JP2003098260A - Monitor for radioactive dust - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a consumption of a long filter paper while securing prescribed measuring precision for a concentration of a radioactive nuclide. SOLUTION: A first suction part 31 and a second suction part 32 are formed in a suction head 3a to partition a width direction of the long filter paper 1 into two dust capturing areas, a first solenoid valve 33 is connected to the suction part 31, a second solenoid valve 34 is connected to the suction part 32, and pipings from the both solenoid valves are integrated into one in a flow measuring side. The solenoid valves 33, 34 are switched to operate the suction parts 31, 32 separately, and the two dust capturing areas corresponding to both the suction parts 31, 32 of the long filter paper 1 are used independently to make an effective filter paper length double. A conveying speed of the filter paper 1 is slowed down to cope with a negative suction pressure value of a suction pump and a radiation detection signal from a radiation detector.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring technique for measuring the concentration of radioactivity existing in the air of a facility for handling radioactive substances.

[0002]

2. Description of the Related Art Radioactive dust monitors pass air at a monitoring point of a radioactive material handling facility through a filter paper,
The dust floating in the air is collected on the filter paper, the radiation from the collected dust is detected by the radiation detector, and the monitoring point is determined by the amount of air passing through the filter paper and the detection signal of the radiation detector. This is a device for measuring and monitoring the radioactivity concentration existing in the air of.

FIG. 6 is a perspective view showing the structure of an example of a dust collecting portion of a conventional radioactive dust monitor. In this example, as a filter paper for collecting dust, a long filter paper 1 supplied from a supply pulley 9 and wound around a winding pulley 10
Is used. This long filter paper 1 is a motor (M) 7
Is continuously and intermittently conveyed in the direction of the arrow by a pair of filter paper feed rollers 2 coupled to and driven by. The supply pulley 9 is constantly braked, and the take-up pulley 10 is connected to the motor (M) 7, so that the long filter paper 1 is conveyed at a predetermined speed without slack. An intake head 3 and a radiation detector 8 are arranged to face each other with the long filter paper 1 sandwiched therebetween at an intermediate position between the supply pulley 9 and the take-up pulley 10, and the intake head 3 comes into contact with the long filter paper 1 to prevent radiation. A space is provided between the detector 8 and the long filter paper 1 for supplying air to the dust collecting portion of the long filter paper 1. A suction pump 6 for sucking air is connected to the intake head 3 by piping, and a flow meter (FI) for measuring the flow rate of the air sucked by the intake head 3 is provided in the middle of the piping.
4 and a pressure gauge (PI) 5 for measuring the suction negative pressure on the intake side of the suction pump 6 are attached.

When the suction pump 6 is activated, the air in front of the suction head 3 is sucked through the long filter paper 1, and as a result, the dust in the air in front of the suction head 3 is applied to the surface of the long filter paper 1. Are captured. Since air at the monitoring point is introduced to the front surface of the intake head 3 by a pipe or the like (not shown), dust floating in the air at the monitoring point is collected on the surface of the long filter paper 1.

FIG. 7 is an explanatory view showing a dust collecting state of the long filter paper 1 which is most commonly used in the conventional radioactive dust monitor. Normally, a long filter paper 1 having a width of 75 mm is used, and the intake head 3 is manufactured so that a dust collecting area 12 is formed in a central portion having a width of 50 mm.
The shape of the intake port is 50mm x 50mm). Further, the conveying speed of the long filter paper 1 (in this section, "the conveying speed of the long filter paper 1" is simply referred to as "conveying speed" hereinafter) is set to a constant value, which is set to 25 mm / h. The most common. As shown in FIG. 7, the dust collecting state on the long length filter paper 1 is shown by hatching, that is, a portion having a width of 50 mm on the right side from the dust collecting starting position 11 where dust collecting starts. Dust is collected in the part. In FIG. 7, this portion is shown as a "dust collecting portion 121". This portion is, for example, as the long filter paper 1 is conveyed.
It extends to the right at a speed of 25 mm / h.

The measurement target of the radioactive dust monitor is the radioactivity concentration existing in the air at the monitoring point,
The radioactivity concentration is indicated by the ratio of radioactivity contained in a fixed volume of aspirated air. Therefore, a flow meter 4 for measuring the flow rate of the sucked air is attached in the middle of the pipe, and the driving condition of the suction pump 6 is controlled by this output signal to keep the air flow rate at a constant value. ing.

