JPH0785117B2 - Structure around the once bent duct hole in the radiation shielding wall - Google Patents

Description

TECHNICAL FIELD The present invention relates to a structure capable of reducing radiation leakage through a bent duct hole formed in a radiation shielding wall.

“Conventional Technology and Its Problems” Conventionally, various ducts are installed in a so-called radiation shielding wall that requires radiation shielding property, such as a secondary shielding wall of a nuclear reactor, and penetrate the shielding wall.

In such a duct, there arises a problem that a small gap around the pipe passed through the duct becomes a radiation leakage passage along the length direction of the pipe. In particular, if the inner diameter of a duct is relatively large, such as the main steam pipe or ventilation duct in a nuclear reactor facility, the amount of radiation that leaks through the duct will increase, and the duct will be bent to reduce the amount of radiation leakage. I'm trying to do it.

However, even if the duct is bent once, the amount of radiation leakage at the duct outlet may not be sufficiently reduced. In such a case, the duct outlet should be installed in a place where people cannot enter or exposed to human radiation. Although it is difficult to install it in a high place to reduce the radiation exposure of workers, this method limits the placement of ducts.
In addition, there are radiation facilities that cannot fully control the exposure of workers by this method.

In this case, if there is a spatial allowance in either of the entrance and exit of the duct, for example, as shown in FIG. 14, a shield 3 for covering the outer circumference of the pipe 2 is attached to the outside of the radiation shield wall 1. By doing so, the radiation dose at the exit of the duct 4 can be reduced, but in facilities with little space, there are problems to be solved such as deterioration of workability and reduction of the duct diameter. There is.

As a method of solving this, it is conceivable to increase the number of bends of the duct 4 formed in the radiation shielding wall 1, but there is a problem that the structure becomes complicated.

Incidentally, apart from such a problem, conventionally, as shown in FIG. 15, in the case where the sleeve 5 forming the duct 4 is arranged and the shield wall 1 is driven, the embedded portion (of the sleeve 5 There is a possibility that a defective portion K shown by hatching may occur on the lower surface) and the shielding property of the embedded portion may be impaired.

Therefore, normally, a shielding performance confirmation test using an RI radiation source is carried out before using the facility. However, if the presence of the defect K is found by this test, in the duct of the conventional structure, the concrete around the defect is confirmed. Therefore, there was a problem that repair work for embedding concrete in the defective portion K was required.

The present invention has been proposed in view of the above circumstances, without changing the shape of the duct or the outer shape of the radiation shielding wall,
It is an object of the present invention to provide a duct hole structure that can reduce the amount of radiation leaking through a duct and can eliminate the need for repairing a defective portion in the embedded portion due to construction.

"Means for solving the problem" Therefore, in the present invention, an additional shield made of a material having a better radiation shielding performance than concrete is installed on the inner surface of the bent duct hole formed in the radiation shielding wall made of concrete. In addition, the additional shielding body is incorporated into the radiation shielding wall in a form in which a part of the duct hole is formed along the inner surface on the entrance side from the entrance of the duct hole to the exit via the corner portion on the entrance corner side. It is

"Operation" With the duct hole having such a structure, the passage of radiation toward the outlet of the duct hole by changing the traveling direction due to scattering or the like is blocked on the way by the additional shield in addition to the concrete portion, Since the radiation near the duct outlet is attenuated, the leakage radiation dose is suppressed.

Further, since the additional shield is incorporated so as to form a part of the duct hole in the shield wall, the device or the like can be installed near the shield wall without changing the shape of the duct or the wall surface of the shield wall. It also has an advantageous effect.

[Examples] Hereinafter, examples of the present invention will be described with reference to the drawings.

First, explaining the basic idea when implementing the structure of the duct hole according to the present invention, an important point in reducing the amount of radiation leaking from the bent duct is to reduce scattered radiation. . In other words, the radiation reaching the exit of the once-bent duct has few direct rays, and the main component is the radiation scattered on the inner surface of the duct and the concrete shielding wall. Therefore, if this scattered radiation is reduced, the duct exit It is possible to reduce the radiation dose at.

Therefore, in the first embodiment of the present invention, consideration is given so that it can be applied regardless of which direction the radiation enters.

