EP1055241B1 - Transport container for nuclear fuel assemblies - Google Patents

Description

The invention relates to a transport container for assemblies. of nuclear fuel and in particular a transport container for new fuel assemblies intended for recharging a nuclear reactor cooled by pressurized water.

Nuclear reactors such as nuclear reactors cooled by pressurized water have a core consisting of assemblies nuclear fuel in a straight prismatic shape, usually cross-sectional square and slender. Fuel assemblies generally have a section in the shape of a square whose side has a length about 20 cm, the length of the fuel assembly, in its direction longitudinal, being of the order of 4 meters. The assemblies of fuel have a framework inside which are arranged nuclear fuel rods, essentially along the entire length of the fuel assembly. The framework is constituted itself by transverse grids for holding rods distributed according to the length of the fuel assembly, by parallel guide tubes with pencils engaged in the spacer grids and by end caps end of the fuel assembly.

Before commissioning the reactor, it is necessary to loading of the core with new fuel assemblies. It is also necessary to replace certain assemblies of the heart with a certain periodicity. Fuel assemblies new ones must be loaded into the core or substituted for assemblies used fuel that is extracted from the nuclear reactor core. It is therefore necessary to have new fuel assemblies which must be transported from the fuel fabrication plant to the nuclear power plant in which charging or recharging is carried out from the heart of a nuclear reactor.

The transport of new fuel assemblies, which is carried out by rail or road requires the use of transport containers ensuring effective protection of fuel assemblies whose pencils are not protected laterally between two spacer grids successive. Transport containers must also be provided to avoid destruction or even limited deterioration of the assemblies of fuel, in the case of a container falling, for example during a transshipment operation of a container, during transport.

We know, from EP-A-0,506,512 and US-A-5,481,117, containers for transporting fuel assemblies that have an envelope sheet metal external made up of two half-shells of slightly shaped near semi-cylindrical attached and fixed one on the other along a frame rectangular disposed along an axial plane of diametrical direction of the container. The container is generally designed for the transport of two assemblies of fuel and has a chassis on which you can attach two fuel assemblies, which rests on a cradle fixed via shock-absorbing support elements inside the half-shell bottom of the outer shell of the container. The support frame and holding fuel assemblies is pivotally mounted on the cradle, by one of its ends, so that it can be moved between a loading position of fuel assemblies in which the support is substantially vertical and a transport position in which the fuel assembly support frame rests on the cradle in a substantially horizontal position.

The fuel assembly support frame has, generally, a T-shaped cross section that has a support base for fuel assemblies and a center partition longitudinal direction perpendicular to the base. The support base for fuel assemblies and the middle partition delimit, on the part and on the other side of the middle partition, two housings in each of which can place a fuel assembly. Fuel assemblies are held on the chassis, by means of flanges articulated on the lateral edges of the base and on the upper edge of the central partition of the chassis, so that the flanges can be moved between a open position in which the housing for a fuel assembly is accessible and a closed position in which the flanges maintain a fuel assembly. The flanges are assembled between them, in their closed position, by sets with screw and nut and are arranged along the length of the chassis, so that come to bear on the fuel assemblies placed in the housings of the chassis, at each of the successive spacer grids fuel assemblies.

Transport containers are designed so that the assemblies fuel placed side by side in the transport position cannot in no case constitute a critical mass leading to the start of neutron chain reactions. It is usually necessary to place neutron-absorbing elements between the fuel assemblies in position transport in the container, so as to avoid any risk of criticality.

In addition, it is also necessary to minimize the risks for disseminating the fissile material contained in the assemblies of fuel, in the event that the fuel assembly is subjected to damage or destruction resulting in the rupture of protective sheaths fuel rods, for example as a result of container fall.

