fuel assembly

Abstract

To provide a fuel assembly that has a structure in which a spring is less likely to be a loose part and can prevent vibration of a fuel rod and an increase in pressure drop in the fuel assembly.SOLUTION: A fuel assembly of the present invention comprises: end plugs that are provided at both upper and lower ends of a fuel rod; and tie plates that each support at least an upper part of the end plug. The end plug includes a plurality of support projections on its surface, and has a spring that is partially stored in a single space formed inside the end plug through an opening formed in the end plug and has a remaining part projecting to the outside to be formed into a closed loop. The plurality of support projections and the spring formed into the closed loop are brought into contact with an inner wall of an insertion hole formed in the tie plate to support the end plug.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a fuel assembly, and particularly to a fuel assembly suitable for use in a reactor comprising a plurality of fuel rods densely arranged in a core within a reactor pressure vessel and a tie plate for supporting and fixing the plurality of fuel rods. [Background technology]

[0002] As a background art in this type of technical field, for example, there is an "upper tie plate of a fuel assembly" described in Patent Document 1.

[0003] Patent Document 1 describes that in order to provide an upper tie plate with a structure that maintains a substantially constant restraining force between the upper tie plate and the fuel elements even when differences in elongation occur between the fuel elements and that easily absorbs longitudinal elongation of the fuel elements and vibrations caused by water flow, insertion holes are drilled into which upper end plugs of the fuel elements can be inserted, and the fuel elements inserted into these insertion holes are held at their upper parts. In this upper tie plate of a fuel assembly, multiple leaf springs are attached to the inner surface of the insertion holes at symmetrical positions relative to the center of the holes.These leaf springs have convex surfaces that come into contact with the upper end plugs of the fuel elements to apply a pressing force to the upper end plugs. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 1-232290 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, a boiling water reactor (hereinafter referred to as a reduced-moderation boiling water reactor) has been under development in which multiple fuel assemblies are loaded into the reactor core and control rods with cross-shaped cross sections are inserted between the fuel assemblies. In this reactor, multiple fuel rods are densely arranged in a channel box of the fuel assembly, and voids are generated in the channel box during operation to harden the neutron spectrum and improve the fission plutonium conversion ratio.

[0006] In a reduced-moderation boiling water reactor, as in a conventional boiling water reactor, upper and lower end plugs are provided at the top and bottom of the fuel rods, respectively. The upper end plugs are inserted into insertion holes in the upper tie plate, and the lower end plugs are inserted into insertion holes in the lower tie plate to support the upper and lower ends of the fuel rods.

[0007] In the reduced-moderation spectrum boiling water reactor (RMWR) currently under development, the diameter of the fuel rods is narrower than that of conventional BWR fuel (e.g., a 9x9 fuel arrangement) in order to arrange more fuel rods densely. Therefore, measures to prevent fuel rod damage due to flow-induced vibration are required. In the latest boiling water reactors (e.g., an 11x11 fuel arrangement), there are already designs in which fuel spacers are placed at the top and bottom ends of the fuel rods to prevent fuel rod vibration.

[0008] The above-mentioned Patent Document 1 describes that when the upper end plug of a fuel rod is inserted into the insertion hole of the upper tie plate, leaf springs can be installed in four directions at 90° intervals on the inner wall of the insertion hole of the upper tie plate, and the leaf springs can suppress vibration of the upper end plug of the fuel rod.

[0009] However, in Patent Document 1, four leaf springs are welded to the inner wall surface of the insertion hole in the upper tie plate, and because the leaf springs and the upper tie plate are presumably made of different materials (for example, the leaf springs are made of Inconel and the upper tie plate is made of stainless steel), there is a risk that the leaf springs will become loose parts due to damage to the welded joint between the dissimilar metals.

[0010] The present invention has been made in consideration of the above points, and an object of the present invention is to provide a fuel assembly having a structure in which springs are less likely to become loose parts, and which can suppress vibration of the fuel rods and an increase in pressure loss in the fuel assembly. [Means for solving the problem]

[0011] In order to achieve the above-mentioned object, the fuel assembly of the present invention is a fuel assembly comprising end plugs provided at both the upper and lower ends of a fuel rod, and a tie plate that supports at least the upper part of the end plugs, wherein the end plugs have a plurality of support protrusions on their surfaces and a closed-loop spring, a portion of which is housed in a single space formed inside the end plug through an opening formed in the end plug, and the remaining portion of which protrudes outside, and the plurality of support protrusions and the closed-loop spring contact the inner wall of an insertion hole formed in the tie plate to support the end plug.

[0012] In order to achieve the above-mentioned object, the fuel assembly of the present invention is a fuel assembly comprising end plugs provided at the upper and lower ends of fuel rods and a tie plate supporting at least the upper portions of the end plugs, and further comprising a tubular plate disposed around the end plugs and having a cylindrical or polygonal cross section, wherein the end plugs are inserted into the tubular plate and brought into contact with the tubular plate, thereby fixing the tubular plate onto the end plugs, and the tubular plate has a protruding spring and a plurality of support protrusions on the outside of the tubular plate so as to face the inner wall surface of the tie plate, and the protruding spring, the plurality of support protrusions, and the inner wall of an insertion hole formed in the tie plate form a lateral support structure for the end plugs.

[0013] In order to achieve the above-mentioned object, the fuel assembly of the present invention is a fuel assembly comprising end plugs provided at both the upper and lower ends of fuel rods and tie plates supporting at least the upper portions of the end plugs, and further comprising a tubular plate disposed around the end plugs and having a cylindrical or polygonal cross section, wherein the end plugs are inserted into the tubular plate and brought into contact with the tubular plate, thereby fixing the tubular plate onto the end plugs, and the tubular plate has a protruding spring and a plurality of support protrusions on the inside of the tubular plate so as to face the outer surface of the end plugs, and the protruding spring, the plurality of support protrusions and the end plugs form a lateral support structure for the end plugs. [Effects of the Invention]

