EP3766082B1 - Packaging for the transport and/or storage of radioactive materials, permitting easier production and improved heat conductivity - Google Patents

Description

TECHNICAL AREA

The present invention relates to the field of containers for the transport and/or storage of radioactive materials, for example nuclear fuel assemblies or radioactive waste.

More specifically, the present invention relates to a packaging comprising at its periphery an outer envelope for radiological protection.

PRIOR ART

From the prior art, it is known to add an outer envelope for radiological protection, around a side body of a package. The function sought with this casing lies in protection against gamma radiation, and/or in neutron absorption in order to comply with regulatory radiological criteria around the casing, when the latter is loaded with radioactive materials.

This envelope can be obtained by stacking unitary annular structures, as is for example known from the documents EP 1 524 673 Where EP 2 041 753 . In the known embodiment of the document EP 2 041 753 , the axially stacked structures together define an outer radial surface of the package, which turns out to be quite easily decontaminated, and able to meet current decontamination requirements.

Each unitary annular structure of the stack is traversed axially by a multitude of orifices. The axial alignment of the orifices passing through the various structures makes it possible to form a plurality of axial cavities each extending over the entire length of the casing. These cavities are then filled by the radiological protection material, which then takes the form of a plurality of axial bands of radiological protection distributed circumferentially in the casing.

This design certainly makes it possible to achieve the objective of easy decontamination of the outer radial surface of the packaging, but it requires a complicated assembly of the unitary annular structures. Indeed, these must be perfectly indexed angularly relative to each other, in order to properly reconstitute the axial cavities for housing the radiological protection strips.

Many other drawbacks arise from this design, including a greatly degraded thermal conduction function within the envelope. This is explained by the fact that the axial bands partially overlap each other in the radial direction, in order to best limit radiological leaks in this direction. This covering leads to a notable complexification of the shape of the radial walls which define the axial cavities, thus creating poorly optimized radial thermal conduction paths.

Consequently, there is a need to optimize the design of existing packaging, in order to overcome the drawbacks described above.

DISCLOSURE 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 the characteristics of claim 1.

The invention thus proves to be advantageous in that it allows the preservation of an easily decontaminable outer packaging envelope, produced by the multiplicity of the outer annular walls of the unitary structures, while improving the heat conduction function thanks to the radial walls. thermal conduction which may have a more direct radial path. In addition, the internal annular wall in contact with the lateral packaging body makes it possible to improve heat exchange between this lateral body and the unitary annular structure, thanks to a large contact surface. The fact of integrating the internal annular wall to the annular structure unit avoids having to attach fixedly, on the packaging side body, a heat transfer plate between this same side body and the unitary annular structure. This internal annular wall, in addition to conferring protection against gamma radiation, facilitates the installation and maintenance of the radiological protection in the cavity, by participating in the delimitation of the latter.

In addition, the proposed design greatly facilitates the assembly of the outer casing, since the formation of the cavities for housing the radiological protection elements no longer requires precise angular indexing of the structures with respect to each other. Also, the radiological protection elements can advantageously be put in place gradually, as the stacking of the unitary annular structures is carried out.

Other advantages flow from the design specific to the invention, such as for example the improvement of the radiological protection which can now be annular, in comparison with the less efficient axial bands of the prior art.

It also becomes possible to locally adapt the radiological performance of the material, to the need for specific protection associated with the axial position of this material. Indeed, the annular cavities which follow one another axially may not all be filled with the same radiological protection material. In this respect, at the center of the packaging, a material will for example be used having a higher capacity for radiological protection than that of another material used to fill the annular cavities located close to the axial ends of the packaging. This leads to a significant economic gain, while providing satisfactory radiological protection. This specificity proves to be all the more advantageous in that it is obtained without modifying the thickness of the radiological protection elements, nor that of the annular cavities which receive them.

Still among the other advantages conferred by the invention, mention is made of improving the quality control of the radiological protection, in particular when the protection is cast in situ. Indeed, it is possible to have visual access to the radiological protection placed in its associated cavity, before the latter is closed by the placement of the directly consecutive structure in the stack. This visual access can advantageously take place over the entire perimeter of the radiological protection. Thus, in the event of non-compliance, the protection can be touched up or replaced before closing the cavity in which it is housed.

