A method for handling fuel assembly geometry uncertainty based on subchannel program

Abstract

This invention proposes a method for handling geometric uncertainties in fuel assemblies based on subchannel programs, belonging to the field of reactor fuel assembly thermal-hydraulic analysis technology. It solves the technical problem of considering geometric uncertainties in subchannel programs. The method includes: classifying the geometric uncertainty parameters of the fuel assembly and correcting the fuel rod center coordinates; classifying the fuel rods into corner rods, side rods, and center rods according to their positions in the fuel assembly; calculating the coordinates of the wall projection points; classifying the coolant channels within the fuel assembly into channel types and matching calculation methods; determining the actual diameter of the fuel rods; calculating the flow area of ​​the corner channels, side channels, and center channels; calculating the heating share of each channel by the fuel rods; and calculating the wetted perimeter and thermal perimeter of the channels. This invention is applied to the high-precision conversion calculation of geometric parameter deviations in subchannel programs during fuel assembly manufacturing and installation.

Description

Technical Field

[0001] This invention belongs to the field of thermal-hydraulic analysis technology of reactor fuel assemblies, and specifically relates to a method for handling geometric uncertainties of fuel assemblies in subchannel programs. It is specifically applied to the high-precision conversion calculation of geometric parameter deviations in subchannel programs during the manufacturing and installation of fuel assemblies. Background Technology

[0002] Geometric uncertainty, as an inherent source of error in the thermal-hydraulic calculations and safety analysis of reactor fuel assemblies, is mainly related to manufacturing deviations of the fuel rods, such as diameter deviations, and installation deviations, such as offset distances and angles. These deviations directly alter the structural morphology of the coolant flow channels, thereby disturbing the temperature distribution of the fuel rods and the flow characteristics of the coolant. This not only affects key safety parameters such as the minimum deviation nucleus boiling ratio, but also ultimately threatens the reactor's safety margin.

[0003] From the current research status, the analysis methods for the geometric uncertainty of fuel assemblies still have obvious simplification problems: on the one hand, traditional studies often focus on square arrangements, which have poor universality for different arrangements; on the other hand, due to the lack of a systematic geometric parameter conversion logic, it is impossible to accurately convert the original geometric uncertainty parameters such as fuel rod diameter, offset distance, and offset angle into the calculation parameters required by the sub-channel program.

[0004] To accurately assess the impact of geometric uncertainties on the thermal-hydraulic properties of fuel assemblies, it is crucial to establish a method for handling geometric uncertainties in adaptable subchannel procedures with different arrangements. This method needs to perform refined transformation of geometric parameters and perturbation propagation to provide reliable input for subsequent tolerance range estimation and sensitivity analysis, ultimately achieving the goal of improving reactor design safety and economy. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method for handling geometric uncertainties of fuel components based on subchannel procedures, so as to solve the technical problem of considering geometric uncertainties in subchannel procedures.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention proposes a method for handling geometric uncertainties in fuel assemblies based on subchannel procedures, the method comprising: S1. Classify the geometric uncertainty parameters of the fuel assembly and correct the center coordinates of the fuel rod; the geometric uncertainty parameters include fuel rod diameter deviation and installation position deviation; the installation position deviation includes offset distance and offset angle; decompose the offset distance and offset angle into offset components in the x and y directions, and superimpose the offset components onto the nominal center coordinates of the fuel rod to obtain the actual center coordinates of the disturbed fuel rod; S2. Based on the position of the fuel rods in the fuel assembly, the fuel rods are divided into corner rods, side rods, and center rods; for the corner rods and side rods, the actual center coordinates of the disturbed fuel rods are vertically projected onto the adjacent wall surface, and the coordinates of the projection points on the wall surface are calculated; the center rod is not subject to projection. S3. Divide the coolant channels within the fuel assembly into channel types, including corner channels, side channels, and center channels, and match the calculation method according to the channel types; S4. Determine the actual diameter of the fuel rod based on the fuel rod diameter deviation; S5. Based on the coordinates of the wall projection points, the channel type, and the actual diameter of the fuel rods, calculate the flow area of ​​the corner channels, side channels, and center channels; S6. Based on the relative angle between the fuel rod and each adjacent channel, calculate the heating share of the fuel rod to each channel; S7. Calculate the wet and hot perimeters of the channel based on the channel type, the actual diameter of the fuel rod, and the circumferential angle.

[0007] Furthermore, in S1, the x-direction offset component Δx and the y-direction offset component Δy satisfy: , where d is the offset distance and θ is the offset angle.

[0008] Furthermore, in S1, the actual center coordinates (x, y) of the disturbed fuel rod n , y n )satisfy: , where x and y are the nominal coordinates of the fuel rod center before the disturbance.

