Method of and analysis device for evaluating reduction rate of radiation leakage dose of reinforcing bar

Abstract

To provide a method and an analysis device, each enabling a reduction rate of radiation leakage dose of a reinforcing bar of a reinforced-concrete shield to be easily evaluated.SOLUTION: In a method of evaluating a reduction rate of radioactive-ray leakage dose on a reinforcing bar includes: defining as variables at least one or more of elements of radioactive-ray energy irradiated from a surface source 20 to a reinforced-concrete shield wall 10, a diameter of a reinforcing bar and an arrangement pitch of reinforcing bars; determining a radioactive-ray leakage dose of a concrete shield wall not arranged with reinforcing bars and a radioactive-ray leakage dose of a reinforced-concrete shield wall 10 arranged with reinforcing bars in the concrete shield wall, by a three-dimensional Monte Carlo transport calculation code of radioactive rays; determining a reduction rate of radioactive-ray leakage dose of the reinforced-concrete shield wall 10 relative to the radioactive-ray leakage dose of the concrete shield wall; and evaluating the reduction rate of radioactive-ray leakage dose with the reinforcing bars based on a relation of the reduction rate of radioactive-ray leakage dose of the reinforced-concrete shield wall 10 to the one or more elements.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and an analysis device for evaluating the radiation leakage dose reduction rate of reinforcing bars, which can easily evaluate the shielding effect of reinforcing bars in a reinforced concrete shielding wall. [Background technology]

[0002] Concrete walls are usually installed to shield radiation in hospital linac rooms, radiation sterilization facilities, and other radiation-using facilities (see Patent Document 1). The thickness and structure of these concrete walls must be evaluated and appropriately set in consideration of the type, amount, and energy of the radiation used, so that the effective leakage dose (leakage dose) is below the dose limit regulated by the Act on the Control of Radioactive Isotopes, etc.

[0003] Here, the shielding walls of radiation facilities that use X-rays and gamma rays are made of concrete. Compared to iron or lead, concrete has lower shielding performance against X-rays and gamma rays per unit thickness, but by making the concrete thicker, it can provide sufficient shielding. Concrete is cheaper and easier to work than iron, so it has a cost advantage even when made thick. Since shielding walls are generally several tens of centimeters to several meters thick, double reinforcing bars (two layers, one on the inside and one on the outside of the shielding wall) are used to prevent cracks in the reinforced concrete and increase the structural strength.

[0004] The thickness of this shielding concrete wall against X-rays and gamma rays can be evaluated using three methods: an effective dose transmittance table for photons generated from radioactive isotopes, a simple calculation formula, and a radiation transport calculation method. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-151617 Summary of the Invention [Problem to be solved by the invention]

[0006] Meanwhile, reinforced concrete shielding walls have rebar in two layers, on the inside and outside of the wall. Furthermore, because the position and lattice shape of the rebar are localized when viewed from the perspective of the entire wall, it is difficult to properly incorporate rebar elements into concrete, which is treated as a homogeneous material. Furthermore, the exact locations where the rebar will be installed cannot be determined at the design stage, and only the approximate number is known. The exact locations can only be determined after the rebar has actually been installed on-site. Furthermore, when designing the shielding wall to determine its thickness, there is no information on the exact locations of the rebar.

[0007] Generally, deformed steel bars are used for the reinforcing bars in shielding walls, and although they contain about 2 wt% of impurity elements such as Mn and C, these amounts are so small that they can be considered to be iron. Iron has a higher shielding ability against X-rays and gamma rays than concrete, and can reduce leakage doses. Therefore, if reinforcing bars could be incorporated into shielding walls and evaluated, they would be able to block X-rays and gamma rays better, but because there was no easy way to incorporate them, safety assessments were made by ignoring the reinforcing bars and overestimating the leakage dose.

[0008] While it is possible to simulate lattice-shaped rebars using a 3D Monte Carlo transport calculation code, a radiation transport calculation method, modeling each individual rebar in a lattice-shaped shielding wall several meters to several tens of meters long and incorporating it into a calculation system is impractical and has not been implemented. For example, if a 10-m-long, 3-m-high shielding wall incorporates lattice-shaped rebars with a 0.2-m pitch, the rebars would be in two layers, inside and outside, so 50 × 2 = 100 vertical rebars and 15 × 2 = 30 horizontal rebars would need to be modeled. If this shielding wall has five surfaces (four side walls and one ceiling), modeling approximately 650 rebars would require a significant amount of effort. Therefore, modeling rebars is not currently implemented, partly because the actual shielding effect of the rebars is unknown. Furthermore, when modeling rebars, changing the thickness of the shielding wall requires changing the position of the corresponding rebars.

[0009] The present invention has been made in view of the above, and aims to provide a method and an analysis device for evaluating the radiation leakage dose reduction rate of reinforcing bars, which can easily evaluate the shielding effect of the reinforcing bars in a reinforced concrete shielding wall. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the object, the method for evaluating the reduction rate of radiation leakage dose from reinforcing bars according to the present invention is a method for evaluating the reduction rate of radiation leakage dose from reinforcing bars arranged in a reinforced concrete shielding wall from a surface radiation source, and is characterized in that at least one of the elements of the radiation energy irradiated to the reinforced concrete shielding wall, the reinforcing bar diameter of the reinforcing bars, and the reinforcing bar arrangement pitch are used as variables, and a three-dimensional Monte Carlo radiation transport calculation code is used to calculate the radiation leakage dose of a concrete shielding wall without reinforcing bars and the radiation leakage dose of a reinforced concrete shielding wall with reinforcing bars arranged in the concrete shielding wall, and the reduction rate of the radiation leakage dose from the reinforced concrete shielding wall with respect to the radiation leakage dose of the concrete shielding wall is calculated, and the reduction rate of the radiation leakage dose from the reinforcing bars is evaluated based on the relationship between the reduction rate of the radiation leakage dose from the reinforced concrete shielding wall with respect to the one or more elements.

