The present invention relates to a radiation monitor and the like.
Known types of radiation monitors include semiconductor detectors and the like in addition to so-called gas detection units and scintillation detection units. However, it is difficult to properly measure radiation with any of the above-described types under an environment with a high dose rate. Therefore, as a radiation monitor capable of measuring radiation even under the environment with the high dose rate, for example, a technique described in PTL 1 below is known.
That is, PTL 1 describes a radiation monitor including “a radiation emitting element having a light emitting unit emitting light of an intensity corresponding to a dose rate of incident radiation, . . . , and an electric pulse converter which is connected to the optical fiber and transmits one electric pulse for one photon of the transmitted light”.
PTL 1: JP 2016-114392 A
However, in a radiation measurement environment (for example, a nuclear power plant), radiation beams of various energies coexist, and radiation enters the radiation emitting element at various incident angles. Therefore, even if the technique described in PTL 1 is used, the sensitivity to radiation is too high or too low depending on the energy of the radiation or the magnitude of the incident angle. That is, there is room for further enhancement of radiation measurement accuracy regarding the radiation monitor described in PTL 1.
Therefore, an object of the present invention is to provide a radiation monitor or the like capable of appropriately measuring radiation.
In order to solve the above problems, the present invention includes: a plurality of radiation detection units each of which includes a radiation detection element that emits light with incidence of radiation, and a housing that houses the radiation detection element; an optical transmission line that transmits light generated by the plurality of radiation detection elements to merge; a light detection unit that converts the light after merging guided to the light detection unit through the optical transmission line into an electric pulse; and an analysis unit that calculates a dose rate of radiation based on a count rate of the electric pulse, the plurality of housings including at least one housing made of a first material and another housing made of a second material.
According to this invention, it is possible to provide the radiation monitor and the like capable of appropriately measuring radiation.
Incidentally, optical fibers 13p and 13q are illustrated by thick lines, and wirings k1 and k2 are illustrated by thin lines in
The radiation monitor 100 is a device that measures a dose rate of radiation. As illustrated in
The radiation detection units 11 and 12 detect radiation incident on themselves, and are arranged at radiation measurement target points. As illustrated in
Each of the radiation detection elements 11a and 12a has a property of emitting light with incidence of radiation. As such radiation detection elements 11a and 12a, for example, a scintillation element containing a rare earth element in yttrium aluminum garnet, which is a base material, can be used. Examples of the rare earth element include praseodymium in addition to neodymium, ytterbium, and cerium.
In the present embodiment, a case where the radiation detection elements 11a and 12a are Nd:YAG (neodymium-added yttrium aluminum garnet) will be described as an example. When radiation, such as gamma rays, is incident on the Nd:YAG, photons having an emission wavelength of about 1064 nm are generated.
More specifically, when radiation is incident on Nd:YAG, the energy of the radiation causes an energy level of the rare earth element and the like contained in Nd:YAG to transition to a predetermined excited state. Then, when transiting from the above-described excited state to a ground state having a low energy level, photons having an emission wavelength of about 1064 nm are generated in Nd:YAG. In this manner, it is possible to suppress deterioration of the optical fibers 13p and 13q accompanying transmission of light by using Nd:YAG having an emission wavelength of 800 nm or more as the radiation detection elements 11a and 12a.
Incidentally, when radiation is incident on Nd:YAG, not only photons having the emission wavelength of about 1064 nm are generated, but also photons having a wavelength different from 1064 nm are also generated although the number of such photons is small. That is, the “emission wavelength” of the radiation detection elements 11a and 12a means a wavelength at which a photon generation rate is higher than other wavelengths.
The housing 11b illustrated in
The other housing 12b is a spherical shell-like member that houses the radiation detection element 12a. In the example of the present embodiment, stainless steel (so-called “SUS”) is used as a material (second material) forming the housing 12b. One of the main features of the present embodiment is that the housings 11b and 12b are made of different kinds of materials.
Note that there may be almost no gap between the radiation detection element 11a and the housing 11b (that is, the radiation detection unit 11 is solid), and the above-described gap may exist. The same applies to the other radiation detection unit 12.
