FAST NEUTRON REACTOR FUEL ROD

Abstract

The invention relates to nuclear technology and may be used in preparing fuel rods and fuel assemblies for the cores of fast-neutron reactors utilizing a liquid-metal coolant. The invention reduces metal content of a fuel rod the contact stresses occurring in a fuel rod casing in a reactor core during nuclear fuel burnup. The fast neutron reactor fuel rod includes nuclear fuel disposed in a hermetically-sealed container in the form of a thin-walled tubular casing, and a spacing element wound in a wide-pitch spiral and secured to the casing or to the end components. The spacing element is a thin-walled tube having a longitudinal through-slot along the length thereof. Alternatively, the spacing element is made of a thin-walled tube or a thin band having a middle portion in the form of a tube with a longitudinal through-slot of a set width, and end components of fragments of the cylindrical casing.

Claims

1. A fuel rod of a fast-neutron reactor, comprising: nuclear fuel disposed in a hermetically-sealed container being comprised of a thin-walled tubular casing and end components, and a spacing element wound in a wide-pitch spiral around an outer surface of the casing and secured to ends of the casing or to said end components, wherein said spacing element is comprised of a thin-walled tube having a longitudinal through-slot along a length thereof and end components to secure said spacing element.

2. The fuel rod, according to claim 1, wherein a slot width in the spacing element tube is in the range from 0.1 to 0.3 of the outer diameter of the tube.

3. The fuel rod, according to claim 2, wherein a slot width in a middle part of the tube is more than that of the slot on the periphery.

4. The fuel rod, according to claim 1, wherein a wall thickness of the tube is in the range from 0.25 to 1 of the thickness of the fuel rod casing.

5. The fuel rod, according to claim 1, wherein the spacing element is comprised of the same steel as the fuel rod casing.

6. The fuel rod, according to claim 1, wherein end sections of the spacing element are comprised of a fragment of a cylindrical casing to be secured to the casing and/or the end component of the fuel rod.

7. The fuel rod, according to claim 1, wherein end sections of the spacing element are welded to the casing of the fuel rod.

8. The fuel rod, according to claim 1, wherein end sections of the spacing element are welded to the end components of the fuel rod.

9. The fuel rod, according to claim 1, wherein one end section of the spacing element is welded to the end component, and another one is welded to the casing of the fuel rod.

10. The fuel rod, according to claim 1, wherein the spacing element is comprised of a thin-walled tube provided with a longitudinal slot.

11. The fuel rod, according to claim 1, wherein the spacing element is comprised of a longitudinal fragment cut out from a tube for production of the fuel rod casing.

12. The fuel rod, according to claim 1, wherein the spacing element is comprised of a thin tape of stainless steel which is used to produce the fuel rod casing.

13. The fuel rod, according to claim 1, wherein the slot is formed by folding inside longitudinal edges of the tube.

14. The fuel rod, according to claim 1, wherein the tube of the spacing element is filled with coolant material.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0037] The present invention is explained drawings shown in FIGS. 1 to 6, where some embodiments of the fuel rod, the spacing element, and the method are illustrated in detail.

[0038] FIG. 1 is a cross-section view of a fuel rod with a spacing element in the form of a thin-walled tube with a longitudinal slot is shown.

[0039] FIG. 2 is a cross-section view of a fuel rod with a spacing element in the form of a thin-walled tube with a longitudinal slot is shown, where the tube is filled, entirely or partially, with a coolant material, e.g., with lead.

[0040] FIG. 3 is an end elevation view of an end section of the fuel rod is shown with a spacing element welded to a casing.

[0041] FIG. 4 are sectional views of a scheme of cutting out a longitudinal segment is shown for making a spacing element from a tube for a fuel rod casing according to a second embodiment of the method.

[0042] FIG. 5 are sectional views of a scheme of forming a spacing element according to the second embodiment of the method: a) without an insert, c) with an insert in the form of a lead wire.

[0043] FIG. 6 is an overall elevation view of a spacing element is shown.

DETAILED DESCRIPTION OF THE INVENTION

[0044] A fuel rod (1) in accordance with one of the embodiments of the present invention (see FIG. 1, FIG. 2 and FIG. 3) comprises a thin-walled casing (2) which has ends sealed with end components (3). A spacing element (4), comprising a tube (5) with a longitudinal slot (6), end sections (7) and a transition section (8), is wound around an outer surface of the casing (2) a wide-pitch spiral. An edge (9) of the end section (7) is welded to the casing (2). Nuclear fuel (10) and, if necessary, other components and materials, such as fuel holders, elements from non-fissible materials, metal melts, etc. (not shown) are arranged inside the casing (2). Inside the tube (5) can comprise a coolant material (11), e.g., lead which is included in the form of a wire into a composition of the spacing element during manufacturing thereof.