[0011] In addition, the method for evaluating the reduction rate of radiation leakage dose from reinforcing bars according to the present invention is characterized in that, in the above invention, the reinforcing bar pitch is set as a constant, the radiation energy or the reinforcing bar diameter is set as a variable, and the reinforcing bar diameter or the radiation energy is set as a parameter, respectively, to determine the relationship between the reduction rate of radiation leakage dose and the radiation energy or the reinforcing bar diameter, and to identify the reinforcing bar diameter that satisfies the desired reduction rate for the radiation energy.

[0012] Furthermore, the method for evaluating a radiation leakage dose reduction rate of reinforcing bars according to the present invention is a method for evaluating a radiation leakage dose reduction rate of reinforcing bars arranged in a reinforced concrete shielding wall, characterized in that the method uses as variables at least one of the following elements: radiation energy irradiated from a point radiation source to the reinforced concrete shielding wall, the reinforcing bar diameter of the reinforcing bars, the reinforcing bar arrangement pitch of the reinforcing bars, the distance between the reinforced concrete shielding wall and the point radiation source, and the vertical projection position of the point radiation source onto the reinforced concrete shielding wall; calculates the radiation leakage dose of a concrete shielding wall without reinforcing bars and the radiation leakage dose of a reinforced concrete shielding wall with reinforcing bars arranged in the concrete shielding wall using a three-dimensional Monte Carlo radiation transport calculation code; calculates the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to the radiation leakage dose of the concrete shielding wall; and evaluates the reduction rate of the radiation leakage dose due to the reinforcing bars based on the relationship between the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to the one or more elements.

[0013] Furthermore, the method for evaluating the reduction rate of radiation leakage dose from reinforcing bars according to the present invention is characterized in that, in the above invention, the vertical projection position of the point radiation source onto the reinforced concrete shielding wall, the radiation energy, and the reinforcing bar pitch are constants, the distance between the reinforced concrete shielding wall and the point radiation source is a variable, and the reinforcing bar diameter is a parameter, the relationship between the reduction rate of radiation leakage dose and the distance is determined, and the reinforcing bar diameter that satisfies the desired reduction rate for the distance is specified.

[0014] Furthermore, the method for evaluating the radiation leakage dose reduction rate of reinforcing bars according to the present invention is characterized in that, in the above invention, the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is a reinforcing bar lattice intersection.

[0015] Furthermore, the method for evaluating the reduction rate of radiation leakage dose from reinforcing bars according to the present invention is characterized in that, in the above invention, when the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is a position other than a reinforcing bar lattice intersection and the distance between the reinforced concrete shielding wall and the point radiation source is 100 cm or more, the reinforcing bar diameter that satisfies the desired reduction rate for the distance is specified using the relationship of the reduction rate of radiation leakage dose for the distance when the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is at a reinforcing bar lattice intersection.

[0016] Furthermore, the method for evaluating the reduction rate of radiation leakage dose from reinforcing bars according to the present invention is characterized in that, in the above invention, the distance between the reinforced concrete shielding wall and the point radiation source, the vertical projection position of the point radiation source onto the reinforced concrete shielding wall, and the reinforcing bar pitch are constants, the radiation energy or the reinforcing bar diameter is a variable, and the reinforcing bar diameter or the radiation energy is a parameter, respectively, to determine the relationship between the reduction rate of radiation leakage dose and the radiation energy or the reinforcing bar diameter, and to specify the reinforcing bar diameter that satisfies the desired reduction rate for the radiation energy.

[0017] Furthermore, the method for evaluating the radiation leakage dose reduction rate of reinforcing bars according to the present invention is characterized in that, in the above invention, when the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is set to a reinforcing bar grid intersection, the position of the reinforcement is displayed on the front surface of the reinforced concrete shielding wall.

[0018] Furthermore, the method for evaluating the radiation leakage dose reduction rate of reinforcing bars according to the present invention is characterized in that, in the above invention, the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is set to a reinforcing bar lattice intersection, and if the reinforcing bars passing through the reinforcing bar lattice intersection are made thicker than the other reinforcing bars, the reinforcing bar arrangement positions of the thicker reinforcing bars are displayed on the front surface of the reinforced concrete shielding wall.

[0019] Furthermore, the method for evaluating the radiation leakage dose reduction rate of reinforcing bars according to the present invention is characterized in that, in the above invention, the reinforcing bars are arranged on the front surface of the concrete shielding wall on the radiation irradiation side and the rear surface on the radiation leakage side.

[0020] The analysis device according to the present invention is an analysis device for evaluating a rate of reduction in radiation leakage dose from reinforcing bars arranged in a reinforced concrete shielding wall, and is characterized by comprising an analysis unit that uses as variables at least one of the elements of radiation energy irradiated from a surface radiation source to the reinforced concrete shielding wall, the reinforcing bar diameter of the reinforcing bars, and the reinforcing bar arrangement pitch, and calculates the radiation leakage dose of a concrete shielding wall without reinforcing bars and the radiation leakage dose of a reinforced concrete shielding wall with reinforcing bars arranged in the concrete shielding wall using a three-dimensional Monte Carlo radiation transport calculation code, calculates the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to the radiation leakage dose of the concrete shielding wall, and evaluates the reduction rate of the radiation leakage dose due to the reinforcing bars based on the relationship between the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to the one or more elements.

