Natural convection heat dissipation structure for packaging radioactive materials for transport

Abstract

The invention relates to a natural convection heat dissipation structure (30) intended to equip the outer surface of a lateral body of a packaging (1) for the transport of radioactive materials, the structure comprising, at each of a first (46a) and a second side (46b) of a fictitious median plane (P) of the structure: - a first heat dissipation sub-assembly (40a), comprising first primary fins (42a) having a first inclination such that, going in a first direction (8a) of the axial direction, each first primary fin (42a) extends in a first direction (7a) of the circumferential direction (7); - a second heat dissipation sub-assembly (40b), comprising second primary fins (42b) having a second inclination different from the first.Furthermore, the first and second subsets form first and second sets incorporating first and second fins (52a, 52b) in a general V shape. Figure 7.

Description

Title of the invention: NATURAL CONVECTION HEAT DISSIPATION STRUCTURE FOR TRANSPORT PACKAGING OF RADIOACTIVE MATERIALS Technical field

[0001] The present invention relates to the field of the evacuation of heat produced by radioactive materials loaded into a radioactive material transport package.

[0002] More specifically, the present invention relates to a structure for dissipating heat by natural convection, intended to equip the outer surface of a lateral body of a packaging for the transport of radioactive materials, for example nuclear fuel assemblies or radioactive waste. STATE OF THE PRIOR ART

[0003] From the prior art, it is known to assemble an external heat evacuation device around an external surface of a lateral body of a package, with the aim of evacuating, to the ambient environment, the calories emitted by the radioactive materials contained in the package.

[0004] This heat evacuation device is designed in particular to limit the temperature reached by the various constituent elements of the packaging during its transport, in particular the seals and the radiological protections, in order to avoid any risk of degradation of these elements.

[0005] Furthermore, in addition to being able to perform its main function of heat exchanger with the ambient environment, this device is designed to be compatible with the service constraints of the packaging, such as decontaminability, durability, resistance to atmospheric aggression, resistance to operating conditions, or even confinement of the neutron shielding resin.

[0006] During transport, the packaging is in a horizontal lying position, i.e. with its longitudinal axis oriented horizontally, or substantially horizontally. The natural convection heat dissipation structure must therefore have high performance in the horizontal transport position of the packaging.

[0007] A known solution consists of a covering shell surrounding the lateral body of the packaging, and onto which longitudinal straight fins of appropriate section are welded. These fins are also called vertical, because they are oriented in the vertical direction when the packaging itself rests vertically.

[0008] However, due to the orientation of the fins, this solution does not allow for correct heat evacuation when the packaging is in a horizontal transport position.

[0009] A solution disclosed in document FR 3 045 143 A1 is also known. This has a design that is also suitable for the evacuation of heat in the vertical storage position of the packaging, but is not intended to maximize thermal performance during horizontal transport of the packaging.

[0010] Therefore, there remains a need to improve the design of external heat removal devices, in order to provide increased thermal performance when the package is in a horizontal, lying transport position. Statement of the invention

[0011] To this end, the invention firstly relates to a structure for dissipating heat by natural convection, intended to equip the external surface of a lateral body of a package for the transport of radioactive materials, the heat dissipating structure extending around a longitudinal axis of the structure, intended to correspond to a longitudinal axis of the package, of horizontal orientation when the package is in a horizontal transport position,

[0012] the heat dissipation structure comprising at least, at each of a first and a second side of a fictitious median plane of the structure passing through its longitudinal axis:

[0013] - a first heat dissipation subassembly, comprising first primary fins parallel to each other and inclined locally with respect to a circumferential direction of the structure and with respect to an axial direction of this structure, so as to have a first inclination such that each first primary fin extends in a first direction of the circumferential direction, going in a first direction of the axial direction;

[0014] - a second heat dissipation subassembly, comprising second primary fins parallel to each other and inclined locally with respect to the circumferential direction of the structure and with respect to the axial direction, so as to have a second inclination different from the first, and such that each second primary fin extends in a second direction of the circumferential direction opposite to the first direction, going in the first direction of the axial direction.

