Fuel rod for a water-cooled water-moderated nuclear reactor
The simplified fuel element design for PWR reactors addresses complexity and assembly issues by using a cylindrical shell, solid pellets, and a toroidal lower plug, enhancing energy efficiency and safety through increased fuel load and simplified assembly.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- JOINT CO TVEL
- Filing Date
- 2025-09-24
- Publication Date
- 2026-05-21
AI Technical Summary
Existing fuel elements for PWR reactors have complex designs with multiple components, leading to increased labor costs, reduced reliability, and complicated assembly processes, while lacking a lower compensation volume, which affects safety and energy production.
A simplified fuel element design with a cylindrical shell, solid fuel pellets, a spring retainer, and a spacer forming a lower compensation volume, using contact butt welding and a lower plug with a toroidal surface for easy assembly and repair, and incorporating a helium inert atmosphere for corrosion resistance.
Enhances energy efficiency, reliability, and safety by increasing fuel load, simplifying assembly, and reducing pressure within the fuel element, while maintaining structural integrity and thermal conductivity.
Smart Images
Figure RU2025000284_21052026_PF_FP_ABST
Abstract
Description
[0001]
[0002] Fuel element
[0003] water-cooled water-moderated nuclear power reactor
[0004] The invention relates to nuclear engineering and concerns fuel elements (fuel rods) that are part of a fuel assembly (FA) from which the active zone is assembled in a pressurized water-moderated nuclear reactor of the PWR type.
[0005] A nuclear reactor fuel element is known (JPH0540187A, IPC G21C3 / 28, published 1993), which consists of the following parts: an upper plug, a cladding, a lower plug, a fuel column assembled from fuel pellets, a spring clamp, an upper spacer and a lower spacer. The fuel element is sealed by welding the cladding to the upper and lower plugs, while the space
[0006] The space beneath the cladding is filled with an inert gas. The interior of the fuel element is structurally divided into three regions, counting from the bottom plug: the lower compensation volume, containing the lower spacer, which is a hollow tube with a plug and a small hole for gas passage, the fuel column, and the upper compensation volume, containing the upper spacer.
[0007] and a spring lock.
[0008] The disadvantages are that the fuel element structurally consists of a larger number of components (along with the lower one there is an upper spacer), which has a negative impact
[0009] This affects fuel rod reliability, as well as the more complex fuel rod assembly process, leading to increased labor costs. Furthermore, the spring retainer rests directly against the top cap, complicating the process of welding the cladding to the top cap.
[0010] A rod-type fuel element and its manufacturing method are known (RU2092915, IPC G21C3 / 10, G21C21 / 00, published 1997). The fuel element comprises a tubular cladding, a stepped plug welded to it, and ceramic fuel loaded inside the cladding in the form of lower screen pellets made of depleted UO2 and fuel bushings, and again upper screen pellets. The entire column of pellets rests on a spacer and is restrained from above by a clamp to prevent movement of the column during transportation of the fuel elements.
[0011] The fuel element is equipped with a gas cavity—a compensation volume located in the cooler part of the fuel element and designed to collect gaseous fission products during fuel irradiation and pressure increase. The upper plug seals the cladding.
[0012] On the nuclear fuel loading side, it has a smooth, cylindrical, flange-free configuration with a stripping band. A spacer wire is wound at a specific pitch onto the outer surface of the fuel rod cladding, the ends of which are welded to the plugs.
[0013] The disadvantages are that the spacer is a solid column of small height, and it does not provide a lower compensation volume, which reduces the reliability of the heat-generating element.
[0014] The closest analogue is the fuel element (RU2748538, IPC G21C1 / 18, G21C3 / 00, published 2021), which consists of the following parts: a fuel column assembled from fuel pellets with a central hole, a spring retainer, a cylindrical cladding, and upper and lower plugs. The fuel column is placed within the fuel element cladding; the lower end of the lower fuel pellet contacts the lower plug; the upper fuel pellet contacts the spring retainer, which is tension-secured within the cylindrical cladding and maintains the integrity of the fuel column. The upper and lower plugs are hermetically welded into the cylindrical cladding, thereby creating a sealed cavity within the fuel element. When welding the top plug to the cylindrical shell, an inert gas is supplied under pressure into the fuel element to ensure corrosion resistance, strength of the fuel element and thermal conductivity.The lower plug is unique in that it has a slot, a cylindrical recess, a collet section, and a flange with a conical section. During fuel assembly assembly, the lower fuel plug is secured in the fuel assembly support grid by the elasticity of the collet section with the slot. During fuel assembly assembly, the slot is compressed, reducing the outer diameter of the flange to match the inner diameter of the fuel assembly grid. The collet section of the plug is then pushed into the fuel assembly grid until it stops. The slot then expands to its original position, resting the flange's original outer diameter against the fuel assembly grid, thereby preventing axial movement of the lower plug and the fuel element.