[0009] Furthermore, in S2, the angle bar is adjacent to two adjacent walls at the same time, and needs to be vertically projected onto the two adjacent walls respectively to obtain two independent wall projection point coordinates; the side bar is only adjacent to one wall, and only vertically projected onto that single wall to obtain a unique wall projection point coordinate.

[0010] Furthermore, in S2, the fuel assembly is arranged in a hexagonal or square pattern; the wall of the hexagonal assembly is an inclined plane structure; the wall of the square assembly includes a vertical structure and a horizontal plane structure.

[0011] Furthermore, in S4, the actual diameter D of the fuel rod n Satisfy: D n = D + δD, where D is the nominal diameter of the fuel rod and δD is the diameter deviation.

[0012] Furthermore, in S5, the flow area is obtained by subtracting the fuel rod obstruction area from the reference geometric area; wherein the obstruction area of ​​the fuel rod is fan-shaped.

[0013] Furthermore, in S5, the central channel of the hexagonal arrangement component is formed by the outer contours of three central rods, and the central channel of the square arrangement component is formed by the outer contours of four central rods.

[0014] Furthermore, in S7, the wet perimeter and hot perimeter of the channel are equal; wherein, the corner channel is adjacent to one fuel rod, and the side channel is adjacent to two fuel rods.

[0015] Furthermore, the fuel assembly is arranged in a hexagonal or square pattern. When it is arranged in a hexagonal pattern, the central channel is adjacent to three fuel rods. When it is arranged in a square pattern, the central channel is adjacent to four fuel rods.

[0016] Compared with the prior art, the beneficial effects of the present invention are: The fuel assembly geometric uncertainty handling method based on subchannel programs described in this invention is based on establishing a standardized conversion process capable of handling key geometric deviations in fuel assemblies with different arrangements, including fuel rod diameter deviations and internal installation position deviations. This process, through predefined mapping rules and dedicated data interfaces, completely and accurately converts these physical geometric deviations into specific format input parameters that can be recognized and read by downstream subchannel analysis programs. The aim is to solve the problem of mismatch between fuel assembly geometric uncertainty parameters and subchannel program input formats through a standardized and precise parameter conversion process, providing reliable data support for subsequent flow and heat transfer characteristic analysis.

[0017] This invention can match calculation methods for corner channels, side channels, and center channels in a fuel assembly. By independently applying perturbation to each fuel rod, the fuel rod diameter deviation, offset distance, and offset angle are converted into the actual center coordinates of the perturbed fuel rod. The corner and side rods are then projected onto adjacent walls, and the coordinates of the projected points on the walls are calculated. Based on these coordinates, channel type, and actual fuel rod diameter, the flow area is calculated by subtracting the fuel rod shading area from the baseline geometric area, where the fuel rod shading area is fan-shaped. Simultaneously, based on the relative angular relationship between the fuel rod and each adjacent channel, the heating share of each channel by the fuel rod is allocated according to the circumferential contact angle ratio, and the wetted perimeter and thermal perimeter of the channel are calculated according to the channel type and the number of adjacent fuel rods. This achieves accurate conversion of fuel rod geometric uncertainty parameters into core calculation parameters of the sub-channel program, providing reliable geometric input for the thermo-hydraulic uncertainty analysis of fuel assemblies.

[0018] This invention applies disturbances independently to each fuel rod and divides them into corner rods, side rods, and center rods based on their location. Simultaneously, the coolant channels are divided into corner channels, side channels, and center channels. This allows the corner and side rods to obtain wall projection coordinates by vertical projection onto adjacent walls, while the center channel is formed by the outer contours of three or four center rods, depending on their arrangement. Furthermore, parameters such as flow area, heating share, wetted perimeter, and thermal perimeter are determined using dedicated calculation methods matched to the channel type. This improves the calculation accuracy of key parameters like flow area, wetted perimeter, and thermal perimeter, accurately reflecting actual deviations during manufacturing and installation, and providing reliable geometric input for the thermal-hydraulic uncertainty analysis of fuel assemblies.

[0019] The corner channels of this invention are adjacent to only one fuel rod, the side channels are adjacent to two fuel rods, the central channel of the hexagonal arrangement assembly is adjacent to three fuel rods, and the central channel of the square arrangement assembly is adjacent to four fuel rods, ensuring that the wetted perimeter and thermal perimeter of the channels are naturally consistent in the calculation. At the same time, the heating share of the fuel rods to each channel strictly follows the angular proportion principle, that is, it is determined by the circumferential contact angle of the fuel rod corresponding to that channel. Since the diameter deviation, offset distance, and offset angle of each fuel rod are independently modeled and processed through position-aware vertical projection and adaptive channel enclosure, the final parameters such as flow area, wetted perimeter, thermal perimeter, and heating share inherently satisfy the physical constraints of the fuel assembly geometry, requiring no subsequent correction or empirical adjustment.