[0015] Furthermore, on the first side of the fictitious median plane, the first and second subsets are adjacent and follow one another in the axial direction so as to form a first set within which at least some of the first and second primary fins form two by two of the first fins in the general shape of a V which follow one another in the circumferential direction, with the tip of the V oriented in the first circumferential sense,

[0016] and on the second side of the fictitious median plane, the first and second subsets are adjacent, succeeding each other in the axial direction so as to form a second set within which at least some of the first and second primary fins form two by two second fins in the general shape of a V which succeed each other in the circumferential direction, with the tip of the V oriented in the second circumferential direction.

[0017] The invention offers great ease of manufacturing of the heat dissipation structure, while providing high thermal performance when the packaging, equipped with such a structure, is arranged in a horizontal transport position. Indeed, by judiciously adjusting the angular position of the heat dissipation structure around the longitudinal axis of the packaging, for example by providing that the fictitious median plane of its heat dissipation structure is oriented vertically or substantially vertically, the tips of the first and second fins arranged on either side of this plane can be oriented upwards.

[0018] Thus, on either side of the packaging in relation to the fictitious median plane, primary channels are defined between the directly consecutive primary fins. These primary channels form two by two channels also in the general shape of a V, the tips of which are also all oriented upwards.

[0019] This inverted V shape is advantageous in that it allows the air particles to be accelerated within the primary channels, which provides increased thermal performance. Indeed, this is explained by the presence of vortices which form above the primary channels, and which promote the acceleration of the air between the suction zones located at the base of the inverted Vs and the discharge zones located at the tip of the inverted Vs on these primary channels.

[0020] Furthermore, thanks to the proposed design, the heat dissipation structure can also offer satisfactory thermal performance when the transport packaging rests in a vertical position, resting on its bottom.

[0021] The invention furthermore preferably has at least one of the following optional features, taken alone or in combination.

[0022] Preferably, on the first side of the fictitious median plane, several first sets are adjacent, succeeding one another in the axial direction and / or in the circumferential direction, their numbers preferably being greater than or equal to three in each of these two directions, and on the second side of the fictitious median plane, several second sets are adjacent, succeeding one another in the axial direction and / or in the circumferential direction, their numbers preferably being greater than or equal to three in each of these two directions.

[0023] As will be described below, the manner in which these sets follow one another according to the circumferential direction may differ depending on the preferred embodiments of the invention. Thus, on each side of the fictitious median plane, the assemblies may, for example, adopt a matrix arrangement, or even a staggered arrangement.

[0024] According to a preferred embodiment of the invention, the fictitious median plane forms a plane of symmetry for the heat dissipation structure, each first assembly then being arranged symmetrically with respect to one of the second assemblies.

[0025] Preferably, any transverse plane of the structure passes through:

[0026] or:

[0027] - a succession of first subsets of the first side of the fictitious median plane, the first subsets succeeding one another in the circumferential direction, extending jointly over an angular sector preferably equal to or close to 180°; and

[0028] - a succession of second subsets on the second side of the fictitious plane, the second subsets succeeding one another in the circumferential direction, extending jointly over an angular sector preferably equal to or close to 180°,

[0029] or:

[0030] - a succession of first subsets on the second side of the fictitious median plane, the first subsets succeeding one another in the circumferential direction, extending jointly over an angular sector preferably equal to or close to 180°; and

[0031] - a succession of second subsets on the first side of the fictitious median plane, the second subsets succeeding one another in the circumferential direction, extending jointly over an angular sector preferably equal to or close to 180°.

[0032] According to another preferred embodiment of the invention, the heat dissipation structure is asymmetrical with respect to any fictitious median plane passing through the longitudinal axis.

[0033] Preferably, any transverse plane of the structure then passes through:

[0034] or a succession of first subsets of the first and second sides of the plane median fictitious, the first subsets succeeding one another in the circumferential direction, extending jointly over an angular sector preferably equal to or close to 360°,

[0035] or a succession of second subsets on the first and second sides of the fictitious median plane, the second subsets succeeding one another in the circumferential direction, extending jointly over an angular sector preferably equal to or close to 360°.

[0036] According to yet another preferred embodiment of the invention, the heat dissipation structure is symmetrical with respect to the fictitious median plane, or asymmetrical,

[0037] and on the first side of the fictitious median plane, several first sets are arranged in a staggered pattern, while on the second side of the fictitious median plane, several second sets are arranged in a staggered pattern.

