Fuel rod and fuel assembly based on TPMS structure

Abstract

The invention discloses a fuel rod and a fuel assembly based on a TPMS (Tire Pressure Monitor System) structure, the TPMS structure is introduced into the fuel rod on the basis of the original configuration, and the interior of the fuel rod or a cooling channel of the fuel assembly has a height-adjustable three-dimensional periodic topological form by regulating and controlling geometric parameters of the TPMS structure; therefore, the heat exchange area in the fuel rod or the fuel assembly cooling channel is optimized, the heat exchange efficiency of the coolant and the fuel surface is improved, and the heat exchange capacity is enhanced. Meanwhile, the formation of a local high-flow-speed path is reduced, the flowing pressure drop is reduced, and the effect of optimizing the flowing uniformity of a coolant is achieved, so that the thermal management performance of the whole fuel assembly is improved, the burn-up uniformity and the fuel utilization rate are improved, and the requirements of a high-power-density nuclear reactor for higher safety and economical efficiency of the fuel assembly are met.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear reaction, and in particular relates to a fuel rod and a fuel assembly based on a TPMS structure. Background Art

[0002] At present, advanced nuclear reactors such as pressurized water reactors (PWR) and fast reactors (LFR, SFR) widely use traditional columnar fuel rods as core fuel elements. Traditional fuel rods are usually made of stacked cylindrical fuel pellets, and are covered with corrosion-resistant metal cladding (such as zirconium alloy or stainless steel) on the outside. There is an air gap (filled with helium) between the cladding and the fuel pellets. Figure 1 As shown, Ru is the pellet radius, Rci is the cladding inner diameter, and Rcs is the cladding inner diameter. The coolant flows between the fuel rods and removes the heat generated by fission through convection. The existing design has the following technical bottlenecks:

[0003] 1. Limited heat exchange efficiency: The heat exchange surface area of ​​traditional fuel rods is relatively limited, resulting in a high temperature inside the fuel pellets, affecting the uniformity of burnup and fuel utilization;

[0004] 2. Large flow pressure drop: When the coolant flows in a traditional fuel assembly, it is restricted by the shape and spacing of the flow channels, resulting in greater flow resistance, which in turn increases the energy consumption of the circulation pump;

[0005] 3. Limited room for optimization of fuel structure safety: fuel pellets may crack or expand under high temperature and high radiation environment, and traditional structures are difficult to effectively alleviate thermal stress and fission gas release problems;

[0006] 4. Demand for high power density reactors: With the development of new generation nuclear reactor technology, improving power density and thermal management capabilities have become key technical challenges. The heat dissipation capacity of existing fuel assemblies has reached its design limit.

[0007] Invention patent application CN102947890B, which was published on May 18, 2016, takes into account that the surface area of ​​the cylindrical tube of the conventional fuel rod limits the heat that can be transferred from the rod to the primary coolant, and improves the fuel element from a cylindrical shape to a multi-lobed shape. Figure 2 It is shown that due to the increased surface area in the multi-lobed fuel elements, even at the increased power rating of 6.0 GWth, the average surface heat flux of the multi-lobed fuel elements is shown to be 4-5% lower than that of cylindrical uranium oxide fuel elements operated at a thermal power rating of 4.59 GWth.

[0008] However, the multi-lobed fuel element is still an improvement based on the traditional cylindrical fuel element, which can only increase the surface area of ​​the fuel element to a certain extent, and does not achieve a qualitative improvement. Summary of the invention

[0009] Aiming at the problems existing in the existing nuclear reactor fuel rods, such as limited heat transfer capacity, large flow resistance, and uneven burnup, the present invention proposes a fuel rod and a fuel assembly based on the TPMS structure.

[0010] The present invention protects a fuel rod based on the TPMS structure. On the basis of the original configuration of the fuel rod, the TPMS structure is introduced, so that the cooling channels inside the fuel rod or the fuel assembly have a three-dimensional periodic topological morphology with adjustable height.

[0011] Furthermore, the original configuration of the fuel rod is columnar, including cylindrical, multi-prismatic, etc.; the TPMS structure adopts the Diamond structure, the Gyroid structure or the Schwarz-D structure.

