Method for optimizing shielding performance of boron-containing polyethylene composite material for radioactive substance transportation container

Abstract

The invention relates to a method for optimizing the shielding performance of a boron-containing polyethylene composite material for a radioactive substance transportation container. The method comprises the following steps: establishing a comparable baseline model in Monte Carlo, and dispersing a shielding layer and a material library; determining a source item based on the loading and obtaining an inner surface unified incident spectrum; generating a multi-group macroscopic cross section changing along with the boron content A; obtaining a transmittance R (N) and a dose baseline according to a uniform formula; 2%, setting a gradient according to'low inside and high outside ', performing iterative calculation, comparing delta R (N), and introducing a layer number increase stopping threshold value (lt; 2%) and local'small-amplitude single-point' correction until a target is met. According to the method, the surface transmission and dosage are remarkably reduced under the condition of meeting regulatory limit values, weight and cost are reduced, and manufacturing and reuse are easy.

Description

Technical Field

[0001] This invention relates to the field of radiation shielding composite material design technology in the safety of radioactive material transportation, and in particular to a method for optimizing the shielding performance of boron-containing polyethylene composite material for radioactive material transportation containers. Background Technology

[0002] To prevent or reduce radiation hazards to workers and the public during the transport of radioactive materials, my country's national standard GB11806-2019 clearly stipulates the limits for radiation levels during transport. To comply with regulations and standards, systems transporting or storing radioactive materials typically employ shielding materials between the radiation source and personnel / environment to absorb and attenuate radiation, ensuring that dosimetric parameters at the outer surface of the container and at specified distances meet the limits. For neutron radiation, various neutron shielding composite materials have been developed, with boron-containing polyethylene (B-PE) being the most widely used, typically containing approximately 5%–20% (mass fraction). In B-PE, hydrogen atoms facilitate the slowing down of fast neutrons, while boron has a high capture cross-section for thermal neutrons; the synergy of these two components effectively shapes and attenuates neutron flux and the energy spectrum.

[0003] However, radioactive material transport containers are typically multi-layered composite shielding structures (such as steel, concrete, lead, boronized polymers, etc.), and the energy range adaptability and material utilization efficiency of a single homogeneous B-PE material are limited. Specifically, under neutron fields of different energy groups, a uniform hydrogen / boron ratio is difficult to simultaneously achieve efficient moderation and efficient capture. Often, it is necessary to "harden" meet the limits by increasing the thickness or boron content, leading to a significant increase in the overall mass and volume of the container. Simultaneously, the addition of high-density materials such as steel and lead increases the structural weight and manufacturing difficulty, adversely affecting lifting, transportation organization, and operational safety, limiting the amount transported per shipment, and increasing the total life-cycle cost. Furthermore, homogeneous materials often have insufficient shielding margin in local channels such as corners and penetration paths, easily leading to the contradiction of "overfilling but still having weak points," making it difficult to achieve lightweighting and optimal material configuration while ensuring regulatory compliance. Therefore, there is an urgent need to develop neutron shielding optimization methods that can improve shielding efficiency, reduce mass and volume, and ensure manufacturing and acceptance consistency under thickness-limited conditions, considering actual source terms and geometric boundary conditions.

[0004] In view of the above problems, this invention is proposed. Summary of the Invention

[0005] This invention discloses a method for optimizing the shielding performance of boron-containing polyethylene composite materials for radioactive material transport containers, aiming to solve the technical problems existing in the prior art.

[0006] To achieve the above objectives, according to the present invention, a method for optimizing the shielding performance of boron-containing polyethylene composite materials for radioactive material transport containers is provided, comprising: In Monte Carlo, the baseline geometry and detectors of the transport container were established, the boundary and source strength were normalized, the statistical caliber was unified, and the neutron shield was discretized into several layers according to thickness and a material library was prepared to provide a comparable and reusable benchmark model for subsequent gradient assignment and comparative optimization. The source terms of energy groups and relative intensities are determined based on loading and radiation characteristics, and a uniform incident spectrum reaching the inner surface of the neutron shield is obtained through geometric coupling / shaping when the contents are significantly modulated. A boron-containing polyethylene material library was established, and multiple macroscopic cross sections varying with boron content A were generated under a selected kernel database. Using a homogeneous composite material as the neutron shield input, the neutron transmission and dose at the surface of the transport container and at 1m / 2m were calculated according to the energy group. The transmittance R(N) was calculated statistically and the relevant dosimetric quantities were recorded. The boron content A of the homogeneous composite material is set to increase monotonically from "lower in the inner layer and higher in the outer layer," so that the inner layer promotes deceleration and the outer layer promotes capture. Under the premise of meeting the target average boron content A, the formulation of each layer is rapidly generated according to the number of layers n, and the gradient composite material is calculated using the following formula: in, For a given boron content gradient; n is the number of gradients; A represents the target average boron content.