As shown in FIG. 5, the suction pump 6 has a fixed suction negative pressure-air flow rate characteristic when the driving condition is constant, and when the driving frequency is increased, the suction negative pressure value is the same. When the flow rate value increases and the drive frequency is lowered, the flow rate value for the same suction negative pressure value decreases. Therefore, in order to control the air flow rate to a constant value, it is necessary to control the drive frequency of the suction pump 6 by increasing or decreasing the concentration of dust existing in the air at the monitoring point. When the long filter paper 1 is conveyed at a constant speed, if the dust concentration increases, the amount of dust collected on the filter paper increases and the fluid resistance of that portion increases, so the drive frequency of the suction pump 6 is increased. Then, the suction negative pressure is increased to maintain the air flow rate at a constant value. When the dust concentration is low, the amount of collected dust is reduced and the fluid resistance is reduced. Therefore, the driving frequency is lowered, the suction negative pressure is reduced, and the air flow rate is maintained at a constant value.

Both the air flow rate and the conveying speed are set to constant values in order to keep the trapping condition of the trapped dust, which is the object of measurement by the radiation detector 8, constant. The fluctuation of the air flow rate and the fluctuation of the transport speed are both fluctuations in the collection condition of the collected dust, and are coefficients for calculating the radioactivity concentration from the radiation count rate value obtained from the output signal of the radiation detector 8. To decrease the measurement accuracy.

The set value of the air flow rate is determined from the condition for obtaining the radioactivity concentration with desired measurement accuracy. 25 mm /
The transport speed set to h is a transport speed that satisfies the condition that the dust trapping portion of the long filter paper 1 can secure a necessary air flow rate even if the air having the assumed highest dust concentration is sucked. . When collecting dust at this transportation speed, the maximum dose rate value of the radiation detected by the radiation detector is smaller than the upper limit dose rate value at which the radiation detector can detect the radiation with a predetermined detection accuracy. It is supposed.

Although a circular radiation detector 8 is shown in FIG. 6, the shape of the sensitive portion of the radiation detector 8 is the same as the shape of the suction port of the suction head 3, and the shape of the dust collecting portion. The shape does not need to be the same as that of the above, and may be any shape as long as accurate sensitivity calibration is possible. An example of the shape and dimensions shown in FIG.
The shape of the dust collecting portion is 50 mm × 50 mm, whereas the shape of the sensitive portion of the radiation detector 8 is φ50 mm.

In the above description, the case where the long filter paper 1 is continuously conveyed has been described, but when the long filter paper 1 is intermittently conveyed, dust is generated at regular time intervals, for example, every two hours. The other points are exactly the same, except that the long filter paper 1 is conveyed by the length of the shape of the collection unit.

[0012]

In the conventional radioactive dust monitor using the long filter paper as described above, the dust trapping portion does not become clogged even at the assumed maximum dust concentration, and The radiation detector can detect radiation normally even at the maximum expected radioactivity concentration,
The above-mentioned transport speed of 25 mm / h is set to satisfy the above condition. Therefore, the conventional radioactive dust monitor consumes a large amount of long filter paper and requires a large amount of operating costs. Furthermore, since the long filter paper after measurement becomes radioactive waste, its large consumption is a problem.

In order to alleviate these problems, an object of the present invention is to reduce the consumption of long filter paper while ensuring the conditions under which the radioactivity concentration in the air to be measured can be measured with a predetermined accuracy. It is to provide a dust monitor.

[0014]

[Means for Solving the Problems] "Conventional technology" is a condition for measuring the radioactivity concentration in the air to be measured with a predetermined accuracy.
As explained in the section of (1), it is to always ensure a predetermined air flow rate and a predetermined radiation detection accuracy, and as a means to reduce the consumption of long filter paper, (1) It is possible to increase the length, and (2) to lower the transport speed as much as possible.

The invention of claim 1 is based on the means of (1), and the inventions of claim 2 and 3 are based on the means of (2). The invention of claim 2 slows down the conveying speed while satisfying the condition of ensuring a predetermined air flow rate, and the invention of claim 3 ensures both a predetermined air flow rate and a predetermined radiation detection accuracy. The transport speed is reduced while satisfying the condition.