[0038] Preferably, any transverse plane of the structure crosses in this case, on each of the first and second sides of the fictitious median plane, an alternation of first and second sub-assemblies in the circumferential direction, this alternation extending over an angular sector preferably equal to or close to 180°.

[0039] Whatever the preferred embodiment envisaged, the heat dissipation structure is preferably produced using several longitudinal plates succeeding one another in the circumferential direction, each plate comprising an alternation in the axial direction of first and second sub-assemblies.

[0040] Thus, each plate has primary fins with alternating orientations, forming a zig-zag configuration along the axial direction. The plates may nevertheless have another configuration of primary fins, without departing from the scope of the invention. For the implementation of the primary fins, it is also possible to replace the successive plates in the circumferential direction, by successive rings in the axial direction of the structure, around the packaging body, each ring preferably comprising several adjacent sets following one another in the circumferential direction.

[0041] Preferably, each plate extends over the entire or substantially the entire axial length of the structure, preferably being made in one piece. These primary fin plates can nevertheless be cut along the axial direction, without departing from the scope of the invention.

[0042] Preferably, the first and second primary fins are produced by machining, preferably from aluminum or copper, or from one of their alloys.

[0043] Preferably, at the tip of the V of at least some of the first and second fins, the first and second primary fins are in contact with each other, or an axial spacing is provided between them. In the latter case, the spacing adopted may contribute to forming a sort of circumferential channel passing through the tip of the Vs of several fins.

[0044] Preferably, the heat dissipation structure has a generally annular shape, centered around its longitudinal axis.

[0045] Finally, the invention also relates to a packaging for the transport of radioactive materials, comprising a heat dissipation structure as described above, equipping the outer surface of the lateral body of the packaging.

[0046] Other advantages and characteristics of the invention will appear in the detailed non-limiting description below. Brief description of the drawings

[0047] This description will be made with regard to the attached drawings among which;

[0048] [Fig. 1] represents a front view of a packaging for the transport of radioactive materials, in a lying position, comprising a heat dissipation structure according to a first preferred embodiment of the present invention;

[0049] [Fig.2] represents a partial sectional view taken along line II-II of [Fig.l];

[0050] [Fig.3] is an enlarged front view of a longitudinal plate forming part of the heat dissipation structure;

[0051] [Fig.3A] is an enlarged view of a longitudinal plate similar to that shown in [Fig.3], but intended to be located on a second side of a fictitious median plane of the annular heat dissipation structure;

[0052] [Fig.4] is a sectional view taken along line IV-IV of [Fig.3]; and

[0053] [Fig.5] is an enlarged view of a portion of the plate shown in [Fig.3];

[0054] [Fig.6] is a view similar to that of [Fig.5], according to an alternative embodiment;

[0055] [Fig.7] is an enlarged and more detailed perspective view of a portion of the heat dissipation structure, according to the first preferred embodiment of the invention;

[0056] [Fig.8] is a front view of the structure shown in the preceding figure;

[0057] [Fig.9] is a view similar to that of [Fig.7], in which the sets of dis heat sipation have been highlighted;

[0058] [Fig. 10] is a view similar to that of [Fig.8], in which the first and second heat dissipation assemblies have been highlighted;

[0059] [Fig. 11] is a view similar to that of [Fig.7], in which the structure is in the form of a second preferred embodiment of the invention;

[0060] [Fig.12] is a view similar to that of [Fig.11], in which the first and second heat dissipation assemblies have been highlighted;

[0061] [Fig. 13] is a view similar to that of [Fig. 8], in which the structure is in the form of a third preferred embodiment of the invention; and

[0062] [Fig.14] is a view similar to that of [Fig.13], in which the first heat dissipation assemblies have been highlighted. DETAILED DISCLOSURE OF PREFERRED EMBODIMENTS

[0063] Referring firstly to figures 1 and 2, there is shown a package 1 for the transport of radioactive materials, such as nuclear fuel assemblies or radioactive waste (not shown).

[0064] This packaging 1 is shown in [Fig.l] in the horizontal transport position, called lying position, in which its longitudinal axis 2 is oriented horizontally or substantially horizontally.

