Package comprising packaging for transporting and / or storing radioactive content comprising a compact internal shock-absorption system

Abstract

The invention relates to a package comprising radioactive content and to packaging for transporting and / or storing said content, the packaging comprising an internal shock-absorption system (22) housed in the confinement chamber between the radioactive content and an axial blocking member of the chamber, the radioactive content comprising a storage device and one or more radioactive elements. The internal shock-absorption system (22) comprises a first shock-absorption device (40) for absorption by plastic deformation in order to provide shock absorption for the storage device (30), and a second shock-absorption device (50a-50f) for absorption by plastic deformation associated with a radioactive assembly formed of one or more radioactive elements, the first and second shock-absorption devices being designed to operate independently of each other and to take account of the maximum decelerations that can be withstood by the storage device and the radioactive elements accommodated in said device.

Description

[0001] DESCRIPTION

[0002] TITLE: PACKAGE COMPRISING PACKAGING FOR THE TRANSPORT AND / OR STORAGE OF RADIOACTIVE CONTENTS, AND COMPRISING AN INTERNAL SHOCK ABSORBING SYSTEM WITH REDUCED OBSTACLE

[0003] TECHNICAL FIELD

[0004] The present invention relates to the field of packages of radioactive materials, comprising a packaging and radioactive contents housed in a containment enclosure defined by the packaging.

[0005] The packaging may be of the type comprising a removable cover, such as for example used for the transport of nuclear fuel assemblies. It may alternatively be a packaging of the case or container type, in which the cover is preferably permanently fixed to the lateral packaging body, for example by welding.

[0006] In the containment enclosure delimited by the packaging, the radioactive contents comprise a storage device as well as one or more radioactive elements, the latter being able to be nuclear fuel assemblies, preferably fresh, containers / cases of vitrified waste or technological waste, containers / cases of shells and end caps, or even cases for the transport of powder (PuO2 powder for example).

[0007] The invention relates more specifically to an internal damping system, housed axially in the containment enclosure between the radioactive contents and an axial sealing member of the package, namely its lid or its bottom. In this regard, it is noted that such a damping system is preferably associated with the lid of the package to protect the integrity of the containment enclosure in the event of the package falling axially. Nevertheless, such an internal damping system may simultaneously, or alternatively, be provided in association with the bottom of the package. STATE OF THE PRIOR ART

[0008] A package for storing and / or transporting radioactive materials generally comprises, as a sealed outer envelope, a packaging having a lateral body, a base and a lid. These parts of the packaging define a cavity, called a containment enclosure, for housing radioactive contents, for example formed by a storage device housing nuclear fuel assemblies. The storage device is usually called a storage basket. It comprises one or more axial housings each intended to house a radioactive element, namely a nuclear fuel assembly in the example given above. In another case where the radioactive elements are cases and / or containers, several of them can be stacked axially in each housing of the storage basket.

[0009] The safety demonstration of the packaging loaded with radioactive contents is based in particular on regulatory drop tests. Thus, during an axial drop of nine meters onto a head shock-absorbing cap covering the lid of the packaging, the radioactive contents can move axially in the cavity of the packaging towards the lid due to a functional clearance between the radioactive contents and the lid. While the head shock-absorbing cap is crushed, the radioactive contents can then impact this same lid during this fall, known as an "axial drop". Very significant forces are thus generated with a delay in the closing system of the removable lid of the packaging, under the effect of the radioactive contents housed in the containment enclosure. In particular, the lid fastening device is highly stressed, which can, for example, be made using fixing screws, or include a bayonet ring.

[0010] In order to ensure the tightness of the container after the axial fall, it may be necessary to limit the forces transmitted by the radioactive contents to the lid, by means of an internal shock absorber system placed in the containment enclosure, between the lid and the radioactive contents. The system is also called an internal shock absorber system. Generally, such a system comprises one or more plastic deformation damping devices, such as metal foam. To obtain optimal crushing of each damping device, and therefore to dissipate the mechanical energy as best as possible through the plastic deformation of each damping device, numerous solutions have already been proposed in previous developments.