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

Each unitary annular structure is in one piece, which makes it possible to limit manufacturing costs, while retaining the desired functionalities for this unitary annular structure.

avec :

• « n » correspondant au nombre total de structures annulaires unitaires empilées ;
• « E1 » correspondant à l'épaisseur de la paroi radiale de conduction thermique ; et
• « H » correspondant à la hauteur de l'enveloppe extérieure.

Said radiological protection element is a neutron protection element, and each unitary annular structure corresponds to the following formula: $$0.02<\mathrm{not}.\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">E</figure-callout>}1/\mathrm{H}<0.3$$

with :

• "n" corresponding to the total number of stacked unitary annular structures;
• “E1” corresponding to the thickness of the radial heat conduction wall; and
• "H" corresponding to the height of the outer envelope.

It has in fact been determined, surprisingly, that the higher the n.E1/H ratio, the lower the maximum temperature observed within the neutron protection elements. This ratio is thus greater than 0.02, while remaining less than 0.3 in order to maintain sufficient neutron protection. The interval adopted for the n.E1/H ratio makes it possible to very satisfactorily satisfy the thermal criterion, as well as the neutron protection criterion as a whole within the package.

avec « H » exprimée en mètres.Preferably, the packaging also corresponds to the following formula: $$\mathrm{not}/\mathrm{H}>2$$

with "H" expressed in meters.

With this dimensioning, the thickness E1 of the radial heat conduction walls is limited, so that the neutron leaks observed locally at the level of these walls are advantageously reduced.

avec « L » correspondant à l'écartement radial entre les parois annulaires interne et externe.Also with the aim of locally reducing neutron leakage, in particular the neutron dose rate at 2 meters from the outer surface of the outer casing of the packaging, each unitary annular structure preferably corresponds to the following formula: $$\mathrm{I}/\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">E</figure-callout>}1<10$$

with "L" corresponding to the radial spacing between the inner and outer annular walls.

Surprisingly, it has in fact been determined that the thickness E1 of the radial heat conduction wall constitutes a determining factor for the neutron dose rate at 2 meters, more so than the spacing L for which an effect of threshold was also detected, beyond which the increase in this spacing L no longer really acts on the neutron dose rate at 2 meters.

Preferably, each unitary annular structure has a half cross-section in the general shape of a U, with the base of the U formed by the radial heat conduction wall, and the two branches of the U respectively formed by the outer and inner annular walls, the inside the U forms the annular cavity housing said at least one radiological protection element.

Preferably, for each U-shaped unitary annular structure, the two free ends of the two outer and inner annular walls are located in the same transverse plane of the packaging.

Other shapes are of course possible, such as an H-shape, which is also particularly simple to obtain, while offering high thermal conduction performance.

The radial heat conduction wall of each unitary annular structure has, in half cross-section, the shape of a straight segment, preferably oriented orthogonally to the central longitudinal axis.

This specificity makes it possible to obtain a high-performance heat transfer function, since the radial wall then forms a direct heat conduction path. Alternatively, the line segment could be tilted differently by relative to the central longitudinal axis. The thermal conduction path would then be less direct, but the radiological protection would be more effective.

According to another embodiment, the radial heat conduction wall of each unitary annular structure has, in half cross-section, at least one level axial break between a radially outer portion of the wall, and a radially inner portion of the wall. Here again, this provides better radiological protection, since no radial leakage occurs via the radial heat conduction walls.

In each annular cavity, the radiological protection element(s) forms a protection ring extending over 360°. This ring extends continuously or discontinuously, and in the latter case obtained with several protective elements arranged end to end, circumferential overlap zones are preferably provided at the junction between these elements.

In each annular cavity, each radiological protection element is an element cast in the cavity, or a prefabricated element arranged in this cavity.

At least several of said unitary annular structures are identical, and preferably all of them. This allows for greater ease of manufacture. But on the contrary, for at least some of them, the annular structures can have different geometries to adapt the volume of the annular cavities and the radiological protections housed therein, to the local need for radiological protection.

