Coolant bypass flow control structure for pressurized water reactor test loop

Abstract

The invention relates to the technical field of nuclear reactor irradiation, in particular to a coolant bypass flow control structure for a pressurized water reactor test loop, which comprises a pressure pipe, the pressure pipe is arranged in a heat insulation pipe, a spherical lower joint is arranged at the bottom of the pressure pipe, a shunt pipe is mounted in the pressure pipe, and a square and round joint is arranged at the bottom of the shunt pipe; the loop coolant flows to the spherical lower joint through the pressure pipe and is folded back, and the loop coolant is divided into a main flow and a bypass flow through the square and round joint at the bottom of the shunt pipe; a fuel assembly is installed in the flow dividing pipe. A lower pipe base is arranged at the end of the lower side of the fuel assembly, a main flow loop coolant flows through the interior of the fuel assembly through a center through hole of the lower pipe base, and a bypass flow loop coolant flows through an annular space between the lower pipe base and the shunt pipe from an annular space between the square and round connector and the lower pipe base. The invention aims to retain a small part of bypass flow in the irradiation test of the fuel assembly to form a stable and controllable main flow and bypass flow distribution mechanism.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear reactor fuel irradiation, and in particular to a coolant bypass flow control structure for a pressurized water reactor test loop. Background Art

[0002] The passive residual heat removal (PRHR) system is an important means to improve the inherent safety of reactors and is widely used in various reactor designs. The existence of bypass flow will significantly change the resistance characteristics and heat transfer characteristics of the natural circulation loop of the PRHR system, thereby affecting the residual heat removal capacity.

[0003] The test loop of a pressurized water reactor is generally used to carry out irradiation tests on fuel assemblies. Similar to the hydraulic design of a prototype reactor, the fuel assembly also has mainstream and side flows in the test loop. The coolant temperature at the outlet of the fuel assembly is a parameter that needs to be considered in the thermal hydraulic design and characteristic analysis of the irradiation test, and it is also one of the important factors that limit the heat removal capacity of the fuel assembly. Therefore, it is necessary to study the effect of the side flow on the outlet temperature. When the test loop is in operation, a positive pressure difference will be generated at both ends of the fuel assembly. This is the main reason why the coolant in the test loop generates a large side flow on both sides of the fuel assembly. The side flow has little effect on the removal of residual heat from the fuel assembly, but it can take away some of the residual heat from the outer cladding of the fuel assembly. The presence of the side flow will reduce the main flow of the fuel assembly, increase the outlet temperature of the fuel assembly, and lead to a decrease in the residual heat removal capacity of the fuel assembly. However, completely eliminating the side flow will form a coolant quiescent area outside the fuel assembly cladding, which will cause the fuel assembly cladding to overheat, seriously affecting the safety of the test loop operation. Therefore, it is necessary to carry out the operation of the pressurized water reactor test loop on the basis of retaining a small part of the side flow. Summary of the invention

[0004] The object of the present invention is to provide a coolant bypass flow control structure for a pressurized water reactor test circuit, thereby realizing the operation of the pressurized water reactor test circuit on the basis of retaining a small part of the bypass flow.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention provides a coolant bypass control structure for a test loop of a pressurized water reactor, comprising a pressure tube, wherein the pressure tube is placed inside an insulating tube, a spherical lower joint is arranged at the bottom of the pressure tube, a shunt tube is installed inside the pressure tube, and a square-round joint is arranged at the bottom of the shunt tube; the loop coolant flows through the pressure tube to the spherical lower joint and returns, and is divided into a mainstream and a bypass through the square-round joint at the bottom of the shunt; a fuel assembly is installed inside the shunt tube; a lower tube seat is arranged at the lower end of the fuel assembly, the mainstream loop coolant flows through the center through hole of the lower tube seat and flows through the inside of the fuel assembly, and the bypass loop coolant flows from the annular gap between the square-round joint and the lower tube seat through the annular gap between the lower tube seat and the shunt tube.

[0007] Furthermore, it also includes a support ring and a bracket, the bracket is fixedly connected in the pressure tube, a support ring is fixed on the side of the bracket facing the fuel assembly, one end of the lower tube seat at the lower end of the fuel assembly is inserted into the support ring for supporting and fixing the fuel assembly.

