FR3064809A1 - PACKAGING OF TRANSPORT AND / OR STORAGE OF RADIOACTIVE MATERIALS WITH IMPROVED CONVICTIVE EXCHANGES - Google Patents

Abstract

The invention relates to a package for transporting and / or storing radioactive materials comprising a plurality of natural convection heat dissipating structures each having two half-structures (30a, 30b) comprising primary fins (40a, 40b) parallel and inclined relative to the longitudinal axis (2) of the package. The packaging also comprises an outer air duct wall (31) facing the heat dissipating structures so as to together form a longitudinal space (33) in which two cooling air vortices (39) can circulate. by convection upwards. In addition, the ratio "R" between firstly the radial distance "De" between the outer wall (31) and the top of the primary fins (40a, 40b), and secondly the width "L" Of each half-structure (30a, 30b) is between 0.8 and 1.2.

Description

DESCRIPTION

TECHNICAL AREA

The present invention relates to the field of the evacuation of the heat produced by radioactive materials loaded in a package for transport and / or storage of radioactive materials, for example nuclear fuel assemblies or radioactive waste.

More specifically, the present invention relates to a package comprising at its periphery a structure of heat dissipation by natural convection.

STATE OF THE PRIOR ART

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

This heat evacuation device is in particular designed so as to limit the temperature reached in service by the various constituent elements of the packaging, in particular the seals and the radiological protections, in order to avoid any risk of degradation of these elements.

Furthermore, in addition to being able to perform its main function of heat exchanger with the ambient environment, this device is designed so as to be compatible with the constraints of packaging services, such as decontaminability, resistance in the weather, resistance to atmospheric attack, resistance to operating conditions such as immersion during loading and unloading, or even confinement of the neutron shielding resin.

A known solution for this type of external heat dissipation device is in the form of a covering ferrule enveloping the lateral body of the packaging, and onto which are welded longitudinal straight fins of appropriate section. These fins are also said to be vertical, because they are oriented in the vertical direction when the packaging itself lies vertically.

However, there is a constant need to optimize the performance of the external heat dissipation device.

STATEMENT OF THE INVENTION

To meet this need, the subject of the invention is a packaging for the transport and / or storage of radioactive materials comprising a lateral body externally equipped with several heat dissipation structures by natural convection, distributed circumferentially around an axis longitudinal of the packaging.

According to the invention, each heat dissipation structure has two circumferentially adjacent half-structures each comprising primary fins which are parallel and inclined with respect to the longitudinal axis of the package around which the heat dissipation structures are arranged, the primary fins of the two half-structures forming two by two of the fins in the general shape of an inverted V, when the packaging is arranged vertically with its bottom facing downwards. The packaging also comprises an external wall of air duct situated opposite at least one of the heat dissipation structures, externally and radially away from it so as to form together a longitudinal space in which two eddies of cooling air can circulate by convection upwards respectively along the two adjacent half-structures of said heat dissipation structure. Finally, the ratio “R” between on the one hand the radial spacing distance “De” between the outer wall and the top of the primary fins, and on the other hand the width “L” of each half-structure in a direction transverse of the structure orthogonal to the longitudinal axis, is between 0.8 and 1.2.

The particular arrangement defined above makes it possible to substantially improve the cooling performance of the packaging, in particular with respect to the vertical straight fins known from the prior art.

In fact, in the vertical position of the packaging, the air flows upward through the primary channels defined between the primary fins. At the outlet of these two primary channels, the two air flows meet and generate the aforementioned two vortices in the longitudinal space delimited by the outer wall of the air duct.

Thanks to the particular geometry adopted, the air vortices take a substantially circular shape in the longitudinal space. More precisely, these vortices adopt a helical shape of circular section with a longitudinal axis.

This shape reinforces the intensity of these vortices and contributes to a particularly efficient mixing of air, as well as to a diffusion of air throughout this longitudinal space formed with the external wall of air ducting. This advantageously results in an increase in convective exchanges which contributes to the reduction of the temperature of the packaging, in particular in critical zones such as its lower part when it rests in a vertical position.

The invention also has at least one of the following optional features, taken individually or in combination.

The outer wall entirely surrounds at least one longitudinal section of the packaging body equipped with heat dissipation structures. Alternatively, the wall could not be closed, for example by having a C-shaped cross section. According to another alternative, there could be provided several outer walls spaced circumferentially from each other, each facing radially from one or more heat dissipation structures.

