Nuclear reactor assembly having a reversible weldless connection between a casing and an element inserted therein

Abstract

An assembly to be inserted into a nuclear reactor, such as a liquid sodium-cooled fast neutron reactor, includes an assembly hollow body of elongate shape along a longitudinal axis X. The wall of the hollow body includes at least one through-opening. The assembly also includes an assembly element inserted into the hollow body. The assembly element includes at least one flexible blade of which the free end is shaped into a clip-fastening hook collaborating in clip-fastening fashion with the through-opening from inside the hollow body, so as to connect the assembly element to the hollow body. The assembly also includes at least one removable structure for locking the flexible blade clip-fastened into the through-opening. The removable locking structure makes it possible to prevent the flexible blade from flexing and thus the removable locking structure makes it possible to lock a connection between the assembly element and the hollow body.

Claims

1. An assembly intended to be inserted into a nuclear reactor, comprising: an assembly hollow body, of elongate shape along a longitudinal axis X, a wall of the hollow body comprising at least one through-opening that extends through the wall; an assembly element inserted at least in part into the hollow body, the assembly element comprising at least one flexible blade of which a free end is shaped into a clip-fastening hook collaborating in clip-fastening with the through-opening from inside the hollow body, so as to connect the assembly element to the hollow body; and at least one removable means for locking the at least one flexible blade clip-fastened into the through-opening, each of the at least one removable means for locking including a locking screw making it possible to prevent the at least one flexible blade from flexing and thus lock the connection between the assembly element and the hollow body.

2. The assembly according to claim 1, wherein the clip-fastening hook is produced by a thickening of the free end of the at least one flexible blade.

3. The assembly according to claim 1, wherein the hollow body is of hexagonal cross section and each face of the hexagon comprises one through-opening, and the at least one flexible-blade includes a flexible blade clip-fastened into each of the through-openings.

4. The assembly according to claim 1, wherein the locking screw of each of the at least one removable means for locking, when in a position in which the locking screw is screwed into the at least one flexible blade, makes it possible to prevent the at least one flexible blade from flexing and from becoming unclipped.

5. The assembly according to claim 1, wherein each of the at least one flexible blade is produced by cutting into a thickness of the assembly element.

6. The assembly according to claim 5, wherein the wall of the assembly hollow body comprises at least one open-ended bore designed to allow the locking screw to pass from the outside of the hollow body and a screw head to be housed.

7. The assembly according to claim 1, wherein each of the at least one flexible blade is attached and fixed to the assembly element by a fixing screw.

8. The assembly according to claim 7, wherein each fixing screw is welded to the assembly element and/or to the at least one flexible blade in its screwed-in position.

9. The assembly according to claim 8, wherein the assembly element comprises at least one cavity in which the clip-fastening hook can become lodged when the at least one flexible blade is in the flexed position, the locking screw being screwed through the clip-fastening hook and housed in the cavity when the at least one flexible blade is clipped in, so as to prevent the at least one flexible blade from flexing.

10. The assembly according to claim 1, wherein the assembly is a nuclear fuel assembly, the hollow body being a central portion forming a casing configured to clad fuel pins, the assembly element being an upper neutron shield (UNS) device or the assembly element forming an upper portion forming a gripper head of the assembly.

11. The assembly according to claim 1, wherein the nuclear reactor is a liquid sodium-cooled fast neutron reactor.

12. The assembly according to claim 1, wherein the assembly element includes a shoulder and, when the assembly element is inserted into the assembly hollow body, a top of the assembly hollow body abuts the shoulder of the assembly element.

13. A method for assembling the assembly according to claim 1, wherein the assembly comprises at least two of the flexible blades, the method comprising: a/ inserting the assembly element into the assembly hollow body by a translational movement, so as to achieve simultaneous flexing of the at least two flexible blades toward the inside of the hollow body, lowering of the assembly element down inside the hollow body until the at least two flexible blades return to their position with their hooks clip-fastened into the corresponding through-openings of the hollow body so as to connect the hollow body to the assembly element; and b/ locking each of the at least two flexible blades clip-fastened into the through-opening using the at least one removable means for locking.