Each unitary annular structure has a half cross-section of constant shape, again for ease of manufacture.

In any half cross section of each unitary annular structure, the radial heat conduction wall has the same thickness. This helps to impart uniform thermal performance in the radial direction.

The number of unitary annular structures is between 10 and 50, and the height of the outer radiological protection envelope formed by the stacking of these structures is between 1 and 4 m.

• mise en place de l'une des structures annulaires unitaires dans l'empilement autour du corps latéral ;
• mise en place de chaque élément de protection radiologique dans la cavité annulaire définie en partie par la structure annulaire unitaire mise en place à l'étape précédente.

The invention also relates to a method of manufacturing such packaging for the transport and/or storage of radioactive materials; comprising the repetition of the following successive steps:

• positioning one of the unitary annular structures in the stack around the side body;
• placing each radiological protection element in the annular cavity defined in part by the unitary annular structure put in place in the previous step.

Thus, when the unitary annular structures must be heated before they are placed in the stack, it can then advantageously be waited for the cooling of the annular structure assembled around the lateral body, before the establishment of each radiological protection element. These radiological protection elements are then not exposed to any risk of thermal degradation.

• mise en place de chaque élément de protection radiologique dans la cavité annulaire définie en partie par l'une des structures annulaires unitaires ;
• mise en place, dans l'empilement autour du corps latéral, de la structure annulaire unitaire mentionnée à l'étape précédente, équipée de chaque élément de protection radiologique.

The invention also relates to another method for manufacturing such packaging for the transport and/or storage of radioactive materials, comprising the repetition of the following successive steps:

• placing each radiological protection element in the annular cavity defined in part by one of the unitary annular structures;
• installation, in the stack around the side body, of the unitary annular structure mentioned in the previous step, equipped with each radiological protection element.

This implementation makes it very easy to assemble the components of the packaging, thanks in particular to the sequencing of steps as well as the possibility of manufacturing the means of radiological protection separately from the side body of the packaging, or even on a different manufacturing site. It also allows easy verification of the conformity of the radiological protection elements, before the installation of the associated annular structure around the side body of the packaging. In the event of failure of one of the radiological protection elements, it can be reworked or replaced, always before the installation of the associated annular structure around the side body of the packaging.

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

BRIEF DESCRIPTION OF DRAWINGS

• la figure 1 représente une vue en coupe axiale longitudinale d'un emballage pour l'entreposage et/ou le transport de matières radioactives, selon un mode de réalisation préféré de la présente invention ;
• la figure la représente une vue en coupe transversale de l'emballage montré sur la figure 1, selon la ligne la-la de cette figure ;
• la figure 2 représente une vue en perspective de l'emballage montré sur la figure 1 ;
• la figure 3 représente une vue partielle en perspective de l'une des structures annulaires unitaires qui forment une enveloppe extérieure de protection radiologique de l'emballage montré sur les figures précédentes ;
• la figure 4 est une vue en coupe transversale de la structure montrée sur la figure 3 ;
• la figure 5 est une vue en demi-section transversale de la structure annulaire unitaire montrée sur les figures 3 et 4 ;
• la figure 6 représente schématiquement un procédé de fabrication de l'emballage montré sur les figures précédentes, selon une première possibilité de mise en œuvre ;
• la figure 7 représente schématiquement un procédé de fabrication de l'emballage montré sur les figures 1 à 5, selon une seconde possibilité de mise en œuvre ;
• la figure 8 représente une partie de l'emballage montré sur les figures 1 à 5, selon une alternative de réalisation ;
• la figure 9 représente une vue similaire à celle de la figure 5, avec la structure annulaire unitaire se présentant selon une alternative de réalisation ;
• la figure 10 est une vue partielle en perspective de l'une des structures annulaires unitaires, selon encore une autre alternative de réalisation ; et
• la figure 11 est une vue en coupe transversale de la structure montrée sur la figure 10.

