JP2013122425A - Radiation monitor and method of monitoring radiation dose - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation monitor in a nuclear power plant, especially a radiation monitor suitable for measurement in a wide range.SOLUTION: Plural radiation monitoring detectors including radiation light-emitting elements having different excitation or emission wavelengths are optically coupled in series using optical fibers. One end of the detectors optically coupled in series is optically coupled with a light source on which light with plural wavelengths can be incident. The other end is optically coupled with a measuring device that measures the intensity of light of each wavelength. An arithmetic device specifies a radiation monitoring detector among the plural detectors and obtains a radiation dose rate of the specified detector, on the basis of the intensity of light of each excitation and emission wavelength. In another embodiment, a light reflector or the like is coupled with one end of radiation monitoring detectors optically coupled in series in order to reflect light. The other end is optically branched. The branched end is optically coupled with a light source on which light of plural wavelengths can be incident and the other end is optically coupled with a measuring device that measures the intensity of light of each wavelength.

Description

  The present invention relates to a radiation monitor in a nuclear power plant or the like, and more particularly to a radiation monitor suitable for measurement over a wide range and a method for monitoring a radiation dose.

  Conventionally, radiation monitors in nuclear power plants use scintillation detectors or semiconductor detectors. The scintillation detector uses a scintillation element that emits light when radiation is incident, and it is necessary to supply a high voltage power source for the detector and a power source for the preamplifier to the installation position of the detector. Also in the semiconductor detector, it is necessary to apply a bias voltage to the semiconductor element, and since a preamplifier is necessary like the scintillation detector, a high voltage power source and a power source for the preamplifier are installed at the detector installation position. There was a need to supply. Therefore, it is necessary to lay the power cable for high voltage application and preamplifier and the signal cable at the installation position of the detector, and when multiple detectors are installed to measure the radiation intensity distribution, many There was a need to lay a cable of books.

  As a radiation measurement apparatus that does not require a power cable for applying a high voltage and a preamplifier, apparatuses that transmit and measure scintillation light through an optical fiber are disclosed in Patent Document 1, Patent Document 2, and the like. Patent Document 1 uses a scintillation fiber, and Patent Document 2 has a configuration in which a plurality of scintillators are provided in the middle of a transmission optical fiber. These determine the scintillation position from the difference in arrival time of the scintillation light at both ends of the fiber, and obtain the radiation intensity distribution from the light emission frequency at each position.

  A device using a scintillation fiber has a large optical transmission loss of the scintillation fiber, and it is difficult to transmit several tens of meters or more. Therefore, it is impossible to construct an apparatus for measuring a radiation intensity distribution that requires a long transmission distance (up to 100 m or more). In addition, when a plurality of scintillators are provided in the middle of one transmission optical fiber, the determination of the scintillation position due to the difference in arrival time of the scintillation light is accompanied by uncertainties due to the influence of scattering and reflection components due to scattering inside and outside the scintillator.

  As a radiation measurement apparatus that does not require a power cable for applying a high voltage and a preamplifier, there are other apparatuses that combine a photoluminescent OSL (Optically Stimulated Luminescence) crystal and an optical fiber. Is shown in Patent Document 3 specifies the light emission position from the time from the arrival of the stimulation light to the time when the radiated light reaches the photoelectric conversion element. As in the case of the scintillator, scattering / The determination of the light emission position based on the light arrival time difference due to the influence of the reflection component involves uncertainty. Patent Document 4 is a device that irradiates an optical fiber having an OSL crystal at the tip of the optical fiber with laser light, and receives and measures the OSL light emitted from the OSL crystal through the optical fiber. On the other hand, since it is necessary to use two optical fiber cables, there is a problem that when a plurality of detectors are installed to measure the radiation intensity distribution, it is necessary to lay many optical fiber cables. .

JP-A-5-249247 JP-A-6-258446 Japanese Patent No. 2891198 Japanese Patent No. 3591275

  An object of the present invention relates to a radiation monitor in a nuclear power plant, and particularly to provide a radiation monitor suitable for measurement in a wide range.

