Nuclear powered spacecraft combined shadow shield

Abstract

The application relates to a combined shadow shielding body of a nuclear power spacecraft and belongs to the technical field of nuclear radiation safety protection. The application solves the problem of large mass of the conventional combined shielding body. The combined shadow shielding body comprises first to fourth shielding layers arranged along an axial direction in sequence, each shielding layer is in a circular truncated cone structure, the material of the first shielding layer and the third shielding layer is boron carbide, the material of the second shielding layer is tungsten, the material of the fourth shielding layer is 304 stainless steel, and a ring cavity is arranged in each shielding layer. The ring cavity is arranged in each shielding layer, the internal structure of the combined shadow shielding body is reasonably cut, the mass of the combined shadow shielding body is further obviously reduced, the shielding weight is reduced, the combined shadow shielding body is suitable for a higher-power reactor, the mass proportion of the shielding body is not excessively large, the weight of necessary equipment of the spacecraft is not reduced, and the normal function of the spacecraft is not affected.

Description

Technical Field

[0001] This invention relates to a combined shadow shield for nuclear-powered spacecraft, belonging to the field of nuclear radiation safety protection technology. Background Technology

[0002] Nuclear-powered spacecraft using fission reactors as their power source need to consider not only space radiation but also nuclear radiation from the reactor itself. Radiation safety protection primarily involves shielding against neutrons and gamma rays from the reactor. Currently, nuclear-powered spacecraft are mainly used for space exploration missions. Shielding of the reactor only requires radiation shielding of the electronic instruments and equipment downstream of the reactor to ensure the radiation safety of electronic components and equipment. However, due to the extremely strict limitations on the overall mass of spacecraft, and with the increasing demands of unmanned deep space exploration missions, the power levels of space reactors are constantly increasing, leading to a continuous increase in the mass required for radiation protection shielding. Consequently, the requirements for reducing the weight of radiation protection shielding while meeting radiation safety standards are becoming increasingly stringent.

[0003] Benefiting from the expansion of commercial nuclear power plants and the development of nuclear medicine, numerous scholars have conducted research on shielding material development, material property analysis, and shielding scheme design. Since current radiation protection for nuclear-powered spacecraft targets electronic equipment behind the reactor, its shielding method is typically shadow-type, aiming to create a shielding area larger than the reactor diameter. The included angle of the shield is determined by the specific spacecraft structure and the required protective width.

[0004] Modular shielding is a widely used shielding scheme in current research. It involves the sequential combination of multiple shielding materials. Compared to earlier designs using single materials, modular shielding can simultaneously shield neutrons, gamma photons, and secondary gamma photons generated during neutron absorption. Furthermore, the combination of materials can improve shielding effectiveness and reduce the overall mass of the shield. Further reducing the mass of modular shadow shields remains an important area of ​​ongoing research for those skilled in the art. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems and thereby provide a combined shadow shield for nuclear-powered spacecraft.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] A combined shadow shield for nuclear-powered spacecraft includes first to fourth shielding layers arranged sequentially along the axial direction. Each shielding layer is a frustum-shaped structure. The first and third shielding layers are made of boron carbide, the second shielding layer is made of tungsten, and the fourth shielding layer is made of 304 stainless steel. Each shielding layer has an annular cavity inside.

[0008] Furthermore, the first to third shielding layers are combined to form a frustum-shaped structure, and the large-diameter end of the frustum of the fourth shielding layer is connected to the large-diameter end of the frustum of the third shielding layer.

[0009] Furthermore, the shielding angle β formed by the combination of the first to third shielding layers is 5° to 9°.

[0010] Furthermore, the truncated cone angle of the fourth shielding layer is 60° to 70°.

[0011] Furthermore, the annular cavities are arranged coaxially and radially offset.

