to suppress positron annihilation γ-rays, the conventional radiation measurement apparatuses described in Patent Document 1 (Japanese Patent Laid-Open No. 7-218638) and Patent Document 2 (Japanese Patent Laid-Open No. 2001-235546) both have two systems. Radiation detection system and its inverse coincidence processing circuit. However, the conventional radiation measurement apparatuses described in Patent Document 1 and Patent Document 2 are provided with two radiation detection systems and their inverse coincidence processing circuit, so that the measurement system is large and complicated, and the shielding thereof is performed. Including the system, there was a problem that it was large and expensive.

  In addition, any of the conventional radiation measurement devices described in Patent Document 3 (Japanese Patent Laid-Open No. 2005-9890) and Patent Document 4 (Japanese Patent Laid-Open No. 2001-141929) is an obstacle to measurement mixed in the measurement fluid. There is no device to suppress the influence of positron emitting nuclides. For this reason, in the conventional radiation measuring apparatus described in Patent Document 3 and Patent Document 4, it is difficult to effectively eliminate annihilation γ-rays (511 keV) emitted from positron emitting nuclides mixed in the measurement fluid. There was a problem.

  An object of the present invention is to provide a small-sized and low-cost positron annihilation γ-ray suppression type radioactive gas measuring device and damaged fuel inspection device with a simple configuration.

In order to achieve the above object, a radioactive gas measurement device of the present invention includes an inflow pipe and an exhaust pipe, and flows in and through the inflow pipe and the exhaust pipe, a radioactive gas containing a measurement target nuclide and a positron emission nuclide. A cone-shaped radiation measurement cell to be discharged, a radiation detector for measuring radiation generated from the radioactive gas, the radiation measurement cell and the radiation detector are communicated, and the radiation measurement cell and the radiation detector A radiation collimator that sets a predetermined radiation measurement geometric condition between the radiation measurement cells, and an inner wall area of the radiation measurement cell that the radiation detector expects through the radiation collimator as the predetermined radiation measurement geometric condition is The length of the radiation measurement cell is set under 1/2 of the total inner wall area of the measurement cell and under the condition that the side inner wall of the radiation measurement cell is not expected. (H) and the ratio (h / D) between the circle-converted diameter (D) of the inner wall area existing at the farthest location of the radiation measurement cell expected by the radiation detector is set to 1 or more, and the measurement object An index nuclide for nuclear reactor damaged fuel inspection is measured as a nuclide, and the presence or absence of fuel breakage is detected.

Further, the damaged fuel inspection apparatus of the present invention was collected by the sampling unit for sampling the radioactive gas containing the measurement target nuclide and the positron emitting nuclide that passed through the reactor fuel stored in the reactor, and the sampling unit A radioactive fuel measuring device that measures radiation generated from the radioactive gas, and a damaged fuel inspection device, the radioactive gas measuring device comprising an inflow pipe connected to the sampling unit, and an exhaust pipe, A cone-shaped radiation measurement cell that flows in and out the radioactive gas containing the measurement target nuclide and the positron emission nuclide through the inflow pipe and the discharge pipe, and a radiation detector that measures radiation generated from the radioactive gas. The radiation measurement cell and the radiation detector are connected to each other, and a radiation measurement geometrical condition is set between the radiation measurement cell and the radiation detector. An internal wall area of the radiation measurement cell expected by the radiation detector via the radiation collimator is set to ½ or less of a total internal wall area of the radiation measurement cell as the predetermined radiation measurement geometric condition The circular conversion of the length (h) of the radiation measurement cell and the inner wall area existing at the farthest location of the radiation measurement cell expected by the radiation detector under the condition that the side inner wall of the radiation measurement cell is not expected The ratio (h / D) with respect to the diameter (D) is set to 1 or more, an index nuclide for nuclear reactor damage fuel inspection is measured as the measurement target nuclide, and the presence or absence of fuel breakage is detected.

  According to the present invention, there is provided a small-sized and low-cost positron annihilation γ-ray suppression type radioactive gas measuring device and damaged fuel inspection device with a simple configuration without providing a complicated radiation measurement system for performing reverse coincidence processing and the like. can do.