Hereinafter, referring to FIGS. 1 to 3, a specific example thereof will be described. An inlet side passage (first leg passage) 11a of a bent duct hole 11 formed in a concrete radiation shield wall 10a.
In addition, in the passage (second leg passage) 11b on the exit side, four-sided cylindrical additional shields A and D that form the duct hole 11 on the inner peripheral surface are installed respectively, and the corners of the duct hole 11 on the corner side The additional shield C having the shape of a quadrangular prism having a thickness larger than that of the additional shields A and D is installed at the position.

These additional shields A, C, D are made of a material superior in radiation shielding performance to concrete (for example, iron against γ rays), and as shown in FIG. 1, the additional shields A, C, D The side surface of D is incorporated into the shielding wall 10 so that the side surface on the corner side of the duct hole 11 is formed.

The reason for this will be described below with reference to FIG. For example, as shown in FIG. 4 (a), if the radiation 6A travels perpendicularly to the entrance face of the entrance side passage 11a, the entrance side passage 11a
Scattering occurs at the position of the point U that reaches the mean free path (depending on the energy of radiation and the material of the wall) around the entrance-side passage 11a including the wall at the end of
If the radiation advances as shown by 6B, it will reach the duct outlet through the corners of the bent portion and the walls on the corner and exit sides. However, in the embodiment shown in FIG. 1 and the like, since the additional shield D is provided at the position where the radiation 6B is transmitted, the passage path of the radiation is blocked and the leakage of the radiation is attenuated.

Further, as shown in FIG. 4 (b), the radiation 7A traveling from the entrance corner side of the entrance-side passage 11a passes through the rim of the duct hole entrance and exits the entrance-side passage 11a (FIG. 4). After scattering at the point V on the (right side) wall and proceeding as shown by arrow 7B, the light passes through the corners on the corners of the bent portion and the wall on the corners of the bent portion to reach the duct outlet. However, in this case, the entrance-side passage through which the radiation passes before and after scattering
The passage of the radiation is blocked by the additional shields A, C, etc. at the corners of the wall of 11a and the bent side, and the leakage of the radiation is attenuated.

Further, as shown in FIG. 4C, when the radiation 8A progresses from the corner of the entrance-side passage 11b, it passes through the edge of the duct hole entrance, and then, for example, the entrance-side passage 11a and the exit-side passage 11b.
After scattering at the point W on each wall, the light passes through as shown by the arrow 8B or directly through the corner on the entry side and reaches the duct outlet.

In this case, the additional shields A, C, and
Since D is arranged, the passage of radiation is blocked here, and leakage of radiation is attenuated.

In addition, in the above, it is clear from the analysis of the experiment that the radiation transmitted from the incident directions of the radiations 7A and 8A through the corners on the inward side of the bent portion or scattered has a great influence on the radiation dose at the duct exit. Therefore, particularly in this embodiment, by providing the additional shield C in the shape of a quadrangular prism that covers a wide range of the corner portion on the entry side, the shielding performance of the most affected portion is improved. It is designed to reliably dampen the leakage.

In this way, when the additional shields A, C, and D are arranged around the duct, the radiation passage route toward the exit direction of the duct hole 11 is blocked by the radiation scattering action, etc. Also has the effect of reducing the radiation dose at the duct outlet.

Moreover, in the above structure, there is no protruding portion on the outer surface of the shielding wall 10 and a part of the duct hole 11 is formed by the additional shielding bodies A, C, D, so that the shape of the conventional duct should be changed. The shielding performance can be improved with a simple structure. Further, in order to construct the shielding wall 10 having the above structure,
Since the additional shields A, C, D can be set in the formwork for constructing the shield wall in advance and then the concrete can be poured, the construction is easy and the additional shields A, C, D etc. can be ducted. If the lining stretched inside is integrated, there is an advantage that the lining can be easily installed.

Further, when the additional shields A, C, and D are installed in this way, as shown in FIG. Since the radiation that exists on the outer side passes through the additional shields A, C, and D, the radiation that passes through the defective portion K attenuates and reaches the duct outlet. However, there is no need to clear the allowable value and repair work in this part.

