Modeling method of non-uniform power distribution rod bundle CHF test piece and CHF prediction method

Abstract

The invention mainly relates to the technical field of nuclear power reactors, in particular to a modeling method of a non-uniform power distribution rod bundle CHF test piece and a CHF prediction method. The modeling method of the non-uniform power distribution rod bundle CHF test piece mainly comprises the following ten steps: determining geometric parameters of a fuel rod bundle, dividing a radial channel, dividing an axial node block, determining geometric parameters of a channel, determining heating power distribution, determining a working condition range, selecting a two-phase flow model, determining a turbulence mixing coefficient, determining a flow resistance coefficient and determining a grillwork position. The invention provides a complete and systematic sub-channel modeling method for a non-uniform power distribution rod bundle CHF test piece, and the CHF parameters of the non-uniform power distribution rod bundle can be predicted more accurately.

Description

Technical Field

[0001] The invention mainly relates to the technical field of nuclear power reactors, and in particular to a modeling method of a CHF test piece of a rod bundle with non-uniform power distribution and a CHF prediction method. Background Art

[0002] Critical heat flux (CHF) refers to the heat transferred per unit surface area per unit time when the boiling heat transfer mechanism changes, resulting in deterioration of heat transfer on the surface of the heating element. It is a key thermal performance parameter of the fuel assembly and an important limiting thermal parameter related to reactor safety. Its size directly affects the safety and economy of the reactor.

[0003] The CHF test usually uses a rod bundle test piece composed of a small-scale grid that represents the design characteristics of the real fuel assembly grid and an electric heating rod that simulates the fuel rod as the object. Tests are carried out in high-temperature and high-pressure test circuits under different pressures, coolant inlet flow rates, coolant inlet temperatures and other working conditions to obtain the CHF value when the heat transfer on the heating rod surface deteriorates. The heating rod used in the CHF test is a key test piece. The axial and radial distribution of the resistance of the electric heating rod directly affects the heating value at each position. For an electric heating rod with uniform wall thickness, its resistance is uniform along the axial and radial directions, so the heating value at each position is basically the same. However, in reality, the heating value of a real fuel rod along the axial direction is non-uniform, and it is necessary to change the resistance of the electric heating rod along the length direction so that it changes according to a certain trend along the length direction, thereby achieving non-uniform power distribution.

[0004] One of the difficulties in conducting CHF tests using electric heating rods with non-uniform power distribution is the reasonable arrangement of temperature monitoring points. The rationality of the temperature monitoring points is directly related to the success of the test. Therefore, the temperature monitoring points should be arranged at the locations where the CHF phenomenon may occur according to the CHF prediction relationship or the sub-channel analysis program. However, the CHF prediction relationship is usually developed based on CHF test data and has a clear parameter application range. Before conducting a CHF test, generally speaking, a CHF test sub-channel analysis model is usually established based on the sub-channel analysis program to pre-analyze the CHF characteristics of the fuel assembly. Therefore, it is urgent to establish a sub-channel analysis model for the CHF test of a fuel rod bundle with non-uniform power distribution, to reasonably predict the CHF of a fuel rod bundle with non-uniform power distribution, and to provide necessary data reference and test guidance for the formal conduct of the CHF test. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a modeling method and a CHF prediction method for a CHF test piece of a rod cluster with non-uniform power distribution, so as to solve the problem of lack of a modeling method for a CHF test piece of a rod cluster with non-uniform power distribution.

[0006] In order to solve the above technical problems, the present invention provides a modeling method for a CHF test piece with non-uniform power distribution, comprising: (1) Determine the geometric parameters of the non-uniform power distribution rod bundle CHF test piece, wherein the geometric parameters include the specifications and quantity of the heating rods, the specifications and quantity of the grids, and the specifications and dimensions of the flow channels; (2) Radial channel division: Based on the cross-section of the flow channel and the rod bundle of the test body, each flow channel is divided into different types of channels, including typical grid elements and atypical grid elements; (3) Axial segment division: based on the actual heating section length of the non-uniform power distribution rod bundle CHF test piece, the starting point of the heating section is taken as the 0 elevation and divided into multiple regions and multiple segments along the axial direction; (4) Determine the channel geometry parameters, including the flow area, wetted perimeter, heated perimeter, gap width and center distance of each type of channel; (5) Determine the heating power distribution, measure the resistance of each heating rod after processing, and then calculate the radial power factor, axial power factor, and connection relationship between the heating rod and the sub-channel corresponding to the CHF test piece of the non-uniform power distribution rod bundle; (6) Determine the operating range, which includes pressure, temperature, flow rate and power range; (7) Select the two-phase flow model; (8) Determine the turbulent mixing coefficient; (9) determining a flow resistance coefficient, wherein the flow resistance coefficient includes a turbulent axial resistance coefficient, a turbulent lateral resistance coefficient, a laminar axial resistance coefficient, and a laminar lateral resistance coefficient; (10) Determine the grid position, grid resistance coefficient and corresponding elevation.

