JP7072793B2 - Underwater radioactivity measuring device with early warning function by turbidity estimation, underwater radioactivity measuring system - Google Patents

Description

The present invention relates to an underwater radioactivity measuring device including an underwater radioactivity measuring device and an underwater radioactivity measuring device capable of measuring the radioactivity concentration in suspended water and giving an early warning.

Currently, according to the Japanese Industrial Standards and the regulations of the Ministry of the Environment of Japan, there are some control standards for the radioactivity concentration in water depending on the purpose of use of the monitored water. Also, from a scientific and medical point of view, this control standard changes frequently and may change in the future. For example, at present, the drinking water management standard is always 10 Bq / L, and the river management standard is 100 Bq / L in terms of cesium-137 on average for one month.

In Patent Document 1 below, in order to measure the radioactivity concentration in water, an underwater radioactivity meter and a turbidity meter are provided, and the radioactivity concentration in waste water is measured over a wide range by the radiation amount and turbidity. Radioactive material monitoring methods that can be described are described.

According to this monitoring method, the radioactivity concentration in water is estimated using an underwater radiometer in the high radioactivity concentration range (100 Bq / L or more), and the underwater radiation in the medium radioactivity concentration range (30 to 100 Bq / L). The radioactivity concentration in water is estimated using a meter and a turbidity meter, and the radioactivity concentration in water is estimated using a turbidity meter in the low radioactivity concentration range (30 Bq / L or less) (paragraph 0031).

Patent No. 5758556

Although this monitoring method has low measurement accuracy in the low radioactivity concentration range, it is said that there is no particular safety problem in the case of a concentration of 10 Bq / L (tap water standard) or less. However, since a problem may occur at a slightly higher concentration of 10 to 30 Bq / L, it is necessary to notify at an appropriate radioactivity concentration to improve safety.

The present invention has been made in view of such circumstances, and provides an underwater radioactivity measuring device capable of measuring an underwater radioactivity concentration and reliably issuing an alarm at a cautionary radioactivity concentration. With the goal.

The underwater radioactivity measuring device of the first invention includes a radiation counter for measuring the count number of radiation emitted from suspended water containing radioactive cesium per unit time, and a turbidity meter for measuring the turbidity of the suspended water. , The radioactivity that calculates the radioactivity concentration of the suspended water with respect to the radioactive cesium from the control unit that controls the measurement of the radiation counter and the turbidity meter, and the count number and the concentration conversion coefficient measured by the radiation counter. From the concentration calculation unit and the relational expression between the radioactivity concentration and the turbidity calculated by the radioactivity concentration calculation unit, the turbidity corresponding to the radioactivity concentration for which an alarm is required is determined as the alarm turbidity and measured. It is characterized by comprising an alarm unit that issues an alarm on condition that the turbidity is higher than the alarm turbidity.

The control unit of the underwater radioactivity measuring device controls a radiation counter and a turbidity meter to measure the number of radiation counts of radioactive cesium and the turbidity of suspended water containing radioactive cesium . Since the radioactivity concentration calculation unit calculates the radioactivity concentration for radioactive cesium from the count number and the concentration conversion coefficient measured by the radiation counter, the concentration of the becquerel value, which is an absolute amount, can be obtained.

It is known that the radioactivity concentration and the turbidity are generally in a proportional relationship, and when the turbidity is high, the radioactivity concentration is also high. Therefore, the turbidity corresponding to the predetermined alarm radioactivity concentration (for example, 10 Bq / L of the drinking water management standard) is set as the alarm turbidity , and the measured turbidity is the alarm turbidity in the alarm unit. If it is larger than that, an alarm is issued to notify it. As a result, it is possible to measure the radioactivity concentration in water and issue an alarm at an early stage by estimating the radioactivity concentration to be cautious and by estimating the turbidity.

In the underwater radioactivity measuring apparatus of the first invention, when the count rate obtained by dividing the count number for radioactive cesium in the suspended water by the integration time is measured by the radiation counter, the lower limit of quantification of the count rate is calculated and measured. It is preferable to further include a measurement time management unit that outputs a measured value when the counted rate reaches a value equal to or lower than the lower limit of quantification.

In the present invention, when measuring the measured number of radioactive cesium in suspended water, the minimum amount that can be quantified as an analytical value is grasped by calculating the lower limit of quantification of the measured number. When the measured number reaches a value below the lower limit of quantification , the measurement time management unit outputs the measured value as having high statistical reliability. As a result, the radioactivity concentration of the suspended water can be measured when the number of measurements is confirmed.