[0014] According to the present invention, the spring is unlikely to become a loose part, and vibration of the fuel rods and an increase in pressure loss in the fuel assembly can be suppressed. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a longitudinal sectional view showing an outline of the overall configuration of a boiling water reactor in which a fuel assembly according to the present invention is adopted. [Figure 2] 1 is a partial cross-sectional view showing a conventional fuel assembly used in a boiling water reactor. [Figure 3] 1 is an overall view showing a fuel rod installed in a conventional fuel assembly employed in a boiling water reactor. [Figure 4] FIG. 1 is a partial cross-sectional view showing a support state of an upper end plug with fuel rods installed in a conventional fuel assembly used in a boiling water reactor. [Figure 5] FIG. 1 is a partial cross-sectional view showing a support state of a lower end plug with fuel rods installed in a conventional fuel assembly used in a boiling water reactor. [Figure 6] FIG. 1 is a perspective view showing a lateral support structure provided on an upper end plug of a fuel rod in a first embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 7(a)]FIG. 1 is a front view showing a lateral support structure provided on an upper end plug of a fuel rod in a first embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 7(b)] FIG. 7(a) is a side view of FIG. [Figure 7(c)] FIG. 7(b) is a plan view of FIG. [Figure 8] FIG. 7(c) is a cross-sectional view taken along line AA in FIG. [Figure 9] FIG. 1 is a partial detailed cross-sectional view showing a state in which an upper end plug having a lateral support structure for a fuel rod in a fuel assembly according to a first embodiment of the present invention, which is used in a boiling water reactor, is incorporated into the fuel assembly. [Figure 10(a)] FIG. 1 is a front view showing a lateral support structure provided on a lower end plug of a fuel rod in a first embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 10(b)] FIG. 10(a) is a side view of FIG. [Figure 10(c)] FIG. 10(b) is a plan view of FIG. [Figure 11] FIG. 10(c) is a cross-sectional view taken along line DD in FIG. [Figure 12] FIG. 1 is a partial detailed cross-sectional view of a fuel rod in a first embodiment of a fuel assembly of the present invention, which is used in a boiling water reactor, and shows a state in which a lower end plug provided with a lateral support structure is incorporated into the fuel assembly. [Figure 13] FIG. 1 is a perspective view showing a leaf spring constituting a lateral support structure used in an upper end plug or a lower end plug of a fuel rod in a first embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 14] FIG. 7( a ) is a cross-sectional view taken along line BB in FIG. 7( a ), showing an opening required for attaching a leaf spring used in an upper end plug of a fuel rod in a first embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 15] FIG. 1 is a cross-sectional view showing a state in which the end of a leaf spring is beginning to be inserted into the upper opening of the upper end plug of a fuel rod in a first embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 16]16 is a cross-sectional view showing a state in which the leaf spring middle portion of the leaf spring is housed in the leaf spring middle portion housing portion in the upper end plug, following the state shown in FIG. 15. FIG. [Figure 17] 17 is a cross-sectional view showing a state in which both end portions of the leaf spring in the state of FIG. 16 are joined by welded portions. FIG. [Figure 18] 18 is a cross-sectional view showing a state in which both end portions of the leaf spring joined by welds are housed in the leaf spring end housing portions in the upper end plug, following the state shown in FIG. 17. FIG. [Figure 19] FIG. 10 is a perspective view showing a leaf spring constituting a lateral support structure used in an upper end plug or a lower end plug of a fuel rod in a second embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 20] 20 is a perspective view showing a state in which notches provided at both ends of the leaf spring shown in FIG. 19 are fitted together. FIG. [Figure 21] FIG. 10 is a perspective view showing a leaf spring constituting a lateral support structure used in an upper end plug or a lower end plug of a fuel rod in a third embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 22] 22 is a view corresponding to FIG. 18, in which the leaf spring shown in FIG. 21 is attached to the upper end plug of a fuel rod. [Figure 23] FIG. 10 is a perspective view showing a lateral support structure provided on an upper end plug of a fuel rod in a fourth embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 24] FIG. 24 is a plan view of FIG. 23. [Figure 25] FIG. 10 is a development view of a hexagonal cylindrical plate provided around the upper end plug of a fuel rod in a fourth embodiment of a fuel assembly of the present invention used in a boiling water reactor. [Figure 26] FIG. 10 is a perspective view showing a hexagonal cylindrical plate provided around the upper end plug of a fuel rod in a fourth embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 27] FIG. 25 is a cross-sectional view taken along line EE in FIG. 24. [Figure 28] FIG. 10 is a perspective view showing a lateral support structure provided on an upper end plug of a fuel rod in a fifth embodiment of a fuel assembly of the present invention employed in a boiling water reactor. [Figure 29] FIG. 29 is a plan view of FIG. 28. [Figure 30] FIG. 10 is a perspective view showing a hexagonal cylindrical plate provided around the upper end plug of a fuel rod in a fifth embodiment of a fuel assembly of the present invention used in a boiling water reactor. [Figure 31] FIG. 30 is a cross-sectional view taken along line FF in FIG. 29. DETAILED DESCRIPTION OF THE INVENTION

[0016] The fuel assembly of the present invention will be described below based on the illustrated embodiments. In each embodiment described below, the same reference numerals will be used for the same components.

[0017] First, a boiling water reactor 100 employing the fuel assembly of the present invention will be described with reference to Fig. 1. The boiling water reactor 100 employing the fuel assembly of the present invention shown in Fig. 1 is a reduced moderation spectrum boiling water reactor.

[0018] As shown in FIG. 1, a boiling water reactor 100 includes a cylindrical core shroud 102 disposed inside a reactor pressure vessel 101, a core 103 disposed inside the core shroud 102 and having a plurality of fuel assemblies 120 arranged in a square lattice pattern, a shroud head 104 disposed inside the reactor pressure vessel 101 and covering the core 103, a steam-water separator 105 disposed in the shroud head 104 and extending upward, a steam dryer 106 disposed above the steam-water separator 105, an upper grid plate 129 disposed inside the core shroud 102 and at the upper end of the core 103, and a core 103 disposed inside the core shroud 102 and at the lower end of the core 103. The reactor pressure vessel 101 is generally composed of a support plate 108, a fuel support bracket 109 arranged on the core support plate 108, a control rod guide tube 110 arranged inside the reactor pressure vessel 101 and enabling a control rod having a cross-sectional shape (a cross-shaped control rod 132 shown in FIG. 2) to be inserted into the core 103 in order to control the nuclear reaction of the fuel assembly 120, a control rod drive mechanism 111 arranged inside a control rod drive mechanism housing (not shown) arranged below the bottom of the reactor pressure vessel 101 and connected to the cross-shaped control rod 132, and an internal pump 113 equipped with an impeller 117 arranged at the bottom of the reactor pressure vessel 101 so as to penetrate into the interior of the reactor pressure vessel 101 from below.