This description will be given with regard to the appended drawings, among which;

• the figure 1 represents a view in longitudinal axial section of a packaging for the storage and/or transport of radioactive materials, according to a preferred embodiment of the present invention;
• Figure la shows a cross-sectional view of the package shown in figure figure 1 , along the line la-la of this figure;
• the figure 2 represents a perspective view of the packaging shown in the figure 1 ;
• the picture 3 shows a partial perspective view of one of the unitary annular structures which form an outer envelope for radiological protection of the packaging shown in the preceding figures;
• the figure 4 is a cross-sectional view of the structure shown in the picture 3 ;
• the figure 5 is a half cross-sectional view of the unitary ring structure shown in the figure 3 and 4 ;
• the figure 6 schematically represents a method of manufacturing the packaging shown in the preceding figures, according to a first possibility of implementation;
• the figure 7 schematically represents a manufacturing process for the packaging shown in the figures 1 to 5 , according to a second possibility of implementation;
• the figure 8 represents part of the packaging shown on the figures 1 to 5 , according to an alternative embodiment;
• the figure 9 represents a view similar to that of the figure 5 , with the unitary annular structure occurring according to an alternative embodiment;
• the figure 10 is a partial perspective view of one of the unitary annular structures, according to yet another alternative embodiment; and
• the figure 11 is a cross-sectional view of the structure shown in the figure 10 .

DETAILED DISCUSSION OF PREFERRED EMBODIMENTS

With reference first to the figure 1 and 2 , there is shown a packaging 1 for the storage and/or transport of radioactive materials, such as nuclear fuel assemblies or radioactive waste (not shown).

This packaging 1 is shown in a vertical storage position, in which its central longitudinal axis 2 is oriented vertically. It rests on a packaging bottom 4, opposite a removable lid 6 in the direction of the height 8, parallel to the longitudinal axis 2. Between the bottom 4 and the lid 6, the packaging 1 comprises a side body 10 extending around the axis 2, and internally delimiting a housing 12 for the radioactive materials. This housing can constitute a containment enclosure 12 intended to receive the radioactive materials, for example arranged in a storage basket also located in the containment enclosure. Alternatively, the containment enclosure is fully defined by a case, also referred to as a “canister”, placed in the aforementioned housing 12. The latter is closed axially upwards by cover 6, and downwards by bottom 4.

The side body 10 can be made in one piece, as shown in the figure 1 , or by several concentric ferrules.

Around the side body 10, the packaging 1 includes an outer radiological protection casing 14, specific to the present invention.

The casing 14 is made using the axial stack of a plurality of unitary annular structures 16, for example provided in a number n between 10 and 50, over a cumulative height "H" of the order of 1 to 4m. This height "H" of the outer casing 14 corresponds substantially to that of the housing 12 in the direction 8.

In this preferred embodiment, all the structures 16 stacked along the axis 2 are identical, each secured to and in contact with an outer radial surface 18 of the lateral body 10. At one of the ends of the stack, corresponding to the low end on the figure 1 , the last structure 16 can nevertheless be covered with a closure plate 20.

With reference now to figures 3 to 5 , the design of one of the unitary annular structures 16 will be detailed, represented in its position as adopted when it is on the packaging in a vertical position, with the lid upwards as on the figure 1 and 2 .

The structure 16 is preferably made in one piece. In other words, the annular structure 16 is in one piece, for example produced by forging then machining, or else by molding, preferably by casting in cast iron. These techniques make it possible to limit the production costs.

The structure 16 has a half cross-section in the general shape of a U, with its base facing upwards. A reverse orientation with the base down would obviously be possible, without departing from the scope of the invention. This half-cross-section maintains a constant shape, regardless of the plane of section along the circumferential direction of this structure 16.

The base of the U forms a radial heat conduction wall 22. It takes the form of a straight segment which is preferably orthogonal to the axis 2, for a more direct conduction path towards the outside of the package. This wall 22 has the same thickness "E1" in any cross-section half. This thickness “E1” is for example between 5 and 40 mm, and preferably between 15 and 25 mm. As will be described later, its thickness is correlated to the number of structures 16, in particular with the aim that all the radial walls joined together can evacuate a determined quantity of heat, given off by the radioactive materials.