[0045] The fuel rod (1) configuration compensates the irradiation-induced swelling of casings in a reactor core in the result of compressibility and deformation of the tube (5) provided with the slot (6) having a width from 0.1 to 0.3 of an outer diameter of the tube (5). The transversal deformation of the tube (5) within the slot width doesn't provoke any considerable increase of contact stresses in the casing (2), thus, making the casing more reliable at high burnout temperatures. In addition, such configuration of the fuel rod (1) with the longitudinal slot (6) of said width allows in the reactor core coolant entering and exiting in the tube (5) both in a longitudinal and transverse direction. This decreases the risk of formation of local areas for the accumulation of active impurities from the coolant, as well as superheating and corrosion centers in the casing (2). Including the nonuniform burnout and swelling of the casing (2) in the height of the fuel rod, the slot (6) width can be made unequal and in the middle part of the tube (5) it can be something higher than on the periphery. Such configuration helps to optimize the geometrics stability and the rigidity of fuel assemblies.

[0046] To provide an optimal combination of rigidity of the spacing element (4) and to reduce stresses caused by the transverse deformation, the thickness of a tube (5) wall and end sections (7) of the spacing element is selected in the range of 0.25 to 1 of the thickness of the casing (2) of the fuel rod. Said thickness of the spacing element (4) wall and the use of the same steel as for the casing (2) of the fuel rod helps to create the best possible conditions to achieve strong and reliable welded joints between the end sections (7) and the casing (2) and/or the end components (3). Thanks to such configuration of the fuel rod, various types of welded joints of structural elements can be obtained, such as the end sections (7) can be welded to the casing (2) or to the end components (3), or one end section (7) can be welded to the end component (3) and another one to the casing (2). The width of the slot (6) can be defined not only by the width by inside folding the edges (16) of the tube (5). Such foldings (16) increase the stability of the spacing element (4) shape during fuel rod manufacturing.

[0047] The fuel rod (1) can be made with the spacing element (4) having the tube (5) fully or partially filled with the coolant material (11), e.g., with lead. Such configuration provides the improved structural strength and rigidity of the fuel rod and fuel assemblies formed from this fuel rod during formation of a fast-neutron reactor core. At the reactor start-up and supplying the hot coolant into its core, the lead (11) in the tube (5) is melted and transits into the coolant composition.

[0048] The configuration of the spacing element for the fuel rod according to the present invention and the method of production of the spacing element is illustrated by FIG. 4, FIG. 5 and FIG. 6.

[0049] FIG. 4 shows an overall view a blank (12) which after being wound in a wide pitch around an outer surface of a casing (2) and secured thereon creates a spacing element (4) of a fuel rod. The blank is made in the form of a thin-walled tube (5) and end sections (7) in the form of a fragment of a cylindrical casing with an inner diameter for welding with the casing (2) or an end component (3). The tube (5) and the end sections (7) are interconnected via transition sections (13) the shape of which provides the coupling for welding the end sections (7) with the casing (2) or the end component (3). The end sections (7) can comprise technological sections (not shown) which are specifically used in winding the blank around the fuel rod casing and are removed after the spacing element (4) is secured. The ratio of the dimensions of blank components, the characteristics of the material used for manufacturing thereof are given above with respect to the spacing element (4) in the fuel rod configuration according to the invention.

[0050] The tube (5) can be fully or partially filled with a coolant material (11), e.g., with lead, to fix the shape and sizes the tube (5) when producing the fuel rod and winding the blank (12) around the casing (2).

[0051] In accordance with the first embodiment of the method of production of the spacing element, the blank (12) is formed from a thin-walled tube the casing of which is provided with a through-cut creating a longitudinal slot (6) of a pre-defined width. The width of the slot (6) can be defined not only by the width by inside folding the edges (16) of the tube (5). Such foldings (16) increase the stability of the spacing element (4) shape during fuel rod manufacturing.