Further, a size of each of the housings 11b and 12b (a size of each circle) in
The optical fibers 13p and 13q illustrated in
The optical fiber 13p has one end connected to the radiation detection element 11a and the other end connected to the radiation detection element 12a. Further, the other optical fiber 13q has one end connected to the radiation detection element 12a and the other end connected to the light detection unit 14.
That is, the radiation detection elements 11a and 12a are connected in series through the optical fibers 13p and 13q. Such a configuration is also one of the main features of the present embodiment. Then, the light generated by the radiation detection elements 11a and 12a merge in the optical fiber 13q, and the light after merging is guided to the light detection unit 14.
In the example illustrated in
Incidentally, the matter that the optical fiber 13p is “connected” to the end face i1 includes not only a configuration where one end of the optical fiber 13p is in close contact with the end face i1 but also a configuration where one end of the optical fiber 13p is brought to face close to the end face i1.
Further, a light-reflecting material j is provided on the other end face i2 and a peripheral wall surface of the radiation detection element 11a. As such a light-reflecting material j, for example, gold or silver having a high light reflectance and a low heat radiation rate (also referred to as emissivity) can be used. As a result, a predetermined ratio of the photons generated by the radiation detection element 11a is transmitted through the optical fiber 13p. Further, thermal radiation (noise) from the light-reflecting material j is suppressed even under a high-temperature environment, so that an error in radiation detection can be reduced.
In this manner, the radiation detection element 11a is optically polished in the vicinity (the end face i1) of the connection point with the optical fiber 13p, and the light-reflecting material j is provided in a region (the end face i2 and the peripheral wall surface) other than the vicinity of the above-described connection point. Incidentally, light slightly leaks at the end face i1 of the radiation detection element 11a, but an error caused by this leakage of light is corrected by the analysis/display device 16 (see
On the other hand, the columnar radiation detection element 12a illustrated in
For example, photons generated by the radiation detection element 11a due to the incidence of radiation are guided to the light detection unit 14 through the optical fiber 13p, the radiation detection element 12a, and the optical fiber 13q in order. Incidentally, both the radiation detection elements 11a and 12a are light-transmissive (transparent or translucent), and thus, attenuation of light in the radiation detection elements 11a and 12a is relatively small.
Meanwhile, photons generated by the radiation detection element 12a due to the incidence of radiation are guided to the light detection unit 14 through the optical fiber 13q. That is, photons incident on the light detection unit 14 include the photons generated by the radiation detection element 11a and the photons generated by the radiation detection element 12a.
Note that there are also photons guided from the radiation detection element 12a to the other radiation detection element 11a through the optical fiber 13p. Such photons are reflected by the light-reflecting material j (see
The light detection unit 14 illustrated in
The inventors have found that there is a proportional relationship between the dose rate of the radiation incident on the radiation detection element 11a and the number of photons generated by the radiation detection element 11a per unit time through experiments (the same applies to other radiation detection elements 12a). In the present embodiment, the number (count rate) of electric pulses output from the light detection unit 14 to the measurement device 15 per unit time is converted into the dose rate of radiation based on such a proportional relationship.
The measurement device 15 is a device that measures the count rate of the electric pulses input from the light detection unit 14, and is connected to the light detection unit 14 through the wiring k1. The measurement device 15 includes electronic circuits such as a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and various interfaces although not illustrated. Then, a program stored in the ROM is read and loaded in the RAM so that the CPU executes various processes.
Although not illustrated, the analysis/display device 16 also includes electronic circuits such as a CPU, a ROM, a RAM, and various interfaces, and is connected to the measurement device 15 through the wiring k2. The analysis/display device 16 calculates the dose rate of radiation based on the count rate of the electric pulses input from the measurement device 15 (an analysis process), and displays a calculation result. Incidentally, the count rate of the electric pulses and the dose rate of the radiation are in a proportional relationship, and the proportional coefficient is stored in the analysis/display device 16 in advance.
As described above, the radiation detection units 11 and 12 illustrated in
In the example illustrated in
Incidentally, it is preferable that the other housing 12b not be arranged within a predetermined angle range (−60°≤θ≤+60°) from the reference line Y1 (θ=0°) passing through one housing 11b, in consideration of the International electrotechnical commission standard (IEC standard). Similarly, it is preferable that one housing 11b not be arranged within a predetermined angle range (−60°≤θ≤+60°) from the reference line Y2 (θ=0°) passing through the other housing 12b. As a result, one of the radiation detection units 11 and 12 does not become a hindrance against the other so that the radiation detection error can be reduced.
