A coolant bypass control structure for a pressurized water reactor test loop

Abstract

The present application relates to nuclear reactor irradiation technology field, especially provide a kind of coolant bypass control structure for pressurized water reactor test loop, including pressure pipe, the pressure pipe is placed in the inside of heat pipe, spherical lower connector is arranged at the bottom of pressure pipe, the inside of pressure pipe is equipped with shunt pipe, and square round connector is arranged at the bottom of shunt pipe;Loop coolant flows to spherical lower connector through pressure pipe and turns back, and loop coolant is divided into main stream and bypass stream by square round connector at the bottom of shunt pipe;Fuel assembly is installed in the inside of shunt pipe;Lower tube base is arranged at the lower side end of fuel assembly, main stream loop coolant flows through the inside of fuel assembly through the center through-hole of lower tube base, and bypass stream loop coolant flows through the annular gap between lower tube base and shunt pipe from the annular gap between square round connector and lower tube base.The purpose is to retain a small part of bypass stream in fuel assembly irradiation test, and form stable and controllable main stream bypass stream distribution mechanism.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor fuel irradiation technology, and more specifically, to a coolant bypass control structure for a pressurized water reactor test loop. Background Technology

[0002] Passive Residual Heat Removal (PRHR) systems are an important means of improving the inherent safety of reactors and are widely used in various reactor designs. However, the presence of a bypass stream can significantly alter the drag and heat transfer characteristics of the natural circulation loop in a PRHR system, thereby affecting its residual heat removal capacity.

[0003] Pressurized water reactor (PWR) test loops are generally used for irradiation testing of fuel assemblies. Analogous to the hydraulic design of prototype reactors, fuel assemblies in the test loop also have a main flow and a bypass flow. The coolant temperature at the fuel assembly outlet is a key parameter to consider in the thermal-hydraulic design and characteristic analysis of irradiation tests, and it is also one of the important factors limiting the heat dissipation capacity of the fuel assembly. Therefore, it is necessary to study the impact of the bypass flow on the outlet temperature. During test loop operation, a positive pressure difference is generated across the fuel assembly, which is the main reason for the large bypass flow of coolant on both sides of the fuel assembly. The bypass flow has a small effect on the residual heat removal of the fuel assembly, but it can remove some residual heat from the fuel assembly cladding. The presence of the bypass flow reduces the main flow rate of the fuel assembly, increases the fuel assembly outlet temperature, and leads to a decrease in the residual heat removal capacity of the fuel assembly. However, completely eliminating the bypass flow would create a stagnant coolant region outside the fuel assembly cladding, leading to overheating of the fuel assembly cladding and seriously affecting the safe operation of the test loop. Therefore, it is necessary to operate the PWR test loop while retaining a small amount of bypass flow. Summary of the Invention

[0004] The purpose of this invention is to provide a coolant bypass control structure for a pressurized water reactor test loop, thereby enabling the operation of the pressurized water reactor test loop while retaining a small portion of the bypass flow.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a coolant bypass control structure for a pressurized water reactor test loop, comprising a pressure pipe housed inside an insulating pipe, a spherical lower connector located at the bottom of the pressure pipe, a diverter pipe installed inside the pressure pipe, and a square-round connector at the bottom of the diverter pipe; the loop coolant flows through the pressure pipe to the spherical lower connector and is reversed, and is divided into a main stream and a bypass stream by the square-round connector at the bottom of the diverter pipe; a fuel assembly is installed inside the diverter pipe; a lower tube seat is located at the lower end of the fuel assembly, the main loop coolant flows through the central through-hole of the lower tube seat into the fuel assembly, and the bypass loop coolant flows from the annular gap between the square-round connector and the lower tube seat into the annular gap between the lower tube seat and the diverter pipe.

[0007] Furthermore, it also includes a support ring and a bracket. The bracket is fixedly connected inside the pressure pipe. A support ring is fixed on the side of the bracket facing the fuel assembly. One end of the lower pipe seat at the lower end of the fuel assembly is inserted into the support ring to support and fix the fuel assembly.

[0008] Furthermore, the lower tube seat has bolt holes on the side near the fuel assembly, and the lower tube seat is bolted to the fuel assembly.

[0009] Furthermore, the cross-sectional area of ​​the bypass inlet channel is less than 5% of the cross-sectional area of ​​the main inlet channel. The bypass inlet is the annular gap between the square-round connector and the lower pipe seat, and the main inlet is the central through hole of the lower pipe seat.