[0011] Among the design criteria for the internal shock absorber system, the maximum decelerations that the storage basket and the radioactive elements housed in the basket can withstand are taken into account. Usually, the lowest maximum deceleration of the two is chosen for the design of the shock absorber, in addition to other criteria such as the need to absorb all the potential energy of the radioactive contents in the event of an axial fall, without the risk of the shock absorber system bottoming out, or the need to limit the forces transmitted by the radioactive contents to the cover fixing device.

[0012] Considering the lowest maximum permissible deceleration, this can lead to a significant oversizing of the internal damping system and the entire packaging, especially in the axial direction. There is therefore a need to improve these internal damping systems, so as to offer a better compromise in terms of size, cost and performance.

[0013] Finally, it is noted that this problem also exists for an internal damping system associated with a non-removable packaging lid, such as a welded case lid, or for an internal damping system associated with the packaging base, which is generally also non-removable. In these two cases, even if there is no problem of holding the fastening device of the closure system as for a removable lid, the maximum decelerations in the event of an axial fall on the non-removable lid / base side also need to be taken into account in certain situations.

[0014] STATEMENT OF THE INVENTION

[0015] To meet the need identified above, the subject of the invention is a package comprising radioactive contents as well as a packaging for the transport and / or storage of these contents, the packaging comprising a lateral body extending around a longitudinal central axis of the packaging, as well as a base and a cover respectively arranged at the axial ends of the lateral packaging body and forming two axial closure members delimiting, with the lateral packaging body, a containment enclosure in which the radioactive contents are housed, the packaging also comprising an internal damping system housed in the containment enclosure and arranged axially between the radioactive contents and one of the two axial closure members, called the associated axial closure member, the radioactive contents comprising a storage device as well as one or more radioactive elements,the storage device delimiting one or more axial housings open axially in the direction of the associated axial closure member, and in each of which at least one radioactive element is arranged. According to the invention, the internal damping system comprises a first plastic deformation damping device for damping the storage device, as well as a second plastic deformation damping device associated with a radioactive assembly formed of one or more radioactive elements, the first and second damping devices being arranged so as to operate independently of each other in the event of axial fall of the package, the first damping device being associated with the following first parameters:,

[0016] - oi, corresponding to the crushing constraint of this first damping device;

[0017] - If, corresponding to the active surface of the first damping device intended to be axially impacted by the storage device in the event of the package falling axially;

[0018] - Mi, corresponding to the mass of the storage device intended to be cushioned by the first cushioning device;

[0019] - Yi, corresponding to a first value representative of the deceleration of the storage device in the event of an axial fall of the package leading this storage device to plastically crush the first damping device, the first representative deceleration value yi being determined by the following formula: yi = (oi*Si) / Mi, the second damping device being associated with the following second parameters: - 02, corresponding to the crushing stress of this second damping device;

[0020] - S2, corresponding to the active surface of the second damping device intended to be axially impacted by its associated radioactive assembly, in the event of axial fall of the package;

[0021] - M2, corresponding to the mass of the radioactive assembly intended to be damped by the second damping device;

[0022] - V2, corresponding to a second value representative of the deceleration of the associated radioactive assembly, in the event of axial fall of the package leading this radioactive assembly to plastically crush the second damping device, the second representative deceleration value Y2 being determined by the following formula: Y2 = (a2*S2) / M2, the first and second parameters being such that the second representative deceleration value Y2 is different from the first representative deceleration value yi. The invention makes it possible to have a high-performance internal damping system, exhibiting satisfactory compactness.This compactness is increased compared to the achievements of the prior art, thanks to the taking into account of a differentiated maximum admissible deceleration on the one hand for the storage device, and on the other hand for the radioactive assembly formed of one or more radioactive elements, such as one or more nuclear fuel assemblies, and preferably a single assembly.

[0023] Each of the independent damping devices can thus be designed as precisely as possible, to improve the compactness of the assembly. In other words, the invention is constructed based on the observation that the radioactive elements can withstand greater decelerations than the storage device that houses them, or vice versa. The second associated damping device can therefore have a greater crushing stress, or a larger active surface, and therefore adopt a lower axial height, synonymous with reduced bulk and greater compactness. These advantageous measures can be adopted while respecting the maximum admissible deceleration for the radioactive elements, and being capable of absorbing all of the potential energy of the latter, without risk of bottoming out of this second damping device.

