Nuclear fuel element and nuclear fuel rod

Abstract

The application provides a nuclear fuel element and a nuclear fuel rod, and relates to the technical field of nuclear fuel. The nuclear fuel element comprises a peripheral wall and two end faces. Each end face comprises a concave structure, a shoulder structure, a first chamfer and a second chamfer. The concave structure is concave in the axial direction along a central axis. The shoulder structure extends horizontally from the periphery of the concave structure to one side of the peripheral wall. The first chamfer extends obliquely from the periphery of the shoulder structure to one side of the peripheral wall and forms a first included angle with a horizontal plane. The second chamfer extends obliquely from the periphery of the first chamfer to the periphery of the peripheral wall and forms a second included angle with the horizontal plane. The sum of the first included angle and the second included angle is 90°. The nuclear fuel rod comprises a cladding and a plurality of nuclear fuel elements. The plurality of nuclear fuel elements are accommodated in the containing cavity and are stacked in the axial direction with the adjacent shoulder structures as the contact surfaces. The application reduces the contact stress between the adjacent nuclear fuel elements and between the nuclear fuel element and the cladding, and significantly reduces the risk of PCI failure.

Description

Technical Field

[0001] This application relates to the field of nuclear fuel technology, specifically to a nuclear fuel element and a nuclear fuel rod. Background Technology

[0002] For water-cooled reactors (including pressurized water reactors (PWRs), boiling water reactors (BWRs), or pressurized heavy water reactors (PHWRs)) using zirconium alloy cladding, pellet-cladding interaction (PCI) affects the performance of nuclear fuel elements, and in severe cases, can lead to fuel element failure. During reactor operation, the pellets, i.e., nuclear fuel elements, experience localized stress on the cladding due to thermal expansion and radiation swelling. This localized stress, combined with the nuclear fission products such as iodine and cesium, causes stress corrosion cracking, leading to cladding failure, especially in cases of missing pellet surfaces (MPS). Conventional nuclear fuel elements are designed as cylindrical structures, including an outer wall and two end faces. Each end face includes a spherical / disc-shaped concave structure formed along the central axis and a chamfered structure formed between the concave structure and the outer wall.

[0003] In existing technologies, nuclear fuel elements generally adopt a single-bevel structure design. When the upper and lower core blocks in a nuclear fuel rod are stacked, the contact stress between the core blocks and between the core blocks and the cladding is relatively large at the bevel. This can easily lead to problems such as core block breakage and chipping due to excessive stress concentration at the contact surface ends of adjacent core blocks or between the core blocks and the cladding. This increases the risk of PCI failure of nuclear fuel elements and reduces the mechanical properties of nuclear fuel elements and nuclear fuel rods. Summary of the Invention

[0004] This application provides a nuclear fuel element and a nuclear fuel rod to address the technical problem that the existing single-chamfer structure design of nuclear fuel elements is prone to breakage and debris shedding due to excessive stress concentration, thus increasing the risk of PCI failure. The nuclear fuel element and nuclear fuel rod provided in this application, through an improved double-chamfer structure design combined with optimized shoulder structure on the end face, reduces the contact stress between adjacent nuclear fuel elements and between the nuclear fuel element and the cladding during reactor operation, significantly reducing the risk of PCI failure.

[0005] In some embodiments of this application, a nuclear fuel element is provided, the nuclear fuel element including an outer wall extending along a central axis to form a cylindrical structure, and two end faces respectively disposed at both ends axially on the outer wall. Each end face includes a concave structure, a shoulder structure, a first chamfer, and a second chamfer. The concave structure is formed concavely along the central axis. The shoulder structure extends horizontally from the periphery of the concave structure away from the central axis toward the outer wall. The first chamfer extends obliquely from the periphery of the shoulder structure away from the concave structure toward the outer wall and forms a first angle with a horizontal plane perpendicular to the central axis. The second chamfer extends obliquely from the periphery of the first chamfer away from the shoulder structure to the periphery connecting the outer wall and forms a second angle with a horizontal plane perpendicular to the central axis. Both the first angle and the second angle are acute angles, and the sum of the angles of the first angle and the second angle is 90°.

[0006] In some embodiments, the length of the slope formed by the first chamfer extending obliquely toward one side of the outer wall is equal to the length of the slope formed by the second chamfer extending obliquely toward the periphery of the outer wall, so that the first chamfer and the second chamfer are arranged symmetrically.

[0007] In some embodiments, the first included angle is between 13.4° and 40°, and the second included angle is between 50° and 76.6°.