  Embodiments of the present invention will be described below 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 is a diagram showing a positron annihilation γ-ray suppression type radioactive gas measuring apparatus according to a first embodiment of the present invention. The positron annihilation γ-ray suppression type radioactive gas measuring device of this embodiment includes a measurement cell 1 for introducing a measurement gas, a radiation detector 2 for measuring radiation emitted from the measurement cell 1, a measurement cell 1 and radiation detection. And a shield 3 for preventing background radiation incident from the outside of the measurement cell 1 and a measurement radioactive gas inflow for introducing the gas to be measured to the measurement cell 1 from the outside of the shield 3 A pipe 10a, a measurement radioactive gas discharge pipe 10b that discharges a measurement gas from the measurement cell 1, and a collimator 11 that guides radiation from the measurement cell 1 to the radiation detector 2 are provided.

  Moreover, the positron annihilation γ-ray suppression type radioactive gas measurement apparatus according to the first embodiment of the present invention processes the detection data from the radiation detector 2 using the amplifier 6a and the pulse height analyzer 6b, and measures the radiation. A device 7, a data processing device 8 that analyzes and determines the presence or absence of fuel damage from the measured value, and a monitor display device 9 that displays the result are provided.

  In the radioactive gas measurement device according to the first embodiment of the present invention, the shield 3 is generally formed of lead (Pb) or tungsten (W). The shield 3 is made of iron in order to reduce costs depending on use conditions. Further, the collimator 11 determines a field of view (measurable range) in which a measurement target in the measurement cell 1 is expected from the radiation detector 2. The present invention defines the measurement geometric conditions between the collimator 11, the radiation detector 2 and the measurement cell 1.

  FIG. 2 is a diagram showing a damaged fuel inspection apparatus including the positron annihilation γ-ray suppression type radioactive gas measurement apparatus according to the first embodiment of the present invention. The damaged fuel inspection device of the present invention is installed in the nuclear reactor 35. Hereinafter, the operation of the positron annihilation γ-ray suppression type radioactive gas measuring device of the present invention will be described as an example when applied to the damaged fuel inspection device of the present invention.

  The reactor fuel 36 is stored in the nuclear reactor 35, and the measurement target gas that has passed through the nuclear reactor fuel 36 is collected from the collection unit 37. The measurement target gas collected from the collection unit 37 passes through the measurement radioactive gas inflow pipe 10a, flows through the measurement cell 1, and is discharged from the measurement radioactive gas discharge pipe 10b. The radiation emitted from the measurement gas is measured by the radiation detector 2 and the measuring device 7 through the collimator 11 provided in the shield 3. The measurement result is sent to the data processing device 8, and the presence or absence of fuel breakage is analyzed and determined, and the result is displayed on the monitor display device 9.

  The principle of the present invention will be described below. First, the annihilation γ-ray emission process of the positron emitting nuclide will be described with N-13 as an example. The positron emitted by N-13 has an energy of 1.19 MeV. When these positrons annihilate by combining with normal negative electrons existing around them, annihilation γ rays are emitted. This γ ray simultaneously generates two γ rays (511 keV) in the opposite direction of 180 degrees. This gamma ray is called annihilation gamma ray. Under the condition that the sample to be measured contains a large amount of positron emitting nuclides such as N-13, the γ-ray measurement of the target nuclides having an energy smaller than the energy of the annihilation γ-ray (511 keV) is performed. Background radiation caused by scattering makes it difficult.

  In the present invention, attention is paid to the positron emission process of the positron emitting nuclide. The range of positron depends on its emission energy. In the case of N-13 (1.19 MeV), the range of positrons is a range of several meters in gas, and a range of several mm in solids. In other words, the positrons emitted in the gas are mostly combined with negative electrons at a distance of several meters to emit annihilation gamma rays.

  On the other hand, a general radiation detector has a diameter of about 5 cm to 10 cm or less, and a measurement cell (container for measurement gas) is provided in accordance with these detector dimensions. Therefore, a normal measurement cell has a diameter of about 5 cm to 10 cm. The dimension of the measurement cell is about two orders of magnitude smaller than the range of positrons, and the positrons emitted in the measurement cell immediately reach the inner wall of the measurement cell and emit annihilation γ rays at the inner wall.