The inner end of the radial heat conduction wall 22 is intended to be in contact with and secured to the outer radial surface 18 of the side body 10. At its opposite end, namely the outer end, the radial wall 22 is integral with an outer annular wall 24. In half cross-section, this wall 24 takes the form of a straight segment parallel to the axis 2, and which projects downwards from the outer end of the radial wall 22. As an indication, it is noted that the thickness "E2" of the wall 24 is essentially dependent on its capacity to absorb the gamma radiation generated by the neutrons, when the latter are absorbed within the radiological protection , in the case where the latter is a neutron shield as will be described below. The thickness "E2" can be between 5 and 40 mm, and preferably between 15 and 25 mm.

Finally, at its inner end, the radial wall 22 is integral with an internal annular wall 26 forming a second branch of the U. The internal annular wall 26 is also in contact with and integral with the outer radial surface 18 of the side body 10. The contact is preferably a surface contact, over the entire internal surface of the annular wall 26. The joining is effected for example by hooping, as will be described below. Alternatively, the contact may simply be sliding between, on the one hand, the internal annular wall 26 and the inner end of the radial heat conduction wall 22 which extends it axially, and, on the other hand, the external radial surface 18 of the lateral body 10. .

In half cross-section, this wall 26 also takes the form of a straight line segment parallel to the axis 2, and which projects downwards from the inner end of the radial wall 22. By way of indication, it is noted that the thickness “E3” of the wall 26 is notably dictated by its ability to limit gamma radiation. The greater its thickness, the more that of the side body 10 can be reduced. The manufacturing costs of the assembly formed by the side body 10 and the outer casing 14 can then be reduced, since the cost of the internal parts of the annular structures 16, which are preferably made of cast iron, is lower than that of the body. 10, preferably made of forged steel.

Thanks to the design of these unitary annular structures 16, when they are stacked around the side body 10, they form annular cavities housing radiological protection elements. More specifically, with reference again to the figure 1 , each annular cavity 30 is delimited by two structures 16 directly consecutive in the stack. In the preferred embodiment which is described, the cavity 30 is closed radially towards the outside by the external annular wall 24 of one of the two directly consecutive annular structures 16, and closed radially towards the interior by the internal annular wall 26 of this same annular structure 16. In addition, the annular cavity 30 is closed axially upwards by the radial wall 22 of this same structure 16, and closed axially downwards by the radial wall 22 of the annular structure 16 directly consecutive in the stack, which closes off the opening between the two branches of the U of the first structure 16.

Once the annular structures are stacked, the outer annular walls 24 are adjacent along the direction 8, and they together form an outer radial surface of the packaging which is substantially continuous, and easily decontaminated.

The annular cavities 30 thus follow one another along the axis 2, each being filled entirely or almost entirely with a radiological protection material. As mentioned above, it may be a material for protection against gamma radiation, and/or a neutron absorption material aimed at satisfying regulatory radiological criteria around the packaging when it is loaded with radioactive materials. Preferably, it is a neutron-absorbing material, comprising on the one hand neutron-absorbing elements, and on the other hand hydrogenated elements. For information, it is recalled that by "neutron absorber elements", it is understood elements which have an effective section greater than 100 barns for thermal neutrons. By way of indicative examples, these are elements of the boron, gadolinium, hafnium, cadmium, indium, etc. type. It is also recalled that hydrogen (light atom) makes it possible to slow down the neutrons so that they are then absorbed by the neutron absorbing elements. Thus, the temperature criterion must be respected essentially to avoid a substantial loss of hydrogen, which could harm the neutron shielding functions, and this for the entire duration of use of the packaging.

For the dimensioning of the various constituents of the packaging, it is first of all ensured that each structure 16 corresponds to the following formula: $$0.02<\mathrm{not}.\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">E</figure-callout>}1/\mathrm{H}<0.3$$

By remaining below 0.3, this ratio makes it possible to maintain sufficient neutron shielding in the cavities 30. Moreover, by being greater than 0.02, this ratio surprisingly makes it possible to maintain the neutron shielding material at a reasonable maximum temperature. , limiting the risk of accelerated ageing. This ratio thus offers a very satisfactory compromise in terms of thermal conduction and neutron protection as a whole.