[0052] An outer diameter of the thin-walled tube is equal to the diameter of the tube (5) of the spacing element. Then, end sections (7) for welding of the spacing element (4) are formed as fragments of a cylindrical surface with a diameter equal to the outer diameter of the casing and/or an end component. The thin-walled tube is made of stainless steel which is used in the production of the fuel rod casing. To improve the stability of the geometrics of the spacing element (4), prior to forming a longitudinal through-cut in the thin-walled tube, the tube is pre-filled with a coolant material, e.g., by pouring with a lead melt. The length of the blank (12) is defined based on the length and diameter of the casing (2) of the fuel rod, as well as on the pre-define winding pitch of the blank (12) around the casing (2) when the spacing element (4) of the fuel rod is formed.

[0053] In accordance with a second embodiment of the method, the spacing element is formed from a thin stainless steel tape. The most appropriate solution is to make the tape of steel which is used for the fuel rod casing. This steel is highly corrosion-resistant in a metal coolant, e.g., in lead. The tape can be obtained from tubes produced according to the technology used to manufacture fuel rod casings. For this, for instance, the tube (15) can be cut into longitudinal pieces (14) of a fixed length and width and fragments can be further processed (e.g., to increase the thickness), such as they can be rolled out.

[0054] The tube (15) is either identical to tubes for fuel rod casing or is a tube produced after some additional processing of the tube for the casing, e.g., for thickness reduction. The method includes forming (rolling-up) the resulted piece (14) in the form of a tube (5) with a longitudinal through-slot (6) of the pre-defined width having end sections (7) for welding with a casing (2) or end components (3) of a fuel rod. The length of the blank (12) is defined based on the length and diameter of the casing (2) of the fuel rod, as well as on the pre-define winding pitch of the blank (12) around the casing (2) when the spacing element (4) of the fuel rod is formed. If prior to forming a spacing element (4) a longitudinal piece (12) is rolled out, the initial length and width of the piece are selected based on the growth of its sized after rolling-out is finished.

[0055] The tube (5) is formed by any known method, such as by rolling up the piece (14) with its drawing through an outer gauge or by pressing it (rolling up) with forming rollers. A working diameter of forming devices is selected equal to the outer diameter of the tube (5). The width of the slot (6) is formed by calculating the arc length of the piece (14) depending on the tube (4) diameter. The width of the slot (6) can be precisely calibrated by forming folding (16) on one or two edges of the slot (6). The excessive part of the circumference of the tube (5) can be removed during slot (6) calibration when the blank (12) is formed. Peripheral sections (7) of the blank for welding are formed, e.g., using a mandrel with a working diameter equal to the outer diameter of the casing (2) or corresponding to geometrical parameters of the end component (3). To precisely fix the geometrical shape and sizes of elements of the blank (12), a tubular section of the blank is formed by using a central bar in the form of a wire (11) having a diameter equal to the inner diameter of the tube (5). In accordance with one the possible embodiments of blank production, a lead wire (11) is used having a diameter equal to the inner diameter of the tube (5). Thus, it is not necessarily to remove the wire from the tube (5) upon completion of blank (12) formation and to use the blank in the form of such composition in the formation of the spacing element (4) by winding the wire around the casing (2) and then in the production of a fuel rod. Such technical solution allows to make the geometrical shape and sizes of fuel rods more stable and to space them from each other and arrange inside a fuel assembly more regularly.

[0056] In accordance with the first and second embodiment of the method of production of a spacing element, during forming a blank (12) with the use of a drawing die or a mandrel the width of the slot (6) in the tube (5) is needed to be calibrated. In accordance with one of the specific embodiments of the method, such calibration includes forming an increased width of the slot (6) in the middle part of the blank (12) to take into account the nonuniform irradiation-induced fuel swelling in the height of the fuel rod.

[0057] Further are shown examples of production of a spacing element for a fuel rod according to the present invention.

Example 1

[0058] In accordance with the first embodiment of the method, a spacing element (4) is produced having an outer diameter of a tube (5) equal to 4 mm for a fuel rod with an outer diameter of a casing of 12 mm and thickness of 0.5 mm. The casing (2) is made of steel which is highly corrosion-resistant in a lead coolant environment. To produce a blank (12) a thin-walled tube of stainless steel with an outer diameter of 4 mm and a wall thickness of 0.3 mm (i.e., equal to 0.6 of the thickness of the fuel rod casing) is formed by any known methods. The length of the thin-walled tube is defined based on the length and diameter of the casing (2) of the fuel rod, as well as on the pre-define winding pitch of the spacing element (4) around the casing of the fuel rod (1). A longitudinal through-cut with a width of 1 mm (i.e. 0.25 of the outer diameter of the thin-walled tube) is made along the entire thin-walled tube and a tubular part (5) with a slot (6) of the spacing element (4) are formed. Then, end sections (7) are created by expending the thin-walled tube for welding with the casing (2) or end components (3) of the fuel rod in the form of fragments of a cylindrical surface having a radius equal to the radius of the casing (2), i.e. 12 mm.