  In order to achieve the above object, a radiation monitor according to the present invention is a radiation monitor detector in which a plurality of radiation monitor detectors each having radiation emitting elements having different stimulation or emission wavelengths are optically connected in series. A row, a light source optically connected to one end of the row and capable of receiving light of multiple wavelengths, and a measurement optically connected to the other end of the row to measure the intensity of light per wavelength And an arithmetic unit for obtaining a dose rate of radiation in the specified detector among the plurality of detectors for radiation monitoring from the intensity of light for each wavelength of stimulation and emission wavelengths. Radiation monitor.

  The method for monitoring radiation dose according to the present invention provides a row of radiation monitor detectors in which a plurality of radiation monitor detectors each having a radiation emitting element having a different stimulus or emission wavelength are optically connected in series. Measuring the intensity of the light having the emission wavelength emitted during irradiation of the stimulating light, and entering the stimulating light according to the radiation monitor detector to be monitored from the plurality of radiation monitoring detectors From the step of measuring the time from the previous irradiation end time of the stimulus light to the current irradiation start time, the intensity of the light measured for the radiation monitor detector to be monitored, and the time, Deriving a dose rate at the detector.

  According to the present invention, it is not necessary to lay a large number of cables and it is possible to measure a radiation intensity distribution that requires a long transmission distance. For example, a wide range of radiation monitors in a nuclear power plant can be measured. can do.

1 shows a configuration of a radiation monitor according to a first embodiment of the present invention. The structure of the radiation monitor of Example 2 of this invention is shown. The structure of the radiation monitor of Example 3 of this invention is shown. The structure of the radiation monitor of Example 4 of this invention is shown. The structure of an example of the detector for radiation monitors used for Examples 1 to 4 of the present invention is shown. The structure of the other example of the detector for a radiation monitor used for Example 1-4 of this invention is shown. The structure of an example of the detector for radiation monitors used for Example 2, 4 of this invention is shown. The structure of the other example of the detector for radiation monitors used for Example 2, 4 of this invention is shown. An example of the time change of the count rate which concerns on this invention is shown. An example of the dose rate measurement procedure which concerns on Example 5 of this invention is shown. The other example of the dose rate measurement procedure which concerns on Example 5 of this invention is shown. An example of the peak value spectrum which concerns on Example 5 of this invention is shown. An example of the stimulation wavelength and light emission wavelength of the detection element which concerns on this invention is shown.

  Multiple radiation monitor detectors using radiation emitting elements with different stimuli or emission wavelengths are optically connected in series using optical fibers, and one end of the optically connected series is incident on multiple wavelengths. The other end is optically connected to a measuring device that measures the intensity of light for each wavelength.

  Select the detector at the position to be measured, and irradiate the light of the stimulation wavelength according to the detector. The detector emits light having a specific wavelength corresponding to the detection element by the stimulation light applied to the detector. The emitted light is incident on a measuring device that measures the intensity of light for each wavelength through an optical fiber. The measuring device has a spectral filter or a spectroscope for discriminating the peak value of incident light, and is discriminated into light having a specific wavelength corresponding to the detection element. The discriminated light is measured for intensity by a photomultiplier tube, an amplifier, and a multichannel wave height analyzer. Instead of the photomultiplier tube, a photoelectric conversion element such as an avalanche photodiode may be used.

  The difference between the time when the last stimulation light irradiation ends and the time when the stimulation light irradiation starts this time is taken as the measurement time. The dose rate is derived using the measured light intensity, the database of the relationship between the light intensity and the dose obtained in advance by measurement, and information on the measurement time. The time change of the dose rate distribution is derived by repeating the measurement of the dose rate for each detector. Since a power cable for high voltage application and a preamplifier is not required and a plurality of measurement points can be measured with a single optical cable, a radiation monitor suitable for measurement over a wide range can be provided.

Several embodiments of the present invention will be described below with reference to the drawings.
[Example 1]
FIG. 1 shows the configuration of a radiation monitor of Example 1, which is a preferred embodiment of the present invention. As shown in FIG. 1, the radiation monitor of the first embodiment uses optical fibers 1 to optically connect radiation monitor detectors 2 a having different stimulation and emission wavelengths in series. FIG. 13 shows an example of the stimulation wavelength and the emission wavelength of the detection element. One end optically connected in series is connected to the optical switch 3. The optical switch 3 is connected to a plurality of laser diodes 9 having different emission wavelengths and a laser diode driver 10 for driving the laser diode 9, and a radiation monitor at a measurement target position is controlled by a control signal 11 of a data collection control personal computer 8. The radiation detector 2a is controlled to irradiate the radiation detector 2a with a laser having a wavelength corresponding to the stimulation wavelength.