[0012] Furthermore, the TPMS structure adopts the Gyroid structure, and the nuclear fuel is arranged in sheets. Specifically: a metal cladding is arranged along the Gyroid surface, and nuclear fuel is arranged between two layers of metal claddings; or, the nuclear fuel is arranged in blocks. Specifically: inside each Gyroid unit is a metal frame, the metal frame extends outward, and an accommodation space is formed on the outer periphery, and nuclear fuel is arranged in this accommodation space. Each Gyroid unit and other adjacent Gyroid units enclose the nuclear fuel inside the metal cladding; whether the nuclear fuel is arranged in sheets or in blocks, an air gap is left between the nuclear fuel and the cladding.

[0013] Furthermore, control terms containing a control factor α are respectively introduced into the three additive terms of the standard Gyroid function to form an improved Gyroid function. By adjusting the size of the control factor α, the size of the straight through holes in the Gyroid structure and the tortuosity of the surface structure are regulated; at the same time, the control terms of the additive terms in the xy plane contain the associated variable z, the control terms of the additive terms in the yz plane are associated with the variable x, and the control terms of the additive terms in the zx plane contain the associated variable y.

[0014] The present invention also protects a fuel assembly, including fuel rods, control rods, a fuel grid that supports the fuel rods and the control rods, a guide tube that accommodates the control rods and measuring instruments, a coolant channel for heat dissipation and temperature reduction, and the fuel rods adopt the fuel rods based on the TPMS structure described above.

[0015] The present invention also protects a coolant channel of a fuel assembly. The fuel rod adopts the Gyroid structure with nuclear fuel arranged in sheets, and its peripheral space serves as the coolant channel.

[0016] The present invention also protects a fuel grid of a fuel assembly. The fuel rod adopts the Gyroid structure with nuclear fuel arranged in blocks, and the center of each Gyroid unit serves as a support frame.

[0017] Based on the original configuration of the fuel rod, the TPMS structure is subversively introduced, which can achieve the following technical advantages:

[0018] 1. Improve heat transfer capacity: The TPMS structure provides a larger specific surface area, enabling the coolant to more efficiently carry away the heat generated by the fuel, reducing the maximum temperature of the fuel rod, and improving the uniformity of fuel burnup;

[0019] 2. Reduce flow resistance: Compared with the traditional straight-through flow channel, the TPMS structure can optimize the coolant flow path, reduce local turbulence, improve the flow efficiency of the coolant, and thus reduce the pressure drop loss;

[0020] 3. Enhance structural stability: The three-dimensional periodicity of the TPMS structure helps to improve the thermal stress resistance of the fuel assembly and reduce structural damage caused by thermal expansion or irradiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the Gyroid unit for the nuclear fuel flakes disclosed in Example 1;

[0022] Figure 2 Schematic diagram of the Gyroid unit for the nuclear fuel blocks disclosed in Example 2;

[0023] Figure 3 Schematic diagram of the standard Gyroid unit structure and its array structure;

[0024] Figure 4 Three-dimensional view and top view of the improved Gyroid unit structure disclosed in Example 3, where Figure 4 (a) is the three-dimensional view, Figure 4 (b) is the top view. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention are given for the purpose of illustration and description, and are not exhaustive or limit the present invention to the disclosed form. Many modifications and variations are obvious to those of ordinary skill in the art. The embodiments are selected and described to better illustrate the principles and practical applications of the present invention, and enable those of ordinary skill in the art to understand the present invention and design various embodiments with various modifications suitable for specific purposes.

[0026] The TPMS structure is a type of complex topological structure with periodicity, connectivity, and minimum surface characteristics, and its unique geometric features can significantly optimize the thermal management and hydrodynamic performance of the fuel assembly.

[0027] By introducing a TPMS structure on the basis of the original columnar fuel rod configuration and regulating the geometric parameters of the TPMS structure, the internal cooling channels of the fuel rod or the fuel assembly are provided with a three-dimensional periodic topological form with adjustable height, thereby optimizing the heat transfer area of the internal cooling channels of the fuel rod or the fuel assembly, improving the heat exchange efficiency between the coolant and the fuel surface, and enhancing the heat transfer capacity.

[0028] In addition, while optimizing the heat exchange structure, the present invention utilizes the inherent fluid guiding characteristics of the TPMS structure to reduce the formation of local high-flow velocity paths, reduce the flow pressure drop, achieve the effect of optimizing the flow uniformity of the coolant, thereby improving the thermal management performance of the entire fuel assembly, improving the burnup uniformity and fuel utilization rate, so as to meet the higher safety and economic requirements of high-power density nuclear reactors for fuel assemblies.