Incidentally, the additional shield A, C, D does not particularly need to be formed integrally with the concrete of the shield wall 10, for example, the size that the additional shield A, C, D can be arranged. The hole may be formed in advance, and after the concrete is poured, the additional shields A, C, D, etc. may be arranged in the hole to form the duct hole 11.

Next, an experiment conducted to clarify the shielding effect of the structure of the present application will be described below.

In the experiment, first, a first shield 20 as shown in FIGS. 5 and 6 having a structure basically similar to the structure shown in FIG. 1 was produced.

However, in the first shield 20 produced for this experiment, the additional shield B is also incorporated in the corner portion on the protruding side of the duct hole 11, and the additional shields A, B, C, and D are used to form the duct hole 11. Is formed.

The same parts as those shown in FIG. 1 are designated by the same reference numerals.

Here, the first shield 20 is a rectangular parallelepiped concrete block having a height T of 1 m, a width W of 1.7 m, and a depth L of 1.
It is set to 2 m, and the duct hole 11 has a side a of 20 cm in length.
The cross section of is formed in a square shape, and the additional shield A,
The following sizes were used for B, C, and D.

Additional shield A: Height (l ₁ ) 40cm Length (l ₂ ) 45cm Thickness (t) 10cm Additional shield B: Height (l ₁ ) 40cm Length of both sides (l ₃ ) 50cm Thickness (t ) 10cm additional shield C: height (l ₁ ) 40cm width (l ₄ ) 20cm additional shield D: height (l ₁ ) 40cm length (l ₅ ) 55cm thickness (t) 10cm A, B, C, D can be removed respectively, and concrete blocks of the same size can be installed at these installation positions, and experiments can be performed with various combinations of additional shields A, B, C, D. I was able to do it.

The experiment was carried out using the parallel beam of γ-rays from the reactor and using iron as the material of the additional shields A, B, C and D in the following procedure.

First, a block of iron or concrete was placed at each installation position of the additional shields A, B, C, D, and the γ-dose rate at each point (point X shown in Fig. 5) in the outlet passage 11b was measured. .

As shown in FIG. 5, the incident angle of the γ-ray is a predetermined angle θ (θ is 0 °, 20 °, −20 with respect to the central axis Z of the duct hole 11.
It is set to incline.

The point closest to the outlet of the duct at the measurement point (X =
Table 1 shows the ratio of the γ-dose rate in the case where each additional shield is installed with respect to the case where each part is a concrete block at the point (Z = 75 cm).

This revealed the following.

(1) 0 °; the effect of the additional shields C and D is great. The additional shield A is also effective, albeit slightly. However, the additional shield B, on the contrary, increases the dose rate. Additional shield A, B, C,
Even if all D are arranged in the duct hole 11, the additional shield B provided at the corner on the projecting side has a large effect and the dose rate does not decrease.

(2) 20 °; the effect of the additional shield A is large, followed by the additional shields C and D in that order. In this case as well, the additional shield B increases the dose rate. When all the additional shields A, B, C and D are arranged in the duct hole 11, the dose rate is attenuated to about 1/2.

(3) -20 °; the effect of the additional shield C is the greatest,
Next, the additional shields A and D are in this order. The additional shield B has almost no effect. When all the additional shields A, B, C and D are arranged in the duct hole 11, the dose rate is attenuated to 1/7 to 1/8.

From the experimental results described above, A, C, D alone and A, C, D were used to attenuate the dose rate at the duct outlet according to the incident angle of radiation.
It was found that installing all of C and D is an effective installation method of the additional shield.

Further, the placement of the additional shield alone can be selected depending on how much the attenuation is performed, the amount of the additional shield is limited, and the like.

FIG. 7 to FIG. 9 show the measurement results of the dose rate in the outlet side passage 11b in the case of effective single arrangement for each incident direction.

Further, since the additional shield B arranged at the corner portion on the corner side of the duct hole 11 had almost no effect, it seems that the portion on the corner side of the additional shield D also has little effect. From this, it is estimated that the shapes shown in FIGS. 10 and 11 also have a sufficient radiation shielding effect.

The arrangement structure of the additional shield shown here is one in which the additional shields located on the projecting corner side are all omitted, and the additional shields A, C, and D are arranged only on the entering corner side. It constitutes the second embodiment.

