EP2319049A1

EP2319049A1 - Method for making a packaging for transporting and / or storing nuclear material using the weld shrinkage phenomenon

Info

Publication number: EP2319049A1
Application number: EP09809333A
Authority: EP
Inventors: Gilles Bonnet; Céline FONTANET; Julien Laborde
Original assignee: TN International SA
Current assignee: TN International SA
Priority date: 2008-08-27
Filing date: 2009-08-26
Publication date: 2011-05-11
Also published as: FR2935532A1; FR2935532B1; WO2010023214A1; US20110142571A1; JP2012500986A

Abstract

The invention relates to a method for making a packaging (2) for transporting and/or storing nuclear material, said packaging including an inner ferrule (20), an outer ferrule, as well as heat conduction means (16), wherein said method includes: making a substantially circular envelope (22') having at least one longitudinal slot defined by two opposite longitudinal edges (42); welding the opposite longitudinal edges in order to form the outer ferrule, said step being carried out so that the weld shrinkage results in a compression strain of the heat conduction means in a radial direction, and so that each weld bead ensures only the attachment onto one another of the two edges connected by the same.

Description

PROCESS FOR MANUFACTURING PACKAGING FOR TRANSPORT

AND / OR STORAGE OF NUCLEAR MATERIALS, USING THE

PHENOMENON OF WELDING WITHDRAWAL

DESCRIPTION

TECHNICAL AREA

The present invention relates generally to the field of manufacture of packaging for the transport and / or storage of nuclear material.

In particular, the invention relates to a method of manufacturing a package for the transport and / or storage of nuclear materials, comprising an inner shell, an outer shell and thermal conduction means in contact with each of the inner and outer ferrules .

STATE OF THE PRIOR ART

Conventionally, to ensure the transport and / or storage of nuclear materials, it is used storage devices, also called "basket" or "rack" storage. These storage devices, usually of cylindrical shape and of substantially circular section, are able to receive the nuclear material. 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 nuclear materials, in which they are perfectly confined. The aforesaid cavity is generally defined by a lateral body extending in a longitudinal direction of the package, this lateral body usually comprising two concentric metallic shells jointly forming an annular space inside which are housed thermal conduction means, and a radiological protection device, in particular to form a barrier against neutrons emitted by the nuclear material housed in the cavity.

The thermal conduction means make it possible to conduct the heat released by the nuclear material 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 materials constituting the packaging, or an abnormal pressure rise in the cavity.

The establishment of these thermal conduction means during the packaging manufacturing process is often long and tedious, and therefore relatively expensive.

An exemplary embodiment is described in EP-A-0 741 628. Thermal conduction ribs are provided in the inter-ring space, with an internal radial end fixedly attached to a contact portion of the inner ferrule, and an outer radial end housed in a recess of the outer shell, formed by two ferrule sectors placed edge to edge. For each rib, it is the assembly by welding of the two ferrule sectors which creates the pinch hold of the outer radial end of the rib, in the circumferential direction. Accordingly, this method of operation requires as many ferrule sectors as thermal conduction ribs, and also requires the realization of as many weld beads as there are ferrule sectors. As the number of thermal conduction ribs is generally very high, for example up to several tens, the packaging manufacturing process is therefore strongly penalized, in terms of assembly time, by the setting up and welding of the multitude. of sectors forming the outer shell and ensuring the retention by pinching of the thermal conduction ribs.

In addition, the manufacturing time of the package is further penalized by performing machining on the longitudinal edges of the ferrule sectors, aiming to form the recesses enclosing the outer radial ends of the thermal conduction ribs.