[0015] The disadvantages include the shorter fuel rod and fuel column, as well as its diameter, compared to the fuel rods of the proposed design, resulting in a smaller total fuel load in the core, leading to lower power generation. The presence of a collet at the bottom plug and the need to secure the fuel rod in the fuel assembly support grid, which leads to less manufacturability of the fuel rod and its components, as well as complicating the assembly and disassembly process of the fuel rods. The absence of a lower compensation volume negatively impacts the reliability of the lower welded joint and leads to a greater increase in pressure inside the fuel rod during operation.The objective of the invention is to develop and create a new fuel element for fuel assemblies of a PWR-type water-moderated power reactor with increased energy production and a high level of safety, both during operation in the reactor core and during transport and technological operations, to simplify the process of assembling fuel assemblies by optimizing the design of the fuel element using existing technological equipment, and to simplify the repair of fuel assemblies in the event of fuel element depressurization.
[0016] The technical result is an increase in fuel loading and thereby an increase in energy efficiency with an increase in the reliability and safe operation of the fuel element of a water-moderated power reactor, a simplification of the fuel assembly process, and a simplification of the repair of fuel assemblies in the event of fuel element depressurization.
[0017] The essence of the invention is that the fuel element of a water-moderated nuclear power reactor consists of a cylindrical shell sealed with lower and upper plugs concentrically welded to the shell, with an inert atmosphere inside the fuel element containing a fuel column concentrically located in the cylindrical shell, assembled from fuel pellets; a spring retainer consisting of compensating group turns providing an axial force for pressing the fuel column, buffer group turns used when installing the spring retainer in the fuel element shell, and retaining group turns ensuring that the spring retainer is held in a given position due to an interference fit on the inner surface of the cylindrical shell, wherein the fuel column is pressed in the axial direction; wherein the cylindrical shell and the plugs are connected by contact butt welding with a weld joint length,comprising from one to three thicknesses of the wall of the cylindrical shell, and the weld zone does not protrude beyond the diameter of the original cylindrical shell. In this case, helium acts as an inert atmosphere; the fuel pellets are made solid with an outer diameter of 8.17 to 8.22 mm; a spacer is placed under the fuel column, which forms the lower compensation volume and is pressed through the fuel column to the lower plug by means of a spring clamp, and the spacer consists of a tube-shaped body, at the ends of which plugs with through coaxial holes are pressed, and grooves are made on the outer ends of the plugs for the flow of helium into the internal cavity of the spacer, the outer diameter of the plugs is equal to the outer diameter of the spacer body; the lower plug has a stepped profile, while the middle part of the lower plug, located outside the cylindrical shell, is made with a diameter greater than the outer diameter of the cylindrical shell,And the lower end of the lower plug has a toroidal surface, the cross-section of which does not exceed the outer diameter of the cylindrical shell. The compensating group of the spring latch can have from 10 to 80 turns. The diameter of the spring latch wire can be from 1 to 1.7 mm. The length of the fuel column Ьз can be from 4191 to 4209 mm. The length of the lower compensating volume 2 can be from 107 to 127 mm. The length of the fuel element Lo can be from 4548 to 4552 mm. The length of the cladding Li can be from 4523 to 4533 mm. The length of the upper compensating volume of the fuel element Ь can be from 180 to 220 mm. The mass of the fuel column can be from 2260 to 2320 g. The cylindrical shell can be made of zirconium alloy E1 UM, consisting of zirconium with the addition of alloying elements and the content of the main impurities in the following ratio, mass. %: niobium - 0.90-1.10, iron - 0.075-0.135, oxygen - 0.100-0.140, carbon - up to 0.010, hafnium - up to 0,010, zirconium is the rest. The cylindrical shell can be made of zirconium alloy E110 o.c., consisting of zirconium with the addition of alloying elements and the content of main impurities in the following ratio, mass. %: niobium - 0.90-1.10, iron - 0.04-0.07, oxygen - 0.070-0.099, carbon - up to 0.010, silicon - up to 0.02, hafnium - up to 0.010, zirconium is the rest. Fuel pellets can be made with chamfers on the ends.
