GB2445269A

GB2445269A - Modular arrangement comprising a storage device for transport and/or storage of nuclear fuel assemblies

Info

Publication number: GB2445269A
Application number: GB0724995A
Authority: GB
Inventors: Jacques Gardin; Julien Legeay; Laurent Stachetti
Original assignee: TN International SA
Current assignee: TN International SA
Priority date: 2006-12-22
Filing date: 2007-12-21
Publication date: 2008-07-02
Anticipated expiration: 2027-12-21
Also published as: GB2445269B; FR2910691A1; FR2910691B1; GB0724995D0

Abstract

An modular arrangement 1 is disclosed comprising a storage device 2 for the transport and/or storage of nuclear fuel assemblies. The device has at least one housing L1 with a transversal cross section (S1 ,Fig.2a) dimensioned to accommodate a nuclear fuel assembly with a transversal cross section (S'1 ,Fig.2b). The assembly further comprises at least one fuel assembly reduction adaptor device 10 that may be mounted removably within the storage device 2. The adaptor device 10 penetrates inside one of the housings L1 to form a new housing having a reduced transversal cross section (S2,Fig.3a) dimensioned to accommodate a nuclear fuel assembly with a transversal cross section (S'2,Fig.3b) smaller than the transversal cross section (S'1,Fig.2b), for its transport and/or storage.

Description

* 2445269

MODULAR ASSEMBLY COMPRISING A STORAGE DEVICE FOR THE

TRANSPORT AND/OR STORAGE OF NUCLEAR FUEL ASSEMBLIES

DESCRI PTION

TECHNIc FIELD

This invention relates in general to the field of

the transport and/or storage of nuclear fuel assemblies, and in particular fresh fuel, for example of the Mox type. Nevertheless, the invention could also apply to the field of the transport and/or storage of irradiated fuel assemblies, without leaving the scope of the invention.

STATE OF THE PRIOR ART

Classically, to transport and/or store nuclear fuel assemblies, storage devices are used, also called storage "baskets" or "racks". These storage devices, which are usually cylindrical in shape and with a cross section that is substantially circular, have a * ..15 plurality of adjacent housings each capable of * * . * accommodating a nuclear fuel assembly. Furthermore, the

I

IS... . storage device is designed to be housed in a packaging in order to form Conjointly with it a container for the transport and/or storage of a nuclear fuel assembly, in which the nuclear material is completely confined.

a. sSs * S It is known that the dimensioning of a storage basket housing, and in particular its transversal cross section, is defined according to the transversal cross section of the fuel assembly that this same housing is designed to accommodate. For this purpose, it is indicated that a clearance is usually provided between the inside surface defining the housing, and the fuel assembly packaged inside this housing.

The minimum clearance value is determined according to the operating constraints. In other terms, this clearance must be sufficient to authorjse the introduction of the assembly inside the housing, as well as its extraction, without causing any damage, it being underlined that these introduction / extraction operations are generally carried out in the vertical position.

Furthermore, the maximum value of the clearance is, according to a first criterion, fixed so as to limit as much as possible the risks of damage to the assembly that may be caused by shocks in the event of accidents during the transport of the container, such as being dropped vertically and/or horizontally, wherein it is clear that these risks increase with the size of the clearance provided. According to a second criterion, the maximum value of the clearance is fixed so as to ensure the integrity of the assembly which should not * s... suffer, in normal transport conditions or during the handling of the container, mechanical solicitations above the permissible limit defined by the designer of the assembly model, in particular when this concerns the transport and/or storage of fresh nuclear fuel.

* : For information, the clearance used is usually Sss*..

* between 5 and 8 mm, for example 6 mm. Once determined, this data relative to the value of the clearance thus permits the designer to determine the dimension of the transversal cross section of the housing according to O 3 the transversal cross section of the nuclear fuel assembly that it is designed to accommodate.

However, for the reasons of respecting thern clearance that have just been mentioned, it is obvious that a storage device may only be used for the transport and/or storage of fuel assemblies with a given transversal cross section, and not for the transport and/or storage of fuel assemblies with a smaller transversal cross section, likely to take the value of the clearance to an unacceptable level.