[0024] The invention preferably provides for the implementation of one or more of the following optional features, taken individually or in combination.

[0025] Preferably, the ratio | yz - Yi I / min (Yz, YI) is greater than 1.1.

[0026] Preferably, the internal damping system comprises one or more other second plastic deformation damping devices, each associated with a separate radioactive assembly formed of one or more other radioactive elements, the first and second parameters of the first and second damping devices being such that the second representative deceleration value y2 associated with each of at least several second damping devices, and preferably with each of all these second damping devices, is different from the first representative deceleration value yi associated with the first damping device.

[0027] Preferably, the radioactive assembly associated with the second damping device, or with each second damping device, is formed from a single radioactive element.

[0028] Preferably, each radioactive element is a nuclear fuel assembly, preferably a fresh fuel assembly, even more preferably of the MOX type, or a container / case of vitrified waste or technological waste, or a container / case of shells and tips, or a case for transporting powder.

[0029] Preferably, the or each second damping device is formed from a single block of damping material, preferably made of metal foam, wood, honeycomb or using a metal tubular structure. Alternatively, each second damping device may comprise several blocks spaced apart from each other and operating independently in the event of axial fall of the package. In all cases, for the damping of radioactive elements, all the blocks preferably have the same crushing stress.

[0030] Preferably, the first damping device is formed from several blocks of damping material spaced apart from each other, preferably made of foam, wood, honeycomb or even using a metal tubular structure. All these damping blocks associated with the storage device preferably have the same crushing stress. Alternatively, the first damping device could be formed from a single block of damping material.

[0031] Preferably, the aforementioned blocks are cylindrical, or pyramidal in shape.

[0032] Preferably, the crushing stress 02 of the or each second damping device is different from the crushing stress 01 of the first damping device. Alternatively, identical crushing stresses may be retained for the first and second damping devices, without departing from the scope of the invention. In this case, the differentiated decelerations of the entities are controlled by the extent of the active surfaces of the first and second damping devices, or by the masses of the storage device and of each radioactive assembly.

[0033] Preferably, the first damping device and the or each second damping device all have an identical or substantially identical axial thickness. For example, a variation in thickness of the order of a maximum of 10% may be tolerated between the largest value and the smallest value.

[0034] Preferably, the first damping device and the or each second damping device are arranged in the same transverse plane of the package.

[0035] Preferably, the first damping device and the or each second damping device are arranged in the same envelope.

[0036] Preferably, the storage device comprises a perforated head plate, and the internal damping system is preferably fixed to said perforated head plate. Alternatively, the internal damping system may be fixed to the associated axial closure member, for example the lid of the packaging, or simply be freely arranged between the storage basket and this associated axial closure member. Preferably, the associated axial closure member is the lid of the packaging, preferably removably mounted on the lateral body of the packaging. Alternatively, the associated axial closure member is the bottom of the packaging. Indeed, even if there is no problem of holding the screws of the closure system on the bottom side, the control of decelerations in the event of an axial fall on the bottom side may also be taken into account in certain situations.Other advantages and characteristics of the invention will appear in the detailed non-limiting description below.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] This description will be made with regard to the attached drawings, among which;

[0039] [Fig 1] represents a schematic axial sectional view of a package according to a preferred embodiment of the present invention;

[0040] [Fig 2] represents a perspective view of the radioactive contents shown in the preceding figure, according to a preferred embodiment of the invention;

[0041] [Fig 3] is a perspective view of the internal shock absorber system fitted to the package shown in Figure 1;

[0042] [Fig 4] represents an exploded perspective view of the internal damping system shown in the previous figure;

[0043] [Fig 5] shows a perspective view of the internal damping system similar to that of Fig. 3, with one of the two half-shells removed for clarity;

[0044] [Fig 6] is a cross-sectional view of the internal damping system, taken along plane P of Fig. 5, passing through the ends of the damping blocks; and

[0045] [Fig 7] represents a sectional view taken along line VI I -VII of Figure 6.

[0046] DESCRIPTION OF EMBODIMENTS

[0047] Referring firstly to FIG. 1, there is shown a package 100 for storing and / or transporting radioactive contents 12, in the form of a preferred embodiment of the present invention.

