Assemblable Lightweight Composite Neutron Reflector for Mobile Micro Nuclear Reactors

Abstract

An assembled lightweight composite neutron reflector for a mobile micro nuclear reactor, the reflector being composed of a reflector main body and a reflector box body; the reflector main body is composed of a reflector main layer and a reflector sub-layer from the inside out and is arranged in the reflector box body. Among them, the reflector main layer is composed of metal beryllium reflector main layer reflector rods arranged in a closely staggered regular triangular grid in a beryllium oxide reflector main layer matrix, and the reflector sub-layer is composed of metal beryllium powder uniformly dispersed in a wholly aromatic polybenzimidazole reflector sub-layer matrix; the reflector box body consists of an internal space evacuated or filled with inert gas, a reflector box wall, coolant flow holes and limit holes opened on the surface. A complete neutron reflector can be assembled using multiple identical reflector box bodies; the reflector of the present invention has the characteristics of light weight, small volume, convenient manufacturing and installation, and can effectively improve the mobility of the mobile micro nuclear reactor and reduce its transportation cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear reactor engineering, and particularly relates to an assembled lightweight composite neutron reflector for a mobile micro nuclear reactor. Background Art

[0002] A neutron reflector is a device closely arranged outside the core active area of a reactor to reduce the neutron leakage of the core active area, improve neutron economy, and thus increase the core reactivity. The neutron reflector material usually selects a material with very weak absorption ability and certain moderation ability. For example, in a mobile micro nuclear reactor, generally solid metals with relatively high melting points and relatively low densities such as beryllium, beryllium oxide ceramics, graphite, or alumina are selected as the reflector material to meet the requirements of reactor mobility and safety. Among them, because some nuclear reaction channels of beryllium can generate new neutrons, metal beryllium or beryllium oxide ceramics are often the preferred materials for neutron reflectors.

[0003] However, since any material arranged outside the core active area actually has a certain reflection effect on neutrons, the neutron reflector of a nuclear reactor must ensure a certain thickness for subsequent shielding layer design and reactivity control design. This thickness is the reflector thickness corresponding to the obvious turning point of the curve of the effective multiplication factor of the nuclear reactor with the reflector thickness. Since the reflector of the current international mobile micro nuclear reactor often adopts a single material solid design and to meet the above purposes, even if a relatively light reflector material is used, the neutron reflector is still large and heavy. A typical example is that the reflector mass of the 5MW mobile micro power reactor of the Idaho National Laboratory in the United States is 8.41 tons, about 1.61 times the mass of the core active area. This not only seriously affects the mobility of the mobile micro nuclear reactor, but also places higher requirements on the transport vehicle, greatly increasing the transportation cost.

[0004] In addition, the reflectors of some reactors also adopt an integrated design, which also brings great challenges to the manufacture and installation of the reflectors. Summary of the Invention

[0005] To solve the above problems, the present invention provides an assembled lightweight composite neutron reflector for a mobile micro nuclear reactor. On the premise of meeting the design requirements of the mobile micro nuclear reactor, compared with the currently commonly used all beryllium oxide ceramic neutron reflector scheme, the mass can be reduced by 20%-40%, and the volume is reduced by 10%-30%. It has the characteristics of small volume, light weight, and low engineering manufacturing and installation difficulty.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] An assembled lightweight composite neutron reflector for a mobile micro nuclear reactor, the reflector consists of a reflector main body and a reflector box body, and the reflector main body is arranged in the internal space of the reflector box body; the reflector main body is successively composed of a reflector main layer 1 and a reflector sub-layer 2 from the inside out. The reflector main layer 1 is arranged on the side close to the reactor core and is in contact with the reflector box wall 3 and the reflector sub-layer 2 respectively at the front and back. The reflector sub-layer 2 is arranged on the outside close to the reflector main layer 1 and is in contact with the reflector main layer 1 and the reflector box wall 3 respectively at the front and back. A coolant flow channel 4 is opened inside the reflector sub-layer 2; the reflector box body is closely arranged on the outside of the reactor core and consists of an internal space, a reflector box wall 3, coolant flow holes 5 and limit holes 6 opened on the surface. The centers of the coolant flow holes 5 opened on the top and bottom surfaces of the reflector box body are in the same position as the centers of the coolant flow channels 4 in the reflector sub-layer 2, and the centers of the limit holes 6 are in the same position as the centers of the positioning pins 8 on the reflector fixing base 7, and the position of the entire reflector box body is fixed by the positioning pins 8.