[0008] In some embodiments, the projected width of the first chamfer on a horizontal plane perpendicular to the central axis is between 0.1 mm and 0.5 mm, and the projected width of the second chamfer on a horizontal plane perpendicular to the central axis is between 0.02 mm and 0.41 mm.

[0009] In some embodiments, the projection height of the first chamfer on the central axis is between 0.02 mm and 0.41 mm, and the projection height of the second chamfer on the central axis is between 0.1 mm and 0.5 mm.

[0010] In some embodiments, the ratio of the projected width of the first chamfer on a horizontal plane perpendicular to the central axis to the diameter of the outer wall is 0.011 to 0.067; the ratio of the projected width of the second chamfer on a horizontal plane perpendicular to the central axis to the diameter of the outer wall is 0.002 to 0.055.

[0011] In some embodiments, the ratio of the projected height of the first chamfer on the central axis to the distance between the shoulder structures of the two end faces on the central axis is 0.001 to 0.068; the ratio of the projected height of the second chamfer on the central axis to the distance between the shoulder structures of the two end faces on the central axis is 0.007 to 0.083.

[0012] In some embodiments, the projected width of the shoulder structure on a horizontal plane perpendicular to the central axis is between 0.85 mm and 1.28 mm.

[0013] In some embodiments, the ratio of the projected width of the shoulder structure on a horizontal plane perpendicular to the central axis to the diameter of the outer perimeter wall is 0.094 to 0.171.

[0014] In some embodiments, the concave structure is dish-shaped, and the diameter of the periphery of the concave structure away from the central axis is between 4.23 mm and 5.51 mm, and the depth of the concave structure along the central axis is between 0.15 mm and 0.35 mm.

[0015] In some embodiments, the ratio of the projected width of the shoulder structure on a horizontal plane perpendicular to the central axis to the diameter of the periphery of the concave structure away from the central axis is 0.154 to 0.303.

[0016] In some embodiments, the ratio of the distance between the shoulder structures of the two end faces on the central axis to the diameter of the peripheral wall is 0.8 to 1.7.

[0017] In some embodiments, the two end faces have the same structure and are arranged symmetrically at both ends of the outer perimeter wall.

[0018] In some embodiments of this application, a nuclear fuel rod is provided, the nuclear fuel rod including a cladding and a plurality of nuclear fuel elements as described in any one of the above, the cladding extending along the central axis and having an internal receiving cavity, the plurality of nuclear fuel elements being housed in the receiving cavity and stacked sequentially in the axial direction with adjacent shoulder structures as contact surfaces.

[0019] The nuclear fuel element provided in this application features a double-beveled structure at the connection between the outer wall and the end face, including a first bevel and a second bevel. The angle between the first and second bevels and the horizontal plane is optimized and improved, resulting in a smoother connection between the outer wall and the end face of the nuclear fuel element. Furthermore, the connection between the double-beveled structure (including the first and second bevels) and the concave structure is designed as a horizontally extending shoulder structure. This allows adjacent nuclear fuel elements in the fuel rod to be stacked axially with the shoulder structure as the contact surface, increasing the contact area between the nuclear fuel elements, sharing the axial load, and, combined with the angle optimization of the first and second bevels in this application, significantly improving the interaction effects between nuclear fuel elements in the nuclear fuel rod and between the nuclear fuel elements and the cladding during reactor operation. This significantly reduces the generation of contact stress, avoids the stress concentration problem of single-beveled structures, reduces the risk of PCI failure of the nuclear fuel element, and improves the operational safety margin. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0021] Figure 1 This is a schematic cross-sectional view of the overall structure of a specific embodiment of the nuclear fuel element of this application;

[0022] Figure 2 This is a schematic cross-sectional view of the upper structure of a specific embodiment of the nuclear fuel element of this application;

[0023] Figure 3 for Figure 2 Enlarged view of the local structure at point A Figure 1 ;

[0024] Figure 4 for Figure 2 Enlarged view of the local structure at point A Figure 2 ;

[0025] Figure 5 This is a schematic cross-sectional view of the overall structure of a specific embodiment of the nuclear fuel rods of this application;

[0026] Figure 6 The figure shows experimental data used to simulate and calculate the power history of fuel rods. Detailed Implementation

[0027] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various implementations. At the same time, the steps or actions in the method description can also be rearranged or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for clearly describing a particular embodiment and do not imply a necessary order, unless otherwise stated that a certain order must be followed.