[0021] Furthermore, an analysis device according to the present invention is an analysis device for evaluating a rate of reduction in radiation leakage dose from reinforcing bars arranged in a reinforced concrete shielding wall, and is characterized in that the analysis device uses as variables at least one of the following elements: radiation energy irradiated from a point radiation source to the reinforced concrete shielding wall, the reinforcing bar diameter of the reinforcing bars, the reinforcing bar arrangement pitch, the distance between the reinforced concrete shielding wall and the point radiation source, and the vertical projection position of the point radiation source onto the reinforced concrete shielding wall, and calculates the radiation leakage dose of a concrete shielding wall without reinforcing bars and the radiation leakage dose of a reinforced concrete shielding wall with reinforcing bars arranged in the concrete shielding wall using a three-dimensional Monte Carlo radiation transport calculation code, calculates a reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to the radiation leakage dose of the concrete shielding wall, and evaluates the rate of reduction in radiation leakage dose due to the reinforcing bars based on the relationship between the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to the one or more elements. [Effects of the Invention]

[0022] According to the present invention, the shielding effect of the reinforcing bars of a reinforced concrete shielding wall can be easily evaluated. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram showing an example of an evaluation model of the method for evaluating a radiation leakage dose reduction rate of a reinforcing bar according to the present embodiment. [Figure 2] FIG. 2 is a diagram showing an example of data on leakage dose reduction ratios for combinations of radiation energy and reinforcing bar diameters. [Figure 3] FIG. 3 is a diagram showing the relationship between the leakage dose reduction ratio and the reinforcing bar diameter, with radiation energy as a parameter, based on the data shown in FIG. [Figure 4] FIG. 4 is a diagram showing the relationship between the leakage dose reduction ratio and radiation energy, with the reinforcing bar diameter as a parameter, based on the data shown in FIG. [Figure 5] FIG. 5 is a block diagram showing the configuration of the analysis device. [Figure 6] FIG. 6 is a diagram showing an example of an evaluation model of a method for evaluating a radiation leakage dose reduction rate of a reinforcing bar, which is a modified example of this embodiment. [Figure 7] FIG. 7 is a diagram showing the change in the angle of radiation irradiated from a point radiation source to a reinforcing bar with respect to the distance from the point radiation source. [Figure 8] FIG. 8 is a diagram showing the distance dependency of radiation leakage dose when there is no rebar and when there is a rebar and the vertical projection position of a point radiation source is a rebar lattice intersection. [Figure 9] FIG. 9 is a diagram showing the distance dependency of the radiation leakage dose reduction ratio obtained from the results of FIG. [Figure 10] FIG. 10 is a diagram showing the distance dependency of the radiation leakage dose reduction ratio for reinforcing bars with different diameters, similar to FIG. [Figure 11] FIG. 11 is a diagram showing the relationship between the leakage dose reduction ratio and the reinforcing bar diameter, with radiation energy as a parameter, generated in the same manner as in FIG. [Figure 12] FIG. 12 is a diagram showing the relationship between the leakage dose reduction ratio and radiation energy, with the reinforcing bar diameter as a parameter, similar to FIG. [Figure 13]FIG. 13 is a diagram showing the distance dependency of the radiation leakage dose reduction ratio when the vertical projection position of a point radiation source is located on a reinforcing bar other than a reinforcing bar lattice intersection. [Figure 14] FIG. 14 is a diagram showing the distance dependency of the radiation leakage dose reduction ratio when the vertical projection position of a point radiation source is not located on a rebar other than a rebar lattice intersection. [Figure 15] FIG. 15 is a diagram showing an example of a reinforcing bar position display. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0025] 1 is a diagram showing an example of an evaluation model of the method for evaluating the radiation leakage dose reduction rate of reinforcing steel according to this embodiment. In this evaluation model, a surface radiation source 20 that emits radiation (X-rays and gamma rays) toward a reinforced concrete shielding wall 10 is placed 100 cm from the front surface (XZ plane at the end in the -Y direction) of the reinforced concrete shielding wall 10, and emits radiation perpendicular to the front surface of the reinforced concrete shielding wall 10 (in the +Y direction).

[0026] The reinforced concrete shielding wall 10 has reinforcing bars 12 and 13 arranged (double reinforcing) on ​​the front side in the -Y direction and the rear side in the +Y direction of the concrete layer 11, respectively. Cover concrete layers 14 and 15 are further arranged on the front and rear sides of the reinforcing bars 12 and 13. An evaluation layer E of air for evaluating the leakage dose is formed on the rear side of the covering concrete layer 15. Air is also present between the surface radiation source 20 and the reinforced concrete shielding wall 10. The thickness T of the reinforced concrete shielding wall is, for example, 80 cm, 100 cm, 150 cm, or 200 cm. The concrete density is 2.1 g / cm 3 is.

[0027] As shown in Figure 1(b), the reinforcing bars 12 and 13 are arranged in a grid pattern with vertical reinforcing bars 16 and horizontal reinforcing bars 17, with a reinforcing bar pitch P of 20 cm. The reinforcing bar diameters are eight types: 19.2 mm (D19), 22.2 mm (D22), 25.4 mm (D25), 28.6 mm (D29), 31.8 mm (D32), 34.9 mm (D35), 38.1 mm (D38), and 41.3 mm (D41). For evaluation purposes, a model without reinforcing bars 12 and 13 is also included. Five types of radiation energy are used: 0.3 MeV, 0.662 MeV, 1.25 MeV, 2.5 MeV, and 10 MeV.

[0028] <Evaluation method> First, the five types of radiation energy mentioned above are emitted using a three-dimensional Monte Carlo transport calculation code (MCNP5) for a model with a reinforced concrete shielding wall thickness T of 150 mm, a reinforcing bar pitch of 20 cm, and no reinforcing bars 12 or 13, and the radiation leakage doses are calculated for each of the five types of radiation energy in the evaluation layer E. This allows five radiation leakage doses to be calculated for the concrete shielding wall without reinforcing bars for the five types of radiation energy.