[0008] The reflector main layer 1 is composed of a reflector main layer matrix 9 and reflector main layer reflector rods 10 arranged in the reflector main layer matrix 9; the material of the reflector main layer matrix 9 is beryllium oxide material, and the material of the reflector main layer reflector rods 10 is metallic beryllium.

[0009] The reflector main layer reflector rods 10 are arranged in a regular triangular grid and closely staggered in the reflector main layer matrix 9. The center distance between adjacent reflector main layer reflector rods 10 is 0.8 cm - 1.2 cm, and the radius of the reflector main layer reflector rods 10 is 0.3 cm - 0.5 cm.

[0010] The reflector sub-layer 2 is composed of a reflector sub-layer matrix 11, a coolant flow channel 4 opened inside and a coolant flow channel wall 12. The coolant flow channel 4 is arranged at the radial center of the reflector sub-layer matrix 11 and is arranged at equal intervals in the circumferential direction; the material of the reflector sub-layer matrix 11 adopts a form in which 40% - 80% by mass of metallic beryllium powder is uniformly dispersed in a polybenzimidazole (abbreviated as PBI) material of all aromatic groups, and the coolant flow channel wall 12 adopts HT9 stainless steel or Mo - 14Re alloy.

[0011] The coolant flow channel 4 is cylindrical with a radius of 1.2 cm - 2.0 cm. The center distance between adjacent coolant flow channels 4 is 10 cm - 20 cm, and the thickness of the coolant flow channel wall 12 is 0.5 mm.

[0012] The internal space of the reflector box body arranges the reflector main body, and the remaining space is vacuum or filled with inert gas; the material of the reflector box wall 3 adopts HT9 stainless steel or Mo - 14Re alloy, and the wall thickness is 0.9 mm.

[0013] The reflector box body is provided with a number of circular coolant flow holes 5. At the four corner positions of the top and bottom surfaces of the reflector box body, 4 circular limit holes 6 are respectively opened. The distance between each limit hole 6 and the adjacent two sides is 1 cm - 1.5 cm and the diameter is 8 mm. The number of coolant flow holes 5 corresponds to the number and central position of the coolant flow channels 4 in the reflector sub-layer matrix 11 respectively. The radius of the coolant flow holes 5 is the same as that of the coolant flow channels 4, both being 1.2 cm - 2.0 cm.

[0014] The reflector box body is in the shape of a quadrangular prism. The top and bottom surfaces are isosceles trapezoids, and the other four surfaces are all rectangles. The apex angles of the isosceles trapezoids are all 120°, and the base angles are 60°. Six such reflector box bodies can be assembled into a complete regular hexagonal prism neutron reflector by closely fitting the side surfaces of the box bodies, and once assembled, these reflector box bodies are fixed and no longer move.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. The neutron reflector of the present invention adopts a box-type design. The reflector main body inside the box adopts a double-layer structure of a reflector main layer and a reflector sub-layer. The box-type design divides the complete neutron reflector into multiple identical reflector box bodies, which is convenient for flexible assembly and effectively reduces the difficulty of the overall manufacturing and integral installation of the neutron reflector. In the double-layer structure, each layer structure adopts a composite design of different materials, and its parameter design can be freely adjusted according to the characteristics and target requirements of different mobile micro nuclear reactors, thus greatly enhancing the flexibility of the lightweight design of the neutron reflector.