[0007] Optionally, selecting a two-phase flow model includes: the two-phase flow model adopts a Levy supercooling model, a uniform volume boiling model, and a uniform two-phase resistance factor.

[0008] Optionally, determining the turbulence mixing coefficient includes: for the conservatism of the CHF prediction value, the turbulence mixing coefficient takes a value corresponding to the light rod area, and the turbulence mixing factor conservatively takes 0.

[0009] Optionally, determining the flow resistance coefficient includes: taking the turbulent axial resistance coefficient as f 1=0.184Re -0.2 The laminar axial drag coefficient is f 2=64.0Re -1.0 , the turbulent lateral drag coefficient and the laminar lateral drag coefficient are both K G =2.66Re L -0.2 . .

[0010] Optionally, the atypical grid cells include cold wall grid cells, edge grid cells and corner grid cells.

[0011] Optionally, the wetted perimeter of the test body flow channel in the cell is considered when calculating the wetted perimeter of the edge cell and the corner cell.

[0012] Optionally, the specifications and quantity of the heating rods include the number and type of the electric heating rods, the distribution positions of each type of electric heating rods, and the basic geometric parameters of each type of electric heating rods.

[0013] Optionally, the basic geometric parameters of the electric heating rod include the outer diameter, length, grid pitch, and gap between the electric heating rod and the inner wall of the flow channel.

[0014] In order to solve the above technical problems, the present invention provides a CHF prediction method, comprising: The CHF test piece model was constructed using the modeling method described above; The heating power distribution is input into the CHF test piece model to obtain the CHF prediction parameters of the rod bundle with non-uniform power distribution.

[0015] Optionally, the CHF prediction parameters include: CHF value, gas content, CHF occurrence location and effectiveness of CHF pre-analysis conditions.

[0016] Compared with the prior art, the present invention has the following advantages: The present invention provides a modeling method and a CHF prediction method for a CHF test piece of a rod bundle with non-uniform power distribution. The modeling method of the CHF test piece of a rod bundle with non-uniform power distribution mainly includes 10 steps: determining the geometric parameters of the fuel rod bundle, radial channel division, axial block division, determining the channel geometric parameters, determining the heating power distribution, determining the working condition range, selecting a two-phase flow model, determining the turbulent mixing coefficient, determining the flow resistance coefficient, and determining the grid position. The present invention proposes a complete and systematic sub-channel modeling method for the CHF test piece of a rod bundle with non-uniform power distribution, which can more accurately predict the CHF parameters of the rod bundle with non-uniform power distribution; the CHF prediction method of the present invention can more accurately predict the CHF of the rod bundle with non-uniform power distribution, and can provide necessary guidance and data support for the working condition setting and thermocouple arrangement scheme of the CHF test according to the CHF prediction value, which is of great value for ensuring the smooth development of the CHF test of the rod bundle with non-uniform power distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are included to provide a further understanding of the present application. They are included and constitute a part of the present application. The accompanying drawings illustrate embodiments of the present application and together with the present specification serve to explain the principles of the present invention. In the accompanying drawings: Figure 1Schematic diagram of a modeling method for a rod cluster CHF test piece with non-uniform power distribution according to an embodiment of the present invention.

[0018] Figure 2 Schematic diagram of typical grid cell and cold wall grid cell division according to an embodiment of the present invention.

[0019] Figure 3 Schematic diagram of the division of edge cells and corner cells according to an embodiment of the present invention.