In the case of transport containers known in the art, it turned out that the neutron absorbing means of the assemblies of fuel could be insufficient and the containers did not have not a structure allowing an effective containment of the matter fissile in case of deterioration of the fuel assembly inside the container. Indeed, the fuel assembly is neither protected nor confined inside the outer envelope of the container, the chassis not comprising that means for holding the fuel assemblies, under the form of flanges spaced along the longitudinal direction of the assemblies fuel, in the same way as the spacer grids.

In addition, simulations of dynamic behavior of containers and fuel assemblies, in the event of a fall in the direction axial of the fuel assemblies container and in the event of a fall a dish. showed that it was necessary to have absorbers energy efficient to guarantee the mechanical strength of the chassis and fuel assemblies contained in the container shell, in case fall.

It therefore seems desirable to have transport containers ensuring better protection of fuel assemblies.

The object of the invention is therefore to propose a container for transport for nuclear fuel assemblies of prismatic shape straight with an external envelope and an internal structure delimiting the less a receiving housing for maintaining a fuel assembly having side faces arranged in a straight prismatic surface and a end face at each of the longitudinal ends of the housing and comprising an assembly for receiving and holding at least one assembly of fuel comprising a support frame of at least one assembly of fuel comprising at least two bearing walls of two lateral faces a fuel assembly and at least one element pivotally mounted on the frame between an open position to give access to the housing the fuel assembly and a closed position in which the element ensures closure of the fuel assembly housing, this container transport allowing effective protection of the assembly (s) of transported fuels and to confine the fissile material contained in the fuel assemblies to prevent fissile material from forming spreads inside the outer envelope of the container in case of deterioration or destruction of fuel assemblies.

For this purpose, the fact that it also has two end walls pivoting retaining longitudinal end portions of the assembly combustible and that the element is a door which secures with the end walls and the supporting walls of the chassis a complete closure of the housing fuel assembly and protection and containment of the fuel assembly, regardless of the outer shell.

The internal structure constitutes a housing for receiving at least a fuel assembly that can be opened to provide access to the fuel assembly housing.

In order to clearly understand the invention, we will describe, with reference to in the attached figures, a container for transporting assemblies of new fuel from a pressurized water nuclear reactor according to the invention.

Figure 1 is a side elevational view of the container in a closed transport configuration.

FIG. 2 is an end view along 2 of FIG. 1.

FIG. 3A is a partial view in elevation of the container, the upper shell of the outer shell is removed, so as to make visible the internal structure of the container.

Figure 3B is a top view along 3B of Figure 3A of open container.

Figure 4 is an end view along 4-4 of Figure 3A or the Figure 3B.

Figure 5 is an exploded perspective view of the components of the internal structure of the fuel assembly transport container.

Figure 6 is an exploded perspective view of the components of the support frame for the fuel assemblies of the structure internal container.

Figure 7 is a top view of the support frame of the assemblies of fuel from the internal structure of the container.

Figure 8 is a cross-sectional view along 8-8 of the figure 7.

Figure 9 is a perspective view of a side door of the internal structure of the fuel assembly transport container.

Figure 10 is a cross-sectional view of the side door. at the side holding devices of a fuel assembly.

Figure 11 is an end view, in elevation, with parts broken away a side door of the internal structure of the transport container.

In Figures 1 and 2, we see a container for transporting assemblies of new fuel from a designated pressurized water nuclear reactor generally by the reference 1.

The transport container 1. which is designed for the transport of two fuel assemblies in horizontal position, has an envelope outer 2 consisting of a lower shell 2a and an upper shell 2b, both of semi-cylindrical shape and attached one on the other along a junction plane of the envelope 2 passing through the longitudinal axis of the cylindrical envelope.

Each of the shells 2a and 2b is made of sheet steel and has respective reinforcing arches 3a, 3b, of semi-circular shape distributed along the length of the half-shell.

At the lower part of the lower half-shell 2a are also fixed profiles 4 and 4 'constituting support legs of the container. Of plus, adjustable support elements 5 and 5 ′ comprising screw jacks and integral with a longitudinal end portion of the container allow adjust the tilt of the container resting on a support surface, around from the longitudinal axis of the container and around a transverse axis, respectively. Using the adjustable feet 5 and 5 'of the container, you can place the container, on its transport support, in a perfectly positioned position horizontal, i.e. in a position in which the longitudinal axis of the container is perfectly horizontal.