  With the stimulation light irradiated to the radiation monitor detector 2a, light having a specific wavelength corresponding to the emission wavelength of the element is emitted from the detection element in the detector. On the other hand, since the stimulation wavelength is selected to be different depending on the element, no light is emitted from the radiation monitor detector 2a in which detection elements having different stimulation wavelengths are installed. Thus, by selecting the stimulation wavelength, an arbitrary detector among the plurality of radiation monitor detectors 2a can be selected.

  The emitted light and the stimulation light generated by the stimulation light are distributed by the optical switch 3 installed at the other end of the plurality of radiation monitor detectors 2a optically connected in series through the optical fiber 1, and are distributed to the spectral filter 4. Incident. Multiple spectral filters 4 that pass light of different wavelengths are installed in parallel, and correspond to the emission wavelength of the radiation monitor detector 2a at the measurement target position by the control signal 11 of the data collection control personal computer 8 sent to the optical switch 3 Stimulation light and emitted light are guided to the spectral filter 4 that selectively transmits only the wavelength to be emitted.

  Since the spectral filter 4 does not transmit the stimulation light, only the emitted light is guided to the light measurement system. The emitted light is converted into an electric signal by the photomultiplier tube 5, amplified by the amplifier 6, and then the intensity is measured by the multichannel wave height analyzer 7, and the data collection control personal computer 8 is obtained as the light intensity data 12. Collected in

  Information on the time when the last irradiation of the stimulation light is completed and the time when the irradiation of the stimulation light is started this time is stored in the data collection control personal computer 8, and the difference between them is used as the measurement time. A database of the relationship between the light intensity and the dose obtained in advance by measurement is also stored in the data collection control personal computer 8. The dose rate is derived using a database of the relationship between the measured light intensity, the measurement time, and the relationship between the light intensity and the dose determined in advance. By repeating the measurement of the dose rate for each detector, the time change of the dose rate distribution can be derived. Since a power cable for high voltage application and a preamplifier is not required and a plurality of measurement points can be measured with a single optical cable, a radiation monitor suitable for measurement over a wide range can be provided.

[Example 2]
FIG. 2 shows the configuration of the radiation monitor of Example 2, which is another preferred embodiment of the present invention. In the second embodiment, the basic configuration is the same as that of the first embodiment, but the optical fiber 1 is used to connect the radiation monitor detector 2a having different stimulation and emission wavelengths to one end optically connected in series. The radiation monitor detector 2b provided with the reflector is installed, and the other end optically connected in series is connected to the optical coupler 19 to have a different configuration.

  One side branched by the optical coupler 19 is connected to the optical switch 3. The optical switch 3 is connected to a plurality of laser diodes 9 having different emission wavelengths and a laser diode driver 10 for driving the laser diode 9, and is used for radiation monitoring at a measurement target position by a control signal 11 of a data collection control personal computer 8. Control is performed to irradiate the radiation monitor detector 2a or 2b with a laser having a wavelength corresponding to the stimulation wavelength of the detector 2a or 2b.

  The light emitted by the stimulation light and the stimulation light are distributed by the optical switch 3 through the other branched by the optical coupler 19 and then enter the spectral filter 4. A plurality of spectral filters 4 that pass light of different wavelengths are installed in parallel, and the emission wavelength of the radiation monitor detector 2a at the measurement target position is determined by the control signal 11 of the data collection control personal computer 8 sent to the optical switch 3. Stimulation light and emitted light are guided to the spectral filter 4 that selectively transmits only the wavelength corresponding to. Since the spectral filter 4 does not transmit the stimulation light, only the emitted light is guided to the light measurement system.

  The emitted light is converted into an electric signal by the photomultiplier tube 5, amplified by the amplifier 6, and then the intensity is measured by the multichannel wave height analyzer 7, and the data collection control personal computer 8 is obtained as the light intensity data 12. Collected in Information on the time when the last irradiation of the stimulation light is completed and the time when the irradiation of the stimulation light is started this time is stored in the data collection control personal computer 8, and the difference between them is used as the measurement time. A database of the relationship between the light intensity and the dose obtained in advance by measurement is also stored in the data collection control personal computer 8.

