A method for iteratively optimizing the design of a marine containment shield based on regional isodose

Abstract

The present application belongs to the technical field of marine radiation protection, and discloses a kind of marine containment shielding iterative optimization design method based on regional isodose, comprising the following steps: completing the transport calculation of neutron and gamma radiation field in containment, obtaining the radiation distribution of inner wall of containment;According to the design target value of dose rate of outer wall of containment, obtain the initial scheme of thickness distribution of each shielding layer of containment;Complete the fine transport calculation of neutron and gamma radiation in containment and shielding material in containment, obtain the radiation distribution of outer wall of containment under the scheme;Combined with the design target value of dose rate of outer wall of containment, obtain the optimized scheme of thickness distribution of each shielding layer of containment using iterative optimization algorithm;Carry out multi-round iterative optimization calculation until the thickness difference between the optimized scheme and the scheme before optimization reaches the expected target.The present application is based on the principle of regional isodose, forms the optimized thickness distribution scheme of marine containment shielding, optimizes shielding weight while ensuring the radiation safety of personnel, and saves the overall resources of ship.

Description

Technical Field

[0001] This invention belongs to the field of marine radiation protection technology, specifically relating to an iterative optimization design method for marine containment shielding based on regional equal dose. Background Technology

[0002] Nuclear-powered ships inevitably generate radioactivity during operation and maintenance. To ensure the life, health, and radiation safety of personnel and to maintain the nuclear radiation environment in the cabins at a reasonably feasible and as low a level as possible, it is necessary to calculate, design, test, and verify the nuclear radiation shielding of the cabin environment. The shielding design of nuclear-powered ships must not only ensure the radiation safety of personnel but also optimize the shielding design within the overall allowable weight and space conditions of the nuclear-powered ship, thereby achieving an optimized shipboard containment shielding scheme that matches the overall design.

[0003] Land-based nuclear power plants utilize the containment vessel and its internal concrete structures as shielding, with relatively low requirements for shielding weight and size. The radiation shielding design employs a uniform thickness approach to ensure the radiation safety of personnel. In contrast, radiation sources within the containment vessel of nuclear-powered ships are complexly distributed due to system piping and equipment, exhibiting significant differences in neutron and gamma radiation intensity and energy spectrum. These radiation sources, located at varying distances from the containment vessel, result in substantial variations in radiation intensity distribution, neutron and gamma component ratios, and energy spectrum across the containment wall—sometimes by a factor of 10 to 100. If a uniform thickness design method is used for marine containment shielding, applying the same thickness of radiation shielding material in areas of lower radiation intensity as in areas of higher intensity would not only significantly increase the weight and cost of the shielding material but also further increase the structural strength and weight of the containment vessel. This substantial increase in the weight of the containment shielding structure encroaches on valuable weight resources of the nuclear-powered ship, leading to increased local loads and stresses on the hull structure and impacting the ship's navigation and overall performance, such as increased drag, reduced speed, and decreased usable payload. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing an iterative optimization design method for marine containment shielding based on regional iso-dose. According to the characteristics of the radiation field distribution inside the containment of nuclear-powered ships, and based on the principle of regional iso-dose, an optimized distribution scheme for the thickness of marine containment shielding is formed. While ensuring the radiation safety of personnel, the shielding weight is optimized, saving a lot of overall ship resources.

[0005] To address the technical problem proposed in this invention, this invention provides an iterative optimization design method for marine containment shielding based on regional equal doses, comprising the following steps:

[0006] (1) Based on the equipment layout and radioactive source term data inside the containment, the equipment and source terms are abstracted and simplified to complete the transport calculation of neutron and gamma radiation fields inside the containment and obtain the radiation distribution of the inner wall of the containment.

[0007] (2) Based on the radiation distribution on the inner wall of the containment and the target value of the dose rate on the outer wall of the containment, and combined with the attenuation formula of neutron and γ radiation in the containment shielding material, the initial scheme of the thickness distribution of each shielding layer of the containment is obtained.