[0020] This invention belongs to the field of thermal-hydraulic analysis technology of reactor fuel assemblies, and is specifically applied to the high-precision conversion calculation of geometric parameter deviations in sub-channel programs during the manufacturing and installation of fuel assemblies. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 This is a flowchart of a fuel assembly geometric uncertainty handling method based on a sub-channel program, as described in this invention.

[0023] Figure 2 A schematic diagram showing the offset installation of fuel rods.

[0024] Figure 3 This is a schematic diagram of a hexagonal arrangement component.

[0025] Figure 4 This is a schematic diagram of a square-arranged component.

[0026] Figure 5 This is a mapping diagram of hexagonal arrangement components.

[0027] Figure 6 This is a mapping diagram of square-arranged components.

[0028] Figure 7 This is a schematic diagram of the corner channel offset of a hexagonal array component.

[0029] Figure 8 This is a schematic diagram showing the offset of the center channel of the hexagonal arrangement component. Detailed Implementation

[0030] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Specific implementation methods are as follows Figure 1 As shown in this embodiment, a method for handling geometric uncertainties of fuel assemblies based on subchannel procedures is described. The method includes: In this embodiment, the method begins with step one, in which the geometric uncertainty parameters of the fuel assembly are classified and the center coordinates of the fuel rod are corrected; the geometric uncertainty parameters include fuel rod diameter deviation and installation position deviation; the installation position deviation includes offset distance and offset angle; the offset distance and offset angle are decomposed into offset components in the x and y directions, and the offset components are superimposed on the nominal center coordinates of the fuel rod to obtain the actual center coordinates of the disturbed fuel rod; Specifically, the classification of geometric uncertainty parameters and the correction of fuel rod center coordinates; The geometric uncertainty of fuel assemblies mainly comes from manufacturing tolerances and installation errors. The sampling algorithm generates a sample set covering various deviations by statistically simulating the uncertainty factors in the manufacturing and installation process.

[0032] First, the sample set is classified to identify two main categories of geometric uncertainty parameters for fuel assemblies: First, there is the dimensional deviation of the fuel rod itself, namely the diameter deviation parameter δD, which is determined by the sample obtained by the sampling algorithm and can be positive or negative. Second is the fuel rod installation position deviation, i.e., the installation deviation parameter. This parameter further includes two key dimensions: the offset distance d, which represents the straight-line distance between the actual and nominal positions of the fuel rod, and the offset angle θ, which represents the angle between the offset direction and the positive x-axis of the reference coordinate system. The geometric relationship of the fuel rod installation deviation is as follows: Figure 2 As shown.

[0033] To achieve a quantitative representation of installation deviation, the offset distance d and offset angle θ in the two-dimensional plane need to be decomposed into independent offset components in the x and y directions according to equation (1): (1) In equation (1), Δx is the offset component in the x-direction and Δy is the offset component in the y-direction.

[0034] During the decomposition process, the design reference coordinate system of the fuel assembly is used as a reference, and the offset angle θ is measured counterclockwise to ensure that the decomposed components accurately reflect the impact of the installation deviation on the two coordinate axes. After obtaining the offset components in the x and y directions, they are superimposed on the nominal center coordinates (x, y) of the fuel rod, and the actual center coordinates (x, y) of the disturbed fuel rod are obtained through coordinate correction. n y n The specific calculation formula is shown in equation (2): (2) In equation (2), x and y are the nominal coordinates of the fuel rod center before the disturbance, which are clearly marked in the fuel assembly design drawings and serve as the theoretical reference for assembly; x n and yn The coordinates of the fuel rod center after disturbance are a quantitative representation of the actual installation position of the fuel rod, providing a precise location reference for subsequent projection calculations and channel parameter analysis.

[0035] The samples obtained by the sampling algorithm are classified into diameter deviations and installation deviations, thus clarifying that the geometric uncertainty parameters of the fuel assembly include diameter deviation parameters. By clearly defining the two core sources of geometric uncertainty—the installation deviation parameters, offset distance d, and offset angle θ—the deviation parameters are systematically classified, providing a logical foundation for subsequent precise calculations across different dimensions. Based on the offset distance d and offset angle θ, the installation deviation is decomposed in the x and y directions, transforming the composite installation deviation in the two-dimensional plane into independent deviations in the two coordinate axes, reducing the complexity of deviation quantification calculation and achieving an intuitive representation of the deviation. The decomposition results of the installation deviations in the x and y directions are superimposed onto the nominal coordinates (x, y) of the fuel rod center to obtain the disturbed coordinates (x, y) of the fuel rod center. n y n It can accurately quantify the difference between the actual installation position and the nominal position of the fuel rod, and output the center coordinates that reflect the true installation state, providing an accurate position reference for subsequent fuel rod projection calculation and channel boundary division. The output of this step is the center coordinates (x) of the fuel rod after disturbance. n y n As the core input data for fuel rod classification and wall projection point coordinate calculation in step 2, the precise coordinates accurately define the fuel rod position type and its relative relationship with the wall in order to calculate the projection.