[0048] The package 100 firstly comprises a packaging 1 provided with a lateral body 2, a base 4 and a removable cover 6 closing an opening of the packaging opposite the base 4. The packaging has a longitudinal central axis 8 around which the lateral body 2 extends, this axis 8 passing through the cover 6 and the base 4 respectively arranged at the front and rear ends of the lateral packaging body 2. As has been schematically illustrated in FIG. 1, the base 4 can be made in one piece with the lateral packaging body 2. The cover 6 is attached to the front end of the lateral body 2, corresponding to the upper end in the vertical position of the packaging shown in FIG. 1. The fixing of this cover 6 is preferably carried out using screwed elements 14, distributed around the periphery of the cover.

[0049] The lateral body 2, the cover 6 and the base 4 delimit a containment enclosure 10 used to house the radioactive contents 12. The cover 6 and the base 4 thus form the two opposite axial closure members of the containment enclosure 10.

[0050] The radioactive content 12, also centered on the axis 8, comprises a storage device and one or more radioactive elements, here nuclear fuel assemblies, preferably fresh such as MOX fuel. Instead of the nuclear fuel assemblies, the radioactive elements within the meaning of the invention could alternatively be vitrified waste containers / cases, shell and end-cap containers / cases, or even cases for transporting powder. In these alternative examples, the containers / cases housed in the storage device are also leaktight.

[0051] As shown in dotted lines in Figure 1, at the ends of the package considered in the direction of axis 8, the packaging can be equipped with shock-absorbing covers 20 protecting respectively the removable cover 6 and the bottom 4 of the packaging.

[0052] The package 1 is also equipped with an internal damping system 22 specific to the invention, shown only schematically in FIG. 1. This internal damping system 22 is housed in the containment enclosure 12, axially between an internal surface 24 of the cover 6, and an axial end surface 26 of the radioactive content 12. Preferably, the internal damping system 22 is fixed to the axial end surface 26 of the radioactive content 12, for example using screwed elements or by welding. It could alternatively be fixed to the internal surface 24 of the cover 6, or else freely arranged between the radioactive content 12 and the cover 6. Thus, the internal damping system 22 can be arranged in several ways between the radioactive content 12 and its associated axial closure member, formed by the removable cover 6.

[0053] Referring now to Figure 2, the radioactive content 12 is shown, comprising the storage device / basket 30 and the nuclear fuel assemblies 32a-32f. These assemblies 32a-32f are each arranged in a housing 34 defined by the basket 30. The housings 34 are axially open at an openwork head plate 36 of the basket, on which the internal damping system is intended to be fixed. The head plate 36, by virtue of its openwork nature, thus forms the axial end of the housings 34. The axial end surface 26 of the radioactive content 12 is thus formed by the flat outer surface of the head plate 36, and by the axial end surface of the assemblies 32a-32f located close to or in the same plane as the flat outer surface of the head plate 36.

[0054] One of the particular features of the invention lies in the dissociation and independence of the means used to dampen, on the one hand, the basket 30, and on the other hand, each of the assemblies 32a-32f, in the event of axial fall of the package from the cover side. This particular feature will now be described with reference to Figures 3 to 7, showing the internal damping system 22 which generally comprises a first plastic deformation damping device for damping the basket 30, as well as a second plastic deformation damping device associated with each of the assemblies 32a-32f. In this preferred embodiment, each nuclear fuel assembly 32a-32f thus forms, within the meaning of the claimed invention, a radioactive assembly composed of a single radioactive element (the assembly as such).

[0055] The first damping device 40 is here formed of several cylindrical blocks 40a-40e distributed around the periphery of the damping system 22 of generally cylindrical shape, and centered on the axis 8. Each of the blocks 40a-40e is thus cylindrical with an axis orthogonal or substantially orthogonal to the flat outer surface 26 of the head plate 36, in the direction of which these blocks are oriented. The latter are spaced from each other, and they are preferably made of foam, wood, honeycomb or even using a metal tubular structure, preferably with the same crushing stress oi (in MPa).