[0019] The internal pump 113 is disposed facing an annular downcomer 114 formed between the outer surface of the cylindrical core shroud 102 and the inner surface of the reactor pressure vessel 101 .

[0020] In addition, cooling water (subcooled water: cooling water at a temperature lower than the saturated state) 118 inside the reactor pressure vessel 101 flows into the inside of the core 103 from the bottom side of the reactor pressure vessel 101 by an internal pump 113. The cooling water 118 that has flowed into the inside of the core 103 is heated by the nuclear reaction of the fuel assemblies 120 (see Figure 2) and becomes a gas-liquid two-phase flow, which then flows into the steam separator 105.

[0021] The gas-liquid two-phase flow that flows into the steam-water separator 105 is separated into moisture-containing steam (gas phase) and water (liquid phase), and the water (liquid phase) flows down again to the downcomer 114 as cooling water 118, while the steam (gas phase) flows into the steam dryer 106 where moisture is removed and is supplied to the turbine (not shown) via the main steam pipe 115. The steam supplied to the turbine is returned to water in a condenser (not shown) and flows into the reactor pressure vessel 101 via the feedwater pipe 116.

[0022] As will be described later, the core 103 has a plurality of (four) fuel assemblies 120 arranged in a square lattice pattern, and cross-shaped control rods 132 arranged between the fuel assemblies 120 to control the nuclear reactions of the fuel assemblies 120.

[0023] Next, the fuel assembly 120 will be described with reference to FIG.

[0024] As described above, a plurality of fuel assemblies 120 shown in FIG. 2 are arranged in the core 103 in a square lattice pattern.

[0025] As shown in FIG. 2, the fuel assembly 120 is roughly composed of a rectangular cylindrical (quadrilateral or square) channel box 125, fuel rods 121 densely arranged in a square shape in this channel box 125, a plurality of spacers 122 arranged vertically (in the height direction of the fuel assembly 120: the vertical direction) and supporting the fuel rods 121 at regular intervals in the lateral direction (horizontal direction) (supporting the fuel rods 121 at any intervals so that the fuel rods 121 do not come into contact with each other in the height direction of the fuel assembly 120), an upper tie plate 124 that fixes the upper parts of the fuel rods 121, a lower tie plate 123 that fixes the lower parts of the fuel rods 121, and a handle 130 arranged on the upper tie plate 124.

[0026] The fuel assembly 120 shown in FIG. 2 is supported at its upper part by an upper grid plate 129 and at its lower part by a fuel support bracket 109 .

[0027] In addition, a movement space 140 for the cross-shaped control rod 132 is formed between adjacent fuel assemblies 120, allowing the cross-shaped control rod 132 to move up and down, and the movement space 140 for the cross-shaped control rod 132 is formed by a channel spacer 133 arranged in the channel box 125.

[0028] In addition, the fuel support bracket 109 is formed with upper openings 127 into which the lower part of the lower tie plate 123 is fitted, and between adjacent upper openings 127, control rod movement openings 128 are formed to allow the cross-shaped control rods 132 to move up and down.

[0029] FIG. 3 shows a fuel rod 121 employed in the fuel assembly 120 shown in FIG.

[0030] As shown in FIG. 3, the upper and lower ends of the fuel rod 121 are provided with upper end plugs 134 and lower end plugs 135, respectively.

[0031] A conventional support for the upper end plugs 134 of the fuel rods 121 in the fuel assembly 120 is shown in FIG. 4, and a conventional support for the lower end plugs 135 is shown in FIG.

[0032] 4 and 5 show fuel rods 121 other than a few fuel rods (not shown) that connect upper tie plate 124 and lower tie plate 123.

[0033] As shown in Figure 4, the upper part of the fuel rod 121 is supported by inserting the upper end plug 134 of the fuel rod 121 into an insertion hole 138 formed in the upper tie plate 124. To prevent the body of the fuel rod 121 from contacting the upper tie plate 124 due to thermal expansion, an expansion spring 136 is provided between the fuel rod 121 and the upper tie plate 124, and the expansion and contraction of this expansion spring 136 absorbs the thermal expansion of the body of the fuel rod 121. The force applied to the expansion spring 136 is received by the underside 137 of the upper tie plate 124.

[0034] On the other hand, as shown in FIG. 5, the lower portion of the fuel rod 121 is supported by inserting the lower end plug 135 of the fuel rod 121 into the insertion hole 139 formed in the lower tie plate 123, and the load of the fuel rod 121 is borne by the tapered portion 135a formed above the lower end plug 135. [Example]

[0035] Next, a first embodiment of the fuel assembly 120 of the present invention will be described.

[0036] The characteristic components of the fuel assembly 120 according to the first embodiment of the present invention are the leaf spring 1, the plurality of support projections 2a and 2b, and the support projections 3a and 3b provided on the upper end plug 134 of the fuel rod 121 shown in Figures 6, 7(a), 7(b), 7(c), 8, and 9. These will be described in detail below.

[0037] Figure 6 is a perspective view of the lateral support structure provided on the upper end plug 134 of the fuel rod 121, Figure 7(a) is a front view of the lateral support structure provided on the upper end plug of the fuel rod, Figure 7(b) is a side view of Figure 7(a), Figure 7(c) is a plan view of Figure 7(b), Figure 8 is a cross-sectional view along line AA of Figure 7(c), and Figure 9 is a partial detailed cross-sectional view of the upper end plug 134 of the fuel rod 121 provided with the lateral support structure installed in the fuel assembly 120.

[0038] As shown in Figures 6, 7(a), 7(b) and 7(c), the upper end plug 134 of the fuel rod 121 is provided with a leaf spring 1, a plurality of support projections 2a and 2b, and support projections 3a and 3b.

[0039] That is, as shown in Figure 7(c), support protrusions 2a and support protrusions 3a are provided in two directions at 120° intervals, and leaf spring 1 is provided in one direction on the surface of upper end plug 134. As shown in Figure 7(a), support protrusions 2a and 2b and support protrusions 3a and 3b are provided in two locations in the vertical direction, and the positions of support protrusions 2a and 2b and support protrusions 3a and 3b are at the same level as the height of upper opening 4a and the height of lower opening 4b formed in upper end plug 134, into which leaf spring 1 is inserted (support protrusions 2a and 2b and support protrusions 3a and 3b are arranged at the same intervals, centered on protruding portion 1d of leaf spring 1).