Hereinafter, each claim will be described in more detail.
According to the first aspect of the invention, a suction pump causes air at a monitoring point of a radioactive substance handling facility to pass through a dust collecting portion of a long filter paper that is continuously or intermittently conveyed, and floats in the air. Radioactive dust for collecting dust in the dust collection part, detecting the radiation emitted from the collected dust with a radiation detector, and continuously measuring the radioactivity concentration existing in the air at the monitoring point. In the monitor, the long filter paper is divided into a plurality of areas having the same width in the width direction, and each of the divided areas is an independent dust collecting area for moving the dust collecting section.

Since each area obtained by dividing the width direction of the long filter paper into a plurality of areas is an independent dust collecting area for moving the dust collecting section, the effective length of the filter paper is equal to that of the long filter paper. It is the same as the length extended by the number of divisions. According to the invention of claim 2, the air at the monitoring point of the radioactive substance handling facility is passed through the dust collecting portion of the continuous filter paper, which is controlled at a constant flow rate by a suction pump, and is introduced into the air. For collecting the floating dust in the dust collecting part, detecting the radiation emitted from the collected dust with a radiation detector, and continuously measuring the radioactivity concentration existing in the air at the monitoring point. A radioactive dust monitor, pressure measuring means for measuring a suction negative pressure of air on the intake side of the suction pump,
A variable speed motor and a variable speed motor driver for adjusting the conveying speed of the long filter paper, and the correspondence relationship between the suction negative pressure value and the dust collection amount of the dust collection unit, which are acquired in advance, and The conveying speed of the long filter paper is adjusted at predetermined time intervals according to the suction negative pressure value measured by the pressure measuring means.

The fluid resistance value of the dust collecting portion of the long filter paper is
The suction negative pressure value of the suction pump is determined by the dust collection amount of the dust collection unit, and the fluid resistance value of the dust collection unit and the dust collection unit are passed if the fluid resistance value of the piping unit can be ignored. Determined by the product of the air flow rate value. In other words,
When the amount of collected dust in the dust collecting section changes, the suction negative pressure value changes due to the change in the fluid resistance value accompanying it. On the other hand, as described in the section “Prior Art”, the flow rate of the air sucked by the suction pump and the suction negative pressure have a constant relationship as shown in FIG. 5 with the driving frequency of the suction pump as a parameter. There is. Therefore, when the air flow rate is controlled to a constant value, the suction negative pressure value of the suction pump indicates the dust collection state of the dust collection unit, and the suction negative pressure value and the dust collection unit dust collection state. If the correspondence relationship with the collection amount is acquired in advance, it is possible to determine the transport speed of the long filter paper that can control the air flow rate to a predetermined value in accordance with the measured suction negative pressure value, and it is possible to determine the normal environmental conditions. It is possible to set the conveying speed to be much slower than 25 mm / h in a state where there is little dust. Since most of the operation time of the radioactive dust monitor is operated under such a condition, if the conveying speed is adjusted according to the suction negative pressure value measured by the pressure measuring means, the average conveying speed will be changed. In addition, it is possible to significantly reduce the transport speed as compared with the constant transport speed in the prior art.

The reason why the conveyance speed is adjusted at every predetermined time interval is to enable the radioactivity concentration to be calculated from the radiation detection signal of the radiation detector. If the transport speed determined by the dust collection amount that changes with the passage of time is used as it is, it is very troublesome to calculate the radioactivity concentration from the radiation detection signal of the radiation detector. The invention of claim 3 is
The air at the monitoring point of the radioactive material handling facility is passed at a constant flow rate by a suction pump through the dust collection part of the continuous filter paper that is continuously conveyed, and the dust floating in the air is collected. A radioactive dust monitor for collecting radiation in a part, detecting radiation emitted from the collected dust by a radiation detector, and continuously measuring the radioactivity concentration existing in the air at the monitoring point, A pressure measuring unit that measures a suction negative pressure of air on the intake side of the suction pump, a variable speed motor and a variable speed motor driver for adjusting the conveyance speed of the long filter paper, and are acquired in advance. The long length is set at predetermined time intervals by the corresponding relationship between the suction negative pressure value and the dust collection amount of the dust collecting section and the suction negative pressure value measured by the pressure measuring means. According to the ratio of the paper conveyance speed and the count rate value of the radiation detected by the radiation detector and the maximum count rate value that can maintain the predetermined measurement accuracy of the radiation detector acquired in advance, every predetermined time interval The conveyance speed of the long filter paper is adjusted to the larger conveyance speed of the conveyance speed of the long filter paper set to.