[0012] Furthermore, the distances A1, A3, and A4 between the outer wall of each annular cavity in the first, third, and fourth shielding layers and the outer wall of the shielding layer on the plane containing the center of the annulus are all 1 cm. The distance A2 between the outer wall of the annular cavity in the second shielding layer and the side of the shielding layer on the plane containing the center of the annulus is 8 cm. The annular radii R1, R2, R3, and R4 of each annular cavity in the first to fourth shielding layers are 19.89 cm, 13.73 cm, 24.93 cm, and 20.05 cm, respectively.

[0013] Furthermore, the cross-sectional shape of each annular cavity is circular, and the radius r of the circular cross-section is 2cm.

[0014] Furthermore, the axial thicknesses of the first to fourth shielding layers are 40cm, 8cm, 40cm, and 12cm, respectively. The radius of the small diameter end of the first shielding layer is 20cm, the radius of the large diameter end of the first shielding layer and the small diameter end of the second shielding layer are both 24.2cm, the radius of the large diameter end of the second shielding layer and the small diameter end of the third shielding layer are both 25.05cm, the radius of the large diameter end of the third shielding layer and the large diameter end of the fourth shielding layer are both 29.25cm, and the radius of the small diameter end of the fourth shielding layer is 22.32cm.

[0015] Furthermore, the distances from the center of each annular cavity to the rear center of the frustum to which it is located, B1, B2, B3 and B4, are all 3 cm.

[0016] Furthermore, a stainless steel cover is provided on the outer side of the shielding body formed by the first to fourth shielding layers.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] This invention, through optimized selection and arrangement of shielding materials, can reduce the overall mass of the shielding to a certain extent. For high-power reactors, the shielding mass is relatively large. This invention further significantly reduces the mass of the combined shadow shielding by creating annular cavities within each shielding layer and rationally removing parts of the internal structure, thus achieving weight reduction for shielding. This makes it suitable for higher-power reactors and avoids reducing the weight of essential spacecraft equipment due to excessive shielding mass, which could affect the normal functioning of the spacecraft. Attached Figure Description

[0019] Figure 1 This is a perspective view of the three-dimensional structure of the present invention;

[0020] Figure 2 This is a three-dimensional sectional view (perspective) of the present invention;

[0021] Figure 3 This is a perspective view of the main view of the present invention;

[0022] Figure 4 This is a neutron distribution cloud map along the axial direction for a conventional combined shadow shield in the prior art;

[0023] Figure 5 This is a photon distribution cloud map along the axial direction for a conventional combined shadow shield in the prior art.

[0024] Figure 6 This is a neutron distribution cloud map along the axial direction of the combined shadow shield described in a specific embodiment of the present invention;

[0025] Figure 7 This is a photon distribution cloud map along the axial direction of the combined shadow shield described in a specific embodiment of the present invention;

[0026] Figure 8 This is a comparison chart of the normalized neutron fluence, secondary gamma photon dose, and reactor emitted photon dose at a position 10cm behind the rear of a specific embodiment of the present invention and a conventional combined shadow shield.

[0027] In the picture:

[0028] 1. First shielding layer; 2. Second shielding layer; 3. Third shielding layer; 4. Fourth shielding layer; 5. Annular cavity. Detailed Implementation

[0029] Combination Figures 1 to 7This description aims to clearly and completely illustrate the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] It should be noted that the descriptions of "left," "right," "left side," "right side," "upper part," "lower part," "top," and "bottom" in this invention are defined based on the orientation or positional relationships shown in the accompanying drawings. They are merely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the described structure must be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0031] In the description of this invention, unless otherwise expressly 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 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.

[0032] Specific implementation method one: Combining Figures 1-3 This embodiment describes a combined shadow shield for a nuclear-powered spacecraft, comprising first to fourth shielding layers arranged sequentially along the axial direction. Each shielding layer is a frustum-shaped structure. The first shielding layer 1 and the third shielding layer 3 are made of boron carbide (B4C), the second shielding layer 2 is made of tungsten (W), and the fourth shielding layer 4 is made of 304 stainless steel (S304). Each shielding layer has an annular cavity 5 inside.

[0033] The reactor is located at the front end of the first shielding layer 1, and the radiation protection target is located in the area behind the fourth shielding layer 4.

