JP6656440B1 - Activation suppression structure and wall management method - Google Patents

Abstract

An object of the present invention is to solve the problem of the prior art, that is, an activation suppressing structure capable of suppressing the activation of the wall in the neutron generation chamber with a higher effect than the prior art. Is to provide. SOLUTION: The activation suppressing structure of the present invention is a structure for suppressing activation of a wall that closes the neutron generation chamber, and includes a first shield 110. Further, the activation suppression structure of the present invention may include the first shield 110 in which the intermediate plate 112 and the back plate 113 are laminated. The back plate 113 is a thin film (or plate) member containing a boron compound such as boron carbide. In this case, the first shield 110 is installed on the front surface of the wall body so that the back plate 113 faces the wall body. [Selection diagram] FIG.

Description

  The present invention relates to a technique for suppressing the activation of a wall in a room such as a radiation medical facility or a research facility where neutrons are generated, such as neutron capture therapy (BNCT: Boron Neutron Capture Therapy), and more specifically. The present invention relates to an activation suppression structure provided with a shield including wood and a boron-containing plate, and a method for managing activation of a wall provided with this structure.

  Neutron capture therapy is a treatment method in which a boron compound is incorporated into cancer cells and the cancer cells are destroyed by a nuclear reaction between the boron and neutrons. Boron (especially 10B) has the property of reacting strongly with low-energy neutrons such as thermal neutrons. As a result of the nuclear fission reaction between boron and neutrons in cancer cells, particle beams (alpha rays) are generated. Destroy cancer cells by lines.

  The range of the particle beam generated by the nuclear fission reaction is about the diameter of a cancer cell (about 10 to 14 μm) and does not affect normal cells other than the cancer cell. Neutron capture therapy is also called "selective cancer cell therapy" because conventional X-ray and gamma-ray treatments cause almost the same physical damage to normal cells as cancer cells, especially for malignant brain tumors and malignant melanomas. It is currently considered the most ideal treatment for treatment.

  By the way, in neutron capture therapy, a patient is irradiated with neutron rays using an irradiator, an accelerator, or the like. Naturally, this irradiation is performed in a room closed with a wall or the like so that the neutron rays do not leak outside. Of course, not all the irradiated neutron beams are absorbed by the patient, and are partially absorbed by the wall and the like. Since neutrons have no charge, they can relatively easily reach nuclei in a substance, and the absorption phenomena of low-energy neutrons that are suitably used in neutron capture therapy are remarkable. Then, as a result of the absorption of neutrons, a part of the material constituting the wall may cause a so-called activation phenomenon in which stable isotopes are converted to radioisotopes.

  It is known that concrete activated by short-lived nuclides emits a large amount of radiation. Therefore, those who are indoors receive unnecessary exposure. Also, when neutrons are irradiated for many years, concrete walls are activated, and long-lived nuclides are generated in large quantities. As a result, the activated concrete walls are disposed of as radioactive waste. Required, resulting in higher disposal costs than ordinary waste.

  As described above, in a facility or the like where neutrons causing activation are generated, activation of a wall has been one of the major problems. Therefore, Patent Document 1 discloses an invention that suppresses activation of a concrete wall by a neutron shielding structure including a shielding body made of a boron-containing resin and an attenuation space.

Japanese Patent No. 6349574

  In the invention proposed in Patent Document 1, the neutrons are absorbed by a shield (containing boron) installed on the indoor side, and the neutrons that have passed through the shield are attenuated (the space formed between the shield and the wall). ), Thereby suppressing the activation of the concrete wall.