Finally, the performance of a package obtained in this way, in terms of heat removal, are limited. Indeed, instead of a substantial homogeneity of the temperature of the outer shell, in the circumferential direction, it is instead found the existence of hot spots on this shell, at the outer radial ends of the thermal conduction ribs. SUMMARY OF THE INVENTION

The object of the invention is therefore to remedy at least partially the disadvantages mentioned above, relating to the embodiments of the prior art. To do this, the subject of the invention is a method of manufacturing a package for the transport and / or storage of nuclear materials, said package comprising an inner shell, an outer shell and thermal conduction means in contact with each inner and outer rings, said method comprising the following steps: the realization, around the heat conduction means equipping the inner ring, a substantially circular envelope having at least one longitudinal slot defined by two longitudinal edges facing; and the assembly by welding of the longitudinal edges opposite, in order to obtain, from said envelope, said outer shell, this step being performed in such a way that the welding shrinkage causes a compressive stress of the thermal conduction means between the inner and outer rings, in a radial direction of the package, and so that each weld bead obtained between two longitudinal edges facing only ensures the attachment of these two longitudinal edges on one another.

Thus, the invention is based on the welding shrinkage phenomenon used to obtain the contact or increase the intensity of this contact of the thermal conduction means with the two ferrules, in the radial direction. In other words, the welding assembly operation makes it possible, due to the welding shrinkage, to obtain a reduction in the perimeter of the envelope intended to form the outer shell, resulting in radial compression of the heat conduction means. in the inter ^¬ ring space. This way of operating leads to a substantially uniform radial stress of the thermal conduction means between the two rings, in the circumferential direction, ensuring a satisfactory contact all along it.

The main advantage of this method lies in the simplicity of implementation and the low manufacturing time, since unlike the solution presented in EP-A1-0 741 628, the number of angular sector (s) forming the envelope is in no way conditioned by the number of thermal conduction elements running radially in the inter-ring space, the latter number may actually be much higher. Here, it is stated that the angular sector (s) must be understood as the constituent elements of the envelope, defining the longitudinal slots.

In addition, the method according to the invention is applicable regardless of the design of the thermal conduction means. Finally, it does not advantageously require any particular machining of the longitudinal edges forming the slit (s) of the substantially circular envelope. In this respect, it is noted that the stage of realization of this envelope can be implemented so that each slit extends discontinuously or continuously throughout this envelope in the longitudinal direction. As an indicative example, discontinuities can be created by connection points, such as welding points, between the longitudinal edges facing each other, aiming to ensure their pre-assembly before the welding assembly step. This preassembly is particularly sought when there is provided a plurality of angular sectors of envelope defining these longitudinal edges, and arranged around the thermal conduction means, to ensure the maintenance and positioning with respect to each other. Indeed, such sectors can be placed one by one around the heat conduction means, each time pre-assembling the last angular sector on the previous sector, using the connection points mentioned above. This preassembly is then particularly judicious when this step of producing the envelope is implemented with the packaging arranged substantially horizontally.

It is noted that in this particular case where a plurality of envelope angular sectors are arranged around the thermal conduction means to form said envelope, the maintenance and positioning of the sectors before the welding assembly step can be provided by connecting points, and / or by tools provided for this purpose, such as cylinders positioning the sectors to allow said slots to appear between directly consecutive sectors. In the latter case, connection points are no longer necessary, the longitudinal slots then being preferentially continuous in the longitudinal direction.

In addition, it is noted that the envelope formed of several sectors could be achieved other than by gradually arranging angular sectors of envelope around the conduction means, such as for example by placing around these means of thermal conduction , a prefabricated envelope using several sectors revealing the longitudinal slots.

As will be recalled below, it is also possible to provide an envelope formed of a single angular sector, so close to 360 °, still leaving a longitudinal slot.

As mentioned above, the welding step is implemented so that each weld bead obtained between two longitudinal edges facing only ensures the attachment of these two longitudinal edges to one another. In other words, the outer casing obtained after welding is free with respect to the elements located in the inter- ^ferrule space, against which it is pressed radially inwards. Each cord thus provides no other fixation than that of the two songs that it connects, whether it is located opposite the thermal conduction means, the means of radiological protection, or else any other means likely to be arranged in the inter-ring space. During the welding withdrawal observed during the assembly step, a movement is created relative in the circumferential direction between the inner surface of the shell and the heat conduction elements. The fact that each weld bead connecting two edges is not fixed on the heat conduction means has the advantageous consequence of not overly constraining the latter in the circumferential direction, thus avoiding damage to the radiological protection means that may be arranged between these thermal conduction means. Preferably, said thermal conduction means are chosen so as to have first contact portions intended to be in contact with the inner ferrule, as well as second contact portions intended to be in contact with the outer ferrule, said first and second portions being arranged alternately in the circumferential direction, with each second contact portion connected to the first two contact portions being directly consecutive thereto respectively using two junction portions.