[0056] The active surface Si (in m 2) of the first damping device 40 corresponds to the surface of the blocks 40a-40e intended to be axially impacted by the flat outer surface 26 of the head plate 36, in the event of axial fall of the package. More precisely, this active surface Si corresponds to the addition of the active surfaces Si a -If e of all the blocks 40a-40e forming the first damping device 40. These surfaces Si a -If e correspond to the lower axial ends of the blocks 40a-40e, and they are very preferably all flat or substantially flat, orthogonal or substantially orthogonal to the axis 8, and coplanar. In the event of non-flatness of these lower axial ends of the blocks 40a-40e, each active surface Si a -If e then corresponds to the projected surface of the lower axial end of the block concerned, in a plane orthogonal to axis 8, and in the direction of this same axis.

[0057] Moreover, due to the cylindrical character of the block, each active surface Si a -If e also corresponds, in terms of dimension and shape, to any cross-section of its corresponding block 40a-40e. Alternatively, the blocks could have a pyramidal shape, the active surfaces then being able to vary according to the thickness of the block and thus generate lower decelerations at the start of the impact. In this case, the general principle of the invention according to which the first and second parameters are such that the second representative deceleration value y2 is different from the first representative deceleration value yi, is verified at each instant during an axial fall of the package leading the radioactive assembly to plastically crush the first and second damping devices.

[0058] These active surfaces are represented schematically on the section of figure 6 taken in the plane of these surfaces or in close proximity, orthogonal to axis 8, and also partly visible on figure 7.

[0059] The mass Mi (in kg) corresponding to the mass of the basket 30 intended to be cushioned by the first cushioning device 40.

[0060] Thus, using the aforementioned parameters relating to this first damping device 40, the value of yi is determined, corresponding to a first value representative of the deceleration of the basket 30 in the event of an axial fall of the package leading this basket to plastically crush the first damping device 40. This first representative deceleration value yi is determined by the following formula: yi =

[0061] (oi*Si) / Mi.

[0062] As indicated previously, the internal damping system 22 also comprises several second damping devices 50a-50f, each associated with one of the assemblies 32a-32g to dampen it in the event of axial fall of the package. Thus, the second damping devices 50a-50f are independent of each other, and also independent of the blocks of the first damping device 40. This has the consequence that in the event of axial fall of the package, each of these elements deforms plastically freely, without being hindered by the deformation of the other elements located at a distance. This independence of the blocks during their crushing is notably obtained due to the absence of a force distribution plate found in certain solutions of the prior art, and which is usually arranged between the damping systems and the radioactive content.

[0063] In this preferred embodiment of the invention, all the second damping devices 50 are identical, so only one of them will be described in detail below. Each second damping device is here formed from a single cylindrical block 50a-50f, the blocks being distributed at the periphery and in the center of the damping system 22, according to the same distribution as that of the assemblies 32a-32f. The blocks 50a-50f are thus cylindrical with axes orthogonal or substantially orthogonal to the flat outer surface 26 of the head plate 36, as well as to the axial end surface of the nuclear fuel assemblies in the direction of which these blocks 50a-50f are oriented, respectively. The blocks 50a-50f are spaced from each other, and also spaced from the blocks of the first damping device 40.They are preferably made of foam, wood or honeycomb, preferably with the same crushing stress 02 (in MPa), itself preferably different from the aforementioned crushing stress 01.

[0064] The active surface S2 (in m 2) of each second damping device 50a-50f corresponds to the surface of the block intended to be axially supported against the axial end surface of the associated assembly 32a-32f, in the event of axial fall of the package. This surface S2 is therefore formed by the lower axial end of the damping block 50a-50f, which is very preferably flat or substantially flat, orthogonal or substantially orthogonal to the axis 8. All the active surfaces S2 are moreover preferably coplanar. In the event of non-flatness of this lower axial end of the damping block, the active surface S2 then corresponds to the projected surface of the lower axial end of this block, in a plane orthogonal to the axis 8, and in the direction of this same axis.

[0065] Moreover, due to the cylindrical nature of the block, the active surface S2 also corresponds, in terms of size and shape, to any cross-section of its corresponding block 50a-50f. In axial view, this active surface S2 also preferably corresponds, in size and shape, to that of the axial end surface of the associated assembly 32a-32f, a perfect or almost perfect correspondence being effectively sought between these two surfaces, in the direction of the axis 8. Nevertheless, the active surface S2 could be of smaller or larger dimension, without departing from the scope of the invention.