[0029] Then, using a three-dimensional Monte Carlo transport calculation code (MCNP5), the five types of radiation energy mentioned above are emitted into a model with a reinforced concrete shielding wall thickness T of 150 mm, a reinforcing bar pitch of 20 cm, and eight types of reinforcing bar diameters: "D19," "D22," "D25," "D29," "D32," "D35," "D38," and "D41," and the radiation leakage dose in evaluation layer E is calculated for each. This results in a radiation leakage dose of 8 (number of reinforcing bar diameters) x 5 (number of radiation energies) = 40.

[0030] Then, for each radiation energy, the radiation leakage dose for the eight rebar diameters is divided by the radiation leakage dose without the rebar to determine the leakage dose reduction ratio for each rebar diameter. As a result, data on the leakage dose reduction ratio for each combination of radiation energy and rebar diameter shown in Figure 2 is obtained. This leakage dose reduction ratio is the leakage dose reduction ratio for rebars 12 and 13. Note that the leakage dose reduction ratio may also be expressed as a percentage.

[0031] After that, a relationship diagram of the leakage dose reduction ratio versus rebar diameter, with radiation energy as a parameter, is created, as shown in Figure 3. Characteristic curves L1 to L5 shown in Figure 3 are polynomial approximations of the leakage dose reduction ratio for eight rebar diameters for each radiation energy, based on the data obtained in Figure 2. Characteristic curves L1 to L5 show the relationship of the leakage dose reduction ratio versus rebar diameter, with radiation energies of 10 MeV, 2.5 MeV, 1.25 MeV, and 0.662 MeV as parameters, respectively. This relationship diagram makes it possible to evaluate the leakage dose reduction ratio due to rebars.

[0032] Once this relationship for the leakage dose reduction ratio has been determined, when a certain radiation energy is irradiated and the radiation leakage dose of a concrete shielding wall without reinforcing bars is determined, and a desired radiation dose reduction ratio is required, the reinforcing bar diameter (reinforcing bar pitch P is 0.2 m) used in the reinforced concrete shielding wall that will achieve this required radiation dose reduction ratio can be obtained based on the relationship diagram shown in Figure 3. Conversely, the thickness of the reinforced concrete shielding wall can be reduced by taking into account the radiation dose reduction ratio obtained with the reinforcing bar diameter of reinforcing bars with a reinforcing bar pitch P of 0.2 m.

[0033] Since the radiation dose reduction ratio is the ratio between the radiation leakage dose from a concrete shielding wall without reinforcing bars and the radiation leakage dose from a reinforced concrete shielding wall, the influence of the thickness of the concrete shielding wall and the concrete density on the radiation dose reduction ratio due to reinforcing bars can be ignored.

[0034] In the above embodiment, the radiation dose reduction ratio is calculated with the reinforcing bar pitch P constant, but the radiation dose reduction ratio may be calculated with the reinforcing bar pitch P as a variable in addition to or instead of the radiation energy and the reinforcing bar diameter. For example, the reinforcing bar diameter may be kept constant and the reinforcing bar pitch P may be changed.

[0035] That is, at least one of the elements of radiation energy, reinforcing bar diameter, and reinforcing bar pitch is used as a variable, and a three-dimensional Monte Carlo radiation transport calculation code is used to calculate the radiation leakage dose of a concrete shielding wall without reinforcing bars and the radiation leakage dose of a reinforced concrete shielding wall with reinforcing bars arranged in the concrete shielding wall, and the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall relative to the radiation leakage dose of the concrete shielding wall is calculated, and the reduction rate of the radiation leakage dose due to the reinforcing bars can be evaluated based on the relationship between the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to one or more elements.

[0036] In addition, in the above embodiment, the characteristic curves L1 to L5 are generated by polynomial approximation or the like, and the radiation dose attenuation ratio is obtained by interpolation processing such as interpolation and extrapolation, but if you want to improve the accuracy of the radiation dose attenuation ratio, you can simply increase the number of types of radiation energy, rebar diameter, and reinforcing bar pitch.

[0037] Fig. 4 is a diagram showing the relationship between the leakage dose reduction ratio and radiation energy, with the rebar diameter as a parameter, based on the data shown in Fig. 2. For ease of explanation, Fig. 4 shows only characteristic curves L11 to L13 for three rebar diameters, "D41," "D29," and "D22." In this case, the characteristic curves L11 to L13 are fitted using exponential approximation, as shown by the dashed lines.

[0038] Furthermore, the radiation energy is a surface source, but may be a volume source. Note that the size of the surface source must be larger than the diameter of the reinforcement.

[0039] <Device configuration> FIG. 5 is a block diagram showing the configuration of the analysis device 1. As shown in FIG. 5, the analysis device 1 has an input unit 3, a display unit 4, a memory unit 5, and a control unit 6. The input unit 3 is an input interface for inputting various types of information. The display unit 4 is a display output interface for displaying and outputting various types of information. The memory unit 5 is a storage device such as a nonvolatile memory that stores a calculation model MD including at least a model consisting of a surface radiation source and a concrete shielding wall without reinforcing bars, and a model consisting of a surface radiation source and a reinforced concrete shielding wall. The control unit 6 is a control unit that controls the entire analysis device 1 and has an analysis unit 7. The control unit 6 stores programs corresponding to the analysis unit 7 in a storage device such as a nonvolatile memory, loads these programs into the memory, and executes them on the CPU to execute the corresponding processes.

[0040] The analysis unit 7 assigns various specifications and variable values ​​to the concrete shielding wall and the reinforced concrete shielding wall in the calculation model MD, and uses at least one of the elements of radiation energy, reinforcing bar diameter, and reinforcing bar arrangement pitch as variables, and uses a three-dimensional Monte Carlo radiation transport calculation code to calculate the radiation leakage dose of a concrete shielding wall without reinforcing bars and the radiation leakage dose of a reinforced concrete shielding wall in which reinforcing bars are arranged in the concrete shielding wall, calculates the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall relative to the radiation leakage dose of the concrete shielding wall, and evaluates the reduction rate of the radiation leakage dose due to the reinforcing bars based on the relationship between the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall and one or more elements.