Thus, it is the two junction portions, preferably running substantially radially from the inner ring to the outer shell, which provide heat transfer to the second contact portion, bearing against the inner surface of the outer shell. This second contact portion may extend over a given length in the circumferential direction, which limits the appearance of hot spots on the outer shell, and thus promotes its temperature homogeneity along this same direction. Preferably, each assembly formed by a second contact portion and its two associated junction portions forms a pattern, the successive patterns in the circumferential direction being interconnected by said first contact portions.

In this configuration, it can likewise be noted that each assembly formed by a first contact portion and its two associated junction portions disposed on either side of it forms a pattern, the successive patterns in the circumferential direction. being connected to each other by said second contact portions.

Thus, if we consider a first set formed by a second contact portion and its two associated junction portions, and a second directly consecutive set formed by a first contact portion and its two associated junction portions, then these two sets have in common one of the junction portions. Preferably, if the first set forms a first pattern and the second set a second pattern, then the first and second patterns sharing one of the join portions are preferably of the same shape, but reverse arranged relative to one another. to the other, in the radial direction.

As an indicative example, each pattern takes in cross section the shape of a niche or a wave. In the case of the slot, it may be a substantially square, rectangular or parallelogram shape without one of the sides, or even a trapezoid shape without one of its bases, the largest or the smallest.

Preferably, each first contact portion has a length substantially identical to that of each second contact portion, even if different lengths could be provided, without departing from the scope of the invention.

As mentioned above, said envelope is made using one or more angular sectors of envelope, the number Nf of longitudinal slots, each intended to be the seat of a weld seam, being identical to the number Ns angular sectors.

Preferably, the number Nf of longitudinal slots is strictly less than the number Np of second contact portions belonging to the thermal conduction means. The ratio between these two numbers is preferably between 0.02 and 0.5.

In this respect, the number Nf of longitudinal slots, thus also said number Ns of angular sectors, is less than or equal to four.

It is noted that each slot can be indifferently facing a first or a second contact portion of the thermal conduction means. In the case of the facing with a second contact portion, it is still preferably made so that the weld bead made during the assembly step does not come to secure the outer shell on this second portion of contact. In this regard, as mentioned above, each second contact portion is preferably intended to be simply resting on an inner surface of the outer shell, after the implementation of said assembly step, and that the second portion is supported on a portion of the envelope with or without a weld seam.

Preferably, there is therefore no additional element for fixing these elements clad on each other.

As explained above, during the welding withdrawal observed during the assembly step, a relative movement in the circumferential direction between the inner surface of the envelope and some or all of the second contact portions bearing on this surface, this movement resulting therefore from the decrease in the diameter of the envelope provided to form the outer shell, after welding shrinkage. This movement makes it possible not to overly constrain the thermal conduction means in the circumferential direction, particularly in order to avoid damaging the radiological protection means preferably arranged in the patterns of the thermal conduction means. To facilitate this relative movement, each angular sector has an inner surface having, in cross section, a circular arc shape. Such an arcuate shape can also be adopted for the second portions of contact, even in the case of patterns in the form of quadrilaterals mentioned above. A substantially straight shape is also suitable.

Finally, since each angular sector also preferably has an outer surface having, in cross section, a circular arc shape, it is therefore easy to manufacture such sectors of constant thickness, for example by a simple and inexpensive technique for profiling, using a suitable tool, an initially flat sheet, so as to obtain the sector arcuate circle desired.