Example 2

[0059] A spacing element (4) for a fuel rod is produced with sizes shown in Example 1. To produce a blank (12) a thin-walled tube of stainless steel with sizes shown in Example 1 with the outer diameter of 4 mm and a wall thickness of 0.3 mm (i.e., equal to 0.6 of the thickness of the fuel rod casing) is formed. A longitudinal through-cut with a width of 0.4 mm is made along the entire thin-walled tube. Then, by means of a calibration, the final width of the slot (6) of 1.2 mm is formed, i.e. 0.3 of the outer diameter of the thin-walled tube. During calibration, one or both longitudinal edges of the slot are folded inside the tube (5) to form folds (16) with the overall height is 0.7 mm (1.2-0.4). Then, end sections (7) are created by expending the thin-walled tube for welding with the casing (2) or end components (3) of the fuel rod in the form of fragments of a cylindrical surface having a radius equal to the radius of the casing (2), i.e. 12 mm.

Example 3

[0060] A fuel rod element (12) is made with a casing outer diameter of 12 mm, a thickness of 0.5 mm, wherein the outer diameter of the tube (5) is equal to 4 mm. The casing is made of steel which is highly corrosion-resistant in a lead coolant environment. To produce the element (12), a tube (15) is used the diameter, wall thickness and material of which are identical to that of tubes used to produce the fuel casing, i.e. with an outer casing diameter of 12 mm and a thickness of 0.5 mm. The length of the tube (15) for the fragments (14) and blanks (12) is defined based on the length and diameter of the casing (2) of the fuel rod, as well as on the pre-define winding pitch of the spacing element (4) around the casing of the fuel rod (1).

[0061] The tube (15) having a circumference of 37.68 mm is cut into three equal longitudinal fragments (14) having an arc length of 12.56 mm (37.68:3) minus a thickness of a cutting wheel. Having the tool thickness of 0.56 mm, we obtain three fragments (14) with the arc length of 12 mm. These fragments (14) are used to form the blank (12) the outer diameter of the tube (5) equal to 4 mm and the width of the slot (6) equal to 0.25 of the outer diameter of the tube (5) which is 1 mm. The excessive part of the circumference of the tube (5), which in the present case is 0.44 mm, can be compensated by forming folds (16) facing inside the tube (5) on one or two edges of the slot (6). The excessive part of the circumference of the tube (5) is defined as the difference between the sum of the arc length of the fragment (14) which is 12 mm and the width of the slot (6) which is 1 mm and the circumference of the tube (5) which is 12.56 mm (i.e.: 12+112.56=0.44).

[0062] In accordance with a further embodiment, the excessive part of the circumference of the tube (5) can be removed during slot (6) calibration when the blank (12) is formed. The end sections (7) are formed for welding with the casing (2) in the form of fragments of the cylindrical surface having a radius equal to the radius of the casing (2), i.e. 12 mm.

Example 4

[0063] The element (12) for a fuel rod having sizes explained in Example 1 (with a casing outer diameter of 12 mm, a thickness of 0.5 mm, wherein the outer diameter of the tube (5) is equal to 4 mm) is made. To produce the blank (12), the tube (15) is used the diameter, wall thickness and material of which are identical to that of tubes used to produce the fuel casing. As in Example 1, three fragments (14) having an arc length of 12 mm are made. These fragments (14) are used to form the blank (12) the outer diameter of the tube (5) equal to 4 mm and the width of the slot (6) equal to 0.25 of the outer diameter of the tube (5) which is 1 mm. The tube (5) is formed using a lead wire (11) having a diameter of 3 mm, which is previously placed in the center of the blank (12) along the length of the tube (5).

Example 5

[0064] The element (12) for a fuel rod having sizes explained in Example 1 (with a casing outer diameter of 12 mm, a thickness of 0.5 mm, wherein the outer diameter of the tube (5) is equal to 4 mm) is made. To produce the blank (12) the tube (15) is used having a wall thickness of 0.6 of the thickness of the fuel rod casing, i.e. 0.3 mm. The tube (15) is made in the result of a further thermal and mechanical treatment of the tube used to produce the fuel rod casing. The length of the tube (15) for the fragments (14) and blanks (12) is defined based on the length and diameter of the casing (2) of the fuel rod, as well as on the pre-define winding pitch of the spacing element (4) around the casing of the fuel rod (1).