  FIG. 3 is a diagram for explaining the measurement principle of the present invention. The measuring device shown in FIG. 3 is configured to be suitable for explaining the measurement principle of the present invention. That is, the measuring apparatus shown in FIG. 3 measures the radiation emitted from the measuring cell 1 provided in the shield 3 by the radiation detector 2, the amplifier 6a, and the wave height analyzer 6b, and the measured values are the data processing apparatus 8. And the result is displayed on the monitor display device 9.

  The measurement gas sample flows through the inlet / outlet pipes 10 a and 10 b of the measurement cell 1. The installation relationship between the measurement cell 1 and the radiation detector 2 provided in the shield 3 is a measurement geometric condition for allowing radiation emitted from the entire measurement cell 1. In the measurement apparatus shown in FIG. 3, the expected range of radiation measurement is indicated by 4, 4 '.

  In the configuration of the measurement apparatus shown in FIG. 3, most of the radiation of the measurement sample fluid and the annihilation γ rays generated on the inner wall 5 (shown by dotted lines) of the measurement cell 1 are measured by the detector 2. For this reason, in the conventional apparatus, if the special and complicated measurement circuit such as the reverse coincidence counting process as shown in FIG. 17 is employed and the annihilation γ-ray suppression process is not performed, the index nuclide (Xe) is detected from the measurement sample gas. -133 etc.) could not be measured with good sensitivity and accuracy.

  Based on the physical phenomenon of the positron annihilation process, the present invention was created by new knowledge that can reduce the contribution of annihilation γ rays by taking measures to make the inner wall of the measurement cell that the detector expects as small as possible. Is. This knowledge is realized by optimally setting the radiation measurement geometric condition determined by the collimator provided between the radiation detector and the measurement cell.

  By providing the collimator 11 in the shield 3, the expected measurement range 12 of radiation emitted from the measurement cell 1 (a range effective for radiation measurement) has a conical shape. FIG. 1 shows the relationship between the cylindrical measuring cell 1 and the detector 2 in a plan view. FIG. 4 shows a three-dimensional arrangement of the cylindrical measurement cell 1 and the detector 2 (illustration of the shield 3 and the collimator 11 is omitted). Under this measurement geometric condition, the amount of interference annihilation γ rays generated on the inner wall of the measurement cell 1 is limited to a part of the inner wall 13 of the measurement cell 1 facing the detector 2. In the apparatus shown in FIG. 3, the influence of the interference annihilation γ-ray can be greatly reduced depending on the ratio of the inner wall of the measurement cell 1 expected as compared with the case where the entire measurement cell 1 is a measurement target.

  FIG. 5 shows the spectrum measured by the present invention and the spectrum measured by the conventional example. Compared with the conventional measurement spectrum, the measurement spectrum of the present invention can greatly reduce the detection amount of N-13 (511 keV), can also greatly reduce the Compton scattering portion, and has an energy higher than 511 keV emitted by annihilation gamma rays. It can be seen that the measurement target nuclide Xe-133 (81 keV) having a small value can be remarkably measured.

  Next, the optimal geometric arrangement of the collimator 11 and the detector 2 will be described. The annihilation γ-ray suppression effect of a conventional apparatus employing an inverse coincidence apparatus or the like is 50% to 20%. The measurement geometric condition of the present invention equivalent to this suppression effect is examined.

  FIG. 6A to FIG. 6C are diagrams showing the geometric arrangement of the detector 2 and the collimator 11. 6A to 6C, the conditions under which the detector 2 expects the cylindrical measurement cell 1 through the collimator 11 are different. FIG. 6A shows a measurement geometric condition in which only the bottom inner wall 13 of the measurement cell 1 facing the detector 2 is expected, and a prospective range 12 thereof. The inner wall area of the bottom inner wall 13 of the measurement cell 1 facing the detector 2 indicates the inner wall area of the measurement cell present at the farthest place in the expected direction of the radiation detector 2. FIG. 6B shows a measurement geometric condition where the intercept 20 of the expected range 12 of the measurement cell 1 is ½ of the cylindrical body length of the measurement cell 1 and the expected range 12. Similarly, FIG. 6C shows a measurement geometric condition where the intercept 20 of the expected range 12 is 4/5 of the cylindrical body length dimension of the measurement cell 1 and the expected range 12.