The two half-shells 2a and 2b are attached to each other by through rectangular peripheral flanges constituting an upper planar support part of the lower half-shell 2a and a flat lower support part of the upper half-shell 2b of the container.

In the closed position of the container shown in the figures 1 and 2, the flanges of the two half-shells 2a and 2b are attached and fixed to each other by screws and nuts and constitute a flange assembly 6.

Figures 3A and 3B show part of the container in the open state. i.e. with the upper half-shell of the container shell separated from the lower half-shell and removed.

Figures 3A and 3B show the internal structure of the container. designated generally by the reference 7, which includes in particular a cradle 8 coming to rest on supports 9 constituted by absorber pads shock, in the lower half-shell 2a of the outer casing 2 of the container. A second part of the internal structure of the container is consisting of a set 10 for receiving and supporting two assemblies of fuel in the honzontal position placed side by side. All 10, which rests on the cradle 8 delimits two entirely housings closed, for two fuel assemblies, as will be explained further.

The cradle 8 comprises two longitudinal members 8a, 8b constituted by angles fixed on the support pads 9 which are held in parallel arrangements with a spacing corresponding to the width of the container receiving assembly 10, by crosspieces. To one of his ends, the cradle has a stiffening and mounting assembly pivoting comprising two plates 11a and 11b parallel to each other and two sleepers formed by hollow sections fixed to the side members of the cradle and to plates 11a and 11b.

The pivoting mounting of the assembly 10 on the cradle, around an axis horizontal in transverse direction; is insured through the whole stiffening and pivoting assembly comprising the plates 11a and 11b.

In addition, as will be explained later, a retaining plate for fuel assemblies is also mounted between the plates 11a and 11b.

As can be seen in FIG. 3B, so as to limit the effect of a shock of the fuel assemblies, for example the effect of a fall of the container, between the longitudinal end of the internal structure 7 and the wall inner end of the outer casing 2, of circular shape, is interposed a shock absorber 43. The shock absorber 43, in the form of a disc, the cross section of which is identical to the internal section of the container shell, consists by a balsa disc surrounded by a stainless steel sheet envelope. Of course, an identical shock absorber is placed at the second longitudinal end of the container, between the second longitudinal end of the internal structure and the second end of the external envelope.

As can be seen in FIG. 4, the support and reception assembly 10 of the fuel assemblies comprises a chassis 12 having a T-shaped section and two doors 14a and 14b pivotally mounted on the sides of the chassis 12, as will be explained later.

In the closed position of the doors, as shown in the Figure 4, the door 14a defines, with the right part of the frame 12, a housing 13a for a fuel assembly and the door 14b delimits, with the left part of the chassis 12, a second housing 13b. Housing have a square section which has the dimensions of the section of a spacer grid of a fuel assembly for a nuclear water reactor under pressure whose container 1 provides transport.

To load the container, we tilt the assembly 10 in a substantially vertical position around the transverse axis located at one end of the cradle.

In its tilted position, the support and reception assembly of fuel assemblies 10 is in a vertical arrangement. The doors 14a and 14b are tilted outwards, so as to give access to housings 13a and 13b.

A fuel assembly can be placed in each of the housings 13a and 13b, by a fuel assembly lifting tool, for example by the winch of an overhead crane. Fuel assemblies come to rest, via their lower ends, on the plate support for fuel assemblies fixed between the two plates 11a and 11b of the cradle 8.

We close the doors of the assembly and support assembly assembly 10 and we tilt to the horizontal position the assembly 10 which then comes to rest on the cradle 8.

After replacing the upper half-shell on the half-shell lower of the casing 2 and fixed the two half-shells by screws and nuts, the container can be handled and transported by example by lifting the container through the legs lifting 15 and 15 'fixed on the upper half-shell of the casing external, as shown in Figure 1.