The underwater radioactivity measurement system of the second invention comprises an upstream tank into which suspended water containing a radioactive substance flows, an intermediate tank having a filter for decontaminating the suspended water flowing in from the upstream tank, and the suspended water in the intermediate tank. The underwater radioactivity measuring device comprises a water tank composed of a downstream tank into which the water flows into, and an underwater radioactivity measuring device installed in the upstream tank and the downstream tank, and the underwater radioactivity measuring device discharges from the suspended water per unit time. A radiation counter that measures the number of radiation counts, a turbidity meter that measures the turbidity of the suspended water, a control unit that controls the measurement of the radiation counter and the turbidity meter, and the radiation counter. The underwater radioactivity measuring device in the downstream tank has a radioactivity concentration calculation unit that calculates the radioactivity concentration corresponding to any radioactive substance in the suspended water from the count number measured by the above. The control unit of the upstream tank further has an alarm unit that issues an alarm when the conditions are satisfied, and the control unit of the upstream tank determines the control reference value of the radioactive substance from the radioactivity concentration and the turbidity acquired in the upstream tank. The control unit of the downstream tank determines whether or not the radioactivity concentration and the turbidity acquired in the downstream tank satisfy the control reference value, and does not satisfy the control reference value. The alarm unit issues an alarm under the predetermined condition , and the relational expression between the radioactivity concentration calculated by the radioactivity concentration calculation unit and the turbidity corresponding to the radioactivity concentration is stored in advance. It is characterized in that a new alarm turbidity is set based on the stored relational expression when it is necessary to lower the value from the determined alarm turbidity .

The second invention is an underwater radioactivity measurement system consisting of an upstream tank, an intermediate tank, and a downstream tank. The suspended water in the upstream tank passes through the filter of the intermediate tank to reduce the concentration of radioactive substances, and further, the downstream tank. Guided by. Underwater radioactivity measuring devices are installed in the upstream tank and the downstream tank. First, the radioactivity concentration and turbidity are obtained by measurement in the upstream tank, and the control standard value for radioactive substances (alarm radioactivity concentration described later). And the alarm turbidity). After that, the radioactivity concentration and the turbidity are acquired also in the downstream tank, and an alarm is issued by the alarm unit on the condition that these values do not meet the control standard values. As a result, it is possible to measure the radioactivity concentration in water and issue an alarm at an early stage by estimating the radioactivity concentration to be cautious and by estimating the turbidity.
In addition, when the radioactivity concentration and turbidity of the suspended water are obtained by the measurement of the underwater radioactivity measurement system, these relational expressions are stored. Then, for example, when it is necessary to lower the predetermined alarm turbidity as compared with the relational expression that is the current standard, a new alarm turbidity based on the memorized relational expression is set. As a result, it is possible to make a system that can give an alarm more safely.

The underwater radioactivity measurement system of the third invention includes an upstream tank into which suspended water containing a radioactive substance flows in, an intermediate tank having a filter for decontaminating the suspended water flowing in from the upstream tank, and the suspended water in the intermediate tank. The underwater radioactivity measuring device comprises a water tank composed of a downstream tank into which the water flows into, and an underwater radioactivity measuring device installed in the upstream tank and the downstream tank, and the underwater radioactivity measuring device discharges from the suspended water per unit time. A radiation counter that measures the number of radiation counts, a turbidity meter that measures the turbidity of the suspended water, a control unit that controls the measurement of the radiation counter and the turbidity meter, and the radiation counter. The underwater radioactivity measuring device in the downstream tank has a radioactivity concentration calculation unit for calculating the radioactivity concentration corresponding to any radioactive substance in the suspended water from the count number measured by the above. The control unit of the upstream tank further has an alarm unit that issues an alarm when the conditions are satisfied, and the control unit of the upstream tank determines the control reference value of the radioactive substance from the radioactivity concentration and the turbidity acquired in the upstream tank. The control unit of the downstream tank determines whether or not the radioactivity concentration and the turbidity acquired in the downstream tank satisfy the control reference value, and does not satisfy the control reference value. The alarm unit issues an alarm under the predetermined condition.

The third invention is an underwater radioactivity measuring system in which an underwater radioactivity measuring device equipped with a radiation counter, a turbidity meter, etc. is installed in a water channel. In the present invention, the radioactivity concentration and turbidity calculated from the maximum value of the number of counts measured by the radiation counter are acquired, and the control reference value of the radioactive substance (warning radioactivity concentration and warning turbidity described later) is obtained. decide. Then, when the radioactivity concentration and the turbidity are newly acquired, these values are compared with the control reference value, and an alarm is issued by the alarm unit on condition that the control reference value is not satisfied. This also makes it possible to measure the radioactivity concentration in water and give an early warning at the radioactivity concentration that should be watched, and further by estimating by turbidity.

In the underwater radioactivity measurement system of the second invention or the third invention, the relational expression between the radioactivity concentration calculated by the radioactivity concentration calculation unit and the turbidity corresponding to the radioactivity concentration is stored in advance. When it is necessary to lower the value from the determined alarm turbidity, it is preferable to set a new alarm turbidity based on the stored relational expression.