  In FIG. 6A, the annihilation γ-rays emitted from the bottom inner wall 13 of the measurement cell 1 facing the detector 2 which is the expected range 12 of the detector 2 and the radiation of the measurement sample gas are measured. 6 (b) and 6 (c), emission is made from the inner wall area (indicated by arrows in FIGS. 6 (b) and 6 (c)) below the conical section 20 of the prospective range 12 of the detector 2. The annihilation gamma rays and the radiation of the measurement sample gas are measured. As is clear from FIGS. 6A to 6C, the reduction rate of the annihilation γ rays in FIG. 6B is about ½ (50%), and the annihilation γ rays in FIG. The reduction ratio is about 4/5 (80%). FIG. 6A is more effective than FIG. 6B. The relationship between the reduction rates of these annihilation γ rays is determined by the ratio of the total inner wall area (ST) of the measurement cell 1 to the inner wall area (S) expected by the radiation detector 2.

  Fig.7 (a)-FIG.7 (c) show measurement geometric conditions and its prospective range 12 (a detector and a collimator are not shown in figure). For the cylindrical measurement cell shown in FIG. 7 (a), there is a relationship between the measurement geometric conditions shown in FIGS. 6 (a) to 6 (c), its expected range 12, and the reduction rate of annihilation γ rays. In addition, the same relationship is established with respect to a vertical column cell having an arbitrary shape, such as the rectangular measurement cell (b) shown in FIG. 7B and the hexagonal measurement cell (c) shown in FIG. 7C. Furthermore, the present invention is sufficiently applicable to an irregularly shaped cell, a spherical cell, an elliptical cell, and the like.

  FIG. 8 shows the relationship between the total inner wall area (ST) of the measurement cell 1 and the inner wall area (S) expected by the radiation detector 2 and their ratio (detector and collimator not shown). When the intercept height of the prospective range 12 of the measurement cell 1 determined by the arrangement of the detector and the collimator is h1 with respect to the diameter D of the vertical cylindrical measurement cell, the total inner wall area expected by the detector is S (depending on the paint color in FIG. 8) Show). Here, the ratio of S to ST (S / ST) is a ratio for suppressing annihilation γ-rays. These relationships will be described below.

  FIG. 9 is a diagram illustrating examples of calculation parameters in which the diameter D of the measurement cell 1 is 10 cm and the intercept (h) of the expected range 12 of the measurement cell 1 is 2.5, 5, 7.5, and 10 cm. FIG. 10 shows the height (h) of the intercept of the expected detection range, the expected inner wall area of the measurement cell, and the total inner wall area when the length (height h) of the vertical cylindrical measurement cell 1 is 10 cm. It is a figure showing ratio (S / ST). Furthermore, FIG. 10 also shows the result of changing the parameter of the measurement cell diameter D to 10, 5, and 2.5 cm. In the process of obtaining the results, the area of the measurement cell window (W portion in FIG. 9) expected by the detector is ignored because the area is small.

  As is apparent from FIG. 10, when the height of the vertical column measuring cell is h = 10 cm and the detector expects the entire length of the vertical column measuring cell (10 cm), the S / ST ratio is 1. A condition with an S / ST ratio of 1 indicates a state (performance) that has no effect of suppressing annihilation γ rays. Similarly, when the length of the vertical column measuring cell expected by the detector is half (height h = 5 cm), the S / ST ratio is 0.5. This indicates that the ratio of suppressing annihilation gamma rays is 50%. Further, when the height h of the vertical column measuring cell is further reduced, the S / ST is also reduced, and when h = 2.5 cm, the S / ST is about 0.3. Further, when the height of the vertical column measurement cell is h = 0 (a state in which no side inner wall in the length direction of the measurement cell is expected), S / ST is 0.2 or less.

  Although the case where the length of the vertical column measurement cell is 10 cm has been described above, the same can be said even if the diameter D of the measurement cell is changed. In other words, even if the length of the vertical column measurement cell is changed, the measurement cell intercept in the range expected by the detector is designed to be ½ or less of the cell length, so that the suppression equivalent to the annihilation gamma ray suppression effect of the conventional device is achieved. A ratio of 50% or less can be achieved.