[0017] 2. In the double-layer structure of the neutron reflector of the present invention, the reflector main layer uses metal beryllium reflector rods arranged in a staggered manner in a beryllium oxide matrix, and the reflector sub-layer adopts the form of uniformly dispersing metal beryllium powder in a lighter all-aromatic polybenzimidazole matrix. This not only avoids the disadvantages of increased mass and volume caused by using all beryllium oxide ceramics or all metal beryllium materials for the neutron reflector, but also ensures a good neutron reflection effect of the reflector, thereby effectively improving the mobility of the mobile micro nuclear reactor and reducing the transportation cost. Compared with the all beryllium oxide ceramic neutron reflector scheme commonly used in current mobile micro nuclear reactors, the mass can be reduced by 20% - 40%, and the volume can be reduced by 10% - 30%.

[0018] 3. In the double-layer structure of the neutron reflector of the present invention, the all-aromatic polybenzimidazole matrix adopted by the reflector sub-layer contains a large amount of carbon and hydrogen elements, which can effectively slow down neutrons. Therefore, the reflector sub-layer can not only play the role of neutron reflection, but also play the role of neutron moderation material in the shielding layer, thus effectively reducing the difficulty of subsequent lightweight shielding design of the mobile micro nuclear reactor and realizing a direct transition from the reflector to the shielding layer.

[0019] 4. The box-type design adopted for the neutron reflector layer in the present invention has a built-in vacuum or inert environment, and coolant flow holes are arranged at equal intervals on the box body. The vacuum or inert environment inside the box body can raise the long-term service temperature of the special engineering plastic wholly aromatic polybenzimidazole material from 315 °C to 375 °C, which can greatly increase the service temperature range of the reflector layer. The coolant flow holes on the box body provide an inlet for the coolant flow, so that the sub-layer of the reflector layer can be fully cooled, thereby effectively increasing the service life of the neutron reflector layer. Description of the Drawings

[0020] Figure 1 It is a schematic diagram of the overall structure of the reactor core and the reflector layer.

[0021] Figure 2 It is a top view of a single reflector layer box body.

[0022] Figure 3 is Figure 2 A schematic sectional view along A-A.

[0023] Figure 4 It is a schematic diagram of the assembly of multiple reflector layer box bodies.

[0024] Figure 5 It is a schematic diagram of the main layer structure of the reflector layer.

[0025] Figure 6 It is a schematic diagram of the sub-layer structure of the reflector layer. Detailed Description of the Invention

[0026] The structure of the present invention will be described in detail below in conjunction with the drawings and specific embodiments.

[0027] As Figure 1 shown, a lightweight composite neutron reflector layer for a mobile micro nuclear reactor is assembled. The reflector layer is composed of a reflector layer main body and a reflector layer box body, and the reflector layer main body is arranged in the internal space of the reflector layer box body; the reflector layer main body is sequentially composed of a reflector layer main layer 1 and a reflector layer sub-layer 2 from the inside to the outside. The reflector layer main layer 1 is arranged on the side close to the reactor core and is respectively in contact with the reflector layer box wall 3 and the reflector layer sub-layer 2 before and after. The reflector layer sub-layer 2 is arranged on the outside close to the reflector layer main layer 1 and is respectively in contact with the reflector layer main layer 1 and the reflector layer box wall 3 before and after. A coolant flow channel 4 is opened inside the reflector layer sub-layer 2 for the coolant to flow through to cool the reflector layer sub-layer 2 and extend its service life.

[0028] As Figure 2 and Figure 3As shown, the reflector box body is closely arranged on the outer side of the core and consists of an internal space, a reflector box wall 3, coolant flow holes 5 and limit holes 6 opened on the surface. The centers of the coolant flow holes 5 opened on the top and bottom surfaces of the reflector box body are in the same position as the centers of the coolant flow channels 4 in the sub-layer 2 of the reflector. The centers of the limit holes 6 are in the same position as the centers of the positioning pins 8 on the reflector fixing base 7, and the position of the entire reflector box body is fixed by the positioning pins 8. Among them, the reflector main body is arranged in the internal space of the reflector box body, and the remaining space is vacuum or filled with inert gas, that is, a vacuum or inert gas environment is formed in the internal space of the reflector box body to increase the available temperature range of the sub-layer 2 of the reflector and extend its service life.