[0020] Figure 4 Schematic diagram of an axially non-uniformly heated CFH test piece according to an embodiment of the present invention.

[0021] Figure 5 is a schematic diagram of a CHF prediction method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0023] Before conducting CHF tests, generally speaking, a CHF test sub-channel analysis model is usually established based on a sub-channel analysis program to pre-analyze the CHF characteristics of fuel assemblies. Therefore, it is urgent to establish a sub-channel analysis model for the CHF test of non-uniform power distribution fuel bundles, make reasonable predictions of the CHF of non-uniform power distribution fuel bundles, and provide necessary data references and test guidance for the formal conduct of CHF tests.

[0024] Figure 1 FIG. 1 is a schematic diagram of a modeling method for a CHF test piece with a non-uniform power distribution rod cluster according to an embodiment of the present invention. Figure 1 As shown in the figure, the modeling method of the CHF test specimen with non-uniform power distribution mainly includes 10 steps: 1. Determine the geometric parameters of the CHF test piece with non-uniform power distribution; Optionally, the geometric parameters include specifications and quantity of heating rods, specifications and quantity of grids, and specifications and dimensions of flow channels.

[0025] In some embodiments, the specifications and quantity of the heating rods include the number and type of the electric heating rods, the distribution position of each type of electric heating rods, and the basic geometric parameters of each type of electric heating rods. The basic geometric parameters of the electric heating rods include the outer diameter, length, grid pitch, and gap between the electric heating rods and the inner wall of the flow channel.

[0026] In some embodiments, the grid specifications and quantity include the grid type and quantity of the non-uniform power distribution rod cluster CHF test piece, and the corresponding installation position.

[0027] 2. Radial channel division Based on the cross-section of the test body flow channel and the rod bundle, each flow channel is divided into different types of channels, including typical grid cells and atypical grid cells.

[0028] In some embodiments, non-typical cells include cold wall cells, edge cells, and corner cells. The drag coefficient of the corner cells of the fuel assembly (the subchannel formed by the fuel rods and the gap between the two assemblies) is different from the drag coefficient of the typical cell (the subchannel surrounded by four fuel rods in the fuel assembly) and the cold wall cell (the subchannel surrounded by the fuel rods and the guide tube in the fuel assembly). The drag coefficient of the corner cells of the fuel assembly is greater than the drag coefficient of the typical cell and the cold wall cell. Generally, the drag coefficient of the fuel assembly grid is derived from test data, which is based on the entire grid. The data obtained from the test does not distinguish the cells where the grid is located. The usual subchannel analysis does not distinguish between edge and corner cells and typical and cold wall cells. Generally, when performing subchannel analysis, the edge and corner cells still use the drag coefficient of the typical or cold wall cell according to whether they contain guide tubes.

[0029] Based on the grid loss coefficient obtained from the experiment, this application calculates more precise sub-channel resistance coefficients of edge grid elements, corner grid elements, typical grid elements, and cold wall grid elements through empirical relationships.

[0030] Figure 2 FIG. 1 is a schematic diagram of typical grid cells and cold wall grid cell division according to an embodiment of the present invention. Figure 2 As shown in the figure, the standard sub-channel model division is performed for 1 / 8 of the core. First, the 1 / 8 position of the central assembly is selected as the hot assembly and divided into 11 channels and 13 rods; then the remaining fuel assemblies are lumped as channels and rods, and the number of assemblies represented is increased in sequence, namely channel 12 (rod 14), channel 13 (rod 15), and channel 14 (rod 16). In this embodiment, channel 3 is a cold wall grid element and channel 5 is a typical grid element.

[0031] Figure 3 FIG. 1 is a schematic diagram of the division of edge cells and corner cells according to an embodiment of the present invention. Figure 3As shown in the figure, the division of the corner grid element sub-channel model is also carried out for the 1 / 8 part of the core. First, the position of the adjacent component (between channel 12 and channel 13 of the standard sub-channel model) is selected as the 1 / 8 hot component, which is divided into 11 channels and 16 rods (because there is no guide tube, 3 more fuel rods are added in this part); then, the remaining fuel assemblies are lumped as channels and rods, and the number of components represented is increased in sequence, namely channel 12 (rod 17), channel 13 (rod 18), channel 14 (rod 19). In this embodiment, channels 3, 4, 6, and 8 are edge grid elements, and channel 5 is a corner grid element.