[0065] The tube (15) is cut into longitudinal fragments (14) with an arc length of 12 mm. These fragments (14) are used to form the blank (12) the outer diameter of the tube (5) equal to 4 mm and the width of the slot (6) equal to 0.25 of the outer diameter of the tube (5). The blank (12) is formed as in Example 1. If the blank (12) is formed as in Example, the diameter of the lead wire (11) is 3.4 mm.

Example 6

[0066] In accordance with the second embodiment of the method, a blank (12) is made for the spacing element (4) of a fuel rod having sizes explained in Example 1 (with a casing outer diameter of 12 mm, a thickness of 0.5 mm, wherein the outer diameter of the tube (5) is equal to 4 mm). To produce the element (12) a thin-walled tube of stainless steel with an outer diameter of 4 mm and a wall thickness of 0.3 mm (i.e., equal to 0.6 of the thickness of the fuel rod casing) is formed by any known methods. A longitudinal through-cut with a width of 1 mm (i.e. 0.25 of the outer diameter of the thin-walled tube) is made along the entire thin-walled tube and a tubular part (5) with a slot (6) of the spacing element (4) are formed. Then, end sections (7) are created by expending the thin-walled tube for welding with the casing (2) or end components (3) of the fuel rod in the form of fragments of a cylindrical surface having a radius equal to the radius of the casing (2), i.e. 12 mm.

Example 7

[0067] A fuel rod element (12) is made with a casing outer diameter of 12 mm, a thickness of the casing of 0.5 mm, wherein the outer diameter of the tube (5) is equal to 4 mm. The casing is made of steel which is highly corrosion-resistant in a lead coolant environment. To produce the element (12) a tape is used made of a material for the fuel rod casing. The tape width is 12 mm, the thickness is 0.15 mm (i.e., 0.3 of the casing thickness). Then, the element (12) is formed according to modes explained n Example 3.

Example 8

[0068] In accordance with the first embodiment of the method, a spacing element (4) is produced having an outer diameter of a tube (5) equal to 4 mm for a fuel rod with an outer diameter of a casing of 12 mm and thickness of 0.5 mm. The casing (2) is made of steel which is highly corrosion-resistant in a lead coolant environment. To produce a blank (12) a thin-walled tube of stainless steel with an outer diameter of 4 mm and a wall thickness of 0.3 mm (i.e., equal to 0.6 of the thickness of the fuel rod casing) is formed by any known methods. The length of the thin-walled tube is defined based on the length and diameter of the casing (2) of the fuel rod, as well as on the pre-define winding pitch of the spacing element (4) around the casing of the fuel rod (1). The thin-walled tube is filled with a coolant melt from a nuclear reactor core, e.g., with a lead melt. After cooling down the tube, a longitudinal through-cut with a width of 1 mm (i.e. 0.25 of the outer diameter of the thin-walled tube) is made along the entire tube and a tubular part (5) with a slot (6) of the spacing element (4) are formed. Then, end sections (7) are created by expending the thin-walled tube for welding with the casing (2) or end components (3) of the fuel rod in the form of fragments of a cylindrical surface having a radius equal to the radius of the casing (2), i.e. 12 mm.

[0069] The inventive configuration allows the considerable reduction of metal consumption of a fuel rod by means of a spacing element made in the form of a thin-walled tube. A longitudinal through-slot made in the spacing element of the tube allows to improve its transverse deformability and to reduce local stresses arising in the fuel rod casing when fuel in a reactor core is burnt out. Said technical results help to improve neutron and physical parameters of a fast-neutron reactor core, as well as to improve the operational reliability of fuel rods and fuel assemblies. The technical solution allows to reduce the longitudinal rigidity of the spacing element. This makes possible to wind the blank of the spacing element at the desired tension around a surface of a thin-walled casing without significant deformations of geometrics of the fuel rod. In addition, the inventive configuration provides highly reliable welded joints between the spacing element and the casing which are achieved due to the uniform composition, structure and geometric shape of welded fragments. Said features of the technical solution allow to assume the possibility of its practical application in the manufacture of a fuel rod and fuel assemblies for fast-neutron reactors, for example, with a lead coolant.