When the number of incident radiations exceeds the limit, the radiation detector cannot detect the pulse signals of the individual radiations as independent signals and cannot accurately count the incident radiations. The maximum count rate value that can ensure a predetermined measurement accuracy is the maximum coefficient rate value. Therefore, if the count rate value of the radiation detected by the radiation detector is used as a signal and the count rate of the radiation detected by the radiation detector does not exceed the maximum count rate value, it is always possible to adjust the transport speed of the long filter paper. The radiation detector can be used within a predetermined accuracy, and if the transportation speed is adjusted as low as possible within that range, the long filter paper consumption is minimized. Regarding the radioactive dust concentration in the air at the monitoring point of the radioactive material handling facility, the situation is the same as the dust concentration described in the description of claim 2, so in this case as well, the average transport speed is significantly larger than that of the conventional technology. Can be late.

In the present invention, the conveying speed determined by the count rate value of the radiation detected by the radiation detector, and the suction negative pressure value indicating the dust collecting state of the dust collecting section, similar to the invention of claim 2. The transport speed determined by the larger one is selected, so it is possible to ensure the predetermined air flow rate and the predetermined radiation detection accuracy even if dust is collected under any circumstances. In addition, the average transport speed of the long filter paper can be made significantly slower than that of the prior art.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the radioactive dust monitor according to the present invention will be described with reference to examples. It should be noted that parts having the same functions as those in the prior art are designated by the same reference numerals. [First Embodiment] In this embodiment, the width direction of the long filter paper used in the prior art is divided into a plurality of regions to increase the effective length of the filter paper, thereby increasing the consumption amount of the long filter paper. Is to reduce.

FIG. 1 is a block diagram showing the construction of the main part of a dust collecting portion for explaining this embodiment, and FIG. 2 shows a long filter paper in the case where the filter paper is continuously conveyed by this embodiment. It is an explanatory view showing an example of a dust collection state, and Drawing 3 is an explanatory view showing an example of a dust collection state of long length filter paper at the time of carrying filter paper intermittently by this example. The air intake head 3a of this embodiment includes two air intake parts, a first air intake part 31 and a second air intake part 32, each having an air intake of the same shape, and the first air intake part 31 has a first air intake part 31a. The solenoid valve 33 and the second solenoid valve 34 are attached to the second intake section 32 by separate pipes, respectively, and both pipes are joined together behind the solenoid valves 33 and 34 to form a flow meter. It is connected to the. The structure after the flow meter and the structure other than the above are the same as those of the conventional technique.

The widths (dimensions in the height direction in FIG. 1) of the two intake portions 31 and 32 are the widths of the long filter paper 1 divided into two areas, and the width of 75 mm used in the prior art. In the case of a filter paper, it is formed to have a size of 30 mm, for example. This 2
As shown in FIG. 2, the two lengthwise areas of the lengthy filter paper 1 corresponding to the two air intake portions 31 and 32 are the first dust collection area 13 and the second dust collection area 14, respectively. is there. If the first solenoid valve 33 is opened and the second solenoid valve 34 is closed to collect dust, the dust is collected in the first dust collection area 13, and conversely, the second dust collection area 14 is formed. Dust is collected at. FIG. 2 shows a state in which the dust is continuously collected in the entire first dust collecting region 13 and then continuously in the middle of the second dust collecting region 14. is there.
FIG. 3 shows that the first dust collecting region 13 and the second dust collecting region 14 are alternately used to collect dust intermittently, and (n + 2) of the intermittent dust collecting portion 15n. It shows the state of collecting dust up to the second. The arrows in FIGS. 2 and 3 indicate
The conveyance direction of the long filter paper 1 is shown.