It is also noted that in the formula n.E1/H, as well as in the formula L/E1 < 10 described below and also including the thickness E1, this corresponds to the average thickness when it is not is not constant along the radial heat conduction wall 22.

To improve the neutron protection criterion, locally at the level of the radial heat conduction walls 22, the packaging is such that it corresponds to the following formula:
n/H > 2, “H” here being expressed in meters.

With this dimensioning, the thickness E1 of the radial walls 22 is limited, and the neutron leaks observed locally are thereby reduced.

avec « L » correspondant à l'écartement radial entre les parois annulaires interne et externe 26, 24. Il est par ailleurs précisé que cette distance L correspond également de préférence sensiblement à la longueur radiale de la protection neutronique. Plus généralement, il est indiqué que la cavité annulaire est remplie en totalité ou en grande partie par la protection neutronique, de préférence sur au moins 90% de son volume total.Still with the aim of locally reducing neutron leakage, in particular the neutron dose rate at 2 meters from the outer surface of the envelope 14, each structure 16 preferably responds to the following formula: $$\mathrm{I}/\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">E</figure-callout>}1<10$$

with "L" corresponding to the radial spacing between the inner and outer annular walls 26, 24. It is further specified that this distance L also preferably corresponds substantially to the radial length of the neutron shield. More generally, it is indicated that the annular cavity is filled in whole or in large part by the neutron shielding, preferably over at least 90% of its total volume.

This geometric condition makes it possible to limit the thickness E1 of the radial wall 22, which constitutes a determining factor for the neutron dose rate at 2 meters. A dimensioning of the annular structure 16 with such a higher ratio or equal to 10 would result in a high radial length of the casing 14 to satisfy the neutron dose rate criterion at 2 meters, and therefore a substantial overall mass of the package. This is explained at least in part by the fact that from a given radial length of the neutron shield, a threshold effect occurs and the increase in this length has little effect on the throughput of neutron dose at 2 meters.

In each cavity 30, the radiological protection material is for example in the form of one or more cast elements, preferably a single continuous ring cast over 360° in the cavity 30. It can alternatively be in the form of one or more several prefabricated elements, arranged in the cavity 30. In the latter case schematized on the picture 1a , a neutron protection ring 34 is formed discontinuously using several protection elements 32 arranged end to end. To limit radiological leaks in the radial direction, these latter elements 32 preferably have circumferential overlap zones 36 at their circumferential ends ensuring the junction between these different elements.

The figure 6 represents a first method of manufacturing the packaging 1, for the steps which relate to the assembly of the outer casing 14 of radiological protection around the side body 10. This method consists of the repetition of two successive steps. The first of these two steps consists in setting up one of the unitary annular structures 16 in the stack around the lateral body 10, even though its annular cavity 30 is not yet filled by the radiological protection element(s). . This step is schematized by the arrow 36 on the figure 6 . To perform this insertion, the structure 16 can be heated beforehand, for example to a temperature of the order of 200°C. It is brought into contact with the rest of the stack, so as to close the cavity 30 of the structure 16 previously placed in the stack, and which is filled with the radiological protection material.

Once the structure has cooled, for example to a temperature below 160° C., it adheres by shrinking to the outer radial wall 18 of the side body, via the inner end of the radial wall 22 and via the inner annular wall 26 .

The radiological protection material can then be placed in the annular cavity 30 of the cooled structure 16, without risk of thermal degradation of this material. In this respect, it is noted that these steps are carried out with the packaging 1 in the vertical position, but with its bottom facing upwards so that each cavity 30 to be filled is open upwards. The material is put in place by casting or by arranging prefabricated elements in the cavity 30, then the radiological protection thus obtained is inspected before repeating these same two first and second steps.