[0040] FIG. 8 shows a longitudinal cross-sectional view (a cross-sectional view taken along line AA in FIG. 7(c)) of the portion of upper end plug 134 where support projections 3a and 3b and leaf spring 1 are provided, and FIG. 9 shows a partial detailed cross-sectional view of the state in which upper end plug 134 of FIG. 8 has been inserted into insertion hole 138 formed in upper tie plate 124.

[0041] As shown in FIG. 9, the shapes of the support protrusions 3a and 3b and the leaf spring 1 are semicircular so that when the upper end plug 134 is inserted into the insertion hole 138 formed in the upper tie plate 124, the contact areas between the support protrusions 3a and 3b and the leaf spring 1 are in point contact or near point contact. The leaf spring 1 is also shaped to have a protruding portion 1d that protrudes in one place (for example, the protruding portion 1d is formed by partially deep drawing using a punch).

[0042] The support protrusions 2a and 2b have the same shape as the support protrusions 3a and 3b. As shown in Fig. 9, the support protrusions 3a and 3b provided on the upper end plug 134 and the leaf spring 1 are in point contact with the inner wall surface of the insertion hole 138 formed in the upper tie plate 124 (although not shown, the support protrusions 2a and 3a are similar to the support protrusions 3a and 3b).

[0043] With this configuration, even if a flow of cooling water occurs during reactor operation, the upper end plugs 134 of the fuel rods 121 can be suppressed from vibrating in the lateral direction by being supported by the leaf springs 1, the support protrusions 2a and 2b, and the support protrusions 3a and 3b. Furthermore, spacers as a countermeasure against vibration of the fuel rods 121 are no longer necessary, and an effect of suppressing an increase in pressure loss can also be expected.

[0044] As shown in FIG. 9, the fuel rods 121 are supported by expansion springs 136, so there is no problem with their vertical movement.

[0045] Next, Figures 10(a), 10(b), 10(c), 11 and 12 show the leaf spring 11, the plurality of support projections 12a and 12b and the support projections 13a and 13b provided on the lower end plug 135 of the fuel rod 121.

[0046] 10(c), similar to FIG. 7(c), the lower end plug 135 of the fuel rod 121 has support protrusions 12a and 13a on two sides at 120° intervals and a leaf spring 11 on one side on the surface of the lower end plug 135. As shown in FIG. 10(a), the support protrusions 12a and 12b and the support protrusions 13a and 13b are provided at two locations in the vertical direction, and the positions of the support protrusions 12a and 12b and the support protrusions 13a and 13b are at the same level as the heights of the upper opening 14a and the lower opening 14b formed in the lower end plug 135 into which the leaf spring 11 is inserted (the support protrusions 12a and 12b and the support protrusions 13a and 13b are arranged at the same intervals around the protruding portion 11d of the leaf spring 11).

[0047] FIG. 11 shows a longitudinal cross-sectional view (a cross-sectional view taken along line DD in FIG. 10(c)) of the portion of the lower end plug 135 in FIG. 10(b) where the support projections 13a and 13b and the leaf spring 11 are provided, and FIG. 12 shows a partial detailed cross-sectional view of the state in which the lower end plug 135 in FIG. 11 has been inserted into an insertion hole 139 formed in the lower tie plate 123.

[0048] As shown in FIG. 12, the shapes of support protrusions 13a and 13b and leaf spring 11 are semicircular so that when lower end plug 135 is inserted into insertion hole 139 formed in lower tie plate 123, the contact areas between support protrusions 13a and 13b and leaf spring 11 are in point contact or near point contact. Leaf spring 11 is also shaped to have a protruding portion 11d that protrudes in one location (for example, protruding portion 11d is formed by partially deep drawing using a punch).

[0049] The support protrusions 12a and 12b have the same shape as the support protrusions 13a and 13b. As shown in Fig. 12, the support protrusions 13a and 13b provided on the lower end plug 135 and the leaf spring 11 are in point contact with the inner wall surface of the insertion hole 139 formed in the lower tie plate 123 (although not shown, the support protrusions 12a and 12b are also the same as the support protrusions 13a and 13b).

[0050] With this configuration, even if a flow of cooling water occurs during reactor operation, the lower end plug 135 can suppress lateral vibrations by being supported by the support protrusions 13a and 13b and the leaf spring 11, as in FIG.

[0051] Next, the procedure for attaching the leaf spring 1 employed in the fuel assembly 120 of this embodiment to the upper end plug 134 will be described with reference to FIGS.

[0052] FIG. 13 shows the leaf spring 1 prior to attachment to the upper end plug 134 of the fuel rod 121.

[0053] As shown in FIG. 13, the leaf spring 1 has a rectangular shape with its end forming a short side 1e and a long side 1f extending upward from the short side 1e, and the length of the short side 1e is shorter than the outer diameter of the upper end plug 134.

[0054] As shown in FIG. 13, before the leaf spring 1 is attached to the upper end plug 134 of the fuel rod 121, the leaf spring 1 is folded in half around the middle portion 1a of the leaf spring. At the center of the leaf spring 1 located outside the upper end plug 134 (the middle position between the middle portion 1a of the leaf spring and the end portion 1b of the leaf spring), a protruding portion 1d is formed. This protruding portion 1d is for contacting the inner wall surface of the insertion hole 138 formed in the upper tie plate 124 after the folded leaf spring 1 is attached to the upper end plug 134.

[0055] FIG. 14 shows a cross-sectional view (a cross-sectional view taken along line BB in FIG. 7(a)) of the portion where the leaf spring 1 folded in two is attached to the upper end plug 134.

[0056] As shown in Figure 14, two openings, an upper opening 4a and a lower opening 4b, are provided on the surface of the upper end plug 134 of the fuel rod 121. The upper opening 4a and the lower opening 4b are connected through an opening communication part 6, which is a single space within the upper end plug 134. Above the opening communication part 6, a leaf spring middle part storage part 5a is formed in which the leaf spring middle part 1a of the leaf spring 1 can be stored, and below the opening communication part 6, a leaf spring end storage part 5b is formed in which the leaf spring end parts 1b and 1c of the leaf spring 1 can be stored.

[0057] FIG. 15 shows the state where the leaf spring end 1c is beginning to be inserted into the upper opening 4a of the upper end plug 134 of the fuel rod 121, and FIG. 16 shows the state where the leaf spring end 1c inserted through the upper opening 4a of the upper end plug 134 of the fuel rod 121 has been removed from the upper end plug 134 through the lower opening 4b.

[0058] As shown in FIG. 16, the leaf spring middle portion 1a of the leaf spring 1 is housed in the leaf spring middle portion housing portion 5a in the upper end plug .

