JP6254455B2 - Air dose monitoring method - Google Patents

Description

  The present invention relates to an air dose monitoring method.

  2. Description of the Related Art Conventionally, as pretreatment for disposing of radioactive waste, an operation for separating the soil and plants contaminated with radioactive materials to reduce the volume of waste has been performed. In this work environment, it is strongly desired to perform radioactivity monitoring from the viewpoint of worker safety and security.

  Here, area monitoring is known as a radioactivity monitoring technique. Area monitoring is to measure the air dose of radiation continuously in the measurement target area and to sound an alarm when the air dose exceeding a predetermined value is measured.

  As a technique for two-dimensionally measuring the spatial dose of radiation, a gamma camera and a system using the same are known (for example, see Patent Document 1). If a gamma camera is used, the spatial dose of radiation can be grasped in a plane, and it is easy to visually recognize the position of the radiation source and its radiation intensity.

JP 2013-33009 A

  However, radiation measuring instruments capable of two-dimensional measurement are generally expensive and have a limited measurement visual field, and it takes time to measure the visual field as a single “plane”. For this reason, in order to continuously monitor the air dose of the entire site in a work environment where the presence or absence of radioactivity that generates an air dose of a predetermined value or more is unknown, the cost for installing and operating the measuring instrument is Become enormous.

  Therefore, an object of the present invention is to provide an air dose monitoring method capable of efficiently operating a radiation measuring instrument capable of two-dimensional measurement at low cost.

  The present invention relates to a first measurement step of measuring an air dose of radiation with a first radiation measuring instrument having a fixed installation position, and when the air dose is equal to or greater than a predetermined value, A second measurement step of measuring an air radiation dose with a second radiation measuring instrument capable of two-dimensional measurement for an estimated region estimated as a radiation source position based on a measurable range; Provide a method for monitoring air dose.

  According to this, the second radiation measuring instrument capable of two-dimensional measurement is used only when the air dose of a predetermined value or more is measured by the first radiation measuring instrument. In addition, since the measurement by the second radiation measuring instrument is intended for the estimation region estimated as the radiation source position based on the measurable range of the first radiation measuring instrument, the second radiation measuring instrument to be used is used. The “empty shots” that are measured without a radioactivity that generates an air dose greater than or equal to a predetermined value are greatly suppressed. Therefore, according to the present invention, a radiation measuring instrument capable of two-dimensional measurement can be efficiently operated at low cost.

  Here, it is preferable that the first radiation measuring instrument is a radiation arrival direction measuring instrument capable of identifying two or more directions. According to this, the precision which specifies the said estimation area | region which is a measuring object by a 2nd radiation measuring device increases.

  The radiation is preferably a gamma ray, and the second radiation measuring instrument is preferably a gamma camera. Since the gamma camera is excellent in grasping the spatial dose of radiation in a plane, it is easy to visually identify the radiation source. The present invention can also be applied when a gamma camera is used.

  In addition, both the first radiation measuring instrument and the second radiation measuring instrument are used indoors, and in the second measuring step, the second radiation measuring instrument is set in the estimation area according to the guide structure provided on the indoor ceiling. It is preferable to guide to a position where measurement is possible. According to this, in the measurement by the second radiation measuring instrument, the second radiation measuring instrument is guided to measure the air dose in the estimated area according to the guide structure provided on the ceiling. The measuring instrument does not become an obstacle to workers and work machines. In addition, since measurement can be performed from the vicinity of the ceiling, the radiation source is less likely to enter a shadow or a human figure, and measurement accuracy is high.

  In the second measurement step, the estimation area is divided into a plurality of measurement units, and the air dose is measured for each measurement unit, and the width of the measurement unit is preferably equal to or less than the measurable range of the second radiation measuring instrument. . By dividing the estimation area into a plurality of measurement units and measuring the air dose for each measurement unit, even if the estimation area is wide, the second radiation measuring instrument with a narrow measurement field can be used. Here, since the width of the measurement unit is equal to or smaller than the measurable range of the second radiation measuring instrument, the entire estimation area can be measured.

  In the second measurement step, it is preferable to use a plurality of second radiation measuring instruments. By increasing the number of second radiation measuring instruments within a range where the cost does not increase, the measurement of the air dose in the estimated region can be completed quickly.

  ADVANTAGE OF THE INVENTION According to this invention, the monitoring method of the air dose which can operate efficiently the radiation measuring instrument in which two-dimensional measurement is possible at low cost can be provided.