The figure 7 represents a second method of manufacturing the packaging 1, for the steps which relate to the assembly of the outer casing 14 of radiological protection around the side body 10. This method consists of the repetition of two successive steps. The first of these two steps here consists in placing each radiological protection element in the annular cavity 30 defined in part by one of the unitary annular structures 16, not yet placed in the stack. This step can advantageously be carried out on a site different from that on which the stacking of the unitary annular structures 16 is carried out. The quality of the radiological protection elements can be inspected before the installation of the structure 16 around the body 10, this operation corresponding to the second step. This insertion of the structure 16, equipped with its radiological protection, can also be carried out by heating, as has been described above.

In the embodiment which has just been described, each unitary annular structure 16 has a half cross-section in the general shape of a U, with the base of the U formed by the radial wall 22, and the two branches of the U respectively formed by the external 24 and internal 26 annular walls. In addition, the two free ends of the two annular walls 24, 26 are located in the same transverse plane of the packaging. Nevertheless, the free ends of the two annular walls 24, 26 can be offset axially from each other, without departing from the scope of the invention. Maintaining the free ends of the two annular walls 24, 26 in the same transverse plane makes it easier to cast the neutron shield in the annular cavity 30.

Referring now to the figure 8 , alternative embodiments are shown in which the half cross-section of the structures 16 is different.

On the figure 8 , it is an H whose central bar 22 is substantially orthogonal to the axis 2, to form the radial heat conduction wall. The two lateral branches of the H are thus oriented in the direction 8, and they participate in the delimitation of two directly consecutive annular cavities 30, arranged on either side of the central bar 22 of this H. In other words, each cavity 30 is delimited radially outwards by a part of the external wall 24 (the external lateral branch of the H) of one of the structures 16, and by a part of the external wall 24 of the structure 16 directly consecutive in stacking.

Each annular cavity 30 is also delimited radially towards the inside by a part of the internal wall 26 (the internal lateral branch of the H) of one of the structures 16, and by a part of the internal wall 26 of the structure 16 directly consecutive in the stack.

Here too, the two side branches could be offset axially from one another, without departing from the scope of the invention.

The figure 9 represents another alternative embodiment mentioned above, in which the unitary structure 16 of half cross-section in the shape of a general U no longer has a base 22 substantially orthogonal to the axis 2, but this base 22 is inclined with respect to this same axis 2 by an angle "A" different from 90°. This angle can preferably be between 20 and 70°.

The base 22 forming the radial heat conduction wall may be an inclined straight segment, connecting the ends of the two annular walls 24, 26. Alternatively, as shown in the figure 9 , only a central part of this base 22 of can be a straight segment, or even a curved portion, and the two connecting ends 40 can be rounded.

Finally, the figures 10 and 11 represent another alternative embodiment, on which the radial heat conduction wall 22 of each unitary annular structure 16 has a different shape. It is no longer straight and radial as in the previous embodiments, but it includes, in half-section transverse, at least one level axial rupture 22c between a radially outer wall portion 22a and a radially inner wall portion 22b. This embodiment, like the previous one, makes it possible to improve radiological protection, since no radial leakage occurs via the radial heat conduction walls 22. The axial rupture at level 22c takes the form of a riser oriented parallel to the axis 2, and substantially centered between the two portions 22a, 22b. The axial offset observed between these two portions 22a, 22b is found between the annular portions 24, 26, so that during the stacking of the structures 16, the radial wall 22 at two levels properly closes the opening defined between the annular portions offset 24, 26 from the structure 16 previously placed in the stack.

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 and according to the scope defined by the appended claims. In particular, the different alternatives can be combined.