[0059] FIG. 17 shows the state where both ends of the leaf spring 1, leaf spring end 1b and leaf spring end 1c, are joined by welded portion 7, and FIG. 18 shows the state where the welded portion 7 joining both ends of the leaf spring 1, leaf spring end 1b and leaf spring end 1c, is stored in the leaf spring end storage portion 5b inside the upper end plug 134.

[0060] 18, when the upper end plug 134 is inserted into the insertion hole 138 of the upper tie plate 124, the protruding portion 1d of the leaf spring 1 comes into contact with the inner wall surface of the insertion hole 138 of the upper tie plate 124, and the protruding portion 1d of the leaf spring 1 is pressed toward the upper end plug 134. In response to this movement, the middle portion 1a and the end portion 1b of the leaf spring move upward and downward within the middle portion 1a of the leaf spring and the middle portion housing portion 5a and the end portion housing portion 5b of the leaf spring, respectively.

[0061] Therefore, even if a flow of cooling water occurs during reactor operation, the leaf spring 1 will not come off the upper end plug 134 and will not become a rule part. Furthermore, even if the welded portion 7 joining the leaf spring end portions 1b and 1c of the leaf spring 1 together is damaged, the leaf spring 1 will not come off the upper end plug 134 because the leaf spring end portions 1b and 1c of the leaf spring 1 are inside the leaf spring end storage portion 5b.

[0062] In this embodiment, the procedure for attaching the leaf spring 1 to the upper end plug 134 has been described, but the procedure for attaching the leaf spring 11 to the lower end plug 135 is similar. Also, Figures 13, 14, 15, 16, 17, and 18 simply explain the procedure for installing the leaf spring 1 in the upper end plug 134 in an easy-to-understand manner, and any structure may be used as long as the leaf spring 1 is formed into a closed loop and a portion of the leaf spring 1 is disposed within the upper end plug 134, and the present embodiment is not limited to this.

[0063] According to this embodiment, it is possible to provide a fuel assembly 120 in which the upper end plugs 134 and the lower end plugs 135 of the fuel rods 121 have a lateral support structure that is effective in suppressing vibration of the fuel rods 121, using closed-loop leaf springs 1, 11 and multiple support protrusions 2a, 2b, 3a, 3b, 12a, 12b, 13a, and 13b, which can reduce the risk of the leaf springs 1, 11 becoming loose parts, without significantly changing the structure of the conventional fuel assembly 120.

[0064] Furthermore, by taking the above measures, spacers as a measure against vibration of the fuel rods 121 are no longer necessary, and an effect of suppressing an increase in pressure loss can also be expected. [Example]

[0065] A second embodiment of the fuel assembly 120 of the present invention will be described with reference to FIGS.

[0066] 19 and 20 show the closed loop leaf spring 1 in Example 2 of the fuel assembly 120 of the present invention, and a characteristic component of Example 2 is that notches 15a and 15b are provided at leaf spring end 1b and leaf spring end 1c of the leaf spring 1.

[0067] FIG. 19 shows the state of the leaf spring 1 before it is made into a closed loop. Before the leaf spring 1 is attached to the upper end plug 134, it is folded in half around the middle part 1a of the leaf spring, as in Example 1 shown in FIG. 13.

[0068] In addition, in Example 1 shown in FIG. 17, both ends of leaf spring end 1b and leaf spring end 1c of leaf spring 1 are joined by welded portion 7, but in Example 2 shown in FIGS. 19 and 20, notch 15a provided on leaf spring end 1b of leaf spring 1 and notch 15b provided on leaf spring end 1c are fitted together as shown in FIG. 20, thereby realizing a closed loop using only leaf spring 1 and preventing leaf spring 1 from becoming a loose part.

[0069] Furthermore, the work of providing a welded portion for joining both ends of the leaf spring 1b and the leaf spring end 1c of the leaf spring 1 as in the first embodiment shown in FIG. 17 is not necessary.

[0070] It goes without saying that the configuration of the second embodiment described above can be applied to the lower end plug 135 in the same manner as the upper end plug 134.

[0071] Even with this configuration of the present embodiment, the same effects as those of the first embodiment can be obtained. [Example]

[0072] A third embodiment of the fuel assembly 120 of the present invention will be described with reference to FIGS. 21 and 22. FIG.

[0073] 21 and 22 show a closed loop of the leaf spring 1 in Example 3 of the fuel assembly 120 of the present invention. The characteristic components of Example 3 are an opening 8 formed near both ends of the leaf spring 1, leaf spring end 1b and leaf spring end 1c, a fastener 9 for preventing the position of the opening 8 from shifting up and down, a fastener insertion hole 8a for passing the fastener 9 into the upper end plug 134, and an insertion hole stopper 10 for preventing the fastener 9 from slipping out of the fastener insertion hole 8a.

[0074] FIG. 21 shows the state of the leaf spring 1 before it is made into a closed loop, and like Example 1 shown in FIG. 13, it is folded in half around the middle part 1a of the leaf spring before being attached to the upper end plug 134.

[0075] In addition, in Example 1 shown in FIG. 16, after the leaf spring 1 is passed through the opening communicating portion 6 in the upper end plug 134, the leaf spring end portion 1c of the leaf spring 1 is removed from the upper end plug 134 through the lower opening 4b, but in Example 3 shown in FIGS. 21 and 22, the leaf spring end portion 1c of the leaf spring 1 is not removed from the upper end plug 134, but is stored as is in the leaf spring end storage portion 5b.

[0076] Then, fasteners 9 are inserted into the openings 8 formed in the leaf spring ends 1b and 1c of the leaf spring 1 arranged in the leaf spring end storage section 5b and into the fastener insertion holes 8a in the upper end plug 134, so that the positions of the two leaf spring ends 1b and 1c of the leaf spring 1 are not shifted.

[0077] Finally, by blocking both ends of the fastener insertion hole 8a with insertion hole stoppers 10 to prevent the fastener 9 from coming out of the fastener insertion hole 8a, the leaf spring end 1b and the leaf spring end 1c of the leaf spring 1 will not come out of the upper end plug 134 from the leaf spring end storage section 5b located below within the upper end plug 134.

[0078] According to the configuration of the third embodiment, a closed loop can be realized without welding both ends of the leaf spring 1b and the leaf spring end 1c of the leaf spring 1, and the leaf spring 1 does not become a loose part.