Hereinafter, first, a description will be given regarding radiation sensitivity characteristics (see
Subsequently, a description will be given regarding radiation sensitivity characteristics (see
Further, a description will be given regarding sensitivity characteristics (see
Incidentally, the horizontal axis in
As illustrated in
Note that the sensitivity of the radiation detection unit 12 is affected by the thickness of the spherical shell-shaped housing 12b as described above, but the influence of the diameter (size) of the housing 12b on the sensitivity is relatively small.
In the present embodiment, the stainless steel housing 12b having a thickness of 7.5 mm is used as an example in consideration of the characteristics illustrated in
That is, for high-energy radiation, the sensitivity to radiation falls within a predetermined allowable range (within the IEC standard range to be described later). However, the sensitivity is too high for radiation with a low energy of about 200 keV. Specifically, when radiation with an energy of 200 keV is applied, the radiation detection unit 12 reacts sensitively with a sensitivity of 4000 or more. In consideration of such a situation, if the stainless steel housing 12b is too thick, the sensitivity of the radiation detection unit 12 to high-energy radiation becomes low.
Incidentally, the horizontal axis in
In the present embodiment, the housing 11b having a thickness of 2.5 mm is used as an example in consideration of the characteristics illustrated in
Next, characteristics in a case where the radiation detection unit 11 including the tungsten housing 11b and the radiation detection unit 12 including the stainless steel housing 12b are optically connected in series will be described with reference to
Incidentally, the horizontal axis in
Further, good results with small radiation measurement errors were obtained when a diameter φ of the radiation detection element 11a having the columnar shape (diameter of circles of the end faces i1 and i2 illustrated in
As described above, the radiation detection unit 12 including the stainless steel housing 12b is sensitive to the high-energy radiation, and has a predetermined sensitivity to low-energy radiation. On the other hand, the radiation detection unit 11 including the tungsten housing 11b has a relatively low sensitivity to low-energy radiation, and has a predetermined sensitivity to high-energy radiation.
When both the housings 11b and 12b having different materials and thicknesses are used, the sensitivity to radiation can be kept within a predetermined IEC standard range regardless of the magnitude of radiation energy as illustrated in
Incidentally, a light attenuation filter (not illustrated) may be additionally provided when the number (total number) of photons generated by the radiation detection elements 11a and 12a per unit time exceeds an upper limit value that allows photoelectric conversion by the light detection unit 14. For example, the light attenuation filter may be provided in a stage preceding the light detection unit 14, or the light attenuation filter may be provided between the radiation detection elements 11a and 12a. Further, the types of the radiation detection elements 11a and 12a and the materials and thicknesses of the housings 11b and 12b may be appropriately selected such that the light attenuation filter becomes unnecessary.
Incidentally, the horizontal axis in
Note that one of the radiation detection units 11 and becomes the hindrance against the other when the irradiation angle is ±90°, and thus, the sensitivity to radiation is low (two “reference values” illustrated in
According to the first embodiment, the radiation can be appropriately measured regardless of the energy of the radiation or the magnitude of the irradiation angle with the simple configuration where the two radiation detection elements 11a and 12a are optically connected in series. That is, the radiation monitor 100 having the sensitivity characteristics (energy-sensitivity characteristics or incident angle-sensitivity characteristics) within the IEC standard range can be provided by appropriately selecting the material and thickness of the housings 11b and 12b.
Further, the “optical transmission lines” that cause the light generated by the radiation detection elements 11a and 12a to merge and be guided to the light detection unit 14 are formed in common as the optical fiber 13q. Therefore, the total length of the “optical transmission line” is reduced as compared with a configuration (not illustrated) in which light generated by the radiation detection elements 11a and 12a are separately guided to the light detection unit 14, and thus, cost can be reduced.