[0008] Furthermore, a bolt hole is designed on a side of the lower tube seat close to the fuel assembly, and the lower tube seat is bolted to the fuel assembly.

[0009] Furthermore, the cross-sectional area of ​​the flow channel of the side flow inlet is less than 5% of the cross-sectional area of ​​the flow channel of the main flow inlet, the side flow inlet is the annular gap between the square-circular joint and the lower tube seat, and the main flow inlet is the central through hole of the lower tube seat.

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

[0011] Furthermore, the wall thickness of the lower tube seat interface section is more than twice the wall thickness of the square and round joint interface section, and the lower tube seat interface section and the square and round joint interface section cooperate with each other to form an annular gap.

[0012] Furthermore, the lower tube seat interface section and the square-round joint interface section are both cylindrical in design, and the top of the lower tube seat interface section is designed as a conical groove.

[0013] Furthermore, the annular gap formed between the lower tube seat interface section and the square-circular joint interface section is less than 0.1 mm.

[0014] Furthermore, the portion of the square-circle joint away from the interface section is a square section, the square section is designed with rounded corners, and the square section is tangent to the circumscribed circle of the interface section of the square-circle joint.

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

[0016] The technical solution of the present invention has at least the following advantages and beneficial effects: the structure is suitable for a pressurized water reactor test loop, and an annular gap is formed between the square-circular joint and the lower tube seat, which can retain a small part of the bypass flow in the fuel assembly irradiation test, forming a stable and controllable mainstream bypass flow distribution mechanism; under the test conditions, the lower tube seat and the square-circular joint will produce radial thermal expansion under the action of temperature, realizing "gap elimination", so that the designed gap is reduced under the test conditions, and the bypass rate is shifted to the reverse direction; the structure can achieve the smallest possible bypass rate, and the bypass rate fluctuation is also small under hot conditions; it can improve the stability of the mainstream flow under the test conditions and improve the heat dissipation capacity of the fuel assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

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

[0019] Figure 2 A schematic diagram of the structure of the lower tube base provided by an embodiment of the present invention;

[0020] Figure 3 A schematic diagram of the square-circle joint structure provided by an embodiment of the present invention;

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

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

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

[0024] Figure 7 A schematic diagram of the change trend of the bypass flow control structure under the test conditions provided by the embodiment of the present invention;

[0025] Icons: 1-insulation tube; 2-pressure tube; 3-spherical lower joint; 4-diverter tube; 5-fuel assembly; 6-lower tube seat; 7-square and round joint; 8-support ring; 9-bracket. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0027] Example:

[0028] like Figure 1As shown, an embodiment of the present 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 joint 3, a shunt tube 4, a fuel assembly 5, a lower tube seat 6, a square and round joint 7, a support ring 8 and a bracket 9. The pressure tube 2 is placed inside the insulating tube 1, and the insulating tube 1 can be used for heat insulation and protect the pressure tube 2 as a layer of pressure boundary of 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, which is part of the main circuit of the loop coolant and can provide a high-temperature, high-pressure physical field and radiation field for irradiation test fuel assemblies. The spherical lower joint 3 is arranged at the bottom of the pressure tube 2, and a shunt tube 4 is installed inside the pressure tube 2, which cuts and forms an area for reverse flow of the loop coolant inside the pressure tube 2. The fuel assembly 5 is also installed inside the shunt tube 4, and a square and round joint 7 is arranged at the bottom of the shunt tube 4. The loop coolant flows through the pressure tube to the spherical lower joint 3 and returns, and is divided into a mainstream and a bypass flow by the square and round joint 7 at the bottom of the shunt tube 4; the lower tube seat 6 is located at the lower end of the fuel assembly 5, and the central through hole of the lower tube seat 6 is the mainstream channel of the fuel assembly 5. This part of the loop coolant flows through the inside of the fuel assembly 5 and is used to cool the fuel core of the fuel assembly; the annular gap between the square and round joint 7 and the lower tube seat 6 is the entrance of the bypass channel, and the annular gap where the lower tube seat 6 contacts the shunt tube 4 is the bypass channel of the fuel assembly 5. This part of the loop coolant flows through the slit between the outside of the fuel assembly 5 and the shunt tube 4, and is used to cool the external structural parts of the fuel assembly 5, and the cross-sectional area of ​​the bypass flow inlet is controlled to be less than 5% of the cross-sectional area of ​​the mainstream inlet. This structure retains a small portion of the side flow during the irradiation test of fuel assembly 5, forming a stable and controllable mainstream side flow distribution mechanism.