[0029] At the technical implementation level, the means of additive manufacturing can be considered. Some foreign companies have already conducted research on this. This part is not the main technical problem to be solved by the present invention, so it will not be discussed in detail.

[0030] The Diamond structure, Gyroid structure, or Schwarz-D structure are three typical TPMS structures. The main advantage of the Gyroid structure lies in its complex three-dimensional surface, which gives it significant advantages in fluid flow, heat conduction performance, mechanical stability, and adaptability. Especially in applications that require uniform heat flux distribution and high heat exchange efficiency, the Gyroid structure performs excellently. Therefore, the present invention preferably selects the Gyroid structure. However, it can be understood that as typical TPMS structures, the Diamond structure and Schwarz-D structure can also be fully used as the TPMS structure of the fuel rod.

[0031] Example 1

[0032] The nuclear fuel is arranged in sheets. Refer to Figure 1 , a metal cladding is arranged along the Gyroid surface, nuclear fuel is arranged between the two metal claddings, and an air gap layer is left between the nuclear fuel and the cladding.

[0033] Fuel with uneven thickness will introduce local temperature hot spots in the thicker areas, thereby limiting the power. The sheet-type TPMS fuel structure of this embodiment does not have this problem, and the fuel thickness is constant and relatively thin.

[0034] At the same time, the peripheral space of the Gyroid structure can all be used as a coolant channel to achieve full heat exchange between the coolant and the fuel.

[0035] Example 2

[0036] The nuclear fuel is arranged in sheets. Refer to Figure 2, inside each Gyroid unit is a metal frame that extends outward to form an accommodation space on the periphery, where nuclear fuel is disposed. Each Gyroid unit and other adjacent Gyroid units enclose the nuclear fuel inside the metal cladding, and there is an air gap between the nuclear fuel and the cladding.

[0037] Different from Embodiment 1, the nuclear fuel in this embodiment relies on the periodically arranged Gyroid units to enclose the nuclear fuel. From Figure 2 it can be clearly seen that the centers of the Gyroid units all serve as support frames. Therefore, compared with Embodiment 1, it is more suitable as the support frame of the fuel rod, and at the same time has excellent mechanical properties and flow optimization characteristics.

[0038] Embodiment 3

[0039] Regarding Embodiment 2, the Gyroid structure still has certain limitations in heat transfer applications. First, the standard Gyroid structure has "through holes" that seemingly penetrate the flow channels. Refer to Figure 3 . Such a structure will cause some fluids to directly pass through the "through holes" without participating in lateral mixing and directly flow out of the heat exchanger, resulting in less heat absorption of this part of the fluid, not only reducing the overall heat transfer efficiency but also causing uneven temperature distribution in the heat exchanger; second, although the TPMS structure can provide continuous flow channels, the walls of the standard Gyroid structure bend slowly, and the three-dimensional spiral perturbation of fluid flow is relatively small, making it difficult to form stronger turbulent mixing.

[0040] Standard Gyroid function equation:

[0041]

[0042] In response to this, this embodiment proposes an improved Gyroid function and regulates the TPMS structure based on this Gyroid function, significantly improving its convective heat transfer performance and achieving more efficient heat energy transfer. The improvement purpose of the Gyroid function is to introduce control terms containing the control factor α to the three additive terms of the standard Gyroid function respectively to form an improved Gyroid function, and adjust the size of the control factor α to regulate the size of the straight through holes and the tortuosity of the surface structure in the Gyroid structure; at the same time, the control terms of the additive terms in the xy plane contain the associated variable z, the control terms of the additive terms in the yz plane are associated with the variable x, and the control terms of the additive terms in the zx plane contain the associated variable y. In response to this purpose, this embodiment proposes a variety of concepts, and the description of the one that is more suitable as the Gyroid structure of the fuel rod is as follows.

[0043] The main idea of the concept is that the control terms are sine or cosine terms, and the independent variable of the sine or cosine term includes the control factor α; the independent variable of the control term of the additive term in the xy plane includes the product of the sine and cosine of the variable z, the independent variable of the control term of the additive term in the yz plane includes the product of the sine and cosine of the variable x, and the independent variable of the control term of the additive term in the zx plane includes the product of the sine and cosine of the variable y. Based on this concept, there is an improved Gyroid function equation:

[0044]

[0045] Among them, L represents the unit length of the TPMS structure, and C represents the offset of the original unit surface. These control terms are selected because they can precisely control the structure without damaging its inherent topological structure and connectivity.