Incidentally, the arrangement of the radiation detection units 11 and 12 is not limited to the example illustrated in
In the example illustrated in
As illustrated in
As illustrated in
The hemispherical portion n1 is provided on one side in the central axis direction (direction of the reference line Y1) of the columnar portion m1. The radiation detection element 11a is arranged in the vicinity of the center O1 based on a curvature of a spherical surface of the hemispherical portion n1. Further, a center axis of the radiation detection element 11a having the columnar shape and a center axis of the columnar portion m1 of the housing 11Bb are perpendicular to each other in the example illustrated in
In this manner, the housings 11Bb and 12Bb include the hemispherical portions (hemispherical portions n1 and n2) on the outer shapes, respectively. Further, the other housing 12Bb is not arranged within a predetermined angle range (−60°≤θ≤60°) from the reference line Y1 passing through the housing 11Bb. The above-described reference line Y1 is a predetermined line segment passing through the center O1, and is perpendicular to the center axis of the radiation detection element 11a having the columnar shape.
Similarly, the other housing 11Bb is not arranged within a predetermined angle range (−60°≤θ≤60°) from the reference line Y2 passing through the housing 12Bb. As a result, it is possible to prevent one of the radiation detection units 11B and 12B from being a hindrance against the other and to reduce an error accompanying radiation detection.
Incidentally, a gap may be provided between the radiation detection element 11a and the housing 11Bb, or a gap may not be necessarily provided. In any case, the radiation detection element 11a can be firmly fixed to the thick columnar portion m1 (the same applies to the other radiation detection unit 12B).
Note that the matter that the housings 11b and 12b (see
As illustrated in
A second embodiment is different from the first embodiment in that the radiation detection units 11 and 12 (see
The radiation monitor 100D includes a sealed container 17 in addition to the same configurations as those in the first embodiment (see
Since the radiation detection units 11 and 12 are housed in such a sealed container 17, for example, it is possible to suppress the entry of water vapor into the radiation detection units 11 and 12 even under a high-humidity environment. Incidentally, in the optical fiber 13q, a range from the sealed container 17 to the light detection unit 14 may be covered with a metallic flexible tube (not illustrated), and one end of the flexible tube may be fastened to a wall of the sealed container 17. As a result, it is possible to further suppress the entry of water vapor or the like into the sealed container 17.
According to the second embodiment, the radiation detection units 11 and 12 are housed in the single sealed container 17. As a result, the entry of water vapor or the like into the radiation detection units 11 and 12 can be suppressed even under the high-humidity environment. Therefore, it is possible to prevent the water vapor from adhering to inner wall surfaces of the housings 11b and 12b and the radiation detection elements 11a and 12a, so that the radiation detection units 11 and 12 are less likely to break down.
A third embodiment is different from the first embodiment in that the optical fiber 13q connecting the radiation detection element 12a (see
The radiation monitor 100E illustrated in
The optical connector 18 is provided at a portion (the optical fiber 13q), which connects the light detection unit 14 and a serially connected body K to which the radiation detection elements 11a and 12a are directly connected, in the above-described “optical transmission lines” (13p and 13q). The optical connector 18 includes a plug 181 and a receptor 182 corresponding to the plug 181.
In the example illustrated in
Incidentally, a plurality of connectors 18 may be provided in the optical fiber 13q or the like.
According to the third embodiment, when a failure occurs in the radiation detection elements 11a and 12a or the like, a point where the failure has occurred can be easily separated from the optical fiber 132q. Incidentally, a distance from installation sites of the radiation detection units 11 and 12 to a control room (an installation site of the light detection unit 14 and the like) is often several hundred meters. That is, a length of the optical fiber 132q is sometimes several hundred meters.
In the present embodiment, the optical fiber 131q having a relatively short length and the optical fiber 132q having a relatively long length are connected through the optical connector 18. As a result, even if a failure occurs in the radiation detection elements 11a and 12a or the like, the replacement can be easily performed.
A fourth embodiment is different from the first embodiment in that a radiation monitor 100F (see
The radiation monitor 100F illustrated in
The radiation detection elements 11a and 12a illustrated in
The light emitting unit 21 illustrated in
In the example illustrated in
The inventors have found that there is a proportional relationship between the light intensity of the light emitting unit 21 and the number (total number) of photons generated by the radiation detection elements 11a and 12a per unit time through experiments. In the present embodiment, the relationship between the light intensity of the light emitting unit 21 and the count rate of the electric pulses in the light detection unit 14 is specified based on such a proportional relationship.
