Patent Number: 
Section: claims

1. A method comprising:providing a plurality of tristructural-isotropic fuel particles;mixing the plurality of tristructural-isotropic fuel particles with silicon carbide powder and at least two different rare earth oxide neutronic poisons to form a precursor mixture in which the silicon carbide powder separates at least one of the plurality of tristructural-isotropic fuel particles embedded in the silicon carbide powder from the other tristructural-isotropic fuel particles embedded in the silicon carbide powder; andcompacting the precursor mixture at a predetermined pressure and temperature to form a fuel element in which the silicon carbide powder becomes a silicon carbide matrix having a density substantially equal to the theoretical density of stoichiometric silicon carbide and having pockets of porosity of not more than 4%,wherein the pockets include the rare earth oxide neutronic poisons,wherein one of the rare earth oxide neutronic poisons is Eu2O3, andwherein the rare earth neutronic poisons are in an amount of up to 6 weight percent. 2. The method according to claim 1, wherein the rare earth oxide neutronic poisons include rare earth oxides having a large neutron capture cross-section and ability to suppress a sintering temperature of the silicon carbide powder below a critical damage temperature of the tristructural-isotropic fuel particles. 3. The method according to claim 1, wherein additional rare earth oxide neutronic poisons are selected from the group consisting of Gd2O3, Er2O3, and Dy2O3. 4. The method according to claim 1, further comprising: mixing additional sintering additives to the precursor mixture of the silicon carbide powder and the rare earth oxide neutronic poisons. 5. The method according to claim 4, wherein the additional sintering additives include alumina, yttria, or other rare earth oxides, or combinations thereof. 6. The method according to claim 1, wherein one or more of the rare earth oxide neutronic poisons are oxide sintering additives in the precursor mixture. 7. The method according to claim 1, wherein the precursor mixture consists essentially of the silicon carbide powder and the rare earth oxide neutronic poisons. 8. The method according to claim 1, wherein the precursor mixture includes the rare earth oxide neutronic poisons in an amount up to 10 weight percent of a total weight of the precursor mixture. 9. The method according to claim 1, wherein a combination of the rare earth oxide neutronic poisons and any additional sintering additives is in an amount up to 10 weight percent of a total weight of the precursor mixture. 10. The method according to claim 1, wherein the predetermined temperature is less than 1900° C. 11. A nuclear fuel comprising:a fuel element comprising a plurality of tristructural-isotropic fuel particles intermixed in a silicon carbide matrix,wherein the silicon carbide matrix separates a least one of the plurality of tristructural-isotropic fuel particles embedded in the silicon carbide matrix from the other tristructural-isotropic fuel particles embedded in the silicon carbide matrix,wherein the silicon carbide matrix has a density substantially equal to the theoretical density of stoichiometric silicon carbide and has pockets of porosity of not more than 4%,wherein the pockets include at least two different rare earth oxide neutronic poisons,wherein one of the rare earth rare earth oxide neutronic poisons is Eu2O3, andwherein the rare earth neutronic poisons are in an amount of up to 6 weight percent. 12. The nuclear fuel according to claim 11, wherein the pockets consist essentially of the rare earth oxide neutronic poisons. 13. The nuclear fuel according to claim 11, wherein the pockets consist essentially of the rare earth oxide neutronic poisons and sintering additives. 14. The nuclear fuel according to claim 11, wherein additional rare earth oxide neutronic poisons are selected from the group consisting of Gd2O3, Er2O3, and Dy2O3. 15. A nuclear fuel comprising:a fuel element comprising a plurality of tristructural-isotropic fuel particles intermixed in a silicon carbide matrix,wherein the silicon carbide matrix separates a least one of the plurality of tristructural-isotropic fuel particles embedded in the silicon carbide matrix from the other tristructural-isotropic fuel particles embedded in the silicon carbide matrix,wherein the silicon carbide matrix has a density substantially equal to the theoretical density of stoichiometric silicon carbide and has pockets of porosity of not more than 4%,wherein the pockets include rare earth oxide neutronic poisons, andwherein the rare earth oxide neutronic poisons include combinations of Gd2O3 and Er2O3 in a range of 1.57 to 2.07 total weight percent. 16. The nuclear fuel according to claim 15, wherein the pockets consist essentially of the rare earth oxide neutronic poisons. 17. The nuclear fuel according to claim 15, wherein the pockets consist essentially of the rare earth oxide neutronic poisons and sintering additives. 18. The nuclear fuel according to claim 15, wherein additional rare earth oxide neutronic poisons further include Dy2O3.