Finally, it is noted that each envelope sector can be made in one piece, or with the aid of several elements that are attached to each other, for example by welding, preferably before the sector is put in place. on the means of thermal conduction.

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

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 represents a cross-sectional view of a container for transporting and / or storing nuclear fuel assemblies, comprising a package obtained by a manufacturing method according to a preferred embodiment of the present invention; FIG. 2 represents a perspective view of the package during the process of manufacturing, after the step of producing the envelope for subsequently forming the outer shell of the package;

FIG. 3 represents a cross-sectional view of the package shown in FIG. 2;

- Figure 4 shows a partial cross-sectional view of the package, schematizing the next step of assembly by welding the longitudinal edges of the envelope; and - Figure 5 shows an envelope for forming the outer shell of the package, according to an alternative embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Firstly with reference to Figure 1, we see a container 1 for the transport and / or storage of nuclear fuel assemblies. It is recalled in this regard that the invention is in no way limited to the transport / storage of this type of nuclear material. As an indicative example, the invention can also be applied to the transport / storage of PuO ₂ powder.

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 shown schematically in FIG. 1, in which it is also possible to see the longitudinal axis 8 of this package, coinciding with the longitudinal axes. storage device and the housing cavity. Throughout the description, the term

"Longitudinal" shall be understood to be parallel to the longitudinal axis 8 and to the longitudinal direction of the package, and the term "transverse" shall be understood to be orthogonal to that same longitudinal axis 8.

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

Still with reference to FIG. 1, it is possible to see in detail the design of the lateral body 10, which firstly presents two concentric metal 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, here of double thickness design, and an outer shell 22 also centered on the axis 8. This outer shell 22 has the particularity of be formed by a plurality of angular sectors of ferrule 24, for example four in number, of the same angular extent, as has been shown in FIG. 1. These sectors 24 are joined to each other by their longitudinal sides facing each other, using longitudinal weld seams 26 connecting these longitudinal edges two by two. The annular space 14 is filled by thermal conduction means 16, as well as by a radiological protection device 18 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 ferrule 20 whose inner surface corresponds to the inner lateral surface 12 of the cavity 6, and the outer ferrule 22.

More specifically, the thermal conduction means 16 have, alternately in the circumferential or tangential direction, first contact portions 28 in contact with the outer surface of the inner ferrule 20, as well as second contact portions 30 in contact with the inner surface of the outer shell 22. In addition, each second contact portion 30 is connected to its ends to the first two contact portions 28 being directly consecutive thereto, respectively using two junction portions 32 running substantially radially from the inner ring to the outer shell, thus ensuring the transfer of heat to the second contact portion. The second contact portions 30 extend over an angular length which may be substantially identical to that of the first portions 28, even if a different circumferential length could be provided for the first and second portions 28, 30. As a guide, the length circumferentially of each second portion 30 may be such that its ratio to the perimeter of the inner surface of the outer shell 22 is greater than 0.01. This relatively large extent limits the appearance of hot spots on the outer shell 22, and promotes its temperature homogeneity in the circumferential direction. As can be seen in FIG. 1, each assembly formed by a second contact portion 30 and its two associated junction portions 32 forms a pattern 34, the successive patterns 34 being interconnected by the first contact portions 28. Of the same way, each assembly formed by a first contact portion 28 and its two associated junction portions 32 disposed on either side of it, forms a pattern 36, the successive patterns 36 being connected to each other by the second portions The patterns 34, 36 which succeed one another, and which share the joining portions, are preferably of the same shape, but arranged inversely with respect to one another in the radial direction.

As an indicative example, each pattern 34, 36 takes in cross section the shape of a square or a wave. In the illustrated case of the slot, it is for example a substantially trapezoidal shape without one of its bases, or else any other form deemed appropriate. The portions 28, 30 may take in cross-section the form of straight segments, or else arcs of circle, preferably of radius substantially identical to that of the ferrule surface with which they are in contact, in order to accentuate the extent of this contact and thus improve the heat transfer. Moreover, to ensure the existence of such a contact, the thermal conduction means 16 are maintained, or even compressed radially between the two rings 20, 22, in a manner which will be detailed later.