[0032] 3. Axial segment division Based on the actual heating section length of the CHF test piece with non-uniform power distribution, the starting point of the heating section is taken as the 0 elevation and divided into multiple regions and multiple blocks along the axial direction.

[0033] Figure 4 Schematic diagram of an axial non-uniform heating CFH test piece according to an embodiment of the present invention. Figure 4 As shown, the actual length of the heating section is from the starting point of the heating section to the ending point of the heating section. The starting point of the heating section is taken as the 0 elevation and is divided into several areas and several blocks along the axial direction, which are labeled TC-1, TC-2, TC-3, TC-4, TC-5, TC-6, and TC-7 respectively.

[0034] 4. Determine channel geometry parameters Determine the flow area, wetted perimeter, heated perimeter, connecting channel gap width and center distance for each type of channel.

[0035] In some embodiments, the wetted perimeter of the edge cells and corner cells is calculated taking into account the wetted perimeter of the test body flow channel within the cell.

[0036] 5. Determine the heating power distribution During the processing, the wall thickness of the heating rod will deviate from the theoretical design value. Therefore, after the processing is completed, it is necessary to measure the resistance of each heating rod, and then calculate the radial power factor corresponding to the CHF test piece of the non-uniform power distribution rod bundle as the reference input data of the sub-channel analysis program.

[0037] Optionally, determining the heating power distribution also includes determining the axial power factor and the connection relationship between the heating rod and the sub-channel.

[0038] 6. Determine the operating range The operating range includes but is not limited to pressure, temperature, flow rate and power range.

[0039] 7. Select two-phase flow model In the steam generator, the fluid enters the secondary flow field in a supercooled state, leaves the flow field in a high cavitation rate state and enters the steam-water separator. Considering the two-phase flow state and the flow heterogeneity, this application adopts a two-phase flow model to describe the boiling two phases in the reactor.

[0040] In some embodiments, the two-phase flow model uses the Levy subcooling model, the uniform volume boiling model, and the uniform two-phase resistance factor, and the CHF prediction value is calculated using the WLOP relationship.

[0041] The Levy subcooling model is a model proposed by Levy to predict the cavitation fraction based on the relationship between mass gas content and heat balance value. The Levy subcooling model is used to predict the steam volume fraction in the forced convection subcooled boiling process. The Levy subcooling model calculation method includes three steps: 1) The point at which the bubble leaves the heated surface (i.e., where the vapor volume fraction is significantly above zero) is determined by the bubble force balance and the single-phase liquid turbulent temperature distribution away from the heated wall.

[0042] 2) Assume that there is a relationship between the true local vapor weight fraction and the corresponding heat balance value.

[0043] 3) The steam volume fraction is obtained from the true local steam mass fraction and the recognized relationship between steam mass and volume fraction.

[0044] In some embodiments, the CHF prediction value is calculated using the WLOP relationship.

[0045] 8. Determine the turbulent mixing coefficient Turbulent mixing is non-directional mixing caused by the diffusion of natural eddies during fluid pulsation. Turbulent mixing between subchannels is generally characterized by the turbulent mixing coefficient, which represents the mass flow rate caused by turbulent mixing per unit length in the mainstream direction between two adjacent subchannels.

[0046] In some embodiments, in order to ensure the conservatism of the CHF prediction value, the turbulence mixing coefficient takes the value corresponding to the light rod area, and the turbulence mixing factor is conservatively taken as 0.

[0047] 9. Determine the flow resistance coefficient The flow resistance coefficient includes the turbulent axial resistance coefficient, the turbulent lateral resistance coefficient, the laminar axial resistance coefficient and the laminar lateral resistance coefficient.

[0048] In some embodiments, the turbulent axial drag coefficient is f 1=0.184Re -0.2 The laminar axial drag coefficient is f 2=64.0Re -1.0 , the turbulent lateral drag coefficient and the laminar lateral drag coefficient are both K G=2.66Re L -0.2 .

[0049] 10. Determine the grid position Determining the grid position includes determining the grid resistance coefficient and the corresponding elevation.

