Neutron shielding concrete with double-layer structure based on energy grading absorption and verification method

Abstract

The present application relates to a kind of double-layer structure neutron shielding concrete based on energy hierarchical absorption and verification method, including inner layer and outer layer, inner layer includes hydrogen-containing concrete, outer layer includes the concrete of high capture cross-section element;Inner layer is used to slow down incident neutron to thermal neutron energy range, and outer layer is used to absorb the thermal neutron after slowing down.For hydrogen-containing concrete in inner layer, fast neutron is preferentially slowed down, and the main part of neutron energy spectrum is reduced to thermal neutron energy area;Through the concrete of high capture cross-section element in outer layer, thermal neutron after slowing down is efficiently captured;Based on the physical law of neutron transport and slowing down process, the critical thickness of inner and outer layer materials is accurately deduced by establishing mathematical model, to ensure the maximum shielding efficiency.Through the above function-structure coupling design, the present application significantly improves the comprehensive shielding ability of concrete to full-spectrum neutron, and provides key material support for the miniaturization, light-weight construction and safe operation of advanced nuclear facilities such as thorium-based molten salt reactor.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, and specifically relates to a double-layer neutron-shielded concrete structure based on energy graded absorption and a verification method. Background Technology

[0002] As a core material for the biological shielding layer of nuclear facilities, the performance of neutron shielding concrete directly affects whether the miniaturization and lightweight design goals of the reactor system can be achieved. Its core function is to effectively shield against highly penetrating and hazardous neutrons and gamma rays, ensuring the safety of personnel and the environment. However, existing neutron shielding concrete technologies mainly rely on two complementary but each functionally limited technical approaches: Hydrogen-moderating concrete: represented by serpentine concrete, magnetite concrete, etc., mainly relies on the abundant hydrogen element in the material to effectively slow down fast neutrons, but its ability to absorb slowed thermal neutrons is relatively limited.

[0003] High-capture-section additive concrete: By incorporating substances with high neutron absorption cross sections, such as boron carbide (B4C) and gadolinium oxide (Gd2O3), into the concrete matrix, thermal neutrons can be captured efficiently, but the effect on slowing down fast neutrons is not good.

[0004] However, it is difficult to simultaneously optimize the shielding effectiveness for both fast neutron moderation and thermal neutron absorption using a single type of neutron shielding concrete. Therefore, to achieve effective full-spectrum neutron shielding, it is often necessary to significantly increase the thickness and weight of the shielding layer, which severely limits the potential of advanced nuclear energy systems in compact designs, such as small modular reactors and mobile / remote applications.

[0005] Therefore, how to provide a double-layer neutron-shielded concrete structure based on energy graded absorption and a verification method is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] This invention provides a double-layer neutron shielding concrete based on energy graded absorption and a verification method, aiming to solve the problem that single-component shielding materials cannot simultaneously achieve fast neutron moderation and efficient thermal neutron absorption.

[0007] To solve the above technical problems, the present invention includes the following technical solutions: A double-layer neutron-shielding concrete structure based on energy graded absorption includes an inner layer and an outer layer. The inner layer comprises hydrogen-containing concrete, and the outer layer comprises concrete containing elements with high capture cross-sections. The inner layer is used to moderate incident neutrons to the thermal neutron energy range, and the outer layer is used to absorb the moderated thermal neutrons.

[0008] Furthermore, the hydrogen-containing concrete is serpentine concrete, and the concrete containing high capture cross-section elements is concrete containing gadolinium oxide, with a volume fraction of gadolinium oxide of 3% to 8%.

[0009] Furthermore, the thickness of the inner layer is determined based on the neutron slowing age theory. Specifically, this is achieved by calculating the macroscopic scattering cross section, average logarithmic energy drop, and slowing age of the serpentine concrete, ensuring that the neutron spatial distribution satisfies the condition of slowing down the required proportion of neutrons to the thermal neutron energy range. The slowing age is... The calculations include: Establish the neutron slowing equation (Fermi age theory), the slowing age at which the neutron energy decreases from the initial value E0 to E. Defined as: , Where E0 is the initial neutron energy, generally considered to be 2 MeV; E is the target neutron energy, and serpentine concrete needs to reduce the neutron energy to below 10⁻⁷ MeV; D （E’） The neutron diffusion coefficient at energy E' is expressed in cm. The macroscopic scattering cross section at energy E' is expressed in cm. -1 The neutron diffusion coefficient, D, characterizes the neutron's ability to diffuse in space. , in, For macroscopic transport cross-section, The cosine of the average scattering angle is typically taken as 0.82 for serpentine concrete. Substituting D into... And separate the variables: , The energy of the moderated neutron follows a Gaussian distribution: , Where Q is the total number of source neutrons; X is the penetration depth, and the standard deviation of its spatial distribution when neutrons are moderated to energy E. To moderate 99.9999% of neutrons to the easily absorbed region, the following conditions must be met: , D is the critical thickness.