[0034] The end faces of each two adjacent shielding layers are bonded together. The parameters of each part of the shielding body, including the thickness of each shielding layer, the opening position of each annular cavity 5, and the specific dimensions of the annular cavity 5, are all calculated based on the selected shielding angle.

[0035] The basic principle of the combined shadow shield of this invention is as follows: high-density, high atomic number materials are used for photon shielding, and lightweight, high-medium neutron-absorbing materials are used for neutron shielding. During combined shielding, high-density photon shielding material and neutron shielding material are used alternately, with one layer of high-density photon shielding material inserted inside the neutron shielding material. Since photons require high-density, high atomic number materials for effective shielding, a significant portion of the shield's mass is contributed by the photon shielding material. Placing the high-density photon shielding material at the front reduces the overall mass of the shield.

[0036] When neutrons pass through the first shielding layer 1 (boron carbide material), they undergo radiative trapping reactions such as (n,γ) and (n,α), resulting in absorption of the neutrons and the emission of secondary γ photons. When passing through the second shielding layer 2 (tungsten material), photon shielding is achieved through photoelectric effect, Compton scattering, and electron-electron pairing effects. This shielding layer simultaneously shields the secondary γ photons generated during neutron absorption and the photons emitted from the reactor. When passing through the third shielding layer 3 (boron carbide material), neutrons continue to undergo (n,γ) and (n,α) reactions. Reactions such as neutron absorption and secondary gamma photons are absorbed. The neutron-absorbing material boron carbide is arranged in two layers, and the photon-shielding material tungsten is inserted between them. Compared with the scheme of placing all tungsten at the back, this can significantly reduce the overall shielding mass, and at the same time absorb the secondary gamma photons generated during the neutron absorption reaction. After passing through the fourth shielding layer of 304 stainless steel, the secondary gamma photons and reactor-emitted photons are further shielded. 304 stainless steel has a lower density than tungsten, so its rear mass is not too large, and it can also achieve partial photon shielding.

[0037] Through optimized selection and arrangement of shielding materials, this invention can reduce the overall mass of the shielding to a certain extent. For high-power reactors, the shielding mass is relatively large. This invention further significantly reduces the mass of the combined shadow shielding by creating annular cavities 5 inside each shielding layer, thereby rationally removing parts of the internal structure of the combined shadow shielding. This achieves weight reduction in shielding, making it suitable for higher-power reactors and avoiding the reduction of the weight of necessary spacecraft equipment due to excessive shielding mass, which could affect the normal functioning of the spacecraft.

[0038] The first to third shielding layers 3, when combined, form a frustum-shaped structure. The large-diameter end of the frustum of the fourth shielding layer 4 aligns with the large-diameter end of the frustum of the third shielding layer 3. With this design, the outer circular surfaces of the first to third shielding layers 3 have the same inclination angle, and the small-diameter end of each shielding layer aligns with the large-diameter end of the layer preceding it, resulting in an overall frustum-shaped structure when the first to third shielding layers 3 are combined axially. By arranging the inclined surface of the frustum of the fourth shielding layer 4 in the opposite direction to that of the frustums of the first to third shielding layers 3, the radiation shadow region is essentially formed after the shielding of the first three layers. The reverse arrangement of the last shielding layer allows for weight reduction of the shielding body without significantly affecting the formation of the shadow region or the shielding effect against neutrons and photons. Compared with existing conventional shielding bodies made of the same materials, with the same thickness, and arranged in the same order, this design effectively reduces the overall mass of the shielding body while maintaining the shielding effect.

[0039] The shielding angle β formed by the combination of the first to third shielding layers is 5° to 9°. With this design, the truncated cone-shaped structure formed by the combination of the first to third shielding layers has an inclination of 5° to 9°. The angle between the low-dose shadow region of neutrons and photons formed behind the shield is also 5° to 9°. Within the region behind the shield, the diameter of the low-dose shadow region increases with the distance from the shield, thus providing a larger radiation safety area.