14. A method for dismantling the assembly according to claim 1, wherein the assembly comprises at least two of the flexible blades, the method comprising: a1/ unlocking each of the at least two flexible blades, the hook of each of which is clip-fastened into the corresponding through-opening, by removing the at least one removable means for locking; b1/ applying a radial force to the hook of each of the at least two flexible blades from the outside of the through-opening, so as to cause the at least two flexible blades to flex simultaneously toward the inside of the hollow body, unclipping the hooks; and c1/ extracting the assembly element from inside the assembly hollow body via a translational movement.

15. The dismantling method according to claim 14, wherein the assembly element comprises a plurality of the flexible blades and the hook of each of the flexible blades is individually clip-fastened into the corresponding through-opening of the hollow body and locked, step b1/ being performed by simultaneous actuation of actuators, and arranged individually facing one of the through-openings.

Description

DETAILED DESCRIPTION

(1) Further advantages and features of the invention will become better apparent from reading the detailed description of the invention which is given by way of nonlimiting illustration and with reference to the following figures among which:

(2) FIG. 1 is an external perspective view of a fuel assembly according to the prior art, already used in an SNF sodium-cooled nuclear reactor;

(3) FIG. 2 is a view in cross section of the assembly depicted in FIG. 1;

(4) FIGS. 3, 3A and 3B are external perspective views of, respectively, part of a fuel assembly with the connection according to the invention made between the central portion constituting the assembly body and the UNS body; the assembly body and the UNS body before they are connected;

(5) FIGS. 4, 4A and 4B depict the same elements as FIGS. 3 to 3B from a different perspective;

(6) FIGS. 5A and 5B show, schematically in a view in longitudinal section, a first alternative form of embodiment of the flexible-blade connection with locking according to the invention in a fuel assembly, respectively in the locked position and in the process of assembly, in instances in which the flexible blade is produced by cutting into the UNS body;

(7) FIGS. 6A and 6B show, schematically in a view in longitudinal section, a second alternative form of embodiment of the flexible-blade connection with locking according to the invention in a fuel assembly, respectively in the locked position and in the process of assembly, in instances in which the flexible blade is mounted on the UNS body;

(8) FIGS. 7A, 7, 8 and 8A are views of the central portion in the region of the pad ring with and without the pad ring in the assembled position;

(9) FIGS. 9 and 10 illustrate the method of uninserting an element assembled in a hollow component according to the invention.

(10) For the sake of clarity, the same references denoting the same elements of fuel assembly and of strap spacer devices according to the prior art and according to the invention are used throughout FIGS. 1 to 10.

(11) Throughout the present application, the terms vertical, lower, upper, bottom, top, below and above are to be understood with reference to a fuel assembly such that it is in a vertical configuration inside a nuclear reactor.

(12) FIGS. 1 and 2 which relate to the prior art have already been described in detail in the preamble and are therefore not commented upon hereinafter.

(13) The weldless connection according to the invention between the assembly hollow body 12 (central portion) and an assembly element 14 which is the UNS of a fuel assembly is depicted in FIGS. 3 to 4B from different angles. The central portion 12 and the UNS 14 are depicted in the assembled position and separately.

(14) A thickening 21 is produced at the end of the flexible blade 20 of the UNS and, in the assembled position, namely when the UNS body 14 is inserted into the central portion 12, clips into an open-ended opening 122 of the central portion. For preference, as illustrated, the lower part of the thickening 21 is chamfered to make it easier for the blade 20 to flex as the UNS 1 engages in the end of the hexagonal tube.

(15) As shown in FIGS. 5A to 6B, once the thickening 24 has clip-fastened into the opening 122 of the tube 12, the shoulder 22 produced on the upper part of the UNS 14 comes into abutment with the top of the tube 12, whereas the shoulder 24 produced on the upper part of the thickening 21 is in abutment against the upper edge 124 of the opening 122.

(16) According to this alternative form illustrated, extraction of the UNS from the hollow component 12 is prevented by the discontinuous profile of the thickening 21 defined by the shoulder 24 at the end of the blade, whereas deeper insertion of the UNS into the hollow component 12 is prevented by the profile defined by the shoulder 22 of the UNS 14, of which the exterior cross section above the head designed for insertion into the hollow component is substantially identical to that of the hollow component.