Preferably, the outer wall extends so as to cover, in the direction of the longitudinal axis, at least 50% of said heat dissipation structure. In addition, in order to improve the convective exchanges in a lower part of the packaging which is deemed to be particularly hot, a lower end of the outer wall is preferably located near a lower end of said heat dissipation structure.

Preferably, the two adjacent half-structures of each heat dissipation structure are arranged in a substantially symmetrical manner.

Preferably, the primary fins are straight and inclined by a value between 30 and 60 ° relative to the longitudinal axis orthogonal to said transverse direction, and preferably inclined by a value of 45 ° relative to this same axis .

Preferably, the packaging has at least one of the following parameters:

- H: the height of each half-structure, in the direction of the height (8) along which the inclined primary fins follow one another, this height being between 2 and 5 m;

- h: the height of each primary fin in a radial direction of the packaging, between 10 and 100 mm;

- d: the width of each primary air circulation channel defined between two directly consecutive primary fins, this width being between 10 and 50 mm;

- Ep: the thickness of each primary fin, meeting the condition d / Ep> 2.5;

- L: the width of each half-structure in the transverse direction, this width being between 150 and 300 mm.

Preferably, the two half-structures of each heat dissipation structure are distinct from each other, each having a plate and its own primary fins projecting from the plate. This provides ease of manufacture and assembly. Alternatively, the two half-structures can be produced on the same plate of height H, possibly segmented in the direction of the height.

Preferably, each heat dissipation structure is substantially planar.

Preferably, a spacing "Ec" between two directly adjacent dissipation structures in the circumferential direction is substantially equal to a spacing "Ec" between the two half-structures of each dissipation structure. This spacing "Ec" preferably meets the condition Ec / L <0.2. Alternatively, there is no provision for spacing between the half-structures, implying that the primary fins are joined two by two.

Other advantages and characteristics of the invention will appear in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made with reference to the accompanying drawings, among which;

- Figure 1 shows a front view of a package for the storage and / or transport of radioactive materials, comprising heat dissipation structures according to a preferred embodiment of the present invention;

- Figure 2 shows a partial sectional view taken along the line II-II in Figure 1;

- Figure 3 is an enlarged front view of part of the heat dissipation structure; and

- Figure 4 is a sectional view taken along the line IV-IV of Figure 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

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

This package 1 is shown in Figure 1 in the vertical storage position, in which its longitudinal axis 2 is oriented vertically. It rests on a packaging bottom 4, opposite a removable cover 6 in the direction of the height 8, parallel to the longitudinal axis 2. Between the bottom 4 and the cover 6, the packaging 1 has a lateral body 10 extending around the axis 2, and internally defining a cavity 12 for housing the radioactive materials.

The lateral body 10 generally comprises an inner ferrule 14 and an outer concentric ferrule 16, defining an annular or longitudinal space 18 centered on the axis 2. The space 18 is filled by means of thermal conduction 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.

The outer shell 16 is produced using a plurality of heat dissipation structures 30 according to the invention. These structures 30 are distributed circumferentially around the axis 2, and each extend at a height H of between 2 and 5 m depending on the direction of the height 8. In the example shown in FIG. 2, the structures 30 include bases in the form of rectangular plates, these plates each comprising two longitudinal edges. These plates are assembled end-to-end by welding at their facing edges, so as to reconstitute the outer shell 16. Also, these plates could be segmented in the direction of the height 8, but they are preferably made of one piece depending on the height H.

One of the features of the invention resides in the presence of an outer wall of air duct 31 here in the form of a ferrule surrounding the body 10, and located opposite the heat dissipation structures 30. This wall 31 is preferably mechanically connected to the body 10, by conventional means. As will be detailed below, the outer wall 31 is arranged externally and radially away from the structures so as to form together a longitudinal space 33 in which eddies of cooling air can circulate upwards by natural convection. Thus, the outer wall 31 entirely surrounds a longitudinal section of the packaging body 10, over at least 50% of the height H of the dissipation structures 30. However, the wall 31 can extend vertically over a greater length, for example corresponding to 80% or more of the height H of the structures 30. In this preferred embodiment, as best seen in FIG. 1, the lower end of the outer wall 31 is located near the lower end structures 30. More precisely, these ends are arranged in the same transverse plane, or close to the same transverse plane of the packaging.

As can be seen in FIG. 1, the longitudinal space 33 is open at its two longitudinal ends. It is first of all a lower longitudinal opening 33a defined between the lower end of the structures 30 and the lower end of the wall 31, this opening 33a serving to supply the channels and the vortices with fresh air. . It is also an upper longitudinal opening 33b defined between the end of the structures 30 and the upper end of the wall 31, allowing the evacuation of the hot air in the form of vortices. Other configurations can nevertheless be envisaged, such as that aiming to provide that the fresh air is introduced between the external wall and the fins by gills in the lower part of the wall 31, allowing the fresh air to enter the longitudinal space 33.

