Nuclear fuel element and nuclear fuel rod

Abstract

The invention provides a nuclear fuel element and a nuclear fuel rod, and relates to the technical field of nuclear fuels, 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, and the concave structure is axially concave along the central axis; the shoulder structure horizontally extends from the periphery of the concave structure to one side of the peripheral wall; the first chamfer obliquely extends from the periphery of the shoulder structure to one side of the peripheral wall and forms a first included angle with the horizontal plane; the second chamfer obliquely extends from the periphery of the first chamfer to be connected with 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 degrees. The nuclear fuel rod comprises a cladding and a plurality of nuclear fuel elements, and the nuclear fuel elements are contained in the containing cavity and sequentially stacked in the axial direction with the adjacent shoulder structures as the contact surfaces. According to the invention, the contact stress between the adjacent nuclear fuel elements and between the nuclear fuel elements and the cladding is reduced, and the risk of PCI failure is remarkably reduced.

Description

Technical Field

[0001] The present application relates to the field of nuclear fuel technology, and in particular to a nuclear fuel element and a nuclear fuel rod. Background Art

[0002] For nuclear fuel rods of water-cooled reactors (including pressurized water reactors (PWR), boiling water reactors (BWR) or pressurized heavy water reactors (PHWR)) using zirconium alloy cladding, the pellet-cladding interaction (PCI) affects the performance of nuclear fuel elements and may cause failure of nuclear fuel elements in severe cases. During the operation of the reactor, the pellets, i.e., the nuclear fuel elements, will form local stress on the cladding due to factors such as thermal expansion and radiation swelling. The stress corrosion cracking caused by the combined action of such local stress and nuclear reaction fission products such as iodine and cesium will cause the cladding of the nuclear fuel rod to fail, especially in the case of missing pellet surface (MPS). The structure of conventional nuclear fuel elements is designed to be cylindrical, including an outer wall and two end faces, each of which 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] The nuclear fuel elements in the prior art generally adopt a single chamfer structure design. When the upper and lower pellets in the nuclear fuel rod are stacked, the contact stress between the pellets and between the pellets and the cladding at the chamfer is relatively large, which can easily lead to the pellets breaking and chipping due to excessive concentration of stress at the ends of the contact surfaces of adjacent pellets or between the pellets and the cladding, increasing the PCI failure risk of the nuclear fuel elements and reducing the mechanical properties of the nuclear fuel elements and nuclear fuel rods. Summary of the invention

[0004] The present application provides a nuclear fuel element and a nuclear fuel rod, which are used to solve the technical problem that the single chamfer structure design of the existing nuclear fuel element is easy to cause the nuclear fuel element to break and fall off due to excessive stress concentration, and increase the risk of PCI failure. The nuclear fuel element and the nuclear fuel rod provided by the present application, through the improved double chamfer structure design, combined with the optimization of the shoulder structure on the end face, reduce the contact stress between adjacent nuclear fuel elements in the nuclear fuel rod and between the nuclear fuel element and the cladding during the operation of the reactor, and significantly reduce the risk of PCI failure.

[0005] In some embodiments of the present application, a nuclear fuel element is provided, which includes an outer wall extending along a central axis to form a cylindrical structure, and two end faces respectively arranged at both ends of the outer wall in the axial direction, each of the end faces includes a concave structure, a shoulder structure, a first chamfer, and a second chamfer, the concave structure is formed by being concave along the axial direction of the central axis; the shoulder structure extends horizontally from the peripheral edge of the concave structure away from the central axis to one side of the outer wall; the first chamfer extends obliquely from the peripheral edge of the shoulder structure away from the concave structure to one side of the outer wall, and forms a first angle with a horizontal plane perpendicular to the central axis; the second chamfer extends obliquely from the peripheral edge of the first chamfer away from the shoulder structure to the peripheral edge connected to the outer wall, and forms a second angle with a horizontal plane perpendicular to the central axis; the first angle and the second angle are both acute angles, and the sum 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 peripheral wall is equal to the length of the slope formed by the second chamfer extending obliquely toward the periphery of the peripheral wall, so that the first chamfer and the second chamfer are arranged symmetrically.