[0028] Please see Figures 1 to 2 This application provides a method for filling nuclear fuel rods 100 (such as...) Figure 5 The nuclear fuel element 10 shown in the diagram includes an outer wall 1 extending along a central axis 11 to form a cylindrical structure, and two end faces 2 respectively located at both ends of the outer wall 1 in the axial direction. Each end face 2 includes a concave structure 21, a shoulder structure 22, a first chamfer 23, and a second chamfer 24, wherein:

[0029] The concave structure 21 is formed axially inward along the central axis 11 toward the interior of the nuclear fuel element 10 and has a certain curvature. In some embodiments, the concave structure 21 can be a butterfly-shaped concave structure 21 or a spherical concave structure 21, and this application does not limit it in this way.

[0030] The shoulder structure 22 extends horizontally from the periphery of the concave structure 21 away from the central axis 11 towards the outer periphery wall 1. When the central axis 11 is vertically set and the nuclear fuel element 10 is placed vertically along the central axis, for the corresponding end face 2 at the upper end of the outer periphery wall 1, the height of the shoulder structure 22 on the central axis 11 is greater than the height of the upper end of the outer periphery wall 1, so that the shoulder structure 22 protrudes slightly in the axial direction from the outer periphery wall 1, thereby forming the upper contact surface of the nuclear fuel element 10. Similarly, for the corresponding end face 2 at the lower end of the outer periphery wall 1, the height of the shoulder structure 22 on the central axis 11 is less than the height of the lower end of the outer periphery wall 1, so that the shoulder structure 22 protrudes slightly in the axial direction from the outer periphery wall 1, thereby forming the lower contact surface of the nuclear fuel element 10.

[0031] Please see Figure 3The first chamfer 23 extends obliquely from the periphery of the shoulder structure 22 away from the concave structure 21 toward the outer wall 1, and forms a first included angle α with a horizontal plane perpendicular to the central axis 11. Specifically, the horizontal plane refers to the plane formed by extending horizontally outward from the periphery of the shoulder structure 22 away from the concave structure 21.

[0032] The second chamfer 24 extends obliquely from the periphery of the first chamfer 23 away from the shoulder structure 22 to the periphery connecting the outer wall 1, and forms a second included angle β with a horizontal plane perpendicular to the central axis 11. Specifically, the horizontal plane refers to the plane formed by extending horizontally outward from the periphery of the first chamfer 23 away from the shoulder structure 22.

[0033] Both the first included angle α and the second included angle β are acute angles, and the sum of the first included angle α and the second included angle β is 90°. That is, the first included angle α and the second included angle β are complementary angles. Under this condition, the first chamfer 23 and the second chamfer 24 can be set in three different ways.

[0034] Please see Figure 3 The length of the slope formed by the first chamfer 23 extending obliquely towards one side of the outer wall 1 is denoted as the first slope length L11, and the length of the slope formed by the second chamfer 24 extending obliquely towards the periphery of the outer wall 1 is denoted as the second slope length L21. The three different configurations of the first chamfer 23 and the second chamfer 24 are as follows:

[0035] In the first configuration, the length of the first slope L11 is greater than the length of the second slope L21. In this case, the first chamfer 23 has a greater inclined extension length than the second chamfer 24, and the degree of stress dispersion is more significant compared to the second chamfer 24. Figure 3 As shown, in the second configuration, the length of the first slope L11 is equal to the length of the second slope L21. In this case, the inclined extension lengths of the first chamfer 23 and the second chamfer 24 are the same, and the degree of stress dispersion is more uniform. In the third configuration, the length of the first slope L11 is less than the length of the second slope L21. In this case, the inclined extension length of the second chamfer 24 is greater than that of the first chamfer 23, and the degree of stress dispersion is more significant than that of the first chamfer 23.

[0036] The nuclear fuel element 10 provided in this application has a double chamfer structure at the connection between the outer wall 1 and the end face 2, including a first chamfer 23 and a second chamfer 24. Furthermore, the angle relationship between the first chamfer 23 and the second chamfer 24 and the horizontal plane is optimized and improved, making the connection between the outer wall 1 and the end face 2 of the nuclear fuel element 10 smoother. Meanwhile, the nuclear fuel element 10 provided in this application sets the connection between the double-bevel structure including the first bevel 23 and the second bevel 24 and the concave structure 21 as a horizontally extending shoulder structure 22, so that adjacent nuclear fuel elements 10 in the fuel rod can be stacked axially with the shoulder structure 22 as the contact surface. This increases the contact area between nuclear fuel elements 10, shares the axial load, and, combined with the angle optimization of the first included angle α and the second included angle β in this application, significantly improves the interaction effect between nuclear fuel elements 10 in the nuclear fuel rod 100 and between nuclear fuel elements 10 and cladding during reactor operation. This significantly reduces the generation of contact stress, avoids the stress concentration problem of the single-bevel structure, reduces the PCI failure risk of nuclear fuel element 10, and improves the operational safety margin.