[0010] Furthermore, the cross-sectional area of ​​the main flow channel inlet is 707 mm². 2 The cross-sectional area of ​​the bypass inlet channel is 28mm². 2 .

[0011] Furthermore, the wall thickness of the lower pipe seat interface section is more than twice that of the square-round connector interface section, and the lower pipe seat interface section and the square-round connector interface section cooperate to form an annular gap.

[0012] Furthermore, both the lower pipe seat interface section and the square-round connector interface section are cylindrical in design, and the top of the lower pipe seat interface section is designed with a tapered bevel.

[0013] Furthermore, the annular gap formed between the lower pipe seat interface section and the square-round connector interface section is less than 0.1 mm.

[0014] Furthermore, the portion of the square-round connector away from the interface segment is a square segment with rounded corners, and the square segment is tangent to the outer circle of the interface segment of the square-round connector.

[0015] Furthermore, the wall thickness of the square-round joint is less than 2mm.

[0016] The technical solution of the present invention has at least the following advantages and beneficial effects: the structure is suitable for pressurized water reactor test loops, forming an annular gap between the square-circular joint and the lower tube seat, which can retain a small portion of the bypass flow during fuel assembly irradiation tests, forming a stable and controllable mainstream bypass flow distribution mechanism; under test conditions, the lower tube seat and the square-circular joint will undergo radial thermal expansion under temperature action, achieving "gap elimination", which reduces the design gap under test conditions and causes the bypass flow rate to shift in the opposite direction; the structure can achieve the smallest possible bypass flow rate, and the bypass flow rate fluctuation is also small under hot conditions; it can improve the stability of the mainstream flow under test conditions and improve the heat dissipation capacity of the fuel assembly. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of a coolant bypass control structure for a pressurized water reactor test loop provided by the present invention;

[0019] Figure 2 This is a schematic diagram of the lower tube seat structure provided in an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of a square-round joint structure provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the bevel of the straight edge section of the square-round joint provided in an embodiment of the present invention;

[0022] Figure 5 This is a schematic diagram of the bevel of the R-zone of the square-round joint provided in an embodiment of the present invention;

[0023] Figure 6 A schematic diagram of the main traffic and side traffic allocation interface provided in an embodiment of the present invention;

[0024] Figure 7 A schematic diagram illustrating the changing trend of the bypass control structure under test conditions provided in this embodiment of the invention;

[0025] Icons: 1-Insulation pipe; 2-Pressure pipe; 3-Spherical lower connector; 4-Diverter pipe; 5-Fuel assembly; 6-Lower pipe seat; 7-Square-round connector; 8-Support ring; 9-Bracket. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0027] Example:

[0028] like Figure 1As shown in the figure, this invention proposes a coolant bypass control structure for a pressurized water reactor test loop, which includes an insulating tube 1, a pressure tube 2, a spherical lower connector 3, a diverter tube 4, a fuel assembly 5, a lower tube seat 6, a square-round connector 7, a support ring 8, and a bracket 9. The pressure tube 2 is placed inside the insulating tube 1. The insulating tube 1 provides thermal insulation and acts as a pressure boundary to protect the pressure tube 2. If the pressure tube 2 is damaged, the insulating tube 1 can prevent the loop coolant from leaking into the pressurized water reactor. The pressure tube 2 is the pressure boundary of the test loop and is part of the main loop coolant pipeline, providing a high-temperature, high-pressure physical field and radiation field for the irradiated test fuel assembly. A spherical lower connector 3 is located at the bottom of the pressure pipe 2. A diversion pipe 4 is installed inside the pressure pipe 2, which is divided into a region where the coolant flows in reverse. The fuel assembly 5 is also installed inside the diversion pipe 4. A square-round connector 7 is located at the bottom of the diversion pipe 4. The coolant flows through the pressure pipe to the spherical lower connector 3 and then back, and is divided into a main stream and a bypass stream by the square-round connector 7 at the bottom of the diversion pipe 4. The lower pipe seat 6 is located at the lower end of the fuel assembly 5. The central through hole of the lower pipe seat 6 is the main stream channel of the fuel assembly 5. This part of the coolant flows through the inside of the fuel assembly 5 to cool the fuel core of the fuel assembly. The annular gap between the square-round connector 7 and the lower pipe seat 6 is the inlet of the bypass channel. The annular gap where the lower pipe seat 6 contacts the diversion pipe 4 is the bypass channel of the fuel assembly 5. This part of the coolant flows through the slit between the outside of the fuel assembly 5 and the diversion pipe 4 to cool the external structural components of the fuel assembly 5. The cross-sectional area of ​​the bypass inlet channel is controlled to be less than 5% of the cross-sectional area of ​​the main stream inlet. This structure retains a small portion of the bypass flow from the fuel assembly 5 irradiation test, forming a stable and controllable mainstream bypass flow distribution mechanism.