It is the top view (a) and side view (b) of the work site in the building which performs the volume reduction work of radioactive waste. It is a figure which shows the structure and measurable range of a radiation arrival direction measuring device. It is the top view (a) and side view (b) which show the positional relationship of the measurable range of several radiation arrival direction measuring devices, and a radiation source. It is the top view (a) and side view (b) which show the positional relationship of the measurable range of several radiation arrival direction measuring devices, and an estimation area | region. It is the top view (a) and side view (b) which show a mode that it measures with a gamma camera for every measurement unit. It is the top view (a) and side view (b) which show the positional relationship of the measurable range of several radiation arrival direction measuring devices, and a radiation source. It is the top view (a) and side view (b) which show a mode that it measures with a gamma camera for every measurement unit.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same part or an equivalent part, and the overlapping description is abbreviate | omitted.

  In the present specification, the terms “radiation source” and “radiation source” are used as terms representing a position where a substance that emits radiation or a substance that emits radiation exists.

  First, various configurations used for air dose monitoring will be described. FIG. 1 shows a plan view (FIG. 1 (a)) and a side view (FIG. 1 (b)) of a work site 1 in a building that performs a volume reduction operation of radioactive waste. Here, the area of the work site 1 is 100 m × 50 m, and the ceiling height is 10 m.

  A rail (guide structure) 2 is fixedly attached to the ceiling C of the work site 1. The rail 2 has a plurality of linear portions extending in parallel to each other up to the vicinity of the end of the ceiling C in the short direction of the work site 1 (vertical direction in FIG. 1A), and the adjacent end portions thereof However, the rails 2 as a whole are connected by a curved portion so as to be one. Here, the pitch of the adjacent straight portions of the rail 2 is 8 m.

In a region between the straight portions of the rail 2 on the ceiling C, n (n is a natural number) radiation arrival direction measuring devices (first radiation measuring devices) D (D ₁ , D ₂ , D ₃ , D ₄ , .., D _n−1 , D _n ) are fixedly attached to each other in the longitudinal direction and the short direction of the work site 1 at predetermined intervals. Here, the predetermined interval is 24 m. In this case, as shown in FIG. 1, there are three linear portions of the rail 2 in the longitudinal direction of the work site 1 between the radiation arrival direction measuring instruments D. This is interposed, and the rail 2 is not interposed in the short direction.

Radiation DOA meter D, as in (for example radiation DOA meter D ₃ in this case.) Shown in FIG. 2, such that the circumferential direction four uniformly arranged in plan view, four detector d ₃ (d ₃₁ , d ₃₂ , d ₃₃ , d ₃₄ ). The four detection units d ₃₁ , d ₃₂ , d ₃₃ , and d ₃₄ each have a gamma ray measurable range R (R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ ), and each of the detection units d ₃₁ , d ₃₂ , d ₃₄ , The direction in which the radiation has arrived can be estimated from the dose rate ratios at d ₃₃ and d ₃₄ .

For example, in FIG. 2, the source S _1, since within the scope of the measurement range R _31, detecting unit d ₃₁ can detect the gamma rays generated from the radiation source. Similarly, since the source S ₂ is within the measurable range R ₃₂ , it can be detected by the detection unit d ₃₂ , and since the source S ₃ is within the measurable range R ₃₃ , the detection unit d ₃₃ Since the source S ₄ is within the measurable range R ₃₄ , it can be detected by the detection unit d ₃₄ . Source _{S 5} present straddling two measurable range _{R 31, R 32} is detected by the two detector _{d 31, d 32,} each of the detection strength, it is the beam source _{S 5} weaker than when it is detected by one detector unit d _31. In this way, radiation DOA meter D ₃ as the direction of arrival of the incident radiation, it is possible to identify the four directions. Incidentally, one of the measurable range in the source does not contain even S ₆ because they are not detected in any of the detection unit, it can not be measured in the radiation DOA meter D _3.

As shown in FIG. 1, the radiation direction-of-arrival measuring instrument D is different by 45 degrees in the direction in which the four detection units d ₁ , d ₂ , d ₃ , and d ₄ face each other. (See D ₃ and D ₄ in FIG. 1).

  A single gamma camera (second radiation measuring instrument) 3 is attached to the rail 2. The gamma camera 3 can be run along the rail 2 by computer control.

  The gamma camera 3 is a camera capable of two-dimensional measurement of gamma rays, and a known one can be used. Here, “two-dimensional measurement” means that the radiation dose can be measured with a planar distribution instead of a point. Here, the measurable range V (see FIG. 5B) of the gamma camera 3 is set to 8 m × 8 m so as to coincide with the pitch of the adjacent linear portions of the rail 2. This measurable range V can be appropriately changed by adjusting the viewing angle of the gamma camera 3 in consideration of the ceiling height.

  Although not shown, the radiation direction-of-arrival measuring instrument D and the gamma camera 3 are each connected to a computer to process radiation measurement information.