[0066] The active surfaces S2 are represented schematically in the section of figure 6 taken in the plane of these surfaces or in close proximity, orthogonal to axis 8, and one of them is also visible in figure 7.

[0067] The mass M2 (in kg) corresponds to the mass of each nuclear fuel assembly 32a-32f, intended to be damped by the second damping device 50a-50f located axially opposite it.

[0068] Thus, using the aforementioned parameters relating to each of these second damping devices 40, the value of y2 is determined corresponding to a second value representative of the deceleration of each assembly 32a-32f, in the event of an axial fall of the package leading this assembly to plastically crush its associated second damping device, the second representative deceleration value y2 being determined by the following formula: y2 = (O2*S2) / M2.

[0069] Thanks to the proposed design, the first and second aforementioned parameters are advantageously chosen such that the second representative deceleration value y2 is different from the first representative deceleration value yi. In this respect, the ratio | y2 - yi| / min (y2, yi) is preferably greater than 1.1. This leads to a reduction in the overall size of the internal damping system 22, since the maximum admissible deceleration for the basket 30, and that of each of the assemblies 32a-32f, often greater than that of the basket, is specifically taken into account. Each of the independent damping devices 40, 50a-50f can thus be designed as precisely as possible, to improve the compactness of the assembly.

[0070] The design is also retained by adapting the extent of the active surfaces Si, S2 so that all the blocks 40a-40e, 50a-50f are located in the same transverse plane of the package, having an identical or substantially identical axial thickness. Nevertheless, the blocks 50a-50f could alternatively comprise an axial thickness greater than that of the blocks 40a-40e by extending axially in the housings of the basket by crossing the openings of the perforated head plate 36.

[0071] In the case of the first hypothesis, this makes it possible in particular to facilitate the enclosing of these blocks 40a-40e, 50a-50f in the same generally cylindrical envelope 54, shown in FIG. 3 and corresponding to an outer envelope of the internal damping system 22. This envelope 54 can be produced using two half-envelopes 54a, 54b welded at an axial middle part of the system 22 and closed at its two axial ends by two disc-shaped plates 58a, 58b, these half-envelopes also being visible in FIGS. 4 and 5. It is noted that on this envelope 54, the closing plate 58b arranged opposite / in contact with the radioactive content remains thin, so as to maintain the operational independence of the different damping blocks by plastic deformation 40a-40e, 50a-50f. In other words, this plate 58b does not fulfill any function as a load distribution plate in the event of the package falling axially.Inside the envelope, the active surfaces Si, S2 of the blocks 40a-40e, 50a-50f are intended to be in contact with the inner surface of the plate 58b, even if axial clearances have been retained in the representation of figure 7, for reasons of clarity.

[0072] Of course, various modifications may be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples and the scope of which is defined by the appended claims. For example, the packaging 1 could comprise a non-removable cover, for example welded to the lateral packaging body, so as to form a sealed case containing the basket and radioactive elements, this case also being called a "canister". Furthermore, the internal shock-absorbing system according to the invention could be associated with the bottom 4 of the packaging, without departing from the scope of the invention.