In FIG. 5, there is shown, in an exploded perspective view, the cradle 8 and the various elements constituting the support assembly and receiving fuel assemblies 10.

The chassis 12, which has a T-shaped cross section, has a base 12a of parallelepiped shape and a perpendicular partition 12b at the base 12a for separating the housings 13a and 13b for two fuel assemblies 16a and 16b of which the spacer grids 17a and 17b as well as the lower end pieces 18a and 18b and the upper end pieces 18'a and 18'b.

The housings 13a and 13b of the fuel assemblies 16a and 16b are delimited at one end of the chassis 12, by a plate support 20 intended to be fixed pivotally by means of axis ends between the plates 11a and 11b of the cradle 8 and a second end plate 21 pivotally mounted at the second end of the chassis 12, around a transverse pivot axis. Fuel assemblies come to rest, via their upper end caps 18'a and 18'b on the plate 20. The transverse holding plate 21 comprises adjustable stops 22 for bearing on the lower end pieces 18a and 18b of the fuel assemblies. The plate 21 could also include adjustable means for holding the fuel assemblies in the longitudinal direction.

When the end plates 20 and 21 are folded back into their position the fuel assemblies are kept in the longitudinal direction by clamping between the support devices 22 and the plate 20.

The pivoting side doors 14a and 14b of the support assembly and holding 10 of the fuel assemblies 16a and 16b have a section inverted L-shaped and have, along their lower edge, at the end of one of the branches of the L, articulation pieces 23 in the form of hinges spaced along the length of doors 14a and 14b.

The doors shown in Figure 5 have six hinges 23 spaced from each other along the length of a first lower edge of doors 14a or 14b.

According to its second opposite edge, at the end of the second branch L, each of the doors 14a and 14b has fixing lugs 24 having a part pierced with an opening, slightly projecting towards the outside in relation to the edge of the door.

The articulation pieces 23 in the form of hinges all have openings aligned in a direction parallel to the edge of the door and each engage on a hinge pin 25 projecting from a lateral edge of the base 12a of the chassis 12 for assembly support. Of even, the openings of the protrusions of the ears 24 arranged according to the second edge of the doors are aligned in a parallel direction at the edge of the door.

The middle wall 12b of the chassis 12 has on its upper edge guide pieces 26 and 26 'having openings which are all aligned in a direction parallel to the upper edge of the middle wall 12b of the chassis 12.

When the doors which are mounted hinged on the hinge pins 25 by means of the hinges 23 are folded into position closure, the second edges of the doors 14a and 14b along which are arranged the ears 24 are folded over the upper edge of the wall middle 12b of the chassis 12, each of the ears 24 coming into position interposed between two successive guide pieces 26 and 26 'fixed on the upper edge of the central wall 12b of the chassis 12. The doors 14a and 14b in the closed position can be locked by inserting a rod in the aligned openings of parts 26 and 26 'and ears 24.

In addition, the doors 14a and 14b have respective slots. 27a and 27'a and 27b and 27'b at their longitudinal ends projecting towards the outside in the longitudinal direction.

The end plates 20 and 21 of the chassis 12 each have along their upper and lateral edges, notches 28 and 28 'intended to each receive one of the slots 27a or 27b or one of the slots 27'a and 27'b respectively, in the closed position of the doors, after that the end walls 20 and 21 have been folded down.

The walls 20 and 21 are further crossed by openings in face of each of the ends of the fuel assemblies, in their transport position inside the housings 13a and 13b.

Each of the housings 13a or 13b for a fuel assembly which is delimited on two lateral faces by two perpendicular surfaces between them of the chassis 12, on its side faces opposite by two internal perpendicular surfaces of a door 14a or 14b and at its ends by plates 20 and 21, is completely closed and ensures containment efficient fuel assembly. In the event of a shock to the container, causing partial destruction of the fuel assembly, fragments of fuel assemblies, for example fragments pencils or fuel pellets, cannot come out of the housing of the fuel assembly and spill into the container.