[0029] Preferably, the material of the reflector box wall 3 is HT9 stainless steel or Mo-14Re alloy with good anti-irradiation performance and stability, and the wall thickness is 0.9 mm.

[0030] The reflector box body is provided with a number of circular coolant flow holes 5. Four circular limit holes 6 are respectively opened at the four corner positions on the top and bottom surfaces of the reflector box body. The distance between each limit hole 6 and the adjacent two sides is 1 cm - 1.5 cm and the diameter is 8 mm. The number and center positions of the coolant flow holes 5 correspond to the number and center positions of the coolant flow channels 4 in the sub-layer matrix 11 of the reflector respectively. The radius of the coolant flow holes 5 is the same as the radius of the coolant flow channels 4, both being 1.2 cm - 2.0 cm.

[0031] As Figure 2 and Figure 4 shown, a single reflector box body is in the shape of a quadrangular prism, the top and bottom surfaces are isosceles trapezoids, and the other four surfaces are rectangles. The top angles of the isosceles trapezoids are all 120°, and the bottom angles are 60°. Six such reflector box bodies can be assembled into a complete regular hexagonal prism neutron reflector by closely fitting the side surfaces of the box bodies, and once assembled, these reflector box bodies are fixed and no longer move.

[0032] As Figure 5 shown, the main layer 1 of the reflector consists of a main layer matrix 9 of the reflector and main layer reflector rods 10 of the reflector. Among them, the main layer reflector rods 10 of the reflector are arranged in a closely staggered manner in a regular triangular grid in the main layer matrix 9 of the reflector. The center distance between adjacent main layer reflector rods 10 of the reflector is 0.8 cm - 1.2 cm, and the radius of the main layer reflector rods 10 of the reflector is 0.3 cm - 0.5 cm.

[0033] To ensure the stability and neutron reflection effect under high-temperature irradiation, preferably, the material of the main layer matrix 9 of the reflector is beryllium oxide material with a high melting point, and its melting point is 2570 °C. To further reduce the mass of the reflector, preferably, the material of the main layer reflector rods 10 of the reflector is beryllium metal material with excellent neutron reflection effect but a smaller density compared to beryllium oxide.

[0034] As Figure 6 shown, the reflection layer 2 is composed of a reflection layer matrix 11, coolant flow channels 4 formed therein, and coolant channel walls 12. The coolant flow channels 4 are arranged at equal intervals circumferentially at the radial center of the reflection layer matrix 11. The coolant flow channels 4 are cylindrical with a radius of 1.2 cm - 2.0 cm, the distance between the centers of adjacent coolant flow channels 4 is 10 cm - 20 cm, and the thickness of the coolant channel walls 12 is 0.5 mm.

[0035] To further reduce the mass and volume of the reflection layer 2, it is preferred that the material of the reflection layer matrix 11 is a special engineering plastic, polyarylbenzimidazole (abbreviated as PBI), which is very light in mass, has a high long-term use temperature, good mechanical properties, and strong stability. Metal beryllium powder with a mass fraction of 40% - 80% is uniformly dispersed in the polyarylbenzimidazole material to ensure good neutron reflection performance. It is preferred that the material of the coolant channel walls 12 is HT9 stainless steel or Mo-14Re alloy with good anti-irradiation performance and strong stability.

[0036] Finally, it should be noted that although the specific embodiments of the present invention have been described and illustrated, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the purpose and spirit of the present invention. For example, modifications to geometric shapes and dimensions, and combinations and substitutions of material types. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. An assembled lightweight composite neutron reflector for a mobile micro nuclear reactor, Characterized in that: The reflector consists of a reflector main body and a reflector box body. The reflector main body is arranged in the internal space of the reflector box body; the reflector main body is composed of a reflector main layer (1) and a reflector sub-layer (2) from inside to outside in sequence. The reflector main layer (1) is arranged on the side close to the reactor core and is in contact with the reflector box wall (3) and the reflector sub-layer (2) respectively in the front and back. The reflector sub-layer (2) is arranged on the outer side close to the reflector main layer (1) and is in contact with the reflector main layer (1) and the reflector box wall (3) respectively in the front and back. A coolant flow channel (4) is opened inside the reflector sub-layer (2); the reflector box body is closely arranged on the outer side of the reactor core and is composed of an internal space, a reflector box wall (3), coolant flow holes (5) and limit holes (6) opened on the surface. The centers of the coolant flow holes (5) opened on the top and bottom surfaces of the reflector box body are in the same position as the centers of the coolant flow channels (4) in the reflector sub-layer (2). The centers of the limit holes (6) are in the same position as the centers of the positioning pins (8) on the reflector fixing base (7), and the position of the entire reflector box body is fixed by the positioning pins (8).