  Next, a method of monitoring the air dose at the work site 1 using the radiation arrival direction measuring device D and the gamma camera 3 will be described. The radiation direction-of-arrival measuring instrument D continuously measures the air dose at the work site 1 (first measurement step). On the other hand, the gamma camera 3 stands by at a predetermined position. Here, when any radiation arrival direction measuring device D measures an air dose of a predetermined value or more, the computer estimates the position of the radiation source of the radiation.

FIG. 3 shows that the detection unit d ₃₁ of the radiation direction-of-arrival measuring instrument D ₃ measures a spatial dose of a predetermined value or more, and the detection units d ₄₂ and d _{43 of} the radiation direction-of-arrival measuring instrument D ₄ receive a weaker spatial dose. The case where it measured is shown. Here, since the detection of the orientation of the radiation DOA meter D ₃ and radiation DOA meter D ₄ are different from 45 degrees to each other, the measurement range R of the detecting portion d ₃₁ of the radiation DOA meter D _{3 31} and a position which is also in the measurable ranges R ₄₂ and R ₄₃ of the detectors d ₄₂ and d ₄₃ of the radiation arrival direction measuring device D ₄ , that is, at least between the radiation arrival direction measuring devices D ₃ and D ₄ . It is estimated that the radiation source S having a high radiation concentration exists at the position of.

Here, as shown in FIG. 4, as the estimation region T where the existence position of the radiation source S is estimated, the detection units d ₃₁ , d ₄₂ , measurement range _R 31 of d _43, R _42, set so as to cover most of _{R 43} (estimating step). The estimated area T has a width and a position of 8 m × 8 m, which is a measurable range V (see FIG. 5B) per gamma camera 3, and a rail on which the gamma camera 3 travels. Each of the positions 2 is considered, and is set to an area of 16 m × 32 m.

The gamma camera 3 is made to travel on the rail 2 under computer control with respect to the estimation region T set in this way, and is guided to a position in the estimation region T where an air dose can be measured in an arbitrary measurement unit. At this time, as shown in FIG. 5, the estimation area T is divided into eight measurement units t (t ₁ , t ₂ ,..., T ₈ ) (each 8 m × 8 m), and the gamma camera is measured for each measurement unit t. The air dose is measured at 3 (second measurement step). For example, starts measurement from the measurement unit t ₁ shown top right After finishing the measurement, with a gamma camera is 8m travel in the direction of the arrow, starts measuring the next measurement unit t _2.

  Thus, by completing all measurements in the estimation region T, the position of the radiation source S and the radiation intensity can be visually grasped as two-dimensional data.

Another example of the air dose monitoring method will be described. 6, the radiation direction of arrival instrument D ₂ of the detector d _21, and the detection unit d ₄₂ of the radiation DOA meter D ₄ indicates the case where both the measured air dose greater than a predetermined value. Here, the radiation source S having a high radiation concentration is located at a position in the measurable range R ₂₁ , R ₄₂ of both detectors d ₂₁ , d ₄₂ , that is, at least a position intermediate between the radiation arrival direction measuring instruments D ₂ , D _4. Presumed to exist.

Here, as shown in FIG. 7, the estimation region T in which the position of the radiation source S is estimated takes into account the possibility that the radiation source S is spread over a wide range, and the detection units d ₂₁ and d ₄₂ . It is set so as to cover most of the measurable ranges R ₂₁ and R ₄₂ . The estimation region T, unlike FIG. 4, is set in the breadth of 24m × 32m, which is 12 one unit of measure _{t (t 1, t 2,} ..., t 12) is divided into (8m × 8m respectively) Yes.

  Thereafter, in the same manner as described above, the measurement by the gamma camera 3 is sequentially performed for each measurement unit t.

  According to the air dose monitoring method described above, the gamma camera 3 capable of two-dimensional measurement is used only when the air dose of a predetermined value or more is measured by the radiation arrival direction measuring device D. In addition, since the measurement by the gamma camera 3 is directed to the radiation source position and the estimated region T estimated based on the measurable range R of the radiation arrival direction measuring device D, the number of gamma cameras 3 is one. In addition, the “empty shot” that is measured even though there is no radioactivity that generates an air dose higher than a predetermined value is greatly suppressed. In the above embodiment, it is only necessary to measure a range of 16 m × 32 m or 24 m × 32 m without measuring the entire range of the work site 1 having an area of 100 m × 50 m with the gamma camera 3. Therefore, according to the air dose monitoring method of this embodiment, the gamma camera 3 capable of two-dimensional measurement can be efficiently operated at low cost.

  Moreover, since the radiation direction-of-arrival measuring instrument D used here can identify four directions, the accuracy of specifying the estimation region T that is a measurement target by the gamma camera 3 is high. Furthermore, since the radiation direction-of-arrival measuring instruments D are adjacent to each other and the direction in which the detection unit d faces differs by 45 degrees, the accuracy of specifying the estimation region T is further increased.