[0010] Furthermore, the macroscopic scattering cross section of the serpentine concrete Calculated by the following formula: , In the formula, N i Let i be the atomic density of atom i in serpentine concrete. The microscopic scattering cross section of atom i is 82.0 for hydrogen, 11.0 for iron, 4.2 for oxygen, 3.4 for magnesium, 2.2 for silicon, and 3.0 for calcium. The unit is barn. -24 cm 2 The hydrogen content in serpentine concrete is a0, the iron content is b0, the oxygen content is c0, the magnesium content is d0, the silicon content is e0, and the calcium content is f0. The density of serpentine concrete is g / cm³. 3 .

[0011] Furthermore, through MCNP simulation, the average logarithmic energy reduction of this type of serpentine concrete was obtained by inputting the elemental proportions and density parameters of the serpentine concrete. Generally speaking, when the neutron radiation energy is 2.0 MeV, .

[0012] Furthermore, the outer layer thickness is determined based on the macroscopic absorption cross section of thermal neutrons. This macroscopic absorption cross section is calculated from the microscopic absorption cross section, abundance, and content of gadolinium isotopes in the outer concrete layer. The calculation method is as follows: , , in, f is the atomic density of gadolinium atoms. 155 for 155 Gd isotopic abundance for 155 The microscopic absorption cross section of Gd; f 157 for 157 Gd isotopic abundance for 157 Microscopic absorption cross section of Gd The density of gadolinium oxide concrete, The mass fraction of gadolinium, is the relative molecular mass of gadolinium oxide; When the moderated thermal neutron shielding efficiency reaches 99.9999%, the thickness of gadolinium oxide concrete can be calculated using the following formula: .

[0013] Furthermore, the sum of the inner layer thickness and the outer layer thickness, which constitutes the total thickness of the neutron shielding concrete in the double-layer structure, is calculated using the following formula: .

[0014] This invention also provides a verification method for a double-layer neutron-shielded concrete structure based on energy graded absorption, comprising: Step S1: Provide two types of concrete with the same thickness, namely single-layer structural concrete and double-layer structural neutron shielding concrete. The double-layer structural neutron shielding concrete is the double-layer structural neutron shielding concrete based on energy graded absorption. The single-layer structural concrete is mainly serpentine concrete with a volume fraction of 3% to 8% gadolinium oxide. Step S2: 2MeV neutrons are emitted in the directions of the two types of concrete respectively, and the neutrons penetrate the two types of concrete; Step S3: Record the number and energy of neutrons transmitted through the two types of concrete.

[0015] Furthermore, the inner layer of hydrogen-containing concrete is serpentine concrete, and the outer layer of concrete containing high-capture cross-section elements is gadolinium oxide concrete.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a double-layer neutron-shielding concrete structure based on energy-grade absorption, comprising an inner layer and an outer layer. The inner layer consists of hydrogen-containing concrete, and the outer layer consists of concrete containing elements with high capture cross-sections. The concrete is designed using a double-layer neutron-shielding concrete structure based on energy-grade absorption and its thickness design method. Functional zoning design: The inner layer of hydrogen-containing concrete preferentially slows down fast neutrons, reducing the main body of the neutron energy spectrum to the thermal neutron energy range (<0.1 eV). Cooperative absorption mechanism: The outer layer of concrete with high capture cross-section elements efficiently captures slowed thermal neutrons. Theoretical-driven thickness optimization: Based on the physical laws of neutron transport and slowing processes, a mathematical model is established to accurately derive the critical thicknesses of the inner and outer layers, ensuring maximum shielding effectiveness. Through the above functional-structural coupling design, this invention significantly improves the comprehensive shielding capability of concrete against the full spectrum of neutrons, providing key material support for the miniaturization, lightweight construction, and safe operation of advanced nuclear facilities such as thorium-based molten salt reactors. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a model of a double-layer neutron-shielded concrete structure based on energy graded absorption, which is verified by MCNP according to an embodiment of the present invention. Figure 2 This is an example diagram of the MCNP program used for neutron shielding simulation studies of double-layer neutron-shielded concrete structures.

