EP2577678B1 - Canister for transporting and/or storing radioactive materials, including improved thermal conduction means - Google Patents

Description

TECHNICAL AREA

The present invention relates to the field of packaging for the transport and / or storage of radioactive materials, preferably of the type of irradiated nuclear fuel assemblies.

STATE OF THE PRIOR ART

Conventionally, to ensure the transport and / or storage of radioactive materials, it is used storage devices, also called "baskets" or "racks" storage. These storage devices, usually of cylindrical shape and of substantially circular or polygonal section, are able to receive the radioactive materials. The storage device is intended to be housed in the cavity of a package in order to form together therewith a container for the transport and / or storage of radioactive materials, in which they are perfectly confined.

The aforesaid cavity is generally defined by a lateral body extending along a longitudinal axis of the package, as well as a bottom and a package cover arranged at opposite ends of the body, in the direction of the longitudinal axis. The lateral body includes a wall internal and an outer wall, generally taking the form of two concentric metal ferrules together forming an annular space inside which are housed thermal conduction means, as well as means of radiological protection, in particular to form a barrier against neutrons emitted by the radioactive material housed in the cavity.

The thermal conduction means make it possible to conduct the heat released by the radioactive materials towards the outside of the container, in order to avoid any risk of overheating which may cause degradation of these materials, an alteration of the mechanical properties of the constituent materials of the packaging, or an abnormal pressure rise in the cavity.

Thermal conduction means have been the subject of many developments, which have led to various achievements. One of the most commonly used resides in the placement of fins / ribs in the annular space between the two ferrules. These fins, which extend in length in the direction of the longitudinal axis of the package, thus allow to conduct the heat of the inner shell to the outer shell. Furthermore, in this embodiment, it is classically interposed radiological protection blocks between the fins.

Although widely used, this heat conduction fin solution can be problematic in that it is susceptible to generate hot spots on the outer shell of the lateral body of the package, at the junctions with these fins.

Another solution, known in particular from the document EP 1 355 320 , makes it possible to partially answer this problem of homogeneity of heat transfer, by employing structures in honeycomb. Nevertheless, the arrangement proposed in this document provides a perfectible thermal conduction capacity. In addition, it requires the use of thermal conduction fins, in combination with the honeycomb structures, which complicates the design of the package.

The document JPH05-172992 also discloses a packaging for the transport and / or storage of radioactive materials comprising radiological protection means as well as thermal conduction means.

STATEMENT OF THE INVENTION

The invention therefore aims to at least partially overcome the disadvantages mentioned above, relating to the achievements of the prior art.

To do this, the subject of the invention is a packaging for transporting and / or storing radioactive materials, said packaging comprising a lateral body defining a cavity for accommodating said radioactive materials extending along a longitudinal axis of the package, the body having an inner wall and an outer wall defining therebetween a space extending about said longitudinal axis, said space housing radiological protection means as well as thermal conduction means. According to the invention, said thermal conduction means comprise a plurality of thermal conduction elements each defining internally a hollow extending in length in a conduction direction from the inner wall to the outer wall. In addition, at least a portion of the thermal conduction elements, and preferably each of them, have a hollow filled at least partially with a radiological protection material, and preferably entirely filled with this material.

The particular orientation of the hollows, as well as the orientation of the heat conduction elements which results from this, make it possible to confer a better heat conduction capacity, in particular with respect to the solution of honeycomb structures described in the document EP 1 355 320 wherein the hollows formed by the honeycomb cells are oriented parallel to the walls and to the longitudinal axis of the package. Indeed, thanks to these orientations specific to the present invention, the thermal conduction path defined by the conduction elements is shortened compared to that encountered in the honeycomb structures of the document. EP 1 355 320 because it joins more directly the two walls of the lateral body. In addition, the thermal conduction path between the two walls does not suffer from multiple interruptions of the type encountered in the honeycomb structures of the document. EP 1 355 320 resulting from the superposition of the metal sheets jointly forming the honeycomb cells.

Moreover, the solution afforded by the present invention makes it easy, by appropriately distributing and in quantity the elements of thermal conduction, avoid the appearance of hot spots on the outer wall of the lateral body.

Finally, since the invention offers excellent heat transfer, it no longer requires the use of thermal conduction fins of the type of those encountered in the prior art. Its design is thus simplified.