[0007] In some embodiments, the first angle ranges from 13.4° to 40°, and the second angle ranges from 50° to 76.6°.

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

[0009] In some embodiments, a projection height of the first chamfer on the central axis is between 0.02 mm and 0.41 mm, and a 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 projection width of the first chamfer on the horizontal plane perpendicular to the central axis to the diameter of the outer wall is 0.011 to 0.067; the ratio of the projection width of the second chamfer on the 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 projection height of the first chamfer on the central axis to the spacing between the shoulder structures of the two end faces on the central axis is 0.001 to 0.068; the ratio of the projection height of the second chamfer on the central axis to the spacing between the shoulder structures of the two end faces on the central axis is 0.007 to 0.083.

[0012] In some embodiments, a projection 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, a ratio of a projection width of the shoulder structure on a horizontal plane perpendicular to the central axis to a diameter of the peripheral wall is 0.094 to 0.171.

[0014] In some embodiments, 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.

[0015] In some embodiments, the ratio of the projection 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 0.154-0.303.

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

[0017] In some embodiments, the two end surfaces have the same structure and are symmetrically arranged at both axial ends of the peripheral wall.

[0018] In some embodiments of the present application, a nuclear fuel rod is provided, comprising a cladding and a plurality of nuclear fuel elements as described above, wherein the cladding extends along the central axis and is provided with a accommodating cavity inside, and a plurality of the nuclear fuel elements are accommodated in the accommodating cavity and are stacked in sequence in the axial direction with adjacent shoulder structures as contact surfaces.

[0019] The nuclear fuel element provided by the present application sets the connection between the peripheral wall and the end face as a double chamfer structure including a first chamfer and a second chamfer, and optimizes and improves the angle relationship between the first chamfer and the second chamfer and the horizontal plane, so that the connection between the peripheral wall and the end face of the nuclear fuel element is smoother. At the same time, the nuclear fuel element provided by the present application sets the connection between the double chamfer structure including the first chamfer and the second chamfer and the concave structure as a horizontally extending shoulder structure, so that the adjacent nuclear fuel elements in the fuel rod can be stacked in the axial direction with the shoulder structure as the contact surface, increasing the contact area between the nuclear fuel elements and sharing the axial load, and combined with the angle optimization of the first angle and the second angle of the present application, significantly improves the interaction effect between the nuclear fuel elements in the nuclear fuel rod during the operation of the reactor, and between the nuclear fuel elements and the cladding, significantly reduces the generation of contact stress, avoids the stress concentration problem of the single chamfer structure, reduces the PCI failure risk of the nuclear fuel element, and improves the operation safety margin. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work, including:

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

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

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

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

[0025] Figure 5 A schematic cross-sectional view of the overall structure of a specific embodiment of the nuclear fuel rod of the present application;

[0026] Figure 6 This is a graph showing experimental data for simulating and calculating the fuel rod power history. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. According to the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application. In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various implementation methods. At the same time, the steps or actions in the method description can also be swapped or adjusted in order in a manner that is obvious to those skilled in the art. Therefore, the various orders in the specification and the accompanying drawings are only for the purpose of clearly describing a certain embodiment, and do not mean that it is a necessary order, unless otherwise specified that a certain order must be followed.

[0028] See also Figure 1 to Figure 2 The present application provides a method for loading a nuclear fuel rod 100 (such as Figure 5 ), the nuclear fuel element 10 comprises an outer wall 1 extending along a central axis 11 to form a cylindrical structure, and two end faces 2 respectively arranged at two ends of the outer wall 1 in the axial direction, each of the end faces 2 comprises an inner concave structure 21, a shoulder structure 22, a first chamfer 23, and a second chamfer 24, wherein:

[0029] The concave structure 21 is formed along the central axis 11 and is axially concave toward the inside 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, which is not limited in this application.

