Nuclear reactor with modular lattice

Abstract

This invention relates to a nuclear reactor with a modular grid. Specifically, a nuclear reactor includes a vessel (2) defining an internal pool (3), a cooling fluid (CF), and a core (6), which is housed within the vessel (2) and has a plurality of fuel elements (8) extending along respective longitudinal axes (A). A grid (10) anchored to the vessel (2) is arranged transversely to the longitudinal axes (A) of the fuel elements (8) to axially suppress the fuel elements (8). The grid (10) includes a plurality of individually removable modular grid members (13). In the operating position, adjacent modular grid members (13) are reversibly locked to each other to prevent relative axial sliding. The modular grid members (13) are custom-shaped such that when a modular grid member (13) is removed from the grid (10), the grid (10) allows the corresponding fuel element (8) to be removed through the open channel left by the removed modular grid member (13).

Description

[0001] Cross-reference to related applications This patent application claims priority to Italian Patent Application No. 102024000029940, filed on December 24, 2024, the entire disclosure of which is incorporated herein by reference. Technical Field

[0002] This invention relates to a nuclear reactor with a modular grid. Background Technology

[0003] As is known, maintaining the correct positioning of the fuel elements forming the core in a nuclear reactor is crucial to ensuring desired performance and safety levels. A common approach involves using grids anchored to the reactor vessel or container to restrain the upper ends of the fuel elements, preventing relative movement in both the axial and radial directions. The role of the grids is particularly important in nuclear reactors that use heavy liquid metals (such as liquid lead) to cool the core. In this case, the cooling fluid effectively provides strong buoyancy to the rising fuel elements, in addition to causing fluid-induced vibrations and drag forces in that velocity direction. Therefore, in this type of nuclear reactor, the grids have the task of counteracting the buoyancy caused by the cooling fluid.

[0004] However, regardless of the cooling fluid used, the stability of fuel elements through a known grid is significantly limited and can cause problems in certain situations. In particular, for maintenance purposes, it is necessary to intervene in fuel elements periodically and in a predetermined sequence, such as to redistribute or replace partially or completely depleted fuel elements. For this purpose, fuel elements must be removed from the reactor core. However, to allow the removal of fuel elements, the grid must be removed, but removing the grid reduces the stability of the fuel element, which may suffer displacement. For example, when a fuel element is removed, the remaining fuel elements typically tend to fill the radial clearance. In such cases, a so-called local "flowering" condition may occur, which can lead to the unintended displacement of one or more fuel elements and persist until the grid is repositioned.

[0005] In reactors cooled by heavy liquid metal, temporary removal of the grid is even more critical because the fuel elements are still subject to the buoyancy of the cooling fluid, and therefore the risk of accidental removal is even greater than for a mere localized "bloom".

[0006] Regardless of the cooling fluid used, the fuel element must therefore be held in place in other ways, either fully or partially submerged in the cooling fluid. However, the operation typically performed using specialized machinery is complex and not without risk. Summary of the Invention

[0007] Therefore, the object of the present invention is to provide a nuclear reactor that allows for overcoming or at least mitigating the described limitations.

[0008] According to one aspect of the present invention, a nuclear reactor is provided, comprising: A container within a defined pool; Cooling fluid in the pool; A reactor core, which is housed in a container and includes a plurality of fuel elements at least partially submerged in cooling fluid, wherein each fuel element extends along a respective longitudinal axis; A grid, which is anchored to the container and arranged transversely to the longitudinal axis of the fuel element, in order to suppress the fuel element axially; The grid comprises multiple individually removable modular grid members, wherein, in the working position, adjacent modular grid members are reversibly locked to each other to prevent relative sliding in a direction parallel to the longitudinal axis of the fuel element, and wherein the modular grid members are custom-shaped such that when a modular grid member is removed from the grid, the grid allows the corresponding fuel element to be removed through the open channel left by the removed modular grid member.

[0009] The grid according to the invention is modularly designed and configured such that individual modular grid members can be removed individually, allowing the removal of the corresponding fuel element while keeping other grid members restrained (or constrained) in the correct operating position. The reversible connection between adjacent modular grid members can be released to release individual modular grid members at a time, leaving other modular grid members axially restrained as in a fully functional normal operating configuration. Therefore, the removal of the fuel element is greatly simplified and can be performed safely and at a significantly lower cost.