(17) In this way is obtained a weldless connection which allows the manufacture and sizing of a fuel assembly to be simplified considerably as described. Furthermore, the risk of migrating bodies (screws, pegs, etc.) becoming introduced into the primary cooling circuit is avoided.

(18) As illustrated in FIGS. 5A and 5B, the flexible blade 20 may be respectively cut into the assembly element 14, if the latter is of small thickness.

(19) Alternatively, as shown in FIGS. 6A and 6B the blade 20 may be attached to the element 14 using a fixing screw 40, in cases in which the element 14 is of sufficient thickness. Once the connection has been assembled, the fixing screw 40 is itself secured by the presence of the tube 12.

(20) In the assembled position illustrated in FIGS. 5A and 6A, the flexible blade 20 is mechanically locked, by a locking screw 42 which is added after the element 14 has been inserted into the hollow component 12.

(21) In the alternative form of FIG. 5A, the locking screw 42 is screwed through a hole 123 provided for this purpose in the tube 12 into a tapping 23 made in the blade 20, this tapping 23 being opposite the tapping 123 when the blade 20 is in the clip-fastened position.

(22) In the alternative form of FIG. 6A, the locking of the blade by the screw 42 to prevent the blade from flexing is achieved via its end which comes into abutment against the body of the assembly element 14.

(23) If a locking screw 42 is used, a retaining weld needs to be performed in order to prevent it from accidentally loosening and therefore to safeguard its position within the assembly. This screw 42 has no mechanical strength function and therefore the risk of losing this screw is minimal. Furthermore, loss of this screw would not necessarily lead to loss of the connection. Care would be taken to ensure, by design, that the head of the screw 42 is sunk into the thickness of the casing 12 or of the flexible blade 20, so that this head does not extend beyond the volume formed by the casing.

(24) As illustrated in FIGS. 5A and 5B, the flexible blade 20 comprises an overhang 25 measuring a few millimeters around the entire periphery of the thickened portion 21. The role of this overhang 25 is to best cover the open-ended opening 122 of the casing and thus form a kind of labyrinth for the liquid metal, thus making it possible to minimize the leakage of metal through this opening.

(25) FIGS. 7A to 8A illustrate the weldless connection according to the invention in a shutdown rod between a pad ring 17 and a hollow component 12, the pads 18 being situated in the same plane as the spacer straps 121 of the hollow component 12. The two components are depicted separately and in the assembled positon.

(26) In this instance, there are two flexible blades 20 on one same face of the ring 17 facing in two opposite directions so that in the assembled position the thickened portions 21 lock the position of the pad ring both with respect to an upward movement and with respect to a downward movement of the ring within the hollow component.

(27) Another advantage of a connection according to the invention is the possibility of dismantling an assembly according to the invention fairly easily, even if it is irradiated. Thus, an assembly head for example, which has received far less radiation than a central portion, could be reused, leading to savings in terms of economy and in terms of waste management.

(28) One way of uninserting two elements assembled according to the invention is given in FIGS. 9 and 10. In this example, a collar 3 supporting actuators 30 is inserted around the hollow component 12. The number of actuators 30 is equal to the number of flexible blades 20, 21. Each actuator is positioned facing a thickening 21 of a blade 20.

(29) When the assembly is to be dismantled, the actuators 30 are actuated simultaneously and thus apply radial pressure to the thickened portion 21 of each blade, so that the element 14 is no longer connected to the hollow component 12 and can be extracted through an upward translational movement.

(30) Other alternative forms and improvements may be made without in any way departing from the scope of the invention.

(31) Thus, while in the embodiments illustrated the flexible blades are locked by a locking screw, it is also possible to envision preventing a flexible blade from flexing by using an internal elastic ring housed in a groove provided for this purpose in the flexible blade on the inside.

(32) The invention is not restricted to the examples which have just been described. In particular, features of the examples illustrated can notably be combined with one another in alternative forms of embodiment which are not illustrated.

(33) The expression comprising a is to be understood as meaning comprising at least one, unless specified to the contrary.