[0029] Specifically, in this embodiment, the support ring 8 and the bracket 9 are structural parts 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, the bracket 9 and the pressure tube 2 are fixed together by welding, forming a structure inside the pressure tube 2 to support and fix the fuel assembly 5.

[0030] like Figure 2As shown, the end of the lower tube seat 6 fixed to the fuel assembly 5 is square, and the cross-sectional dimensions are consistent with the fuel assembly 5. The axial height of the square structure is ≥5mm, and a mixing structure is designed in the central irregular cavity. Four bolt holes are set on the square structure of the lower tube seat 6. 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 whole. The interface section of the lower tube seat 6 adopts a cylindrical design, and the axial height of the cylindrical surface is about 15mm. The top of the interface section of the lower tube seat 6 is designed as a conical groove, which is convenient for inserting the square and round joint 7 when installed vertically. An annular gap of ≤0.1mm is formed between the lower tube seat 6 and the square and round joint 7, and the annular gap is the bypass channel inlet of the loop coolant. Under the design condition, the gap at the inlet of the bypass channel will change to a narrower direction based on the design value of 0.1mm, and the gap range is 0.01~0.1mm. At this time, the bypass rate is 0.5%~5%. It can ensure that the main flow of the fuel assembly 5 is not reduced and the waste heat extraction capacity is not reduced.

[0031] like Figure 3 As shown, the interface section of the square-round joint 7 is cylindrical, and cooperates with the cylindrical surface of the lower tube seat 6 to form an annular gap. The square-round joint 7 is close to the end of the diverter tube 4 as a square section, and the cross-section of the square section is consistent with the square diverter tube 4. The wall thickness of the square-round joint 7 is ≤2mm, and the upper square section needs to be rounded, requiring the square section to be tangent to the circumscribed circle of the interface section, which can maximize the inner cavity size of the square-round joint 7 and allow the fuel assembly 5 to be smoothly loaded.

[0032] Specifically, in this embodiment, the square section of the square-circle assembly is butt-welded to the shunt pipe 4. The butt welding should be divided into straight edge sections and grooves in the R zone. Figure 4 and Figure 5 After welding, the inner and outer corners need to be ground smooth.

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

[0034] Specifically, in this embodiment, if Figure 6 As shown in the figure, it is a schematic diagram of the main flow and bypass flow distribution interface. The coolant entering through the central circular hole of the lower pipe seat 6 is the main flow, and the cross-sectional area of ​​the inlet flow channel is 707mm 2 The coolant entering through the annular gap between the lower pipe seat 6 and the square and round joint 7 is the bypass flow, and the cross-sectional area of ​​the inlet flow channel is 28mm 2 ; The proportion of the side flow channel cross-sectional area to the total flow channel cross-sectional area is 3.8%, and the side flow rate is ≤5%.

[0035] like Figure 7As shown, under the test conditions, the lower tube seat 6 and the square-round joint 7 will produce radial thermal expansion under the action of temperature, so that the designed gap is reduced under the test conditions, and the bypass rate is shifted to the reverse direction. Through this structure, the bypass rate is as small as possible, and the bypass rate fluctuation under hot conditions is as small as possible, which can improve the stability of the main flow under the test conditions and improve the heat dissipation capacity of the fuel assembly 5.

[0036] Specifically, in this embodiment, the steps for installing the coolant bypass flow 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 spacer grid, which is composed of a support ring 8 and a support 9;

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

[0039] Step 3: Lift the manifold 4, the separation tube and the fuel assembly 5;

[0040] Step 4: Sink the pressure pipe 2 below the diversion pipe 4;

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

[0042] Step 6: Place the pressure tube 2 into the insulation tube 1 and connect it to the test loop and the pressurized water reactor.

[0043] The above installation sequence can be operated underwater, that is, the fuel assembly 5 is kept below the water surface, which can protect the operators from being harmed by high radioactivity.