[0007] As a preferred technical solution, after calculating the gradient composite material, the method further includes using the parameters of the gradient composite material as input, calculating the neutron transmission and dose at the surface of the transport container and at 1m / 2m according to the energy group, statistically analyzing the transmittance R(N), and comparing the transmittance reduction ΔR between the gradient composite material and the homogeneous composite material.

[0008] As a preferred technical solution, the transmittance reduction ΔR is calculated using the following formula: .

[0009] As a preferred technical solution, the transmittance R(N) is calculated statistically using the following formula: .

[0010] As a preferred technical solution, after obtaining the transmittance reduction magnitude ΔR, the method further includes determining the marginal gain of the transmittance reduction magnitude ΔR through layer scanning. If the marginal gain of the number of layers for the transmittance reduction magnitude ΔR is <2%, then the increase in the number of layers is stopped.

[0011] As a preferred technical solution, after layer scanning, if the transmittance of a local monitoring surface / corner point exceeds the limit or the energy region leaks abnormally, only a "small single-point" adjustment is made to the relevant gradient layer, and the layer is replaced again for verification.

[0012] As a preferred technical solution, after calculating the gradient composite material, the method further includes determining whether the optimized configuration meets the preset optimization target. If yes, the optimization ends; if no, continue to perform statistical calculation of transmittance R(N) and record relevant dosimetric steps until the gradient composite material step is recalculated, until the preset optimization objective is met.

[0013] As a preferred technical solution, the baseline geometry and detectors for the transport container established in Monte Carlo involve the transport container cavity, contents, neutron shield, outer structure, and external air domain.

[0014] As a preferred technical solution, the neutron shield is discretized into several layers according to its thickness and stored in a material library. This includes discretizing the neutron shield into n sub-layers along the thickness direction, where n=1 when the baseline is uniform. The material library records parameters such as the boron content A, density ρ(A), hydrogen / boron atomic number density, and manufacturing tolerances.

[0015] As a preferred technical solution, the boron-containing polyethylene material library includes boron content A, density ρ(A), hydrogen / boron atomic number density, and mechanical / thermal constraints.

[0016] The technical solution adopted in this invention can achieve at least one of the following beneficial effects: 1. This invention achieves precise deceleration and efficient capture synergy of neutrons in different energy regions through a boron content gradient configuration of "low inner and high outer" and iterative optimization driven by multi-group equivalent cross sections. Under the premise of maintaining the total thickness and the target average boron content, the more uniform material can significantly reduce the neutron transmittance and dosimetry at the container surface and at 1m / 2m, improve the effective contribution of unit boron content, and reduce ineffective filling, thereby achieving weight and material cost reduction while meeting regulatory / standard limits.

[0017] 2. This invention introduces a layer number cessation criterion and a local "small-amplitude single-point" correction strategy: First, the layer number n is scanned. When the marginal gain of the transmittance reduction ΔR of adjacent n layers is less than about 2% (1-3%), layer addition is stopped to avoid overcomplication. Then, for local out-of-limit paths, only the relevant gradient layer formulation or thickness is adjusted and back-substituted for verification. This mechanism enables rapid design convergence, controllability, and verifiability, while taking into account the feasibility of manufacturing processes such as lamination / co-extrusion and dimensional tolerance requirements, improving engineering feasibility and batch consistency.