[0036] Then, proceed to step two. In step two, based on the position of the fuel rods in the fuel assembly, the fuel rods are divided into corner rods, side rods, and center rods. For the corner rods and side rods, the actual center coordinates of the disturbed fuel rods are vertically projected onto the adjacent wall surface, and the coordinates of the projection points on the wall surface are calculated. The center rod is not subject to projection. Specifically, the fuel rod classification and the coordinates of the wall projection points are accurately calculated; The fuel rods in fuel assemblies are mainly arranged in two typical structures: hexagonal and square. Their overall layout diagrams are shown below. Figure 3 and Figure 4 As shown. Based on their location within the assembly, all fuel rods can be divided into three main categories: 1) An angle bar located at the corner of the component, which is adjacent to two adjacent walls at the same time; 2) The side bar located on the side edge of the component is adjacent to only one wall surface, and the other side is connected to multiple channels; 3) The central rod is located in the internal area of ​​the component and is not directly constrained by any wall, but is surrounded only by various channels.

[0037] Since the side bars and corner bars are adjacent to the walls, their center coordinates need to be projected onto the adjacent walls to confirm the channel boundary. The center bar, however, does not contact the walls and therefore does not require projection. For the side bars, which are only adjacent to one side wall of the component, a vertical projection onto that single wall is sufficient to obtain a unique wall projection point coordinate. For the corner bars, which are simultaneously in contact with two orthogonal or oblique walls of the component, vertical projections onto these two adjacent walls are required to obtain two independent wall projection point coordinates.

[0038] In this embodiment, the origin of the coordinate system is set at the center of the component. Taking the corner bar in the upper right corner as an example, the calculation method of the projection point coordinates is explained. For corner bars in other positions and side bars on different sides, the equivalent calculation can be performed by referring to this method based on the direction of their corresponding adjacent wall surfaces and the geometric features of the wall surfaces.

[0039] For a hexagonal arrangement component, whose walls are inclined plane structures, the projection mapping relationship is as follows: Figure 5 As shown, the coordinate values ​​at the sharp corners of the wall need to be derived geometrically by combining design parameters such as the circumscribed circle diameter of the component and the wall inclination angle. The specific calculation formula is shown in equation (3): (3) In equation (3), x c and y c Here are the coordinates of the sharp corner of the wall, and L is the radius of the circumcircle of the hexagonal component. For square-arranged components, whose walls are vertical or horizontal planar structures, the projection mapping relationship is as follows: Figure 6 As shown, the coordinate values ​​at the sharp corners of the wall can be directly calculated based on the side length of the component and the wall position parameters, as shown in equation (4): (4) In equation (4), x c and y c Let S be the coordinate value at the sharp corner of the wall, and S be the side length of the square component. The calculation of the projected coordinate values ​​of the fuel rod on the adjacent wall needs to be discussed separately depending on whether the wall slope exists. The specific calculation formula is shown in equation (5): (5) In equation (5), xw and yw are the coordinate values ​​of the wall projection; A, B, C, and D are coefficients. The formula for calculating D is shown in equation (6): (6) For the case where the wall slope k exists, A, B, and C are: (7) For the case where the wall slope k does not exist, A, B, and C are: (8) In this embodiment, fuel rods are classified into corner rods, side rods, and center rods according to their position in the assembly. This can distinguish the boundary constraint differences of fuel rods in different spatial positions. Corner rods are adjacent to two walls, side rods are adjacent to one wall, and center rods are not adjacent to any wall. This provides a classification basis for performing projection calculations and avoids boundary determination errors caused by uniform calculations. By projecting the center coordinates of the side rods onto the adjacent walls, and the center coordinates of the corner rods onto two adjacent walls, the spatial relative positional relationship between the fuel rods and the walls can be accurately obtained, the wall boundary range of the channel can be clearly defined, and a key reference can be provided for the subsequent boundary division of the channel flow area.

[0040] For hexagonal and square arrangement components, the coordinates (x, y) of the sharp corners of the wall are derived respectively. c y c ) and projection point coordinates (x w y w The calculation method can combine the structural characteristics of different component arrangements to achieve accurate solution of projection point coordinates, ensuring the adaptability and accuracy of projection calculation for components with different arrangement types.

[0041] Based on the center coordinates (x) of the fuel rod after disturbance n y n In projection calculations, the accuracy of the coordinates directly determines the coordinates (x, y) of the projected points on the wall. w y w The accuracy of calculation is a prerequisite for projection calculation.

[0042] The fuel rod classification results in this step—corner rods, side rods, and center rods—directly correspond to the channel classification logic, namely corner channels, side channels, and center channels, providing a direct basis for channel type division and exclusive calculation method matching in step 3.

