JP4230067B2 - Radiation shielding facility - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure of a shielding wall that shields radiation generated by a radiation apparatus, and more particularly to a radiation shielding facility that reduces a neutron duct stream in a wiring duct or the like.
[0002]
[Prior art]
In radiation generators such as accelerators, effective radiation protection must be provided to keep the radiation exposure of workers and others as low as possible. The most important aspect of radiation protection is radiation shielding. Since α-rays and β-rays can be easily blocked by substances, it is mainly γ-rays and neutron rays that are targeted when designing a shielding wall.
The shielding wall is designed so that the radiation is sufficiently attenuated in consideration of the generated γ-rays and neutrons and the constituent elements of the wall.
[0003]
However, it is necessary to supply various utilities such as power supply and cooling water to the radiation generator, and the cables and pipes for supplying these utilities are taken into the room where the radiation generator is installed by a duct penetrating the shielding wall. . For this reason, so-called duct streaming that leaks out of the room through a duct penetrating the shielding wall becomes a problem.
Since γ rays travel almost linearly even though they cause scattered rays, it is relatively easy to take measures such as adding local shielding.
However, since neutron rays are absorbed and attenuated mainly due to the interaction with the substance, especially neutrons with low energy pass through the duct like a smoke and leak to the outside, and duct streaming is suppressed. It becomes an important issue.
[0004]
In JP-A-4-346099, a container for containing a shielding material is inserted in a penetration portion of a radiation shielding wall, and when the penetration material such as a cable or a vacuum chamber is applied, the container is removed to remove the penetration material. The structure of the shielding wall penetration part which was filled with the shielding material and returned to the penetration part after construction is disclosed. With this structure, neutron streaming can be accurately prevented when installing cables individually, but neutron leakage is effectively prevented when cable ducts are used for rational construction. I can't.
[0005]
[Problems to be solved by the invention]
Therefore, the problem to be solved by the present invention is to provide a radiation shielding facility in which a radiation stream in a duct penetrating a radiation shielding wall, particularly a neutron duct stream is reduced.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the radiation shielding facility of the present invention is configured such that a part of the radiation shielding wall provided in the radiation generating device room is divided into a plurality of thicknesses necessary for radiation shielding, In a room that passes through the multiple radiation shielding wall portions and is formed in the radiation shielding wall wall, a pit that communicates with the outside is provided parallel to the wall surface, and the duct is accommodated in the pit. And
Moreover, you may make it embed a duct underground.
[0007]
Neutrons leaking through the duct are attenuated in proportion to the short diameter 2 of the cross section of the passage and inversely proportional to the square of the length of the passage.
The pit of the radiation shielding facility of the present invention does not penetrate the radiation shielding wall linearly, but travels in parallel with the wall in the space formed in the radiation shielding wall. The duct to be bent is bent in the vertical direction several times in the radiation shielding wall and then penetrates the shielding wall.
[0008]
Therefore, not only the total length of the duct becomes long, but also the duct is bent vertically, so that it is possible to enjoy the attenuation effect of the duct of the straight line portion connected to the starting point every time it is bent. That is, the attenuation effect is integrated in the form of a product every time the duct is bent.
The radiation shielding wall is obtained by dividing the thickness that can be shielded by itself into an appropriate number, and the total thickness of the wall enables sufficient shielding against γ rays and neutron rays. Moreover, it is not necessary to significantly increase the amount of the shielding wall material.
Furthermore, since the pit is opened in the radiation shielding wall, it is possible to easily cope with a change in wiring.
[0009]
In addition, after accommodating a duct in a pit, the inside of a pit is filled with a neutron shielding material such as paraffin or polyethylene, and can be used with a lid formed of a neutron shielding material. In such a configuration, neutrons are well absorbed and hardly leak out of the radiation generator room. Further, by reducing the space around the duct, the attenuation effect can be further enhanced by utilizing the property that neutrons are attenuated in proportion to the square of the diameter of the narrower one of the cross sections of the transport passage.
