Patent Number: 053176111
Section: claims

1. A fuel element for a nuclear thermal engine having a fueled truncated conical shell with a base characterized by an annular unfueled lip at said base having radial passages therethrough, wherein said annular lip is integral with said truncated conical shell, and said annular lip extends axially above said base. 2. The fuel element of claim 1 wherein said radial passages are defined by walls in said annular lip which diverge radially inwardly. 3. The fuel element of claim 1 wherein said annual lip is porous with pores forming said radial passages. 4. A fuel element for a nuclear thermal engine having a fueled truncated conical shell with a base characterized by an annular unfueled lip at said base having radial passages therethrough and a plurality of angularly spaced ribs extending radially along a truncated conical surface of said shell forming channels therebetween. 5. The fuel element of claim 4 wherein said truncated conical surface is an outer surface of said truncated conical shell. 6. The fuel element of claim 5 wherein said truncated conical shell has a base and said fuel element includes an annular lip extending radially outward from said base and with radial passages therethrough. 7. A fuel element for a nuclear thermal engine having a fueled truncated conical shell characterized by a plurality of angularly spaced unfueled ribs extending radially along at least one truncated conical surface of said shell forming channels therebetween. 8. A stack of fuel elements for a nuclear thermal engine having a plurality of fuel elements, each fuel element having a truncated conical shell with a base, characterized in that an annular lip with radial passages therethrough extends radially outward from said base, said fuel elements being stacked with said lips positioned on top of one another to form said stack with frusto-conical flow passages between adjacent elements and with said radial passages communicating with said frusto-conical flow passages. 9. The stack of fuel elements of claim 8 wherein each of said fuel elements has a plurality of angularly spaced ribs extending radially along a truncated conical surface of said frusto-conical shell dividing said truncated conical flow passages into flow channels. 10. The stack of fuel elements of claim 9 wherein said truncated conical surface is an outer surface of each of said truncated conical shells. 11. The stack of fuel elements of claim 8 wherein said annular lips of said fuel elements comprise rigid rings having radial passages therethrough and compliant annular supports extending radially inward from said rigid rings and supporting said truncated conical shells at said bases thereof. 12. The stack of fuel elements of claim 11 wherein said compliant annular support defines an annular groove in which said base of the truncated conical shell seats. 13. The stack of fuel elements of claim 13 wherein said compliant annular supports have annular outer sections which are clamped between adjacent rigid rings and annular cantilevered inner sections supporting said truncated conical shells at said bases. 14. The stack of fuel elements of claim 13 wherein said cantilevered inner sections of said compliant supports extend toward said truncated conical shells generally transverse to outer surfaces of said shells and terminate in annular grooves in which said bases of said truncated conical shells are supported. 15. The stack of fuel elements of claim 13 wherein said annular cantilevered inner sections of said compliant supports extend parallel t truncated conical surfaces of said truncated conical shells with adjacent inner sections forming annular slots into which the bases of the truncated conical shells extend, and including spring means in said annular slots resiliently supporting and centering said truncated conical shells. 16. The stack of fuel elements of claim 8 wherein said annular lips comprise rings with radial passages therethrough and having internal annular grooves in which the truncated conical shells seat. 17. The stack of fuel elements of claim 16 wherein the bases of said truncated conical shells have generally radially outwardly extending flanges which seat in said grooves in said rings. 18. The stack of fuel elements of claim 8 wherein said lips are unfueled and integral with the bases of said truncated conical shells.