[0043] Then, step three is performed, in which the coolant channels in the fuel assembly are divided into channel types including corner channels, side channels and center channels, and a matching calculation method is performed according to the channel types. Specifically, the channel classification is matched with a dedicated calculation method; based on the fuel rod classification results and wall projection boundary data, the channel type is accurately divided, and a one-to-one correspondence is formed between the channel type and the fuel rod type to ensure the consistency of the classification logic.

[0044] The coolant channels within the fuel assembly are the core area for coolant flow and heat exchange; changes in their geometry directly affect the coolant's flow and heat transfer characteristics.

[0045] Based on the location of the channels and the distribution characteristics of the surrounding fuel rods and walls, all channels can be divided into three categories: corner channels, edge channels, and center channels. Since the geometric boundaries, constraints, and interactions with the fuel rods of these three types of channels are fundamentally different, a unified calculation method would fail to accurately represent the unique characteristics of each type, leading to significant parameter calculation errors. Therefore, a calculation method must be matched to the channel type: for corner channels, a local geometric modeling method based on the wall projection boundary and the outer contour of the fuel rods is used; for edge channels, considering the coupling effect of wall constraints and adjacent channels, a geometric calculation model using half-wall constraints and multiple fuel rods is employed; for center channels, focusing on the spatial distribution characteristics between the central rods, a free-space calculation model without wall constraints and surrounded by multiple fuel rods is used.

[0046] The channels within the fuel assembly are categorized into corner channels, side channels, and center channels. This classification corresponds to the location type of the fuel rods and the spatial structural characteristics of the channels, clarifies the boundary constraints and spatial morphological differences of different channels, and provides a classification basis for subsequent differentiated calculations. Based on the differences in the types of corner channels, side channels, and center channels, different calculation methods are matched. This allows for the selection of appropriate calculation logic for the structural characteristics of different channels, avoiding parameter calculation deviations caused by uniform calculation methods and ensuring the accuracy and rationality of the calculation of key channel parameters.

[0047] The channel classification results and matching calculation methods determined in this step are the core basis for the differentiated calculation of the circulation area of ​​different types of channels in step 5, and directly determine the selection of the calculation model for the circulation area.

[0048] Then proceed to step four, in which the actual diameter of the fuel rod is determined based on the fuel rod diameter deviation; Specifically, the quantification of fuel rod diameter deviation and the determination of actual diameter; the matching results of channel classification and calculation method in step 3 do not affect the diameter deviation extraction and actual diameter calculation in this step. The two are parallel parameter preparation steps, which together provide support for the subsequent calculation of core parameters.

[0049] The diameter deviation of the fuel rod is a core component of geometric uncertainty, directly affecting the flow space of the channel and the heat exchange area of ​​the fuel rod. Based on a clearly defined diameter deviation parameter δD, and combined with a sample space generated by a sampling algorithm, the specific diameter deviation is further obtained. The sample space, through statistical analysis of factors such as dimensional fluctuations and material shrinkage during the manufacturing process, covers various extreme cases from minimum to maximum deviation, ensuring that the deviation value comprehensively reflects the diameter fluctuation range in actual engineering. The actual diameter of the fuel rod is the new fuel rod diameter D. n It is determined by both the nominal diameter D and the diameter deviation δD, and the specific calculation formula is shown in equation (9): (9) In equation (9), D n Here, δD represents the new fuel rod diameter, i.e., the actual working diameter of the fuel rod; D is the nominal diameter of the fuel rod, explicitly specified by the fuel assembly design specifications; δD is the diameter deviation, determined by a sample obtained through a sampling algorithm, reflecting dimensional deviations during manufacturing, and its value can be positive or negative. During the calculation, the deviation sample values ​​obtained from the sampling must be strictly substituted into the calculation to ensure the accuracy of the actual diameter calculation.

[0050] Based on the sample space obtained by the post-classification sampling algorithm, the diameter deviation δD of the fuel rod is extracted to quantify the dimensional fluctuations during the fuel rod manufacturing process, accurately reflect the geometric uncertainty in the diameter direction, and provide key deviation parameters for actual diameter calculation. Through formula D n =D+δD Calculate the new fuel rod diameter D n This is to obtain the actual working dimensions of the fuel rods, providing core geometric parameters for solving the fuel rod shielding area or shielding length in subsequent channel flow area, wet perimeter, and thermal perimeter calculations. Then proceed to step five, in which the flow area of ​​the corner channel, side channel and center channel is calculated based on the coordinates of the wall projection point, the channel type and the actual diameter of the fuel rod; Specifically, the channel flow area is accurately calculated; the actual fuel rod diameter D n As a key input parameter for calculating the fuel rod obstruction area, including both sector and circular areas, it directly affects the accuracy of the channel flow area calculation. The baseline geometry type is selected based on the channel classification results, and the actual fuel rod diameter D is used as the basis for the calculation. n The calculation of the obstruction area and the calculation of the passage flow area together determine the calculation logic and accuracy.