Also, if the duct is buried underground, it is possible to easily perform construction with a high shielding effect.
[0010]
Further, a tunnel may be formed instead of the pit and cables may be accommodated in the tunnel. By using an underground tunnel that bends many times in the intermediate chamber as a cable duct, neutron rays are significantly attenuated, so that the neutron duct stream can be easily suppressed to a safe level.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on examples with reference to the drawings.
FIG. 1 is a plan view showing an embodiment of a radiation shielding facility according to the present invention, FIG. 2 is a sectional view of a pit portion, and FIG. 3 is a sectional view showing another aspect of the pit.
As shown in FIG. 1, the radiation generator 1 is disposed in a radiation generator chamber 3 surrounded by a concrete radiation shielding wall 2, and a pit 4 is provided through the radiation shielding wall 2.
[0012]
In the portion of the radiation shielding wall 2 through which the pits 4 penetrate, a space is provided in the shielding wall to form one or a plurality of intermediate chambers 5. The wall that partitions the intermediate chamber 5 is one or more so that the total thickness penetrating from the radiation generator chamber 3 to the outside of the radiation shielding wall 2 is sufficient to shield γ rays and neutron rays. The thickness is distributed to the space. Therefore, compared with the case where radiation shielding is performed with a single shielding wall, the amount of shielding material forming the wall does not increase extremely.
The pit 4 led through the radiation shielding wall 2 into the intermediate chamber 5 is laid so as to be bent vertically in the intermediate chamber 5 and parallel to the wall surface, and the bending point is twice the number of the intermediate chambers. Have
[0013]
The pit 4 accommodates a duct that accommodates power supply wiring, control wiring, cooling piping, and the like in order to supply utilities from outside to indoor devices such as the radiation generator 1.
FIG. 2 is a sectional view of the pit 4 in the intermediate chamber 5. The pits 4 are formed by digging down the floor surface of the intermediate chamber 5 formed between the divided shielding walls 6. A duct 7 is installed in the pit 4, and cables 8 are arranged in the duct 7.
[0014]
The periphery of the duct 7, the bottom portion, the side surface, and the like are filled with a filler 9 formed of a neutron absorbing material so as to close a space formed between the pits 4. As the neutron absorber, polyethylene or paraffin containing a lot of hydrogen atoms is used. The filler 9 may be a neutron absorber formed in a block that matches the shape of the space, but may be in the form of particles.
Also, a lid 10 formed in a block having an appropriate thickness is placed on the duct 7 so as to absorb the neutrons leaking from the duct 7 and suppress the amount leaking to the outside. It has become.
[0015]
The neutron concentration H _n (Sv / h) at the end of the duct 7 divided into n straight portions by the refraction point is expressed by the following equation, where the neutron concentration in the radiation generator chamber 3 is H ₀ (Sv / h). It is known that
H _n = H ₀ (a ₁ / L ₁ ) ² (a ₂ / L ₂ ) ² ... (A _n / L _n ) ² (1)
Here, a is the minor axis length (m) in the cross section of the straight duct, L is the straight line length (m), and the subscript is a number representing the order of the straight line portions.
[0016]
At this time, the duct streaming generally decreases as the number of divisions increases. For example, in the case where the height is obtained by dividing the duct is three when the this by 3m with full length 9m having a width smaller than the constant cross section at 0.5 m, the former ^{_{H 0 0.5 2/9 2 =}} H 0 × 3 latter respect × 10 ^-3 is ^{_{H 0 0.5 6/3 6 =}} H 0 × 2.1 × 10 -5 next duct streaming is small.
Thus, the duct 7 not only increases the length of the duct, but also has an effect of reducing the duct stream because the number of inflection points increases.
[0017]
Further, when it is necessary to change the installed cables 8, an operator enters the intermediate chamber 5, removes the cover material 10 and the filler 9, digs the duct 7, and exposes the cables 8. Can be constructed.