  The invention of Patent Document 1 can also be expected to have an extremely high activation suppression effect. However, when the inventors of the present application have researched and developed a higher activation suppression effect, they use wood as a shield. Was found to be effective. Wood, particularly hard wood having a large specific gravity such as purple heart or ipe (hereinafter, referred to as “hard wood”) contains a large amount of hydrogen. Materials containing a large amount of hydrogen have a high ability to slow down fast neutrons, and the slowed down neutrons reach thermal equilibrium with the surroundings and become thermal neutrons (so-called elastic scattering). In other words, neutrons are converted into thermal neutrons when passing through wood containing a large amount of hydrogen, and the thermal neutrons are absorbed by the boron-containing shield, whereby a higher activation suppression effect can be obtained. In addition, since wood containing a large amount of hydrogen can attenuate neutrons, in the case of a small amount of neutrons, it is possible to suppress the activation of the concrete wall.

  On the other hand, even if the activation of the concrete wall is suppressed by using a shield or the like, it is considered that a part of the wall is actually activated. However, in the conventional activation suppression technology, after installing a shield or the like (that is, after countermeasures), it is not very often that the activation state of the concrete wall is inspected or confirmed. In order to avoid unnecessary exposure of people indoors and to minimize the emission of radioactive waste, even after taking measures to suppress activation, the situation of activation of concrete walls was confirmed. Depending on the situation, it is desirable to take some measures at an early stage.

  An object of the present invention is to solve the problems of the related art, that is, to suppress the activation of a wall in a neutron generation chamber (a room where neutrons are generated) with a higher effect than the related art. It is to provide a possible activation suppression structure. Another object of the present invention is to provide a technique capable of confirming the state of activation of a wall body even after measures for suppressing activation.

  The present invention uses wood containing a large amount of hydrogen, and a member containing a boron compound such as boron carbide to suppress the activation of the wall inside the neutron generation chamber, and furthermore, the first shield and The second shield is installed, and at the same time, the presence or absence of activation of the wall is evaluated based on the measurement result of the measuring element to determine whether the second shield needs to be replaced. , Based on unprecedented ideas.

  The activation suppression structure of the present invention is a structure that suppresses activation of a wall that closes a room in which neutrons are generated, and includes a first shield made of an intermediate plate. Note that a plate-like member using wood is used as the intermediate plate. Then, the first shield is installed on the front surface of the wall.

  The activation suppression structure of the present invention may include a first shield in which a surface plate and an intermediate plate are stacked. Note that a plate-like member is used as the surface plate. In this case, the first shield is installed on the front surface of the wall so that the surface plate is on the indoor side.

  The activation suppression structure of the present invention may include a first shield in which an intermediate plate and a back plate are stacked. The back plate is a thin film (or plate) member containing a boron compound such as boron carbide. In this case, the first shield is installed on the front surface of the wall so that the back plate faces the wall.

  The activation suppression structure of the present invention may have a structure further including a gap provided between the first shield and the wall.

  The activation suppression structure of the present invention may be configured to further include a second shield disposed between the gap and the wall. The second shield is a plate-shaped member and is installed so as to be replaceable, and a measuring element for evaluating the degree of activation is installed on the indoor side surface of the second shield. .

  The activation suppression structure of the present invention may be a structure including an inspection hole and a plurality of inspection cores. The inspection hole penetrates the second shield and is further drilled in the thickness direction of the wall, and the inspection core is formed of the same material as the wall, and is provided in the inspection hole. They are arranged side by side in the thickness direction of the wall.

  The wall management method of the present invention is a method for evaluating activation of a wall on which an activation suppression structure is installed, and includes a radiation evaluation step and an exchange determination step. In this activation evaluation step, the presence or absence of activation of the wall is evaluated based on the measurement result of the measuring element, and in the replacement determination step, whether or not replacement of the second shield is necessary according to the evaluation result of the activation evaluation step. Is determined.

  The wall management method of the present invention may be a method further including a core inspection step. In the core inspection step, when it is evaluated that the wall is activated, the inspection core is extracted and the extracted inspection core is inspected. In this case, in the replacement determination step, the necessity of replacement of the second shield is determined according to the evaluation result of the activation evaluation step and the inspection result of the core inspection step.