[0051] The channel flow area is a key parameter in the coolant flow distribution calculation in the sub-channel program. Its size depends on the geometric boundaries of the channel, the actual diameter of the fuel rods, and the arrangement of the fuel assemblies. Based on the wall projection point coordinates obtained in step 2, the channel classification results determined in step 3, and the actual diameter of the fuel rods corrected in step 4, and combined with the structural characteristics of different channel types and fuel arrangement methods, the flow area of ​​each type of channel is calculated using the calculation approach of "baseline geometric area minus fuel rod obstruction area".

[0052] (a) Calculation of the flow area of ​​the hexagonal arrangement components; Corner passage: Its geometric boundary is formed by the projected boundaries of two adjacent walls and the outer contour of the corner bar. The flow space can be simplified into an irregular quadrilateral. Figure 7As shown, the area enclosed by the wall projection points and the feature points of the channel boundary, minus a sector, is the area obstructed by the corner bar within the corner channel. The formula for calculating the area of ​​the irregular quadrilateral is shown in equation (10): (10) In equation (10), S q Let x1 be the area of ​​the quadrilateral; x1, x2, x3, and x4 are the x-coordinates of the four angles of the irregular quadrilateral; y1, y2, y3, and y4 are the y-coordinates of the four angles of the irregular quadrilateral. The lengths of the four sides and the middle diagonal of the irregular quadrilateral need to be calculated using the distance formula, as shown in equation (11): (11) In equation (11), l1 and l4 are the lengths of the two sides adjacent to the fuel rod; 24 Let be the length of the opposite diagonal side of the fuel rod. The shielding area of ​​the fuel rod within the corner channel is fan-shaped, and its angle α1 is calculated by equation (12): (12) In equation (12), α1 is the angle of the fuel rod (central angle of the sector). The final corner channel's flow area Schannel is an irregular quadrilateral with an area S q Subtract the area of ​​the sector, as shown in equation (13): (13) In equation (13), S channel D represents the circulation area. n This is the actual diameter of the fuel rod. Side passage: Its geometric boundary is formed by the projected boundary of a wall, the outer contour of the side bar, and the boundary of adjacent passages. The flow space can be simplified to an irregular quadrilateral minus two sectors, with the side bar occupying two occluded areas within the side passage. The area of ​​the quadrilateral is calculated in the same way as the corner passage, according to Equation 10. The central angles of the two sectors need to be determined based on the relative positions of the side bar and the side passage. The final flow area is the area of ​​the quadrilateral minus the sum of the areas of the two sectors. (14) In the formula, α i Let D be the central angle of the i-th rod. ni Let be the diameter of the i-th rod. Central passage: Its geometric boundary is formed by the outer contours of the three central rods. The flow space can be simplified to a triangle (enclosed by the actual center coordinates of the three central rods) minus three sectors (the areas obstructed by each central rod within the central passage), such as... Figure 8 As shown. The formula for calculating the area of ​​a triangle is shown in equation (15): (15) In equation (14), S t Let be the area of ​​the triangle. The calculation method for each angle of the triangle is shown in equation (12). The final flow area of ​​the central passage is the area of ​​the triangle minus the sum of the areas of the three sectors, as shown in equation (16). (16) (ii) Calculation of the flow area of ​​the square-arranged components; Corner channel: Its geometric boundary is formed by two vertical walls and the outer contour of the corner bar. The flow space can be simplified to a quadrilateral minus a sector. The formula for calculating the area of ​​the quadrilateral is shown in formula (10), and the flow area of ​​the corner channel is shown in formula (13).

[0053] Side passage: Its geometric boundary consists of a wall, the outer contour of the side bar, and the boundary of the adjacent passage. The flow space can be simplified to a quadrilateral minus two sectors (the area blocked by the side bar in the side passage). The formula for calculating the area of ​​the quadrilateral is shown in formula (10), and the flow area of ​​the corner passage is shown in formula (14).

[0054] Central passage: Its geometric boundary is formed by the outer contours of the four central rods. The flow space can be simplified to an irregular quadrilateral minus four sectors (the area blocked by each central rod in the central passage). The area of ​​the irregular quadrilateral is calculated according to formula (10), and the formula for calculating the flow area is referenced to formula (17).

[0055] (17) In the formula, α1~α4 are the central angles of the four sectors.

