Patent Number: 
Section: claims

1. A nuclear fuel assembly body including a lengthways axis and configured to receive nuclear fuel pins to form a nuclear fuel assembly, said body comprising:a frame made from a metal material, the frame being openworked;a first sleeve made from a metal material and connected to a first end of the frame;a second sleeve made from a metal material and connected to a second end of the frame opposite the first sleeve along the lengthways axis, anda ceramic tubular internal structure positioned inside the frame and along the lengthways axis between the first and second sleeves, wherein the ceramic tubular internal structure comprises a plurality of lengthways superimposed segments, includinga first segment positioned at a first end of the ceramic tubular internal structure and partially penetrating into the first sleeve, anda second segment positioned at a second end of the ceramic tubular internal structure, opposite the first end, and partially penetrating into the second sleeve,wherein joints between the segments comprise leakage zones. 2. The assembly body according to claim 1, wherein the ceramic tubular internal structure prevents leakage of the cooling fluid intended to traverse it. 3. The assembly body according to claim 1, wherein the segments are socketed into one another. 4. The assembly body according to claim 3, in which the lengthways ends of the socketed segments comprise, in the case of one, a groove and, in the case of the other, a rib of matching shape. 5. The assembly body according to claim 1, wherein the frame is formed by an assembly of struts defining windows. 6. The assembly body according to claim 5, wherein the frame comprises lengthways and transverse struts. 7. The assembly body according to claim 6, whereinthe transverse struts cover zones where the lengthways superimposed segments are connected. 8. The assembly body according to claim 5, in which the ceramic tubular internal structure is formed from plates attached to the frame so as to block the windows of said frame. 9. The assembly body according to claim 1, wherein the frame is attached to the first and second sleeves by welding. 10. The assembly body according to claim 1, wherein the frame is attached to the first and second sleeves by a mechanical assembly method. 11. The assembly body according to claim 10, wherein the mechanical assembly method is of the dovetail joint type. 12. The assembly body according to claim 1, wherein the frame is formed from a tube perforated with drill holes forming circular or oblong slots. 13. The assembly body according to claim 1, further comprising: a washer with undulations of amplitude 5 mm inserted between an end of an end section of the tubular internal structure and the second sleeve located in an upper part of the assembly. 14. The assembly body according to claim 1, having a regular hexagonal transverse section. 15. The assembly body according to claim 1, in which the ceramic tubular internal structure is made of SiC, fibre-reinforced SiC or MAX-phases of the Ti3SiC2 type. 16. The assembly body according to claim 1 for a sodium-cooled fast neutron reactor, wherein the sleeves and the frame are made from at least one of austenitic, ferritic, and ferritic/martensitic steels. 17. The assembly body according to claim 1 for a sodium-cooled fast neutron reactor, in which the first and second sleeves are made from 316 Ti standard austenitic steel and the frame from EM10. 18. The assembly body according to claim 1 for a gas-cooled fast neutron reactor, in which the first and second sleeves and the frame are made from refractory metals. 19. An assembly, comprising:a foot,the assembly body according to claim 1,nuclear fuel pins positioned in the assembly body, andan upper neutron protection,wherein the body is attached to the foot and to the upper neutron protection in the area of the first and second sleeves respectively by welding.