[0018] The invention is illustrated by the following graphic materials.
[0019] Fig. 1 shows an image of the claimed fuel element.
[0020] Fig. 2 shows an image of the lower plug and spacer.
[0021] Fig. 3 shows an image of the spacer.
[0022] Fig. 4 shows an image of the spacer body.
[0023] Fig. 5 shows an image of the spacer plug.
[0024] Fig. 6 shows an image of the end of the spacer.
[0025] Fig. 7 shows an image of a spring retainer.
[0026] Fig. 8 shows an image of a fuel pellet.
[0027] Fig. 9 shows the calculated maximum fuel temperature depending on local burnout.
[0028] Fig. 10 shows the calculated thickness of the oxide film on the fuel element cladding depending on the local burnup.
[0029] Fig. I shows the calculated circumferential stresses in the fuel element cladding depending on the local burnup.
[0030] Fig. 12 shows the calculated increase in fuel rod diameter as a function of local burnup. Fig. 13 shows the calculated decrease in fuel rod diameter as a function of local burnup.
[0031] Fig. 14 shows the calculated fuel rod elongation depending on the average burnup.
[0032] Fuel element of a water-moderated nuclear power reactor (Fig.
[0033] 1) consists of the following structural elements: a fuel column assembled from fuel pellets (3), a spring retainer (2), a cylindrical shell (4), upper (1) and lower plugs (8), and a spacer.
[0034] The cylindrical cladding (4) is sealed by lower (8) and upper (1) plugs concentrically welded to the cladding (4). The upper (1) and lower (8) plugs are hermetically welded to the cylindrical cladding (4), creating a sealed cavity within the fuel element. When the upper plug (1) is welded to the cylindrical cladding (4), an inert gas is supplied under pressure to the fuel element to ensure corrosion resistance, fuel element strength, and thermal conductivity. Helium can be used as an inert atmosphere.
[0035] The length of the fuel element Lo can be from 4548 to 4552 mm, the length of the cladding Li - from 4523 to 4533 mm.
[0036] The cylindrical shell (4) and plugs (1), (8) are connected by contact butt welding with a weld joint length of one to three times the wall thickness of the cylindrical shell (4). The weld joint zone does not extend beyond the diameter of the original cylindrical shell (4).
[0037] The cylindrical shell (4) can be made of zirconium alloy E110M, consisting of zirconium with the addition of alloying elements and the content of the main impurities in the following ratio, mass. %: niobium - 0.90-1.10, iron - 0.075-0.135, oxygen - 0.100-0.140, carbon - up to 0.010, hafnium - up to 0.010, zirconium - the rest.
[0038] The cylindrical shell (4) can be made of zirconium alloy E110 pure grade, consisting of zirconium with the addition of alloying elements and the content of the main impurities in the following ratio, mass. %: niobium - 0.90-1.10, iron - 0.04-0.07, oxygen - 0.070-0.099, carbon - up to 0.010, silicon - up to 0.02, hafnium - up to 0.010, zirconium - the rest.
[0039] A fuel column assembled from fuel pellets (3) and a spring latch (2) are concentrically placed in a cylindrical shell (4). The fuel column is pressed in the axial direction. The spring latch (2) (Fig. 7) consists of successively arranged turns of a compensating group providing an axial force for pressing the fuel column, turns of a buffer group used when installing the spring latch (2) in the cylindrical shell (4) of the fuel element, and turns of a locking group ensuring that the spring latch (2) is held in a given position due to an interference fit on the inner surface of the cylindrical shell (4). The compensating group of the spring latch may have from 10 to 80 turns. The diameter of the spring latch wire may be from 1 to 1.7 mm.
[0040] Fuel pellets (3) (Fig. 8) are made solid (without a central hole) with an outer diameter d from 8.17 to 8.22 mm. The height L? of the fuel pellet (3) can be selected from 10.0 to 11.0 mm. Fuel pellets (3) can be made with chamfers on the ends, in this case the chamfer angle a can be from 22° to 28°, the chamfer height Ls of the fuel pellet is 0.2 mm, the indentation of the sphere (dimple) Ls of the fuel pellet is from 1.50 to 1.80 mm, the height of the spherical layer Le is 0.12 mm.