[0008] (3) Based on the initial scheme of containment structure and thickness distribution of each shielding layer of containment, establish containment structure and containment shielding model, complete the fine transport calculation of neutrons and γ radiation in containment and shielding materials, and obtain the radiation distribution of the outer wall of containment under this scheme;

[0009] (4) Based on the radiation distribution on the outer wall of the containment and the target value of the dose rate on the outer wall of the containment, an iterative optimization algorithm is used to obtain the optimized scheme of the thickness distribution of each shielding layer of the containment.

[0010] (5) Repeat steps (3) and (4) to perform multiple rounds of iterative optimization calculations until the thickness difference between the optimized scheme and the unoptimized scheme reaches the expected target, thus forming the final optimized containment shielding thickness distribution scheme.

[0011] In the above scheme, in step (1), the source term is abstracted and simplified by using equivalent point source, surface source or volume source, and the equipment is abstracted and simplified by using the principle of equivalent nuclide composition, geometry and density.

[0012] In the above scheme, in step (1), the transport calculation of neutrons and gamma radiation fields inside the containment is performed using the Monte Carlo or point kernel integration method.

[0013] In the above scheme, in step (2), the containment shielding material includes steel, lead, and polyethylene-based composite materials.

[0014] In the above scheme, in step (2), the attenuation formulas for neutrons and gamma radiation in the containment shielding material are empirical formulas, or obtained through Monte Carlo simulation and fitted using the following formula:

[0015] H(t)=φ0·B(t)·e -μ·t ;

[0016] In the formula, H(t) represents the dose rate after a ray with an initial fluence rate of φ0 penetrates a material with a thickness of t;

[0017] φ0 represents the initial fluence rate of the ray;

[0018] B(t) represents the accumulation factor, which is a polynomial of thickness t;

[0019] μ represents the attenuation coefficient of the ray in the material;

[0020] t represents the thickness of the material.

[0021] In the above scheme, the target value of the containment outer wall dose rate is selected based on the containment outer wall dose rate limit, with a certain safety factor, and the specific formula is as follows:

[0022]

[0023] In the formula, H is the design target value of the dose rate on the outer wall of the containment.

[0024] H0 is the dose rate limit for the outer wall of the containment.

[0025] σ is the safety factor.

[0026] Furthermore, the safety factor σ is 1.5 to 2.5.

[0027] In the above scheme, in step (3), detectors are set on the outer wall of the containment according to the size of the containment shielding installation grid to complete the layout and modeling of the detectors on the outer wall of the containment.

[0028] In the above scheme, in step (3), the refined transport calculation is performed by Monte Carlo simulation.

[0029] In the above scheme, in step (4), the iterative optimization algorithm adopts the following formula:

[0030]

[0031] The above formula is derived from the following attenuation formulas for neutrons and gamma rays:

[0032]

[0033] In the formula, t PBC0 t PBC The thicknesses of the polyethylene-based composite material before and after optimization are shown respectively.

[0034] t Pb0 t Pb The thicknesses of the lead layer before and after optimization are shown respectively.

[0035] μ PBC→n μ PBC→γ These are the attenuation coefficients of the polyethylene-based composite material for incident neutrons and gamma rays, respectively.

[0036] μ Pb→γ The attenuation coefficient of the lead layer for incident gamma rays;

[0037] H n H n0These are the target value and the calculated value of the emitted neutron dose, respectively.

[0038] H γ H γ0 These are the target and calculated values ​​for the emitted gamma-ray dose, respectively.

[0039] φ Eγ φ n These are the fluence rates of incident gamma rays and neutrons, respectively;

[0040] B Eγ (t Pb ,t PBC B n (t Pb ,t PBC ) are the accumulation factors of the shield for gamma rays and neutrons, respectively, and is the polynomial of the thickness.

[0041] Furthermore, the target values ​​for the emitted neutron dose and the emitted gamma ray dose account for 20-40% and 60-80% of the design target values ​​for the dose rate of the outer wall of the containment, respectively.