The light emitting unit control device 22 illustrated in
The optical branching unit 23 causes the light from the radiation detection elements 11a and 12a to branch toward the light emitting unit 21 and the wavelength selection unit 24. That is, the optical branching unit 23 has a function of guiding light, incident on a first port 23q through the optical fiber 13q, to the optical fiber 13r through a second port 23r and to the optical fiber 13s through a third port 23s.
Further, the optical branching unit 23 also has a function of guiding light, incident from the light emitting unit 21 through the optical fiber 13s, to the radiation detection units 11 and 12 through the optical fiber 13q and the like. For example, an optical coupler can be used as such an optical branching unit 23.
Incidentally, an “optical transmission line” that transmits light from the light emitting unit 21 to the radiation detection elements 11a and 12a and transmits light from the radiation detection elements 11a and 12a to the light detection unit 14 includes the optical fibers 13p, 13q, 13r, and 13s and the optical branching unit 23.
The light, incident on the optical branching unit 23 from the radiation detection units 11 and 12 through the optical fiber 13q and the like, is split and transmitted to the optical fibers 13r and 13s at a ratio of 1:1. Among them, detection of radiation, an inspection of the radiation monitor 100F, and the like are performed based on the light transmitted through the optical fiber 13r.
The wavelength selection unit 24 selectively transmits light having a wavelength within a predetermined range. As such a wavelength selection unit 24, for example, a wavelength selection filter or a spectroscope can be used.
The wavelength selection unit 24 can be switched from one of a “first mode” and a “second mode”, which will be described below, to the other.
The “first mode” is a mode in which light having the emission wavelength (for example, 1064 nm) of the radiation detection elements 11a and 12a is transmitted and the light from the light emitting unit 21 is blocked.
The “second mode” is a mode in which the light from the light emitting unit 21 is transmitted and the light having the emission wavelength of the radiation detection elements 11a and 12a is blocked.
For example, in a configuration where the wavelength selection unit 24 includes a plurality of wavelength selection filters, the wavelength selection filters corresponding to the above-described respective modes are selected by an autochanger system. Further, when the wavelength selection unit 24 is a spectroscope, an angle of the spectroscope is adjusted so as to correspond to each of the above-described modes.
The light detection unit 14 converts the light that has been transmitted through the wavelength selection unit 24 into an electric pulse.
The measurement device 15 measures a count rate of the electric pulses input from the light detection unit 14.
The analysis/display device 16F calculates a dose rate of radiation based on the above-described count rate and the light intensity of the light emitting unit 21, and determines whether the light emitting unit 21 deteriorates.
In the storage unit 161, count rate-dose rate information 161a, light intensity-count rate first information 161b, light intensity-count rate second information 161c, and wavelength-transmittance information 161d are stored in advance.
The count rate-dose rate information 161a is information indicating a relationship between the count rate of the electric pulses input from the measurement device 15 (that is, the count rate of photons) and the dose rate of radiation. As described above, the count rate and the dose rate are in the proportional relationship.
Incidentally, the light intensity-count rate first information 161b, the light intensity-count rate second information 161c, and the wavelength-transmittance information 161d illustrated in
The operation unit 162 illustrated in
The analysis unit 163 calculates the dose rate of radiation based on the count rate input from the measurement device 15 and the count rate-dose rate information 161a. Further, the analysis unit 163 determines whether the light emitting unit 21 or the like deteriorates based on the count rate input from the measurement device 15 and the light intensity of the light emitting unit 21 input from the light emitting unit control device 22. Incidentally, the processing executed by the analysis unit 163 will be described later.
The display control unit 164 causes the display unit 165 to display an analysis result and the like of the analysis unit 163.
The display unit 165 is a display that displays the analysis result and the like of the analysis unit 163.
The measurement device 15 sets the wavelength selection unit 24 illustrated in
Photons generated by the radiation detection elements 11a and 12a with the incidence of the radiation enter the optical branching unit 23 through the optical fiber 13q and the like. Then, half of the above-described photons enter the wavelength selection unit 24 through the optical fiber 13r, and further pass through the wavelength selection unit 24. A dose rate of radiation is calculated based on the number of the photons per unit time (count rate). Incidentally, there is no particular need to cause the light emitting unit 21 to emit light, except during the inspection to be described below.