Consequently, at present it is necessary to multiply the designs of the storage baskets faced with the diversity of the nuclear fuel assemblies to be transported and/or stored, in particular as concerns their transversal cross section. Naturally, this is translated by very high development, certification and production costs.

OBJECT OF THE INVENTION

The objective of the invention is therefore to overcome the disadvantages mentioned above, concerning

the items of the prior art.

To achieve this, the subject matter of the invention is an assembly, comprising a storage device for the transport and/or storage of nuclear fuel assemblies featuring at least one housing (Li) with a transversal cross section (Si) dimensioned to : accommodate a nuclear fuel assembly with a transversal óross section (S'l), for its transport and/or storage, wherein the housing (Li) has an inside surface (Sil) defining it, wherein the assembly also comprises at * 4 least one accessory device for reducing the fuel assembly housing section that may be mounted on the storage device so that it may also be removed, so that it penetrates inside the housing (Li) and forms a housing (L2) with a reduced transversal cross section (S2) dimensioned to accommodate a nuclear fuel assembly with a transversal cross section (S'2) smaller than the transversal cross section (S' 1), for its transport and/or storage. Furthermore, the accessory device comprises a longitudinal portion with a reduced fuel assembly housing section extending over a length substantially identical to that of the housing (L2) with on any transversal cross section an unclosed line defining the housing designed to be an integral part of an inside surface (S12) defining the housing (L2), wherein this inside surface (Si2) is also partially formed of a portion of the inside surface (Sil) extending along the entire length of the housing (L2).

Furthermore, the accessory device is designed such that 1.10 < S1/S2 < 2.

The invention thus advantageously provides a *::* storage device for the transport and/or storage of *.*.

*.... nuclear fuel assemblies that may be modulated, using one / several accessory devices designed for this * 25 purpose, so as to adapt the transversal cross section of its housings to that of the fuel assemblies that it is designed to accommodate. Consequently, the kit : according to the invention permits the use of a given storage device not only for the transport and/or storage of fuel assemblies for which it is has been initially designed, but also for the transport and/or * 5 storage of fuel assemblies with a smaller transversal cross section, while also respecting the clearance described above provided between the inside surface defining the housing, and the fuel assembly inside this housing. The field of application of the known storage

baskets of the prior art may thus be substantially

extended thanks to the kit according to the invention, wherein the number of storage baskets of different designs required faced with the diversity of the nuclear fuel assemblies may advantageously be reduced, such that the costs of development, certification and production are also substantially reduced. It should be noted that the accessory device (s) in the original housings are preferably fitted in the container maintenance workshops, prior to each transport campaign of new assemblies.

The new housing (L2) formed by the introduction of

the accessory device in the original housing (Ll) has thus an inside surface comprising one part formed by the accessory device, and another part formed by the inside surface of the housing (Li), wherein these two * ** parts each extend along the entire length of the ** housing (L2). Consequently, as the insjde surface of the housing (L2) is partially formed by the inside * .**.* * 25 surface of the housing (Li), the housing (L2) formed by the introduction of the accessory device in the housing (Li) may thus advantageously benefit from high *:*** precision characteristics of the inside surface of the housing (Li), such as the flatness characteristics. For example, in the case of where it is provided that the assembly with a transversal cross section (S'l) is * 6 designed to rest in contact by gravity against two lateral, joined and orthogonal faces that are part of the inside surface (Sil) of the housing (Li), during its transport and/or storage in the horizontal/laid flat position, it is thus advantageously possible, during another transport and/or storage campaign in the horizontal/laid flat position of an assembly with a reduced transversal cross section (S'2), to use these same two lateral, joined and orthogonal faces for the contact of the assembly with a reduced transversal cross section (S'2).

Using this specific aspect, the manufacturing precision required for the accessory device may advantageously be maintained at a reasonable level, synonymous with cost saving.

