JP2965204B1 - Method for quantifying radioactive materials inside structures by gamma-ray measurement - Google Patents

Abstract

Kind Code: A1 The present invention provides a method for quantifying a radioactive substance using gamma rays without destroying or decomposing the structure even when the radioactive substance present inside the structure having a complicated shape does not emit much neutron rays. Provide a way to do it. A collimator having a different γ-ray incident area when a known radioactive substance that emits γ-rays is present in a plurality of regions (2a, 3a) inside a structure (1) having a known shape and material. 10 and 20) with multiple measuring instruments (3
0), from a plurality of gamma-ray intensity measurement results measured through 0) and a theoretical calculation result of gamma-ray intensity when gamma rays from a unit mass of radioactive material reach a plurality of measuring instruments equipped with the collimator, An area where the radioactive substance is present inside the structure and the amount of the radioactive substance in the area are quantified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quantifying a radioactive substance sealed inside a structure, and more particularly to a radioactive substance which can be preferably applied when the structure cannot be destroyed or decomposed when quantifying the radioactive substance. The method relates to a method for quantification of

[0002]

2. Description of the Related Art Non-destructive analysis techniques using neutrons and gamma rays are generally applied when quantifying radioactive materials sealed in a structure.

[0003] Neutrons have the advantage of being applicable irrespective of the shape of the structure. However, if the radioactive material does not emit much neutrons, or if the amount of radioactive material that emits much neutrons is small, the neutron cannot quantify the radioactive material inside the structure.

On the other hand, since γ-rays are greatly affected by the shape of a structure, it is difficult to quantify radioactive materials using γ-rays when the radioactive material exists inside a structure having a complicated shape. Become.

[0005]

As described above, when quantifying a radioactive substance present inside a structure having a complicated shape by measuring a neutron beam or a gamma ray, there are advantages and disadvantages. It was not a satisfactory method.

Therefore, the present invention quantifies radioactive materials using γ-rays without destroying or decomposing the structures, even when the radioactive materials present inside the structure having a complicated shape do not emit much neutron rays. To provide a method that allows the radioactive material to be located in multiple regions within the structure.
In the area where radioactive material is present, even if
Identify areas and quantify radioactive material in each area
It is an object of the present invention to provide a method capable of performing such operations.

[0007]

That is, γ according to the present invention.
The method of quantifying radioactive substances inside a structure by X-rays is based on a collimator with a different γ-ray incident area when there are known radioactive substances that emit γ-rays in multiple areas inside the structure whose shape and material are known. Same through instrument with attached
A plurality of γ-ray intensity measurement results measured at the measurement point ,
From a plurality of γ-ray intensity calculation results when γ-rays from a radioactive substance having a unit mass of the same kind as the known radioactive substance existing in the plurality of regions reach the measuring instrument equipped with the collimator. Identifying a plurality of regions in which the radioactive material is present inside the structure, and determining the amount of radioactive material in each region.
Each is characterized by being quantified.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an example of a structure in which a radioactive substance is sealed, consider a structure 1 in which a cylinder 3 is disposed inside a cylinder 2 as shown in FIG. This structure 1 has the structure shown in FIG.
As shown in FIG. 6, a small amount of radioactive substance is attached to the inner surface 2a of the cylinder 2 and the outer surface 3a of the cylinder 3.

In order to measure γ-rays radiated from such radioactive substance existing areas 2a and 3a and to quantify the radioactive substance, collimators 10 and 20 having different γ-ray incident areas as shown in FIGS. Use Collimator 1
Reference numeral 0 has a cylindrical shape, and is attached so as to cover the outer peripheral surface of the γ-ray detector 30 parallel to the horizontal axis. Collimator 2
Reference numeral 0 denotes an annular shape having a through hole at the center of the disk as shown in FIG.

By arranging the detector 30 at the same measurement point and changing the combination of these collimators 10 and 20, each radioactive substance existing area 2 inside the structure is changed.
The ratio of γ-rays radiated from the radioactive substances existing in the areas a and 3a to the detector 30 differs depending on the radioactive substance existing area. Using this difference, identifies the presence area of the radioactive material, it is possible to quantify the radioactive substance content present respectively in the region.