In the present invention, when the radioactivity concentration and turbidity of the suspended water are obtained by the measurement of the underwater radioactivity measurement system, these relational expressions are stored. Then, for example, when it is necessary to lower the predetermined alarm turbidity as compared with the relational expression that is the current standard, a new alarm turbidity based on the memorized relational expression is set. As a result, it is possible to make a system that can give an alarm more safely.

The figure which shows the whole structure of the underwater radioactivity measuring apparatus of embodiment of this invention. A graph showing the detection limits of the radiation counter and turbidity meter that make up the underwater radioactivity measuring device. A graph showing the turbidity of treated water and the calibration curve of the counting rate. A graph showing the relationship between the counting rate and the radioactivity concentration. Graph showing the relationship between radioactivity concentration and turbidity (low concentration region). The flowchart of the count rate calculation process by the underwater radioactivity measuring device. The figure which shows the whole structure of the underwater radioactivity measurement system (closed waterway system) of this invention. Flow chart of the measurement process of the radioactivity concentration by the underwater radioactivity measurement system (closed waterway system). The figure which shows the whole structure of the underwater radioactivity measurement system (open waterway system) of this invention. Flow chart of the measurement process of the radioactivity concentration by the underwater radioactivity measurement system (open waterway system).

Hereinafter, embodiments of the underwater radiation dose measuring device and the underwater radiation dose measuring system of the present invention will be described.

First, an underwater radioactivity measuring device for measuring the radioactivity concentration in water will be described with reference to FIG. 1.

FIG. 1 is an overall configuration of the underwater radioactivity measuring device 1 according to the embodiment of the present invention. First, the water tank 10 is a water tank in which treated water for measuring the radioactivity concentration (“suspended water” of the present invention) is pumped up and stored. In the water tank 10, an underwater radioactivity measuring device 1 including a radiation counter 2, a turbidity meter 3, a stirrer 4, and the like is installed. Further, the treated water can be drained from the drainage channel 6 by the drain valve 5.

In the water tank 10, the number of radiations (count number) per unit time in the treated water is measured by the radiation counter 2. This count number is called CPS (Count Per Second), and by multiplying this value by the radioactivity concentration conversion coefficient, the becquerel value (Bq / L), which is an absolute quantity indicating the radioactivity concentration, can be calculated. ..

Although the details will be described later (see FIG. 6), the radiation counter 2 can automatically detect the count number of only radioactive substances (here, radioactive cesium) in a specific energy range by using the dedicated firmware. .. In addition, the processing of this firmware excludes the count number due to the originally existing radioactive material (background division). This count number is also referred to as a count rate below.

Further, in the water tank 10, the turbidity of the treated water is measured by the turbidity meter 3. It is known that the turbidity of the treated water has a correlation with the radioactivity concentration, and the turbidity of the treated water is measured at the same time as the measurement of the radiation counter 2.

The sensor of the turbidity meter 3 of the present embodiment is a transmitted / scattered light calculation method. This utilizes the fact that the scattered light with respect to the treated water shows a constant increasing tendency as the turbidity increases, and the transmitted light is attenuated. By acquiring the ratio of the scattered light and the transmitted light, the influence of the color, particle size and particle size of the treated water, which is a problem with the scattered light and the transmitted light alone, becomes extremely small.

At the same time, the temperature of the treated water is measured with a thermometer (not shown). The sensor of the thermometer is a thermistor type, which enables quick and accurate measurement even for small temperature changes, and the standard measurement range is -10.0 to 40.0 ° C.

The underwater radioactivity measuring device 1 is used for automatic measurement of water quality in an interim storage facility or the like. In particular, it is composed of the following units (1) to (3) and can automatically acquire various data. (1) The treated water detection unit (radiation counter 2, turbidity meter 3, etc. described above) is fixed to a suspension carriage with metal fittings and placed in a water tank. The treated water detection unit transmits the count rate (CPS), turbidity, and water temperature to the measurement control unit 7 (“control unit” of the present invention) via the detection cable.

(2) The measurement control unit 7 (data collection unit 7a, radio transmission unit 7b, alarm unit 7c) is installed on an outdoor storage stand, and the data collection unit 7a (“radioactivity concentration calculation unit”, “specification” of the present invention). After processing the measurement data by the "count number extraction unit" and the "measurement time management unit"), the processed data is transmitted to the data display / recording unit (not shown) by the wireless transmission unit 7b.

The alarm unit 7c determines the execution of the alarm in order to prevent the treated water having a high radioactive concentration from being discharged from the running water channel 6. The alarm unit 7c may issue an actual alarm, or may issue an alarm at the data transmission destination.

Although not shown, (3) the data display / recording unit (data receiving unit, data recording unit) is housed in an indoor mount and records / saves data transmitted from the measurement control unit 7.