  The dose rate is derived using a database of the relationship between the measured light intensity, the measurement time, and the relationship between the light intensity and the dose determined in advance. By repeating the measurement of the dose rate for each detector, the time change of the dose rate distribution can be derived. Since a power cable for high voltage application and a preamplifier is not required and a plurality of measurement points can be measured with a single optical cable, a radiation monitor suitable for measurement over a wide range can be provided.

[Example 3]
FIG. 3 shows the configuration of the radiation monitor of Example 3, which is another preferred embodiment of the present invention. In the third embodiment, the basic configuration is the same as that of the first embodiment, but a spectroscope 20 is installed instead of the optical switch 3 and the spectral filter 4, and the measurement target is determined by the control signal 11 of the data collection control personal computer 8. Only the wavelength corresponding to the emission wavelength of the position radiation monitor detector 2a is selectively measured.

[Example 4]
FIG. 4 shows the configuration of the radiation monitor of Example 4, which is another preferred embodiment of the present invention. In the fourth embodiment, the basic configuration is the same as that of the third embodiment, but the optical fiber 1 is used to connect a radiation monitor detector 2a having different stimulation and emission wavelengths optically in series to one end. The radiation monitor detector 2b provided with the reflector is installed, and the other end optically connected in series has a different configuration by connecting to the optical coupler 19.

  5 and 6 show a configuration of an example of the radiation monitor detector used in the first to fourth embodiments. The radiation monitor detector 2 a shown in FIG. 5 includes a radiation monitor detector housing 13, an optical lens 14, a detection element 15, and a detection element fixing tool 16. Stimulation light incident from the optical fiber 1 is expanded to a size approximately equal to the cross-sectional area inside the detector by the optical lens 14 installed inside the detector. The detection element 15 is fixed inside the detector by a detection element fixing tool 16, and its cross-sectional area is sufficiently smaller than the cross-sectional area of light. The detection element 15 emits light by the stimulation light irradiated to the detection element 15. The emitted light and the stimulation light that has passed through the part other than the detection element portion are reduced by the optical lens 14 and incident on the optical fiber 1.

  In addition, as shown in FIG. 6, the light reflector 18 may be installed in a place other than the connection position of the optical fiber 1 without installing the optical lens 14 inside the radiation monitor detector.

  7 and 8 show an exemplary configuration of the radiation monitor detector 2b used in the second and fourth embodiments. The radiation monitor detector 2 b shown in FIG. 7 includes a radiation monitor detector housing 13, a light lens 14, a detection element 15, and a light reflector 18. Stimulation light incident from the optical fiber 1 is expanded to a size approximately equal to the cross-sectional area inside the detector by the optical lens 14 installed inside the detector. The detection element 15 is fixed to the surface of the light reflector 18, and its cross-sectional area is sufficiently smaller than the cross-sectional area of light.

  The detection element 15 emits light by the stimulation light irradiated to the detection element 15. The emitted light and the stimulation light that has passed through other than the detection element portion are reflected by a light reflector disposed on the opposite side of the incident light, and are reduced by the optical lens 14 and incident on the optical fiber 1.

  As shown in FIG. 8, the light reflector 18 may be installed at a place other than the connection position of the optical fiber 1 without installing the optical lens 14 inside the radiation monitor detector.

[Example 5]
Regarding the method for monitoring radiation dose according to the present invention, the radiation dose rate measurement procedure is based on the time change of the count rate in FIG. 9, the dose rate measurement procedure in FIGS. 10 and 11, and the peak value spectrum in FIG. explain. The radiation monitor detectors 2a and 2b are each initialized by irradiating light having a wavelength corresponding to the stimulation wavelength of the detector. The measurement starts from the time of initialization, and the time until each detector is irradiated with light having a wavelength corresponding to each stimulation wavelength is the measurement time. The readout time is during irradiation with light of the stimulation wavelength, and each detector emits light corresponding to the emission wavelength, and thus the intensity of light of that wavelength is measured.

  FIG. 12 shows an example of a spectrum measured by the multichannel wave height analyzer 7. Since counting at a low peak value may include noise, a certain peak value is set as a lower limit value, and the lower limit value or more is counted. FIG. 9 shows an example of a temporal change in the count rate equal to or greater than the lower limit value. The light from the stimulation wavelength is irradiated, the detector is initialized, and the time from the end of the initialization to the next start of irradiation with the stimulation wavelength light is defined as the measurement time. After the measurement time, the time for irradiating light of the stimulation wavelength becomes the readout time.