It should be noted that an additional shield is provided only on the entrance side of such a duct hole 11.
In the case where A, C and D are positioned, if the size of the additional shield C is set to be large as shown by the dashed line in FIG. 10 to improve the shielding effect, the radiation shielding effect is increased. ,preferable.

12 and 13 show the third embodiment of the present invention.

In this embodiment, the additional shield A, which is installed on the wall surface,
Similar to what is shown in FIG. 10 etc., D is arranged only on the corner side of the duct hole 11, and these additional shields A and D are all formed so that they can be removed from the radiation shield wall 10. It has a unit structure.

With such a structure, for example, when using in a facility using a weak radiation source in an RI facility, as shown in FIG. 12, the concrete block E is sandwiched between the shield wall 10 and the additional shield. When the bodies A and D are arranged and it is found that the predetermined shielding performance cannot be obtained in actual use with this arrangement, or when changing to a facility with a strong radiation source, the concrete block E is By replacing the additional shields A and D with each other, the thickness of the additional shield is increased, and leakage from the outlet side passage 11b of the duct hole 11 is caused by γ.
It is possible to easily cope with the reduction of lines.

"Effects of the Invention" As described above, the present invention is provided with an additional shield made of a material having a radiation shielding performance superior to that of concrete on the inner surface of the bent duct hole formed in the radiation shielding wall made of concrete. In addition, the additional shielding body is incorporated in the radiation shielding wall in a form in which a part of the duct hole is formed along the inner surface on the entrance side from the entrance of the duct hole to the exit via the corner portion on the entrance corner side. Since it is a thing that changes the traveling direction due to scattering etc. and the passage of radiation toward the duct exit is blocked in the middle by the additional shield in addition to the concrete part, the radiation near the duct exit is attenuated, so leakage Generation of radiation dose is suppressed.

Therefore, since the radiation can be shielded without providing a special shielding member outside the radiation shielding wall, there is an effect that the radiation can be sufficiently attenuated without increasing the thickness of the shielding wall.

In addition, since the additional shield is incorporated in the shield wall so as to form a part of the duct hole and the shield wall does not have irregularities, various devices can be easily installed near the shield wall. The shielding performance can be improved with a simple structure without changing the shape of the duct or the wall surface of the shielding wall.

[Brief description of drawings]

1 to 3 show a first embodiment of the present invention, and FIG. 1 is a cross-sectional view showing the arrangement state of an additional shield, and FIG.
FIG. 1 is a sectional view taken along the line II-II in FIG. 1, and FIGS. 3 (a) and 3 (b) are sectional views shown for explaining the action.
Figures (a), (b), and (c) are shown to explain the radiation leakage phenomenon, respectively, and cross-sectional views, and Figures 5 and 6 show the shielding effect of the shielding wall with bent duct holes. 5 is a layout drawing, FIG. 6 is a cross-sectional view thereof, and FIGS. 7 to 9 show the results of an experiment carried out to show the shielding effect. Fig. 7 shows the experimental results when the incident angle is 0 °, Fig. 8 shows the experimental results when the incident angle is 20 °,
Figure 9 shows the experimental results when the incident angle is -20 °.
10 and 11 show a second embodiment of the present invention,
FIG. 10 is a sectional view showing the arrangement of the additional shield, and FIG. 11 is
Sectional views taken along the line XI-XI, FIG. 12 and FIG. 13 show a third embodiment of the present invention, respectively, and FIG. 14 is a sectional view showing a structural example of a conventional bent duct hole. FIG. 15 and FIG. 15 are sectional views shown for explaining the operation. A, B, C, D ... Additional shield, E ... Concrete block, 10 ... Radioactive shielding wall, 11 ... Bent duct hole, 11a ... Inlet side passage, 11b ... Outlet side passage, 20 ... First shield.

Claims (1)

[Claims] 1. An additional shield made of a material having a better radiation shielding performance than concrete is installed on the inner surface of a bent duct hole formed in a concrete radiation shielding wall.
Further, the additional shield is incorporated in the radiation shielding wall in a form of being located on the inner surface of the entrance side from the entrance of the duct hole to the exit through the corner part on the entrance corner side and forming a part of the duct hole. The structure around the once bent duct hole in the radiation shielding wall, which is characterized in that