[0041] The length of the fuel column - Ьз can be from 4191 to 4209 mm, the mass of the fuel column can be from 2260 to 2320 g.
[0042] A spacer (Fig. 2) is placed under the fuel column, which forms the lower compensation volume and is pressed through the fuel column to the lower plug (8) by means of a spring clamp (2).
[0043] The spacer (Fig. 3) consists of a housing (5) in the form of a tube (Fig. 4), while plugs (6), (7) are pressed into the ends of the housing (5) (Fig. 5). In the plugs (6), (7) through holes are made coaxial with the fuel element. On the outer ends of the plugs (on the upper end of the plug (6), located on top, and on the lower end of the plug (7), located at the bottom) grooves are made for the flow of gas into the internal cavity of the spacer (Fig. 6). The outer diameter of the plugs (6), (7) is equal to the outer diameter of the housing (5) of the spacer.
[0044] The lower fuel pellet (3) with its lower end touches the end of the spacer - the upper base of the plug (6) (Fig. 2, zone B). The spacer with its other end - the lower base of the plug (7) - touches the lower plug (8) (Fig. 2, zone A). The upper fuel pellet (3) touches the end of the spring retainer (2) (Fig. 7, zone B), which is fixed by tension in the cylindrical shell (4) (Fig. 3, zone D) and ensures compression and maintenance of the continuity of the fuel column.
[0045] The length of the lower compensation volume g may range from 107 to 127 mm, the length of the upper compensation volume of the fuel element 1l - from 180 to 220 mm. A distinctive feature of the lower plug (8) is its stepped profile. The middle part of the lower plug (8), located outside the cylindrical shell (4), is made with a diameter greater than the outer diameter of the cylindrical shell (4). The lower end of the lower plug (8) has a toroidal surface, the cross-section of which does not exceed the outer diameter of the cylindrical shell (4).
[0046] The implementation of the lower plug (8) in the manner described above simplifies the process of assembling the fuel assembly, as well as simplifies the repair of the fuel assembly in the event of a fuel element depressurization due to the lack of a fuel element fastening in the fuel assembly support grid.
[0047] In this case, the upper part of the lower plug (8), located inside the cylindrical shell (4), can be made in various ways, and is not limited to the design shown in Fig. 2. In particular, the upper part of the lower plug (8) can be made in the form of a cylinder, or cylinders of different diameters, or a truncated cone, etc.
[0048] The middle part of the lower plug (8) can be a sequentially located cylinder (which has a diameter larger than the outer diameter of the cylindrical shell (4)) and an inverted truncated cone.
[0049] The lower portion of the lower plug (8) may be shaped as a cylinder with a diameter equal to the diameter of the lower base of the truncated cone of the middle portion of the lower plug (8), which has a neck (a cylinder of smaller diameter). The lower end of the lower plug (8), as described above, has a toroidal surface—a closed torus. Designing the lower end of the lower plug (8) in this manner allows for the centering of the fuel element of a pressurized water nuclear reactor during its installation in the spacer grid, which simplifies the fuel assembly assembly process and also simplifies fuel assembly repairs in the event of a fuel element depressurization due to the absence of a fuel element fastening in the fuel assembly support grid.
[0050] The fuel element of a water-moderated nuclear power reactor operates as follows.
[0051] The lower plug (8) is welded to the cylindrical shell (4) using contact butt welding in an inert gas environment, ensuring a hermetic seal at the bottom of the fuel element. The cylindrical shell (4) can be made, in particular, of E110M zirconium alloy or EIO alloy.
[0052] Solid fuel pellets (3) with chamfered ends and an outer diameter of 8.17 to 8.22 mm are placed within a cylindrical shell (4). By eliminating the central hole and increasing the pellet diameter, the fuel load is increased, thereby improving energy efficiency. The fuel column weight is selected from a range of 2260 to 2320 g.
[0053] During the fuel element manufacturing process, the spring latch (2) exerts force on the fuel column axially against the spacer, maintaining the fuel column's integrity. The compensating coils of the spring latch (2) provide the axial force for compressing the fuel column, while the retaining coils of the spring latch (2) retain the spring latch (2) in a predetermined position by tightly fitting it to the inner surface of the cylindrical shell (4)—preventing axial movement of the spring latch (2) along the cylindrical shell (4). The buffer coils ensure the correct installation of the spring latch (2) in the fuel element, preventing damage to the compensating coils due to the installation force.