[0018] 3. This invention, through an integrated process of Monte Carlo baseline modeling, scenario-based incident spectrum unification, material library / section interpolation, baseline comparison, and gradient back substitution, unifies statistical caliber and uncertainty labeling, forming a comparable and reusable benchmark model. When the load or source spectrum changes, only the incident spectrum and material library interpolation need to be updated to quickly reuse the entire optimization process, significantly shortening the design and verification cycle, reducing the cost of scheme adjustment, and improving the adaptability and robustness to multiple scenarios and multiple batches of transportation tasks. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, forming part of the present invention. The illustrative embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 This is a flowchart illustrating a method for optimizing the shielding performance of a boron-containing polyethylene composite material for a radioactive material transport container according to the present invention. Figure 2 This is a schematic diagram of the structure of the uniform composite material and the gradient composite material of the present invention.

[0020] Explanation of reference numerals in the attached figures: 1. Homogeneous composite material; 2. Gradient composite material. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. In the description of this invention, it should be noted that the term "or" is generally used to include the meaning of "and / or," unless otherwise expressly indicated.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or a magnetic connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, in the description of this application, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0023] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] To address issues such as excessive mass / volume in existing technologies, this invention provides a method for optimizing the shielding performance of boron-containing polyethylene composite materials used in radioactive material transport containers, such as... Figure 1 and Figure 2 As shown, it includes the following steps: S1: Geometric modeling (baseline model construction); In Monte Carlo, the baseline geometry and detectors of the transport container were established, the boundary and source strength were normalized, the statistical caliber was unified, and the neutron shield was discretized into several layers according to thickness and a material library was prepared to provide a comparable and reusable benchmark model for subsequent gradient assignment and comparative optimization. S11: Confirm the model range; A computational model of the transport container was constructed using Monte Carlo software, comprising: the container cavity, contents (which can be equivalent to an equivalent scatterer / absorber), a neutron shield (nominal thickness t), an outer structure (such as a steel shell / layer), and an external air domain; surface source or point detector elements were arranged on the outer surface of the container at 1m and 2m positions (for flux and dose response statistics and for unified comparison of dosimetric criteria at key locations). S12: Boundary and Normalization Processing; The outer domain is set to a vacuum boundary or reflection boundary of sufficient distance (depending on the scenario). The source intensity is normalized according to the unit source particle or absolute source rate to ensure comparability under different configurations. The statistical weights and statistical uncertainties of the outer surface, 1m and 2m are uniformly constrained to ensure the robustness of the comparison. S13: Grid or subdivision; The neutron shield is discretized into n sub-layers along the thickness direction (n=1 when the baseline is uniform), and a material library is reserved for subsequent gradient assignment; preferably, the material library records parameters such as boron content A, density ρ(A), hydrogen / boron atomic number density and manufacturing tolerance. S2: Source Term Information Acquisition (Scenario-based Energy Spectrum); The source terms of energy groups and relative intensities are determined based on loading and radiation characteristics, and a uniform incident spectrum reaching the inner surface of the neutron shield is obtained through geometric coupling / shaping when the contents are significantly modulated, serving as a common benchmark for S4 and S6 calculations. S21: Source term determined; The neutron source terms are determined based on the loaded contents and radiation spectrum characteristics, including at least energy groups and their corresponding relative intensities; S22: Geometric coupling; When the contents significantly modulate the energy spectrum, an energy spectrum shaper needs to be added into the cavity or coupled calculations should be used to obtain the "incident spectrum" reaching the inner surface of the shield, which serves as a consistent starting point for optimization calculations (the incident spectrum serves as a unified benchmark for S4 and S6). S3: Material parameters are determined (equivalent to manufacturability); A boron-containing polyethylene material library was established (boron content A, density ρ(A), H / B atomic number density and mechanical / thermal constraints), and multi-group macroscopic cross sections (with interpolation tables) varying with A were generated under the selected kernel database to enable rapid and continuous assignment of values ​​to each gradient layer, ensuring that the equivalent calculation is consistent with manufacturability. S31: Baseline Material Library; Boron-containing polyethylene composites are composed of a polymer matrix (such as HDPE) and boron-containing components. Key parameters include: boron content A (mass fraction), material density ρ(A), hydrogen atom density, boron atom density, etc., and mechanical / thermal constraints are recorded to meet transportation conditions. S32: Equivalent cross section; Generate multi-group macroscopic cross sections that vary with A under the selected kernel database, and establish interpolation tables as necessary to support rapid assignment and continuous value assignment of gradient layer materials. S4: Neutron transport simulation (baseline assessment for homogeneous materials); Using homogeneous composite material 1 as the input for the neutron shield, neutron transmission and dose at the surface of the transport container and at 1m / 2m were calculated according to energy groups. Transmittance R(N) was statistically calculated and relevant dosimetric quantities were recorded, forming a unified benchmark for subsequent S6 gradient comparison and benefit assessment. Specifically, using the parameters of the aforementioned homogeneous boron-containing polyethylene composite material (i.e., homogeneous composite material 1) as the input for the neutron shield of the transport container, the transmitted neutrons on the outer surface of the container were calculated, and the transmittance R(N) was statistically analyzed according to the neutron energy range. ; The metrological measurements of the outer surface, 1m, and 2m were converted and recorded as a reference for subsequent comparison. S5: Gradient material configuration optimization (for energy regions with low inner and high outer energy); The boron content A of the homogeneous composite material 1 is set to increase monotonically from "lower inside and higher outside" so that the inner layer promotes deceleration and the outer layer promotes capture. Under the premise of meeting the target average boron content A, the formulation of each layer is quickly generated according to the number of layers n to obtain the gradient composite material 2, which is used for subsequent energy zone matching and benefit comparison with the baseline. Preferably, the configuration of the boron-containing polyethylene composite material is optimized, with the boron content gradually increasing from the inside to the outside of the transport container. The gradient content of the boron-containing polyethylene composite material is calculated using the following formula. in, For a given boron content gradient; n is the number of gradients; A represents the target average boron content; Gradient composite material 2 is obtained, such as Figure 2As shown, the inner low boron is used for efficient deceleration, and the outer high boron is used for efficient capture. S6: Iterative simulation (gradient comparison and benefit evaluation); Run the S4 process back using the formula generated in step S5, calculate the transmittance reduction ΔR according to the energy group, and simultaneously perform parallel comparisons and labeling of dosimetric values ​​at the outer surface, 1m, and 2m to evaluate the gradient benefit and support engineering criteria; that is, use the optimized parameters of the gradient composite material 2 obtained in step S5 to perform the calculation in step S4, and compare the transmittance reduction ΔR of the gradient material and the homogeneous material: Simultaneously compare the dosimetric values ​​at the outer surface and at 1m and 2m as engineering criteria; and label the statistical uncertainty with the same caliber to ensure the robustness of the conclusions; S7: Parameter optimization (number of layers and stop-loss criteria for local fine-tuning); The number of layers to be stopped is determined by layer scanning, balancing shielding benefits with manufacturing, cost, and process feasibility; small-scale single-point corrections are implemented for locally exceeding limits, with back-substitution verification to avoid global disturbances; specifically including: S71: Layer scan; Scan for n=2,3,4... and calculate the marginal gain of ΔR. When the gain of ΔR next n is <2% (can be set to 1-3% in engineering), stop increasing the number of layers to balance manufacturing complexity and cost, as well as lamination / co-extrusion feasibility. S72: Local correction; If the transmittance exceeds the limit or the energy region leaks abnormally in the direction of the local monitoring surface / corner, only a "small single-point" adjustment is made to the relevant gradient layer, and the data is replaced again for verification to avoid global fluctuations.