[0010] The modular design also allows for the replacement of individual modular grid components in case of damage. Moving parts used to achieve reversible axial restraint between adjacent modular grid components may be subjected to harsh operating conditions in circulating cooling fluids (especially when using heavy liquid metals), in environments exposed to radiation fields, requiring periodic monitoring and potential subsequent replacements. The grid according to the invention allows for the replacement of only the damaged modular grid component, without interfering with the corresponding fuel element, other fuel elements retained in a normal and correctly operating configuration, or other modular grid components. Therefore, grid maintenance is advantageous in both ease of implementation and cost.

[0011] According to one aspect of the invention, each modular grid member is axially aligned with the corresponding fuel element in order to counteract the buoyancy and / or drag force provided to the corresponding fuel element by the cooling fluid.

[0012] In this way, the grid ensures that only the fuel element corresponding to the removed modular grid component can be actually removed, while all other fuel elements are kept in the correct operating position by the modular grid components that remain in place.

[0013] According to one aspect of the invention, each modular grid member is provided with a locking seat and a reversible locking member having: a corresponding locking position in which the locking member engages a corresponding locking seat of a corresponding adjacent modular grid member; and a corresponding retracted position in which the locking member retracts from the corresponding locking seat.

[0014] Therefore, in practice, the reversible locking component of the modular grid member engages the locking seat of the adjacent modular grid member to prevent relative axial slippage and keep the fuel element in the correct working configuration.

[0015] According to one aspect of the invention, each modular grid member includes a body having a cylindrical or prismatic sidewall coaxial with the corresponding fuel element, wherein the sidewall has a first groove defining a corresponding locking seat and a second groove, and wherein a locking member engages the corresponding locking seat through the corresponding second groove in a corresponding locking position.

[0016] According to one aspect of the invention, the locking seat of each modular grid member faces the corresponding second slot of the adjacent modular grid member.

[0017] According to one aspect of the invention, all modular grid members include an equal number of locking elements and locking seats, and in each modular grid member, the corresponding locking elements and corresponding locking seats alternate along the sidewall of the body.

[0018] These measures, individually and in combination, contribute to the simple and compact construction of the grid according to the invention, while ensuring that no significant axial slippage occurs.

[0019] According to one aspect of the invention, the locking components include tabs movable between a corresponding locking position and a corresponding retracted position, in which they are arranged such that a corresponding locking end engages a corresponding locking seat, and in the corresponding retracted position, the locking end retracts into the body.

[0020] The movable tongue is particularly compact and simple to operate and construct. Therefore, the mechanism for actuating the reversible locking occupies little space, is reliable, and is not prone to failure.

[0021] According to one aspect of the invention, each modular grid member includes an actuating element operable to move the locking element between a corresponding locked position and a corresponding retracted position.

[0022] According to one aspect of the invention, in each modular grid member, the actuating components are independently operable.

[0023] The independent operation of the actuation components allows for the release of only the constraints strictly necessary for removing the modular grid components and corresponding fuel elements, leaving all other constraints unchanged to improve robustness and stability.

[0024] According to one aspect of the invention, the body includes a cover having a corresponding guide opening for each locking member, and the actuating member includes a corresponding actuating rod that passes through the corresponding guide opening and protrudes from the cover.

[0025] According to one aspect of the invention, in each modular grid member, the corresponding locking component is simultaneously operable.

[0026] The advantages of simultaneous operation lie primarily in its simplicity, speed, and reliability, especially considering the harsh environment in which the grid is immersed. In fact, only one external actuator is needed to operate the locking mechanism, and the time the actuator remains submerged in the cooling fluid during this process is reduced, which is particularly advantageous when using liquid metals.

[0027] According to one aspect of the invention, each modular grid member includes a shaft coaxial with the corresponding fuel element, and wherein the actuating component includes a corresponding toothed portion of a locking component and a ring gear rotatably mounted on the shaft and engaging with the toothed portion of the locking component.

[0028] The resulting actuation components are particularly simple and robust.

[0029] According to one aspect of the invention, each modular grid member includes a safety device configured to allow the ring gear to rotate about the axis in an operating configuration and to prevent the ring gear from rotating about the axis in a safety configuration.

