Marine containment vessel shielding iterative optimization design method based on regional equal dose

Abstract

The invention belongs to the technical field of marine radiation protection, and discloses a marine containment vessel shielding iterative optimization design method based on regional equal dose, which comprises the following steps: completing transport calculation of neutrons and gamma radiation fields in a containment vessel to obtain radiation distribution of the inner wall of the containment vessel; obtaining a thickness distribution initial scheme of each shielding layer of the containment according to a containment outer wall dose rate design target value; fine transport calculation of neutrons and gamma radiation in the containment and the shielding material is completed, and the radiation distribution of the outer wall of the containment in the scheme is obtained; a containment outer wall dose rate design target value is combined, and an iterative optimization algorithm is adopted to obtain a thickness distribution optimization scheme of each shielding layer of the containment; and carrying out multiple rounds of iterative optimization calculation until the thickness difference between the optimized scheme and the scheme before optimization reaches an expected target. According to the method, an optimized marine containment vessel shielding thickness distribution scheme is formed on the basis of a regional equal dose principle, the shielding weight is optimized while the radiation safety of personnel is guaranteed, and the overall resources of a ship are saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine radiation protection, and particularly relates to a method for iterative optimization design of marine containment shielding based on regional equal dose. Background Art

[0002] During the operation and maintenance of nuclear-powered ships, radioactivity is inevitably generated. To ensure the life health and radiation safety of personnel and to keep the nuclear radiation environment in the cabin at a reasonably achievable and as low as possible level, it is necessary to calculate, design, test and verify the nuclear radiation shielding of the cabin environment. The shielding design of nuclear-powered ships not only needs to ensure the radiation safety of personnel, but also needs to optimize the shielding design under the weight and space conditions allowed by the overall nuclear-powered ship, so as to realize an optimized shielding scheme of the marine containment that matches the overall design.

[0003] Onshore nuclear power plants use the containment and its internal concrete structures as shielding, with relatively low requirements for shielding weight and size. The radiation shielding design adopts an equal-thickness design method to ensure the radiation safety of the staff. In the containment of nuclear-powered ships, the radiation sources are distributed complexly along with the system pipelines and equipment, and there are significant differences in aspects such as the neutron and γ radiation intensity and energy spectrum. These radiation sources at different distances from the containment result in significant differences in the radiation intensity distribution on the containment wall surface in terms of intensity, neutron and γ component ratio, energy spectrum, etc. For example, the difference in intensity distribution can reach 10 to 100 times. If the equal-thickness design method is used for the shielding design of the marine containment, the same thickness of radiation shielding material is used in the area with weaker radiation intensity of the containment as in the area with stronger radiation intensity, which will not only lead to a significant increase in the weight and cost of the radiation shielding material, but also cause a further increase in the design strength and weight of the containment structure, greatly increasing the weight of the containment shielding structure, occupying a large amount of precious weight resources of the nuclear-powered ship, resulting in an increase in the local load and stress of the hull structure, and affecting the navigation and overall performance of the ship, such as an increase in resistance, a decrease in speed, and a reduction in the available payload. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for iterative optimization design of marine containment shielding based on regional equal dose in view of the deficiencies of the existing technology. According to the characteristics of the radiation field distribution in the nuclear-powered marine containment, based on the principle of regional equal dose, an optimized thickness distribution scheme of the marine containment shielding is formed, which can optimize the shielding weight while ensuring the radiation safety of personnel and save a large amount of overall ship resources.

[0005] To solve the technical problems proposed by the present invention, the present invention provides a method for iterative optimization design of marine containment shielding based on regional equal dose, including the following steps:

[0006] (1) Abstract and simplify the equipment and source terms according to the equipment layout and radioactive source term data inside the containment, complete the transport calculation of the neutron and γ radiation fields inside the containment, and obtain the radiation distribution on the inner wall of the containment.

[0007] (2) According to the radiation distribution on the inner wall of the containment and the designed target value of the dose rate on the outer wall of the containment, and combining with the attenuation formula of neutrons and γ radiation in the containment shielding material, obtain the initial scheme of the thickness distribution of each shielding layer of the containment.

[0008] (3) According to the containment structure and the initial scheme of the thickness distribution of each shielding layer of the containment, establish the containment structure and the containment shielding model, complete the refined transport calculation of neutrons and γ radiation inside the containment in the containment and the shielding material, and obtain the radiation distribution on the outer wall of the containment under this scheme.

[0009] (4) According to the radiation distribution on the outer wall of the containment, and combining with the designed target value of the dose rate on the outer wall of the containment, use the iterative optimization algorithm to obtain the optimized scheme of the thickness distribution of each shielding layer of the containment.

[0010] (5) Repeat steps (3) and (4), conduct multiple rounds of iterative optimization calculations until the thickness difference between the optimized scheme and the pre-optimized scheme reaches the expected target, and form the finally optimized thickness distribution scheme of the containment shielding.

