Patent Number: 
Section: claims

1. A nuclear fuel rod comprising:a tubular cladding constructed from silicon carbide and having interior walls surrounding an interior volume;a first closure sealing off one end of the tubular cladding;a nuclear fuel occupying a portion of the interior volume; anda gland seal end plug sealing off a second end of the tubular cladding;the gland seal end plug comprising:a flexible material made of graphite;an end stopper having an exterior end and an interior end and defining a passage therethrough, the exterior end of the end stopper having a seat that abuts and substantially closes off the second end of the tubular cladding, the interior end of the end stopper having at least one wedge-shaped surface;a ram having a stem that extends through the passage in the end stopper into an interior of the tubular cladding, and an interior end positioned between and in contact with the interior walls of the tubular cladding;the flexible material being positioned between and in contact with each of the interior walls of the tubular cladding, the wedge-shaped surface of the end stopper and the interior end and a portion of the stem of the ram, wherein the ram and the end stopper are configured to support and together exert pressure on the flexible material to radially outwardly expand the flexible material against the interior wall of the tubular cladding and seal off the second end of the tubular cladding; anda spring washer configured to be compressed along with the flexible material and to maintain a force on the flexible material even if there is thermal expansion of the ram or relaxation of the flexible material. 2. The nuclear fuel rod of claim 1 wherein the stem has a threaded exterior, and the gland seal end plug further comprises a nut coupled to a portion of the threaded stem and configured to draw the stem through the end stopper to pressure the flexible material against the wall of the interior of the tubular cladding. 3. The nuclear fuel rod of claim 2 wherein one or more of the seat, ram and nut comprises silicon carbide. 4. The nuclear fuel rod of claim 2 wherein the end stopper is coated with silicon carbide. 5. The nuclear rod of claim 1 wherein the spring washer comprises a partially stabilized Zirconium Oxide. 6. The nuclear fuel rod of claim 1 wherein the spring washer comprises a stack of spring washers. 7. The nuclear fuel rod of claim 1 wherein the end stopper is configured to prevent the flexible material from expanding through an interface between the interior of the tubular cladding and the end stopper. 8. The nuclear fuel rod of claim 1 wherein the flexible material consists of pure graphite. 9. The nuclear fuel rod of claim 1 wherein the flexible material comprises a mixture of graphite fiber and expanded graphite. 10. The nuclear fuel rod of claim 1 wherein one or both of the end stopper and the ram comprises Zirealoy 4. 11. The nuclear fuel rod of claim 1 wherein the seat is constructed in two layers including a gasket between the two layers of the seat that form a seal between the seat and the stem and the seat and the wall of the tubular cladding. 12. The nuclear fuel rod of claim 11, wherein the gasket comprises a plurality of O-ring gaskets.