Next, with reference to FIG. 2, the detection limits of the radioactivity concentration and the turbidity with respect to the measurement time will be described. Note that FIG. 2 is an example in which a 2-inch NaI (sodium iodide) scintillator is used as the radiation counter.

The curve in FIG. 2 shows the limit value of the radioactivity concentration (Bq / L) with respect to the measurement time of the radiation counter 2. For example, when the measurement time is 20 seconds, the detection of about 13 Bq / L is the limit, which means that the radioactivity concentration lower than that cannot be measured. In the radiation counter 2, when the radioactivity concentration is in the region of about 2.0 Bq / L or less, the limit value tends not to decrease even over time.

The detection limit of the radiation counter 2 is about 0.5 Bq / L (exposure time is about 100 minutes). For the radioactivity concentration here, the count rate of radioactive cesium (ROI count rate, which will be described later) is obtained from the spectrum of the LaBr detector having a very high energy resolution, and the count rate is multiplied by the radioactivity concentration conversion coefficient. It is a calculated value.

On the other hand, the straight line in FIG. 2 indicates the limit value of turbidity with respect to the measurement time of the turbidity meter 3. The limit value of the turbidity meter 3 is about 1.8 (degrees), but the becquerel value is about 0.5 Bq / L. The turbidity meter 3 can detect near the limit value in a few seconds, and the measurement time is very short.

Next, FIG. 3 shows a calibration curve of the turbidity and the counting rate of three different samples.

First, the horizontal axis (x-axis) is the turbidity, and the vertical axis (y-axis) is the count rate (CPS). Then, the measured turbidity and the counting rate were plotted against three samples (suspended water in three places). For example, in sample 1, the count rate was 2.0 when the turbidity was 200 degrees, so this point was plotted on the coordinates.

Assuming that the turbidity is 0 (degrees), that is, the counting rate of purified water is 0, the sample 1 can be approximated by a straight line of y ₁ = 0.01x (contribution rate R ² = 0.9617). can. The other data of sample 1 also got on this straight line.

For samples 0 and 2, after plotting any one point on the coordinates, connecting that point and the origin of the coordinates, y ₀ = 0.0185x (contribution rate R ² = 0.9306), y ₂ =, respectively. A straight line of 0.0132x (contribution rate R ² = 0.999) was obtained. In this way, a calibration curve of turbidity and counting rate of each sample is obtained.

Next, the relationship between the counting rate and the radioactivity concentration will be described with reference to FIG.

First, the counting rate (CPS) is plotted on the horizontal axis (x-axis) and the radioactivity concentration is plotted on the vertical axis (y-axis). Then, the value of the counting rate measured by the radiation counter and the radioactivity concentration of the measured value by the underwater radioactivity measuring device 1 were plotted. As a result, the relationship of y = 16.823x (contribution rate R ² = 0.9785) was obtained. The slope of the straight line at this time becomes the radioactivity concentration conversion coefficient.

Next, the relationship between the radioactivity concentration and the turbidity will be described with reference to FIG.

First, the horizontal axis (x-axis) is the turbidity, and the vertical axis (y-axis) is the radioactivity concentration. A sample of a certain water system was measured, and the straight line y0 shown in FIG. ₅ was obtained from the turbidity and the radioactivity concentration measured by the underwater radioactivity measuring device 1.

Specifically, by plotting the measured values at a certain point in time (turbidity 20.0 degrees, radioactivity concentration 40.0 Bq / L) on the coordinates and connecting them to the coordinate origin, the turbidity and the radioactivity concentration can be obtained. The relationship can be approximated by a straight line of y ₀ = α ₀ x (α ₀ = 2.0). Note that y ₁ = α ₁ x (α ₁ = 2α ₀ ) and y ₂ = α ₂ x (α ₁ = 1 / 2α ₀ ) are straight lines obtained from the measured values at different time points.

First, the controlled wastewater standard of this water system is set to 10.0 Bq / L. Further, when the alarm concentration (“alarm radiation concentration” of the present invention) is set to 8.0 Bq / L, the turbidity corresponding to the straight line y ₀ is about 4.0 degrees, and corresponds to the straight lines y ₁ and y ₂ . The turbidity is about 2.0 degrees and about 8.0 degrees, respectively.

In the case of this water system, the gradient (radioactivity concentration / turbidity) of the straight line y0 is initially set as the reference gradient, and the alarm turbidity is set to _4.0 degrees. Basically, when at least one of the conditions of the case where the measured value of the radioactivity concentration at a certain point in time is higher than the alarm concentration and the case where the measured value of the turbidity is higher than the alarm turbidity is satisfied, the alarm unit gives an alarm. I do. Further, when the turbidity and the radioactivity concentration are measured at another time point and the gradient becomes larger than the reference straight line y ₀ as in the straight line y ₁ , the radioactivity concentration is small even though the turbidity is small. Tends to be high, so lower the alarm turbidity level to 2.0 degrees.