[0054] The spacer consists of a tube-shaped housing (5), with plugs (6) and (7) pressed into its ends. Plugs (6) and (7) have through holes aligned with the fuel element. Grooves are machined into the outer ends of the plugs.
[0055] When welding the upper plug (1) to the cylindrical shell (4), after pumping out air from the free volume under the shell, helium is supplied into the fuel element, and the upper welded joint is sealed using contact butt welding.
[0056] In this case, the cylindrical shell (4) and plugs (1), (8) are connected by contact-butt welding with the length of the welded joint being from one to three thicknesses of the wall of the cylindrical shell (4), and the zone of the welded joint does not protrude beyond the diameter of the original cylindrical shell (4).
[0057] The middle section of the lower plug (8), located outside the cylindrical shell (4), is made with a diameter slightly larger than the outer diameter of the cylindrical shell (4). The lower end of the lower plug (8) has a toroidal surface.
[0058] The sealed fuel elements formed in the manner described above are assembled into fuel assemblies loaded into the nuclear reactor core. The design of the lower plug (8) with a toroidal surface of the lower end, as well as with a diameter of the middle part of the lower plug (8) greater than the outer diameter of the cylindrical cladding (4), ensures a simplification of the fuel assembly process. During operation of the fuel element, gas enters the internal cavity of the spacer through the grooves of the plugs (6), (7) and through the through holes in the plugs (6), (7) of the spacer, forming a lower compensation volume. The grooves are made uniformly spaced around the circumference and intersect the axis of the spacer. In Figs. 5, 6 a special case of the design of the grooves is shown - diametrically perpendicular. The presence of the lower compensation volume makes it possible to reduce the gas pressure inside the fuel element during operation.The presence of a spacer in the lower compensation volume significantly reduces the thermal impact of the fuel column on the lower plug and welded joint.
[0059] Table 1 presents the calculated values of the fuel element performance criteria.
[0060] Table 1 - Calculated values of thermophysical, strength and deformation criteria for fuel element performance under steady-state operating conditions
[0061]
[0062] Based on the obtained data, it can be concluded that, under normal operating conditions, compared to the prototype fuel element design, the safety factor for one of the main fuel element performance criteria—hoop stress—has increased, and other criteria do not exceed permissible limits. Furthermore, the fuel temperature has been reduced, which positively impacts the reliability and trouble-free operation of the fuel element, including in emergency situations. Thus, by increasing the fuel load, the safety level of nuclear power plants is simultaneously improved.
[0063] Fig. 9 - Fig. 14 show, respectively:
[0064] - calculated maximum fuel temperature depending on local burnout;
[0065] - calculated thickness of the oxide film on the fuel element cladding depending on local burnup; - calculated circumferential stresses in the fuel element cladding depending on local burnup;
[0066] - estimated increase in fuel element diameter depending on local burnup; - estimated decrease in fuel element diameter depending on local burnup; - estimated elongation of fuel element depending on average burnup.
[0067] The graphs (Fig. 9 - Fig. 14) show the Best Estimate (BE) values (black line) and the BEPU area (gray line) - the area of uncertainty of the calculated parameters obtained using a statistical method with varying values of the input parameters.
[0068] Thus, the developed design of the fuel element of a water-moderated nuclear power reactor ensures an increase in fuel loading and, thereby, an increase in energy efficiency with an increase in the reliability and safe operation of the fuel element of a water-moderated nuclear power reactor, a simplification of the fuel assembly process, as well as a simplification of the repair of fuel assemblies in the event of fuel element depressurization, namely:
[0069] the adopted values for the diameter of fuel pellets made without a central hole ensure an increase in the total fuel loading into the active zone, and thereby an increase in energy efficiency;
[0070] The use of a lower plug with a stepped profile, described above, in the fuel element design simplifies the fuel assembly process and also increases its maintainability;
[0071] The use of contact butt welding allows for increased reliability and simplification of the fuel element assembly process;
[0072] When installing the retainer, the inner surface of the shell is cold-worked in the area from the lower end of the upper plug to the area of the retaining group of turns inclusive, which increases the safety margin according to the criterion of loss of stability during hydraulic testing;
[0073] the selected length of the welded joint, which is from one to three thicknesses of the shell wall, and the welded joint zone does not protrude beyond the diameter of the original shell, ensures the reliability and safe operation of the fuel element;
[0074] the presence of a lower compensation volume in the internal cavity of the spacer allows for a reduction in gas pressure inside the fuel element during operation, which has a positive effect on the performance of the fuel element and increases its reliability;
[0075] io the presence of a spacer in the lower compensation volume significantly reduces the thermal impact of the fuel column on the lower plug and welded joint, which increases the reliability of the fuel element.