The “Inspection” of the radiation monitor 100F is performed in a state where the dose rate of radiation incident on the radiation detection elements 11a and 12a is at a background level (natural radiation level). Such an “inspection” is often performed periodically in a state where devices (radiation generating sources) around the radiation monitor 100F are stopped. Incidentally, the radiation at the “background level” is weak radiation caused by cosmic rays or underground natural radioactive materials.
In Step S101, the radiation monitor 100F sets the wavelength selection unit 24 to the “first mode” using the measurement device 15. That is, the radiation monitor 100F sets the wavelength selection unit 24 so as to transmit the light having the emission wavelength of the radiation detection elements 11a and 12a and block the light from the light emitting unit 21.
In Step S102, the radiation monitor 100F causes the light emitting unit 21 to emit light. That is, the radiation monitor 100F uses the light emitting unit control device 22 to control the light emitting unit 21 to emit light at a wavelength different from the emission wavelength of the radiation detection element 11a based on a predetermined light intensity setting value.
The light emitted from the light emitting unit 21 enters the radiation detection element 11a through the optical fiber 13q and the like. Due to the energy of this light, a photon with a predetermined emission wavelength (for example, 1064 nm) is generated in the radiation detection element 11a at a generation rate proportional to the intensity of the emitted light. This photon enters the wavelength selection unit 24 through the optical fiber 13r and the like, and passes through the wavelength selection unit 24.
Further, light transmitted from the light emitting unit 21 and reflected and scattered in the radiation detection units 11 and 12 also enters the wavelength selection unit 24 through the optical fiber 13r and the like. Here, the direct light from the light emitting unit 21 is blocked by the wavelength selection unit 24 since the wavelength selection unit 24 is set to the “first mode”.
In Step S103 in
In Step S104, the radiation monitor 100F measures a count rate using the measurement device 15. That is, the radiation monitor 100F uses the measurement device 15 to count the number of electric pulses per unit time. This value is not only the count rate of electric pulses but also the count rate of photons transmitted through the wavelength selection unit 24. The count rate and the light intensity of the light emitting unit 21 are in a proportional relationship.
Incidentally, the horizontal axis in
In Step S105 of
In the example illustrated in
Incidentally, three causes of the above-described change can be listed: deterioration of the light emitting unit 21, deterioration of the optical fiber 13q and the like, and deterioration of the radiation detection elements 11a and 12a. In the present embodiment, any one of the three causes is determined by processing in Steps S106 to S118 (see
When the relationship between the light intensity and the count rate has changed in Step S105 in
In Step S106, the radiation monitor 100F uses the analysis/display device 16F to determine whether an actual light intensity of the light emitting unit 21 is lower than a predetermined set value. For example, an inspector may connect a light intensity measurement device (not illustrated) to the light emitting unit 21 such that a measurement value (actual light intensity of the light emitting unit 21) is output from the light intensity measurement device to the analysis/display device 16F.
If the actual light intensity of the light emitting unit 21 is lower than the set value in Step S106 (S106: Yes), the processing of the radiation monitor 100F proceeds to Step S107.
In Step S107, the radiation monitor 100F determines that the light emitting unit 21 has deteriorated, by the analysis/display device 16F. This is because the actual light intensity of the light emitting unit 21 is lower than the set value.
In Step S108, the radiation monitor 100F displays the fact that the light emitting unit 21 has deteriorated on the analysis/display device 16F, and ends the processing (“END” in
In addition, if the actual light intensity of the light emitting unit 21 is not lower than the set value in Step S106 (S106: No), the processing of the radiation monitor 100F proceeds to Step S109. In this case, there is a high possibility that the optical fiber 13q or the like has deteriorated, or the radiation detection elements 11a and 12a have deteriorated.
In Step S109, the radiation monitor 100F sets the wavelength selection unit 24 to the “second mode” using the measurement device 15. That is, the radiation monitor 100F sets the wavelength selection unit 24 so as to transmit the light from the light emitting unit 21 and block the light having the emission wavelength of the radiation detection elements 11a and 12a.
In Step S110 of
In Step S111, the radiation monitor 100F detects photons using the light detection unit 14.
In Step S112, the radiation monitor 100F measures a count rate using the measurement device 15. This count rate is proportional to the light intensity of the light emitting unit 21 as described above.