Further, when the turbidity and the radioactivity concentration are measured at another time point, the gradient may be smaller _than the reference straight line _y0 as in the straight line y2. In this case, the alarm turbidity level is not raised and the alarm turbidity (4.0 degrees) is maintained. Then, when the turbidity is higher than the value of the alarm turbidity, an alarm is given by the alarm unit. On the other hand, if the turbidity is less than that value, no alarm is given because the radioactivity concentration is low. The above is the outline of the measurement principle of the underwater radioactivity measuring device 1.

Next, the calculation process of the counting rate will be described with reference to FIG. The counting rate is calculated by the dedicated firmware of the underwater radioactivity measuring device 1.

The counting rate includes a total counting rate, which is the measured energy range of all radioactive substances (radionuclides), and an ROI (Region Of Interest) counting rate, which is the energy range of the nuclide of interest. In order to obtain the counting rate, it is a prerequisite that the background counting rate in water in which no radioactive substance is present has been obtained.

In measuring the counting rate, first, the radiation counter is reset (step S01). At this time, the measurement time (integrated time) timer is started. Then, the process proceeds to step S02.

In step S02, the total counting rate is acquired. The total count rate is calculated by acquiring the total energy spectrum count value with a multi-channel spectrum analyzer and dividing by the measurement time when the periodic measurement time has elapsed. After that, the process proceeds to step S03.

In step S03, the net total count rate is calculated. The net total count rate is calculated by taking the difference between the total count rate acquired in step S02 and the background count rate acquired in advance. After that, the process proceeds to step S04.

In step S04, the lower limit of quantification of the net total count rate is calculated. Here, in order to ensure the measurement accuracy and accuracy, the lower limit of quantification (the minimum amount that can be quantified as an analytical value) is calculated by 10σ. After that, the process proceeds to step S05.

Next, it is determined whether or not the net total count rate is significant (step S05). Specifically, it is determined whether the net total count rate calculated in step S03 is 10 times or more the lower limit of quantification calculated in step S04. If the net total count rate is 10 times or more of the lower limit of quantification (significant at 0.5% or less, that is, chance occurs only with a probability of 0.5% or less and is reliable), the process proceeds to step S06. If it is smaller than 10 times, the process proceeds to step S07.

If the net total count rate is significant (step S05: YES), record the net total count rate (step S06). Then, the process proceeds to step S07.

In step S07, the ROI count rate is acquired. The ROI count rate is calculated by acquiring the count value of the energy range depending on the nucleus species of interest from the total energy spectrum count rate obtained by the multi-channel spectrum analyzer and dividing it by the measurement time. Then, the process proceeds to step S08.

In step S08, the net ROI count rate is calculated. The net ROI count rate is calculated by taking the difference between the ROI count rate acquired in step S07 and the background ROI count rate acquired in advance. Then, the process proceeds to step S09.

In step S09, the lower limit of quantification of the net ROI count rate is calculated. Here, too, the lower limit of quantification is calculated by 10σ in order to ensure the measurement accuracy and accuracy. After that, the process proceeds to step S10.

Next, it is determined whether or not the net ROI count rate is significant (step S10). Specifically, it is determined whether the net ROI total count rate calculated in step S08 is 10 times or more the lower limit of quantification calculated in step S09. If the net ROI count rate is 10 times or more of the lower limit of quantification (significant at 0.5% or less), the process proceeds to step S11, and if it is less than 10 times, the process returns to step S02 and the subsequent processing is performed.

If the net ROI count rate is significant (step S10: YES), record the net ROI count rate (step S11). Then, the process proceeds to step S12.

Next, it is determined whether or not the total count rate and the ROI count rate have been output (step S12). If the total count rate and the ROI count rate have already been output, the process proceeds to step S13, and if the total count rate and the ROI count rate have not been output, the process returns to step S02, and subsequent processing is performed.

Finally, in step S13, the measurement data and the operation data of the above processing are recorded. After that, a series of counting rate calculation processing is completed.

<First Embodiment>
Next, an underwater radioactivity measurement system for measuring the radioactivity concentration in water will be described with reference to FIGS. 7 and 8.

FIG. 7 is an overall configuration of the underwater radioactivity measurement system 50 (closed waterway system) according to the first embodiment of the present invention. The underwater radioactivity measurement system 50 includes an upstream tank 10A, an intermediate tank 10B, and a downstream tank 10C.

The upstream tank 10A is a water tank into which the treated water for measuring the radioactivity concentration first flows. The upstream tank 10A is provided with an underwater radioactivity measuring device including a radiation counter 2a, a turbidity meter 3a, etc., and the treated water flows in from the running water channel 6a and drains from the running water channel 6b provided with the drain valve 5a. Actually, there are agitators and thermometers that stir the treated water, but they are omitted here.