In this manner, the intake head is provided with a plurality of switchable intake sections having the same shape, and the width direction of the long filter paper is divided into independent dust collecting areas, and the respective areas are separated. If it is used as a dust collecting part, the effective length of the long filter paper is extended to a length obtained by multiplying the length of the long filter paper by the number of divisions, and if the long filter paper is conveyed at the same conveying speed. Therefore, the consumption amount of the long filter paper becomes a fraction. In the case of the above embodiment, since the number of divisions is 2, the consumption amount of the long filter paper is 1/2.

When the lengthwise filter paper is divided in the width direction as described above, the area of the dust collecting portion is reduced and the fluid resistance of the dust collecting portion is increased. However, a suction pump suitable for the fluid resistance is selected. By using it, it is possible to secure a predetermined air flow rate value. The following example is a radioactive dust monitor that continuously conveys a long length of filter paper, and a predetermined air flow rate value and a radiation count rate are obtained according to the collected dust amount and the measurement value related to the collected radioactive dust amount. While maintaining the predetermined measurement accuracy of, the transport speed of the long filter paper (in this section, "the transport speed of the long filter paper" is simply referred to as "transport speed") is adjusted to reduce the consumption amount. It is a thing.

FIG. 4 is a block diagram showing the structure of the main part of the dust collecting section of the following embodiment. The structure of this embodiment is different from the structure of the prior art because the drive of the filter paper feed roller 2 is changed from the constant speed motor to the variable speed motor 7a, and a command from the board computer (cpu) 70 is received. That is, a variable speed motor driver 70 for driving the transmission motor 7a is newly installed.

[Second Embodiment] In this embodiment, the conveying speed is made as slow as possible while securing a predetermined air flow rate value by the amount of dust collected in the dust collecting section.
It is intended to reduce the consumption of long filter paper. The relationship between the amount of collected dust and the suction negative pressure of the suction pump has been described in the section “Means for Solving the Problems”, and thus the description thereof is omitted.

In this embodiment, the correspondence relationship between the amount of dust collected in the dust collecting portion of the long filter paper 1 and the suction negative pressure of the suction pump is acquired in advance and input to the board computer 70. The pressure gauge 5 as a pressure measuring means for measuring the suction negative pressure of the suction pump measures the suction negative pressure, inputs the measured value to the board computer 70, and the board computer 70 inputs the input suction negative pressure value. Convert to the amount of collected dust. The board computer 70 calculates the dust collection amount for each time interval based on the thus obtained series of dust collection amount data for each constant time interval and the corresponding transport speed data, and collects the dust collection amount. Of the variable speed motor driver by grasping the fluctuation tendency of the
A command is issued to 70 to control the number of rotations of the variable speed motor 7a to adjust the transport speed determined as described above. In other words, the transport speed that is set is not adjusted to a slow transport speed that collects dust until the dust collection amount corresponding to the maximum suction negative pressure of the suction pump is reached, and a certain safety factor is expected. The transport speed is set.

The switching of the transport speed is not performed at any time, but is performed at predetermined time intervals. The reason is that the conversion coefficient used for converting the radiation count rate value into the radioactivity concentration changes depending on the transport speed.
The radiation count rate value is obtained by counting radiation detection signals (simply detection signals in FIG. 4) from the radiation detector 8 over a predetermined radiation counting time. Therefore, the transport speed cannot be changed while the board computer 70 is counting the radiation detection signals, and therefore the transport speed can be switched only when the radiation count is reset, and the switching time interval is the radiation count. It is the same as the time or an integral multiple of it.

The conventional transport speed (25 mm / h) described in the section of "Prior Art" can secure a predetermined air flow rate value even at the assumed maximum dust concentration, and the assumed maximum radiation. It is a conveyance speed that can satisfy the condition that the radiation detector can secure a predetermined radiation detection accuracy even in the active concentration. On the other hand, in this embodiment, since the transport speed is adjusted according to the dust concentration, the transport speed is much slower than the conventional transport speed in the normal state where the dust concentration is low, and the average transport speed is also conventional. This is much slower than the transport speed of, and the consumption amount of the long filter paper 1 is significantly reduced.

When the conveying speed is set under the condition that a predetermined air flow rate value can be secured as in this embodiment, the radiation detector has a considerably high probability of securing a predetermined radiation detection accuracy. Therefore, the radioactive dust monitor according to this embodiment can almost certainly measure the radioactivity concentration with a predetermined accuracy. [Third Embodiment] In this embodiment, a condition is added to the second embodiment that the measurement of the radioactivity concentration can be surely performed with a predetermined accuracy.