[0030] The shoulder structure 22 extends horizontally from the periphery of the concave structure 21 away from the central axis 11 to one side of the peripheral wall 1. When the central axis 11 is vertically arranged 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 peripheral 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 peripheral wall 1, so that the shoulder structure 22 protrudes slightly from the peripheral wall 1 in the axial direction to form the upper abutment surface of the nuclear fuel element 10. Similarly, for the corresponding end face 2 at the lower end of the peripheral 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 peripheral wall 1, so that the shoulder structure 22 protrudes slightly from the peripheral wall 1 in the axial direction to form the lower contact surface of the nuclear fuel element 10.

[0031] See also Figure 3The first chamfer 23 extends obliquely from the peripheral edge of the shoulder structure 22 away from the concave structure 21 toward the side of the peripheral wall 1, and forms a first angle α with a horizontal plane perpendicular to the central axis 11. Specifically, the horizontal plane refers to a plane formed by extending horizontally outward from the peripheral edge 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 connected to the peripheral wall 1, and forms a second angle β with a horizontal plane perpendicular to the central axis 11. Specifically, the horizontal plane refers to a plane formed by extending horizontally outward from the periphery of the first chamfer 23 away from the shoulder structure 22.

[0033] The first angle α and the second angle β are both acute angles, and the sum of the first angle α and the second angle β is 90°, that is, the first angle α and the second angle β are complementary angles to each other. Under this condition, the first chamfer 23 and the second chamfer 24 have three different configurations.

[0034] See also Figure 3 The length of the slope formed by the first chamfer 23 extending obliquely toward the side of the peripheral wall 1 is recorded as the first slope length L11, and the length of the slope formed by the second chamfer 24 extending obliquely toward the periphery of the peripheral wall 1 is recorded as the second slope length L21. The three different settings of the first chamfer 23 and the second chamfer 24 are as follows:

[0035] In the first configuration, the length L11 of the first slope is greater than the length L21 of the second slope. In this case, the inclined extension length of the first chamfer 23 is greater than that of the second chamfer 24, and the degree of stress dispersion is more significant than that of the second chamfer 24. Figure 3 As shown in the figure, the second setting form is that the first slope length L11 is equal to the second slope length L21. At this time, 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; the third setting form is that the first slope length L11 is less than the second slope length L21. At this time, the inclined extension length of the second chamfer 24 is larger 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 the present application sets the connection between the outer wall 1 and the end face 2 as a double chamfer structure including a first chamfer 23 and a second chamfer 24, and optimizes and improves the angle relationship formed between the first chamfer 23 and the second chamfer 24 and the horizontal plane, so that the connection between the outer wall 1 and the end face 2 of the nuclear fuel element 10 is smoother. At the same time, the nuclear fuel element 10 provided by the present application sets the connection between the double chamfer structure including the first chamfer 23 and the second chamfer 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 in the axial direction with the shoulder structure 22 as the contact surface, thereby increasing the contact area between the nuclear fuel elements 10 and sharing the axial load. In addition, combined with the angle optimization of the first angle α and the second angle β of the present application, the interaction effect between the nuclear fuel elements 10 in the nuclear fuel rod 100 and between the nuclear fuel elements 10 and the cladding during reactor operation is significantly improved, the generation of contact stress is significantly reduced, the stress concentration problem of the single chamfer structure is avoided, the PCI failure risk of the nuclear fuel element 10 is reduced, and the operating safety margin is improved.

[0037] See also Figure 3 to Figure 4 In some embodiments, the first chamfer 23 and the second chamfer 24 preferably adopt the second arrangement form described above, that is, the length of the slope formed by the first chamfer 23 extending obliquely toward one side of the peripheral wall 1 is equal to the length of the slope formed by the second chamfer 24 extending obliquely toward the periphery of the peripheral wall 1, so that the first chamfer 23 and the second chamfer 24 are arranged symmetrically. In this way, the first chamfer 23 and the second chamfer 24 are arranged symmetrically with the perpendicular bisector of the line between the periphery of the peripheral wall 1 and the periphery of the shoulder structure 22 as the axis.