[0030] Safety devices prevent locking components from accidentally moving from their respective locked positions, and thus prevent the risk of a fuel element being mistakenly released without adequate protection.

[0031] According to one aspect of the invention, the safety device includes a safety ring nut, which is angularly fixedly mounted on a shaft and cooperates with the axial margin of a ring gear to form a releasable front coupling, wherein one of the ring gear and the safety ring nut is axially fixed, while the other of the ring gear and the safety ring nut is slidable along the shaft axially between an operating position and a safe position. In the operating position, the front coupling is released and the ring gear is free to rotate, and in the safe position, the ring gear is engaged with the safety ring nut and the front coupling prevents the ring gear from rotating.

[0032] According to one aspect of the invention, the ring gear engages with the toothed portion of the corresponding locking member in both the operating position and the safe position.

[0033] According to one aspect of the invention, one of the ring gear and the safety ring nut, which is fixed axially, is arranged at the top, and the ring gear and the safety ring nut are held together by buoyancy provided by the cooling fluid in the absence of external force.

[0034] According to one aspect of the invention, one of the ring gear and the safety ring nut is fixed axially at the bottom, and the ring gear and the safety ring nut are held together by gravity in the absence of external force.

[0035] The resulting safety device is particularly simple and reliable. In practice, when the cooling fluid comprises heavy liquid metal, the axially fixed element of the safety device can be positioned at the top, and the buoyancy provided by the cooling fluid itself tends to spontaneously maintain the front connection between the ring gear and the safety ring nut, preventing the ring gear from rotating. When the cooling fluid alternatively comprises water or molten salt, the axially fixed element of the safety device can be positioned at the bottom, and the front connection is maintained by gravity. In either case, once operation is complete, no parts or mechanisms are required to restore the connection between the ring gear and the safety ring nut. Attached Figure Description

[0036] To better understand the present invention, some preferred embodiments are given by way of non-limiting example with reference to the accompanying drawings: - Figure 1 This is a schematic diagram of a nuclear reactor, in which; - Figure 2 yes Figure 1 A simplified and enlarged top plan view of the components of a nuclear reactor; - Figure 3 This is an embodiment of the present invention. Figure 2 A magnified perspective view of the components, in which parts have been cut off for clarity; - Figure 4 yes Figure 3Details along Figure 2 A side view cut by the trace plane IV-IV; - Figure 5 yes Figure 3 Details along Figure 2 A perspective view cut by the trace plane IV-IV; - Figure 6 yes Figure 3 The details are shown in the top plan view of the first configuration, where parts have been cut off for clarity; - Figure 7 yes Figure 3 The details are shown in the top plan view of the second configuration, where parts have been cut off for clarity; - Figure 8 These are different embodiments of the present invention. Figure 2 A magnified perspective view of the components, in which parts have been cut off for clarity; - Figure 9 yes Figure 8 The top plan view of the details, in which parts have been cut off for clarity; - Figure 10 and Figure 11 They were displayed respectively Figure 8 Details are shown in the side views of the first operating configuration and the second operating configuration; - Figure 12 and Figure 13 Different embodiments according to the present invention are shown respectively. Figure 2 Details of the components are shown in the side views of the first operating configuration and the second operating configuration; - Figure 14 and Figure 15 Another embodiment of the invention is shown respectively. Figure 2 Details of the components are shown in side views in the first operating configuration and the second operating configuration; and - Figure 16 and Figure 17 Other embodiments according to the present invention are shown respectively. Figure 2 Details of the components are shown in the side views of the first operating configuration and the second operating configuration. Detailed Implementation

[0037] refer to Figure 1The nuclear reactor according to an embodiment of the invention is designated by number 1 and includes a container 2 that internally defines a pool 3, an internal isolation structure 5 that is open at the bottom, and a core 6 housed within the internal isolation structure 5. The container 2 is also provided with a sealing element 7 at the top. A cooling fluid CF (e.g., a heavy liquid metal, such as, but not limited to, liquid lead, bismuth, or a lead-bismuth eutectic alloy) is contained in the pool 3 and circulates through the core 6 in the internal isolation structure 5 due to a circulation pump not shown or by natural circulation. However, it is understood that the invention can also be used in reactors cooled with different fluids (e.g., molten salt or water).