[0029] Specifically, in this embodiment, the support ring 8 and bracket 9 are structural components used for positioning and supporting the fuel assembly 5 in the test circuit. The lower tube seat 6 at the lower end of the fuel assembly 5 can be inserted into the support ring 8. The support ring 8, bracket 9 and pressure tube 2 are fixed together by welding, forming a structure that supports and fixes the fuel assembly 5 inside the pressure tube 2.

[0030] like Figure 2As shown, the end of the lower tube seat 6 that is fixed to the fuel assembly 5 is square, with the same cross-sectional dimensions as the fuel assembly 5. Its square structure has an axial height ≥ 5mm, and a mixing structure is designed within the irregular central cavity. The square structure of the lower tube seat 6 has four bolt holes. The lower tube seat 6 is fixed to the fuel assembly 5 by bolts and welded to the outer shell of the fuel assembly 5 as a single unit. The interface section of the lower tube seat 6 adopts a cylindrical design, with an axial height of approximately 15mm. The top of the interface section of the lower tube seat 6 is designed with a tapered bevel, facilitating the insertion of the square-round connector 7 during vertical installation. A ≤ 0.1mm annular gap is formed between the lower tube seat 6 and the square-round connector 7, which serves as the inlet for the bypass channel of the loop coolant. Under design conditions, the bypass channel inlet gap will vary from the design value of 0.1mm to a narrower range, from 0.01 to 0.1mm, at which point the bypass rate is 0.5% to 5%. This ensures that the main flow rate of the fuel assembly 5 does not decrease, and the waste heat removal capacity does not decline.

[0031] like Figure 3 As shown, the interface section of the square-round connector 7 is cylindrical, which mates with the cylindrical surface of the lower pipe seat 6 to form an annular gap. The end of the square-round connector 7 near the diverter pipe 4 is a square section, the cross-section of which is the same as that of the square diverter pipe 4. The wall thickness of the square-round connector 7 is ≤2mm. The upper square section needs to be rounded, and the square section is required to be tangent to the outer circle of the interface section. This can maximize the protection of the inner cavity size of the square-round connector 7, so that the fuel assembly 5 can be installed smoothly.

[0032] Specifically, in this embodiment, the square segment of the square-round component is butt-welded to the shunt pipe 4. The butt-welding should consider the beveling of the straight edge segment and the R-zone in sections, as shown in the form of... Figure 4 and Figure 5 After welding, the inner and outer rounded corners need to be ground smooth.

[0033] Specifically, in this embodiment, the wall thickness design value of the lower tube seat 6 interface section is controlled to be more than twice the wall thickness design value of the square and round joint 7 interface section, so as to achieve a greater deformation effect of the lower tube seat 6 than that of the square and round joint 7 under complex physical fields.

[0034] Specifically, in this embodiment, such as Figure 6 The diagram shows the main flow and bypass flow distribution interface. The main flow is the coolant entering through the central circular hole of the lower tube seat 6, with an inlet flow channel cross-sectional area of ​​707 mm². 2 The coolant entering through the annular gap between the lower tube seat 6 and the square-round connector 7 is a bypass flow, and the inlet flow channel cross-sectional area is 28mm². 2 The cross-sectional area of ​​the bypass channel accounts for 3.8% of the total cross-sectional area of ​​the channel, and the bypass rate is ≤5%.

[0035] like Figure 7As shown, under test conditions, the lower pipe seat 6 and the square-round joint 7 will undergo radial thermal expansion due to temperature, which will reduce the design gap under test conditions and cause the bypass rate to shift in the opposite direction. This structure can minimize the bypass rate and minimize the fluctuation of the bypass rate under hot conditions, thereby improving the stability of the main flow under test conditions and improving the heat dissipation capacity of the fuel assembly 5.