[0065] The packaging comprises a packaging base 4, opposite a removable cover 6 in an axial direction 8 of the packaging, parallel to the longitudinal axis 2 and also called the longitudinal direction. This longitudinal direction defines a first direction 8a going from the cover 6 towards the base 4, as well as a second direction 8b opposite the first direction 8a, and going from the base 4 towards the cover 6.

[0066] The packaging 1 also comprises a lateral body 10 extending around the axis 2, and internally defining a cavity 12 for housing the radioactive materials.

[0067] The lateral body 10 generally comprises a concentric inner ferrule 14 and an outer ferrule 16, defining an annular space 18 centered on the axis 2. The space 18 is for example filled by thermal conduction means 20 connecting the two ferrules 14, 16, as well as by neutron protection means 22. The aforementioned means 20, 22 are of conventional design and will therefore not be described further.

[0068] The two ferrules 14, 16 extend along a circumferential direction 7 of the packaging, this direction defining a first direction 7a corresponding to the counterclockwise direction on the section of [Fig.2], as well as a second direction 7b opposite to the first direction 7a, and corresponding to the clockwise direction on this same figure.

[0069] The outer shell 16 comprises an annular heat dissipation structure 30, or such a structure is fixedly attached to the outer surface of the packaging around this shell 16, preferably by welding.

[0070] In the preferred embodiments which will be described below, the heat dissipation structure 30 is produced using several longitudinal plates 32, succeeding one another in the circumferential direction 7, for example being welded to each other, and possibly also welded to the heat conduction elements 20 of the packaging.

[0071] Each longitudinal plate 32 has an axial length “L” extending over the entire axial length of the structure 30, being made in a single piece. This axial length of the plates 32 is also close to the total axial length of the packaging, since it is preferentially provided that each plate covers the entirety or almost the axial length of the lateral body 10 of the packaging, only the cover 6 and the bottom 4 not being covered. The axial length “L” of the plates 32 can be between 2 and 5 m.

[0072] The plates 32, provided with fins, have a width in the circumferential direction which remains largely less than the axial length. Thus, by placing the plates 32 end-to-end in this direction 7, the heat dissipation structure 30 has a generally annular shape, centered around the axis 2 which also corresponds to its longitudinal axis. The number of plates 32 can be between 5 and 40.

[0073] As can be seen in [Fig. 2], the plates 32 each comprise a base in the form of a flat or substantially flat rectangular plate, this base comprising two opposite longitudinal edges. As mentioned previously, the bases of the plates 32 are assembled end-to-end by welding at their facing edges, so as to reconstitute the external shell 16, or to extend around it.

[0074] One of the plates 32 is partly shown in Figures 3 and 4.

[0075] It comprises, in the axial direction 8, an alternation of first sub-assemblies 40a and second sub-assemblies 40b, dedicated to cooling by comprising primary cooling fins projecting radially from the base of the plate 32.

[0076] More precisely, each first heat dissipation subassembly 40a comprises first primary fins 42a parallel to each other. These first primary fins 42a are inclined locally with respect to the two directions 7, 8, that is to say that they form a non-zero angle with each of these two directions. They are made so as to have a first inclination, referenced A1 in [Fig. 3], and which symbolizes the fact that by going in the first direction 8a of the axial direction, each first primary fin 42a extends in the first direction 7a of the circumferential direction 7. As an indication, the angle between the primary fin 42a and each of the two directions 7, 8 can be of the order of 45°, or more broadly between 30 and 60°.

[0077] Similarly, each second heat dissipation subassembly 40b comprises second primary fins 42b parallel to each other. These second primary fins 42b are inclined locally with respect to the two directions 7, 8, that is to say that they also form a non-zero angle with each of these two directions. They are made so as to have a second inclination, referenced A2 in [Fig. 3], and which symbolizes the fact that by going in the first direction 8a of the axial direction, each second primary fin 42b extends in the second direction 7b of the circumferential direction 7. For information, the angle between the primary fin 42b and each of the two directions 7, 8 can be of the order of 45°, or more broadly between 30 and 60°.

[0078] Due to the alternation of the first and second sub-assemblies 40a, 40b within the plate 32, the primary fins 42a, 42b of opposite inclinations, taken as a whole, then have a so-called zig-zag configuration along the plate. Preferably, the primary fins 42a, 42b have a constant section.