[0038] The nuclear fuel element 10 provided in the present application sets the first chamfer 23 and the second chamfer 24 to a symmetrically arranged structure, so that the first chamfer 23 and the second chamfer 24 can evenly disperse the contact stress between the nuclear fuel elements 10 and between the nuclear fuel element 10 and the cladding, so that the force at the connection between the outer wall 1 and the end face 2 is more uniform, and compared with the structural design in which the first slope length L11 is greater than or less than the second slope length L21, the symmetrically arranged first chamfer 23 and the second chamfer 24 have higher structural stability and strength, further reducing the risk of fragmentation and chipping problems caused by uneven force at corners, radiation expansion and other reasons in the sintered nuclear fuel element 10.

[0039] See also Figure 3 to Figure 4In some embodiments, the first angle α is in the range of 13.4° to 40°, and the second angle β is in the range of 50° to 76.6°, and can be applied to any of the three aforementioned configurations of the first chamfer 23 and the second chamfer 24. Preferably, the second configuration is adopted, that is, the first chamfer 23 and the second chamfer 24 are symmetrically arranged. In the figure, the first angle α is 35° and the second angle β is 55° for example.

[0040] The nuclear fuel element 10 provided in the present application sets the first angle α formed between the first chamfer 23 and the horizontal plane extending horizontally outward from the periphery of the shoulder structure 22 away from the concave structure 21 to between 13.4° and 40°, and sets the second angle β formed between the second chamfer 24 and the horizontal plane extending outward from the periphery of the first chamfer 23 away from the shoulder structure 22 to between 50° and 76.6°, and the sum of the first angle α and the second angle β is 90°, so that the first chamfer 23 and the second chamfer 24 have a better inclined extension slope relative to the central axis 11, so that the connection between the peripheral wall 1 and the end face 2 is smoother. Under this condition, the contact stress between the nuclear fuel elements 10 and the hoop stress of the nuclear fuel elements 10 on the cladding are smaller, the mass loss due to impact is less, and the risk of PCI failure of the nuclear fuel rod is significantly reduced.

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

[0042] In the nuclear fuel element 10 provided in the present application, when the first chamfer 23 and the second chamfer 24 are arranged symmetrically, 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°, the first chamfer 23 and the second chamfer 24 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 hoop stress of the nuclear fuel element 10 on the cladding are minimized, the mass loss of the impact is minimized, and the risk of PCI failure of the nuclear fuel rod can be further reduced.

[0043] See also Figure 4 , the projection width of the first chamfer 23 on the horizontal plane perpendicular to the central axis 11 is recorded as the first chamfer width L12, and the projection height of the first chamfer 23 on the central axis 11 is recorded 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 recorded as the second chamfer width L22, and the projection height of the second chamfer 24 on the central axis 11 is recorded as the second chamfer height L23.

[0044] In some embodiments, when the angle range of the first angle α is set between 13.4° and 40° and the angle range of the second angle β is set between 50° and 76.6°, the first chamfer width 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 repeated below) is between 0.1mm and 0.5mm, and the second chamfer width 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 repeated below) is between 0.02mm and 0.41mm, and can be applied to any specific setting form of the above three setting forms of the first chamfer 23 and the second chamfer 24, and preferably adopts the second setting form, 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 repeated 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 repeated below) is between 0.1mm and 0.5mm, and can be applied to any of the three aforementioned setting forms of the first chamfer 23 and the second chamfer 24. Preferably, the second setting form is adopted, that is, the first chamfer 23 and the second chamfer 24 are arranged symmetrically.

[0046] The nuclear fuel element 10 provided in the present application sets the first chamfer width L12 and the second chamfer height L23 between 0.1 mm and 0.5 mm, and sets the first chamfer height L13 and the second chamfer width L22 between 0.02 mm and 0.41 mm, and in combination with the angle range restrictions of the first angle α and the second angle β in the present application, the width, height and other structural features of the double chamfer structure between the peripheral wall 1 and the shoulder structure 22 are optimized and improved. Under this condition, the contact stress between the nuclear fuel elements 10 and the hoop stress of the nuclear fuel elements 10 on the cladding are smaller, the mass loss due to impact is smaller, and the risk of PCI failure of the nuclear fuel rod can be further reduced.