[0038] The reactor core 6 is housed within the container 2, and more specifically, within the internal isolation structure 5, and includes a plurality of fuel elements 8 at least partially submerged in the cooling fluid CF. Each fuel element 8 extends along a corresponding longitudinal axis A, which is substantially vertically arranged in use, and has an active portion 8a (corresponding to the area where fuel resides), a head 8b in an upper position, a rod 8c defined by a structural extension of the element itself having the same or different shape and connecting the head 8b to the active portion 8a, and a foot 8d defined by a sufficiently rigid portion in the lower portion of the element. In the illustrated embodiment, the fuel elements 8 have a hexagonal cross-section perpendicular to the corresponding longitudinal axis A, but they may have different shapes, such as square or circular, depending on design preference.

[0039] The nuclear reactor 1 also includes a grid 10, which is anchored to the vessel 2 and arranged transversely to the longitudinal axis A of the fuel elements 8. In a non-limiting embodiment, the grid 10 has a honeycomb shape, as shown in... Figure 2 As shown in the plan view. The grid 10 can be fixed, for example, to the anchoring structure 12 of the closure element 7, which in turn is rigidly connected to the container 2. Alternatively, the grid 10 can be directly fixed to the internal isolation structure 5. The grid 10 counteracts the buoyancy and drag force provided by the cooling fluid CF (which is particularly strong in the case of liquid metal), and suppresses the fuel element 8 axially, and limits the vibrations induced by the cooling fluid CF in the radial direction.

[0040] refer to Figures 3 to 7 The grid 10 includes a plurality of modular grid members 13, which are arranged coaxially with corresponding fuel elements 8 in the operating position. The modular grid members 13 are individually removable, and adjacent modular grid members 13 are reversibly locked to each other in the operating position to prevent relative sliding in the vertical direction. The outer modular grid members 13a are fixed to the anchoring structure 12 and, through the anchoring structure 12, to the container 2.

[0041] Furthermore, the modular grid member 13 is axially aligned with the head 8b of the corresponding fuel element 8 and is shaped to resist the upward axial force (attributed to the buoyancy and drag force of the cooling fluid CF) and to allow the corresponding fuel element 8 to be removed from the grid 10 through the open channel left by the removed modular grid member when a modular grid member 13 is removed from the grid 10.

[0042] More specifically, each modular grid member 13 includes a body 15 having a sidewall 15a that is conformable to the cross-section of the fuel element 8 (in this case, a prism with a hexagonal base), such that the head 8b of the fuel element 8 remains abutted against the body 15 of the corresponding modular grid member 13 due to the buoyancy provided by the cooling fluid CF.

[0043] Each modular grid member 13 is also provided with a reversible locking component, which, in the non-limiting embodiment described herein, is defined by a rotating lug 17 and a locking seat 18. Alternatively, the reversible locking component may include a sliding lug or pin, other types of cams or eccentric wheels, and any means generally suitable for preventing relative sliding between two bodies along an axis.

[0044] The tongue 17 is rotatably supported by a plate 20 about a corresponding axis of rotation R that is parallel to the longitudinal axis A of the fuel element and is therefore substantially vertical. The plate 20 is fixed to the body 15, for example, to a sidewall 15a and / or to the base 15b of the corresponding body 15. The plate 20 is also drilled and coaxially mounted to a shaft 15c of the body 15 with respect to the corresponding fuel element 8. In the non-limiting embodiment described herein, the shaft 15c allows cooling fluid circulation through the corresponding modular grid member 13. However, in other embodiments, the shaft may be solid, and cooling fluid circulation may be provided by other fluid channels through the body 15.

[0045] exist Figures 3 to 7 In this embodiment, each tongue 17 has a locking end 17a and an actuating end 17b angled relative to each other, and an actuating element is provided at the actuating end 17b. Specifically, the actuating element is defined by an actuating rod 22 perpendicular to the respective axis of rotation R. Furthermore, the body 15 includes a cover 15d having a corresponding circular guide opening 24 for each tongue 17. The actuating rod 22 of the tongue 17 passes through the corresponding guide opening 24 and protrudes upward from the cover 15d for operation by an external actuator (e.g., incorporated into a working machine not shown here). Since the tongue 17 rotates about its respective axis of rotation, the locking end 17a can exit through the sidewall 15a of the body 15; for this purpose, the sidewall 15a is provided with a groove 25 extending along a plane perpendicular to the axis of rotation of the tongue 17.