[0079] Each subassembly 40a, 40b has a generally square or rectangular shape, the sides of which are locally parallel to the directions 7, 8, respectively. Several primary fins 42a, 42b are provided within each subassembly 40a, 40b, by example in a number between 5 and 20. Due to their inclinations, their lengths differ within each subset 40a, 40b.

[0080] Between two first primary fins 42a directly consecutive, a first primary channel 44a is formed for circulating the external cooling air, just as between two second primary fins 42b directly consecutive, a second primary channel 44b is formed for circulating the external cooling air. The primary fins 42a, 42b have a radial height for example of one to several centimeters, while the width of the channels 44a, 44b delimited by these primary fins 42a, 42b is also preferably of the order of one to several centimeters.

[0081] The plate 32 shown in Figures 3 and 4 is intended to be located on one side among a first and a second side of a fictitious median plane P of the structure 30, passing through its axis 2 while being here vertical or substantially vertical. In other words, the fictitious median plane P virtually cuts the structure 30 into two half-shells, each in the shape of a C facing each other.

[0082] As regards the first side 46a of the median plane visible in [Fig.7], also comparable to the first side of the structure 30, each plate 32 is of the type shown in FIGS. 3 and 4. According to a feature of the invention, each pair of first and second sub-assemblies 40a, 40b adjacent and directly consecutive in the axial direction 8, forms a first assembly 50a within which at least some of the first and second primary fins 42a, 42b form two by two of the first fins 52a in the general shape of a V, which follow one another in the circumferential direction. For these plates 32 of the first side 46a of the plane P, the tip of the V is oriented in the first circumferential direction 7a, that is to say upwards to promote the flow of air by natural convection.

[0083] Similarly, with regard to the second side 46b of the median plane, also comparable to the second side of the structure 30, each plate 32 has a design similar to that shown in Figures 3 and 4, and shown very succinctly in [Fig.3A]. Indeed, according to another feature of the invention, each pair of first and second sub-assemblies 40a, 40b adjacent and directly consecutive in the axial direction 8, forms a second assembly 50b within which at least some of the first and second primary fins 42a, 42b form two by two second fins 52b in the general shape of a V, which follow one another in the circumferential direction. For these plates 32 on the second side of the plane P, the tip of the V is oriented in the second circumferential direction 7b, that is to say also towards the top of the lying packaging, always to promote the flow of air by natural convection.

[0084] It is noted that the first and second primary fins 42a, 42b are preferably entially produced by machining, for example in aluminum or copper, or in one of their alloys. During this machining, the two primary fins 42a, 42b may be provided in contact with each other at the tip of the V formed by the fin 52a, 52b, as shown in [Fig. 5]. The tips of V are preferably all located on the same circle centered on the axis 2. This induces a continuity of material for the fin concerned 52a, 52b, but another embodiment shown diagrammatically in [Fig. 6] may be envisaged, namely the continuation of the machining to provide an axial spacing 56 between the opposite ends of the two primary fins 42a, 42b. Of course, this spacing 56 can be implemented even when the primary fins 42a, 42b are produced by a technique other than the machining of the longitudinal plates 32.

[0085] The presence of these spacings 56, shown diagrammatically in [Fig.6], contributes to forming a sort of circumferential channel passing through the tips of the Vs of several fins 52a, 52b, to further promote the circulation of cooling air upwards, around the packaging.

[0086] As has been shown diagrammatically in [Fig. 5], in the horizontal position of transport of the packaging, the air circulates upwards in the primary channels 44a, 44b between the first fins 52a, and the same is true between the second fins 52b of the plates 32 located on the second side of the imaginary median plane ([Fig. 3A]).

[0087] More precisely, when the longitudinal plates 32 are heated, natural convection occurs causing the air to enter the primary channels 44a, 44b, then to propagate upwards within these channels, before meeting the air coming from the primary channels opposite, of the same first set 50a / second set 50b. This impact at the outlet of the primary channels, at the tip of the inverted Vs, causes the air to evacuate vertically upwards. But simultaneously, vortices and recirculations of air are also created above the fins 52a, 52b and the primary channels 44a, 44b, promoting the acceleration of the air in these primary channels. As one moves along the circumferential line formed by these inverted V points, this column of air is amplified by the contribution of the successive primary channels which push it further from the surface.This forced evacuation creates an upward and swirling movement which feeds from the base of the inverted Vs which then constitutes a suction line, and thus allows forced circulation in the channels.