[0041] In this embodiment, in evaluating the leakage dose from a reinforced concrete shielding wall due to a surface radiation source (X-rays and gamma rays), it is possible to easily derive the leakage dose reduction rate due to reinforcing bars without accurately modeling the reinforcing bars using a reinforcing bar arrangement diagram, etc. The radiation leakage dose from a concrete shielding wall without reinforcing bars may be calculated using a calculation result other than a three-dimensional Monte Carlo transport calculation code.

[0042] In addition, in the shielding design of new radiation facilities, it will be possible to reduce the thickness of the reinforced concrete of the shielding wall by reducing the diameter of the rebar.

[0043] Furthermore, it can be confirmed that the use of reinforcing bars reliably reduces radiation leakage from the shielding walls. This makes it possible to evaluate the margin of shielding design even in existing facilities.

[0044] <Modification> In the above embodiment, the leakage dose from a reinforced concrete shielding wall for a surface radiation source is evaluated, but in this modified example, the leakage dose from a reinforced concrete shielding wall for a point radiation source can also be evaluated in the same way.

[0045] Fig. 6 is a diagram showing an example of an evaluation model of a method for evaluating the radiation leakage dose reduction rate of reinforcing bars, which is a modified example of this embodiment. In the evaluation model of the modified example shown in Fig. 6, a point radiation source 30 is used instead of the surface radiation source 20 in the evaluation model shown in Fig. 1. The point radiation source 30 is an isotropic point radiation source. The configuration of the reinforced concrete shielding wall 10 including the reinforcing bars 12 and 13 is the same as in the embodiment.

[0046] Because the radiation from the point radiation source 30 spreads relative to the reinforced concrete shielding wall 10, it is necessary to consider the distance L between the front surface 14a of the reinforced concrete shielding wall 10 and the point radiation source 30 (effectively the distance between the point radiation source 30 and the reinforcing bars 12: see FIG. 7 ) and the vertical projection position of the point radiation source 30 onto the reinforced concrete shielding wall 10. In the embodiment, the distance L is constant at 100 cm, but in the modified example, the distance L is varied to 10 cm, 20 cm, 50 cm, 100 cm, and 200 cm. Furthermore, with regard to the vertical projection position of the point radiation source 30 onto the XZ plane, the position coordinates (XZ coordinates) of one intersection of the reinforcing bar lattice are set as the zero point (position P1), and the leakage dose is also measured at position P1 on the rear side of the reinforced concrete shielding wall 10. The vertical projection positions under consideration are, for example, position P1 at X=0 cm, Z=0 cm, position P2 at X=10 cm, Z=0 cm, position P3 at X=20 cm, Z=0 cm, position P4 at X=10 cm, Z=10 cm, and position P5 at X=20 cm, Z=20 cm. Position P3 is the intersection of adjacent rebars, and position P2 is the midpoint between positions P1 and P3. These positions P1 to P3 are all vertical projection positions on rebars 12 and 13. Meanwhile, position P4 is the center of the plane formed by the grid, and position P5 is the midpoint between positions P1 and P4. The vertical projection positions of positions P4 and P5 are positions where rebars 12 and 13 are not present, and are positions on the diagonal of the rebar grid.

[0047] Figure 7 shows the change in the angle of radiation irradiated from point radiation source 30 to reinforcing bar 12 with the distance L from point radiation source 30. Figure 7 shows the change in the angle of the range irradiated from point radiation source 30 to reinforcing bar 12 when distance L is set to 10 cm, 50 cm, 100 cm, and 200 cm. Note that reinforcing bar 12 is "D22" and has a diameter of 2.22 cm. When distance L is changed to 10 cm, 50 cm, 100 cm, and 200 cm, the irradiation angle to reinforcing bar 12 changes to 3.94 degrees, 1.13 degrees, 0.60 degrees, and 0.31 degrees, respectively. The irradiation angle of the radiation shielded by reinforcing bar 12 gradually decreases, and evaluation must take distance L into account.

[0048] First, we will explain the dependence of the radiation leakage dose on distance L when the vertical projection of the point radiation source 30 is located at position P1, i.e., at a rebar grid intersection. Figure 8 shows the dependence of the radiation leakage dose on distance L when there is no rebar and when there is rebar and the vertical projection of the point radiation source 30 is located at position P1. Note that "D22" rebar is used. The point radiation source 30 is 1 G becquerel. In Figure 8, characteristic curve LA shows the radiation leakage dose when there are no rebars 12 and 13, and the radiation leakage dose decreases as the distance L increases. On the other hand, characteristic curve LB shows the radiation leakage dose when there are rebars and the vertical projection of the point radiation source 30 is located at position P1. Similar to characteristic curve LA, the radiation leakage dose decreases with characteristic curve LB, but the radiation leakage dose is shifted in the direction of decreasing compared to characteristic curve LA, indicating that the rebars 12 and 13 have the effect of reducing the radiation leakage dose.

[0049] Furthermore, Figure 9 is a graph showing the dependency of the radiation leakage dose reduction ratio on distance L obtained from the results of Figure 8. The radiation leakage dose reduction ratio shown in Figure 9 indicates the ratio of the radiation leakage amount of characteristic curve LB to the radiation leakage amount of characteristic curve LA. As shown in Figure 9, the radiation leakage dose reduction ratio is represented by characteristic curve L20, and increases sharply up to a distance L of about 50 cm, and becomes almost flat when distance L exceeds 100 cm.

[0050] Similar to Figure 9, Figure 10 shows the dependency of the radiation leakage dose reduction ratio on distance L for rebars of different diameters. Figure 10 shows rebars with different diameters, "D22," "D29," "D35," and "D41," which increase in diameter as parameters, resulting in characteristic curves L20, L21, L22, and L23, respectively. As shown in Figure 10, as the rebar diameter increases, the leakage dose reduction ratio decreases and the shielding effect of the rebar increases.