Furthermore, the unclosed line is preferably formed by a plurality of straight, joined segments, but which could naturally have any other form Considered to be appropriate by those skilled in the art, especially according to the form of the fuel assembly to be * accommodated, For information, it could also be a single, straight segment. **e*

In the non restrictive case where the unclosed line has the form of a plurality of straight joined segments, it is preferably provided that this unclosed r line is formed by two straight, joined and orthogonal segments. This form is especially adapted for the *:.* formation of a housing (L2) with a square or rectangular transversal cross section, wherein the two straight orthogonal segments of the unclosed line thus form twoconsecutjve sides of the square or rectangle, wherein the two other sides are preferably formed by the portion of the inside surface (Sil) provided to define part of the inside surface (Si2) of the housing (L2).

To this end, it is preferably provided that the unclosed line is identical regardless f the transversal cross section considered along the entire length of the longitudinal portion with a reduced housing section, wherein this portion has a length approximately equal to that of the housing (L2), or even approximately equal to that of the nuclear fuel assembly designed to be placed inside this same housing.

Preferably, the longitudinal portion with reduced fuel assembly housing section has two substantially flat lateral walls conjointly forming an angle, wherein the two lateral walls are designed to form one part of the inside surface (Si2) of the housing (L2). Here again, it should be noted that the longitudinal portion with a reduced housing section may have any other form considered to be adapted by those skilled in the art, such as that of a single, substantially flat, lateral * *. wall. I...

Still preferably, the accessory device further comprises a longitudinal portion with a reduced fuel ****.I * 25 assembly housing length, extending the longitudinal portion with a reduced fuel assembly housing section.

In this way, the accessory device has a first longitudinal portion solely dedicated to the reduction in housing section, as well as a second longitudinal portion extending the first and solely dedicated to the reduction in housing length. However, it is also * 8 possible to provide an accessory device solely comprising the longitudinal portion dedicated to the reduction in housing section, according to the needs encountered. In this last case, it should be understood that the longitudinal portion with a reduced housing section forms the entire accessory device.

Preferably, the accessory device extends over a length substantially identical to that of the housing (Li) in which it is designed to be introduced, whether the device has a longitudinal portion with a reduced housing length extending the longitudinal portion with reduced housing section, or whether it only has this same longitudinal portion with a reduced housing section as mentioned above.

Preferably, the accessory device is designed to rest in contact on a top plate of the storage device, and preferably mounted fixedly on this same top plate by means of any assembly means, for example a type such as bolts.

Preferably, the accessory device is made of stainless steel, wherein this same material is * S. generally used to make the storage device. S...

S..... Still preferably, the assembly has as many accessory devices as there are housings (Li) in the * 25 storage device. Similarly, there may be several sets of accessory devices provided, wherein each clearance is for housing assemblies of a given different section.

Finally, the invention also refers to a container for the transport and/or storage of nuclear fuel assemblies, wherein this container comprises packaging and an assembly as described above placed inside this * 9 packaging, wherein at least one housing (Li) of the assembly is equipped with an accessory device for a reduction in the housing section, and preferably all of the housings (Li) of the assembly are each equipped with an accessory device for the reduction in housing section.

Other advantages and characteristics of the invention will become clearer in the non restrictive

detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made in reference to the

appended drawings, among which; -figures la and lb show perspective views of an assembly for the transport and/or storage of nuclear fuel assemblies briefly illustrating the principle of this invention, wherein the assembly is in two distinct configurations; -figures 2a and 2b show partial cross sectional views taken according to a transversal plane reference Il-Il of figure la, wherein figure 2b has the *..... additional specific aspect of showing the nuclear fuel assembly as it lies inside the housing during transport in the horizontal position; * S....

* 25 -figures 3a and 3b show partial cross sectional views taken according to a transversal plane reference Ill-Ill of figure ib, wherein figure 3b has the : additional specific aspect of showing the nuclear fuel assembly as it lies inside the housing during transport in the horizontal position; a 10 -figure 4 is a detailed perspective view of one of the accessory devices shown in figures la and ib; -figure 5 shows a longitudinal cross sectional view of the accessory device shown in figure 4; -figure 6 is a longitudinal cross sectional view showing one of the housings of the storage device shown in figures la and ib, a housing in which an accessory device and a nuclear fuel assembly of reduced section have been introduced; and -figure 7 shows a diagrammatjc side view of a container for the transport and/or storage of nuclear fuel assemblies, according to a preferred embodiment of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First of all in reference to figures la and lb, an assembly 1 for the transport and/or storage of nuclear fuel assemblies according to this invention is shown, wherein these two figures respectively show two distinct configurations that may be adopted by the assembly 1. * S.