In the upstream tank 10A, the number of radiation counts (counting rate) per unit time of the treated water is measured by the radiation counter 2a. Further, in the upstream tank 10A, the turbidity of the treated water is measured at the same time by the turbidity meter 3a.

Next, the intermediate tank 10B is a water tank into which the treated water stored in the upstream tank 10A flows. The intermediate tank 10B is provided with a filter 8 to which the suspended solids of the treated water are adsorbed, and the treated water flows in from the running water channel 6b and drains from the running water channel 6c provided with the drain valve 5b.

The filter 8 reduces both the radioactivity concentration and the turbidity of the treated water, but since there is no inflow from other than the upstream tank 10A, it is the same water system and can be regarded as having the same properties as the treated water of the upstream tank 10A. ..

Next, the downstream tank 10C is a water tank into which the treated water stored in the intermediate tank 10B flows. The downstream tank 10C is provided with an underwater radioactivity measuring device including a radiation counter 2c, a turbidity meter 3c, etc., and the treated water flows in from the running water channel 6c and drains from the running water channel 6d provided with the drain valve 5c.

In the downstream tank 10C, the radioactivity concentration and the turbidity are measured again for the treated water that has passed through the filter 8 of the intermediate tank 10B. Here, since the radioactivity concentration and turbidity after filtration by the filter 8 are measured, it is possible to acquire data having a concentration difference from that of the upstream tank 10A. Further, in the downstream tank 10C, since the running water channel 6d is connected to a river or the like, the water tank for confirming that the radioactive concentration of the treated water to be discharged is lower than a predetermined control reference value (for example, 10Bq / L). It can be said that.

Next, with reference to FIG. 8, the measurement process of the radioactivity concentration by the underwater radioactivity measurement system 50 will be described. The following processing is executed by the measurement control unit (hereinafter referred to as the control unit) of the upstream tank 10A and the downstream tank 10C.

First, the control unit measures the count rate and turbidity of the treated water in the upstream tank (step S21). Specifically, the counting rate (CPS) and turbidity are obtained from the radiation counter 2a and the turbidity meter 3a of the upstream tank 10A (see FIG. 7), respectively. After that, the process proceeds to step S22.

In step S22, the control unit calculates the radioactivity concentration. Specifically, the control unit calculates the radioactivity concentration from the count rate of the radiation counter 2a acquired in step S22. After that, the process proceeds to step S23.

In step S23, the control unit calculates the gradient α. Specifically, the turbidity and the radioactivity concentration are plotted on the coordinates of FIG. 5, and the gradient α (radioactivity concentration / turbidity) of a straight line is calculated by connecting with the coordinate origin. It is also possible to measure several times at about the same time and calculate the gradient α after taking the average value. Then, the process proceeds to step S24.

Next, the control unit compares the reference gradient α ₀ with the gradient α, and determines whether or not the gradient α is larger than the reference gradient α ₀ (step S24). The reference gradient α ₀ is a gradient that has been determined in advance or has been used for the last time. If the gradient α is larger than the reference gradient α ₀ , the process proceeds to step S25, and if the gradient α is equal to or less than the reference gradient α ₀ , the process proceeds to step S26.

When the gradient α is larger than the reference gradient α ₀ (step S24: YES), the control unit updates the alarm turbidity (step S25). In the example of FIG. 5, the turbidity (2.0 degrees) obtained from the intersection of the predetermined alarm concentration (8.0 Bq / L) and the straight line y ₁ (α ₁ > α ₀ ) is referred to as the new alarm turbidity. do. Then, the process proceeds to step S26.

In step S26, the control unit sets the alarm concentration and the alarm turbidity. Basically, it is a process of setting a predetermined alarm concentration and alarm turbidity for measurement in the downstream tank, but when the alarm turbidity is updated, the updated alarm turbidity is set. After that, the process proceeds to step S27.

In step S27, the control unit measures the count rate and turbidity of the treated water in the downstream tank. Specifically, the counting rate (CPS) and turbidity are obtained from the radiation counter 2c and the turbidity meter 3c of the downstream tank 10C (see FIG. 7), respectively. Then, the process proceeds to step S28.

In step S28, the control unit calculates the radioactivity concentration. Specifically, the control unit calculates the radioactivity concentration from the count rate of the radiation counter 2c acquired in step S27. Then, the process proceeds to step S29.

Next, the control unit determines whether or not the radioactivity concentration in the downstream tank exceeds the alarm concentration (step S29). If the radioactivity concentration exceeds the alarm concentration, the process proceeds to step S31, and if the radioactivity concentration does not exceed the alarm concentration, the process proceeds to step S30.

When the radioactivity concentration does not exceed the alarm concentration (step S29: NO), the control unit determines whether or not the turbidity exceeds the alarm turbidity (step S30). If the turbidity exceeds the alarm turbidity, the process proceeds to step S31, and if the turbidity does not exceed the alarm turbidity, the measurement process ends.