[0088] Figures 7 to 10 show a first preferred embodiment of the invention, in which the fictitious median plane P forms a plane of symmetry for the heat dissipation structure 30. In this mode, on the first side 46a of the plane P, all the plates 32 are identical, and they jointly form a C-shaped half-shell. These are thus several adjacent first sets 50a which follow one another according to each of the two directions 7 and 8, their numbers preferably being greater than or equal to three in each of these two directions. As has been schematized by the rectangles added in Figures 9 and 10, the first adjacent sets 50a adopt a so-called matrix configuration, formed by axial lines and circumferential columns.

[0089] Similarly, on the second side 46b of the plane P, all the plates 32 are also identical to each other, but different from the plates located on the first side 46a. Indeed, as can be seen in Figures 7 and 9, the same axial alternation of first and second sub-assemblies 40a, 40b is provided on these plates 32, but with an offset of half a pitch relative to the plates 32 on the first side 46a, a whole pitch being formed by the total axial length of an assembly 50a, 50b. Consequently, this makes it possible to ensure that each first assembly 50a on the first side is arranged symmetrically relative to one of the second assemblies 50b on the second side. Indeed, the plates 32 of the second side 46b also jointly form a C-shaped half-shell. These are thus several adjacent second sets 50a which follow one another in each of the two directions 7 and 8, their numbers also preferably being greater than or equal to three in each of these two directions.As schematized by the rectangles added in [Fig.9], the second adjacent sets 50b adopt a so-called matrix configuration, formed by axial lines and circumferential columns.

[0090] In this first preferred embodiment, any transverse plane of the structure 30 passes through:

[0091] either a succession of first sub-assemblies 40a of the first side 46a, succeeding one another in the direction 7 while extending jointly over an angular sector preferably equal to or close to 180°, then a succession of second sub-assemblies 40b of the second side 46b, succeeding one another in the direction 7 while also extending jointly over an angular sector preferably equal to or close to 180°,

[0092] or a succession of first sub-assemblies 40a of the second side 46b, succeeding one another in the direction 7 while extending jointly over an angular sector preferably equal to or close to 180°, then a succession of second sub-assemblies 40b of the first side 46a, succeeding one another in the direction 7 while extending jointly over an angular sector preferably equal to or close to 180°.

[0093] It is noted that on the first side 46a, for any two first sets 50a directly consecutive in the circumferential direction 7, certain first primary fins 42a of one of the two sets 50a are respectively in the continuity of certain first primary fins 42a of the other of the two sets 50a. The same is true for certain second primary fins 42b of these two sets 50a. This makes it possible, with one of the two sets 50a, to extend the axial length of certain first fins 52a formed by the other of these two sets 50a, and thus to have first fins 52a all, or substantially all, of the same axial extent, all along the circumferential direction 7. The geometric continuity between certain first primary fins 42a of the two sets 50a, and certain second primary fins 42b of these two sets 50a, does not prevent the provision of circumferential clearance between the facing ends of the primary fins cooperating two by two, as can be seen in the figures. These specificities are also observed on the second sets 50b.

[0094] In this regard, it is also noted that a continuity of material may be provided between the primary fins 42a, 42b of two sets 50a or 50b directly consecutive in the axial direction 8, as also shown in the figures. Alternatively, an axial clearance may be provided between the opposite ends of the primary fins cooperating two by two.

[0095] Here again, it is noted that these specificities are observed both on the first side 46a, and on the second side 46b of the fictitious median plane P.

[0096] A second preferred embodiment of the invention is shown in Figures 11 and 12. It is very similar to the first embodiment described previously, but it is distinguished by the fact that the structure 30 no longer has a plane of symmetry passing through the axis 2, since all the plates 32 are identical on the first and second sides 46a, 46b of the imaginary median plane P. In this way, by providing only a single plate reference 32, the manufacture and assembly of the structure 30 are facilitated.

[0097] The consequence of such an arrangement lies in the fact that the first sets 50a of the first side 46a are axially offset by half a step relative to the second sets 50b of the second side 46b, as has been highlighted by the addition of rectangles in [Fig. 12].