[0018] 1- Neutron source, 2- Neutron, 3- Single-layer concrete structure, 4- Gadolinium atom, 5- Recording surface, 6- Double-layer neutron shielding concrete structure. Detailed Implementation

[0019] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a double-layer neutron-shielded concrete structure based on energy graded absorption and its verification method, according to the present invention. The advantages and features of the present invention will become clearer from the following description.

[0020] The following is combined with Figures 1 to 2 The composition of the double-layer neutron-shielded concrete based on energy graded absorption of the present invention is described in detail.

[0021] Example 1 A two-layer structure, the inner layer uses conventional C25 serpentine concrete, with a cement content of 390 kg / m³. 3 Fine aggregate 690kg / m 3 Coarse aggregate 1060kg / m³ 3 Water 200kg / m 3 Water-reducing agent 5.4 kg / m³ 3 The density after casting is 2300 kg / m³. 3 The mass ratios of each element can be calculated as follows: H (1.77%), Fe (16.30%), Mg (10.42%), O (58.07%), Si (7.04%), and Ca (6.40%).

[0022] Meanwhile, the outer layer uses gadolinium oxide concrete, with gadolinium oxide replacing 5% of the cement volume fraction. Calculations show that the gadolinium content in the entire concrete is 1.81 wt.%, and the density of the gadolinium oxide concrete is 2330 kg / m³. 3 . The slowing age of the serpentine concrete It can be calculated using the following formula: The critical thickness d of the serpentine concrete can be calculated as follows: Atomic density of gadolinium atoms and its macroscopic absorption cross section in gadolinium oxide concrete It can be calculated using the following formula: Critical thickness d of gadolinium oxide concrete m It can be calculated using the following formula: The double-layer neutron-shielded concrete structure has a total thickness of: Please refer to Figure 1This embodiment also provides a verification method for a double-layer neutron-shielded concrete structure based on energy graded absorption, which is verified using MCNP and designed as follows: Step 1: Provide two types of concrete with the same thickness. The two types of concrete are single-layer structural concrete 3 and double-layer structural neutron shielding concrete 6. The single-layer structural concrete 3 is mainly serpentine concrete with gadolinium atoms 4 added. The gadolinium atoms 4 are evenly distributed in the entire 60.5cm thick concrete. The mass fraction of gadolinium atoms 4 in the entire single-layer structural concrete 3 is 0.12%. Step 2: Set up a circular neutron source 1 with a diameter of 50cm on the left side, and emit 2MeV neutrons 2 in the directions of the two types of concrete, which will penetrate the two types of concrete. Step 3: Record the number and energy of the transmitted neutrons through recording surface 5.

[0023] refer to Figure 2 Here is an example of an MCNP program for neutron shielding simulation studies of a double-layer neutron-shielded concrete structure: MCNP calculations show that the neutron transmittance for a single-layer concrete structure is 5.6352 × 10⁻⁶. -4 The weighted energy of the transmitted neutron is 2.7426 × 10⁻⁶. -4 MeV; for a double-layer neutron-shielded concrete 6, the neutron transmittance is 5.0513 × 10⁶. -4 The weighted energy of the transmitted neutron is 2.6163 × 10⁻⁶. -4 MeV.

[0024] The MCNP calculations above show that concrete using a double-layer neutron-shielded concrete structure based on energy-graded absorption and its thickness design method can reduce neutron leakage rate by 10.36% and transmit neutron energy by 4.6% compared to single-layer ordinary neutron-shielded concrete structures. This demonstrates extremely superior neutron protection capabilities and contributes to the safety protection of nuclear facility buildings.

[0025] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. The above embodiments only illustrate several implementations of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A double-layer neutron-shielded concrete structure based on energy-graded absorption, characterized in that, It includes an inner layer and an outer layer, the inner layer comprising hydrogen-containing concrete and the outer layer comprising concrete containing high capture cross-section elements; the inner layer is used to moderate incident neutrons to the thermal neutron energy range and the outer layer is used to absorb the moderated thermal neutrons.

2. The double-layer neutron-shielded concrete structure based on energy-graded absorption according to claim 1, characterized in that, The hydrogen-containing concrete is serpentine concrete, and the concrete containing high capture cross-section elements is concrete containing gadolinium oxide, with a volume fraction of gadolinium oxide of 3% to 8%.