Referring to Figure 3, there are shown two adjacent structures 30 in the circumferential direction 32 of the package. These two structures 30 are identical, and it is preferably the same for all the structures 30 constituting the outer shell 16, their number possibly being between 5 and 40.

Each heat dissipation structure 30 comprises two demistructures 30a, 30b of similar designs, and being arranged substantially symmetrically with respect to a radial plane Pr of the package. The half-structure 30a comprises straight and parallel primary fins 40a. They are inclined relative to the axis 2 parallel to the direction of the height 8 of the packaging, also corresponding to the height direction of the structure 30. In view in a direction substantially orthogonal to the plane of the half-structure 30a (as in Figure 3), the angle of inclination Aa of the primary fins 40a relative to the axis 2 is preferably of the order of 45 °. Similarly and substantially symmetrically, the half-structure 30b comprises primary fins 40b straight and parallel. They are inclined relative to the axis 2 of the packaging, with an inclination angle Ab preferably of the order of 45 °. However, the symmetry may not be perfect, for example by providing a small difference in the value of the two angles Aa, Ab, of the order of 10 to 20 °.

The primary fins 40a, 40b of the two half-structures form two by two of the fins 44 in the general shape of an inverted V, when the packaging is arranged vertically with its bottom facing downwards, as in FIGS. 1 and 3. Each fin 44 thus formed by one of the primary fins 40a, and the primary fin 40b opposite, therefore adopts a chevron shape.

As mentioned above, each half-structure 30a, 30b can be made in one piece in direction 8, or else segmented in this same direction. In the latter case illustrated in Figure 1, the semi-structure segments are then arranged in continuity with each other, being welded end-to-end.

Preferably, the two half-structures 30a, 30b are distinct from each other, that is to say that they each comprise a plate 46 from which the associated primary fins project, as has been shown for the half-structure 30a in FIG. 4. The two plates 46 are joined together by welding at the level of their facing edges in the circumferential direction, so as to reconstitute a substantially planar structure. Thus, the two assembled plates 46 together constitute the aforementioned base in the form of a rectangular plate, participating in reconstituting the outer shell 16.

As illustrated in FIG. 3, the two half-structures 30a, 30b are of symmetrical design. In this same FIG. 3, the primary channels 48a, 48b are also shown, delimited respectively by two fins 40a, 40b directly consecutive, in the direction 8.

In FIGS. 3 and 4, geometric parameters specific to the invention have been identified.

It is first of all the height H of each half-structure 30a, 30b, corresponding to the height H of the structure 30 composed of these two half-structures. As indicated above, the height H is between 2 and 5 m, and preferably close to 4 m.

It is also the height h of each primary fin 40a, 40b in the radial direction 35, between 10 and 100 mm, and preferably identical for all the primary fins. By way of example, this height h can be of the order of 25 mm.

The width d of each primary air circulation channel 48a, 48b is between 10 and 50 mm, and proves to be constant and identical for all the channels 48a, 48b, over the entire height H.

It is also the thickness Ep of each primary fin 40a, 40b, preferably meeting the condition d / Ep> 2.5. This thickness Ep is also preferably identical for all the primary fins.

Finally, the width L of each half-structure 30a, 30b, in a transverse direction 32 orthogonal to directions 8, 35, is preferably between 150 and 300 mm. As an indicative example, this width L is of the order of 215 mm. This width L, extending in the transverse direction 32 comparable to the circumferential direction, is preferably identical for the two half-structures.

Furthermore, a possible spacing Ec can be provided between the ends opposite two primary fins 40a, 40b, jointly forming a fin in the general shape of an inverted V 44. This spacing, arranged at the point of the fin 44, meets for example the condition Ec / L <0.2. The spacings being aligned in direction 8, they together form a sort of vertical air delivery channel 54, at the junction between the two half-structures 30a, 30b of the heat dissipation structure 30.

In addition, a spacing Ec 'is preferably provided between two directly adjacent dissipation structures 30 in the circumferential direction 32. This spacing Ec' is for example substantially equal to the spacing Ec.