[0098] In this second preferred embodiment, any transverse plane of the structure 30 passes through either a succession of first sub-assemblies 40a of the first and second sides 46a, 46b, extending jointly over an angular sector preferably equal to or close to 360°, or a succession of second sub-assemblies 40b of the first and second sides 46a, 46b, extending jointly over an angular sector preferably equal to or close to 360°.

[0099] A third preferred embodiment of the invention is shown in Figures 13 and 14. It is largely similar to the previously described embodiments, but it is distinguished by the fact that on the first side 46a, several first sets 50a, and preferably all of them, are arranged in a staggered pattern. Indeed, any two first sets 50a directly consecutive in the circumferential direction 7 are axially offset from each other by a value of half a pitch, as has been highlighted by the rectangles in [Fig. 14]. To do this, always this first side 46a of the fictitious median plane P, two plates 32 of different designs alternate in the circumferential direction. Their designs differ in that they have an axial offset of half a pitch, like that observed in Figures 7 to 10 between the plates 32 of the first side and that of the second side, in the context of the first preferred embodiment.

[0100] This axial offset of a half-pitch between the plates 32 is also observed on the second side 46b, for the formation of the second sets 50b, not shown for this third preferred embodiment. On this second side, there are therefore also two types of plates 32 arranged alternately which form the half-shell of the structure 30, these two types of plates being preferably the same two as those arranged on the first side.

[0101] In this regard, it is noted that the plates 32 of the first side may be symmetrical to the plates 32 of the second side, in relation to the fictitious median plane P. Alternatively, an axial offset is provided between the plates 32 of the first side and those of the second side, implying an absence of symmetry of the structure 30 in relation to any median plane of this structure passing through the axis 2.

[0102] In this third preferred embodiment, any transverse plane of the structure 30 therefore crosses, on each of the first and second sides 46a, 46b, an alternation of first and second sub-assemblies 40a, 40b in the circumferential direction 7, this alternation of each of the two sides then extending over an angular sector preferably equal to or close to 180°.

[0103] Of course, various modifications can be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples.

Claims

1. Claims Structure (30) for dissipating heat by natural convection, intended to equip the external surface of a lateral body of a package (1) for the transport of radioactive materials, the heat dissipation structure extending around a longitudinal axis (2) of the structure, intended to correspond to a longitudinal axis of the package, of horizontal orientation when the package is in a horizontal transport position, the heat dissipation structure being characterized in that it comprises at least, at each of a first (46a) and a second side (46b) of a fictitious median plane (P) of the structure passing through its longitudinal axis (2): - a first heat dissipation subassembly (40a), comprising first primary fins (42a) parallel to each other and inclined locally with respect to a circumferential direction (7) of the structure and with respect to an axial direction (8) of this structure, so as to have a first inclination (Al) such that each first primary fin (42a) extends in a first direction (7a) of the circumferential direction (7) going in a first direction (8a) of the axial direction; - a second heat dissipation subassembly (40b), comprising second primary fins (42b) parallel to each other and inclined locally with respect to the circumferential direction (7) of the structure and with respect to the axial direction (8), so as to have a second inclination (A2) different from the first, and such that each second primary fin (42b) extends in a second direction (7b) of the circumferential direction opposite to the first direction (7a), going in the first direction (8a) of the axial direction (8); in that on the first side (46a) of the fictitious median plane (P), the first (40a) and the second sub-assembly (40b) are adjacent, following one another in the axial direction (8) so as to form a first assembly (50a) within which at least some of the first and second primary fins (42a, 42b) form two by two of the first fins (52a) in the general shape of a V which follow one another in the circumferential direction (7), with the tip of the V oriented in the first circumferential direction (7a), and in that on the second side (46b) of the fictitious median plane, the first (40a) and the second sub-assembly (40b) are adjacent, succeeding each other in the axial direction (8) so as to form a second assembly (50b) within which at least some of the first and second primary fins (42a, 42b) form two by two second fins (52b) in the general shape of a V which succeed each other in the circumferential direction (7), with the tip of the V oriented in the second circumferential direction (7b).