[0025] S8: Optimal configuration confirmed; Determine whether the optimized configuration meets the preset optimization target; if yes, end the optimization; if no, continue with steps S4-S7 until the preset optimization target is met.

[0026] Through the above design, the core of this invention lies in proposing a boron-containing gradient configuration of "low inner layer and high outer layer" and a closed-loop optimization process combined with the layer number cessation criterion: Under the unified framework of uniform baseline-gradient configuration-sensitivity back-substitution-local correction, the low boron layer on the inner side is used for efficient deceleration and the high boron layer on the outer side is used for high-probability capture according to the scenario-based energy spectrum, thereby achieving directional attenuation and energy spectrum shaping of neutrons with different energies from a mechanistic perspective; at the same time, the consistency of formulation-manufacturing-acceptance is ensured by parameterized material library and equivalent cross-section interpolation, and dosimetric criteria are introduced at the outer surface and at 1 m / 2 m. Compared to homogeneous shielding, gradient structures significantly reduce neutron flux and dose equivalent on the container surface, increase the effective contribution per unit of boron, reduce ineffective filling, and achieve material savings and weight reduction under the same shielding performance, thereby increasing single-transport capacity and reducing costs and operational risks. At the same time, the layer marginal gain threshold and the "small single-point" local correction strategy avoid over-complexity and facilitate rapid convergence, enabling this invention to have higher shielding efficiency, better material utilization, and stronger engineering feasibility, forming a robust and lightweight solution for neutron protection, and supporting rapid reuse and iteration in different source spectrum scenarios.