[0036] Specifically, in this embodiment, the installation steps of the coolant bypass control structure for the pressurized water reactor test loop are as follows:

[0037] Step 1: Place the fuel assembly 5 in the center hole of the positioning grid, which consists of a support ring 8 and a bracket 9;

[0038] Step 2: Insert the splitter pipe 4 into the fuel assembly 5 from top to bottom and use the gripping tool to fix the fuel assembly 5 and the splitter pipe 4 into a whole;

[0039] Step 3: Lift the splitter pipe 4 and the fuel assembly 5;

[0040] Step 4: Lower pressure tube 2 below diverter tube 4;

[0041] Step 5: Insert the shunt tube 4 into the pressure tube 2;

[0042] Step 6: After inserting pressure pipe 2 into insulation pipe 1, connect it to the test circuit and pressurized water stack.

[0043] The above installation sequence can be performed underwater, meaning that fuel assembly 5 remains below the water surface, which can protect operators from high levels of radiation.

[0044] The basic concepts have been described above. Obviously, for those skilled in the art, the detailed disclosure above is merely illustrative and does not constitute a limitation of this specification. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification and therefore remain within the spirit and scope of the exemplary embodiments described herein.

[0045] Similarly, it should be noted that, in order to simplify the description disclosed herein and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of embodiments in this specification may sometimes combine multiple features into a single embodiment, drawing, or description thereof. However, this method of disclosure does not imply that the subject matter of this specification requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of a single embodiment disclosed above.

[0046] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. A coolant bypass control structure for a pressurized water reactor test loop, characterized in that, The system includes a pressure pipe (2), which is placed inside an insulating pipe (1). A spherical lower connector (3) is located at the bottom of the pressure pipe (2). A diversion pipe (4) is installed inside the pressure pipe (2), and a square-round connector (7) is provided at the bottom of the diversion pipe (4). The loop coolant flows through the pressure pipe (2) to the spherical lower connector (3) and turns back. The loop coolant is divided into a main stream and a bypass stream by the square-round connector (7) at the bottom of the diversion pipe (4). A fuel assembly (5) is installed inside the diversion pipe (4). A lower pipe seat (6) is provided at the lower end of the fuel assembly (5). The main loop coolant flows through the central through hole of the lower pipe seat (6) into the fuel assembly (5). The bypass loop coolant flows from the annular gap between the square-round connector (7) and the lower pipe seat (6) through the annular gap between the lower pipe seat (6) and the diversion pipe (4). The wall thickness of the lower pipe seat (6) interface section is more than twice the wall thickness of the square and round connector (7) interface section, and the lower pipe seat (6) interface section and the square and round connector (7) interface section cooperate with each other to form an annular gap. The cross-sectional area of ​​the bypass inlet channel is less than 5% of the cross-sectional area of ​​the main inlet channel. The bypass inlet is the annular gap between the square-round connector (7) and the lower pipe seat (6), and the main inlet is the central through hole of the lower pipe seat (6). The cross-sectional area of ​​the main inlet channel is 707 mm². 2 The cross-sectional area of ​​the bypass inlet channel is 28mm². 2 ; The annular gap formed between the lower pipe seat (6) interface section and the square-round connector (7) interface section is less than 0.1mm; both the lower pipe seat (6) interface section and the square-round connector (7) interface section are cylindrical in design, and the top of the lower pipe seat (6) interface section is designed as a conical bevel.

2. The coolant bypass control structure for a pressurized water reactor test loop as described in claim 1, characterized in that, It also includes a support ring (8) and a bracket (9). The bracket (9) is fixedly connected to the pressure pipe (2). The support ring (8) is fixed on the side of the bracket (9) facing the fuel assembly. One end of the lower pipe seat (6) at the lower end of the fuel assembly (5) is inserted into the support ring (8) to support and fix the fuel assembly (5).

3. The coolant bypass control structure for a pressurized water reactor test loop as described in claim 1, characterized in that, The lower tube seat (6) has bolt holes on the side near the fuel assembly (5), and the lower tube seat (6) is bolted to the fuel assembly (5).

4. The coolant bypass control structure for a pressurized water reactor test loop as described in claim 1, characterized in that, The portion of the square-round connector (7) away from the interface segment is a square segment with rounded corners. The square segment is tangent to the outer circle of the interface segment of the square-round connector (7).

5. The coolant bypass control structure for a pressurized water reactor test loop as described in claim 1, characterized in that, The wall thickness of the square-round joint (7) is less than 2 mm.

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