[0076] Particular variants of the invention are:
[0077] - the use of E110 high-purity or E110M alloy as the material for cylindrical shells, which allows for a reduction in neutron absorption by the shell by reducing the amount of hafnium, leading to an increase in energy production;
[0078] The use of helium as an inert gas under the cladding, with a mass fraction in the final product in the range from 90.0 to 99.9%, increases the thermal conductivity and corrosion resistance of the inner surface of the fuel element cladding.
Claims
Invention formula 1. A fuel element of a water-moderated nuclear power reactor, consisting of a cylindrical shell sealed with lower and upper plugs concentrically welded to the shell, with an inert atmosphere inside the fuel element, containing a fuel column made up of fuel pellets placed in a cylindrical shell, a spring retainer consisting of compensating group turns providing an axial force for pressing the fuel column, buffer group turns used when installing the spring retainer in the fuel element cladding, and locking group turns ensuring that the spring retainer is held in a given position by being pressed against the inner surface of the cylindrical cladding, while the fuel column is pressed in the axial direction, wherein the cylindrical shell and plugs are connected by contact-butt welding with the length of the welded joint being from one to three thicknesses of the wall of the cylindrical shell, and the zone of the welded joint does not protrude beyond the diameter of the original cylindrical shell, characterized in that helium acts as an inert atmosphere, fuel pellets are made solid with an outer diameter of 8.17 to 8.22 mm, a spacer is placed under the fuel column, which forms the lower compensation volume and is pressed through the fuel column to the lower plug by means of a spring clamp, and the spacer consists of a housing in the form of a tube, at the ends of which plugs with through coaxial holes are pressed, and on the outer ends of the plugs there are grooves for the flow of helium into the internal cavity of the spacer, the outer diameter of the plugs is equal to the outer diameter of the spacer housing, the lower plug has a stepped profile, wherein the middle part of the lower plug, located outside the cylindrical shell, is made with a diameter greater than the outer diameter of the cylindrical shell, and the lower end of the lower plug has a toroidal surface, the cross-section of which does not exceed the outer diameter of the cylindrical shell.
2. A heat-generating element according to paragraph 1, characterized in that the compensating group of the spring retainer has from 10 to 80 turns.
3. A heat-generating element according to paragraph 1, characterized in that the diameter of the spring retainer wire is from 1 to 1.7 mm.
4. A fuel element according to paragraph 1, characterized in that the length of the fuel column Ьз is from 4191 to 4209 mm.
5. A fuel element according to paragraph 1, characterized in that the length of the lower compensation volume r is from 107 to 127 mm.
6. A fuel element according to paragraph 1, characterized in that the length of the fuel element Lo is from 4548 to 4552 mm.
7. A fuel element according to claim 1, characterized in that the length of the shell Li is from 4523 to 4533 mm.
8. The fuel element according to paragraph 1, characterized in that the length of the upper compensation volume of the fuel element L4 is from 180 to 220 mm.
9. A fuel element according to paragraph 1, characterized in that the mass of the fuel column is from 2260 to 2320 g.
10. A fuel element according to claim 1, characterized in that the cylindrical shell is made of zirconium alloy E110M, consisting of zirconium with the addition of alloying elements and a content of basic impurities in the following ratio, mass %: niobium - 0.90-1.10, iron - 0.075-0.135, oxygen - 0.100-0.140, carbon - up to 0.010, hafnium - up to 0.010, zirconium - the rest.
11. A fuel element according to claim 1, characterized in that the cylindrical shell is made of a zirconium alloy of ENO high purity grade, consisting of zirconium with the addition of alloying elements and a content of basic impurities in the following ratio, mass %: niobium - 0.90-1.10, iron - 0.04-0.07, oxygen - 0.070-0.099, carbon - up to 0.010, silicon - up to 0.02, hafnium - up to 0.010, zirconium - the rest.
12. A fuel element according to paragraph 1, characterized in that the fuel pellets are made with chamfers on the ends.