[0056] By combining the projection point coordinate data from step 2 and the channel classification results from step 3, corresponding benchmark geometric figures are determined for different fuel arrangement methods (hexagonal and square) and different channel types (corner channels, side channels, and center channels). This achieves accurate matching of the spatial structure of different channels, provides a practical benchmark template for calculating the flow area, and ensures the accuracy of the benchmark area calculation. The flow area of ​​the channel is calculated by subtracting the area obstructed by the fuel rods from the area of ​​the baseline geometry. This effectively deducts the impact of the fuel rods on the channel space and accurately obtains the actual space available for coolant flow, providing key parameters for flow distribution calculation in the sub-channel program. Output channel flow area S channel The angle α1 of the fuel rod serves as the core basis for calculating the heating share in step 6 and the wet and hot perimeters in step 7. The angle parameter is directly related to the calculation of the heat distribution ratio and the contact length.

[0057] Then proceed to step six, in which the heating share of the fuel rod to each channel is calculated based on the relative angle between the fuel rod and each adjacent channel. Specifically, the calculation of the heating share allocation of the fuel rods to the channel; Heating share is a key parameter characterizing the proportion of heat transferred from the fuel rod to adjacent channels, directly affecting the accuracy of heat transfer calculations in the sub-channel program. Based on the channel flow area determined in step 5, and considering the relative angle between the fuel rod and each channel, the heating share q of the fuel rod to different channels can be calculated. i The specific calculation formula is shown in equation (18): (18) In equation (18), q i The heating share of the channel by the fuel rod; α i This refers to the circumferential contact angle of the fuel rod corresponding to that channel. The allocation of heating share follows the principle of angle proportion, that is, the heating share of the fuel rod to a certain channel is consistent with the proportion of the central angle corresponding to that channel to the total circumferential angle of the fuel rod.

[0058] Based on the channel-related angle parameters obtained in step 5, the heating share q of the fuel rod to different channels is calculated by the proportion of the heating angle. i The core technological effect is to quantify the proportion of heat transferred from the fuel rod to each adjacent channel, providing key thermal parameters for heat exchange calculations in the sub-channel program.

[0059] The heating share is calculated based on the angle α1 of the fuel rod obtained in step 5. The accuracy of the angle parameter directly determines the rationality of the heat distribution ratio and is the core premise for the heating share calculation.

[0060] The angle α1 of the fuel rod used in this step shares the same key angle parameter as the wet and hot period calculations in step 7, providing data support for solving the contact arc length in the hot period calculation.

[0061] Finally, step seven is executed, in which the wet and hot perimeters of the channel are calculated based on the channel type, the actual diameter of the fuel rod, and the circumferential angle.

[0062] Specifically, the wetted and hot perimeters of the channel are calculated; based on the actual fuel rod diameter D from step 4. nThe calculations for the channel type in step 5, the sector angle in step 6, and the three factors together determine the accuracy of the wetted perimeter and thermal perimeter calculations. The wetted perimeter and thermal perimeter are core parameters in the sub-channel program for calculating coolant flow resistance and heat transfer coefficient. The wetted perimeter represents the circumference of the channel inner wall in contact with the coolant, while the thermal perimeter represents the heat transfer circumference of the fuel rod in contact with the coolant. Based on determining the channel type and flow area in step 5 and clarifying the circumferential angle corresponding to the heating share in step 6, combined with the actual diameter of the fuel rod corrected in step 4, the calculations for the wetted perimeter and thermal perimeter can be completed. In this specific embodiment, for open channels, the wetted perimeter and thermal perimeter are consistent, and the formula used is: (19) In equation (19), Pw represents the wetted perimeter; Ph represents the thermal perimeter. The key difference lies in the number of fuel rods N involved in the calculation and the value of the angle parameter. The number of fuel rods N is determined according to the channel type and arrangement: Corner channel: Regardless of the arrangement, it is only adjacent to one fuel rod (corner rod), so N=1; Side passages: Each is adjacent to two fuel rods (side rods), therefore N=2, corresponding to α i It is the sum of the contact angles between the two fuel rods and the side channel; like Figure 8 The diagram shows the offset of the center channel of the hexagonal arrangement component. The central channel of the hexagonal arrangement assembly is adjacent to 3 fuel rods (center rods), therefore N=3, corresponding to α. i The contact angle between the three fuel rods and the central channel; The central channel of the square-arranged assembly is adjacent to the four fuel rods (center rods), therefore N=4, corresponding to α. i The contact angle between the four fuel rods and the central channel.

[0063] The number of fuel rods N involved in the calculation is determined based on the channel type (N=1 for corner channels, N=2 for side channels, N=3 for hexagonal center channels, and N=4 for square center channels). This affects the number of fuel rods in the wet and hot perimeters of the channel, providing a basis for quantifying the coolant contact length. The wetted perimeter and thermal perimeter output in this step, together with the channel flow area and heating fraction parameters mentioned earlier, constitute the core input data that the sub-channel program can directly read. This completes the transformation of the original geometric uncertainty parameters into engineering application parameters, laying a solid foundation for subsequent geometric uncertainty analysis of fuel assemblies and simulation of coolant flow and heat transfer characteristics.

