Patent Number: 
Section: claims

1. A method comprising:mixing a powdered fissile material selected from the group consisting of UN and U3Si2 with an additive selected from oxidation resistant materials, the powdered fissile material comprising grains having grain boundaries;pressing the mixed fissile and the additive into a pellet; and,sintering the pellet to a temperature greater than the melting point of the additive sufficient for melting of the additive into the grain boundaries of the fissile material and densifying the pellet,wherein the additive has a melting point greater than the sintering temperature of the fissile material, and has a median particle size less than that of the UN or U3Si2. 2. The method recited in claim 1 wherein the powdered fissile material is UN, and the additive is selected from the group consisting of tungsten and alloys containing at least 50 atomic % thereof, and UO2. 3. The method recited in claim 1 wherein the additive is present in amounts less than 20 weight percent of the fissile material. 4. The method recited in claim 1 wherein the sintering is selected from the group consisting of pressureless sintering, hot pressing, hot isostatic pressing, spark plasma sintering, field assisted sintering, and flash sintering. 5. The method recited in claim 1 wherein the median particle size of the additive is less than 10% of the median particle size of the UN or U3Si2. 6. The method recited in claim 1 wherein the median particle size of the additive is less than 1% of the median particle size of the UN or U3Si2. 7. The method recited in claim 1 wherein the vapor deposition is used to coat the outside of the unsintered pellet with the additive and to penetrate the additive into the pellet body of the UN or U3Si2. 8. The method recited in claim 1, wherein the powdered fissile material is U3Si2, and the additive is selected from the group consisting of molybdenum, titanium, chromium, thorium, tungsten, niobium, and zirconium, alloys containing at least 50 atomic % thereof, BeO, and UO2. 9. The method recited in claim 1 wherein the additive coats to the U3Si2 or UN powders to form protective layers through vapor deposition before pressing into pellets and sintering. 10. The method recited in claim 9 wherein the vapor deposition is selected from the group consisting of physical vapor deposition, chemical vapor deposition, and atomic layer deposition. 11. A method comprising:mixing a powdered fissile material UN with an additive, the powdered fissile material comprising grains having grain boundaries;pressing the mixed fissile and the additive into a pellet; andsintering the pellet to a temperature greater than the melting point of the additive sufficient for melting of the additive into the grain boundaries of the fissile material and densifying the pellet,wherein the additive has a melting point lower than the sintering temperature of the fissile material, and the additive is a borosilicate glass. 12. A method comprising:mixing a powdered fissile material U3Si2 with an additive, the powdered fissile material comprising grains having grain boundaries;pressing the mixed fissile material and the additive into a pellet; andsintering the pellet to a temperature greater than the melting point of the additive sufficient for melting of the additive into the grain boundaries of the fissile material and densifying the pellet, wherein the additive has a melting point lower than the sintering temperature of the fissile material, and the additive is a borosilicate glass.