Preferably, at least some of said thermal conduction elements each extend in a substantially radial direction of the lateral packaging body, which is indeed the direction in which the path is most direct to connect the two walls of the lateral body. In this respect, the radial direction must be understood as being the direction intercepting each of the two walls of the lateral body orthogonally locally. Nevertheless, the invention is not limited to such a direction of conduction, it may for example be inclined relative to a radial plane and / or relative to a transverse plane.

Preferably, at least some of said heat conduction elements each have a substantially cylindrical shape. However, the cylindrical shape could be replaced by a widening shape going from the inner wall to the outer wall, in particular to take into account the difference in average diameters between these walls. In such a case, the geometry of the section of the element remains preferably identical, only the magnitude of this section then being scalable.

As indicative examples, the section of the thermal conduction element may be circular or polygonal, such as square or hexagonal.

Preferably, at least some of said thermal conduction elements each extend in one piece along a length substantially equal to the distance separating the inner and outer walls, in the direction of conduction. This provides an uninterrupted thermal conduction path between the two walls, which is conducive to good heat dissipation. However, at least some of the heat conduction elements could be cut in the direction of conduction, that is to say made in several sections arranged end-to-end. This is of particular interest when the heat conduction elements are closely related to a radiological protection material, for example so as to form blocks, as is preferentially the case in the invention. Indeed, when it is necessary to replace only a portion of the thermal conduction means and / or radiological protection means, the bucking mentioned above makes it possible to replace blocks of smaller dimensions, often better adapted to the size of the cells. defects, and thus reducing the material losses caused during these replacement operations.

Preferably, said heat conduction elements together form an array of recesses which, in section along at least one plane parallel to the longitudinal axis and passing through this network, has at least one zone whose hollow density has an value greater than or equal to 100 troughs / m ² . Such a low minimum density, which is preferably found in all heat conduction means, makes it possible to obtain excellent homogeneity in the heat conduction. It is further indicated that this density can be scalable within the thermal conduction means.

In addition, the walls of the heat conduction elements defining the hollows may be thin, conducive to a reduction in the risk of radiological leakage. Preferably, the average thickness of the walls of the heat conduction elements delimiting the hollows is between 0.02 and 0.5 mm.

Preferably, the recesses each have, in section orthogonal to the direction of conduction, a maximum width of between 2 and 25 mm, this maximum width naturally corresponding to the diameter in the particular case of a circular section.

Also, the ratio between the length of the hollow in the direction of conduction, and its maximum width, is preferably between 3 and 100.

The high density value mentioned above can be achieved by providing that at least some of said thermal conduction elements are made using one or more honeycomb structures, each honeycomb cell forming said hollow of a thermal conduction element. Here, the cells can be of any shape, for example polygonal, as square or hexagonal. In addition, they may be cylindrical or of enlarged shape going from the inner wall to the outer wall, as mentioned above. The advantage of such use is that honeycomb structures are widely distributed commercially in a wide variety of forms. In addition, it is specified that the high density of cells offered by the honeycomb structures is obtained thanks to the walls each delimiting several cells. This aspect also ensures an excellent ratio between the heat conducting capacity of the honeycomb structure and the mass of this structure. By reasoning mass equivalent structure, this ratio is further improved when the structure comprises cells of small section, reflecting a high density of cells, and whose walls are thin.

For the above, it is specified that a honeycomb structure must be understood as a structure formed using a stack of sheets / strips forming the cells, the stacking direction being orthogonal to the direction longitudinal of these cells.

With this solution using honeycomb structures, it is preferably made so that each structure is equipped with holes making the cells communicate with each other. This facilitates the introduction of a radiological protection material into the cells when this material is introduced by casting, in particular when the casting takes place directly between the two walls of the lateral packaging body, with the honeycomb structure already in place in the inter-wall space. Preferably, the holes are made in the stacking direction of the leaves of the honeycomb structure. Their number is chosen according to various parameters, such as the viscosity of the cast material.

Alternatively or simultaneously with the solution of honeycomb structures, it can be provided that at least some of said thermal conduction elements are made using independent elements, spaced from each other, these elements then taking preferentially each in the form of a tube, cylindrical or flared towards the outer wall of the lateral body, and section of any shape. According to a still different solution, combinable with the previous ones, the independent thermal conduction elements can be placed in contact with each other, and possibly fixed together. This leads to a configuration approximating a honeycomb structure.

According to the invention, at least one of the heat conduction elements, and preferably each of them, is externally espoused by said radiological protection material, and also internally, at its hollow. It is thus the same solid material which externally and internally marries at least one of the elements of thermal conduction.