[0042] In the above scheme, the expected goal in step (5) is that the thickness difference between the optimized scheme and the unoptimized scheme is less than 5 mm.

[0043] The above scheme also includes step (6), which involves carrying out containment shielding modeling and transport verification calculations based on the final optimized containment shielding thickness distribution scheme to ensure that the radiation distribution of the outer wall of the containment meets the target limit requirements.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] To reduce the weight of marine containment shielding while ensuring personnel radiation safety, this invention proposes an iterative optimization design method for marine containment shielding based on regional isodose. This method, based on the characteristics of the radiation field distribution within the containment of nuclear-powered ships and the principle of regional isodose, formulates an optimized shielding thickness distribution scheme for the containment. This optimizes shielding weight and saves significant overall ship resources while ensuring personnel radiation safety. This method is applicable to the design optimization of containment shielding for nuclear-powered ships, obtaining an optimized distribution of the thickness of multi-layered shielding materials for the containment, providing support for determining the radiation shielding scheme for the containment, optimizing overall resources, and ensuring operational and personnel radiation safety. Attached Figure Description

[0046] Figure 1 This is the iterative optimization design process for marine containment shielding in an embodiment of the present invention.

[0047] Figure 2 This refers to the dose rate limit requirements for the outer wall of a marine containment vessel in this embodiment of the invention.

[0048] Figure 3 The embodiment of the present invention is a containment shielding thickness distribution scheme based on conventional equal thickness design and regional equal dose design of the present invention.

[0049] Figure 4 The figure shows the dose rate distribution (unit: μSv / h) of the containment forewall according to the conventional equal thickness design and the regional equal dose design of the present invention. The thickness distribution in the figure is: from left to right, it is the port side to the starboard side of the containment forewall, and from top to bottom, it is the upper part to the lower part of the containment forewall. Detailed Implementation

[0050] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0051] Example

[0052] This embodiment employs an iterative optimization design method for marine containment shielding based on regional equal dose to design the containment shielding thickness distribution scheme. The process is as follows: Figure 1 Specifically, it includes the following steps:

[0053] (1) Based on the distribution of radiation sources inside the ship's containment vessel, the layout of reactor and primary loop system equipment and piping (e.g. Figure 3 As shown, the equipment and source terms are abstracted and simplified, and models of source terms inside the marine containment, primary loop system equipment and pipelines, and containment wall detectors are established. The simulation calculation of neutron γ transport inside the marine containment is completed, and the distribution of source terms inside the marine containment wall is obtained.

[0054] The containment source terms mainly include neutron and gamma source terms of the reactor and primary shield, and main coolant activator product source terms in the primary loop piping and equipment. The neutron and gamma source terms of the reactor and primary shield are abstracted and simplified using equivalent point or surface sources, while the main coolant activation product source terms in the primary loop piping and equipment are abstracted and simplified using equivalent point or volume sources. The primary loop system equipment and piping mainly include main pumps, evaporators, and primary loop piping, which are simplified and abstracted using the principle of equivalent nuclide composition, geometry, and density, ensuring both the effectiveness of the shadow shielding and safety. The arrangement of detectors on the containment wall is based on the size range of the containment shielding installation grid, typically 50cm to 100cm in size. The simulation calculation of neutron and gamma transport within the containment is usually performed using the Monte Carlo method or the point kernel integration method.

[0055] (2) Taking the attenuation formulas of γ-rays on the inner wall of a marine containment in lead and typical component polyethylene composite materials, and the attenuation formulas of neutrons on the inner wall in typical component polyethylene composite materials as examples, according to the dose rate limit requirements of the outer wall of a marine containment (such as... Figure 2 To obtain the initial scheme for the shielding layer thickness within each marine containment grid, the following is a typical set of equations:

[0056]

[0057] In the formula, H is the target value of the external wall dose rate, H0 is the limit value of the external wall dose rate, and 2 is the safety factor;