1.' This assembly 1 firstly comprises a storage device *..

2 designed to be placed inside packaging (not shown in this figure) designed for the transport and/or storage of nuclear fuel assemblies (not shown), preferably fresh fuel.

As may be seen in figure la, the storage device 2 comprises a plurality of adjacent housings Li positioned in parallel, wherein the latter each extend according to a longitudinal axis (not shown) parallel to a longitudinal axis 4 of the device/basket 2. The * . . 11 housings Li are each capable of accommodating at least one fuel assembly of square or rectangular section, and preferably only one. They are each defined by an inside surface Sil, whose transversal cross section preferably has the form of a square or a rectangle. This transversal cross section must be orthogonal to the axis of the basket 4 and to that of its housings.

The design of the storage device 2 may have any form known to those skilled in the art, such as for example the type based on the stack of rollers through which pass the sleeves defining the housing, or even of the type intended to obtain the housings 2 juxtaposed next to one another by means of a plurality of stacked and intertwined structural assemblies with notches.

It should be noted that the storage device 2 is shown in a horizontal/laid flat position such as that adopted during the transport of the fuel assemblies.

Nevertheless, as known to those skilled in the art, these assemblies are designed to be introduced beforehand into the housings Li with the device 2 positioned vertically, which is to say resting on a * *.

base 6 located at one end of the device opposed to that * **.

to which the top plate 8 is attached, through which the assemblies pass before entering their respective housings.

As will be described below in reference to figures r' 2a and 2b, the storage device 2, in its original configuration as shown in figure la, is designed and adapted to accommodate nuclear fuel assemblies with a transversal cross section S1]. inside the housings Li with a transversal cross section Si, wherein these * 12 sections are dimensioned with respect to one another so as to authorjse the introduction / extraction of the fuel assemblies, whilst permitting their secure transport and/or storage.

Figure la also shows a plurality of accessory devices 10 that are an integral part of the assembly 1 according to the invention that may be assimilated to a kit. Overall, each fuel assembly housing section reduction accessory device 10 may be mounted removably onto the storage device 2, so that it penetrates inside one of the housings Li to form a new housing L2 with a reduced transversal cross section S2 dimensioned to accommodate a nuclear fuel assembly with a transversal cross section S'2 smaller than that of the above-mentioned transversal cross section S'i, for its transport and/or storage.

The invention permits the storage device 2 to be used indifferently either in its original configuration as shown in figure la for the transport and/or storage of fuel assemblies with a transversal cross section S'l in the housings Li, or in its modulated configuration * ** as shown in figure lb in which it integrates the accessory devices 10 permitting the transport and/or storage of fuel assemblies with a reduced transversal * . S*..

* 25 cross section S'2 in the newly formed housings L2.

Indeed, as may be seen in figure ib, the storage device 2 equipped with the accessory devices 10 has a plurality of adjacent housings L2 positioned in parallel, wherein the latter each extend according to a longitudinal axis (not shown) parallel to the longitudinal axis of the basket 4, and are each issued * 13 front one of the original housings Li. The housings L2 are each able to accommodate at least one fuel assembly of reduced square or rectangular section, and preferably only one. They are each defined by an inside surface Si2, whose transversal cross section is preferably square or rectangular.

They are also each defined by an inside surface Si2, whose transversal cross section is preferably square or rectangular.

In the preferred embodiment described, each accessory device 10 not only has a function of reducing the section of the housing Li, but also a function of reducing the length of this same housing Li. For this purpose, the accessory device 10 comprises in its upper part a longitudinal portion with a reduced fuel assembly housing section 12, and in its lower part a longitudinal portion with reduced fuel assembly housing length 14, extending the longitudinal reduced section portion 12. Of course, this specific aspect is retained when the fuel assembly designed to be accommodated in a housing L2 not only has a section that is too small to * .* ** S. . * *. be accommodated in the associated original housing Li, *SSS but also is too short, it being understood that usually a length of housing substantially equal to that of the assembly that it is designed to accommodate is preferably presented.