In a general way, it is indicated that the hollow defined by each conduction element Thermal is not necessarily closed in section in a plane orthogonal to the direction of conduction, even if the closed character of the hollow is a preferred solution. In addition, the hollow preferably extends continuously along its associated thermal conduction element, in the direction of conduction, remaining open at its two opposite ends considered in the same direction of conduction.

Finally, the lateral body of the package preferably has a conventional cylindrical shape, for example of circular or polygonal section. In all cases, the inner and outer walls adopting this same shape are generally called ferrules, and are concentric, centered on said longitudinal axis around which is the inter-ferrule space.

The invention also relates to a container for the transport and / or storage of radioactive materials, comprising a package as described above.

Other advantages and features of the invention will become apparent in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 représente une vue en coupe transversale d'un conteneur pour le transport et/ou entreposage d'assemblages de combustible nucléaire, selon un mode de réalisation préféré de l'invention ;
• la figure 2 représente une vue partielle en coupe prise le long de la ligne II-II de la figure 1 ;
• la figure 3 représente une vue similaire à celle montrée sur la figure 2, avec les moyens de conduction thermique se présentant sous une forme alternative de réalisation ; et
• la figure 4 représente une vue partielle en perspective d'un bloc formant une partie des moyens de conduction thermique et des moyens de protection radiologique, destiné à être agencé dans l'espace inter-viroles du corps latéral d'emballage.

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

• the figure 1 represents a cross-sectional view of a container for transporting and / or storing nuclear fuel assemblies, according to a preferred embodiment of the invention;
• the figure 2 represents a partial sectional view taken along line II-II of the figure 1 ;
• the figure 3 represents a view similar to that shown on the figure 2 , with the thermal conduction means being in an alternative embodiment; and
• the figure 4 represents a partial perspective view of a block forming part of the thermal conduction means and radiological protection means, intended to be arranged in the inter-ring space of the lateral packaging body.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Firstly with reference to the figure 1 we see a container 1 for the transport and / or storage of nuclear fuel assemblies.

The container 1 generally comprises a packaging 2 object of the present invention, inside which there is a storage device 4, also called storage basket. The device 4 is intended to be placed in a housing cavity 6 of the package 2, as schematically shown in FIG. figure 1 on which it is also possible to see the longitudinal axis 8 of this package, coincident with the longitudinal axes of the storage device and the housing cavity.

Throughout the description, the term "longitudinal" should be understood as parallel to the longitudinal axis 8 and the longitudinal direction of the package.

The container 1 and the device 4 forming receiving housings of the fuel assemblies are here shown in a horizontal / lying position usually adopted during the transport of the assemblies, different from the vertical position of loading / unloading of the fuel assemblies.

In general, the package 2 essentially has a bottom (not shown) on which the device 4 is intended to rest in a vertical position, a lid (not shown) arranged at the other longitudinal end of the package , and a lateral body 10 extending around and along the longitudinal axis 8, that is to say in the longitudinal direction of the container 1.

It is this lateral body 10 which defines the housing cavity 6, with the aid of a lateral inner surface 12 of substantially cylindrical shape and of circular section, and of axis coincident with the axis 8.

The bottom of the package, which defines the bottom of the cavity 6 open at the lid, can be made in one piece with a portion of the lateral body 10, without departing from the scope of the invention.

Still referring to the figure 1 , one can see in detail the design of the lateral body 10, which firstly has two concentric metal walls / ferrules together forming an annular space 14 centered on the longitudinal axis 8 of the package. It is indeed an inner shell 20 centered on the axis 8, and an outer shell 22 also centered on the axis 8.

The annular space 14 is filled by thermal conduction means 16, as well as radiological protection means 18 essentially designed to form a barrier against neutrons emitted by the fuel assemblies housed in the storage device 4. Thus, these elements are housed between the inner shell 20 whose inner surface corresponds to the inner lateral surface 12 of the cavity 6, and the outer shell 22.

The radiological protection device 18 is produced using a solid material known per se, such as a composite material with a polymer matrix, and more specifically whose matrix is a resin, preferably a highly hydrogenated resin, for example of the type vinylester resin. This neutron protection material is also known as "resin concrete".

It can also incorporate additives to make the composite material self-extinguishing.

The thermal conduction means 16 are for example made of an alloy having good heat conduction characteristics, of the aluminum alloy or copper type. It can also be a ceramic or carbon-based material, such as silicon carbide.

Furthermore, boron may be provided in the radiological protection means and / or the thermal conduction means, in order to reinforce the neutron protection function.