The activation suppression structure and the wall management method of the present invention have the following effects.
(1) The neutrons are converted to thermal neutrons when passing through wood containing a large amount of hydrogen, and the thermal neutrons are absorbed by a boron-containing shield, so that the wall is more effectively compared to the conventional technology. Activation can be suppressed. As a result, unnecessary exposure of a person in the neutron generation room can be reliably avoided, and emission of radioactive waste can be suppressed as much as possible.
(2) The degree of activation can be confirmed at an arbitrary timing even after the activation suppression structure is installed, and the second shield can be replaced before activation. This can prevent the second shield from becoming radioactive waste.
(3) It is possible to provide a clean medical facility, a research facility, an inspection facility, an industrial facility, and the like that have high cost rationality throughout the entire life cycle and do not generate radioactive waste.

The top view showing the situation where the activation control structure of the present invention was installed in the neutron generation room. FIG. 2 is a cross-sectional view illustrating the activation suppression structure according to the first embodiment. Sectional drawing which shows the activation suppression structure in 2nd Embodiment. Sectional drawing which shows the activation suppression structure in 3rd Embodiment. The flowchart which shows the main process of the wall management method of this invention. The step figure showing the main steps of the wall management method of the present invention.

1. Overall Overview An example of an embodiment of an activation suppression structure and a wall management method of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing a situation where the activation suppression structure 100 of the present invention is installed in a neutron generation chamber. The neutron generation chamber shown in this figure is closed (closed) with a concrete wall (hereinafter simply referred to as “concrete wall CW”), and an accelerator ND for generating neutrons is installed in the room. Although FIG. 1 shows the neutron generation chamber in which the accelerator ND is installed, the present invention can be effectively implemented in any facility that generates neutrons, not limited to the accelerator ND.

  In the activation suppression structure 100 of the present invention, as shown in FIG. 1, a first shield 110 is installed on the indoor side (front surface) of a concrete wall CW, in other words, so as to cover the surface of the concrete wall CW. Structure. Further, in the activation suppression structure 100, the first shield 110 is installed after securing a predetermined distance from the surface of the concrete wall CW, that is, a space (between the concrete wall CW and the first shield 110). Hereinafter, it may be referred to as “void 120”). Further, as shown in FIG. 1, a structure in which a second shield 130 is provided between the concrete wall CW and the gap 120 may be adopted.

  The first shield 110 includes wood (for example, a hard board or the like) or a boron compound-containing member such as boron carbide, attenuates neutrons with wood, and further converts neutrons into thermal neutrons when passing through wood. By changing the thermal neutrons into boron, the neutrons reaching the concrete wall CW are greatly reduced. The gap 120 has a function of attenuating the energy of neutrons by securing a predetermined distance to reach the concrete wall CW. Further, the second shield 130 absorbs neutrons reaching the concrete wall CW. The second shield 130 is installed so that it can be easily replaced, and when it is recognized that activation has progressed in the future, it is planned to replace it with a new second shield 130, so to speak, concrete wall. It also functions as a protective material for CW.

2. Next, an example of the activation suppression structure 100 of the present invention will be described in detail with reference to the drawings. The wall management method of the present invention is a management method performed on the activation suppression structure 100 of the present invention. Therefore, the activation suppression structure 100 of the present invention will be described first, and then the wall management of the present invention will be described. The method will be described.

  As described above, the activation suppression structure 100 of the present invention includes a form in which the first shield 110 is directly installed on the surface of the concrete wall CW (hereinafter, referred to as a “first embodiment”), and a concrete wall. A mode in which the gap 120 and the first shield 110 are installed on the front surface of the CW (hereinafter, referred to as a “second embodiment”), and the second shield 130, the gap 120, and the front surface of the concrete wall CW. It can be broadly classified into a mode in which the first shield 110 is installed (hereinafter, referred to as a “third embodiment”). Hereinafter, each embodiment will be sequentially described.