In reference to figures 2a and 2b, one of the : housings LI may be seen diagrammatically in transversal cross section, wherein this cross section is substantially identical along the entire length of the * 14 housing Li Concerned, due to the constant character of this housing along its entire height.

In figure 2a, the inside surface Sil defining the housing Li may be seen in cross section, this surface also called lateral housing surface is preferably formed by four substantially flat and joined faces Conjointly forming a "tube", wherein they laterally define the housing Li entirely, over 3600. More precisely, the four inside faces Fila, Filb, Flic and Fild define a housing with a transversal cross section Si that is rectangular, and more preferably square as shown in figures 2a and 2b.

Therefore the transversal cross section of the housing Li is defined laterally by a closed inside line defining the housing Lii, thus preferably in the form of a square with four joined segments Sela, Seib, Seic and Seid respectively forming the four sides of the square. Naturally, the four joined segments Sela, Seib, Seic and Seld respectively correspond to the transversal cross section of the four inside faces Fila, Filb, Filc and Fild, as shown by figures 2a and 2b. * .*

In these figures, the housing Li is shown in a *5* 5**.. position that is generally adopted during transport, *:" which is to say originating from a horizontal position of the storage device 2 defining it. Consequently, the nuclear fuel assembly 16 shown in figure 2b, with a *:" transversal cross section square S'i, may rest in contact by gravity on the two lower joined faces Fiic and Fild, wherein a clearance El subsists between the inside face Fila and the assembly 16, and also between the inside face Fiib and this same assembly 16. For * 15 information, the clearance El may be approximately 6 mm.

This value is effectively considered sufficient to authorise the introduction of the assembly into the housing, as well-as to extract it, without causing any damage. Furthermore, it is also considered sufficiently low on the one hand to limit as desired the risks of damage to the assembly that may occur due to impacts if there is an accident during transport to the container, such as being dropped vertically or horizontally, and on the other hand to ensure the integrity of the fuel assemblies in normal transport conditions or during the handling of the container.

In reference to figures 3a and 3b, one of the housings L2 may be seen diagrammatically in transversal cross section, wherein this cross section is substantially identical along the entire length of the housing L2 concerned, due to the constant character of this housing along its entire height.

In figure 3a, the inside surface Si2 defining the housing L2 may be seen in cross section, this surface also called lateral housing surface is preferably * S. formed by four substantially flat and joined faces S...

*.* conjointly forming a "tube", wherein they laterally define the housing L2 entirely, over 360 . More S.....

* 25 precisely, the four inside faces F12a, Fi2b, Fi2c and Fi2d define a housing with a transversal cross section S2 that is rectangular, and more preferably square.

One of the specific aspects of this invention is that the two inside joined faces Fi2a and Fi2b are formed by the accessory device 10 introduced into the initial housing Li, and more precisely by its * 16 longitudinal portion with a reduced housing section 12, whereas the other two inside joined faces Fi2c and Fi2d are respectively formed by part of the inside face FI].c and part of the inside face Fild also defining the housing Li.

The housing L2 is thus defined laterally in transversal cross section by a closed inside line defining the housing Li2, thus preferably in the form of a square with four joined segments Se2a, Se2b, Se2c and Se2d respectively forming the four sides of the square. Again, the four joined segments Se2a, Se2b, Se2c and Se2d respectively correspond to the transversal cross section of the four inside faces F12a, F12b, Fi2c and Fi2d, as shown in figures 3a and 3b.

Consequently, it is deducted that with any transversal cross section, the housing L2 is conjointly defined by the joined segments Se2c and Se2d also part of the inside surface SI]. of the housing LI., as well as by an unclosed line lnf that is part of the reduced section portion 12, wherein this unclosed line lnf is exclusively defined by the two joined segments Se2a and * I. Se2b. This is explained by the angled shape adopted for S...

the reduced section portion 12, as will be detailed below in relation to the following figures.