3. The double-layer neutron-shielded concrete structure based on energy graded absorption according to claim 1, characterized in that, The thickness of the inner layer is determined based on the neutron slowing age theory. Specifically, it is calculated by examining the macroscopic scattering cross section, average logarithmic energy drop, and slowing age of the serpentine concrete, ensuring that the spatial distribution of neutrons satisfies the condition of slowing down a required proportion of neutrons to the thermal neutron energy range. The slowing age is... The calculations include: Establish the neutron moderation equation, and the moderation age is when the neutron energy decreases from the initial value E0 to E. Defined as: ， Where E0 is the initial neutron energy, considered to be 2 MeV; E is the target neutron energy, which the serpentine concrete needs to reduce to 10 MeV. -7 Below MeV; D （E’） Neutron diffusion coefficient at energy E', in cm; The macroscopic scattering cross section at energy E' is expressed in cm. -1 The neutron diffusion coefficient D characterizes the neutron's ability to diffuse in space. ， in, For macroscopic transport cross-section, Assuming the average scattering angle cosine, and taking 0.82 for serpentine concrete, substitute D into... And separate the variables: ， The energy of the moderated neutron follows a Gaussian distribution: ， Where Q is the total number of source neutrons; X is the penetration depth, and the standard deviation of its spatial distribution when neutrons are moderated to energy E. ; To moderate 99.9999% of neutrons to the easily absorbed region, the following conditions must be met: 。 4. The double-layer neutron-shielded concrete structure based on energy graded absorption according to claim 3, characterized in that, The macroscopic scattering cross section of the serpentine concrete Calculated by the following formula: ， In the formula, N i Let i be the atomic density of atom i in serpentine concrete. The microscopic scattering cross section of atom i is 82.0 for hydrogen, 11.0 for iron, 4.2 for oxygen, 3.4 for magnesium, 2.2 for silicon, and 3.0 for calcium. The unit is barn. -24 cm 2 The hydrogen content in serpentine concrete is a0, the iron content is b0, the oxygen content is c0, the magnesium content is d0, the silicon content is e0, and the calcium content is f0. The density of serpentine concrete is g / cm³. 3 .

5. The double-layer neutron-shielded concrete structure based on energy graded absorption according to claim 3, characterized in that, By using MCNP simulation, after inputting parameters such as the elemental proportions and density of serpentine concrete, the average logarithmic energy drop of this type of serpentine concrete can be obtained. Generally speaking, when the neutron radiation energy is 2.0 MeV, .

6. The double-layer neutron-shielded concrete structure based on energy graded absorption according to claim 3, characterized in that, The outer layer thickness is determined based on the macroscopic absorption cross section of thermal neutrons. This macroscopic absorption cross section is calculated from the microscopic absorption cross section, abundance, and content of gadolinium isotopes in the outer concrete layer. The calculation method is as follows: ， in, f is the atomic density of gadolinium atoms. 155 for 155 Gd isotopic abundance for 155 The microscopic absorption cross section of Gd; f 157 for 157 Gd isotopic abundance for 157 Microscopic absorption cross section of Gd The density of gadolinium oxide concrete, The mass fraction of gadolinium, This represents the relative molecular mass of gadolinium oxide. When the moderated thermal neutron shielding efficiency reaches 99.9999%, the thickness of the gadolinium oxide concrete is calculated using the following formula: 。 7. The double-layer neutron-shielded concrete structure based on energy graded absorption according to claim 1, characterized in that, The sum of the inner and outer layer thicknesses, representing the total thickness of the double-layer neutron shielding concrete, is calculated using the following formula: 。 8. A verification method for a double-layer neutron-shielded concrete structure based on energy graded absorption, characterized in that, include: Step S1: Provide two types of concrete with the same thickness, namely single-layer structural concrete and double-layer structural neutron shielding concrete. The double-layer structural neutron shielding concrete is the double-layer structural neutron shielding concrete based on energy graded absorption as described in any one of claims 1 to 7. The single-layer structural concrete is mainly serpentine concrete with a volume fraction of 3% to 8% gadolinium oxide. Step S2: 2MeV neutrons are emitted in the directions of the two types of concrete respectively, and the neutrons penetrate the two types of concrete; Step S3: Record the number and energy of neutrons transmitted through the two types of concrete.

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