2. The assembled lightweight composite neutron reflector for a mobile micro nuclear reactor according to claim 1, Characterized in that: The reflector main layer (1) is composed of a reflector main layer matrix (9) and reflector main layer reflector rods (10) arranged in the reflector main layer matrix (9); the material of the reflector main layer matrix (9) is beryllium oxide material, and the material of the reflector main layer reflector rods (10) is beryllium metal.

3. The assembled lightweight composite neutron reflector for a mobile micro nuclear reactor according to claim 2, Characterized in that: The reflector main layer reflector rods (10) are arranged in a regular triangular grid and are closely staggered in the reflector main layer matrix (9). The center distance between adjacent reflector main layer reflector rods (10) is 0.8 cm - 1.2 cm, and the radius of the reflector main layer reflector rods (10) is 0.3 cm - 0.5 cm.

4. The assembled lightweight composite neutron reflector for a mobile micro nuclear reactor according to claim 1, Characterized in that: The reflector sub-layer (2) is composed of a reflector sub-layer matrix (11), a coolant flow channel (4) opened inside and a coolant flow channel wall (12). The coolant flow channel (4) is arranged at the radial center of the reflector sub-layer matrix (11) and is arranged at equal intervals in the circumferential direction; the material of the reflector sub-layer matrix (11) is in the form of 40% - 80% by mass of beryllium metal powder uniformly dispersed in a fully aromatic polybenzimidazole material, and the coolant flow channel wall (12) is made of HT9 stainless steel or Mo-14Re alloy.

5. The assembled lightweight composite neutron reflector for a mobile micro nuclear reactor according to claim 4, Characterized in that: The coolant flow channel (4) is cylindrical with a radius of 1.2 cm - 2.0 cm. The distance between the centers of adjacent coolant flow channels (4) is 10 cm - 20 cm. The thickness of the coolant flow channel wall (12) is 0.5 mm.

6. A lightweight composite neutron reflector for a mobile micro nuclear reactor according to claim 1, characterized in that: The main body of the reflector is arranged in the internal space of the reflector box, and the remaining space is vacuum or filled with inert gas; the material of the reflector box wall (3) is HT9 stainless steel or Mo-14Re alloy, and the wall thickness is 0.9 mm.

7. A lightweight composite neutron reflector for a mobile micro nuclear reactor according to claim 6, characterized in that: The reflector box is provided with a number of circular coolant flow holes (5). Four circular limit holes (6) are respectively opened at the four corner positions on the top and bottom surfaces of the reflector box. The distance from each limit hole (6) to the adjacent two sides is 1 cm - 1.5 cm and the diameter is 8 mm. The number and central position of the coolant flow holes (5) are respectively the same as those of the coolant flow channels (4) in the central position and the sub-layer matrix (11) of the reflector layer. The radius of the coolant flow holes (5) is the same as that of the coolant flow channels (4), both being 1.2 cm - 2.0 cm.

8. A lightweight composite neutron reflector for a mobile micro nuclear reactor according to claim 6, characterized in that: The reflector box is in the shape of a quadrangular prism. The top and bottom surfaces are isosceles trapezoids, and the other four surfaces are rectangles. The apex angles of the isosceles trapezoids are all 120°, and the base angles are 60°; six such reflector boxes can be assembled into a complete regular hexagonal prism neutron reflector by closely fitting the side surfaces of the boxes, and once assembled, these reflector boxes are fixed and no longer move.

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