Finally, still in the dimensioning of the packaging, it is provided that the radial spacing distance De between the outer wall 31 and the top of the primary fins 40a, 40b, in the direction 35, is such that the ratio R between this distance From and the width L of each half-structure 30a, 30b is between 0.8 and 1.2 With the proposed arrangement, when the half-structures 30a, 30b are heated by the presence of radioactive materials, there is produced natural convection leading the air to enter the primary channels 48a, 48b, then to propagate upwards within these channels, before meeting the air coming from the opposite channels belonging to the other half-structure. This impact at the outlet of the primary channels 48a, 48b, at the point of the inverted Vs, causes the air to be evacuated vertically upwards. But simultaneously, vortices of cooling air are created above the fins and primary channels 48a, 48b. More specifically, for each heat dissipation structure 30, this makes it possible to generate two eddies of cooling air 39 which are adjacent and counter-rotating, circulating by natural convection up respectively along the two half-structures 30a, 30b, in the longitudinal space 33. Thanks to the specific dimensioning of the invention, the two vortices 39 of substantially circular shape have an increased intensity which contributes to efficient air mixing, as well as to air diffusion throughout the space longitudinal 33. The convective exchanges are accentuated, and the hot spots reduced to the right of the external wall of air duct 31.

Of course, various modifications can be made by those skilled in the art to the invention which has just been described, only by way of nonlimiting examples.

Claims (9)

1. Packaging (1) for the transport and / or storage of radioactive materials comprising a lateral body (10) externally equipped with several structures (30) for dissipation of heat by natural convection, distributed circumferentially around a longitudinal axis ( 2) of the packaging, characterized in that each heat dissipation structure (30) has two half-structures (30a, 30b) which are circumferentially adjacent and each comprising primary fins (40a, 40b) parallel and inclined with respect to the longitudinal axis (2) of the packaging around which the heat dissipation structures (30) are arranged, the primary fins (40a, 40b) of the two half-structures (30a, 30b) forming two by two of the fins (44 ) in the general shape of an inverted V, when the packaging is arranged vertically with its bottom (4) facing downwards, in that the packaging also comprises an outer wall of air ducting (31) located in regar d at least one of the heat dissipation structures (30), externally and radially spaced therefrom so as to form together a longitudinal space (33) in which two eddies of cooling air (39) can circulate by convection up respectively along the two adjacent demistructures (30a, 30b) of said heat dissipation structure (30), and in that the ratio "R" enters on the one hand the distance of radial spacing "From" between the outer wall (31) and the top of the primary fins (40a, 40b), and on the other hand the width "L" of each half-structure (30a, 30b) in a transverse direction (32) of the structure orthogonal to the longitudinal axis (2), is between 0.8 and 1.2. 2. Packaging according to claim 1, characterized in that the outer wall (31) entirely surrounds at least one longitudinal section of the packaging body (10). 3. Packaging according to claim 1 or claim 2, characterized in that the outer wall (31) extends so as to cover, in the direction of the longitudinal axis (2), at least 50% of said structure heat dissipation (30), a lower end of the outer wall (31) preferably being near a lower end of said heat dissipation structure (30). 4. Packaging according to any one of the preceding claims, characterized in that the two adjacent half-structures (30a, 30b) of each heat dissipation structure (30) are arranged in a substantially symmetrical manner. 5. Packaging according to any one of the preceding claims, characterized in that the primary fins (40a, 40b) are straight and inclined by a value between 30 and 60 ° relative to the axis (2) orthogonal to said transverse direction (32), and preferably inclined by a value of 45 ° relative to this same axis. 6. Packaging according to any one of the preceding claims, characterized in that it has at least one of the following parameters: - H: the height of each half-structure (30a, 30b), in the direction of the height (8) along which the inclined primary fins (40a, 40b) follow one another, this height being between 2 and 5 m; - h: the height of each primary fin (40a, 40b) in a radial direction (35) of the packaging, between 10 and 100 mm; - d: the width of each primary channel (48a, 48b) of air circulation defined between two directly consecutive primary fins, this width being between 10 and 50 mm; - Ep: the thickness of each primary fin (40a, 40b), meeting the condition d / Ep> 2.5; - L: the width of each half-structure (30a, 30b) in the transverse direction (32), this width being between 150 and 300 mm. 7. Packaging according to any one of the preceding claims, characterized in that the two half-structures (30a, 30b) of each heat dissipation structure are distinct from each other, each having a plate (46 ) and its own primary fins projecting from the plate. 8. Packaging according to any one of the preceding claims, characterized in that each heat dissipation structure (30) is substantially planar. 5 9. Packaging according to any one of the preceding claims, characterized in that a spacing "Ec '" between two dissipation structures (30) directly adjacent in the circumferential direction (32), is substantially equal to a spacing "Ec" between the two half-structures (30a, 30b) of each dissipation structure. S.62084 1/3