[0064] Based on the systematic calculations of the above seven steps, the original geometric uncertainty parameters of the fuel assembly, namely, diameter deviation δD, offset distance d, and offset angle θ, can be transformed into input parameters that the subchannel program can directly read, including the actual center coordinates of the fuel rod, channel flow area, heating fraction, wet perimeter, and thermal perimeter. This solves the technical problem that geometric uncertainty parameters are difficult to use directly in subchannel simulation, and lays a solid foundation for subsequent geometric uncertainty analysis of fuel assemblies and accurate simulation of coolant flow and heat transfer characteristics.

Claims

1. A method for handling geometric uncertainties in fuel assemblies based on subchannel procedures, characterized in that, The method includes: S1. Classify the geometric uncertainty parameters of the fuel assembly and correct the center coordinates of the fuel rod; the geometric uncertainty parameters include fuel rod diameter deviation and installation position deviation; the installation position deviation includes offset distance and offset angle; decompose the offset distance and offset angle into offset components in the x and y directions, and superimpose the offset components onto the nominal center coordinates of the fuel rod to obtain the actual center coordinates of the disturbed fuel rod; S2. Based on the position of the fuel rods in the fuel assembly, the fuel rods are divided into corner rods, side rods, and center rods; for the corner rods and side rods, the actual center coordinates of the disturbed fuel rods are vertically projected onto the adjacent wall surface, and the coordinates of the projection points on the wall surface are calculated; the center rod is not subject to projection. S3. Divide the coolant channels within the fuel assembly into channel types, including corner channels, side channels, and center channels, and match the calculation method according to the channel types; S4. Determine the actual diameter of the fuel rod based on the fuel rod diameter deviation; S5. Based on the coordinates of the wall projection points, the channel type, and the actual diameter of the fuel rods, calculate the flow area of ​​the corner channels, side channels, and center channels; S6. Based on the relative angle between the fuel rod and each adjacent channel, calculate the heating share of the fuel rod to each channel; S7. Calculate the wet and hot perimeters of the channel based on the channel type, the actual diameter of the fuel rod, and the circumferential angle.

2. The fuel assembly geometric uncertainty handling method based on sub-channel program according to claim 1, characterized in that, In S1, the x-direction offset component Δx and the y-direction offset component Δy satisfy the following: , where d is the offset distance and θ is the offset angle.

3. The method for handling geometric uncertainties of fuel assemblies based on subchannel procedures according to claim 1, characterized in that, In S1, the actual center coordinates (x) of the disturbed fuel rod n , y n )satisfy: , where x and y are the nominal coordinates of the fuel rod center before the disturbance.

4. The method for handling geometric uncertainties of fuel assemblies based on sub-channel procedures according to claim 1, characterized in that, In S2, the angle bar is adjacent to two adjacent walls at the same time, and needs to be vertically projected onto the two adjacent walls respectively to obtain two independent wall projection point coordinates; the side bar is only adjacent to one wall, and only vertically projected onto that single wall to obtain a unique wall projection point coordinate.

5. The method for handling geometric uncertainties of fuel assemblies based on sub-channel procedures according to claim 1, characterized in that, In S2, the fuel assembly can be arranged in a hexagonal or square pattern; the wall of the hexagonal assembly is an inclined plane structure; the wall of the square assembly includes a vertical structure and a horizontal plane structure.

6. The method for handling geometric uncertainties of fuel assemblies based on subchannel procedures according to claim 1, characterized in that, In S4, the actual diameter D of the fuel rod n Satisfy: D n = D + δD, where D is the nominal diameter of the fuel rod and δD is the diameter deviation.

7. The method for handling geometric uncertainties of fuel assemblies based on subchannel procedures according to claim 1, characterized in that, In S5, the flow area is obtained by subtracting the fuel rod obstruction area from the reference geometric area; wherein the fuel rod obstruction area is fan-shaped.

8. The method for handling geometric uncertainties of fuel assemblies based on subchannel procedures according to claim 1, characterized in that, In S5, the central channel of the hexagonal arrangement component is formed by the outer contours of three central rods, and the central channel of the square arrangement component is formed by the outer contours of four central rods.

9. The method for handling geometric uncertainties of fuel assemblies based on sub-channel procedures according to claim 1, characterized in that, In S7, the wetted perimeter and the hot perimeter of the channel are equal; wherein, the corner channel is adjacent to one fuel rod, and the side channel is adjacent to two fuel rods.

10. The method for handling geometric uncertainties of fuel assemblies based on sub-channel procedures according to claim 9, characterized in that, The fuel assembly is arranged in a hexagonal or square pattern. When it is arranged in a hexagonal pattern, the central channel is adjacent to 3 fuel rods. When it is arranged in a square pattern, the central channel is adjacent to 4 fuel rods.

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