[0058] (3) Based on the geometric dimensions and materials of the marine containment structure, the thickness of the shielding layer in the structural grid, etc., establish the marine containment structure and the marine containment shielding model; based on the actual detector and the size of the containment shielding installation grid, complete the layout and modeling of the detectors on the outer wall of the marine containment; combine the source terms inside the marine containment, the primary loop system equipment and pipelines, the containment shielding structure and shielding layer model, and the detector model outside the containment to form a Monte Carlo transport calculation model for the overall calculation of the marine containment; complete the refined Monte Carlo simulation of neutrons and γ rays inside the marine containment in the square marine containment, and obtain the dose rate distribution of the outer wall of the marine containment under this scheme;

[0059] Among them, the marine containment structure model is established based on the nuclide composition, geometry, size, density, etc. of the containment structure; the marine containment shielding material model is established based on the thickness distribution of the shielding material and the nuclide composition, geometry, size, density, etc.; according to the actual detector and the size range of the containment shielding installation grid, the marine containment outer wall detector is usually in the range of 50-100cm; the marine containment internal source term, primary loop system equipment and pipeline model adopts the model established in step (1);

[0060] (4) Based on the radiation distribution of the outer wall of the marine containment, and combined with the target dose of neutron and gamma radiation, an iterative optimization algorithm is used to obtain the optimized thickness distribution of each shielding layer of the marine containment, thus forming an optimized shielding scheme for the marine containment; a typical formula is as follows:

[0061]

[0062] In the formula, t PBC0 t PBC The thicknesses of the polyethylene composite layer before and after optimization are shown in cm.

[0063] t Pb0 t Pb The thicknesses of the lead layer before and after optimization are shown in cm.

[0064] H n H n0 These are the target and calculated values ​​of the emitted neutron dose, respectively, in μSv / h and H. n =30%H;

[0065] H γ H γ0 These are the target and calculated values ​​of the emitted gamma-ray dose, respectively, in μSv / h and H. γ =70%H;

[0066] (5) Based on the optimized containment shielding scheme and combined with the actual installation requirements of the shielding, repeat steps (3) and (4) to perform 2 to 3 rounds of iterative optimization calculations until the thickness difference between the optimized containment shielding scheme and the original scheme is less than 5mm, thus forming the final optimized marine containment shielding scheme.

[0067] (6) Based on the final containment shielding optimization scheme, complete the modeling and shielding transport calculation of the source terms inside the containment, the main system pipelines and equipment, the structure and the containment shielding scheme, etc., to ensure that the radiation distribution outside the containment shielding meets the limit requirements.

[0068] Figure 3 The shielding thickness distribution scheme of the containment structure according to the conventional equal thickness design and the regional equal dose design of the present invention can be seen from the embodiment of the present invention. It can be seen that the containment structure based on the regional equal dose design is not of equal thickness, but has thick and thin parts. Compared with the equal thickness design, it saves a lot of shielding material, effectively reduces the shielding weight, and saves overall resources.

[0069] Figure 4 The dose rate distribution of the containment front wall, according to the conventional equal thickness design and the regional equal dose design of this invention, is obtained by comparing with... Figure 2 Comparing the medium dose rate limit requirements, the radiation distribution outside the shield of the containment vessel designed based on regional equal dose meets the dose limit requirements and can fully ensure the radiation safety of personnel. Although the containment vessel designed according to the traditional equal thickness also meets the limit requirements, it increases the material thickness and shielding weight, occupies more overall resources, and leads to increased stress on the hull structure, which increases the design difficulty of the hull structure.