* 25 In figures 3a and 3b, the housing L2 is also shown in a position that is generally adopted during the transport. Therefore, the nuclear fuel assembly 18 shown in figure 3b, with a square transversal cross section S'2, may rest in contact by gravity on the two lower joined faces F12c and Fi2d formed by a portion of the inside surface Sil extending along the entire * 17 length of the housing L2, wherein a clearance E2 subsists between the inside face Fi2a and the assembly 18, and also between the inside face Fi2b and this same assembly 18. For information, for the same reasons as those discussed for the clearance El, the clearance E2 may be approximately 6 mm. Furthermore, an assembly clearance E'2 of approximately 1 to 2 mm subsists on the one hand between the inside face Fila and the part of the reduced section portion 12 opposite it, and on the other hand between the inside face Filb and the part of this same portion 12 opposite it. It should be noted that this clearance E'2 facilitates the introduction of the accessory device in the housing Li.

It should be noted that the above-mentioned clearances El and E2 may of course be substantially modified, their value would preferably remain between 5 and 8 mm.

Furthermore, it is arranged so that the reduction

in section obtained with the introduction of the

accessory device 10 in the housing Li is quite large, permitting a ratio Sl/S2 to be obtained of between 1.10 * .* * . * and 2. ****

In reference to figures 4 and 5, a preferred * embodiment of the accessory device 10 may be seen in ****** * 25 detail. The latter is preferably made of stainless steel arid is shown in figure 5 inside its associated housing Li.

The longitudinal portion with reduced housing section 12 features two substantially flat and orthogonal lateral walls 20, thus conjointly forming an angle. These two lateral walls 20 are therefore * 18 designed to form, along with their inside surface, part of the inside surface Si2 of the housing L2, and more precisely the two inside lateral faces Fi2a and Fi2b previously mentioned.

Furthermore, even if the lateral walls 20 may be generally assimilated to be substantially flat, it is possible for stiffeners 22 to be provided on their outside surfaces, preferably orientated orthogonally with respect to a longitudinal axis 24 of the accessory device 10. Consequently, the stiffeners 22 distant from one another according to the direction of the height, corresponding to the direction of the axis 24, may alternately be attached fixedly onto the outside surface of the walls 20, for example screwed on, or even made in one piece with these same walls 20, for example by machining.

For this purpose, it should be noted that the two walls 20 may be made separately then subsequently attached to one another, for example screwed together, or even made in one piece without this leaving the scope of the invention. * **

The portion with a reduced housing length 14 is **..

attached solidly at one lower end of the reduced section portion 12, and has any form of wedge whose section is close to the section Si of the housing LI.

The accessory device 10 is held in the housing Li by resting it on the top plate 8, for example by means of a square flange 26 provided at an upper end of the reduced section portion 12. To fit the device 10 in it, this flange 26 is mounted fixedly, for example screwed, onto the top plate 8. Preferably, no other attachment * 19 is provided between the accessory device 10 and the storage device 2, such that the accessory device 10 is * suspended inside the housing Li by the flange 26 from the top plate 8, with a clearance between its lower end and the bottom of the basket. Thisclearance permits an isostatic assembly to be obtained and also permits differential thermal expansion between the walls forming the housing Li and the accessory device 10.

Nevertheless, the length of the housing Li is substantially identical to that of the accessory device 10, considered according to its longitudinal axis 24.

Of course, the specific positioning of the means used to fit the accessory device 10 onto the top plate 8 permits this accessory device 10 to be indexed correctly with respect to the housing Li in which it is located, especially so that the two clearances E'2 are respected.

In reference to figure 6, the fuel assembly 18 with a reduced transversal cross section S'2 may be seen held fixedly in its housing L2, by means of conventional attachment means (not shown) in particular * S. permitting it to be suspended from the top plate 8. ***.