[0037] Please see Figures 3 to 4 In some embodiments, the first chamfer 23 and the second chamfer 24 preferably adopt the second arrangement described above, that is, the length of the slope formed by the first chamfer 23 extending obliquely towards the outer wall 1 is equal to the length of the slope formed by the second chamfer 24 extending obliquely towards the periphery of the outer wall 1, so that the first chamfer 23 and the second chamfer 24 are arranged symmetrically. Thus, the first chamfer 23 and the second chamfer 24 are arranged symmetrically about the perpendicular bisector of the line connecting the periphery of the outer wall 1 and the periphery of the shoulder structure 22.

[0038] The nuclear fuel element 10 provided in this application has a symmetrical arrangement of the first chamfer 23 and the second chamfer 24, which can evenly distribute the contact stress between the nuclear fuel elements 10 and between the nuclear fuel elements 10 and the cladding. This makes the stress at the connection between the outer wall 1 and the end face 2 more uniform. Compared with the structural design where the length of the first slope L11 is greater than or less than the length of the second slope L21, the symmetrical arrangement of the first chamfer 23 and the second chamfer 24 has higher structural stability and strength, further reducing the risk of breakage and chipping of the sintered nuclear fuel element 10 due to uneven stress at the corners and radiation expansion.

[0039] Please see Figures 3 to 4In some embodiments, the angle α of the first included angle is between 13.4° and 40°, and the angle β of the second included angle is between 50° and 76.6°. These angles can be applied to any of the three specific arrangements of the first chamfer 23 and the second chamfer 24 mentioned above. The second arrangement is preferred, where the first chamfer 23 and the second chamfer 24 are arranged symmetrically. The figures illustrate this with the first included angle α at 35° and the second included angle β at 55° as examples.

[0040] The nuclear fuel element 10 provided in this application has a first included angle α formed between a first chamfer 23 and a horizontal plane extending outward from the periphery of the shoulder structure 22 away from the concave structure 21, set between 13.4° and 40°. Simultaneously, a second included angle β formed between a second chamfer 24 and a horizontal plane extending outward from the periphery of the first chamfer 23 away from the shoulder structure 22 is set between 50° and 76.6°, and the sum of the first included angle α and the second included angle β is 90°. This results in a better inclined extension slope of the first chamfer 23 and the second chamfer 24 relative to the central axis 11, making the connection between the outer wall 1 and the end face 2 smoother. Under these conditions, the contact stress between the nuclear fuel elements 10 and the circumferential stress of the nuclear fuel elements 10 on the cladding are lower, resulting in less impact mass loss and significantly reducing the risk of PCI failure of the nuclear fuel rods.

[0041] Furthermore, in some embodiments, the angle range of the first included angle α is preferably between 31° and 40°, and the angle range of the second included angle β is preferably between 50° and 59°.

[0042] The nuclear fuel element 10 provided in this application, when the first chamfer 23 and the second chamfer 24 are symmetrically arranged, and the angle of the first included angle α is set between 31° and 40° and the angle of the second included angle β is set between 50° and 59°, allows the first chamfer 23 and the second chamfer 24 to have an optimal inclined extension slope relative to the central axis 11. Under this condition, the contact stress between the nuclear fuel elements 10 and the circumferential stress of the nuclear fuel elements 10 on the cladding are minimized, and the impact mass loss is minimized, which can further reduce the risk of PCI failure of the nuclear fuel rods.

[0043] Please see Figure 4 The projection width of the first chamfer 23 on the horizontal plane perpendicular to the central axis 11 is denoted as the first chamfer width L12, and the projection height of the first chamfer 23 on the central axis 11 is denoted as the first chamfer height L13; the projection width of the second chamfer 24 on the horizontal plane perpendicular to the central axis 11 is denoted as the second chamfer width L22, and the projection height of the second chamfer 24 on the central axis 11 is denoted as the second chamfer height L23.