The horizontal axis in
In Step S113 of
In the example illustrated in
In Step S114, the radiation monitor 100F determines that the optical fiber 13q and the like have deteriorated, by the analysis/display device 16F. This is because, if the optical fibers 13p and 13q deteriorate due to the influence of radiation, it becomes difficult for light to be transmitted, and the above-described count rate becomes lower than that in a normal state.
In Step S115, the radiation monitor 100F uses the analysis/display device 16F to calibrate the count rate-dose rate information 161a (see
The horizontal axis of
Further, as compared with a state where the optical fiber 13q has not deteriorated (curve h1), the transmittance of light at each wavelength is low in a state where the optical fiber 13q has deteriorated (curve h2) and a state where the optical fiber 13q has further deteriorated (curve h3). In this manner, the relationship between the wavelength and the transmittance of light in the optical fiber 13q is associated with a predetermined numerical value indicating the degree of deterioration of the optical fiber 13q, which is stored in the storage unit 161 in advance as the wavelength-transmittance information 161d (see
The procedure of the “calibration” in Step S115 in FIG. will be specifically described as follows. The analysis/display device 16F first reads the wavelength of light from the light emitting unit 21. This wavelength value is transmitted from the light emitting unit control device 22 to the analysis/display device 16F.
Next, the analysis/display device 16F calculates the transmittance of light of the optical fiber 13q. This transmittance is calculated based on the light intensity of the light emitting unit 21 and the count rate input from the measurement device 15. Then, the analysis/display device 16F calibrates the count rate-dose rate information 161a based on the wavelength of the light of the light emitting unit 21, the transmittance of the light in the optical fiber 13q, and the above-described wavelength-transmittance information 161d.
In the example illustrated in
Then, the analysis/display device 16F multiplies the proportional coefficient of the dose rate relative to the count rate (proportional coefficient when the optical fiber 13q has not deteriorated) by the numerical value φ based on the count rate-dose rate information 161a (see
The description will be continued returning to
In Step S116 of
If there is no change in the relationship between the light intensity and the count rate in Step S113 (S113: No), the processing of the radiation monitor 100F proceeds to Step S117.
In Step S117, the radiation monitor 100F determines that the radiation detection elements 11a and 12a have deteriorated, by the analysis/display device 16F. That is, the analysis/display device 16F determines that at least one of the radiation detection elements 11a and 12a has deteriorated. This is because there is a high possibility that the radiation detection elements 11a and 12a, which are the remaining one among the three causes, deteriorate if neither the light emitting unit 21 nor the optical fiber 13q has deteriorated.
Incidentally, when the emission wavelengths of the radiation detection elements 11a and 12a are different from each other, the measurement device 15 may switch the wavelength selection unit 24 such that one of two wavelengths of light is transmitted and the other is blocked. In this case, the analysis/display device 16F identifies which of the radiation detection elements 11a and 12a has deteriorated based on the count rate measured by the measurement device 15 and the light intensity of the light emitting unit 21.
In Step S118, the radiation monitor 100F causes the analysis/display device 16F to display a determination result in Step S117, and ends the processing (END). In this case, at least one of the radiation detection elements 11a and 12a is replaced with a new one.
According to the fourth embodiment, the light emitting unit 21 emits light at the wavelength different from the emission wavelength of the radiation detection elements 11a and 12a during the inspection of the radiation monitor 100F. Then, which of the light emitting unit 21, the optical fiber 13q and the like, and the radiation detection elements 11a and 12a has deteriorated can be easily identified by appropriately switching the setting (the first mode or the second mode) of the wavelength selection unit 24.
Further, the inspector does not need to go to the vicinity of the radiation detection units 11 and 12 since the above-described inspection is performed by the analysis/display device 16F and the like. As a result, the inspection of the radiation monitor 100F can be easily performed, for example, even under a severe environment with a high dose rate.
Further, it is not necessary to apply a high voltage to the radiation detection units 11 and 12, and thus, there is no possibility that a hydrogen explosion or the like may occur even in a hydrogen/oxygen atmosphere environment, and no electrical noise occurs. In this manner, the highly reliable radiation monitor 100F can be provided according to the fourth embodiment.