[0040] The truncated cone angle of the fourth shielding layer 4 is 60° to 70°. This design allows for weight reduction of the shielding layer while ensuring the diameter of the shadow area formed behind the shielding body, without significantly affecting the shielding effect of the shielding body on neutrons and photons.

[0041] The annular cavities 5 are arranged coaxially and radially offset. This design, through the offset arrangement of the annular cavities 5, avoids the formation of multiple voids within a radius inside the shield, which would prevent neutrons and photons from being effectively shielded and result in areas with excessively high neutron fluence and photon doses behind the shield.

[0042] Specific Implementation Method Two: Combining Figures 1 to 7 In this embodiment, the shielding angle β formed by the combination of the first to third shielding layers is 6°, and the truncated cone slope of the fourth shielding layer 4 is 60°.

[0043] The distances A1, A3, and A4 between the outer wall of each annular cavity 5 in the first shielding layer 1, the third shielding layer 3, and the outer side wall of the shielding layer on the plane containing the center of the annulus are all 1 cm. The distance A2 between the outer wall of the annular cavity 5 in the second shielding layer 2 and the side wall of the shielding layer on the plane containing the center of the annulus is 8 cm. The annular radii R1, R2, R3, and R4 of each annular cavity 5 in the first to fourth shielding layers 4 are 19.89 cm, 13.73 cm, 24.93 cm, and 20.05 cm, respectively. This design ensures that the shielding angle of the radiation shielding shadow area behind the shielding body is equal to the angle between the shielding body and the shielding body, effectively guaranteeing that the diameter of the shielding shadow area increases with the increase of the axial distance.

[0044] Each annular cavity 5 has a circular cross-sectional shape, and the radius r of the circular cross-section is 2cm. This design effectively ensures that the shielding effect against neutrons and photons is not significantly affected, while achieving weight reduction of the shielding body.

[0045] The axial thicknesses of the first to fourth shielding layers are 40cm, 8cm, 40cm, and 12cm, respectively. The radius of the small diameter end of the first shielding layer 1 is 20cm, the radius of the large diameter end of the first shielding layer 1 and the small diameter end of the second shielding layer 2 are both 24.2cm, the radius of the large diameter end of the second shielding layer 2 and the small diameter end of the third shielding layer 3 are both 25.05cm, the radius of the large diameter end of the third shielding layer 3 and the large diameter end of the fourth shielding layer 4 are both 29.25cm, and the radius of the small diameter end of the fourth shielding layer 4 is 22.32cm.

[0046] The distances from the center of each annular cavity 5 to the rear center of its respective frustum, B1, B2, B3, and B4, are all 3 cm. This design, compared to placing the annular cavity 5 in the front region of the shielding layer, allows for better neutron and photon shielding of the shielding layer, while also resulting in a greater reduction in mass.

[0047] A stainless steel cover is fitted around the outer side of the shielding body formed by the first to fourth shielding layers. With this design, the first to fourth shielding layers are placed in the stainless steel cover, and there is no need to use a fixed connection between the shielding layers. The axial and radial displacement between the four shielding layers can be restricted directly by the stainless steel cover.

[0048] Based on the dimensions of each shielding layer and the annular cavity 5, the overall weight of the combined shadow shield in this invention is 843.087 kg, a reduction of 110.138 kg compared to existing conventional shields. The shield still achieves shielding of neutron fluence by approximately eight orders of magnitude and photon dose by seven orders of magnitude, comparable to conventional shields. Specifically, the first layer of boron carbide shielding material reduces neutron fluence by four orders of magnitude; the second layer of tungsten shielding material reduces secondary gamma photon dose by two orders of magnitude and reactor-emitted gamma photon dose by three orders of magnitude; the third layer of boron carbide shielding material reduces neutron fluence by four orders of magnitude; and the fourth layer of 304 stainless steel shielding material simultaneously reduces secondary gamma photon dose by one order of magnitude and reactor-emitted gamma photon dose by two orders of magnitude. Through the combination of multiple shielding materials, the overall shield can simultaneously shield neutrons, gamma photons, and secondary gamma photons generated by neutron absorption reactions.