[0044] In some embodiments, when the angle range of the first included angle α is set between 13.4° and 40° and the angle range of the second included angle β is set between 50° and 76.6°, the width of the first chamfer L12 (i.e., the projection width of the first chamfer 23 on the horizontal plane perpendicular to the central axis 11, which will not be described in detail below) is between 0.1mm and 0.5mm, and the width of the second chamfer L22 (i.e., the projection width of the second chamfer 24 on the horizontal plane perpendicular to the central axis 11, which will not be described in detail below) is between 0.02mm and 0.41mm, and can be applied to any of the three specific arrangement forms of the first chamfer 23 and the second chamfer 24 mentioned above. The second arrangement form is preferred, that is, the first chamfer 23 and the second chamfer 24 are arranged symmetrically.

[0045] In some embodiments, the first chamfer height L13 (i.e., the projection height of the first chamfer 23 on the central axis 11, which will not be described in detail below) is between 0.02mm and 0.41mm, and the second chamfer height L23 (i.e., the projection height of the second chamfer 24 on the central axis 11, which will not be described in detail below) is between 0.1mm and 0.5mm. It can be applied to any of the three specific arrangement forms of the first chamfer 23 and the second chamfer 24 mentioned above. The second arrangement form is preferred, that is, the first chamfer 23 and the second chamfer 24 are arranged symmetrically.

[0046] The nuclear fuel element 10 provided in this application has a first chamfer width L12 and a second chamfer height L23 both set between 0.1 mm and 0.5 mm, and a first chamfer height L13 and a second chamfer width L22 both set between 0.02 mm and 0.41 mm. Combined with the angular range limitations of the first included angle α and the second included angle β in this application, the structural features such as the width and height of the double chamfer structure between the outer wall 1 and the shoulder structure 22 are optimized and improved. Under these conditions, the contact stress between the nuclear fuel elements 10 and the circumferential stress of the nuclear fuel elements 10 on the cladding are smaller, resulting in less impact mass loss and further reducing the risk of PCI failure of the nuclear fuel rods.

[0047] Furthermore, in some embodiments, when the angle range of the first included angle α is set between 13.4° and 40° and the angle range of the second included angle β is set between 50° and 76.6°, the first chamfer width L12 is equal to the second chamfer height L23, and is preferably set between 0.211mm and 0.25mm; the first chamfer height L13 is equal to the second chamfer width L22, and is preferably set between 0.15mm and 0.177mm.

[0048] The nuclear fuel element 10 provided in this application has its first chamfer width L12 and second chamfer height L23 both set between 0.211 mm and 0.25 mm, and its first chamfer height L13 and second chamfer width L22 both set between 0.15 mm and 0.177 mm. Combined with the angular range limitations of the first included angle α and the second included angle β in this application, the structural features such as the width and height of the double-chamfer structure between the outer wall 1 and the shoulder structure 22 are further optimized. Under these conditions, the contact stress between the nuclear fuel elements 10 and the circumferential stress of the nuclear fuel elements 10 on the cladding are minimized, and the impact mass loss is minimized, further reducing the risk of PCI failure of the nuclear fuel rods.

[0049] Please see Figure 1 The diameter of the nuclear fuel element 10 in this application is denoted as D, and is quantified by the diameter of the outer wall 1; the length of the nuclear fuel element 10 in this application is denoted as H, and is quantified by the distance between the shoulder structures 22 on the two end faces 2 on the central axis 11.

[0050] In some embodiments, the ratio of the first chamfer width L12 to the diameter of the outer perimeter wall 1 is 0.011 to 0.067; the ratio of the second chamfer width L22 to the diameter of the outer perimeter wall 1 is 0.002 to 0.055.

[0051] In some embodiments, the ratio of the first chamfer height L13 to the distance between the shoulder structures 22 of the two end faces 2 on the central axis 11 is 0.001 to 0.068; the ratio of the second chamfer height L23 to the distance between the shoulder structures 22 of the two end faces 2 on the central axis 11 is 0.007 to 0.083.

[0052] The nuclear fuel element 10 provided in this application improves the width ratio of the double-chamfered structure on the end face 2 of the nuclear fuel element 10 by limiting the ratio of the first chamfer width L12 and the second chamfer width L22 to the diameter of the nuclear fuel element 10; and improves the length ratio of the double-chamfered structure on the outer wall 1 of the nuclear fuel element 10 by limiting the ratio of the first chamfer height L13 and the second chamfer height L23 to the length of the nuclear fuel element 10, further optimizing the double-chamfered structure. Under these conditions, the contact stress between the nuclear fuel elements 10 and the circumferential stress of the nuclear fuel elements 10 on the cladding are smaller, and the impact mass loss is smaller, which can further reduce the risk of PCI failure of the nuclear fuel rods. In addition, after adopting the above technical solution, while reducing the contact stress and PCI failure risk, it is also possible to further increase the uranium loading of the nuclear fuel rods 100 and improve the reactor operation economy.