  During the readout time, the integrated value of the measured light count is taken as the measured light intensity. Since this count and dose can be handled on a one-to-one basis, a database of the relationship between the known dose and the count is created in advance, and the dose is determined using the database of the relationship between the known dose and the count from the measurement time and the count value. Deriving rate. Set the detector, irradiate the light of the stimulation wavelength according to the set detector, start the measurement, irradiate the light of the stimulation wavelength, measure the light of the emission wavelength during the irradiation, By repeatedly deriving the dose rate from the count value using a database of the relationship between the known dose and the count, the time change of the dose rate at each position can be measured, and the time change of the dose rate distribution can be measured. Can be measured.

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2a ... Radiation monitor detector, 2b ... Radiation monitor detector, 3 ... Optical switch, 4 ... Spectral filter, 5 ... Photomultiplier tube, 6 ... Amplifier, 7 ... Multichannel wave height analyzer, 8 ... PC for data collection control, 9 ... Laser diode, 10 ... Driver for laser diode, 11 ... Control signal, 12 ... Data, 13 ... Housing for detector for radiation monitor, 14 ... Optical lens, 15 ... Detector element, 16 ... Detection element fixing tool, 17 ... Stimulation light and light emission from detection element, 18 ... Light reflector, 19 ... Optical coupler, 20 ... Spectroscope, 21 ... Avalanche photodiode

Claims (8)

A row of radiation monitor detectors optically connected in series with a plurality of radiation monitor detectors each having radiation emitting elements of different stimulation or emission wavelengths;
A light source optically connected to one end of the row and capable of receiving light of a plurality of wavelengths;
A measuring device optically connected to the other end of the row for measuring the intensity of light for each wavelength; and the plurality of detectors for radiation monitoring from the intensity of light for each wavelength of the stimulus and emission wavelengths An arithmetic unit for determining a radiation dose rate in the specified detector of
A radiation monitor comprising: A row of radiation monitor detectors optically connected in series with a plurality of radiation monitor detectors each having radiation emitting elements of different stimulation or emission wavelengths;
A light reflector optically connected to one end of the row;
A light source that is optically branched at the other end of the row and is capable of receiving light of a plurality of wavelengths that is optically connected to the branched one end, and a wavelength that is optically connected to the branched other end A measuring device for measuring the intensity of each light;
A calculation device for determining a radiation dose rate in a specified detector among the plurality of detectors for radiation monitoring from the intensity of light for each wavelength of stimulation and emission wavelengths;
A radiation monitor comprising: The radiation monitor according to claim 1 or 2,
The radiation monitor detector includes an optical lens, and the optical lens expands the stimulation light incident from the optical fiber and irradiates the radiation light emitting element, or reduces the light emitted from the radiation light emitting element. The radiation monitor is incident on the optical fiber. The radiation monitor according to claim 1 or 2,
A radiation monitor comprising a light reflector on each side where the optical fiber is optically connected to the radiation monitor detector. The radiation monitor according to claim 1 or 2,
One of the radiation monitor detectors includes a light lens for enlarging stimulation light incident from the optical fiber, and a light reflector on a side opposite to the side on which the stimulation light is incident. monitor. The radiation monitor according to claim 1 or 2,
One of the radiation monitor detectors has a light reflector on the side where the optical fiber is optically connected and on the side opposite to the optical fiber, respectively. Providing a row of radiation monitor detectors optically connected in series with a plurality of radiation monitor detectors each having radiation emitting elements of different stimulation or emission wavelengths;
Injecting stimulation light corresponding to the radiation monitor detector to be monitored from among the plurality of radiation monitor detectors;
Measuring the intensity of light having an emission wavelength emitted during irradiation of the stimulation light; and
Measuring the time from the previous irradiation end time of the stimulation light to the current irradiation start time;
Deriving a dose rate at the detector from the light intensity and time measured for the radiation monitoring detector to be monitored;
A method of monitoring radiation dose, comprising: The method for monitoring a radiation dose according to claim 7,
Measuring the intensity of light of the emission wavelength emitted during irradiation of the stimulation light,
A method for monitoring a radiation dose, comprising: measuring a peak value of light having an emission wavelength emitted during the time and a count at the peak value, and quantifying the intensity of the light from a count exceeding a certain peak value.

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