[0079] Furthermore, the work of providing the welded portion 7 for joining the leaf spring end 1b and the leaf spring end 1c of the leaf spring 1 as in the first embodiment shown in FIG. 17 is not necessary.

[0080] It goes without saying that the configuration of the third embodiment described above can be applied to the lower end plug 135 in the same manner as the upper end plug 134.

[0081] Even with this configuration of the present embodiment, the same effects as those of the first embodiment can be obtained. [Example]

[0082] A fourth embodiment of the fuel assembly 120 of the present invention will be described with reference to FIGS. 23, 24, 25, 26 and 27. FIG.

[0083] Figure 23 is an oblique view of a hexagonal cylindrical plate 20 provided around the upper end plug 134 of a fuel rod 121, Figure 24 is a plan view of the hexagonal cylindrical plate 20 provided around the upper end plug 134 of a fuel rod 121, Figure 25 is an exploded view of the hexagonal cylindrical plate 20 provided around the upper end plug 134 of a fuel rod 121, Figure 26 is an oblique view of the hexagonal cylindrical plate 20 provided around the upper end plug 134 of a fuel rod 121, and Figure 27 is a partial detailed cross-sectional view (cross-sectional view along line EE in Figure 24) of the upper end plug 134 provided with the hexagonal cylindrical plate 20 installed in the fuel assembly 120.

[0084] The characteristic component of the fourth embodiment shown in Figures 23, 24, 25, 26 and 27 is a hexagonal cylindrical plate 20 that is installed around the upper end plug 134 of the fuel rod 121 and has a plurality of support projections 22a, 22b, 23a, 23b and a protruding leaf spring 21. This will be explained in detail below.

[0085] As shown in Figures 23 and 24, a hexagonal cylindrical plate 20 is installed around the upper end plug 134 of the fuel rod 121. As shown in Figure 24, this hexagonal cylindrical plate 20 has support protrusions 22a and 23a on its outer surface at 120° intervals in two directions and a protruding leaf spring 21 in one direction. This configuration is the same as the arrangement of support protrusions 2a and 3a and leaf spring 1 on the upper end plug 134 shown in Figure 7(c).

[0086] Next, the upper side of the development of the hexagonal cylindrical plate 20 shown in FIG. 25 is the upper side in the installation height direction, and the lower side of the development of the hexagonal cylindrical plate 20 is the lower side in the installation height direction.

[0087] As shown in FIG. 25, the support protrusions 22a, 22b and the support protrusions 23a, 23b are provided at two locations in the vertical direction, and are located above and below the position of the protruding leaf spring 21 in the installation height direction.

[0088] Furthermore, when the protruding leaf spring 21, support protrusions 22a, 22b, and support protrusions 23a, 23b are installed around the upper end plug 134, they are shaped to protrude toward the surrounding area (outward), rather than toward the upper end plug 134 (inward).

[0089] Meanwhile, in order to integrate the upper end plug 134 and the hexagonal cylindrical plate 20, upper end plug holders 25a and 25b are provided in the direction (inward) of the upper end plug 134. As shown in Figure 24, these upper end plug holders 25a and 25b are installed in three directions at 120° intervals on the inner surface of the hexagonal cylindrical plate 20.

[0090] The hexagonal cylindrical plate 20, the support projections 22a, 22b, 23a, 23b, and the protruding plate spring 21 can be easily formed by press working.

[0091] Furthermore, no members other than those required for the support projections 22a, 22b, 23a, 23b and the protruding leaf spring 21 are provided, thereby reducing the amount of material required for the hexagonal cylindrical plate 20.

[0092] FIG. 26 shows the cylindrical plate 20 formed in FIG. 25 bent to form a hexagon when viewed from above.

[0093] In addition, a portion of the ends 20a, 20b of the cylindrical plate 20 shown in Figure 25 is welded at a welding portion 7 as shown in Figure 26, or a notch is made in the ends 20a, 20b of the cylindrical plate 20 (see Figure 19), and the notched portions at both ends are fitted together to realize a closed loop of the hexagonal cylindrical plate 20.

[0094] FIG. 27 shows a partial detailed cross-sectional view of the upper end plug 134 of the fuel rod 121, with the hexagonal cylindrical plate 20 installed around the upper end plug 134, inserted into the insertion hole 138 of the upper tie plate 124.

[0095] As shown in FIG. 27, support protrusions 23a, 23b and protruding leaf spring 21 provided on hexagonal cylindrical plate 20 are in point contact with the inner wall surface of insertion hole 138 of upper tie plate 124 (although not shown, support protrusions 22a, 22b are also in point contact with the inner wall surface of insertion hole 138 of upper tie plate 124, similar to support protrusions 23a, 23b).

[0096] With the configuration of this embodiment, even if a flow of cooling water occurs during reactor operation, lateral vibration of the fuel rods 121 can be suppressed by support provided by the support projections 22a, 22b, 23a, 23b and the protruding leaf springs 21 provided on the hexagonal cylindrical plate 20 that is integral with the upper end plugs 134 of the fuel rods 121.

[0097] Furthermore, as shown in FIG. 25, the hexagonal cylindrical plate 20 shown in FIG. 27 has three bent portions 24a, 24b formed at the top and bottom of the hexagonal cylindrical plate 20 in the vertical direction, respectively, to prevent the cylindrical plate from slipping out. By hooking these bent portions 24a, 24b onto the top and bottom surfaces of the upper tie plate 124, the hexagonal cylindrical plate 20 can be fixed to the insertion hole 138 of the upper end plug 134 without welding.

[0098] Therefore, by placing and fixing the hexagonal cylindrical plate 20 around the upper end plug 134, a closed loop can be achieved without processing the upper end plug 134, and the hexagonal cylindrical plate 20 will not come off the upper end plug 134, and the hexagonal cylindrical plate 20 will not become a loose part.

[0099] 9, there is no problem with thermal expansion or vibration in the vertical direction of the fuel rods 121 because they are supported by expansion springs 136. Furthermore, although the hexagonal cylindrical plate 20 in this embodiment is bent so as to form a hexagon when viewed from above, polygons other than hexagons are also acceptable, but since it is difficult to integrate the cylindrical plate and upper end plug 134 into a single structure with a polygon having a small number of sides, it is desirable to use a polygon having as large a number as possible.

[0100] It goes without saying that the configuration of the fourth embodiment described above can be applied to the lower end plug 135 in the same manner as the upper end plug 134.