In this embodiment, in order to satisfy the condition that the radioactive concentration measurement can be surely measured with a predetermined accuracy,
The maximum count rate value with which the radiation detector 8 can secure a predetermined measurement accuracy is acquired in advance and input to the board computer 70, and the board computer 70 counts the detection signal of the radiation detector 8 over a predetermined time interval. The ratio of the count rate value of radiation obtained to the maximum count rate value (hereinafter referred to as the count rate ratio) is calculated and accumulated as a series of data for each predetermined counting time, and this series of data and corresponding The count rate ratio for each time interval is calculated with the transport speed data of the long filter paper to grasp the trend of change in the count rate ratio, and even if some sudden change occurs, the count rate ratio exceeds 1 Set the transport speed so that it does not exist.

In this embodiment, the larger one of the conveying speed set by the count rate ratio and the conveying speed set by the suction negative pressure value, which corresponds to the invention of claim 2, is used. Adjust the transport speed. As in the case of the second embodiment, also in this embodiment, in the normal state, the set transport speed is much slower than the conventional transport speed, and the average transport speed is also lower than the conventional transport speed. It becomes much slower, and the consumption of the long filter paper 1 is greatly reduced. Moreover, the transport speed in the case of this embodiment is set so as to ensure both a predetermined air flow rate value and a predetermined measurement accuracy of the radiation count rate, and therefore the radioactive dust monitor of this embodiment uses The consumption of the long filter paper is reduced while ensuring the conditions under which the radioactivity concentration in the air can be measured with a predetermined accuracy.

[0035]

According to the first aspect of the present invention, since each area obtained by dividing the lengthwise filter paper in the width direction into a plurality of areas is an independent dust collecting area for moving the dust collecting portion, The effective length of the filter paper is the same as the length of the long length filter paper multiplied by the number of divisions. Therefore,
According to the present invention, the consumption of the long filter paper of the radioactive dust monitor is reduced.

According to the invention of claim 2, pressure measuring means for measuring suction negative pressure of air on the intake side of the suction pump is provided,
By the correspondence relationship between the suction negative pressure value and the dust collection amount of the dust collection unit that have been acquired in advance and the suction negative pressure value measured by the pressure measuring means, the conveyance speed of the long filter paper is determined at predetermined time intervals. "Means to solve the problem" because it adjusts
As described in the section, while maintaining a predetermined air flow rate, the average transport speed of the long filter paper can be made significantly slower than the constant transport speed in the prior art.

Therefore, according to the present invention, it is possible to provide the radioactive dust monitor capable of reducing the consumption of the long filter paper while ensuring a predetermined air flow rate. Moreover, as described in the section of "Prior Art", when a predetermined air flow rate can be secured, there is a high possibility that a predetermined radioactivity concentration measurement accuracy can be secured. According to the invention of claim 3,
Equipped with a pressure measuring means for measuring the suction negative pressure of the air on the intake side of the suction pump, and measured by the pressure measuring means and the correspondence relationship between the suction negative pressure value and the dust collection amount of the dust collection part that were acquired in advance. Based on the suction negative pressure value, the conveyance speed of the long filter paper set at each predetermined time interval, the count rate value of the radiation detected by the radiation detector, and the predetermined measurement accuracy of the radiation detector acquired in advance. How to adjust the transport speed of the long filter paper to the larger one of the transport speed of the long filter paper set at each predetermined time interval and the transport speed of the long filter paper depending on the ratio with the maximum count rate value that can be maintained. Even if dust is collected under various conditions, it is possible to reliably ensure a predetermined air flow rate and a predetermined radiation detection accuracy, and to make the average transport speed of long filter paper significantly slower than the transport speed of the prior art. You can

Therefore, according to the present invention, it is possible to provide the radioactive dust monitor capable of reducing the consumption of the long filter paper while ensuring the condition that the radioactivity concentration in the air to be measured can be measured with a predetermined accuracy. .

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a main part of a dust collecting portion for explaining a first embodiment of a radioactive dust monitor according to the present invention.