  As described above, according to the present embodiment, in the radiation measurement geometric condition configured by the radiation detector and the collimator that expects the measurement cell, by setting the range in which the detector expects the measurement cell to be half or less of the measurement cell length, A complicated measurement system using the reverse coincidence processing of the conventional apparatus is not required. In addition, the shielding body that shields the entire detection system can be reduced by about ½. Thereby, a simple, small and low cost (about 1/3) practical annihilation gamma ray suppression type measuring device can be realized. Furthermore, it is possible to realize a high-performance damaged fuel inspection apparatus that measures and monitors a damaged fuel inspection index nuclide in a radioactive gas mixed with positron emitting nuclides with high sensitivity and high accuracy and detects fuel damage.

  A positron annihilation γ-ray suppression type radioactive gas measuring apparatus according to a second embodiment of the present invention will be described. As the first embodiment of the present invention, the embodiment related to the condition that the detector expects the side inner wall of the vertical column measuring cell is shown. However, the second embodiment of the present invention expects the side inner wall of the vertical column measuring cell. Fig. 6 illustrates an embodiment relating to an optimal measurement geometric condition for a case with no.

  FIG. 11 shows a relationship between the total inner wall area (ST) of the measurement cell 1 and the inner wall area (S) expected by the radiation detector 2 in a case where the side inner wall (S ′) of the vertical column measuring cell 1 is not expected. is there. The inner wall area (S) described here indicates the inner area of the measurement cell inner wall existing at the farthest place in the prospective direction of the radiation detector 2 as described above. In FIG. 11, the detector and the collimator are not shown.

  When the length (height h1, h2) of the vertical column measuring cell 1 with the diameter D changes, the expected inner wall area (S) of the measuring cell (in this case, the bottom area S of the vertical column measuring cell 1) and the total inner wall area The (ST) ratio (S / ST) also varies greatly. Conceptually, the longer the length of the vertical column measurement cell 1, the smaller the S / ST ratio and the greater the effect of suppressing annihilation γ rays.

  FIG. 12 is a diagram showing the relationship between the cell length and the S / ST ratio using the diameter D of the vertical column measuring cell 1 as a parameter. As can be seen from this result, for each diameter D, the S / ST ratio decreases as the length (h) of the measurement cell is increased. In addition, the suppression effect of annihilation γ rays of the conventional device is 50% to 20%, and each cell diameter D is required to achieve the effective suppression effect of 20% or less (S / ST = 0.2 or less) of the conventional device. Thus, it can be seen that the expected detector range should be designed so that the cell length (h) is 10 cm or more.

  FIG. 13 is a diagram illustrating the calculation result of FIG. 12 with the ratio (h / D) of the length (h) and the diameter D of the vertical column measuring cell 1 on the horizontal axis. As is apparent from this result, when the h / D ratio is designed to be 1 or more (indicated by a solid white arrow in FIG. 13), S / ST is 0.2 or less (the effect of suppressing annihilation γ rays is 20%. It can be seen that the following value can be obtained. In addition, the dotted line indicates the relationship between the measurement sample gas volume (V) expected in the detector, the diameter D of each measurement cell, and h / D thereof in the figure. The measurement sample gas volume (V) is directly related to the measurement sensitivity of the index nuclide to be measured. In other words, it is important to select an arbitrary measurement geometric condition in which S / ST is 0.2 or less, taking into account the measurement sample gas volume (V) expected in the detector.

  FIG. 14 is a diagram illustrating a planar configuration example of the measurement cell 1, the collimator 11, and the radiation detector 2 with h / D = 1. In FIG. 14, the measurement sample gas and the expected inner wall area range 12 of the measurement cell 1 are indicated by solid lines. The configuration shown in FIG. 14 is an example in which the diameter D of the square cylindrical measurement cell 1 is 5 cm and the length thereof is 5 cm. Under the design condition of h / D = 1, S / ST is 0.2 or less. This indicates that the suppression rate of annihilation γ rays can be made 20% or less.

  FIG. 15 is a diagram illustrating a planar configuration example of the measurement cell 1, the collimator 11, and the radiation detector 2 in which h / D is 1 or more. In FIG. 15, the measurement sample gas and the expected inner wall area range 12 of the measurement cell 1 are indicated by solid lines. The configuration shown in FIG. 15 is an example in which the diameter D of the vertical rectangular measurement cell 1 is 5 cm and the length thereof is 15 cm. Under the design condition of h / D = 3, S / ST is 0.08 or less. . This means that the suppression of annihilation γ rays can be reduced to 8% or less, and a significant suppression effect is realized as compared with the performance of the conventional apparatus.