The doors 14a and 14b and the end walls 20 and 21 which are pivotally mounted constitute a housing comprising two housings for fuel assemblies, which can be opened to provide access to the fuel assembly housings.

In addition, as will be explained later, the base 12a and the median wall 12b of the chassis as well as the walls of the doors 14a and 14b are formed in the form of a double wall in the thickness of which is placed a neutron absorbing resin, that is to say a synthetic resin added of an element that strongly absorbs neutrons.

In Figure 6, there is shown in exploded perspective the elements constituting the frame 12 of the assembly receiving and supporting assembly of fuel.

The chassis 12 comprises a base plate 30 reinforced by welded ribs 29 and by transverse profiles 31 at the end of which hinge pins 25 of the doors 14a and 14b and of the legs are fixed 32 for fixing the chassis 12 to the lateral sides of the cradle 8, by screws and nuts (Figures 7 and 8).

On either side of each of the profiles 31, above the plate 29, in its middle part are fixed columns 33 perpendicular to the plate 29. At the upper part of the columns 33 are fixed elements guide 26 ′ for the locking means of the doors of the reception assembly and support for fuel assemblies.

The second component of the chassis 12 is a profiled element in folded sheet metal 34 comprising two sheet metal elements folded in L extended towards the bottom by two edges and connected to their upper part by elements folded and / or attached constituting the guide elements 26 of the upper edge of the middle wall 12b of the chassis 12.

On the side edges folded down from the sheet metal element 34 passages are provided for door hinges and the chassis mounting lugs on the cradle attached to the end of the profiles 31 reinforcement.

At the end of the plate 29 are fixed two spacer pieces in T-shape 35a and 35b.

The chassis 12 is produced by assembling the element 34 in folded sheet and the base plate 29 comprising reinforcing elements and the columns 33.

The end spacers 35a and 35b of the base plate 30 are introduced into the internal profile of the element 34 in folded sheet. Likewise, six columns 33 are introduced in the vertical part of the internal profile of the element 34 in folded sheet, between the two vertical branches of the two sheets L-shaped sides

The guide pieces 26 'fixed to the end of the columns come be inserted between two successive guide parts 26 connecting the two sheets bent in L, in the form of the profiled element 34 with cross section T-shaped

In the assembly position of the chassis 12, the horizontal parts sheets bent in L come to rest on the spacers 35 and on the profiles 31, so that a free space is reserved between the horizontal parts of the sheet metal element 34 and the base plate 29.

As can be seen in FIG. 8, this free space 36 is filled of a neutron absorbing resin. The resin is a dense resin whose density is 1.5 to 2.

Similarly, a free space 37 between the vertical parts of the element made of sheet 24 is filled with a high density neutron absorbing resin. Resin and the bracing elements ensure the mechanical strength of the chassis 12.

By assembling the plate 30, its reinforcing elements and columns 33 with the folded sheet metal element 34, a frame 12 is obtained rigid double wall. By filling the free spaces 36 and 37 of the double wall with neutron absorbing resin, we obtain a frame whose plate base 12a and the middle partition wall 12b are susceptible absorb neutron fluxes produced by fuel assemblies arranged in the housings 13a and 13b of the chassis 12.

In Figure 9, there is shown the right door 14a of the assembly for receiving and supporting fuel assemblies.

The door 14a (as well as the second door 14b) is constituted by sheets folded in L which are connected to each other at the ends of the branches of the L by extensions of one of the branches, the articulation parts 23 and the locking lugs 24.

In addition, between the two sheets constituting the L-shaped door, are arranged spacers 38 disposed at a certain distance one of the other along the length of the door 14a.

Each of the spacers 38 comprises, as can be seen in the figure 10, two L-shaped plates spaced from each other according to the longitudinal direction of the door and fixed at their ends on a piece 25 and on a locking lug 24, respectively.