FIG. 2 is an explanatory view showing an example of a dust collecting state of a long filter paper when the filter paper is continuously conveyed according to the first embodiment.

FIG. 3 is an explanatory diagram showing an example of a dust collecting state of a long filter paper when the filter paper is intermittently conveyed according to the first embodiment.

FIG. 4 is a configuration diagram showing a configuration of a main part of a dust collecting unit according to a second embodiment.

FIG. 5 is a diagram showing a suction negative pressure-flow rate characteristic of a suction pump.

FIG. 6 is a perspective view showing a configuration of an example of a dust collecting unit of a conventional radioactive dust monitor.

FIG. 7 is an explanatory view showing a dust collecting state of a long filter paper of a conventional radioactive dust monitor.

[Explanation of symbols]

1 long filter paper 11 Collection start position 12 Dust collection area 13 First dust collection area 14 Second dust collection area 121, 131, 141 Parts collecting dust 15n Intermittent dust collector 2 Filter paper feed roller 3, 3a intake head 31 First air intake section 32 Second air intake section 33 First solenoid valve 34 Second solenoid valve 4 flow meter 5 pressure gauge 6 suction pump 7 motor 7a variable speed motor 8 Radiation detector 9 Supply pulley 10 Take-up pulley 20 pod computer 70 Variable speed motor driver

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2G052 AA01 AB28 AC12 AD02 AD22                       AD42 BA05 BA14 BA22 EA03                       EA06 ED03 FD04 GA18 HA15                       HC02 HC09 HC28 HC42 JA03                       JA23                 2G088 EE12 EE21 FF04 FF05 HH03                       JJ09 JJ22 KK24 LL22

Claims (3)

[Claims] 1. A suction pump that allows air at a monitoring point of a radioactive material handling facility to pass through a dust collecting portion of a long filter paper that is continuously or intermittently conveyed,
Dust floating in the air is collected in the dust collecting part,
A radioactive dust monitor for detecting radiation emitted from collected dust by a radiation detector to continuously measure the radioactivity concentration existing in the air at a monitoring point, wherein the long filter paper is wide. The radioactive dust monitor is characterized in that it is divided into a plurality of regions having the same width in the direction, and each of the divided regions is an independent dust collection region for moving the dust collection unit. 2. An air at a monitoring point of a radioactive substance handling facility is passed through a dust collecting section of a continuous filter paper, which is continuously conveyed, at a constant flow rate by a suction pump to float in the air. Radioactive dust for collecting dust in the dust collection part, detecting the radiation emitted from the collected dust with a radiation detector, and continuously measuring the radioactivity concentration existing in the air at the monitoring point. A monitor, comprising: a pressure measuring means for measuring a suction negative pressure of air on the intake side of the suction pump; a variable speed motor and a variable speed motor driver for adjusting the conveying speed of the long filter paper; The suction negative pressure value obtained in advance and the correspondence relationship between the dust trapping amount of the dust trapping portion and the suction negative pressure value measured by the pressure measuring means are used for the above-mentioned operation at predetermined time intervals. Regulating the transport speed of the continuous filter paper, radioactive dust monitor, characterized in that. 3. An air at a monitoring point of a radioactive substance handling facility is passed through a dust collecting portion of a continuous filter paper, which is continuously conveyed, at a constant flow rate by a suction pump to float in the air. Radioactive dust for collecting dust in the dust collection part, detecting the radiation emitted from the collected dust with a radiation detector, and continuously measuring the radioactivity concentration existing in the air at the monitoring point. A monitor, comprising: a pressure measuring means for measuring a suction negative pressure of air on the intake side of the suction pump; a variable speed motor and a variable speed motor driver for adjusting the conveying speed of the long filter paper; Set at predetermined time intervals by the correspondence relationship between the suction negative pressure value and the dust collection amount of the dust collection unit that have been acquired in advance and the suction negative pressure value measured by the pressure measuring means. According to the ratio between the transport speed of the long filter paper to be stored, the count rate value of the radiation detected by the radiation detector and the maximum count rate value capable of maintaining the predetermined measurement accuracy of the radiation detector acquired in advance, The radioactive dust monitor, wherein the transport speed of the long filter paper is set for each time interval of, and the transport speed of the long filter paper is adjusted to a larger one of the transport speeds.