[0051] FIG. 11 is a graph showing the relationship of the leakage dose reduction ratio to the rebar diameter, with radiation energy as a parameter, generated in the same manner as FIG. 3. FIG. 11 shows the relationship when the distance L is 100 cm. The characteristic curves LL1 to LL5 shown in FIG. 11 are polynomial approximations of the leakage dose reduction ratios for four rebar diameters for each of five radiation energies. The characteristic curves LL1 to LL5 show the relationship of the leakage dose reduction ratio to the rebar diameter, with radiation energies of 10 MeV, 2.5 MeV, 1.25 MeV, and 0.662 MeV as parameters, respectively. This relationship graph allows us to evaluate the leakage dose reduction ratio due to the rebar when the distance L is 100 cm.

[0052] Once the distance L is determined and the relationship of the leakage dose reduction ratio to the rebar diameter with the radiation energy as a parameter corresponding to this distance L is found, similarly to the embodiment, when a certain radiation energy is irradiated, the radiation leakage dose of a concrete shielding wall without reinforcing bars is found, and a desired radiation dose reduction ratio is required, the reinforcing bar diameter (reinforcing bar pitch P is 0.2 m) to be used in the reinforced concrete shielding wall that will achieve this required radiation dose reduction ratio can be obtained based on the relationship diagram shown in Figure 11. Conversely, the thickness of the reinforced concrete shielding wall can be reduced in consideration of the radiation dose reduction ratio obtained with the reinforcing bar diameter of reinforcing bars with a reinforcing bar pitch P of 0.2 m.

[0053] Since the radiation dose reduction ratio is the ratio between the radiation leakage dose from a concrete shielding wall without reinforcing bars and the radiation leakage dose from a reinforced concrete shielding wall, the influence of the thickness of the concrete shielding wall and the concrete density on the radiation dose reduction ratio due to reinforcing bars can be ignored.

[0054] In the above-described modified example, the radiation dose reduction ratio was calculated with the reinforcing bar pitch P constant, but the radiation dose reduction ratio may be calculated using the reinforcing bar pitch P as a variable in addition to or instead of the radiation energy and the reinforcing bar diameter. For example, the reinforcing bar diameter may be kept constant and the reinforcing bar pitch P may be changed.

[0055] In other words, once the distance L has been determined, at least one of the elements of radiation energy, reinforcing bar diameter, and reinforcing bar pitch can be used as variables using a three-dimensional Monte Carlo radiation transport calculation code to calculate the radiation leakage dose of a concrete shielding wall without reinforcing bars and the radiation leakage dose of a reinforced concrete shielding wall in which reinforcing bars have been arranged in the concrete shielding wall, and the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall relative to the radiation leakage dose of the concrete shielding wall can be calculated, and the reduction rate of the radiation leakage dose due to the reinforcing bars can be evaluated based on the relationship between the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to one or more elements.

[0056] Furthermore, in the above-described modified example, similar to the embodiment, the characteristic curves LL1 to LL5 are generated by polynomial approximation or the like, and the radiation dose attenuation ratio is obtained by interpolation processing such as interpolation or extrapolation, but if you want to improve the accuracy of the radiation dose attenuation ratio, you can simply increase the number of types of radiation energy, rebar diameter, and reinforcing bar pitch.

[0057] Similar to Fig. 11, Fig. 12 is a diagram showing the relationship between the leakage dose reduction ratio and radiation energy, with the rebar diameter as a parameter. Similar to Fig. 11, Fig. 12 shows the relationship when the distance L is 100 cm. For ease of explanation, Fig. 12 only shows characteristic curves LL11 to LL14 for four rebar diameters, "D41," "D29," "D35," and "D22." In this case, the characteristic curves LL11 to LL14 are fitted by exponential approximation, as indicated by the dashed lines.

[0058] In this modified example, when the distance L is determined and the vertical projection position of the point radiation source 30 is located at the rebar grid intersection (position P1), the reduction rate of the radiation leakage dose due to the rebar can be evaluated by referring to Figure 11 or Figure 12, as in the embodiment.

[0059] <When the vertical projection position is not a rebar grid intersection> Here, consider the case where the vertical projection position of the point radiation source 30 is not located at a rebar grid intersection (position P1). Fig. 13 is a diagram showing the dependency of the radiation leakage dose reduction ratio on distance L when the vertical projection position of the point radiation source 30 is located on a rebar other than a rebar grid intersection. Note that Fig. 13 shows characteristic curves L32 and L33 at positions P2 and P3 for a rebar "D22" having the same rebar diameter as characteristic curve L20 in Fig. 9. As described above, position P3 is an adjacent rebar grid intersection, and position P2 is the midpoint between positions P1 and P3.

[0060] 13, when the distance L is 10 cm, the radiation leakage dose reduction ratio is greater at positions P2 and P3 than at position P1, and the radiation leakage dose reduction ratio is greater at position P2 than at position P3. However, when the distance L is 100 cm or greater, the characteristic curves L20, L32, and L33 at positions P1, P2, and P3 become approximately equal.

[0061] On the other hand, Fig. 14 is a diagram showing the dependency of the radiation leakage dose reduction ratio on distance L when the vertical projection position of point radiation source 30 is not located on a rebar other than a rebar lattice intersection. Fig. 14 shows characteristic curves L41 to L46 at positions P4, P5, P14, P13, P12, and P11 for rebar "D22" having the same rebar diameter as characteristic curve L20 in Fig. 9. Positions P11, P12, P13, P14, P5, and P4 are located 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, and 10 cm away from position P1 diagonally, respectively, and characteristic curves L41 to L46 show the dependency of the radiation leakage dose reduction ratio on distance L at positions P11, P12, P13, P14, P5, and P4, respectively.