At each of the spacers 38, between the two plates in L shape constituting the spacer, is fixed on each of the branches of the L. a fuel assembly clamping device arranged in the housing delimited by the door, ensuring the maintenance of the assembly of fuel in a transverse direction.

As can be seen in Figure 10, each of the clamping devices 39 has a flat shoe 40 which can be operated from the outside of the door by a screw 41, for its movement in one direction perpendicular to the L branch of the seat in which the device is mounted tightening 39.

At each of the spacers 38, the door 14a has two clamping devices 39 intended to engage with two external faces of a spacer grid of a fuel assembly arranged in the housing delimited by door 14a. In this way, the clamping is carried out of the fuel assembly in its housing, on two perpendicular sides between them.

In FIG. 11, a longitudinal end of the door 14a which is closed by an L-shaped plate 41 on which are fixed projecting outwards the slots 27a for fixing the door 14a on the end wall 21. As can be seen in the torn off part of the Figure 11, a locking rod 42 is slidably mounted in openings aligned with the upper horizontal wall of the door 14a and the slots 27a. In addition, the rod 42 is operable from outside the door 14a.

When the door 14a is in the closed position and the end plate 20 (or 21) folded down in the closed position of the longitudinal ends housings of the assembly and support assembly fuel, rod 42 can be inserted into openings aligned through the external parts of the plate 20 (or 21) between the notches 28, in the transverse direction and the slots openings 27a placed in alignment with the openings of the plates 20 (or 21).

This produces a locking of the end closure plates 20 and 21 on the end parts of the door 14a.

Of course, an identical locking can be achieved at each ends of the door 14a comprising the slots 27a and 27'a.

The same locking rod 42 can ensure the locking of the second door 14b by introduction into openings of the plate 20 (or 21) and slots 27b (or 27'b).

The free space between the two L-shaped wall elements of the doors 14a and 14b is filled with a neutron absorbing resin, so as to absorb possibly a neutron flux from an assembly of fuel and directed outward from the receiving and support assembly fuel assemblies. The resin which is high density (density 1.5 to 2) and the spacers ensure the mechanical strength of the doors.

The internal structure of the container according to the invention defines two compartments for two fuel assemblies which are completely closed and inside which the fuel assemblies are kept laterally and in the axial or longitudinal direction. Housing being fully closed, in the event of a shock resulting in destruction partial of a fuel assembly, fragments of the assembly of fuel are not likely to come out of the internal structure which provides containment of the fuel assembly. The fragments of the fuel assembly is therefore not likely to spread in the outer envelope of the container.

In addition, the fuel assemblies are separated from each other in the internal structure of the container, by a neutron absorbing wall.

The housings of the fuel assemblies delimited by the internal structure also include a neutron absorbing wall closing the housings towards the outside, i.e. towards the internal surface of the envelope container exterior,

We therefore obtain both better mechanical protection of the assemblies fuel during transport inside the container and a reduction in the risks of reaching criticality during grouped transport fuel assemblies.

The invention is not limited to the embodiment which has been described.

This is how the internal structure of the container can present a different form from that which has been described and include different elements T-frame and overhead doors. The shape of the housing of the internal structure of the container depends on the shape of the assemblies of fuel being transported. In all cases, the structure internal has walls assembled together delimiting at least one housing for receiving and holding a fuel assembly entirely closed.

The invention applies to the transport of any fuel assembly nuclear with a straight prismatic shape. The next container the invention can be used not only for transporting assemblies new fuel but still for transporting fuel assemblies used with low activity.