[0046] Figure 4 (a) and 4(b) show the three-dimensional view and top view of the Gyroid unit structure under different α values. It can be seen that by adjusting the magnitude of the control factor α, the surface morphology of the Gyroid structure has changed significantly. When α is 0, the improved Gyroid unit structure is exactly the same as the standard Gyroid unit structure.

[0047] From the top view perspective, as the control factor α increases, the shape and size of the straight through holes in the Gyroid structure change significantly. The straight through holes gradually change from circular to approximately quadrilateral in shape, and the overall area of the straight through holes is continuously shrinking. When α reaches 0.45L, the straight through holes completely disappear. Combining the side view perspective, as the control factor α increases, the surface morphology in the Gyroid structure also gradually becomes tortuous, which is beneficial to increasing the contact area between the fluid and the solid surface and enhancing the formation of turbulence on the structure surface.

[0048] By regulating the magnitude of α, not only can the size of the straight through holes be adjusted to effectively avoid the fluid flowing preferentially through the low flow resistance area, thereby improving the heat transfer efficiency between the fluid and the solid surface. At the same time, the improved Gyroid unit structure also forms surface structures with different degrees of tortuosity, enhancing the perturbation effect of the fluid and making it easier for the fluid to form efficient secondary flow and vortex effects during the flow process.

[0049] Example 4

[0050] A fuel assembly includes fuel rods, control rods, a fuel grid that supports the fuel rods and control rods, a guide tube that houses the control rods and measuring instruments, and a coolant channel for heat dissipation and temperature reduction. The core is that the fuel rods adopt the fuel rods based on the TPMS structure described in Examples 1 - 3.

[0051] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art and related fields based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A fuel rod based on a TPMS structure, characterized in that, Based on the original configuration of the fuel rod, a TPMS structure is introduced to endow the internal part of the fuel rod or the cooling channels of the fuel assembly with a three-dimensional periodic topological morphology with adjustable height.

2. The fuel rod based on the TPMS structure according to claim 1, characterized in that, The TPMS structure adopts a Diamond structure, a Gyroid structure or a Schwarz-D structure.

3. The fuel rod based on the TPMS structure according to claim 1 or 2, characterized in that, The original configuration of the fuel rod is columnar, including cylindrical and multi-prismatic shapes.

4. The fuel rod based on the TPMS structure according to claim 3, characterized in that, The TPMS structure adopts a Gyroid structure, a metal cladding is arranged along the Gyroid surface, nuclear fuel is arranged between two layers of metal claddings, and an air gap layer is left between the nuclear fuel and the cladding.

5. The fuel rod based on the TPMS structure according to claim 3, characterized in that, The TPMS structure adopts a Gyroid structure. Inside each Gyroid unit is a metal frame, which extends outward to form an accommodating space at the periphery. Nuclear fuel is arranged in this accommodating space. Each Gyroid unit and other adjacent Gyroid units enclose the nuclear fuel inside the metal cladding, and an air gap is left between the nuclear fuel and the cladding.

6. The fuel rod based on the TPMS structure according to claim 4 or 5, characterized in that, Control terms containing a control factor α are respectively introduced into the three additive terms of the standard Gyroid function to form an improved Gyroid function. The size of the straight through holes and the tortuosity of the surface structure in the Gyroid structure are regulated by adjusting the size of the control factor α; meanwhile, the control term of the additive term in the xy plane contains the associated variable z, the control term of the additive term in the yz plane is associated with the variable x, and the control term of the additive term in the zx plane contains the associated variable y.

7. A fuel assembly includes fuel rods, control rods, a fuel grid that supports the fuel rods and control rods, a guide tube that houses the control rods and measuring instruments, and a coolant channel for heat dissipation and temperature reduction, characterized in that, The fuel rod adopts the fuel rod based on the TPMS structure described in any one of claims 1-6.

8. A coolant channel of a fuel assembly, characterized in that, The fuel rod adopts the Gyroid structure described in claim 4, and its peripheral space serves as a coolant channel.

9. A fuel assembly fuel grid, characterized in that, The fuel rod adopts the Gyroid structure described in claim 5, and the center of each Gyroid unit serves as a support frame.

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