[0062] 14, when the distance L is 10 cm, the radiation leakage dose reduction ratio increases and the radiation leakage amount increases as the distance from position P1 to positions P11, P12, P13, P14, P5, and P4 increases. However, when the distance L is 100 cm or more, the characteristic curves L20, and L41 to L46 for positions P11, P12, P13, P14, P5, and P4 become approximately equal.

[0063] Therefore, even if the vertical projection position of the point radiation source 30 is not located at the rebar lattice intersection (position P1), if the distance L is 100 cm or more, the reduction rate of the radiation leakage dose due to the rebar can be evaluated using the relationship diagram shown in Figure 11 or Figure 12.

[0064] When the vertical projection position is positions P2 and P3 on the rebar, or positions P11 and P12 close to position P1, which is a rebar grid intersection, it is approximated to characteristic curve L20, and the reduction rate of the radiation leakage dose due to the rebar may be evaluated using the relationship diagram shown in Figure 11 or 12. Furthermore, when the distance L is less than 100 cm, the characteristic curves corresponding to the characteristic curves L32, L33, and L41 to L46 are obtained using the rebar diameter as a parameter, as in the relationship diagram shown in Figure 10, and then the relationship diagram corresponding to Figure 11 or 12 is generated to evaluate the reduction rate of the radiation leakage dose due to the rebar.

[0065] <Rebar position display> In the above modification, it is preferable to position the point radiation source 30 so that its vertical projection is located at the rebar grid intersection (position P1). For this reason, it is advisable to measure and record the exact positions of the vertical and horizontal reinforcement bars when the reinforcement is laid, and then, after the concrete is poured, to mark the positions of the vertical and horizontal reinforcement bars on the concrete surface or on the interior decorative panel, as shown by the rebar position indicator M in Figure 15(a), so that the positions of the rebar grid intersections can be accurately determined. By positioning the point radiation source 30 so that it is located on the perpendicular line (-Y direction) to the rebar grid intersections, the radiation leakage dose reduction ratio can be reduced.

[0066] That is, by displaying the positions of the actually constructed vertical and horizontal reinforcement bars in a visible location on the surface of the concrete shielding wall, it is possible to reliably install the point radiation source 30 on the perpendicular line to the intersection of the rebar grid. Also, if the distance L between the point radiation source 30 and the concrete shielding wall on the perpendicular line to the intersection of the rebar grid is made shorter than 100 cm, the radiation leakage dose reduction ratio can be further reduced.

[0067] In addition, if there is no indication of the rebar position or if the point radiation source 30 cannot be installed perpendicular to the rebar grid intersection, the problem of a large radiation leakage dose reduction ratio due to a position away from the rebar grid intersection can be avoided by making the distance L between the point radiation source 30 and the front of the reinforced concrete shielding wall 100 cm or more.

[0068] 15(b), it is possible to reduce the radiation leakage dose reduction ratio and obtain a higher shielding effect by increasing the diameter of only the rebar closest to the point radiation source 30. In addition, by increasing the diameter of specific rebars near the rebar lattice intersections, it is possible to increase the flexibility to accommodate variations in the rebar pitch interval relative to the position of the point radiation source 30.

[0069] In other words, the radiation leakage dose reduction ratio can be reduced by limiting the diameter of the vertical and horizontal reinforcement bars or the reinforcement bars in the vicinity of the vertical and horizontal reinforcement bars in the concrete shielding wall corresponding to the planned installation location of the point radiation source 30 to thicker reinforcement bars.

[0070] Conversely, if the position of the point radiation source 30 has not been determined, as shown in Figure 15(b), the rebar position display MT of the thick rebar is displayed in the rebar position display ML corresponding to the rebar position display M, and the point radiation source 30 is installed on the perpendicular line of the rebar lattice intersection of the thick rebar, thereby reducing the radiation leakage dose reduction ratio.

[0071] Note that the configurations illustrated in the above embodiments and modifications are merely functional schematics and are not necessarily physically configured as shown. In other words, the distribution and integration of each device and component is not limited to that illustrated, and all or part of them can be functionally or physically distributed and integrated in any unit depending on various usage situations, etc. [Explanation of symbols]

[0072] 1 Analysis device 3 Input section 4 Display section 5 Storage section 6 Control Unit 7 Analysis section 10 Reinforced concrete shielding wall 11 Concrete layer 12,13 Reinforced concrete 14,15 Concrete layer 14a Front wall 16 Vertical reinforcing bars 17 Horizontal reinforcing bars 20 plane source 30 Point source E rating layer L distance L1~L5,L11~L13,L20~L23,L32,L33,L41~L46,LA,LB,LL1~LL5,LL11~LL14 Characteristic curve M, ML, MT rebar position display MD computational model P Reinforcement pitch P1~P5,P11~P14 position T Thickness

Claims

1. A method for evaluating a radiation leakage dose reduction rate of reinforcing bars arranged in a reinforced concrete shielding wall, comprising: a method for evaluating a radiation leakage dose reduction rate of reinforcing bars, the method comprising the steps of: determining, using a three-dimensional Monte Carlo radiation transport calculation code, a radiation leakage dose of a concrete shielding wall without reinforcing bars and a radiation leakage dose of a reinforced concrete shielding wall with reinforcing bars arranged therein, using as variables at least one of the elements of radiation energy irradiated from a surface radiation source to the reinforced concrete shielding wall, the reinforcing bar diameter of the reinforcing bars, and the reinforcing bar pitch; determining a reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to the radiation leakage dose of the concrete shielding wall; and evaluating a reduction rate of the radiation leakage dose due to the reinforcing bars based on a relationship between the reduction rate of the radiation leakage dose of the reinforced concrete shielding wall with respect to the one or more elements.