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

[0012] In the above scheme, in step (1), the transport calculation of the neutron and γ radiation fields inside the containment adopts 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 formula of neutrons and γ radiation in the containment shielding material adopts an empirical formula, or is obtained by fitting through Monte Carlo simulation and using the following formula:

[0015] H(t) = φ0·B(t)·e -μ·t ;

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

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

[0018] B(t) represents the build-up 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 solution, on the basis of the dose rate limit value on the outer wall of the containment, a certain safety factor is selected for the design target value of the dose rate on the outer wall of the containment. The specific formula is:

[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 value on 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 solution, in step (3), detectors are arranged on the outer wall of the containment according to the scale of the shielding installation grid of the containment to complete the layout and modeling of the detectors on the outer wall of the containment.

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

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

[0030]

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

[0032]

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

[0034] t Pb0 , t Pb are the thicknesses of the lead layer before and after optimization, respectively;

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

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

[0037] H n , H n0They are the target value and the calculated value of the outgoing neutron dose, respectively;

[0038] H γ and H γ0 They are the target value and the calculated value of the outgoing gamma-ray dose, respectively;

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

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

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

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

[0043] In the above solution, it further includes step (6), and according to the finally optimized thickness distribution scheme of the containment shield, carry out the containment shield modeling and transport verification calculation to ensure that the radiation distribution on the outer wall of the containment meets the requirements of the target limit.

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

[0045] In order to reduce the shielding weight of the marine containment while ensuring the radiation safety of personnel, the present invention proposes an iterative optimization design method for the marine containment shield based on regional equal dose. According to the characteristics of the radiation field distribution inside the nuclear-powered marine containment, based on the principle of regional equal dose, an optimized thickness distribution scheme of the marine containment shield is formed. While ensuring the radiation safety of personnel, the shielding weight is optimized, saving a large amount of overall ship resources. The method of the present invention is applicable to the optimization design of the nuclear-powered marine containment shield, obtaining the optimized thickness distribution of the multi-layer shielding materials of the marine containment, and providing support for determining the radiation shielding scheme of the marine containment, optimizing the overall resources, ensuring operation and the radiation safety of personnel. Description of the Drawings

[0046] Figure 1 It is the iterative optimization design process of the marine containment shield in the embodiment of the present invention.

[0047] Figure 2 It is the dose rate limit requirement for the outer wall of the marine containment in the embodiment of the present invention.

[0048] Figure 3 This is the containment shielding thickness distribution scheme designed according to the traditional equal - thickness design and the regional equal - dose design of the present invention in the embodiments of the present invention.

[0049] Figure 4 This is the dose rate distribution (unit: μSv / h) of the front wall of the containment designed according to the traditional equal - thickness design and the regional equal - dose design of the present invention in the embodiments of the present invention. The thickness distribution in the figure: from left to right is from the port side to the starboard side of the front wall of the containment, and from top to bottom is from the upper part to the lower part of the front wall of the containment. Detailed implementation manners

[0050] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments.

[0051] Embodiment

[0052] In this embodiment, a method for iterative optimization design of marine containment shielding based on regional equal - dose is adopted to design the containment shielding thickness distribution scheme. The process is as Figure 1 , and specifically includes the following steps:

[0053] (1) According to the distribution of radiation sources in the marine containment, the layout of the reactor and primary loop system equipment and pipelines (as Figure 3 shown), abstract and simplify the equipment and source terms, establish models of source terms, primary loop system equipment and pipelines, and detectors on the inner wall of the containment in the marine containment, complete the neutron - gamma transport simulation calculation in the marine containment, and obtain the source term distribution on the inner wall of the marine containment.

[0054] Among them, the source terms in the containment mainly include the neutron and gamma source terms of the reactor and primary shield, and the source terms of the main coolant activation products in the primary loop pipelines and equipment. The neutron and gamma source terms of the reactor and primary shield are abstracted and simplified using equivalent point sources or surface sources, and the source terms of the main coolant activation products in the primary loop pipelines and equipment are abstracted and simplified using equivalent point sources or volume sources; the primary loop system equipment and pipelines mainly include main pumps, evaporators, primary loop pipelines, etc., and are simplified and abstracted according to the principles of equivalent nuclide composition, geometry, and density, ensuring both the shadow shielding effect and safety; the layout of detectors on the inner wall of the containment is carried out according to the size scale range of the containment shielding installation grid, usually with a grid size of 50 cm - 100 cm; the neutron - gamma transport simulation calculation in the containment is usually carried out using the Monte Carlo method or the point - kernel integration method for simulation calculation;

[0055] (2) Taking the attenuation formulas of gamma rays on the inner wall of the marine containment in lead and typical component polyethylene - based composites and the attenuation formula of neutrons on the inner wall of the containment in typical component polyethylene - based composites as examples, according to the dose rate limit requirements on the outer wall of the marine containment (such asFigure 2 ), obtain the initial scheme of the shielding layer thickness in each marine containment grid; the typical equations are as follows:

[0056]

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

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

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

[0060] (4) According to the radiation distribution on the outer wall of the marine containment, combined with the target doses of neutrons and γ radiation, use the iterative optimization algorithm to obtain the optimized thickness distribution of each shielding layer of the marine containment shielding, and form the optimized scheme of the marine containment shielding; the typical formula is as follows:

[0061]

[0062] In the formula, t PBC0 and t PBC are the thicknesses of the polyethylene-based composite material layer before and after optimization, in cm;

[0063] t Pb0 and t Pb are the thicknesses of the lead layer before and after optimization, in cm;

[0064] H n and H n0 are the target value and the calculated value of the outgoing neutron dose, in μSv / h, H n = 30%H;

[0065] H γ and H γ0 are the target value and the calculated value of the outgoing γ-ray dose, respectively, in μSv / h, where H γ = 70%H;

[0066] (5) According to the containment shielding optimization plan and combined with the actual installation requirements of the shielding, repeat steps (3) and (4) for 2 - 3 rounds of iterative optimization calculations until the thickness difference between the optimized containment shielding plan and the pre-optimization plan is less than 5 mm, forming the final optimized marine containment shielding plan;

[0067] (6) According to the final containment shielding optimization plan, complete the modeling and shielding transport calculations of the internal source terms, main system pipelines and equipment, structures, and containment shielding plans of the containment to ensure that the external radiation distribution of the containment shielding meets the limit requirements.

[0068] Figure 3 This is the containment shielding thickness distribution plan designed according to the traditional equal thickness and the regional equal dose design of the present invention. It can be seen that the containment based on the regional equal dose design is not of equal thickness, with some parts being thick and some being thin, saving a large amount of shielding materials compared to the equal thickness design, effectively reducing the shielding weight and saving overall resources.

[0069] Figure 4 This is the dose rate distribution of the front wall of the containment designed according to the traditional equal thickness and the regional equal dose design of the present invention. By comparing with the dose rate limit requirements in Figure 2 , the external radiation distribution of the containment shielding based on the regional equal dose design meets the dose limit requirements, which can fully ensure the radiation safety of personnel; although the containment 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 at the same time increases the hull structure stress, increasing the design difficulty of the hull structure.

[0070] The above embodiments are merely examples clearly described and not limitations on the implementation modes. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation modes here, and the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A marine containment shielding iterative optimization design method based on regional isodose, characterized in that, It includes the following steps: (1) According to the equipment layout and radioactive source term data inside the containment, abstract and simplify the equipment and source terms, complete the transport calculation of the neutron and γ radiation fields inside the containment, and obtain the radiation distribution on the inner wall of the containment; (2) According to the radiation distribution on the inner wall of the containment and the designed target value of the dose rate on the outer wall of the containment, combined with the attenuation formula of neutrons and γ radiation in the containment shielding material, obtain the initial scheme of the thickness distribution of each shielding layer of the containment; (3) According to the containment structure and the initial scheme of the thickness distribution of each shielding layer of the containment, establish the containment structure and the containment shielding model, complete the refined transport calculation of neutrons and γ radiation inside the containment in the containment and the shielding material, and obtain the radiation distribution on the outer wall of the containment under this scheme; (4) According to the radiation distribution on the outer wall of the containment, combined with the designed target value of the dose rate on the outer wall of the containment, use the iterative optimization algorithm 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 pre-optimized scheme reaches the expected target, and form the final optimized thickness distribution scheme of the containment shielding; 2. The method for iterative optimization design of marine containment shielding based on regional isodose according to claim 1, characterized in that The source term is abstracted and simplified using equivalent point sources, surface sources or volume sources, the equipment is abstracted and simplified according to the principles of equivalent nuclide composition, geometry and density, and the transport calculation of the neutron and γ radiation fields inside the containment uses the Monte Carlo or point kernel integration method.

3. The method for iterative optimization design of marine containment shielding based on regional isodose according to claim 1, wherein The containment shielding material includes steel, lead, and polyethylene-based composite materials.

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

5. The method for iterative optimization design of marine containment shielding based on regional isodose according to claim 1, wherein The designed target value of the dose rate on the outer wall of the containment selects a certain safety factor based on the dose rate limit on the outer wall of the containment; the safety factor is 1.5 - 2.

5.

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

7. The method for iterative optimization design of marine containment shielding based on regional isodose according to claim 1, characterized in that The refined transport calculation is performed through Monte Carlo simulation.

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

9. The iterative optimization design method of the marine containment shielding based on regional isodose according to claim 1, characterized in that, The expected target is that the thickness difference between the optimized scheme and the pre-optimized scheme is less than 5 mm.

10. The method for iterative optimization design of marine containment shielding based on regional isodose according to claim 1, wherein It also includes step (6), according to the final optimized thickness distribution scheme of the containment shielding, carry out the containment shielding modeling and transport verification calculation to ensure that the radiation distribution on the outer wall of the containment meets the requirements of the target limit.

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