[0047] Furthermore, in some embodiments, when the angle range of the first angle α is set between 13.4° and 40° and the angle range of the second 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 the present application sets the first chamfer width L12 and the second chamfer height L23 between 0.211 mm and 0.25 mm, and sets the first chamfer height L13 and the second chamfer width L22 between 0.15 mm and 0.177 mm, and further optimizes the width, height and other structural features of the double chamfer structure between the peripheral wall 1 and the shoulder structure 22 in combination with the angle range restrictions of the present application on the first angle α and the second angle β. Under this condition, the contact stress between the nuclear fuel elements 10 and the hoop stress of the nuclear fuel elements 10 on the cladding are minimized, the mass loss due to impact is minimized, and the risk of PCI failure of the nuclear fuel rod is further reduced.

[0049] See also Figure 1 The diameter of the nuclear fuel element 10 of the present application is denoted as D, which is quantified by the diameter of the outer wall 1; the length of the nuclear fuel element 10 of the present application is denoted as H, which is quantified by the spacing 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 peripheral wall 1 is 0.011 to 0.067; the ratio of the second chamfer width L22 to the diameter of the peripheral wall 1 is 0.002 to 0.055.

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

[0052] The nuclear fuel element 10 provided in the present application improves the width ratio of the double chamfer 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 chamfer 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, and further optimizes the double chamfer structure. Under this condition, the contact stress between the nuclear fuel elements 10 and the circumferential stress of the nuclear fuel element 10 on the cladding are smaller, and the mass loss due to impact is smaller, which can further reduce the risk of PCI failure of the nuclear fuel rod. In addition, after adopting the above technical solution, while reducing the contact stress and the risk of PCI failure, it can also further increase the uranium loading of the nuclear fuel rod 100 and improve the economic efficiency of reactor operation.

[0053] See also Figure 2The projection width of the shoulder structure 22 on the horizontal plane perpendicular to the central axis 11 is recorded as the shoulder width W, the diameter of the periphery of the concave structure 21 away from the central axis 11 is recorded as the concave diameter D1, and the depth of the concave structure 21 along the central axis 11 is recorded as the concave depth H1.

[0054] In some embodiments, the shoulder width W (i.e., the projection width of the shoulder structure 22 on the horizontal plane perpendicular to the central axis 11, which will not be described in detail below) is between 0.85 mm and 1.28 mm. The shoulder structure 22 exists as a horizontal annular structure on the end face 2 of the nuclear fuel element 10, and its projection width on the horizontal plane is essentially the width of its annular structure. The shoulder structure 22 has a certain width and is used 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 accumulation of elements in the nuclear fuel rod 100, reduce the stress concentration between the first chamfer 23 and the concave structure, and reduce the contact stress between the nuclear fuel elements 10. Under this condition, the contact stress between the nuclear fuel elements 10 and the circumferential stress of the nuclear fuel element 10 on the cladding are smaller, the mass loss due to impact is smaller, and the risk of PCI failure of the nuclear fuel rod 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 the nuclear fuel elements 10 and the hoop stress of the nuclear fuel element 10 stack are minimized, and the mass loss due to impact is minimized, which can further reduce the risk of nuclear fuel rod PCI failure.

[0056] See also Figure 2 In some embodiments, the concave structure 21 is butterfly-shaped, and the concave diameter D1 of the periphery 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 the present application, by limiting the inner concave diameter D1 of the inner concave structure 21, combined with the limitation of the shoulder width W of the shoulder structure 22 in the present application, makes the first chamfer 23, the second chamfer 24, the shoulder structure 22 and the inner concave structure 21 on the end face 2 have an optimal width ratio, while ensuring that the double chamfer structure, the shoulder structure 22 and the inner concave structure 21 each have an optimal width range, significantly reduces the risk of stress concentration at the connection between the inner concave structure 21 and the shoulder structure 22 during reactor operation, and avoids the problem of nuclear fuel element 10 breaking and chipping 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 0.8-1.7, that is, the length-to-diameter ratio of the nuclear fuel element 10 of the present application is set at 0.8-1.7.