(First embodiment)
FIG. 2 is a cross-sectional view illustrating the activation suppression structure 100 according to the first embodiment, and is a cross-sectional view of a concrete wall CW that forms a floor surface, cut along a vertical plane. In this figure, the first shield 110 is installed on the upper surface of the concrete wall CW that forms the floor surface. However, the activation suppression structure 100 of the present invention is not limited to the floor surface and forms the ceiling surface and side surfaces. It is also possible to adopt a structure in which the first shielding body 110 is installed on the front surface of the concrete wall body CW.

  The first shield 110 includes an intermediate plate 112, and may have a laminated structure of a front plate 111 and an intermediate plate 112, or a front plate 111 and an intermediate plate 112, and a back plate 113 as shown in FIG. , And is a plate-like member having an extremely large surface area as compared with the thickness dimension (vertical dimension in FIG. 2). Among them, the surface plate 111 is a plate-shaped member using a plaster plaster board or a dolomite plaster board, and the intermediate plate 112 is a plate-shaped wooden member using hardwood such as purple heart or ipe. The reason why hard wood or the like is used as the intermediate plate 112 is that it contains a large amount of hydrogen for elastically scattering neutrons, and has a considerable strength (shear force, compressive force, tensile force) as the first shield 110. Power, etc.). The intermediate plate 112 can be a member having a higher strength than the surface plate 111, or a member having a lower strength than the surface plate 111. When the activation suppression structure 100 is installed on a wall or a ceiling, the surface plate 111 of the first shield 110 may use a quasi-noncombustible material or a noncombustible material.

  One back plate 113 is a thin film or plate member made of a boron-containing resin, and for example, a member formed by molding a resin containing B4C can be used. Of course, if the resin material containing boron is not limited to the B4C resin, another resin material such as a member in which boric anhydride is mixed with the resin or a member in which powdered borax is mixed with the resin may be used as the back plate 113. Can also be used. By the way, as described above, wood containing a large amount of hydrogen can attenuate neutrons. That is, even the intermediate plate 112 alone has an effect of attenuating neutrons, and in the case of a small amount of neutrons, the activation of the concrete wall CW can be suppressed. Therefore, when the activation suppression structure 100 is installed in the neutron generation chamber in which a small amount of neutrons are expected to be generated, the first shield 110 omitting the back plate 113, that is, the first shield 110 including the front plate 111 and the intermediate plate 112 The shield 110 or the first shield 110 composed of only the intermediate plate 112 can be used.

  The first shield 110 is installed using a screw, a nail, an adhesive, or the like so that the front plate 111 is on the indoor side and the back plate 113 is on the concrete wall CW side as shown in FIG. . As a result, the neutrons that have reached the intermediate plate 112 through the surface plate 111 are decelerated by a large amount of hydrogen contained in the hardwood or the like, and the decelerated neutrons reach thermal equilibrium with the surroundings and become thermal neutrons (so-called elastic scattering). Then, the thermal neutrons that have reached the back plate 113 are absorbed by boron, so that the amount of neutrons that reach the concrete wall CW is significantly suppressed, that is, the activation of the concrete wall CW is suppressed. .

(Second embodiment)
FIG. 3 is a cross-sectional view illustrating the activation suppression structure 100 according to the second embodiment, and is a cross-sectional view of a concrete wall CW that forms a floor surface, cut along a vertical plane. As shown in this figure, the activation suppression structure 100 according to the second embodiment includes a gap 120 in addition to the first shield 110. In the case of a neutron generation chamber in which a large amount of neutrons are generated, all the neutrons may not be absorbed by the first shield 110, and the neutrons transmitted through the first shield 110 are attenuated by the gap 120. The gap 120 can be formed by arranging a spacer between the concrete wall CW and the first shield 110. For example, the gap can be formed by arranging the spacers discretely (scattered arrangement) at a plurality of locations. The gap 120 may be formed by arranging the gap 120 in a linear or lattice shape using a section steel such as a channel steel or an H-section steel.

  By providing the void 120, neutrons that have not passed through the first shield 110 without being absorbed by the back plate 113 are forced to move a predetermined distance until they reach the concrete wall CW, whereby energy of the neutrons is reduced. Attenuation, that is, activation of the concrete wall CW is suppressed.