  In the above embodiment, the radiation direction-of-arrival measuring instrument D and the gamma camera 3 are both used indoors, and the gamma camera 3 can measure the estimated region T along the rail 2 provided on the indoor ceiling C. Since the gamma camera 3 is guided to a possible position, the gamma camera 3 does not become an obstacle to a worker or a work machine that performs a volume reduction operation of radioactive waste. In addition, since measurement can be performed from the vicinity of the ceiling C, the radiation source S hardly enters a shadow or a human figure, and the measurement accuracy is high.

  In addition, since the width of the measurement unit t measured by the gamma camera 3 is matched with the measurable range V of the gamma camera 3, the estimated region T can be measured all over. Further, even if the estimation region T is wide, it is possible to cope with the gamma camera 3 that generally has a narrow measurement visual field by dividing the estimation region T into a plurality of measurement units t.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, in the above-described embodiment, a mode in which only one gamma camera 3 is used is shown, but a plurality of gamma cameras 3 may be used. By increasing the number of gamma cameras 3 within a range where the cost is not excessively large, the measurement of the air dose in the estimated region T can be completed more quickly.

  Moreover, in the said embodiment, although the rail 2 was attached to the ceiling C in the form of meandering, the attachment shape and total distance of the rail 2 can be changed suitably. For example, you may attach so that it may become other shapes, such as a spiral shape. If the gamma camera 3 can be swung, a plurality of measurement units can be measured at one position, so that the total distance of the rail 2 can be shortened, and the travel time and travel distance of the gamma camera 3 can be reduced. Can be shorter.

  Further, in the above-described embodiment, the aspect in which the size of the measurement unit coincides with the measurable range V of the gamma camera 3 is shown, but the size of the measurement unit is less than the measurable range V of the gamma camera 3. Also good. At this time, in the measurement of the estimation region T, the distance that the gamma camera 3 travels between the measurement units is the width of one side of the measurement unit.

  The setting of the estimation area T and the movement of the gamma camera 3 may not be computer controlled. For example, a person may set the estimation area T based on the measurable range R of the radiation direction-of-arrival measuring device D where the alarm sounded, and in order to guide the gamma camera 3 to a position where the estimation area T can be measured. Instead of using the rail 2, the gamma camera 3 may be guided by being loaded on the vehicle body or may be guided by a person.

  In the above embodiment, the radiation direction-of-arrival measuring device D capable of identifying four directions is used, but the radiation direction-of-arrival measuring device capable of identifying five or more directions may be used. Good. The more directions that can be identified, the narrower the range of the estimation region T, and the “empty shot” of measurement by the gamma camera 3 can be further reduced.

  The air dose monitoring method of the present invention can also be carried out outdoors. At this time, the radiation direction-of-arrival measuring device D can be installed and fixed on the ground, and the gamma camera 3 can be appropriately handled by hanging and guiding with a crane, loading on the vehicle body, guiding by hand, etc.

  The radiation to be measured may be radiation other than gamma rays. In this case, the first radiation measuring instrument and the second radiation measuring instrument that can measure the radiation to be measured are used. To do.

  2 ... Rail (guide structure), 3 ... Gamma camera (second radiation measuring instrument), C ... Ceiling, D ... Radiation arrival direction measuring instrument (first radiation measuring instrument), R ... Radiation arrival direction measuring instrument Possible range, S ... radiation source, T ... estimated region, t ... measurement unit, V ... measurable range of gamma camera.

Claims (5)

A first measurement step of measuring an air dose of radiation with a first radiation measuring instrument having a fixed installation position;
When the air dose is greater than or equal to a predetermined value, a second dimension capable of two-dimensional measurement is possible for an estimated region estimated as the radiation source position based on the measurable range of the first radiation measuring instrument. a second measurement step of measuring the spatial dose of radiation in the second radiation measurement device, was closed,
The first radiation measuring instrument and the second radiation measuring instrument are both used indoors,
In the second measurement step , the air dose monitoring method of guiding the second radiation measuring instrument to a position where the estimation region can be measured according to a guide structure provided on the indoor ceiling .   The air dose monitoring method according to claim 1, wherein the first radiation measuring instrument is a radiation arrival direction measuring instrument capable of identifying two or more directions. The radiation is gamma rays;
The air dose monitoring method according to claim 1, wherein the second radiation measuring instrument is a gamma camera. In the second measurement step, the estimation area is divided into a plurality of measurement units, and air dose is measured for each measurement unit,
The space dose monitoring method according to any one of claims 1 to 3 , wherein a width of the measurement unit is equal to or less than a measurable range of the second radiation measuring instrument. The air dose monitoring method according to any one of claims 1 to 4 , wherein a plurality of the second radiation measuring devices are used in the second measuring step.

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