2. Heat dissipation structure (30) according to claim 1, characterized in that on the first side (46a) of the fictitious median plane (P), several first sets (50a) are adjacent in succession in the axial direction (8) and / or in the circumferential direction (7), their numbers preferably being greater than or equal to three in each of these two directions, and in that on the second side (46b) of the fictitious median plane (P), several second sets (50b) are adjacent in succession in the axial direction (8) and / or in the circumferential direction (7), their numbers preferably being greater than or equal to three in each of these two directions.

3. Heat dissipation structure (30) according to claim 2, characterized in that the fictitious median plane (P) forms a plane of symmetry for the heat dissipation structure, each first set (50a) being arranged symmetrically with respect to one of the second sets (50b).

4. Heat dissipation structure (30) according to claim 2 or 3, characterized in that any transverse plane of the structure passes through: either: - a succession of first sub-assemblies (40a) on the first side (46a) of the fictitious median plane, the first sub-assemblies (40a) succeeding one another in the circumferential direction (7) while extending jointly over an angular sector preferably equal to or close to 180°; and - a succession of second sub-assemblies (40b) on the second side (46b) of the fictitious median plane, the second sub-assemblies (40b) succeeding one another in the circumferential direction (7) while extending jointly over an angular sector preferably equal to or close to 180°, or: - a succession of first sub-assemblies (40a) on the second side (46b) of the fictitious median plane, the first sub-assemblies (40a) succeeding one another in the circumferential direction (7) while extending jointly over an angular sector preferably equal to or close to 180°, in the circumferential direction (7) extending jointly over an angular sector preferably equal to or close to 180°; and - a succession of second sub-assemblies (40b) on the first side (46a) of the fictitious median plane, the second sub-assemblies (40b) succeeding one another in the circumferential direction (7) extending jointly over an angular sector preferably equal to or close to 180°.

5. Heat dissipation structure (30) according to claim 2, characterized in that it is asymmetrical with respect to any fictitious median plane (P) passing through the longitudinal axis (2).

6. Heat dissipation structure (30) according to claim 2 or 5, characterized in that any transverse plane of the structure passes through: either a succession of first sub-assemblies (40a) of the first and second sides (46a, 46b) of the fictitious median plane (P), the first sub-assemblies (40a) succeeding one another in the circumferential direction (7) while extending jointly over an angular sector preferably equal to or close to 360°, or a succession of second sub-assemblies (40b) of the first and second sides (46a, 46b) of the fictitious median plane (P), the second sub-assemblies (40b) succeeding one another in the circumferential direction (7) while extending jointly over an angular sector preferably equal to or close to 360°.

7. Heat dissipation structure (30) according to claim 2, characterized in that it is symmetrical with respect to the fictitious median plane (P), or asymmetrical, in that on the first side (46a) of the fictitious median plane, several first assemblies (50a) are arranged in a staggered pattern, and in that on the second side (46b) of the fictitious median plane, several second assemblies (50b) are arranged in a staggered pattern.

8. Heat dissipation structure (30) according to claim 2 or 7, characterized in that any transverse plane of the structure crosses, on each of the first and second sides (46a, 46b) of the fictitious median plane, an alternation of first and second sub-assemblies (40a, 40b) in the circumferential direction (7), this alternation extending over an angular sector preferably equal to or close to 180°.

9. Heat dissipation structure (30) according to any one of the preceding claims, characterized in that it is produced using several longitudinal plates (32) succeeding one another in the circumferential direction (7), each plate comprising an alternation, according to the axial direction (8), of first and second subassemblies (40a, 40b).

10. Heat dissipation structure (30) according to claim 10, characterized in that each longitudinal plate (32) extends over all or substantially all of the axial length of the structure, preferably being made in one piece.

11. Heat dissipation structure (30) according to any one of the preceding claims, characterized in that the first and second primary fins (42a, 42b) are produced by machining, preferably from aluminum or copper, or from one of their alloys.

12. A heat dissipation structure (30) according to any preceding claim, characterized in that at the tip of the V of at least some of the first and second fins (52a, 52b), the first and second primary fins (42a, 42b) are in contact with each other, or an axial spacing is provided therebetween.

13. Heat dissipation structure (30) according to any one of the preceding claims, characterized in that it has a generally annular shape, centered around its longitudinal axis (2).

14. Packaging (1) for the transport of radioactive materials, comprising a heat dissipation structure (30) according to any one of the preceding claims, equipping the outer surface of the lateral body of the packaging.

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