[0053] Please see Figure 2The projected width of the shoulder structure 22 on a horizontal plane perpendicular to the central axis 11 is denoted as the shoulder width W. The diameter of the periphery of the concave structure 21 away from the central axis 11 is denoted as the concave diameter D1. The depth of the concave structure 21 along the central axis 11 is denoted as the concave depth H1.

[0054] In some embodiments, the shoulder width W (i.e., the projected width of the shoulder structure 22 on a horizontal plane perpendicular to the central axis 11, hereinafter referred to as such) is between 0.85 mm and 1.28 mm. The shoulder structure 22 exists as a horizontal ring structure on the end face 2 of the nuclear fuel element 10, and its projected width on the horizontal plane is essentially the width of its ring structure. The shoulder structure 22 has a certain width and serves as a contact surface between the upper and lower stacked nuclear fuel elements 10 in the nuclear fuel rod 100. It can share the axial load of the nuclear fuel element 10, prevent abnormal stacking of elements in the nuclear fuel rod 100, reduce stress concentration between the first chamfer 23 and the recessed structure, and reduce the contact stress between the nuclear fuel elements 10. Under these conditions, the contact stress between the nuclear fuel elements 10 and the circumferential stress of the nuclear fuel elements 10 on the cladding are smaller, the impact mass loss is smaller, and the risk of nuclear fuel rod PCI failure can be further reduced.

[0055] Furthermore, in some embodiments, the shoulder width W is preferably set between 1.15 mm and 1.28 mm. Under this condition, the contact stress between nuclear fuel elements 10 and the circumferential stress included in the nuclear fuel element 10 stack are minimized, the impact mass loss is minimized, and the risk of nuclear fuel rod PCI failure can be further reduced.

[0056] Please see Figure 2 In some embodiments, the concave structure 21 is butterfly-shaped, and the concave diameter D1 of the concave structure 21 away from the central axis 11 is between 4.23 mm and 5.51 mm, and the concave depth H1 of the concave structure 21 along the central axis 11 is between 0.15 mm and 0.35 mm.

[0057] The nuclear fuel element 10 provided in this application, by limiting the concave diameter D1 of the concave structure 21 and combining this application with limiting the shoulder width W of the shoulder structure 22, ensures that the first chamfer 23, the second chamfer 24, the shoulder structure 22 and the concave structure 21 on the end face 2 have the optimal width ratio. This ensures that the double chamfer structure, the shoulder structure 22 and the concave structure 21 each have the optimal width range, while significantly reducing the risk of stress concentration at the connection between the concave structure 21 and the shoulder structure 22 during reactor operation, and avoiding the problem of nuclear fuel element 10 breaking and shedding due to excessive stress concentration.

[0058] In some embodiments, the ratio of the distance between the shoulder structures 22 of the two end faces 2 on the central axis 11 to the diameter of the peripheral wall 1 is 0.8 to 1.7, that is, the length-to-diameter ratio of the nuclear fuel element 10 of this application is set to 0.8 to 1.7.

[0059] Please see Figure 1 and Figure 5 In some embodiments, the two end faces 2 have the same structure and are symmetrically arranged at both ends of the outer perimeter wall 1 in the axial direction. In this way, when the nuclear fuel elements 10 are stacked in the axial direction, the two adjacent end faces 2 can contact each other on the horizontal plane through the shoulder structure 22, so that the nuclear fuel elements 10 are subjected to balanced forces, reducing the risk of nuclear fuel element 10 breakage and debris shedding.

[0060] Please see Figure 5 In some embodiments of this application, a nuclear fuel rod 100 is provided, which includes a cladding 3 and a plurality of nuclear fuel elements 10 as described in any of the above. The cladding 3 extends along the central axis 11 and has an internal receiving cavity (not shown). The plurality of nuclear fuel elements 10 are housed in the receiving cavity and are stacked sequentially in the axial direction with adjacent shoulder structures 22 as contact surfaces.