Claims (8)

1. Transport container for nuclear fuel assemblies of vertical prismatic form comprising an external casing (2) and an internal structure (7) defining at least one receptacle (13a, 13b) for receiving and holding a fuel assembly (16a, 16b) having lateral faces disposed along a vertical prismatic surface and an end face on each of the longitudinal ends of the receptacle (13a, 13b) and comprising a unit (10) for receiving and holding at least one fuel assembly (16a, 16b) consisting of a support frame (12) for at least one fuel assembly comprising at least two supporting walls (12a, 12b) for two lateral faces of a fuel assembly (16a, 16b) acid at least one element (14a, 14b) mounted on the frame (12) to pivot between an open position to provide access to the receptacle for the fuel assembly and a closed position in which the element (14a, 14b) assures closure of the receptacle (13a, 13b) of the fuel assembly, characterised in that it additionally comprises two pivoting end walls (20, 21) for holding longitudinal end sections of the fuel assembly (16a, 16b), and that the element (14a, 14b) is a door which with the end walls (20, 21) and the supporting walls (12a, 12b) of the frame (12) assures a complete closure of the receptacle (13a, 13b) of the fuel assembly (16a, 16b) and protection and confinement of the fuel assembly independently of the external casing (2).
2. Container according to Claim 1, characterised in that the frame (12) is a support frame of two fuel assemblies (16a, 16b) having a T-shaped cross-section, a support base (12a) common to both receptacles (13a, 13b) of the two assemblies (16a, 16b) and a separating wall (12b) between the receptacles (13a, 13b) of the fuel assemblies (16a, 16b), and that the internal structure (7) of the container comprises two doors (14a, 14b) having an L-shaped cross-section, each being articulated on a longitudinal edge of the base plate (12a) of the frame (12) in a longitudinal direction of the frame (12) via a first edge of the door.
3. Container according to Claim 2, characterised in that at their longitudinal ends the doors (14a, 14b) have lugs (27a, 27'a, 27b, 27'b) projecting towards the outside in the longitudinal direction, and that on their outer edge, the closure plates (20, 21) of the longitudinal ends of the receptacles (13a, 13b) of the fuel assemblies (16a, 16b) have indentations (28), into which the lugs (27a, 27'a, 27b, 27'b) of the doors (14a, 14b) are inserted in the closed position of the doors (14a, 14b) and the end plates (20, 21).
4. Container according to any one of Claims 2 and 3, characterised in that the doors (14a, 14b), when in their closed position, have a second edge turned down onto the end edge of the separating median wall (12b) of the frame (12), the second edges of the doors (14a, 14b) turned down onto the end edge of the separating median wall (12b) of the frame (12) and the end edge of the median section (12b) of the frame (12) having locking elements (24, 26, 26') with openings aligned in the longitudinal direction of the internal section of the container for insertion of a locking bar into the locking elements (24, 26, 26') with the aligned openings.
5. Container according to any one of Claims 1 to 4, characterised in that the walls (12a, 12b, 14a, 14b) of the internal structure of the container around the lateral walls of the at least one receptacle (13a, 13b) for a fuel assembly (16a, 16b) are double walls formed by metal sheets and cross pieces having a central space filled with a neutron-absorbent resin so that the cross pieces and the high-density neutron-absorbent resin assure the mechanical resistance of the walls.
6. Container according to any one of Claims 1 to 5, characterised in that at least one of the closure walls (20, 21) of the end faces of the receptacle (13a, 13b) of a fuel assembly have adjustable means (22) for holding the fuel assembly (16a, 16b) in the longitudinal direction of the container.
7. Container according to any one of Claims 1 to 6, characterised in that the closure walls (14a, 14b) of lateral faces of the receptacle (13a, 13b) of the fuel assembly (16a, 16b) have means (40, 41) for holding the fuel assembly transversely in the form of skids (40), which are moveable in the transverse directions of the fuel assembly and may be manoeuvred from outside the container (1) so that they abut against the faces of the grid-cross pieces (17a, 17b) of the fuel assembly (16a, 16b).
8. Container according to any one of Claims 1 to 7, characterised in that between each of the longitudinal ends of the internal structure (7) and each of the longitudinal ends of the external casing, it additionally has a damping means (43) formed by a balsa disc covered by a sheet of stainless steel.

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