[0044] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only for example and does not constitute a limitation of this specification. Although not explicitly stated here, 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, so such modifications, improvements and corrections still belong to the spirit and scope of the exemplary embodiments of this specification.

[0045] Similarly, it should be noted that in order to simplify the description disclosed in this specification and thus help understand one or more embodiments of the invention, in the above description of the embodiments of this specification, multiple features are sometimes combined into one embodiment, figure or description thereof. However, this disclosure method does not mean that the features required by the subject matter of this specification are more than the features mentioned in the claims. In fact, the features of the embodiments are less than all the features of the single embodiment disclosed above.

[0046] Finally, it should be understood that the embodiments described in this specification are only used to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, as an example and not a limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly introduced and described in this specification.

Claims

1. A coolant bypass control structure for a pressurized water reactor test circuit, characterized in that: The invention comprises a pressure tube (2), wherein the pressure tube (2) is placed inside an insulating tube (1), a spherical lower joint (3) is arranged at the bottom of the pressure tube (2), a shunt tube (4) is installed inside the pressure tube (2), and a square-round joint (7) is arranged at the bottom of the shunt tube (4); a loop coolant flows through the pressure tube (2) to the spherical lower joint (3) and returns, and is divided into a mainstream and a bypass flow through the square-round joint (7) at the bottom of the shunt tube (4); a fuel assembly (5) is installed inside the shunt tube (4); a lower tube seat (6) is arranged at the lower end of the fuel assembly (5), the mainstream loop coolant flows through the central through hole of the lower tube seat (6) and flows through the inside of the fuel assembly (5), and the bypass loop coolant flows from the annular gap between the square-round joint (7) and the lower tube seat (6) through the annular gap between the lower tube seat (6) and the shunt tube (4).

2. A coolant bypass control structure for a pressurized water reactor test circuit as claimed in claim 1, characterized in that: It also includes a support ring (8) and a bracket (9), wherein the bracket (9) is fixedly connected to the inside of the pressure tube (2), a support ring (8) is fixed on the side of the bracket (9) facing the fuel assembly, and one end of the lower tube seat (6) at the lower end of the fuel assembly (5) is inserted into the support ring (8) for supporting and fixing the fuel assembly (5).

3. A coolant bypass control structure for a pressurized water reactor test circuit as claimed in claim 1, characterized in that: A bolt hole is designed on a side of the lower tube seat (6) close to the fuel assembly (5), and the lower tube seat (6) is bolted to the fuel assembly (5).

4. A coolant bypass control structure for a pressurized water reactor test circuit as claimed in claim 1, characterized in that: The cross-sectional area of ​​the flow channel of the side flow inlet is less than 5% of the cross-sectional area of ​​the flow channel of the main flow inlet. The side flow inlet is the annular gap between the square-circular joint (7) and the lower tube seat (6), and the main flow inlet is the central through hole of the lower tube seat (6).

5. A coolant bypass flow control structure for a pressurized water reactor test circuit as claimed in claim 4, characterized in that: The cross-sectional area of ​​the main inlet flow channel is 707 mm 2 The cross-sectional area of ​​the side channel inlet is 28mm 2 .

6. A coolant bypass flow control structure for a pressurized water reactor test circuit as claimed in claim 1, characterized in that: The wall thickness of the interface section of the lower tube seat (6) is more than twice the wall thickness of the interface section of the square-circle joint (7), and the interface section of the lower tube seat (6) and the interface section of the square-circle joint (7) cooperate with each other to form an annular gap.

7. A coolant bypass control structure for a pressurized water reactor test circuit as claimed in claim 6, characterized in that: The interface section of the lower tube seat (6) and the interface section of the square-round joint (7) are both cylindrical in design, and the top of the interface section of the lower tube seat (6) is designed as a conical groove.

8. A coolant bypass control structure for a pressurized water reactor test circuit as claimed in claim 6, characterized in that: The annular gap formed between the interface section of the lower pipe seat (6) and the interface section of the square-circular joint (7) is less than 0.1 mm.

9. A coolant bypass flow control structure for a pressurized water reactor test circuit as claimed in claim 6, characterized in that: The portion of the square-circle joint (7) away from the interface section is a square section, the square section is designed with rounded corners, and the square section is tangent to the circumscribed circle of the interface section of the square-circle joint (7).

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

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