The radiological protection device 18 preferably takes the form of a plurality of radiological protection blocks 40, housed in the recesses defined by the patterns 34, 36, in order to fill these recesses. Thus, each block or assembly of blocks is delimited circumferentially by two directly consecutive junction portions 32, and radially on the one hand by means of a first or second contact portion, and on the other hand by means of of the ferrule surface opposite this last contact portion. Blocks 40 are made of any material known to those skilled in the art to fulfill a function of radiological protection vis-à- Neutron screws, such as a vinylester resin-based material, and thermal conduction means 16 are for example made of a light alloy of the aluminum alloy type, preferably by stamping sheets.

Referring now to Figures 2 to 4, there is shown schematically a method of manufacturing the package 2 which has just been described.

The manufacture integrates the realization, around the heat conduction means 16 equipping the inner ferrule 20, with a substantially circular envelope 22 'and centered on the axis 8, as can be seen in FIGS. 2 and 3. This envelope 22' is produced with the aid of several angular sectors of envelope 24 ', whose number Ns is here four. Indeed, each sector 24 'is intended to form, once the process implemented, one of the outer shell angular sectors 24 described above. Thus, here too, the sectors 24 'are preferably provided with an inner surface and an outer surface respectively in the form of two circular arcs of the same center, therefore of substantially constant thickness. Moreover, the angular extent is also substantially the same for each of the four sectors 24 '. The latter are made either from a single piece, or by means of several elements that are attached to each other, for example connected to each other by welding in the longitudinal direction, preferably before the introduction of the sector on the means of thermal conduction. The sectors 24 'are arranged edge to edge around the axis 8. Thus, between two longitudinal edges 42 facing each other, respectively belonging to two sectors 24' directly consecutive, there is provided a slot 44 intended to be the seat of a weld seam, subsequently produced during the manufacturing process. Thus, the number Nf of longitudinal slots 44 is identical to the number Ns of angular sectors 24 ', namely, in this case, four. In addition, the number Nf of slots 44 is much smaller than the number Np of second contact portions 30, the ratio between these two numbers may be between 0.02 and 0.5.

In the diagrammatic views of FIGS. 2 and 3, the sectors 24 'have been represented without holding means relative to each other and radially outwardly of the heat conduction means 16. Firstly, it is noted that a pre-assembly of the angular sectors 24 'is nevertheless preferably carried out at the level of the longitudinal edges 42, to ensure the maintenance and positioning with respect to each other. Indeed, such sectors can be placed one by one around the thermal conduction means, each time pre-assembling the last angular sector on the previous sector, using connecting points arranged at the slot. Thus, at the end of the step of producing the envelope 22 ', each slot 44 may extend discontinuously along this envelope, in the longitudinal direction, these discontinuities created by the connecting points being able to take the form of welding points between the longitudinal edges 42 opposite.

Moreover, at the end of the step of producing the envelope 22 ', it is preferably in contact with the thermal conduction means 16.

The next step of the method consists in producing the assembly by welding longitudinal edges 42 opposite, in order to obtain, from the envelope 22 ', the outer shell 22.

With reference to FIG. 4, this step is performed with conventional welding means 56 so that the welding shrinkage observed during the production of the weld seams 26 in the slots provided for this purpose causes a reduction in diameter of the envelope 22 ', which then becomes the outer shell of the package 2. This diameter reduction is intended to obtain the contact, if not yet achieved, or to increase the intensity of this contact means thermal conduction 16 with the ferrule 20 and the casing, in the radial direction, since these means 16 are solicited in compression between these two elements. This way of operating schematically in FIG. 4 in fact leads to a substantially uniform radial stressing of the thermal conduction means 16 between the ferrule 20 and the envelope 22 'whose diameter decreases, as shown schematically by the arrows 50. The compression observed radial can lead to elastic deformation of the second contact portions 30 in order to increase the surface of the this contact with the envelope 22 ', and thus ensure better heat transfer.