Claims

DEMANDS 1. Package (100) comprising radioactive content (12) and packaging (1) for the transport and / or storage of this content (12), the packaging comprising a side body (2) extending around a central longitudinal axis (8) of the packaging, and a base (4) and a lid (6) respectively arranged at the axial ends of the side body of packaging (2) and forming two axial sealing elements delimiting, with the side body of packaging, a containment enclosure (10) in which the radioactive content (12) is housed, the packaging also comprising an internal shock-absorbing system (22) housed in the containment enclosure (10) and arranged axially between the radioactive content (12) and one of the two axial sealing elements, referred to as the associated axial sealing element, the radioactive content (12) comprising a storage device (30) and one or more elements radioactive (32a-32f),the storage device delimiting one or more axial compartments (34) open axially towards the associated axial sealing member (6), and in each of which is arranged at least one radioactive element (32a-32f), characterized in that the internal damping system (22) comprises a first plastic deformation damping device (40) to dampen the storage device (30), as well as a second plastic deformation damping device (50a-50f) associated with a radioactive assembly formed of one or more radioactive elements (32a-32f), the first and second damping devices (40, 50a-50f) being arranged so as to operate independently of each other in the event of axial fall of the package, the first damping device (40) being associated with the following first parameters:, - oi, corresponding to the crushing constraint of this first damping device; - If, corresponding to the active surface of the first damping device intended to be axially impacted by the storage device (30) in the event of an axial fall of the package; - Mi, corresponding to the mass of the storage device (30) intended to be damped by the first damping device (40); - Yi, corresponding to a first representative value of the deceleration of the storage device in the event of an axial fall of the package causing this storage device (30) to plastically crush the first damping device (40), the first representative value of deceleration yi being determined by the following formula: yi = (oi*Si) / Mi, the second damping device (50a-50f) being associated with the following second parameters: - 02, corresponding to the crushing constraint of this second damping device; - S2, corresponding to the active surface of the second damping device intended to be axially impacted by its associated radioactive assembly (32a-32f), in the event of axial fall of the package; - M2, corresponding to the mass of the radioactive set (32a-32f) intended to be damped by the second damping device (50a-50f); - Y2, corresponding to a second representative value of the deceleration of the associated radioactive assembly, in the event of an axial fall of the package causing this radioactive assembly (32a-32f) to plastically crush the second damping device (50a-50f), the second representative value of deceleration Y2 being determined by the following formula: Y2 = (O2*S2) / M2, and in that the first and second parameters are such that the second representative value of deceleration Y2 is different from the first representative value of deceleration yi- 2. Package according to claim 1, characterized in that the ratio | Y2 - Yi I / min (Y2, YI) is greater than 1.

1.

3. Package according to any one of the preceding claims, characterized in that the internal damping system (22) comprises one or more other second damping devices (50a-50f) by plastic deformation, each associated with a separate radioactive set formed of one or more other radioactive elements (32a-32f), and in that the first and second parameters of the first and second damping devices (40, 50a-50f) are such that the second representative deceleration value y2 associated with each of at least several second damping devices (50a-50f), and preferably with each of all such second damping devices, is different from the first representative deceleration value yi associated with the first damping device (40).

4. Package according to any one of the preceding claims, characterized in that the radioactive assembly associated with the second damping device (50a-50f), or with each second damping device, is formed of a single radioactive element (32a-32f).

5. Package according to any one of the preceding claims, characterized in that each radioactive item (32a-32f) is a nuclear fuel assembly, preferably a fresh fuel assembly, even more preferably of the MOX type, or a container / casing for vitrified waste, or a container / casing for shells and end caps, or a casing for transporting powder.

6. Package according to any one of the preceding claims, characterized in that the second or each second damping device (50a-50f) is formed of a single block of damping material, preferably of metallic foam, wood, honeycomb, or even using a metallic tubular structure.

7. Package according to any one of the preceding claims, characterized in that the first damping device (40) is formed of several blocks (40a-40e) of damping material spaced apart from each other, preferably made of foam, wood, honeycomb or even using a tubular metal structure.

8. Package according to any one of the preceding claims, characterized in that the crushing stress 02 of the or of each second damping device (50a-50f) is different from the crushing stress 01 of the first damping device (40).

9. Package according to any one of the preceding claims, characterized in that the first damping device (40) and the or each second damping device (50a-50f) all have an identical or substantially identical axial thickness.

10. Package according to any one of the preceding claims, characterized in that the first damping device (40) and the or each second damping device (50a-50f) are arranged in the same transverse plane of the package.

11. Package according to any one of the preceding claims, characterized in that the first damping device (40) and the or each second damping device (50a-50f) are arranged in the same envelope (54).

12. Package according to any one of the preceding claims, characterized in that the storage device (30) comprises a perforated head plate (36), and in that the internal shock-absorbing system (22) is preferably fixed on said perforated head plate.

13. Package according to any one of the preceding claims, characterized in that the associated axial sealing member is the lid (6) of the package, preferably mounted removably on the lateral body of the package.

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