[0050] The present invention proposes a complete and systematic sub-channel modeling method for a CHF test piece with a non-uniform power distribution rod bundle. According to the non-uniform power distribution characteristics of the CHF test piece, the method mainly includes 10 steps: determining the geometric parameters of the fuel rod bundle, radial channel division, axial block division, determining the channel geometric parameters, determining the heating power distribution, determining the operating range, selecting a two-phase flow model, determining the turbulent mixing coefficient, determining the flow resistance coefficient, and determining the grid position. This method can more accurately predict the CHF parameters of a rod bundle with non-uniform power distribution.

[0051] Figure 5 FIG. 1 is a schematic diagram of a CHF prediction method according to an embodiment of the present invention. Figure 5 As shown, the CHF prediction method 500 includes: Step S51: constructing a CHF test piece model using the modeling method disclosed in the present invention; Step S52: Input the heating power distribution into the CHF test piece model to obtain the CHF prediction parameters of the rod cluster with non-uniform power distribution.

[0052] Optionally, CHF prediction parameters include but are not limited to CHF value, gas content, CHF occurrence location, and effectiveness of CHF pre-analysis conditions.

[0053] like Figure 5 As shown, the predicted CHF occurrence location can guide the thermocouple arrangement plan, and the effectiveness of the CHF pre-analysis conditions can guide the CHF test condition setting.

[0054] The present invention proposes a complete and systematic sub-channel modeling method for the CHF test piece of a rod cluster with non-uniform power distribution, which can more accurately predict the CHF of a rod cluster with non-uniform power distribution, and can provide necessary guidance and data support for the working condition setting and thermocouple layout scheme of the CHF test according to the CHF prediction value, which is of great value for ensuring the smooth implementation of the CHF test of a rod cluster with non-uniform power distribution.

[0055] Flowcharts are used in the present application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed accurately in order. On the contrary, various steps may be processed in reverse order or simultaneously. At the same time, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0056] The basic concepts have been described above. Obviously, for those skilled in the art, the above invention disclosure is only used as an example and does not constitute a limitation of the present application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the present application. Such modifications, improvements and amendments are suggested in the present application, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary embodiments of the present application.

[0057] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0058] Some aspects of the present application may be performed entirely by hardware, entirely by software (including firmware, resident software, microcode, etc.), or by a combination of hardware and software. The above hardware or software may be referred to as "data blocks", "modules", "engines", "units", "components" or "systems". The processor may be one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DAPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or combinations thereof. In addition, various aspects of the present application may be represented as computer products located in one or more computer-readable media, which include computer-readable program codes. For example, computer-readable media may include, but are not limited to, magnetic storage devices (e.g., hard disks, floppy disks, tapes ...), optical disks (e.g., compact disks CDs, digital versatile disks DVDs ...), smart cards, and flash memory devices (e.g., cards, sticks, key drives ...).

[0059] A computer-readable medium may include a propagated data signal containing computer program code, such as in baseband or as part of a carrier wave. The propagated signal may have a variety of manifestations, including electromagnetic, optical, etc., or a suitable combination. A computer-readable medium may be any computer-readable medium other than a computer-readable storage medium, which may be connected to an instruction execution system, device or apparatus to communicate, propagate or transmit a program for use. The program code on the computer-readable medium may be propagated via any suitable medium, including radio, cable, fiber optic cable, radio frequency signal, or similar medium, or any combination of the above mediums.

[0060] Similarly, it should be noted that in order to simplify the description of the disclosure of this application and thus help understand one or more embodiments of the invention, in the above description of the embodiments of this application, 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 object of this application 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.

[0061] In some embodiments, numbers describing the number of components and attributes are used. It should be understood that such numbers used for the description of the embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise specified, "about", "approximately" or "substantially" indicate that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which can be changed according to the required features of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the method of general digit retention. Although the numerical domains and parameters used to confirm the breadth of the range in some embodiments of the present application are approximate values, in specific embodiments, the setting of such numerical values ​​is as accurate as possible within the feasible range.