Therefore traditionally, the assembly 18 is suspended by the inside upper end of the housing L2, where its lower end is slightly offset from the upper end of the wedge 14 of the accessory device 10, in order to deal with the known problems of differential expansion. This especially explains why the length of the housing L2, defined towards the bottom by the wedge 14, is substantially identical to that of the fuel assembly 18. * 20

Finally in reference to figure 7, a container 100 that is also the subject of this invention may be seen, globally comprising a packaging 102 inside which is an assembly 1 such as that described above, and more specifically of the type comprising a storage device 2 with housings Li, each equipped with an housing section reduction accessory device 10. This assembly 1 is designed to be placed inside the packaging 102, as shown diagrammatically in figure 7 in which the longitudinal axis 104 of the packaging 102 may also be seen, merged with the longitudinal axis of the storage device, wherein this packaging 102 essentially has a bottom 106 on which the device 2 is designed to rest in the vertical position, a cover 108, and a lateral body 110 extending around the longitudinal axis 104.

Of course, various modifications may be made by those skilled in the art to the invention described above solely by way of non restrictive examples. * ** * * * * ** * U * S.U

S

S..... * .

*. **. * S

S *... * U * 21

Claims

1. Assembly (1) comprising a storage device (2) for the transport and/or storage of nuclear fuel assemblies featuring at least one housing (Li) with a transversal cross section (Si) dimensioned to accommodate a nuclear fuel assembly with a transversal cross section (S' 1), for its transport and/or storage, wherein said housing (Li) has an inside surface (Sil) defining it, wherein said assembly is characterised by the fact that it also comprises at least one fuel assembly housing section reduction accessory device (10) that may be mounted removably onto the storage device (2), so that it penetrates inside one of the housings (Li) to form a housing (L2) with a reduced transversal cross section (S2) dimensioned to accommodate a nuclear fuel assembly with a transversal cross section (S'2) smaller than said transversal cross section (S'l), for its transport and/or storage, said accessory device (10) comprising a longitudinal portion with reduced fuel * ** assembly housing section (12) extending over a length substantially identical to that of said housing (L2) and with on any transversal cross section an unclosed line defining the housing (Lnf) designed to be an integral part of an inside surface (S12) defining said housing (L2), wherein this inside surface (Si2) also r5 partially formed of a portion of said inside surface (Sii) extending along the entire length of said housing (L2), and in that said accessory device (10) is designed so that: * 22 1.10 < S1IS2 <

2 2. Assembly (1) according to claim 1, characterised in that said unclosed line (lnf) is formed by a plurality of straight joined segments (Se2a, Se2b).

3. Assembly (1) according to any of the previous claims, characterised in that said unclosed line (lnf) is formed by two straight joined orthogonal segments (Se2a, Se2b).

4. Assembly (1) according to any of the previous claims, characterised in that said longitudinal portion with reduced fuel assembly housing section (12) has two substantially flat lateral walls (20) conjointly forming an angle, wherein said two lateral walls (20) are designed to form part of the inside surface (S12) of said housing (L2).

* ,

5. Assembly (1) according to any of the previous claims, characterised in that said accessory device (10) *** S further comprises a longitudinal portion with reduced fuel assembly housing length (14), extending said longitudinal portion with reduced fuel assembly housing section (12).

***..,

S

6. Assembly (1) according to any of the previous claims, characterised in that said accessory device (10) extends over a length substantially identical to that * 23 of said housing (Li) in which it is designed to be introduced.

7. Assembly (1) according to any of the previous claims, characterised in that said accessory device (10) is designed to rest on a top plate (8) of the storage device (2).

8. Assembly (1) according to any of the previous claims, characterjsed in that said accessory device (10) is made of stainless steel.

9. Assembly (1) according to any of the previous claims, characterised in that it comprises as many accessory devices (10) as there are housings (Li) in the storage device (2).

10. Container (100) for the transport and/or storage of nuclear fuel assemblies, said container comprising a packaging (102) and an assembly (1) according to any of the previous claims placed in said *:*::* packaging, where-in at least one housing (LI) of said assembly is equipped with a housing section reduction * accessory device (10) * * *

11. Assembly generally as herein described with *s.s..

* reference to and/or as illustrated in the accompanying S.....

* . drawings.

12. Container generally as herein decribed with reference to and/or as illustrated in the accompanying drawings.