Patent Number: 
Section: claims

1. A cask configured to receive a canister containing radioactive material, said cask having an inner surface delimiting a cask housing to receive the canister, said cask also comprising a canister extraction/insertion assembly bearing against said inner surface, the canister extraction/insertion assembly configured to move the canister inside the cask housing in a longitudinal direction of the cask, in a carried position in which this canister is free of any contact with said inner surface,characterized in that said canister extraction/insertion assembly is provided with a carriage bearing against said inner surface and with a canister support structure carried by said carriage, said carriage and support structure configured to take up a drawn-together position in a radial direction of the cask allowing contact between the canister and said inner surface, and a drawn-apart position in the radial direction of the cask in which the canister carried by the support structure takes up its carried position,and in that one of the two elements from among said carriage and said support structure is provided with at least one guide ramp cooperating with a ramp follower provided on the other of said two elements, said ramp configured so that-application of a relative translational movement between the carriage and canister support structure, in the longitudinal direction of the cask, causes a changeover of said two elements from said drawn-together position to said drawn-apart position, or conversely. 2. A cask according to claim 1, characterized in that said carriage is a travelling carriage, and in that said ramp follower is a roller. 3. A cask according to claim 1, characterized in that said canister extraction/insertion assembly is arranged in a cavity opened towards the cask housing, and defined by said inner surface of the cask. 4. A cask according to claim 3, characterized in that it comprises two canister supports partly defining said inner surface and being spaced at an angle around a longitudinal axis of the cask, so as to partly delimit said open cavity between them. 5. A package of radioactive material, characterized in that it comprises:a cask configured to receive a canister containing radioactive material, said cask having an inner surface delimiting a cask housing to receive the canister, said cask also comprising a canister extraction/insertion assembly bearing against said inner surface, the canister extraction/insertion assembly configured to move the canister inside the cask housing in a longitudinal direction of the cask, in a carried position in which this canister is free of any contact with said inner surface,said canister extraction/insertion assembly is provided with a carriage bearing against said inner surface and with the canister support structure carried by said carriage, said carriage and support structure configured to take up a drawn-together position in a radial direction of the cask allowing contact between the canister and said inner surface, and a drawn-apart position in the radial direction of the cask in which the canister carried by the support structure takes up its carried position,and in that one of the two elements from among said carriage and said support structure is provided with at least one guide ramp cooperating with a ramp follower provided on the other of said two elements, said ramp configured so that-application of a relative translational movement between the carriage and canister support structure, in the longitudinal direction of the cask, causes a changeover of said two elements from said drawn-together position to said drawn-apart position, or conversely, andthe canister containing said radioactive material and arranged inside said cask housing. 6. A package of radioactive material according to claim 5, characterized in that the canister is of cylindrical shape and has a circular section, and contains at least one of irradiated nuclear fuel assemblies and nuclear waste. 7. An extraction/insertion system for a canister containing radioactive material, the canister configured to be extracted from and inserted in a cask housing delimited by an inner surface of a cask, characterized in that said system comprises a canister extraction/insertion assembly configured to bear against said inner surface of the cask and being provided with a carriage and canister support structure carried by said carriage, said carriage and support structure configured to take up a drawn-together position in a radial direction of the cask allowing contact between the canister and said inner surface, and a drawn-apart position in the radial direction of the cask in which the canister carried by the support structure takes up a carried position in which this canister is free of any contact with said inner surface, one of the two elements from among said carriage and said support structure being provided with at least one guide ramp cooperating with a ramp follower provided on the other of said two elements, said ramp configured so that the application of a relative translational movement between the carriage and canister support structure, in a longitudinal direction of the cask, causes a changeover of said two elements from said drawn-together position to said drawn-apart position, or conversely, said extraction system also comprising mobilizing means in the longitudinal direction of the cask connected to one of said two elements, and retractable abutment means cooperating with the other of said two elements. 8. An extraction/insertion system according to claim 7, characterized in that said mobilizing means are connected to the carriage. 9. A method to transfer a canister containing radioactive material, from a first to a second entity chosen from among the group consisting of a cask and a receiver housing delimited by an inner surface, characterized in that it comprises the following successive steps consisting of:bringing the canister located inside the first entity to a carried position in which this canister is free of any contact with said inner surface associated with said first entity;mobilizing said extraction/insertion assembly carrying the canister so as to cause this extraction assembly and the canister to enter inside said second entity. 10. A method according to claim 9, characterized in that said first entity consists of the cask. 11. A method according to claim 10, characterized in that said step consisting of setting in movement said extraction/insertion assembly is conducted in a direction of extraction in the longitudinal direction of the cask, and in that it is followed by the following successive steps consisting of:bringing the canister to a deposited position inside the receiver housing in which this canister is free of any contact with said extraction assembly; andsetting in movement said extraction assembly in an opposite direction to the direction of extraction, so as to re-insert this extraction assembly inside said cask. 12. A method according to claim 11, characterized in that said canister extraction assembly belongs to an extraction system for a canister containing radioactive material, this canister configured to be extracted from and inserted in a cask housing delimited by an inner surface of a cask, said system comprising a canister extraction/insertion assembly configured to bear against said inner surface of the cask and being provided with a carriage and canister support structure carried by said carriage, said carriage and support structure configured to take up a drawn-together position in a radial direction of the cask allowing contact between the canister and said inner surface, and a drawn-apart position in the radial direction of the cask in which the canister carried by the support structure takes up a carried position in which this canister is free of any contact with said inner surface, one of the two elements from among said carriage and said support structure being provided with at least one guide ramp cooperating with a ramp follower provided on the other of said two elements, said ramp configured so that the application of a relative translational movement between the carriage and canister support structure, in a longitudinal direction of the cask, causes the changeover of said two elements from said drawn-together position to said drawn-apart position, or conversely, said extraction system also comprising mobilizing means in the longitudinal direction of the cask connected to one of said two elements, and retractable abutment means cooperating with the other of said two elements, the extraction system being used to implement said transfer method. 13. A method according to claim 12, characterized in that said step consisting of bringing the canister to its carried position inside the cask is conducted by implementing the following successive operations:connecting said mobilizing means of the extraction system to one of said two elements from among said carriage and said support structure of the extraction assembly;actuating a first abutment belonging to said retractable abutment means so as to bring this first abutment from a retracted position to an abutting position allowing the locking in translation of the other of said two elements in the direction of extraction of said longitudinal direction of the cask;actuating mobilizing means in the direction of extraction so as to cause movement of the carriage and support structure from said drawn-together position to said drawn-apart position; andactuating said first abutment so as to bring it from said abutting position to said retracted position. 14. A method according to claim 12, characterized in that said step consisting of bringing the canister to a deposited position inside the receiver housing is conducted by implementing the following successive operations:actuating a second abutment belonging to said retractable abutment means so as to bring this second abutment from a retracted position to an abutting position allowing the locking in translation of the other of said two elements in the opposite direction to the direction of extraction;actuating mobilizing means in said opposite direction to cause displacement of said carriage and support structure from said drawn-apart position to said drawn-together position; andactuating said second abutment so as to bring it from said abutting position to said retracted position.