[0101] Even with this configuration of the present embodiment, the same effects as those of the first embodiment can be obtained. [Example]

[0102] Next, a fifth embodiment of the fuel assembly 120 of the present invention will be described with reference to FIGS. 28, 29, 30 and 31. FIG.

[0103] Figure 28 is an oblique view of a hexagonal cylindrical plate 30 provided around the upper end plug 134 of a fuel rod 121, Figure 29 is a plan view of the hexagonal cylindrical plate 30 provided around the upper end plug 134 of a fuel rod 121, Figure 30 is an oblique view of the hexagonal cylindrical plate 30 provided around the upper end plug 134 of a fuel rod 121, and Figure 31 is a partial detailed cross-sectional view (cross-sectional view along line FF in Figure 29) of the upper end plug 134 provided with the hexagonal cylindrical plate 30 installed in the fuel assembly 120.

[0104] The characteristic components of Example 5 shown in Figures 28, 29, 30, and 31 are that it is a hexagonal cylindrical plate 30 that is installed around the upper end plug 134 of the fuel rod 121 and has a plurality of support projections 32a, 32b, 33a, and 33b and a protruding leaf spring 31, and is substantially the same as the configuration of Example 4. The difference from Example 4 is that what is supported by the support projections 32a, 32b, 33a, and 33b and the protruding leaf spring 31 is the upper end plug 134. This will be explained in detail below.

[0105] As shown in Figures 28 and 29, a hexagonal cylindrical plate 30 is installed around the upper end plug 134 of the fuel rod 121. As shown in Figure 28, this hexagonal cylindrical plate 30 has support protrusions 32a and 32b on the inner surface of the hexagonal cylindrical plate 30, spaced 120° apart in two directions, and a protruding leaf spring 31 in one direction. This configuration is the same as the arrangement of support protrusions 2a and 2b and leaf spring 1 on the upper end plug 134 shown in Figure 7(c).

[0106] As shown in Figure 29, in this embodiment, the protruding leaf spring 31 and support protrusions 32a, 32b, 33a and 33b are shaped to protrude toward the upper end plug 134 (inward) rather than toward the surrounding area (outward) when installed around the upper end plug 134.

[0107] Meanwhile, in order to integrate the upper tie plate 124 and the hexagonal cylindrical plate 30, retaining portions 36a and 36b are provided facing (outward) toward the upper tie plate 124. As shown in Fig. 30, the retaining portions 36a and 36b are installed in three directions at 120° intervals on the inner surface of the hexagonal cylindrical plate 30.

[0108] The hexagonal cylindrical plate 30, the support projections 32a, 32b, 33a, 33b and the protruding plate spring 31 can be easily formed by press working.

[0109] Furthermore, no components other than those required for the support projections 32a, 32b, 33a, and 33b and the protruding leaf spring 31 are provided, thereby reducing the amount of material required for the hexagonal cylindrical plate 30.

[0110] Furthermore, as in Example 4, as shown in Figures 29 and 30, a part of the end of the hexagonal tubular plate 30 is welded with a welding portion 7, or a notch is made in the end of the hexagonal tubular plate 30 and the notched portions at both ends are fitted together, thereby realizing a closed loop of the hexagonal tubular plate 30.

[0111] FIG. 31 shows a partial detailed cross-sectional view of the upper end plug 134 of the fuel rod 121, with the hexagonal cylindrical plate 30 installed around the upper end plug 134, inserted into the insertion hole 138 of the upper tie plate 124.

[0112] As shown in FIG. 31, support protrusions 33a, 33b and protruding leaf spring 31 provided on hexagonal cylindrical plate 30 are in point contact with the inner wall surface of insertion hole 138 of upper tie plate 124 (although not shown, support protrusions 32a, 32b are also in point contact with the inner wall surface of insertion hole 138 of upper tie plate 124, similar to support protrusions 33a, 33b).

[0113] With the configuration of this embodiment, even if a flow of cooling water occurs during reactor operation, the upper end plugs 134 of the fuel rods 121 are supported by the support projections 32a, 32b, 33a, 33b and the protruding leaf springs 31 provided on the hexagonal cylindrical plate 30, thereby suppressing lateral vibration of the fuel rods 121.

[0114] 30 and 31, the hexagonal cylindrical plate 30 shown in FIG. 31 has three bent portions 34a, 34b formed at the top and bottom of the hexagonal cylindrical plate 30 in the vertical direction, respectively, to prevent the cylindrical plate from slipping out. By hooking these bent portions 34a, 34b onto the top and bottom surfaces of the upper tie plate 124, the hexagonal cylindrical plate 30 can be fixed to the insertion hole 138 of the upper end plug 134 without welding.

[0115] Therefore, by wrapping the hexagonal cylindrical plate 30 around the upper end plug 134 and fixing the end, a closed loop can be achieved without processing the upper end plug 134, and the hexagonal cylindrical plate 30 will not come off the upper end plug 134, and the hexagonal cylindrical plate 30 will not become a loose part.

[0116] 9, there is no problem with thermal expansion or vibration in the vertical direction of the fuel rods 121 because they are supported by expansion springs 136. Furthermore, although the hexagonal cylindrical plate 30 in this embodiment is bent so as to form a hexagon when viewed from above, polygons other than hexagons are also acceptable, but since it is difficult to integrate the cylindrical plate and upper end plug 134 into a single structure with a polygon having a small number of sides, it is desirable to use a polygon having as large a number as possible.

[0117] In the configuration of the fifth embodiment, the upper end plug 134 has been mainly described, but it goes without saying that the same can be applied to the lower end plug 135 as to the upper end plug 134.

[0118] Even with this configuration of the present embodiment, the same effects as those of the first embodiment can be obtained.