It should be noted that by installing a radiation shielding door at a position where the pit 4 passes through the wall of the intermediate chamber 5, the upper surface of the pit 4 can always appear on the ground surface. Such a structure makes it very easy for workers to enter and dig out cables.
[0018]
The structure of the intermediate chamber 5 in this embodiment has an advantage that the construction cost does not increase even when the shielding wall 2 is formed of expensive materials such as special radiation shielding concrete or lead.
It is to be noted that the main body of the measuring instrument that may be damaged by strong radiation when installed in the radiation generator chamber 3 prevents the radiation from being disturbed by performing measurement processing near the detection end. It is also possible to perform measurement with high accuracy. For example, many measuring devices such as an electron beam bunch measuring device, a stroke camera, a spectroscope, and the like are preferably arranged close to the measuring device main body and the detection end.
Moreover, the radiation monitor 11 can be provided in the intermediate | middle chamber 5 for management of the exposure of a worker, and confirmation of the shielding effect.
[0019]
In addition, as shown in FIG. 3, after laying the cables 8 in the duct 7, the duct 7 may be covered with a lid, and then the pit 4 may be backfilled with sand 12 so as to have the same level as the floor surface. In such a structure, it takes a little time to dig out the duct 7, but there is an advantage that a special material is not required for the construction material and the initial laying of cables can be easily performed.
[0020]
Further, instead of the pit 4, a tunnel can be formed and used. The tunnel is dug perpendicularly to the floor of the radiation generator room, bent in the horizontal direction in the ground, bent at the position of the intermediate room to form a zigzag passage, passed through the middle chamber, and outside the radiation generator room. Form to stand up at. A manhole for facilitating entry is provided in the refractive part of the intermediate chamber.
Using such a refracted tunnel structure and connecting cables directly to it increases the number of bends in the passage, and because it is deep underground, the rise to the ground is long, so it is filled with neutron absorbers There is also little need to do. Since neutron rays are effectively attenuated in the refracted tunnel, the duct stream can be effectively suppressed.
[0021]
【The invention's effect】
As described above, the radiation shielding facility of the present invention can reduce the neutron duct stream in the duct penetrating the radiation shielding wall without significantly increasing the material forming the radiation shielding wall, and It can be installed easily when re-installation becomes necessary.
[Brief description of the drawings]
FIG. 1 is a plan view showing an embodiment of a radiation shielding facility according to the present invention.
FIG. 2 is a cross-sectional view showing a pit portion in the present embodiment.
FIG. 3 is a cross-sectional view showing another aspect of pits in the present embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Radiation generator 2 Radiation shielding wall 3 Radiation generator room 4 Pit 5 Intermediate room 6 Radiation shielding wall 7 Duct 8 Cables 9 Filling material 10 Lid material 11 Radiation monitor 12 Filling sand

Claims (4)

A part of the radiation shielding wall provided in the radiation generator room is divided into three or more by dividing the thickness necessary for radiation shielding to form two or more rooms in the wall of the radiation shielding wall , A pit that communicates the inside and outside of the radiation generator chamber is formed into a shape that passes through the two or more rooms and is bent so as to be parallel to the wall surface in the two or more rooms. A radiation shielding facility characterized by storing   The radiation shielding facility according to claim 1, wherein the pit is filled with a neutron shielding material and covered with a lid formed of a neutron shielding material.   The radiation shielding facility according to claim 1, wherein the duct is embedded. A part of the radiation shielding wall provided in the radiation generator room is divided into three or more by dividing the thickness necessary for radiation shielding to form two or more rooms in the wall of the radiation shielding wall , An underground tunnel connecting the inside and the outside of the radiation generator room is formed into a shape that passes through two or more rooms and is bent so as to be parallel to the wall surface in the two or more rooms. A radiation shielding facility characterized by containing cables.

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