Incidentally, a mirror 25 illustrated in
The radiation monitor 100G illustrated in
Incidentally, an “optical transmission line” that transmits light from the light emitting unit 21 to the radiation detection elements 11a and 12a and transmits light from the radiation detection elements 11a and 12a to the light detection unit 14 includes the optical fibers 13p, 13q, 13r, and 13s, and the mirror 25.
Then, the analysis/display device 16G executes predetermined processing based on the light intensity of the light emitting unit 21 and the count rate of the electric pulses during the inspection of the radiation monitor 100G. That is, the analysis/display device 16G determines whether the light emitting unit 21 has deteriorated or whether other components (the radiation detection elements 11a and 12a and the optical fiber 13q and the like) have deteriorated, and displays a result of the determination. Even with such a configuration, the reliability of the radiation monitor 100G can be enhanced as compared with the related art.
A fifth embodiment is different from the first embodiment in that the radiation detection unit 11 (see
As illustrated in
The optical fibers 13t, 13u, and 13v and the optical coupler 19 are “optical transmission lines” that transmit light generated by the radiation detection elements 11a and 12a to merge. The optical coupler 19 is provided at a merging point of the light generated by the radiation detection elements 11a and 12a. Further, the “optical transmission line” branches from the optical coupler 19 into two lines toward the respective radiation detection elements 11a and 12a.
The light generated by the radiation detection element 11a is guided to the optical coupler 19 through the optical fiber 13t. The light generated by the radiation detection element 12a is guided to the optical coupler 19 through the optical fiber 13u. Then, the light after merging by the optical coupler 19 is guided to the light detection unit 14 through the optical fiber 13v.
According to the fifth embodiment, the radiation can be detected with high accuracy regardless of the magnitude of the radiation energy or the irradiation angle by causing the light from the radiation detection elements 11a and 12a to merge at the optical coupler 19. That is, an error caused by radiation detection can be reduced as compared with the related art by appropriately selecting materials and thicknesses of the housings 11b and 12b.
Although the radiation monitor 100 and the like according to the present invention have been described in the respective embodiments as described above, the present invention is not limited to these descriptions, and various changes can be made.
For example, the case where each of the radiation detection elements 11a and 12a is Nd:YAG has been described in the respective embodiments, but the invention is not limited thereto. That is, at least one of the radiation detection elements 11a and 12a may contain a scintillation element (for example, Nd:YAG) in which yttrium aluminum garnet as a base material contains a rare earth element.
Further, the configuration where the radiation monitor 100 (see
Further, the same can apply to the fifth embodiment (see
Further, the configuration where the measurement device 15 (see
Further, the configuration where the radiation detection elements 11a and 12a (see
Further, the respective embodiments can be appropriately combined. For example, the analysis/display device 16F may identify a point where a failure occurs in a configuration where the fourth embodiment (see
Further, the configuration where the radiation monitor 100 is installed in the nuclear power plant has been described in the respective embodiments, but the invention is not limited thereto. Examples of other installation sites of the radiation monitor 100 include the following sites. That is, the radiation monitor 100 may be installed in a used-fuel storage pool in the nuclear power plant, inside or outside of a reactor pressure vessel, inside or outside a reactor container vessel, inside or outside a suppression pool, inside or outside a reactor building, in a reprocessing facility, and the like. Further, the radiation monitor 100 may be installed in a radiation medical facility, or may be used for detection of fuel debris (generated as molten reactor fuel cooled and solidified).
Further, the respective embodiments have been described in detail in order to describe the present invention in an easily understandable manner, and are not necessarily limited to one including the entire configuration that has been described above. Further, addition, deletion or substitution of other configurations can be made with respect to some configurations of the embodiments. Further, only mechanisms and configurations considered to be necessary for the description have been illustrated as above, and all the mechanisms and configurations required as a product are not necessarily illustrated.
Number | Date | Country | Kind |
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JP2017-217545 | Nov 2017 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2018/032166 | 8/30/2018 | WO |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2019/092955 | 5/16/2019 | WO | A |
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Japanese Office Action received in corresponding Japanese Application No. 2017-217545 dated May 11, 2021. |
Extended European Search Report received in corresponding European Application No. 18875994.8 dated Jun. 18, 2021. |
International Search Report of PCT/JP2018/032166 dated Oct. 9, 2018. |
Number | Date | Country | |
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20200278458 A1 | Sep 2020 | US |