[0049] Using the parameters in this embodiment, the diameter of the shadow area is 67cm at a distance of 10cm from the rear end of the shield.

[0050] like Figure 4 , Figure 6 As shown, the neutron shielding effect of this embodiment of the invention is not much different from that of conventional combined shadow shielding bodies, and can form a radiation shielding shadow area with a diameter of about 60cm at a position 10cm at the rear end of the shielding body.

[0051] like Figure 5 , Figure 7 As shown, although the neutron fluence, secondary gamma photon dose, and reactor emitted photon dose at a position 10 cm from the rear end of the shield in this embodiment of the invention are all increased compared to conventional combined shadow shields, the increase is no more than one order of magnitude, while the reduction in mass is very significant. Therefore, compared to conventional combined shadow shields, this invention greatly reduces the overall mass of the shield without significantly affecting the shielding effect.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A combined shadow shield for nuclear-powered spacecraft, characterized in that: It includes first to fourth shielding layers arranged sequentially along the axial direction. Each shielding layer is a frustum-shaped structure. The first shielding layer (1) and the third shielding layer (3) are made of boron carbide, the second shielding layer (2) is made of tungsten, and the fourth shielding layer (4) is made of 304 stainless steel. Each shielding layer has an annular cavity (5) inside.

2. The combined shadow shield for a nuclear-powered spacecraft according to claim 1, characterized in that: The first to third shielding layers (3) are combined to form a frustum-shaped structure, and the large diameter end of the frustum of the fourth shielding layer (4) is connected to the large diameter end of the frustum of the third shielding layer (3).

3. A combined shadow shield for nuclear-powered spacecraft according to claim 1 or 2, characterized in that: The shielding angle β formed by the combination of the first to third shielding layers is 5° to 9°.

4. A combined shadow shield for nuclear-powered spacecraft according to claim 1, characterized in that: The truncated cone slope of the fourth shielding layer (4) is 60° to 70°.

5. A combined shadow shield for nuclear-powered spacecraft according to claim 1, characterized in that: The annular cavities (5) are arranged coaxially and radially offset.

6. A combined shadow shield for nuclear-powered spacecraft according to claim 1, characterized in that: The distances A1, A3, and A4 between the outer wall of each annular cavity (5) in the first shielding layer (1), the third shielding layer (3), and the fourth shielding layer (4) and the outer side wall of the shielding layer on the plane containing the center of the annulus are all 1cm. The distance A2 between the outer wall of the annular cavity (5) in the second shielding layer (2) and the outer side wall of the shielding layer on the plane containing the center of the annulus are 8cm. The annular radii R1, R2, R3, and R4 of each annular cavity (5) in the first to fourth shielding layers (4) are 19.89cm, 13.73cm, 24.93cm, and 20.05cm, respectively.

7. A combined shadow shield for nuclear-powered spacecraft according to claim 1, characterized in that: The cross-sectional shape of each annular cavity (5) is circular, and the radius r of the circular cross-section is 2cm.

8. A combined shadow shield for nuclear-powered spacecraft according to claim 1, characterized in that: The axial thicknesses of the first to fourth shielding layers are 40cm, 8cm, 40cm, and 12cm, respectively. The radius of the small diameter end of the first shielding layer (1) is 20cm. The radii of the large diameter end of the first shielding layer (1) and the small diameter end of the second shielding layer (2) are both 24.2cm. The radii of the large diameter end of the second shielding layer (2) and the small diameter end of the third shielding layer (3) are both 25.05cm. The radii of the large diameter end of the third shielding layer (3) and the large diameter end of the fourth shielding layer (4) are both 29.25cm. The radius of the small diameter end of the fourth shielding layer (4) is 22.32cm.

9. A combined shadow shield for nuclear-powered spacecraft according to claim 1, characterized in that: The distances from the center of each annular cavity (5) to the rear center of the frustum to the ...

10. A combined shadow shield for a nuclear-powered spacecraft according to claim 1, characterized in that: The outer side of the shielding body formed by the first to fourth shielding layers is fitted with a stainless steel cover.

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