Claims (16)

1. A package (1) for the transport and/or storage of radioactive materials, the package comprising a package side body (10) extending about a central longitudinal axis (2) and partly delimiting a housing (12) for the radioactive materials, the package also comprising, being arranged around the package side body, an external radiation protection shell (14) made of a plurality of unitary annular structures (16), stacked on each other along the central longitudinal axis (2) and arranged around the package side body (10),

   each unitary annular structure (16) comprising :

   - an outer annular wall (24) ;

   - an inner annular wall (26) ;

   - a radial heat conduction wall (22) having an external end integral with the outer annular wall (24), as well as an internal end in contact with the package side body (10) and integral with the inner annular wall (26) itself in contact with the package side body (10);

   where two unitary annular structures (16) directly consecutive in the stack at least partly delimit an annular cavity (30) housing at least one radiation protection element (32), said cavity being radially closed outwards by the outer annular wall (24) of one or both of the two directly consecutive unitary annular structures, radially closed inwards by the inner annular wall (26) of one or both of the two directly consecutive unitary annular structures, and axially closed on either side by the radial heat conduction wall (22) of one and the other of said two directly consecutive unitary annular structures (16) respectively.
2. The package according to claim 1, characterised in that each unitary annular structure (16) is as a single piece.
3. The package according to claim 1 or claim 2, characterised in that said radiation protection element (32) is a neutron protection element, and in that each unitary annular structure (16) meets the following formula : $$0.02<\mathrm{n}.\mathrm{E}1/\mathrm{H}<0.3$$

   

   with :

   - n" corresponding to the total number of stacked unitary annular structures (16);

   - E1" corresponding to the thickness of the radial heat conduction wall (22); and

   - H" corresponding to the height of the external shell (14).
4. The package according to claim 3, characterised in that it meets the following formula : $$\mathrm{n}/\mathrm{H}>2$$

   

   with "H" expressed in metres.
5. The package according to claim 3 or claim 4, characterised in that each unitary annular structure (16) meets the following formula : $$\mathrm{L}/\mathrm{E}1<10$$

   

   with "L" corresponding to the radial spacing between the inner and outer annular walls (26, 24).
6. The package according to any of the preceding claims, characterised in that each unitary annular structure (16) has a generally U-shaped half transverse cross-section, with the U-base formed by the radial heat conduction wall (22), and the two U-branches formed by the external (24) and internal (26) annular walls respectively, and in that U-interior forms the annular cavity (30) housing said at least one radiation protection element (32).
7. The package according to claim 6, characterised in that for each unitary annular structure (16), the two free ends of the two annular outer (24) and inner (26) walls lie in the same transverse plane of the package.
8. The package according to any of the preceding claims, characterised in that the radial heat conduction wall (22) of each unitary annular structure (16) has, in a half transverse cross-section, a straight segment shape, preferably oriented orthogonally to the central longitudinal axis (2).
9. The package according to any one of claims 1 to 6, characterised in that the radial heat conduction wall (22) of each unitary annular structure has, in half transverse cross-section, at least one axial level change (22c) between a wall radially outer portion (22a) and a wall radially inner portion (22b).
10. The package according to any of the preceding claims, characterised in that in each annular cavity (30) the radiation protection element(s) (32) forms a protective ring (34) extending over 360°.
11. The package according to any of the preceding claims, characterised in that in each annular cavity (30) each radiation protection element (32) is an element cast in the cavity, or a prefabricated element arranged in that cavity.
12. The package according to any of the preceding claims, characterized in that at least several of said unitary annular structures (16) are identical.
13. The package according to any of the preceding claims, characterised in that each unitary annular structure (16) has a half transverse cross-section with a constant shape.
14. The package according to any of the preceding claims, characterised in that the number of unitary annular structures (16) is between 10 and 50, and in that the height (H) of the external radiation protection shell (14) formed by the stack of these structures (16) is between 1 and 4 m.
15. A method for manufacturing a package (1) for the transport and/or storage of radioactive materials according to any of the preceding claims, characterised in that it comprises repeating the following successive steps of:

    - installing one of the unitary annular structures (16) in the stack around the side body (10) ;

    - installing each radiation protection element (32) in the annular cavity (30) partly defined by the unitary annular structure (22) installed in the preceding step.
16. A method for manufacturing a package (1) for the transport and/or storage of radioactive materials according to any one of claims 1 to 14, characterised in that it comprises repeating the following successive steps of:

    - installing each radiation protection element (32) in the annular cavity (30) partly defined by one of the unitary annular structures (16) ;

    - installing, in the stack around the side body (10), the unitary annular structure (16) mentioned in the preceding step, equipped with each radiation protection element (32).

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