[0046] The locking seat 18 is defined by a groove in the side wall 15a of the body 15, corresponding to the tongue 17 of the adjacent modular grid member 13. The groove defining the locking seat 18 faces the corresponding groove 25 and is coplanar with it. Specifically, in Figures 3 to 7 In one embodiment, in each modular grid member 13, the locking seat 18 and the slot 25 are located on alternating surfaces of the sidewall 15a, such that each locking seat 18 of the modular grid member 13 faces a corresponding slot 25 of an adjacent modular grid member 13. All modular grid members 13 include the same number of tabs 17 and locking seats 18, and in each modular grid member 13, the corresponding tab 17 alternates with the corresponding locking seat 18 along the sidewall 15a of the body 15.

[0047] The protruding tongue 17 is rotatable between the corresponding locked position and the corresponding retracted position. In the locked position ( Figure 6 The tab 17 engages the corresponding locking seat 18 of the adjacent modular grid member 13 via a locking end 17a extending through the corresponding slot 25. In this configuration, the modular grid members 13 are axially bound together by the mutual engagement of the tab 17 and the locking seat 18, preventing relative axial slippage. In the retracted position ( Figure 7 The central modular grid member 13 in the body has a tongue 17 that retracts from the corresponding locking seat 18 and is fully arranged inside the body 15, or in any case so as not to impede relative axial sliding with respect to the adjacent modular grid member 13.

[0048] exist Figures 3 to 7 In one embodiment, the actuating rods 22 of the tongue 17 are independently operable to move the tongue 17 itself between a corresponding locked position and a corresponding retracted position.

[0049] Figure 8 and Figure 9Different embodiments of the invention are illustrated, wherein components corresponding to those already shown are indicated by the same reference numerals. In this case, the grid 110 comprises a plurality of modular grid members 113 that are reversibly locked to each other to prevent relative sliding in the vertical direction. Each modular grid member includes a body 115, a reversible locking member defined by a tab 117, and a locking seat 118 defined in a sidewall 115a of the body 115. Essentially as already described, the tab 117 is movable, and in particular rotatable, between a corresponding locked position and a corresponding retracted position. In the corresponding locked position, the tab 117 engages the corresponding locking seat 118 of the adjacent modular grid member 113 to prevent relative sliding. In the corresponding retracted position, the tab 117 retracts from the corresponding locking seat 118 and is fully disposed within the body 115, or in any case so as not to impede relative axial sliding with respect to the adjacent modular grid member 113. The slot 125 of the corresponding locking seat 118 facing the adjacent modular grid member 113 allows the locking end 117a of the tongue 117 to pass through the side wall 115a of the body 115 to reach the corresponding locking seat 118.

[0050] exist Figure 8 and Figure 9 In this embodiment, the tabs 117 operate simultaneously. Specifically, each tab 117 has a corresponding toothed actuating end 117b opposite the locking end 117a, and each modular grid member 113 includes a ring gear 122 that engages with the toothed actuating end 117b of the tab 117. In each modular grid member 113, the body 115 includes a shaft 115c coaxial with the corresponding fuel element 8, and the ring gear 122 is rotatably mounted on the shaft 115c to allow the corresponding tab 117 to rotate between a locked position and a retracted position.

[0051] Each modular grid member 113 also includes a safety device configured to allow the ring gear 122 to rotate about the shaft 115c in an operating configuration and to prevent the ring gear 122 from rotating about the shaft 115c in a safety configuration. The safety device includes a safety ring 130, which is axially and angularly fixed to the shaft 115c and cooperates with the axial edge 122a of the ring gear 122 to form a releasable front coupling 131. Specifically, the ring gear 122 is axially positioned along the shaft 115c in the operating position (… Figure 10 ) and safe location ( Figure 11The front coupling 131 is slidable between the two. In the operating position, the front coupling 131 is released and the ring gear 122 rotates freely. In the safe position, the ring gear 122 is engaged with the safety ring 130 and the front coupling 131 prevents the ring gear 122 from rotating. The ring gear 122 is custom-shaped to engage the toothed actuating end 117b of the corresponding tongue 117 in both the operating and safe positions, and is held engaged with the safety ring 130 by buoyancy provided by the cooling fluid CF in the absence of external force. The working machine (not shown) lowers the ring gear 122 against the buoyancy to operate the tongue 117 and then retracts, allowing the ring gear to engage with the safety ring 130.