[0070] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for iterative optimization design of marine containment shielding based on regional iso-dose, characterized in that, Includes the following steps: (1) Based on the equipment layout and radioactive source term data inside the containment, the equipment and source terms are abstracted and simplified to complete the transport calculation of neutron and gamma radiation fields inside the containment and obtain the radiation distribution of the inner wall of the containment. (2) Based on the radiation distribution on the inner wall of the containment and the target value of the dose rate on the outer wall of the containment, and combined with the attenuation formula of neutron and γ radiation in the containment shielding material, the initial scheme of the thickness distribution of each shielding layer of the containment is obtained. (3) Based on the initial scheme of containment structure and thickness distribution of each shielding layer of containment, establish containment structure and containment shielding model, complete the fine transport calculation of neutrons and γ radiation in containment and shielding materials, and obtain the radiation distribution of the outer wall of containment under this scheme; (4) Based on the radiation distribution on the outer wall of the containment and the target value of the dose rate on the outer wall of the containment, an iterative optimization algorithm is used to obtain the optimized scheme of the thickness distribution of each shielding layer of the containment. (5) Repeat steps (3) and (4) to perform multiple rounds of iterative optimization calculations until the thickness difference between the optimized scheme and the unoptimized scheme reaches the expected target, thus forming the final optimized containment shielding thickness distribution scheme.

2. The iterative optimization design method for marine containment shielding based on regional equal doses according to claim 1, characterized in that, The source terms are abstracted and simplified using equivalent point sources, surface sources, or volume sources. The devices are abstracted and simplified using the principle of equivalent nuclide composition, geometry, and density. The transport calculation of neutrons and gamma radiation fields within the containment is performed using Monte Carlo or point kernel integration methods.

3. The iterative optimization design method for marine containment shielding based on regional equal doses according to claim 1, characterized in that, The containment shielding material includes steel, lead, and polyethylene-based composite materials.

4. The iterative optimization design method for marine containment shielding based on regional equal doses according to claim 1, characterized in that, The attenuation formulas for neutrons and gamma radiation in the containment shielding material are empirical formulas, or obtained through Monte Carlo simulation and fitted using the following formula: H(t)=φ0·B(t)·e -μ·t ; In the formula, H(t) represents the dose rate after a ray with an initial fluence rate of φ0 penetrates a material with a thickness of t; φ0 represents the initial fluence rate of the ray; B(t) represents the accumulation factor, which is a polynomial of thickness t; μ represents the attenuation coefficient of the ray in the material; t represents the thickness of the material.

5. The iterative optimization design method for marine containment shielding based on regional equal dose according to claim 1, characterized in that, The target value for the dose rate on the outer wall of the containment is based on the limit for the dose rate on the outer wall of the containment, with a certain safety factor selected; the safety factor is 1.5 to 2.

5.

6. The iterative optimization design method for marine containment shielding based on regional equal doses according to claim 1, characterized in that, In step (3), detectors are set on the outer wall of the containment according to the size of the containment shielding installation grid, thus completing the layout and modeling of the detectors on the outer wall of the containment.

7. The iterative optimization design method for marine containment shielding based on regional equal doses according to claim 1, characterized in that, The refined transport calculations were performed using Monte Carlo simulations.

8. The iterative optimization design method for marine containment shielding based on regional equal dose according to claim 1, characterized in that, The iterative optimization algorithm uses the following formula: In the formula, t PBC0 t PBC The thicknesses of the polyethylene-based composite material before and after optimization are shown respectively. t Pb0 t Pb The thicknesses of the lead layer before and after optimization are shown respectively. μ PBC→n μ PBC→γ These are the attenuation coefficients of the polyethylene-based composite material for incident neutrons and gamma rays, respectively. μ Pb→γ The attenuation coefficient of the lead layer for incident gamma rays; H n H n0 These are the target value and the calculated value of the emitted neutron dose, respectively. H γ H γ0 These are the target and calculated values ​​for the emitted gamma-ray dose, respectively.

9. The iterative optimization design method for marine containment shielding based on regional equal dose according to claim 1, characterized in that, The expected goal is that the thickness difference between the optimized solution and the original solution is less than 5 mm.

10. The iterative optimization design method for marine containment shielding based on regional equal dose according to claim 1, characterized in that, It also includes step (6), which involves carrying out containment shielding modeling and transport verification calculations based on the final optimized containment shielding thickness distribution scheme to ensure that the radiation distribution on the outer wall of the containment meets the target limit requirements.

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