When measuring γ-rays from a radioactive substance inside a structure, a γ-ray detector 30 equipped with only a collimator 10 as shown in FIG. 5 and a collimator 10 as shown in FIG. The measurement is carried out by the γ-ray detector 30 to which the sensor 20 is attached. The radioactive substance is quantified using the plurality of γ-ray intensity measurement results.

[0012] In order to perform the quantitation of radioactive material from the γ-ray intensity measurements, or γ rays emitted from radioactive material are shielded what kind by structures must from the pre Mewa. In order to know how gamma rays are shielded by structures,
In the present invention, calculation by simulation is performed by theoretical analysis. That is, by simulation, the following a, a ', b, b' amounts, ie ,
When the same type of radioactive substance is present in a unit amount in the plurality of regions, the theoretical value of the γ-ray intensity from each region measured by the γ-ray detector 30 is calculated in advance. This calculation is performed using the actual dimensions and materials of the structure.

A: theoretical amount of γ-ray intensity from the inner surface of cylinder 2 (using collimator 10) a ′: theoretical amount of γ-ray intensity from inner surface of cylinder 2 (using collimators 10 and 20) b: γ from outer surface of cylinder 3 Theoretical amount of line intensity (using collimator 10) b ': Theoretical amount of gamma ray intensity from outer surface of cylinder 3 (using collimators 10 and 20)

Next, the amount of the radioactive substance to be obtained and the result of the γ-ray measurement are shown as follows. X1: Amount of radioactive material present on the inner surface of cylinder 2 X2: Amount of radioactive material present on the outer surface of cylinder 3 G: γ-ray intensity measurement result (using collimator 10) G ′: γ-ray intensity measurement result (using collimators 10 and 20) )

The relationship between these quantities is expressed by the following equation. a X1 + b X2 = G (1) a′X1 + b′X2 = G ′ (2)

Therefore, the amount of radioactive material inside this structure
X1 and X2 can be calculated from the above equations (1) and (2) as follows. X1 = (G / b−G ′ / b ′) / (a / ba−a ′ / b ′) (3) X2 = (G / a−G ′ / a ′) / (b / ab ′) / A ') ... (4)

In the above-described example, two radioactive substance-existing regions are used. Therefore, the gamma ray measurement is performed in two cases, that is, when the collimator 10 is used and when the collimators 10 and 20 are used. Can be appropriately determined depending on the number of radioactive substance existing regions.

[0018]

EXAMPLE A radioactive substance inside a structure as shown in FIG. 7 existing in a nuclear facility plant was quantified by applying the present invention. This structure has two cylinders 5, 6 in a cylinder 4.
Is disposed, and the radioactive substance is almost uniformly present at a low density on the inner surface of the cylinder 4 and the outer surfaces of the cylinders 5 and 6.

At this time, the theoretical calculation value of the γ-ray intensity from the radioactive substance per unit amount, the amount of the radioactive substance to be obtained, and the γ-ray intensity measured by the γ-ray detector are given as follows. a: theoretical amount of gamma ray intensity from the inner surface of the cylinder 4 (using the collimator 10) a ': theoretical amount of gamma ray intensity from the inner surface of the cylinder 4 (using the collimators 10 and 20) b: gamma rays from the outer surfaces of the cylinders 5 and 6 Theoretical amount of intensity (using collimator 10) b ': Theoretical amount of γ-ray intensity from outer surfaces of cylinders 5 and 6 (using collimators 10 and 20) X1: The amount of radioactive material present on inner surface of cylinder 4 X2: On the outer surface of cylinder 5 X3: Amount of radioactive substance present on the outer surface of the cylinder 6 G: Gamma-ray intensity measurement result (using the collimator 10) G ': γ-ray intensity measurement result (using the collimators 10 and 20)

Since the cylinders 5 and 6 are located symmetrically with respect to the γ-ray detector 30, the theoretical amount of γ-ray intensity is common. Here, the theoretical amount of the γ-ray intensity is as follows. Cylinder 4 Cylinders 5, 6 Use collimator 10 a = 0.3794 b = 1.3499 Use collimators 10 and 20 a '= 0.1500 b' = 0.7755

FIG. 8 (when the collimator 10 is attached) and FIG. 9 show the γ-ray spectrum when the γ-ray radiated from the radioactive substance inside the structure is measured by the γ-ray detector.
(When collimators 10 and 20 are attached). From this result, the γ dose at the peak of the γ-ray spectrum is obtained as follows. The γ-ray energy for obtaining the γ dose is 186 eV.