[0027] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A method for optimizing the shielding performance of boron-containing polyethylene composite material for radioactive material transport containers, characterized in that, include: In Monte Carlo, the baseline geometry and detectors of the transport container are established, the boundary and source strength are normalized, the statistical caliber is unified, and the neutron shield is discretized into several layers according to thickness and a material library is prepared to provide a comparable and reusable benchmark model for subsequent gradient assignment and comparative optimization. The source terms of energy groups and relative intensities are determined based on loading and radiation characteristics, and a uniform incident spectrum reaching the inner surface of the neutron shield is obtained through geometric coupling / shaping when the contents are significantly modulated. A boron-containing polyethylene material library was established, and multiple macroscopic cross sections varying with boron content A were generated under a selected kernel database. Using a homogeneous composite material as the neutron shielding input, the neutron transmission and dose at the surface of the transport container and at 1m / 2m are calculated according to the energy group. The transmittance R(N) is statistically calculated and the relevant dosimetric quantities are recorded. The boron content A of the homogeneous composite material is set in a monotonically increasing manner from "lower inside, higher outside" to promote deceleration in the inner layer and capture in the outer layer. Under the premise of meeting the target average boron content A, the formulations for each layer are rapidly generated according to the number of layers n, and the gradient composite material is calculated using the following formula: in, For a given boron content gradient; n is the number of gradients; A represents the target average boron content.

2. The optimization method according to claim 1, characterized in that, After obtaining the gradient composite material, the calculation further includes using the parameters of the gradient composite material as input, calculating the neutron transmission and dose at the surface of the transport container and at 1m / 2m according to the energy group, calculating the transmittance R(N), and comparing the transmittance reduction ΔR of the gradient composite material and the uniform composite material.

3. The optimization method according to claim 2, characterized in that, The reduction in transmittance ΔR is calculated using the following formula: 。 4. The optimization method according to claim 1, characterized in that, The statistical calculation of transmittance R(N) is performed using the following formula: 。 5. The optimization method according to claim 2, characterized in that, After obtaining the transmittance reduction magnitude ΔR, the method further includes determining the marginal gain of the transmittance reduction magnitude ΔR through layer scanning. If the marginal gain of the number of layers for the transmittance reduction magnitude ΔR is <2%, then the increase of the number of layers is stopped.

6. The optimization method according to claim 5, characterized in that, After the layer scanning, if the transmittance of a local monitoring surface / corner point exceeds the limit or the energy region leaks abnormally, only a "small single-point" adjustment is made to the relevant gradient layer, and the data is recycled back for verification.

7. The optimization method according to claim 1, characterized in that, After the gradient composite material is obtained through calculation, the method further includes determining whether the optimized configuration meets the preset optimization target. If yes, the optimization ends; if no, the statistical calculation of transmittance R(N) and recording of relevant dosimetric values ​​continues until the gradient composite material step is recalculated, until the preset optimization objective is met.

8. The optimization method according to claim 1, characterized in that, The establishment of the baseline geometry and detectors for the transport container in Monte Carlo involves the transport container cavity, contents, neutron shield, outer structure, and external air domain.

9. The optimization method according to claim 1, characterized in that, The process of discretizing the neutron shield into several layers according to its thickness and preparing them in a material library includes discretizing the neutron shield into n sub-layers along the thickness direction, where n=1 when there is a uniform baseline; the material library records parameters such as boron content A, density ρ(A), hydrogen / boron atomic number density, and manufacturing tolerances.

10. The optimization method according to claim 1, characterized in that, The boron-containing polyethylene material library includes boron content A, density ρ(A), hydrogen / boron atomic number density, and mechanical / thermal constraints.

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