[0119] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0120] 1, 11... leaf spring, 1a... intermediate portion of leaf spring, 1b, 1c... end portion of leaf spring, 1d, 11d... protruding portion of leaf spring, 1e... short side of leaf spring, 1f... long side of leaf spring, 2a, 2b, 3a, 3b, 12a, 12b, 13a, 13b, 22a, 22b, 23a, 23b, 32a, 32b, 33a, 33b... support protrusion, 4a... upper opening of upper end plug, 4b... lower opening of upper end plug, 5a... intermediate portion of leaf spring storage section, 5b... end portion of leaf spring storage section, 6... opening communication section, 7... welding section, 8... Opening at end of leaf spring, 8a...fastener insertion hole, 9...fastener, 10...insertion hole stopper, 14a...upper opening of lower end plug, 14b...lower opening of lower end plug, 15a, 15b...notch portion, 20, 30...hexagonal tubular plate, 20a, 20b...end of hexagonal tubular plate, 21, 31...protruding leaf spring, 24a, 24b, 34a, 34b...bent portion for preventing tubular plate from slipping out, 25a, 25b...upper end plug retainer, 36a, 36b...retainer, 100...boiling water reactor, 1 01...Reactor pressure vessel, 102...Core shroud, 103...Reactor core, 104...Shroud head, 105...Steam separator, 106...Steam dryer, 108...Core support plate, 109...Fuel support bracket, 110...Control rod guide tube, 111...Control rod drive mechanism, 113...Internal pump, 114...Downcomer, 115...Main steam pipe, 116...Feedwater pipe, 117...Impeller, 118...Cooling water, 120...Fuel assembly, 121...Fuel rod, 122...Spacer, 123...Lower type Plate, 124...upper tie plate, 125...channel box, 127...upper opening, 128...opening for control rod movement, 129...upper grid plate, 130...handle, 132...cross-shaped control rod, 133...channel spacer, 134...upper end plug, 135...lower end plug, 135a...tapered portion of lower end plug, 136...expansion spring, 137...underside of upper tie plate, 138...insertion hole for upper end plug, 139...insertion hole for lower end plug, 140...movement space for cross-shaped control rod.

Claims

1. A fuel assembly comprising end plugs provided at both upper and lower ends of a fuel rod, and a tie plate supporting at least an upper portion of the end plugs, a plurality of support protrusions on a surface of the end plug, a spring having a closed loop, a portion of which is housed in a single space formed inside the end plug through an opening formed in the end plug and a remaining portion of which protrudes to the outside, and the plurality of support protrusions and the closed loop spring contact an inner wall of an insertion hole formed in the tie plate to support the end plug.

2. 2. The fuel assembly of claim 1, 10. A fuel assembly according to claim 9, wherein the support projections are provided on the surface of the end plug in two directions at intervals of 120 degrees, and the springs are provided in one direction.

3. 3. The fuel assembly of claim 2, the support protrusion and the spring are semicircular in shape so that when the end plug is inserted into the insertion hole formed in the tie plate, the contact portion between the support protrusion and the spring is in point contact or near point contact, and the spring is shaped to have a protruding portion that protrudes in one location.

4. 4. The fuel assembly of claim 3, a spring having a closed loop formed by a portion of the spring and an end of the remaining portion being housed in the single space through one of the two openings formed in the end plug, and the support protrusion, the closed loop spring, and an inner wall of the insertion hole formed in the tie plate form a lateral support structure for the end plug.

5. 5. The fuel assembly of claim 4, the two openings are an upper opening and a lower opening formed in the upper and lower parts of the end plug, and the single space is an opening communication part that communicates the upper opening and the lower opening within the end plug.

6. 6. The fuel assembly of claim 5, The fuel assembly is characterized in that the spring is a leaf spring in which a rectangular plate material having short and long sides is folded in half around a middle portion of the plate material to form a closed loop.

7. 7. The fuel assembly of claim 6, a fuel assembly wherein the leaf spring is formed into a closed loop by welding both ends or near both ends of the short sides of the leaf spring, or by forming notches near both ends of the short sides of the leaf spring and fixing the leaf spring by fitting the notched portions together, or by fixing the leaf spring using openings formed near both ends of the short sides of the leaf spring, fasteners for preventing the openings from shifting in position, fastener insertion holes for passing the fasteners into the end plugs, and insertion hole stoppers for preventing the fasteners from slipping out of the fastener insertion holes.

8. 8. The fuel assembly of claim 7, a leaf spring middle portion storage portion capable of storing a leaf spring middle portion of the leaf spring folded in two is formed above the opening communication portion, and a leaf spring end portion storage portion capable of storing both end portions of the leaf spring formed into a closed loop is formed below the opening communication portion.

9. A fuel assembly comprising end plugs provided at both upper and lower ends of a fuel rod, and a tie plate supporting at least an upper portion of the end plugs, a cylindrical plate disposed around the end plug and having a cylindrical or polygonal cross section, wherein the end plug is inserted into the cylindrical plate and brought into contact with the cylindrical plate, thereby fixing the cylindrical plate onto the end plug; and the cylindrical plate has a protruding spring and a plurality of support protrusions on the outside of the cylindrical plate to face the inner wall surface of the tie plate, wherein the protruding spring, the plurality of support protrusions, and the inner wall of an insertion hole formed in the tie plate form a lateral support structure for the end plug.

10. 10. The fuel assembly of claim 9, a support protrusion provided on an outer surface of the hexagonal cylindrical plate in two directions at intervals of 120° and a protruding spring provided in one direction;

11. 11. The fuel assembly of claim 10, a fuel assembly characterized in that a plurality of protruding end plug holders are provided on the inside of the hexagonal cylindrical plate so as to face the end plugs, and the end plugs and the hexagonal cylindrical plate are integrated by point contact between the plurality of end plug holders and the end plugs.

12. A fuel assembly comprising end plugs provided at both upper and lower ends of a fuel rod, and a tie plate supporting at least an upper portion of the end plugs, a cylindrical plate disposed around the end plug and having a cylindrical or polygonal cross section, wherein the end plug is inserted into the cylindrical plate and brought into contact with the cylindrical plate, thereby fixing the cylindrical plate onto the end plug; and the cylindrical plate has a protruding spring and a plurality of support protrusions on the inside of the cylindrical plate so as to face the outer surface of the end plug, wherein the protruding spring, the plurality of support protrusions, and the end plug form a lateral support structure for the end plug.

13. 13. The fuel assembly of claim 12, a support protrusion provided on an inner surface of the hexagonal cylindrical plate in two directions at intervals of 120° and a protruding spring provided in one direction;

14. 14. The fuel assembly of claim 13, a plurality of protruding restraining portions are provided on the outside of the hexagonal cylindrical plate so as to face the tie plate, and the tie plate and the hexagonal cylindrical plate are integrated by point contact between the plurality of restraining portions and the tie plate.

15. 15. The fuel assembly according to any one of claims 12 to 14, a hexagonal cylindrical plate having a tubular bent portion at each of both longitudinal ends thereof for preventing plate slip-out, and the tubular bent portions for preventing plate slip-out are hooked onto the upper and lower surfaces of the tie plate, thereby forming a lateral support structure for the end plug at the installation height of the tie plate.

Images