2. The method for evaluating the radiation leakage dose reduction rate of reinforcing bars described in claim 1, characterized in that the reinforcing bar pitch is set as a constant, the radiation energy or the reinforcing bar diameter is set as a variable, and the reinforcing bar diameter or the radiation energy is set as a parameter, respectively, to determine the relationship between the radiation energy or the reinforcing bar diameter and the reduction rate of the radiation leakage dose, and to identify the reinforcing bar diameter that satisfies the desired reduction rate for the radiation energy.

3. A method for evaluating a radiation leakage dose reduction rate of reinforcing bars arranged in a reinforced concrete shielding wall, comprising: a radiation leakage dose reduction rate of the reinforced concrete shielding wall, the radiation leakage dose of a concrete shielding wall without reinforcing bars and a radiation leakage dose of a reinforced concrete shielding wall with reinforcing bars arranged therein are calculated using a three-dimensional Monte Carlo radiation transport calculation code, with at least one of the following elements as variables: radiation energy irradiated from a point radiation source to the reinforced concrete shielding wall; a reinforcing bar diameter of the reinforcing bars; a reinforcing bar pitch of the reinforcing bars; a distance between the reinforced concrete shielding wall and the point radiation source; and a vertical projection position of the point radiation source onto the reinforced concrete shielding wall.

4. 4. The method for evaluating the reduction rate of radiation leakage dose from reinforcing bars according to claim 3, wherein the vertical projection position of the point radiation source onto the reinforced concrete shielding wall, the radiation energy, and the reinforcing bar pitch are constants, the distance between the reinforced concrete shielding wall and the point radiation source is a variable, and the reinforcing bar diameter is a parameter, and the relationship between the reduction rate of radiation leakage dose and the distance is determined, and the reinforcing bar diameter that satisfies the desired reduction rate for the distance is specified.

5. 5. The method for evaluating a radiation leakage dose reduction rate of reinforcing bars according to claim 4, wherein the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is a reinforcing bar lattice intersection.

6. 6. The method for evaluating the reduction rate of radiation leakage dose from reinforcing bars according to claim 5, wherein, when the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is a position other than a reinforcing bar lattice intersection and the distance between the reinforced concrete shielding wall and the point radiation source is 100 cm or more, the reinforcing bar diameter that satisfies the desired reduction rate for the distance is identified using the relationship between the reduction rate of radiation leakage dose and the distance when the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is at a reinforcing bar lattice intersection.

7. 4. The method for evaluating the reduction rate of radiation leakage dose from reinforcing bars according to claim 3, wherein the distance between the reinforced concrete shielding wall and the point radiation source, the vertical projection position of the point radiation source onto the reinforced concrete shielding wall, and the reinforcing bar pitch are constants, the radiation energy or the reinforcing bar diameter is a variable, and the reinforcing bar diameter or the radiation energy is a parameter, respectively, to determine the relationship between the reduction rate of radiation leakage dose and the radiation energy or the reinforcing bar diameter, and to identify the reinforcing bar diameter that satisfies the desired reduction rate for the radiation energy.

8. The method for evaluating the radiation leakage dose reduction rate of reinforcing steel according to claim 3, characterized in that, when the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is a reinforcing bar grid intersection, the position of the reinforcement is displayed on the front surface of the reinforced concrete shielding wall.

9. 4. The method for evaluating the radiation leakage dose reduction rate of reinforcing bars according to claim 3, characterized in that the vertical projection position of the point radiation source onto the reinforced concrete shielding wall is a reinforcing bar lattice intersection, and when the reinforcing bars passing through the reinforcing bar lattice intersection are made thicker than the other reinforcing bars, the reinforcing bar arrangement positions of the thicker reinforcing bars are displayed on the front surface of the reinforced concrete shielding wall.

10. A method for evaluating the radiation leakage dose reduction rate of reinforcing bars described in any one of claims 1 to 9, characterized in that the reinforcing bars are arranged on the front surface of the concrete shielding wall on the radiation exposure side and the rear surface on the radiation leakage side.

11. An analysis device for evaluating a reduction rate of radiation leakage dose of reinforcing bars arranged in a reinforced concrete shielding wall, comprising: an analysis unit that uses variables at least one of the elements of radiation energy irradiated from a surface radiation source to the reinforced concrete shielding wall, the reinforcing bar diameter of the reinforcing bars, and the reinforcing bar arrangement pitch, and calculates, using a three-dimensional Monte Carlo radiation transport calculation code, a radiation leakage dose from a concrete shielding wall without reinforcing bars and a radiation leakage dose from a reinforced concrete shielding wall with reinforcing bars arranged therein; calculates a reduction rate of the radiation leakage dose from the reinforced concrete shielding wall with respect to the radiation leakage dose from the concrete shielding wall; and evaluates the reduction rate of the radiation leakage dose due to the reinforcing bars based on the relationship between the reduction rate of the radiation leakage dose from the reinforced concrete shielding wall with respect to the one or more elements.

12. An analysis device for evaluating a reduction rate of radiation leakage dose of reinforcing bars arranged in a reinforced concrete shielding wall, comprising: an analysis device which uses as variables at least one of the following elements: radiation energy irradiated from a point radiation source to the reinforced concrete shielding wall, the reinforcing bar diameter of the reinforcing bars, the reinforcing bar arrangement pitch, the distance between the reinforced concrete shielding wall and the point radiation source, and the vertical projection position of the point radiation source onto the reinforced concrete shielding wall; calculates, using a three-dimensional Monte Carlo radiation transport calculation code, a radiation leakage dose from a concrete shielding wall without reinforcing bars and a radiation leakage dose from a reinforced concrete shielding wall with reinforcing bars arranged therein; calculates a reduction rate of the radiation leakage dose from the reinforced concrete shielding wall with respect to the radiation leakage dose from the concrete shielding wall; and evaluates the reduction rate of the radiation leakage dose due to the reinforcing bars based on the relationship between the reduction rate of the radiation leakage dose from the reinforced concrete shielding wall with respect to the one or more elements.

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