(Third embodiment)
FIG. 4 is a cross-sectional view illustrating the activation suppression structure 100 according to the third embodiment, and is a cross-sectional view of a concrete wall body CW that forms a side wall, cut along a horizontal plane. As shown in the figure, the activation suppression structure 100 according to the third embodiment includes a second shield 130 in addition to a first shield 110 and a gap 120. The second shield 130 is a plate-like member such as a RC (Reinforced Concrete) panel, is arranged so as to be in contact with the surface of the concrete wall CW, and is installed so as to be easily replaced by using an anchor bolt or the like. Is done.

  As shown in FIG. 4, a gap 120 is formed on the indoor side of the second shield 130, and the first shield 110 is further installed on the indoor side. Then, a measuring element 140 is attached to a part of the surface of the second shield 130 so as to be located in the gap 120. The measuring element 140 can obtain a measured value for evaluating the degree of activation, and can be manufactured as a dedicated element, or a conventionally used element (for example, a commercially available one) Can also be used.

  Although the thermal neutrons are absorbed by the back plate 113 of the first shield 110 and the energy of the neutrons is attenuated by the voids 120, some neutrons may reach the concrete wall CW. In the example, the second shield 130 is further provided on the front surface of the concrete wall CW. However, if the second shield 130 continues to receive neutrons for a long time, the second shield 130 may be activated and must be treated as radioactive waste. Therefore, the structure is such that the second shield 130 can be replaced before activation. Therefore, the measuring element 140 is installed so that the degree of activation of the second shield 130 can be periodically grasped. That is, the shield 130 is installed in a replaceable manner.

  Further, in the activation suppression structure 100 according to the third embodiment, an inspection hole 150 can be provided as shown in FIG. A plurality (four in the figure) of inspection cores 160 are arranged in the inspection holes 150. The inspection hole 150 is formed by connecting a through hole formed in the second shield 130 and a horizontal hole formed by drilling the concrete wall CW in the thickness direction to form a series of continuous holes. , Or at one or more locations.

  The inspection core 160 is a specimen for inspecting the degree of activation of the concrete wall CW just in case, and therefore, the inspection core 160 is formed of a material equivalent to the concrete wall CW. Also, a plurality of inspection cores 160 are arranged side by side in the depth direction of the concrete wall CW so that the degree of activation according to the depth direction (wall thickness direction) of the concrete wall CW can be confirmed.

3. Next, the wall management method of the present invention will be described with reference to FIGS. The wall management method of the present invention is a management method performed for the activation suppression structure 100 described above. Therefore, the description overlapping with the contents described in the activation suppression structure 100 will be avoided, and the wall management method of the present invention will be described. Only the contents specific to the body management method will be described. That is, the contents not described here are the same as those described in “2. Activation suppression structure”.

  FIG. 5 is a flowchart showing main steps of the wall management method of the present invention, and FIG. 6 is a step diagram showing main steps of the wall management method of the present invention. First, as shown in FIG. 6A, the core CR inserted into the confirmation hole HC provided in the first shield 110 is removed (Step 101), and the state shown in FIG. The measured value of 140 is confirmed (Step 102). When the measurement result of the measuring element 140 is obtained, the presence or absence of activation of the concrete wall CW is evaluated based on the result (Step 103), and when activation is not recognized, the core CR is returned into the confirmation hole HC (Step 109). ). On the other hand, if activation is observed, a core inspection is performed to evaluate the depth of activation. Specifically, as shown in FIG. 6C, after removing the first shield 110, the inspection core 160 is extracted (Step 104), and a predetermined inspection is performed on the extracted inspection core 160 (Step 105). ). Then, based on the measurement result of the measuring element 140 and the inspection result of the inspection core 160, it is determined whether or not the replacement of the second shield 130 is necessary (Step 106).