[0052] Alternatively, for example when the cooling fluid is water or molten salt (whose specific gravity is much lower than that of the fuel element), the ring gear 122 can be fixed axially and movable angularly, while the safety ring 130 can be movable axially and fixed angularly, such as... Figure 12 (Manipulation position) and Figure 13 As shown in (Safety Position). In this configuration, the safety ring 130 engages the ring gear 122 by falling under gravity and is lifted by the machine to allow the ring gear 122 to rotate and the tab 117 to operate.

[0053] According to respectively in Figures 14 to 17 In another embodiment shown, the ring gear 122 can be fixed axially and is angularly movable, and the ring gear 122 and the safety ring 130 are relative to each other. Figures 8 to 13 The embodiment is reversed, in which the safety ring 130 is placed below the ring gear 122.

[0054] exist Figure 14 (Manipulation position) and Figure 15 In the embodiment of the (safe position) configuration, the ring gear 122 is fixed axially and movable angularly, while the safety ring 130 is movable axially and fixed angularly. In this case, when the cooling fluid CF is a heavy liquid metal, the safety ring 130 is held connected to the ring gear 122 by the buoyancy provided by the cooling fluid CF.

[0055] exist Figure 16 (Manipulation position) and Figure 17 In the embodiment of the (safe position), the ring gear 122 is movable axially and angularly, while the safety ring 130 is fixed axially and angularly. In this case, when the cooling fluid is water or molten salt, the ring gear 122 engages the safety ring 130 by falling under gravity and is lifted and rotated by a machine to operate the tongue 117.

[0056] Ultimately, it is clear that modifications and variations can be made to the nuclear reactors described and shown herein without departing from the scope of protection of the invention as defined in the appended claims.

[0057] For example, the shape and type of movement of the locking components may differ from those described, and may specifically include sliding pins and tabs instead of rotating pins and tabs, or cams or other eccentric components.

Claims

1. A nuclear reactor, comprising: Container (2), which internally defines a pool (3); Cooling fluid (CF) in the pool (3); The reactor core (6) is housed in the container (2) and includes a plurality of fuel elements (8) at least partially submerged in the cooling fluid (CF), wherein each fuel element (8) extends along a corresponding longitudinal axis (A); A grid (10; 110) is anchored directly or indirectly to the container (2) and arranged transversely to the longitudinal axis (A) of the fuel element (8) in order to axially suppress the fuel element (8); The grid (10; 110) comprises a plurality of individually removable modular grid members (13; 113), wherein, in the working position, adjacent modular grid members (13; 113) are reversibly locked to each other to prevent relative sliding in a direction parallel to the longitudinal axis (A) of the fuel element (8), and wherein the modular grid members (13; 113) are custom-shaped such that when one of the modular grid members (13; 113) is removed from the grid (10; 110), the grid (10; 110) allows the corresponding fuel element (8) to be removed through the open channel left by the removed modular grid member (13; 113).

2. The nuclear reactor of claim 1, wherein, Each modular grid member (13; 113) is aligned axially with the corresponding fuel element (8) to counteract the buoyancy and / or drag force supplied to the corresponding fuel element by the cooling fluid.

3. The nuclear reactor of claim 1, wherein, Each modular grid member (13; 113) is provided with a locking seat (18; 118) and a reversible locking member (17; 117), the locking member (17; 117) having a corresponding locked position and a corresponding retracted position, in which the locking member (17; 117) engages the corresponding locking seat (18; 118) of the corresponding adjacent modular grid member (13; 113), and in the corresponding retracted position, the locking member (17; 117) retracts from the corresponding locking seat (18; 118).

4. The nuclear reactor of claim 3, wherein, Each modular grid member (13; 113) includes a body (15; 115) having a cylindrical or prismatic sidewall (15a; 115a) coaxial with the corresponding fuel element (8), wherein the sidewall (15a; 115a) has a first groove and a second groove (25; 125) defining a corresponding locking seat (18; 118), and wherein the locking member (17; 117) engages the corresponding locking seat (18; 118) through the corresponding second groove (25; 125) in the corresponding locking position.