[0062] As shown in this application and claims, unless the context clearly indicates an exception, the words "a", "an", "an" and / or "the" do not refer to the singular and may also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0063] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0064] In the description of the present application, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, and therefore cannot be understood as limiting the scope of protection of the present application; the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0065] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0066] In addition, it should be noted that the use of words such as "first" and "second" to define components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above words have no special meaning and cannot be understood as limiting the scope of protection of this application. In addition, although the terms used in this application are selected from well-known and commonly used terms, some terms mentioned in the specification of this application may be selected by the applicant at his or her discretion, and their detailed meanings are explained in the relevant parts of the description of this article. In addition, it is required to understand this application not only by the actual terms used, but also by the meaning implied by each term.

[0067] Although the present application has been described with reference to the current specific embodiments, ordinary technicians in this technical field should recognize that the above embodiments are only used to illustrate the present application, and various equivalent changes or substitutions may be made without departing from the spirit of the present application. Therefore, as long as the changes and modifications to the above embodiments are within the essential spirit of the present application, they will fall within the scope of the claims of the present application.

Claims

1. A modeling method for a non-uniform power distribution rod cluster CHF test piece, characterized in that: include: Determine the geometric parameters of the non-uniform power distribution rod bundle CHF test piece, wherein the geometric parameters include the specifications and quantity of the heating rods, the specifications and quantity of the grids, and the specifications and dimensions of the flow channels; Radial channel division: Based on the cross-section of the test body flow channel and the rod bundle, each flow channel is divided into different types of channels, including typical grid elements and atypical grid elements; Axial segment division: based on the actual heating section length of the CHF test piece with non-uniform power distribution, the starting point of the heating section is taken as 0 elevation, and it is divided into multiple regions and multiple segments along the axial direction; Determine the channel geometry parameters, determine the flow area, wetted perimeter, heated perimeter, gap width and center distance of each type of channel; Determine the heating power distribution, measure the resistance of each heating rod after processing, and then calculate the radial power factor, axial power factor, and connection relationship between the heating rod and the sub-channel corresponding to the CHF test piece of the non-uniform power distribution rod bundle; Determine the operating range, which includes pressure, temperature, flow rate and power range; Select the two-phase flow model; Determine the turbulent mixing coefficient; Determining a flow resistance coefficient, wherein the flow resistance coefficient includes a turbulent axial resistance coefficient, a turbulent lateral resistance coefficient, a laminar axial resistance coefficient, and a laminar lateral resistance coefficient; Determine the grid position, grid resistance coefficient and corresponding elevation.

2. The modeling method according to claim 1, characterized in that: Select two-phase flow models including: The two-phase flow model adopts the Levy subcooling model, uniform volume boiling model and uniform two-phase resistance factor.

3. The modeling method according to claim 1, characterized in that: Determining the turbulent mixing coefficient involves: In order to ensure the conservatism of the CHF prediction value, the turbulence mixing coefficient is taken as the value corresponding to the light rod area, and the turbulence mixing factor is conservatively taken as 0.

4. The modeling method according to claim 1, characterized in that: Determining the flow resistance coefficient includes: The turbulent axial drag coefficient is f 1=0.184Re -0.2 The laminar axial drag coefficient is f 2=64.0Re -1.0 , the turbulent lateral drag coefficient and the laminar lateral drag coefficient are both K G =2.66Re L -0.2 .

5. The modeling method according to claim 1, characterized in that: The atypical grid cells include cold wall grid cells, edge grid cells and corner grid cells.

6. The modeling method according to claim 5, characterized in that: When calculating the wetted perimeter of the edge grid element and the corner grid element, the wetted perimeter of the test body flow channel in the grid element is taken into account.

7. The modeling method according to claim 1, characterized in that: The specifications and quantity of the heating rods include the number and type of the electric heating rods, the distribution positions of each type of electric heating rods, and the basic geometric parameters of each type of electric heating rods.

8. The modeling method according to claim 7, characterized in that: The basic geometric parameters of the electric heating rod include the outer diameter, length, grid pitch, and the gap between the electric heating rod and the inner wall of the flow channel.

9. A CHF prediction method, characterized in that: include: A CHF test piece model is constructed using the modeling method described in any one of claims 1 to 8; The heating power distribution is input into the CHF test piece model to obtain the CHF prediction parameters of the rod bundle with non-uniform power distribution.

10. The CHF prediction method according to claim 9, characterized in that: The CHF prediction parameters include: CHF value, gas content, CHF occurrence location and effectiveness of CHF pre-analysis conditions.

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