In the embodiment shown on the figures 1 and 2 , the radiological protection means 18 take the form of a single block of material cast between the two rings 20, 22, penetrating into the heat conduction means 16, as will be detailed below.

First of all, the thermal conduction means are here formed using several honeycomb structures 30, which are placed circumferentially next to one another in the inter-ring space 14. Each structure 30 For example, it has a shape of annular ring sector, extending at an angle of preferably between 5 and 60 °. Each structure 30 also extends over the entire length of the space 14 along the direction of the axis 8, as well as over substantially the entire radial length of this space, or may alternatively be cut according to the one and / or the other of these two directions.

Each structure 30 forms heat conduction elements 31 each defining a cavity 32 corresponding to a cell / cell of the structure. Thus, because of the design of the "honeycomb" type, the cavity walls / cells 34 forming the elements 31 make it possible to define each several cavities / cells 32.

One of the peculiarities of the invention lies in the fact that the recesses 32 each extend in length in a conduction direction 36 going from the inner shell 20 to the outer shell 22, this direction corresponding to the longitudinal axis of the honeycomb cell concerned. As shown on the figure 1 this direction 36 is preferably radial or substantially radial. In this respect, on the leftmost honeycomb structure 30 on the figure 1 , the conduction elements 31 are substantially cylindrical and parallel to each other, as well as the recesses 32 that they define. The conduction directions 36 are here very close to the radial direction, therefore qualified as substantially radial, even though they may be inclined by a few degrees with respect to this same radial direction. In this configuration, several recesses 32 may nevertheless have a conduction direction 36 corresponding precisely to the radial direction of the body 10, that is to say orthogonally intercepting the axis 8. On the other hand, on the honeycomb structure 30 the most right on the figure 1 , the conduction elements 31 are no longer cylindrical, but each have a shape extending from the inner shell 20 to the outer shell 22, in particular to take into account the difference in diameters between these two rings. The geometry of the section of each element 31 remains preferentially identical, only the magnitude of this section then being increasing towards the outer shell 22.

Here, the conduction direction 36 of each of the elements 31 corresponds to the radial direction of the body 10, orthogonally intercepting the axis 8.

As mentioned above, the heat conduction elements 31 and the recesses 32 that they define each extend over a length substantially identical to the distance separating the two rings, in the direction of conduction 36 of the element 31 concerned. As an indication, it is noted that only a mounting set is preferentially retained, in order to allow the introduction of the structures 30 into the inter-shell space 14.

In the preferred embodiment described and shown on the figures 1 and 2 , the honeycomb structures 30 define heat conduction elements 31 of hexagonal section, even if any other form could be envisaged, without departing from the scope of the invention. This hexagonal shape is conventionally produced by means of a stack of embossed sheets / strips 40 forming the hollows / cells 32, the stacking direction 42 of these sheets being orthogonal to the longitudinal direction 36 of the cells.

Each recess 32, considered in section orthogonal to the direction of conduction 36 as is the case on the figure 2 , has a maximum width "l" of between 2 and 25 mm. In addition, the walls of the heat conduction elements 31 delimiting the recesses 32 are of small thickness, for example of average thickness between 0.02 and 0.5 mm. Here, some parts of the walls are formed by a single sheet 40, while other parts are formed by the superposition of two sheets 40. Thus, the average thickness mentioned above is defined as corresponding to about 1.5 times the thickness of the superimposed sheets 40 constituting the honeycomb structures 30.

Also, the ratio between the length "L" of each recess 32 in its direction of conduction 36, and its maximum width "1" mentioned above, is preferably between 3 and 100. Here, the length "L" is preferentially between 75 and 200 mm.

The advantage of using honeycomb structures lies in the high density of conduction elements 31 and recesses 32 that it is able to provide. Indeed, the heat conduction elements 31 together form a network of recesses 32 which, in section along at least one plane parallel to the axis 8 and passing through this network, has at least one zone whose cavity density 32 has a value greater than or equal to 100 troughs / m ² . The figure 2 shows such a section taken according to the plane of line II-II shown on the figure 1 . Of course, in the same area of the means 16, there may be several section planes in which this density value is observed. Moreover, it is preferably made that this minimum density value is encountered in all areas of the conduction means 16, even if it can be scalable within these same means 16.