  If it is determined that the replacement of the second shield 130 is not necessary, the inspected inspection core 160 is placed in the inspection hole 150 (Step 109). On the other hand, when it is determined that the second shield 130 needs to be replaced, the first shield 110 and the existing second shield 130 are removed as shown in FIG. The shield 130 is installed (Step 107). When the second shield 130 is replaced, the inspection core 160 inspected as shown in FIG. 6E is put in the inspection hole 150, and the first shield 110 is returned as shown in FIG. 6F. (Step 109). At this time, of the inspection cores 160 that have been inspected, those whose activation has been recognized may be replaced with new inspection cores 160 and then housed in the inspection holes 150 (Step 108).

  The activation suppression structure of the present invention, and the wall management method, proton therapy and heavy ion beam therapy, including medical facilities in which neutrons such as neutron capture therapy occurs, research facilities, inspection facilities, industrial facilities, etc., especially It can be used effectively. The present invention solves the problems that neutron-generating facilities currently face, that is, promotes the spread of particle beam cancer treatment, reduces unnecessary exposure of radiation workers, and generates radioactive waste. In view of the above, the invention of the present application is an invention which can be expected to make a great contribution not only to industrial use but also to society.

Reference Signs List 100 activation suppression structure of the present invention 110 first shield (of activation suppression structure) 111 top plate (of first shielding) 112 intermediate plate (of first shielding) 113 back plate (of first shielding) 120 Void (of activation suppression structure) 130 Second shield (of activation suppression structure) 140 Measurement element (of activation suppression structure) 150 Inspection hole (of activation suppression structure) 160 (of activation suppression structure) Inspection core HC Confirmation hole ND accelerator CR Core (in the confirmation hole) CW Concrete wall

Claims (7)

In the structure that suppresses the activation of the wall that closes the room where neutrons are generated,
A first shield installed on a front surface of the wall,
A gap provided between the first shield and the wall,
A second shield disposed between the gap and the wall,
The second shield is a plate-shaped member, is installed so as to be replaceable,
On the indoor side surface of the second shield, a measuring element for evaluating the degree of activation was installed.
An activation suppression structure, characterized in that: The first shield includes a plate-shaped intermediate plate using wood,
The activation suppression structure according to claim 1, wherein: The first shield is formed by stacking a plate-shaped surface plate and the intermediate plate,
The first shield was installed such that the surface plate was on the indoor side,
3. The activation suppression structure according to claim 2, wherein: The first shield is formed by stacking the intermediate plate and the back plate,
The back plate is a thin or plate-like member containing a boron compound,
The first shield was installed such that the back plate was on the wall side,
The activation suppression structure according to claim 2 or 3, wherein: An inspection hole penetrating the second shield, and further drilled in the thickness direction of the wall;
A plurality of inspection cores installed in the inspection hole,
The inspection core is formed of a material equivalent to the wall body,
Further, the plurality of inspection cores are arranged side by side in the thickness direction of the wall body,
The activation suppression structure according to any one of claims 1 to 4, wherein: In a method for evaluating activation of a wall closing a room where neutrons are generated,
The activation suppression structure according to any one of claims 1 to 4, which is provided on a surface side of the wall body,
An activation evaluation step of evaluating the presence or absence of activation of the wall based on the measurement result of the measurement element,
An exchange determination step of determining whether or not the second shield needs to be replaced, according to the evaluation result of the activation evaluation step;
A wall management method, comprising: The activation suppression structure includes an inspection hole that penetrates through the second shield and is further drilled in a thickness direction of the wall, and a plurality of inspection cores installed in the inspection hole,
The inspection core is formed of the same material as the wall, and is arranged side by side in the thickness direction of the wall,
A core inspection step of extracting the inspection core and inspecting the inspection core when the wall is evaluated to be activated in the activation evaluation step,
In the replacement determination step, according to the evaluation result of the activation evaluation step, and the inspection result of the core inspection step, determine whether the second shield needs to be replaced,
The method for managing a wall according to claim 6, wherein:

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