[0059] See also Figure 1 and Figure 5 In some embodiments, the two end faces 2 have the same structure and are symmetrically arranged at the axial ends of the peripheral wall 1. 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, and the forces between the nuclear fuel elements 10 are balanced, reducing the risk of the nuclear fuel elements 10 breaking and falling off.

[0060] See also Figure 5 In some embodiments of the present application, a nuclear fuel rod 100 is provided, which includes a cladding 3 and a plurality of nuclear fuel elements 10 as described above, wherein the cladding 3 extends along the central axis 11 and is provided with a receiving cavity (not shown) inside, and the plurality of nuclear fuel elements 10 are accommodated in the receiving cavity and are stacked in sequence in the axial direction with the adjacent shoulder structures 22 as contact surfaces.

[0061] It can be understood that only one group of nuclear fuel elements 10 stacked in sequence along the central axis 11 can be provided in the cladding 3 of the nuclear fuel rod 100, that is, the axis of the nuclear fuel rod 100 coincides with the central axis 11 of a single group of nuclear fuel elements 10; multiple groups of nuclear fuel elements 10 stacked in sequence along their respective central axes 11 can also be provided in the cladding 3 of the nuclear fuel rod 100 at the same time, that is, the axis of the nuclear fuel rod 100 is misaligned with the central axis 11 of at least one group of nuclear fuel elements 10. This application does not limit this, and it is sufficient to ensure that there is at least one group of nuclear fuel elements 10 stacked in sequence along the central axis 11 in the cladding 3.

[0062] The nuclear fuel rod 100 provided in the present application adopts a double chamfer structure and a shoulder structure 22 to improve the interaction effect between the nuclear fuel elements 10 and between the nuclear fuel elements 10 and the cladding 3 during reactor operation, thereby significantly reducing the generation of contact stress, avoiding the problem of nuclear fuel elements 10 breaking and chipping due to excessive stress concentration, and reducing the risk of PCI failure of the nuclear fuel rod due to the interaction between the nuclear fuel elements 10 and the cladding 3.

[0063] The technical solution of the present application is further described below through several specific embodiments and comparative examples. The specific implementation methods of the nuclear fuel elements 10 of 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 elements 10 in each embodiment and comparative example are the same.

[0064]

[0065]

[0066] Table 1: Specific implementation methods of nuclear fuel elements 10 of Examples 1-4 and Comparative Examples 1-2

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

[0068] The nuclear fuel element 10 sample in Comparative Example 1 is an existing commercial nuclear fuel element 10 with a double-chamfered structure, in which the first chamfer 23 directly transitions to the concave structure 21, and no shoulder structure 22 is provided therebetween. During the operation of the reactor, stress will be concentrated at the starting position of the chamfer 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 an existing commercial nuclear fuel element 10 with a single chamfer structure, without a second chamfer 24 , and transitioning to the shoulder structure 22 through its single chamfer structure.

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

[0071]

[0072] Table 2: Maximum hoop stress and radial displacement results of cladding 3 of Examples 1-4 and Comparative Examples 1-2 after transient

[0073] Table 2 shows the maximum circumferential stress of the nuclear fuel element 10 on the cladding 3 of the nuclear fuel rod 100 and the radial displacement of the cladding 3 during the simulation analysis. The results show that the maximum circumferential stress and the maximum displacement of the cladding 3 of the nuclear fuel element 10 with a symmetrical double chamfer structure provided in the present application under transient conditions are both smaller than those of comparative examples 1-2.

[0074] See also Figure 6 The experimental results of the fuel rod power history simulation calculation show that, under normal circumstances, after the nuclear fuel rod 100 has been running in the reactor for more than 10,000 hours, the nuclear fuel element 10 and the cladding 3 will contact each other. In this simulation calculation process, the nuclear fuel element samples of Examples 1-4 contacted the cladding 3 at 17,000 hours, so that the power transient rise condition occurred at 18,000 hours to study the interaction between the nuclear fuel element 10 and the cladding 3 under transient conditions, and evaluate the maximum hoop stress of the nuclear fuel element 10 on the cladding 3 and the radial displacement of the cladding 3 to evaluate the PCI risk. The transient power rise rate simulated and analyzed in this application adopts the standard Ramp test power rise rate, which is 10kW / m / min.