5. The nuclear reactor according to claim 4, wherein, The locking seat (18; 118) of each modular grid member (13; 113) faces the corresponding second slot (25; 125) of the adjacent modular grid member (13; 113).

6. The nuclear reactor of claim 4, wherein, All of the modular grid members (13; 113) include an equal number of locking elements (17; 117) and an equal number of locking seats (18; 118), and in each modular grid member (13; 113), the corresponding locking element (17; 117) and the corresponding locking seat (18; 118) alternate along the sidewall (15a; 115a) of the body (15; 115).

7. The nuclear reactor of claim 3, wherein, The locking member (17; 117) includes a tongue movable between the respective locked position and the respective retracted position, wherein in the respective locked position the tongue is arranged to engage the respective locking seat (18; 118) by a respective locking end (17a; 117a), and in the respective retracted position the locking end (17a; 117a) is retracted inside the body (15; 115).

8. The nuclear reactor of claim 3, wherein, Each modular grid member (13; 113) includes an actuating element (22; 122) operable to move the locking element (17; 117) between the corresponding locked position and the corresponding retracted position.

9. The nuclear reactor of claim 8, wherein, In each modular grid member (13; 113), the actuating component (22) can operate independently of each other.

10. The nuclear reactor of claim 8, wherein, The body (15) includes a cover (15d) having a corresponding through guide opening for each locking member (17), and the actuating member (22) includes a corresponding actuating rod that engages the corresponding guide opening and protrudes from the cover (15d).

11. The nuclear reactor of claim 8 wherein, In each modular grid component (113), the corresponding locking component (117) can operate simultaneously.

12. The nuclear reactor of claim 11, wherein, Each modular grid member (113) includes a shaft (115c) coaxial with the corresponding fuel element (8), and wherein the actuating member (122) includes a corresponding toothed portion (117b) of the locking member (117) and a ring gear (122) rotatably mounted on the shaft (115c) and engaging the toothed portion (117b) of the locking member (117).

13. The nuclear reactor of claim 12, wherein, Each modular grid member (113) includes a safety device (122a, 130, 131) configured to allow the ring gear (122) to rotate about the shaft (115c) in an actuation configuration and to prevent the ring gear (122) from rotating about the shaft (115c) in a safety configuration.

14. The nuclear reactor of claim 13, wherein, The safety device (122a, 130, 131) includes a safety ring (130) which is angularly fixedly mounted on the shaft (115c) and cooperates with the axial edge (122a) of the ring gear (122) to form a releasable front coupling (131). One of the ring gear (122) and the safety ring (130) is axially fixed, while the other of the ring gear (122) and the safety ring (130) is axially slidable along the shaft (115c) between an operating position and a safe position. In the operating position, the front coupling (131) is released and the ring gear (122) is free to rotate. In the safe position, the ring gear (122) is engaged with the safety ring (130) and the front coupling (131) prevents the ring gear (122) from rotating.

15. The nuclear reactor of claim 14, wherein, The ring gear (122) engages the toothed portion (117b) of the corresponding locking member (117) in both the operating position and the safe position.

16. The nuclear reactor of claim 14, wherein, One of the ring gear (122) and the safety ring (130) is fixed axially above, and in the absence of external force, the ring gear (122) and the safety ring (130) are kept connected to each other by the buoyancy provided by the cooling fluid (CF).

17. The nuclear reactor of claim 14, wherein, One of the ring gear (122) and the safety ring (130) is fixed axially at the top, and the ring gear (122) and the safety ring (130) are connected to each other by gravity in the absence of external force.

18. The nuclear reactor of claim 1, wherein, The modular grid members (13; 113) include external modular grid members (3a; 13a) anchored to the container (2) via an anchoring structure (12).

19. The nuclear reactor of claim 1, wherein, The cooling fluid (CF) includes liquid metal, molten salt, or water.

20. The nuclear reactor of claim 1, wherein, Each fuel element (8) has an active portion (8a), a head (8b), and a rod (8c) connecting the head (8b) to the active portion (8a), wherein the head (8b) is arranged to abut against the corresponding modular grid member (13; 113) axially opposed.

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