  In the case where the side wall of the vertical column measurement cell is not expected as in the present embodiment described above, the diameter D (circular diameter) of the vertical column measurement cell is obtained in the radiation measurement geometric condition including the radiation detector and the collimator that anticipates the measurement cell. ) And the length h (h / D) is set to 1 or more, thereby eliminating the need for a complicated measurement system that employs the reverse coincidence processing of the conventional apparatus and shielding the entire detection system by 1 / An annihilation γ-ray suppression type measuring apparatus that can be reduced by about 2 and that is simple and low in cost by about 1/3 can be realized.

  Although the vertical column measurement cell has been described above, the measurement cell length h and the inner diameter of the measurement cell existing in the farthest position in the expected direction of the detector, even for a measurement cell having an arbitrary external shape D can be designed optimally. Moreover, although the said inner area diameter D describes the collimation shape of the collimator as a circle, the diameter D (circle equivalent diameter) determined by the estimated inner area for the shape of an ellipse, square, hexagon, etc. As described above, an optimum design equivalent to a circular shape is possible, and a measurement apparatus similar to the above can be realized. In the present application, “circle converted diameter” is used in a broad sense including “circle diameter”.

  FIG. 16 is a diagram showing a positron annihilation γ-ray suppression type radioactive gas measuring apparatus according to a third embodiment of the present invention. The radioactive gas measuring device of the third embodiment shown in FIG. 16 is used instead of the square and vertical column measuring cell used in the radioactive gas measuring device of the first embodiment and the second embodiment of the present invention. Measurement cells of cones, triangle cones and square cones are used.

  The design geometry of the detector 2, the collimator 11, and the measurement cell 1 included in the radioactive gas measurement device of the third embodiment is the same as those of the devices included in the radioactive gas measurement device of the first embodiment and the second embodiment. The design geometry is the same. In the third embodiment shown in FIG. 16, the measurement cell 1 having a cone shape along the solid line indicating the measurement sample gas and the expected inner wall area range 12 of the measurement cell 1 is used. The third embodiment shown in FIG. 16 shows an example in which the cone measurement cell 1 has a bottom area diameter D of 10 cm and a length of 20 cm. Under the design condition of h / D = 2, S / ST is 0. .1. This means that the suppression of annihilation γ rays can be reduced to 10%, and the effect of suppressing annihilation γ rays similar to those in the first and second embodiments described above can be exhibited.

  In the third embodiment, the vertical column measuring cell is compared with the shielding material required in the first and second embodiments in the region indicated by the one-dot chain line in FIG. The corresponding shielding material can be greatly reduced. As described above, the positron annihilation γ-ray suppression type radioactive gas measuring device of the third embodiment can further reduce the size of the shielding body of the detection system, and can achieve a reduction in size and cost of the entire device. .