[0075]

[0076] Table 3: Fuel pellet mass loss results at different impact angles

[0077] The experimental results in Table 3 show the mass loss of the nuclear fuel elements 10 of each embodiment and comparative example due to impact damage when dropped from different angles (5°, 45°, 85°). The research results show that the mass loss of the nuclear fuel element 10 samples of Examples 1-4 of the present application is the smallest under the condition of an impact angle of 45°, among which 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 the conventional experimental method in the field, and the impact energy is 0.13J.

[0078] According to Table 2, Table 3 and Figure 6 As shown in the experimental results, the maximum hoop stress of the cladding 3 of the nuclear fuel rod 100 and the radial displacement of the cladding 3 of the symmetrical double chamfered structure nuclear fuel element 10 provided by the present application during the reactor power transient process are both smaller than those of the existing commercial nuclear fuel elements shown in Comparative Examples 1 and 2, and can effectively reduce the mass loss of the nuclear fuel element 10 under impact. Therefore, it can be seen that the improved nuclear fuel element 10 and nuclear fuel rod 100 provided by the present application can improve the impact on the cladding 3 during the reactor transient period, reduce the risk of PCI failure, have important reference significance for improving the reliability of reactor fuel operation, and are suitable for promotion and use in this field.

[0079] The above are only preferred implementation methods of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present 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 arranged at two ends of the outer wall in an axial direction, characterized in that: Each of the end faces comprises: The concave structure is formed by being axially concave along the central axis; A shoulder structure extending horizontally from the periphery of the concave structure away from the central axis toward one side of the peripheral wall; A first chamfer extends obliquely from the peripheral edge of the shoulder structure away from the concave structure toward one side of the peripheral wall, and forms a first angle with a horizontal plane perpendicular to the central axis; A second chamfer extends obliquely from the first chamfer away from the peripheral edge of the shoulder structure to the peripheral edge connected to the peripheral wall, and forms a second angle with a horizontal plane perpendicular to the central axis; The first angle and the second angle are both acute angles, and the sum of the first angle and the second angle is 90°.

2. The nuclear fuel element according to claim 1, characterized in that: The length of the slope formed by the first chamfer extending obliquely toward one side of the peripheral wall is equal to the length of the slope formed by the second chamfer extending obliquely toward the periphery of the peripheral wall, so that the first chamfer and the second chamfer are arranged symmetrically.

3. The nuclear fuel element according to claim 1, characterized in that: The first angle ranges from 13.4° to 40°, and the second angle ranges from 50° to 76.6°.

4. The nuclear fuel element according to claim 3, characterized in that: The projection width of the first chamfer on the 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 the horizontal plane perpendicular to the central axis is between 0.02 mm and 0.41 mm.

5. The nuclear fuel element according to claim 3, characterized in that: 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.

6. The nuclear fuel element according to any one of claims 1 to 5, characterized in that: The projection width of the shoulder structure on a horizontal plane perpendicular to the central axis is between 0.85 mm and 1.28 mm.

7. The nuclear fuel element according to any one of claims 1 to 5, 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.

8. The nuclear fuel element according to any one of claims 1 to 5, characterized in that: The ratio of the distance between the shoulder structures of the two end surfaces on the central axis to the diameter of the peripheral wall is 0.8 to 1.

7.

9. The nuclear fuel element according to any one of claims 1 to 5, characterized in that: The two end surfaces have the same structure and are symmetrically arranged at two axial ends of the peripheral wall.

10. A nuclear fuel rod, characterized in that: It comprises a cladding and a plurality of nuclear fuel elements as described in any one of claims 1 to 9, wherein the cladding extends along the central axis and is provided with a containing cavity inside, wherein a plurality of the nuclear fuel elements are accommodated in the containing cavity and are stacked in sequence in the axial direction with adjacent shoulder structures as contact surfaces.

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