In the preferred embodiment described, the radiological protection material 18 preferably completely fills the recesses 32 of the honeycomb structures 30. Since the casting of this material is made directly in the inter-ring space 14, with the structures 30 already in place in the package being in the vertical position, it is expected to make holes 46 in the sheets 40 to communicate the hollows 32 between them. During the gravitational casting of the material 18, the latter can then borrow the holes 46 in order to distribute the best in each of the recesses 32 of the structures 30. The holes 46 are here made in the stacking direction 42 of the sheets 40 as evidenced by the figure 2 . Their number is chosen according to various parameters, such as the viscosity of the cast material.

According to an alternative embodiment shown on the figure 3 , the thermal conduction elements are no longer made by honeycomb structures, but by independent elements 31 spaced apart from each other. They therefore each have, unlike the previous embodiment, a wall of their own, that is to say that is not shared with other elements 31. It may be tubes, for example of circular section, as shown on the figure 3 . Alternatively, the elements can take a widening shape by going from the inner wall to the outer wall, such as a frustoconical shape. The geometry of the section of the element then remains preferentially identical here, only the magnitude of this section being scalable.

Their shape, their size and their arrangement in the inter-shell space 14 are identical or similar to those described for the solution with honeycomb structures. Moreover, these tubes 31 internally defining the recesses 32 may also be provided with holes, in order to be more easily filled with the neutron protection material 18.

Finally, with reference to figure 4 , there is shown a block 100 in the form of an angular sector of ferrule, intended to be introduced into the inter-ferrule space 14. This solution, also envisaged for the present invention, contrasts with the previous solution in that it consists to make several sectors of ferrule 100 outside the space 14, before introducing them into this same space, so that they are arranged circumferentially next to each other.

Each block 100 integrates the neutron protection material 18 and a plurality of heat conduction elements 31, filled with this material which defines the quasi-totality of the peripheral surface of the block. Nevertheless, it is expected that the ends of the conduction elements 31 remain visible at the two concentric surfaces 110, 112 of the block, respectively intended to be facing / contacting the surfaces of the rings 20, 22 delimiting the space 14. This allows to establish a better heat transfer between the ferrules 20, 22 and the thermal conduction elements of the block 100. It is noted that if the thermal conduction elements of the block 100 are here of the type of those shown on FIG. figure 3 , they could nevertheless adopt any form according to the present invention, in particular that shown on the figures 1 and 2 .
Of course, various modifications may be made by those skilled in the art to the invention as defined in the appended claims.

Claims (9)

1. Package (2) for the transport and/or storage of radioactive materials, where said package includes a lateral body (10) which defines a cavity (6) for housing said radioactive materials which extends along a longitudinal axis (8) of the package, where the body (10) includes an interior wall (22) together with an exterior wall (22) which between them define a space (14) which extends around said longitudinal axis, where said space houses means of radiological protection (18) as well as means of thermal conduction (16),
   characterised in that said means of thermal conduction include multiple thermal conduction elements (31) which each define internally a void (32) which extends lengthways in a conduction direction (36) going from the interior wall (20) towards the exterior wall (22), and in that at least a part of the thermal conduction elements (31) has its void (32) at least partially filled with a radiological protection material, and in that at least one of the said thermal conduction elements (31) fits externally against the radiological protection material, and also internally, at its voids (32).
2. Package according to claim 1, characterised in that certain of said thermal conduction elements (31) each extend in a direction which is essentially radial to the package lateral body.
3. Package according to claim 1 or claim 2, characterised in that at least some of said thermal conduction elements (31) each exhibit an essentially cylindrical form.
4. Package according to any one of the preceding claims, characterised in that at least some of the said thermal conduction elements (31) each extend lying together over a length essentially equal to the distance separating the interior and exterior walls, along the direction of conduction (36).
5. Package according to any one of the preceding claims, characterised in that the said thermal conduction elements (31) together form a network of voids (32) which, in cross section along at least one plane parallel to the longitudinal axis (8) and traversing this network, exhibits at least one zone whose density of voids has a value greater than or equal to 100 voids/m².
6. Package according to any one of the preceding claims, characterised in that at least some of the said thermal conduction elements (31) are made using one or more honeycomb structures (30), with each honeycomb cell forming said void (32) of a thermal conduction element.
7. Package according to claim 6, characterised in that each honeycomb structure is equipped with holes (46) linking the cells (32) together.
8. Package according to any one of the preceding claims, characterised in that at least some of the said thermal conduction elements (31) are made using independent elements, spaced apart from each other.
9. Container (1) for the transport and/or storage of radioactive materials containing a package (2) according to any one of the preceding claims whatsoever.

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