[0061] Understandably, the cladding 3 of the nuclear fuel rod 100 may contain only one set of nuclear fuel elements 10 stacked sequentially along the central axis 11, meaning the axis of the nuclear fuel rod 100 coincides with the central axis 11 of a single set of nuclear fuel elements 10; alternatively, the cladding 3 of the nuclear fuel rod 100 may contain multiple sets of nuclear fuel elements 10 stacked sequentially along their respective central axes 11, meaning the axis of the nuclear fuel rod 100 is misaligned with the central axis 11 of at least one set of nuclear fuel elements 10. This application does not impose any limitations on this, as long as the cladding 3 contains at least one set of nuclear fuel elements 10 stacked sequentially along the central axis 11.

[0062] The nuclear fuel rod 100 provided in this application adopts a double-beveled structure and a shoulder structure 22 to improve the interaction effect between nuclear fuel elements 10 and between nuclear fuel elements 10 and cladding 3 during reactor operation. This significantly reduces the generation of contact stress, avoids the problem of nuclear fuel elements 10 breaking and shedding due to excessive stress concentration, and reduces the risk of nuclear fuel rod PCI failure caused by the interaction between nuclear fuel elements 10 and cladding 3.

[0063] The technical solution of this application will be further described below through several specific embodiments and comparative examples. The specific implementation methods of the nuclear fuel element 10 in each embodiment and comparative example are shown in Table 1. The manufacturing method, sintering raw materials, overall length, diameter and other characteristics of the nuclear fuel element 10 in each embodiment and comparative example are the same.

[0064]

[0065]

[0066] Table 1: Detailed Implementation of Nuclear Fuel Element 10 in Examples 1-4 and Comparative Examples 1-2

[0067] In the nuclear fuel element 10 samples of Examples 1-4, both the first chamfer 23 and the second chamfer 24 are arranged symmetrically. The length L11 of the first slope formed by the first chamfer 23 extending obliquely towards the outer wall 1 is equal to the length L21 of the second slope formed by the second chamfer 24 extending obliquely towards the periphery of the outer wall 1. The length L11 of the first slope can be defined based on the angle of the first included angle α, the width L12 of the first chamfer, and the height L13 of the first chamfer. The length L21 of the second slope can be defined based on the angle of the second included angle β, the width L22 of the second chamfer, and the height L23 of the second chamfer.

[0068] The nuclear fuel element 10 sample in Comparative Example 1 is a commercially available double-beveled structure nuclear fuel element 10. Its first bevel 23 transitions directly to the concave structure 21, and no shoulder structure 22 is provided between the two. During reactor operation, stress will be concentrated at the bevel initiation position in the concave structure 21, and thermal stress will affect the integrity of the nuclear fuel element 10.

[0069] The nuclear fuel element 10 sample in Comparative Example 2 is a commercially available single-bevel structure nuclear fuel element 10 without a second bevel 24, and transitions to the shoulder structure 22 through its single bevel structure.

[0070] The nuclear fuel element 10 samples of each embodiment and comparative example were sequentially stacked along the central axis 11 into the internal cavity of the cladding 3 with the same structure to form nuclear fuel rods. The following comparative analysis of the implementation effect of this application is based on transient operating conditions, the interaction between nuclear fuel element 10 and cladding 3, simulated calculation of fuel rod power history, and nuclear fuel element 10 drop impact test. The experimental results of the interaction between nuclear fuel element 10 and cladding 3 under transient conditions are shown in Table 2, and the experimental results of simulated calculation of fuel rod power history are shown in Table 2. Figure 6 As shown in the figure, the results of the nuclear fuel element 10 drop impact test are shown in Table 3.

[0071]

[0072] Table 2: Results of maximum circumferential stress and radial displacement of the shell 3 in Examples 1-4 and Comparative Examples 1-2 after the transient period.

[0073] Table 2 shows the maximum circumferential stress and radial displacement of the cladding 3 of the nuclear fuel element 10 on the nuclear fuel rod 100 during the simulation analysis. The results show that the maximum circumferential stress and maximum displacement of the cladding 3 of the nuclear fuel element 10 with the symmetrical double-bevel structure provided in this application are both less than those of Comparative Example 1-2 in the transient state.

[0074] Please see Figure 6 Based on the experimental results of the power history simulation of fuel rods, it is generally observed that after more than 10,000 hours of operation in the reactor, the nuclear fuel rod 100 will come into contact with the cladding 3. In this simulation, the nuclear fuel element samples of Examples 1-4 came into contact with the cladding 3 at 17,000 hours, and then experienced a power surge at 18,000 hours to study the interaction between the nuclear fuel element 10 and the cladding 3 under transient conditions. The maximum circumferential stress of the nuclear fuel element 10 on the cladding 3 and the radial displacement of the cladding 3 were evaluated to assess the PCI risk. The transient power surge rate analyzed in this application adopts the standard Ramp test power surge rate of 10 kW / m / min.