Calculation formulas corresponding to the above formulas (3) and (4) for calculating the amount of radioactive material are as follows. Cylinder 4
X1 = (G / b−G ′ / b ′) / (a / ba−a ′ /
b ') For cylinders 5 and 6: X2 = X3 = 1 / 2.times. (G / a-G' / a ') / (b /
ab '/ a') In this calculation, since the total amount of radioactive material of the cylinders 5 and 6 is obtained for the cylinder, the average value is given by multiplying by 1/2.

By substituting the theoretically calculated value of the γ-ray intensity from the radioactive substance per unit amount and the measured value of the γ-ray intensity measured by the γ-ray detector into the above formula, the amount of the radioactive substance to be obtained is It can be calculated as follows. Note that the above calculated values are values when the range in the height direction where the radioactive substance exists is 1 m in width around the γ-ray detector.

In a nuclear power plant, a plurality of such structures exist, and by repeating the above-described measurement and calculation using a collimator, the plurality of such structures exist inside the plurality of structures existing in the plant. The amount of radioactive material present can be calculated.

[0025]

As can be seen from the above description, according to the present invention, a radioactive substance inside a structure, to which conventional nondestructive analysis technology is difficult to apply, can be used without destroying or decomposing the structure. The amount can be quantified and further
Is the amount of radioactive material present in multiple areas inside the structure.
Can be quantified for each region, and the accuracy of management of radioactive substances can be improved.

[Brief description of the drawings]

FIG. 1 is a plan view and a side view showing an example of a container shape as a structure for sealing a radioactive substance.

FIG. 2 is an explanatory diagram showing an example of a γ-ray detector to which a cylindrical collimator is attached.

FIG. 3 is a plan view and a cross-sectional view illustrating an example of an annular collimator.

FIG. 4 is an explanatory diagram showing an example of a γ-ray detector to which a cylindrical collimator and an annular collimator are attached.

FIG. 5 is an explanatory diagram showing an example in which γ-rays of a radioactive substance inside the structure in FIG. 1 are measured by the γ-ray detector in FIG. 2;

FIG. 6 is an explanatory view showing an example in which γ-rays of a radioactive substance inside the structure of FIG. 1 are measured by the γ-ray detector of FIG. 4;

FIG. 7 shows γ-rays of radioactive material inside a structure having another shape as γ.
Explanatory drawing which shows the Example measured by the line detector.

8 is a γ-ray spectrum measured by a γ-ray detector equipped with one collimator in the embodiment of FIG.

9 is a γ-ray spectrum measured by a γ-ray detector equipped with two collimators in the embodiment of FIG. 7;

[Explanation of symbols]

 1: Structure 2, 4: Cylinder 3, 5, 6: Cylinder 2a, 3a: Radioactive substance existing area 10, 20: Collimator 30: γ-ray detector

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01T 1/00-7/12

Claims (1)

(57) [Claims] 1. When a known radioactive substance that emits gamma rays exists in a plurality of regions inside a structure having a known shape and material, the same measurement is performed through a measuring instrument equipped with a collimator having a different gamma ray incidence area. a plurality of γ-ray intensity measurements measured in points, present and the already in the plurality of regions
From a plurality of gamma ray intensity theoretical calculation results when gamma rays from a radioactive substance of the same kind of unit mass as the intellectual radioactive substance reach the measuring instrument equipped with the collimator, the radioactive substance is present inside the structure. identify a plurality of areas are quantitative methods of radioactive materials internals radioactive material amount by γ-rays, which comprises quantifying each in each territory <br/> zone.