It is a figure which shows the positron annihilation gamma ray suppression type radioactive gas measuring apparatus of the 1st Embodiment of this invention. It is a figure which shows the damaged fuel test | inspection apparatus provided with the positron annihilation gamma ray suppression type radioactive gas measuring apparatus of the 1st Embodiment of this invention. It is a figure explaining the measurement principle of this invention. It is a figure which shows the three-dimensional arrangement | positioning of the cylindrical measurement cell and detector of this invention. It is a figure which shows the spectrum measured by this invention, and the spectrum measured by a prior art example. In the 1st Embodiment of this invention, it is a figure which shows the geometric arrangement of the detector and collimator from which the conditions which look at a measurement cell differ. It is a figure which shows the cylindrical measurement cell of the 1st Embodiment of this invention, a square-shaped measurement cell, and a hexagonal measurement cell. It is a figure which shows the relationship between the total inner wall area of a measurement cell, and the inner wall area which a radiation detector anticipates. It is a figure which shows the example of the parameter which calculates the inner wall area of a measurement cell. It is a figure showing ratio of the prospective inner wall area of a cylindrical measurement cell, and the total inner wall area. It is a figure which shows the relationship between the total inner wall area of the case which does not anticipate the side inner wall of the vertical column measurement cell 1, and the inner wall area which the radiation detector 2 anticipates. It is a figure which shows the relationship between the length of a cell, and S / ST ratio by using the diameter D of a vertical column measurement cell as a parameter. It is a figure which takes the ratio (h / D) of the length (h) and the diameter D of the vertical column measurement cell 1 on a horizontal axis, and shows S / ST ratio. It is a figure which shows an example of a structure of a measurement cell, a collimator, and a detector in case the ratio (h / D) of the length (h) of the vertical column measurement cell 1 and the diameter D is 1. FIG. It is a figure which shows an example of a structure of a measurement cell, a collimator, and a detector in case the ratio (h / D) of the length (h) of the vertical column measurement cell 1 and the diameter D is 3. FIG. It is a figure which shows an example of a structure of the measurement cell, collimator, and detector which concern on the 3rd Embodiment of this invention. It is a figure which shows the conventional radioactive gas measuring apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Measurement cell, 2 ... Radiation detector, 3, Shield, 4, 4 '... Expected range of radiation detector, 5 ... Measurement cell inner wall, 6a ... Amplifier, 6b ... Wave height analyzer, 7 ... Radiation measurement apparatus, DESCRIPTION OF SYMBOLS 8 ... Data processing apparatus, 9 ... Monitoring display apparatus, 10a ... Radioactive gas inflow piping, 10b ... Radioactive gas discharge piping, 11 ... Collimator, 12 ... Measurement range, 13 ... Bottom inner wall of measurement cell, 35 ... Reactor, 36 ... Reactor fuel, 37 ... Sampling part, 38 ... Damaged fuel inspection device, 40a ... Radioactive gas inflow piping, 40b ... Radioactive gas exhaust piping, 41 ... Shield, 42 ... Measuring cell, 43 ... Main detector, 44 ... Sub Detector

Claims (2)

A cone-shaped radiation measurement cell comprising an inflow pipe and an exhaust pipe, through which the radioactive gas containing the measurement target nuclide and the positron emission nuclide flows in and out through the inflow pipe and the exhaust pipe;
A radiation detector for measuring radiation generated from the radioactive gas;
A radiation collimator that communicates the radiation measurement cell and the radiation detector and sets a predetermined radiation measurement geometric condition between the radiation measurement cell and the radiation detector;
As the predetermined radiation measurement geometric condition, an inner wall area of the radiation measurement cell expected by the radiation detector via the radiation collimator is set to be equal to or less than ½ of a total inner wall area of the radiation measurement cell, and the radiation measurement The length (h) of the radiation measurement cell and the circular equivalent diameter (D) of the inner wall area existing at the farthest location of the radiation measurement cell expected by the radiation detector under the condition that the side inner wall of the cell is not expected Ratio (h / D) is set to 1 or more,
An apparatus for measuring a radioactive gas comprising measuring an index nuclide of a reactor damaged fuel inspection as the measurement target nuclide and detecting the presence or absence of fuel breakage. A sampling unit for sampling a radioactive gas including a measurement target nuclide and a positron emitting nuclide that has passed through the reactor fuel stored in the reactor;
A radioactive gas measurement device for measuring radiation generated from the radioactive gas collected by the collection unit;
A damaged fuel inspection device comprising:
The radioactive gas measuring device is
A cone-shaped radiation measurement comprising an inflow pipe connected to the sampling unit and an exhaust pipe, and through which the radioactive gas containing a measurement target nuclide and a positron emission nuclide flows in and out through the inflow pipe and the exhaust pipe Cell,
A radiation detector for measuring radiation generated from the radioactive gas;
A radiation collimator that communicates the radiation measurement cell and the radiation detector and sets a predetermined radiation measurement geometric condition between the radiation measurement cell and the radiation detector;
As the predetermined radiation measurement geometric condition, an inner wall area of the radiation measurement cell expected by the radiation detector via the radiation collimator is set to be equal to or less than ½ of a total inner wall area of the radiation measurement cell, and the radiation measurement The length (h) of the radiation measurement cell and the circular equivalent diameter (D) of the inner wall area existing at the farthest location of the radiation measurement cell expected by the radiation detector under the condition that the side inner wall of the cell is not expected Ratio (h / D) is set to 1 or more,
A damaged fuel inspection apparatus for measuring an index nuclide for nuclear reactor damaged fuel inspection as the measurement target nuclide and detecting the presence or absence of fuel damage.

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