When the radioactivity concentration exceeds the alarm concentration (step S29: YES) or the turbidity exceeds the alarm turbidity (step S30: YES), the control unit executes an alarm (step S31). As a result, it is possible to prevent the treated water having a radioactivity concentration higher than the control reference value from being discharged into a river or the like from the flow channel 6d shown in FIG. With the above, the measurement process of the radioactivity concentration by the underwater radioactivity measurement system 50 is completed.

<Second Embodiment>
Next, another form of the underwater radioactivity measuring system for measuring the radioactivity concentration in water will be described with reference to FIGS. 9 and 10.

FIG. 9 shows the overall configuration of the underwater radioactivity measurement system 50'(open waterway system) according to the second embodiment of the present invention. The illustrated underwater radioactivity measurement system 50'is a immersion type measurement system in which a radiation counter 20 with a turbidity meter is provided in an open water channel 30 such as a drainage ditch. The radiation counter 20 with a turbidity meter is a kind of underwater radioactivity measuring device, and is composed of a radiation counter 2'and a turbidity meter 3', and its functions are the above-mentioned radiation counter and turbidity meter. Is the same as.

In the underwater radioactivity measurement system 50', the control reference value is determined from the radioactivity concentration converted from the maximum count rate (maximum CPS) measured in the past and the turbidity at that time. Then, when the radioactivity concentration of the treated water at the time of measurement is higher than a predetermined control reference value (for example, 10 Bq / L), an alarm is issued.

Next, with reference to FIG. 10, the measurement process of the radioactivity concentration by the underwater radioactivity measurement system 50'will be described. The following processing is executed by the measurement control unit (hereinafter referred to as the control unit) of the open water channel 30.

First, the control unit measures the count rate and turbidity of the treated water (step S41). Specifically, the counting rate (CPS) and turbidity are measured from the radiation counter 2'and the turbidity meter 3'of the open water channel 30, respectively. Then, the process proceeds to step S42.

In step S42, the control unit calculates the radioactivity concentration. Specifically, the control unit calculates the radioactivity concentration from the count rate of the radiation counter 2'acquired in step S41. Then, the process proceeds to step S43.

In step S43, the control unit calculates the gradient α. Specifically, the turbidity and the radioactivity concentration are plotted on the coordinates of FIG. 5, and the gradient α (radioactivity concentration / turbidity) of a straight line is calculated by connecting with the coordinate origin. Then, the process proceeds to step S44.

Next, the control unit compares the reference gradient α ₀ with the gradient α, and determines whether or not the gradient α is larger than the reference gradient α ₀ (step S44). If the gradient α is larger than the reference gradient α ₀ , the process proceeds to step S45, and if the gradient α is equal to or less than the reference gradient α ₀ , the process proceeds to step S46.

When the gradient α is larger than the reference gradient α ₀ (step S44: YES), the control unit updates the alarm turbidity (step S45). Then, the process proceeds to step S46.

In step S46, the control unit sets the alarm concentration and the alarm turbidity. Basically, it is a process of setting a predetermined alarm concentration and alarm turbidity for measurement, but when the alarm turbidity is updated, the updated alarm turbidity is set. Then, the process proceeds to step S47.

Next, the control unit determines whether or not the radioactivity concentration exceeds the alarm concentration (step S47). If the radioactivity concentration exceeds the alarm concentration, the process proceeds to step S49, and if the radioactivity concentration does not exceed the alarm concentration, the process proceeds to step S48.

When the radioactivity concentration does not exceed the alarm concentration (step S47: NO), the control unit determines whether or not the turbidity exceeds the alarm turbidity (step S48). If the turbidity exceeds the alarm turbidity, the process proceeds to step S49, and if the turbidity does not exceed the alarm turbidity, the measurement process ends.

When the radioactivity concentration exceeds the alarm concentration (step S47: YES) or the turbidity exceeds the alarm turbidity (step S48: YES), the control unit executes an alarm (step S49). As a result, it is possible to prevent the treated water having a radioactivity concentration higher than the control reference value from being discharged from the open water channel 30 into a river or the like. With the above, the measurement process of the radioactivity concentration by the underwater radioactivity measurement system 50'is completed.

In the above description of the embodiment, a 2-inch NaI scintillator is used as the radiation counter, but a scintillator having a higher energy resolution such as Ge (germanium) may be used. This time, we focused on cesium-134 and cesium-137, but the method for measuring the counting rate is the same even for other radioactive substances, and the underwater radioactivity measuring device and measuring system of the present invention can be adopted.

In addition, the condition for the effectiveness of the lower limit of quantification when calculating the counting rate is also an example, and even if the minimum amount that can be quantified as an analytical value (for example, 3σ to 10σ) is calculated according to the sample and measurement conditions. good.