In this preferred embodiment, each weld bead 26, extending over substantially the entire length of the envelope 22 ', is intended to be facing and contacting one of the second contact portions 30. Nevertheless, it is still made so that the weld bead 26 does not come to secure the envelope 22 'on this second contact portion 30. Indeed, each second contact portion is simply supported on the inner surface of the outer shell 22 after the implementation of the assembly step. Thus, during the welding withdrawal observed during the assembly step, a relative movement in the circumferential direction is created between the inner surface of the envelope 22 'and some or all of the second contact portions 30 resting on this surface, this movement schematized by the arrow 52 of Figure 4 thus resulting from the decrease in the diameter of the envelope 22 'provided to form the outer shell 22, after the welding shrinkage. On the other hand, it is indicated that the first contact portions 28 of the conduction means 16 are preferably fixedly mounted on the inner ferrule 20, for example by means of welded studs and nuts, or any other similar means.

According to an alternative embodiment shown diagrammatically in FIG. 5, the envelope 22 'is formed of a single angular sector 24', thus close to 360 °, revealing a longitudinal slot 44 between its two songs facing each other 42, 42. The welding assembly step is then performed in a manner similar to that described above, by producing a weld bead in the slot provided for this purpose, in order to obtain the expected welding shrinkage.

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.

Claims

A method of manufacturing a package (2) for the transport and / or storage of nuclear material, said package comprising an inner shell (20), an outer shell (22) and heat conduction means (16) contact with each of the inner and outer rings, said method comprising the following steps: - the realization, around the thermal conduction means (16) equipping the inner ring

(20), a casing (22 ') substantially circular having at least one longitudinal slot (44) defined by two longitudinal edges (42, 42) facing; and assembling by welding the facing longitudinal edges (42, 42), in order to obtain, from said envelope (22 '), said outer shell (22), this step being carried out in such a way that the withdrawal welding process causes compressive stress of the thermal conduction means (16) between the inner and outer rings (20, 22) in a radial direction of the package, and in such a way that each weld bead obtained between two longitudinal edges (42, 42) only ensures the attachment of these two longitudinal edges one on the other.

2. Method according to claim 1, characterized in that said thermal conduction means (16) are chosen so as to present first contact portions (28) intended to be in contact with the inner ferrule (20), as well as second contact portions (30) intended to be in contact with the outer ferrule (22), said first and second portions being arranged alternately in the circumferential direction, with each second contact portion (30) connected to the two first contact portions (28, 28) being directly consecutive thereto respectively by two joining portions (32, 32).

3. Method according to claim 2, characterized in that each assembly formed by a second contact portion (30) and its two joint portions (32, 32) associated forms a pattern (34), the successive patterns in the circumferential direction. being interconnected by said first contact portions (28).

4. Method according to claim 2 or claim 3, characterized in that each pattern (34) is in cross section in the form of a crenel or wave.

5. Method according to any one of claims 2 to 4, characterized in that each first contact portion (28) has a substantially identical length to that of each second contact portion (30).

6. Method according to any one of the preceding claims, characterized in that said envelope (22 ') is made using one or more angular sectors of envelope (24'), the number Nf of longitudinal slots ( 44), each intended to be the seat of a weld seam (26), being identical to the number Ns of angular sectors

(24 ').

7. The method of claim 6 combined with claim 2, characterized in that the number Nf of longitudinal slots (44) is strictly less than the number Np of second contact portions (30) belonging to the thermal conduction means (16).

8. The method of claim 6 or claim 7, characterized in that said number Ns of angular sectors (24 ') is less than or equal to four.

9. Method according to any one of claims 6 to 8, characterized in that each angular sector (24 ') has an inner surface having, in cross section, a circular arc shape.

10. Method according to any one of the preceding claims combined with claim 2, characterized in that each second contact portion (30) is intended to be simply supported on an inner surface of the outer shell (22), after the implementation of said assembly step.