[0075]

[0076] Table 3: Mass loss results of fuel pellets under different impact angles

[0077] Table 3 shows the experimental results of nuclear fuel element 10 in each embodiment and comparative example, which are subjected to impact damage when dropped from different angles (5°, 45°, 85°). The results indicate that the nuclear fuel element 10 samples of Examples 1-4 of this application have the smallest mass loss under the 45° impact angle condition. Among them, the mass loss of Examples 1-4 is slightly less than that of Comparative Example 1 and significantly better than that of Comparative Example 2. The impact test method adopts conventional experimental methods in the art, and the impact energy is 0.13J.

[0078] According to Table 2, Table 3 and Figure 6 The experimental results show that, during reactor power transients, the symmetrical double-beveled nuclear fuel element 10 provided in this application exhibits lower maximum circumferential stress and radial displacement of the cladding 3 on the nuclear fuel rod 100 compared to existing commercial nuclear fuel elements shown in Comparative Examples 1 and 2. Furthermore, it effectively reduces the mass loss of the nuclear fuel element 10 under impact conditions. Therefore, it can be seen that the improved nuclear fuel element 10 and nuclear fuel rod 100 provided in this application can improve the impact on the cladding 3 during reactor transients, reduce the risk of PCI failure, and have significant reference value for improving reactor fuel operation reliability. They are suitable for widespread use in this field.

[0079] The above are merely preferred embodiments of this application and do not limit the scope of this patent application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A nuclear fuel element, comprising an outer wall extending along a central axis to form a cylindrical structure, and two end faces respectively disposed at both ends axially on the outer wall, characterized in that, Each of the aforementioned end faces includes: The concave structure is formed axially inward along the central axis. The shoulder structure extends horizontally from the periphery of the concave structure away from the central axis toward one side of the outer wall; The first chamfer extends obliquely from the periphery of the shoulder structure away from the concave structure toward the outer wall side, and forms a first included angle with the horizontal plane perpendicular to the central axis; The second chamfer extends obliquely from the periphery of the first chamfer away from the shoulder structure to the periphery connecting the outer wall, and forms a second angle with the horizontal plane perpendicular to the central axis; the length of the slope formed by the first chamfer extending obliquely towards the outer wall is equal to the length of the slope formed by the second chamfer extending obliquely towards the periphery of the outer wall, so that the first chamfer and the second chamfer are arranged symmetrically. Both the first included angle and the second included angle are acute angles, and the sum of the angles of the first included angle and the second included angle is 90°; the angle of the first included angle is between 13.4° and 40°, and the angle of the second included angle is between 50° and 76.6°.

2. The nuclear fuel element according to claim 1, characterized in that, The projection width of the first chamfer on a horizontal plane perpendicular to the central axis is between 0.1 mm and 0.5 mm, and the projection width of the second chamfer on a horizontal plane perpendicular to the central axis is between 0.02 mm and 0.41 mm.

3. The nuclear fuel element according to claim 1, characterized in that, The projection height of the first chamfer on the central axis is between 0.02mm and 0.41mm, and the projection height of the second chamfer on the central axis is between 0.1mm and 0.5mm.

4. The nuclear fuel element according to any one of claims 1-3, characterized in that, The projected width of the shoulder structure on a horizontal plane perpendicular to the central axis is between 0.85 mm and 1.28 mm.

5. The nuclear fuel element according to any one of claims 1-3, characterized in that, The concave structure is disc-shaped, and the diameter of the periphery of the concave structure away from the central axis is between 4.23 mm and 5.51 mm, and the depth of the concave structure along the central axis is between 0.15 mm and 0.35 mm.

6. The nuclear fuel element according to any one of claims 1-3, characterized in that, The ratio of the distance between the shoulder structures of the two end faces on the central axis to the diameter of the outer perimeter wall is 0.8 to 1.

7.

7. The nuclear fuel element according to any one of claims 1-3, characterized in that, The two end faces have the same structure and are symmetrically arranged at both ends of the outer perimeter wall.

8. A nuclear fuel rod, characterized in that, It includes a casing and a plurality of nuclear fuel elements as described in any one of claims 1-7, the casing extending along the central axis and having an internal receiving cavity, the plurality of nuclear fuel elements being housed in the receiving cavity and stacked sequentially in the axial direction with adjacent shoulder structures as contact surfaces.

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