1 ... Underwater radioactivity measuring device, 2,2a, 2c ... Radiation counter, 3,3a, 3c ... Turbidity meter, 4 ... Stirrer, 5,5a, 5b, 5c ... Drain valve, 6,6a, 6b, 6c ... Flow channel, 7 ... Measurement control unit, 7a ... Data collection unit, 7b ... Radio transmission unit, 7c ... Alarm unit, 8 ... Filter, 10 ... Water tank, 10A ... Upstream tank, 10B ... Intermediate tank, 10C ... Downstream tank , 20 ... Radiation counter with turbidity meter, 30 ... Open channel, 50, 50'... Underwater radioactivity measurement system.

Claims (5)

A radiation counter that measures the count of radiation emitted per unit time from suspended water containing radioactive cesium ,
A turbidity meter that measures the turbidity of the suspended water and
A control unit that controls the measurement of the radiation counter and the turbidity meter,
A radiation concentration calculation unit that calculates the radioactivity concentration of the suspended water for radioactive cesium from the count number and the concentration conversion coefficient measured by the radiation counter, and the radioactivity concentration calculation unit.
The turbidity measured by determining the turbidity corresponding to the radioactivity concentration requiring an alarm from the relational expression between the radioactivity concentration and the turbidity calculated by the radioactivity concentration calculation unit as the alarm turbidity. An underwater radioactivity measuring device comprising an alarm unit that issues an alarm on condition that the alarm turbidity is higher than the alarm turbidity. In the underwater radioactivity measuring apparatus according to claim 1,
When the counting rate obtained by dividing the count number of radioactive cesium in the suspended water by the integration time is measured by the radiation counter, the lower limit of quantification of the counting rate is calculated, and the measured counting rate is equal to or less than the lower limit of quantification. An underwater radioactivity measuring device characterized by further equipped with a measurement time management unit that outputs a measured value when a numerical value is reached. An upstream tank into which suspended water containing radioactive substances flows in, an intermediate tank having a filter for decontaminating the suspended water flowing in from the upstream tank, and a water tank composed of a downstream tank into which the suspended water in the intermediate tank flows. ,
The upstream tank and the underwater radioactivity measuring device installed in the downstream tank are provided.
The underwater radioactivity measuring device includes a radiation counter for measuring the count number of radiation emitted from the suspended water per unit time, a turbidity meter for measuring the turbidity of the suspended water, and the radiation counter. A control unit that controls the measurement of the turbidity meter and a radioactivity concentration calculation unit that calculates the radioactivity concentration corresponding to any radioactive substance in the suspended water from the count number measured by the radiation counter. Have and
The underwater radioactivity measuring device in the downstream tank further has an alarm unit that issues an alarm when a predetermined condition is satisfied.
The control unit of the upstream tank determines a control reference value of the radioactive substance from the radioactivity concentration and the turbidity acquired in the upstream tank.
The control unit of the downstream tank determines whether or not the radioactivity concentration and the turbidity acquired in the downstream tank satisfy the control reference value, and determines that the control reference value is not satisfied. As a condition of, the alarm unit issues an alarm , stores the relational expression between the radioactivity concentration calculated by the radioactivity concentration calculation unit and the turbidity corresponding to the radioactivity concentration, and predetermines an alarm. An underwater radioactivity measurement system comprising setting a new alarm turbidity based on the stored relational expression when it is necessary to lower the value below the turbidity . Waterways into which suspended water containing radioactive substances flow in,
It is equipped with an underwater radioactivity measuring device installed in the waterway.
The underwater radioactivity measuring device includes a radiation counter for measuring the count number of radiation emitted from the suspended water per unit time, a turbidity meter for measuring the turbidity of the suspended water, and the radiation counter. A control unit that controls the measurement of the turbidity meter, a radioactivity concentration calculation unit that calculates the radioactivity concentration corresponding to any radioactive substance in the suspended water from the count number measured by the radiation counter, and a predetermined unit. It has an alarm unit that issues an alarm when the conditions of
The control unit
The control reference value of the radioactive substance is determined from the radioactivity concentration calculated from the maximum value of the count number measured by the radiation counter in the past and the turbidity at the time of the measurement.
It is determined whether or not the radioactivity concentration and the turbidity newly acquired by the underwater radioactivity measuring device satisfy the control reference value.
An underwater radioactivity measurement system characterized in that the alarm unit issues an alarm on the condition that the control reference value is not satisfied. In the underwater radioactivity measurement system according to claim 3 or 4 .
When it is necessary to store the relational expression between the radioactivity concentration calculated by the radioactivity concentration calculation unit and the turbidity corresponding to the radioactivity concentration and lower the value from the predetermined alarm turbidity. , An underwater radioactivity measuring device, characterized in that a new alarm turbidity is set based on the stored relational expression.

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