Patent Number: 
Section: claims

1. A nuclear fuel pin comprising a linear element defined by a bar or billet in a cylindrical shape of metal nuclear fuel material including uranium and/or plutonium and a cladding comprising Fe and Cr or an alloy comprising at least these two elements, further comprising: a main shell positioned around the linear element of metal nuclear fuel material, said main shell being disposed between an inside surface of the cladding and the linear element of metal nuclear fuel material, said main shell comprising yarns or fibers made of SiC; and a primary shell of silica or quartz fibers inserted between the linear element of metal nuclear fuel material and the main shell, the primary shell being disposed directly onto an outer surface of the cylinder of metal nuclear fuel material. 2. The nuclear fuel pin as claimed in claim 1, further comprising:a plenum to receive said discharge of fission gasses; anda reservoir, wherein the linear element is disposed at a first end of said nuclear fuel pin, the plenum is disposed at a second end of said nuclear fuel pin, and said reservoir is disposed between said plenum and said linear element, the cladding is configured to cover and contain said linear element, said reservoir, and said plenum. 3. The nuclear fuel pin as claimed in claim 2, wherein said reservoir comprises an annulus made of a material which is resistant to a corrosion of molten actinides. 4. The nuclear fuel pin as claimed in claim 3, wherein said annulus is made of tantalum. 5. The nuclear fuel pin as claimed in claim 1, wherein the SiC constituting the fibers is of cubic β allotropic variety. 6. The nuclear fuel pin as claimed in claim 1, wherein the main shell also comprises free Si fillers. 7. The nuclear fuel pin as claimed in claim 1, wherein said main shell comprises strips comprising SiC yarns or fibers. 8. The nuclear fuel pin as claimed in claim 1, wherein the main shell comprises a plurality of wrapped layers of SiC fibers wound around the linear element of metal nuclear fuel material. 9. The nuclear fuel pin as claimed in claim 8, wherein the primary shell comprises a plurality of wrapped layers of silica or quartz fibers wound around the linear element of metal nuclear fuel material. 10. A process for manufacturing a metal nuclear fuel pin as claimed in claim 1, further comprising the production of the main shell around the linear element of metal nuclear fuel material by weaving or braiding SiC fibers. 11. The process for manufacturing a metal nuclear fuel pin as claimed in claim 10, further comprising a prior step of surface oxidation of the linear element of metal nuclear fuel material. 12. The process for manufacturing a metal nuclear fuel pin as claimed in claim 10, further comprising a prior step of coating the linear element of metal nuclear fuel material with a binder comprising a soft brazing powder, the soft brazing powder including a conductive material. 13. The process for manufacturing a metal nuclear fuel pin as claimed in claim 10, further comprising the production of the primary shell between the linear element of metal nuclear fuel material and the main shell, said primary shell comprising silica or quartz fibers. 14. A process for manufacturing a metal nuclear fuel pin as claimed in claim 1, further comprising the production of the main shell with strips of SiC fibers wound around the linear element of metal nuclear fuel material. 15. The nuclear fuel pin as claimed in claim 1, wherein the primary shell comprises a plurality of wrapped layers of silica or quartz fibers wound around the linear element of metal nuclear fuel material.