Nuclear fuel elements including protective structures, and related method of forming a nuclear fuel element

1. A nuclear fuel element, comprising:

a core comprising a fissile element comprising uranium and an additional element comprising silicon, the core comprising uranium silicide (U 3 Si 2 ); and

a protective structure around the core, the protective structure comprising:

a first region comprising a different concentration of the fissile element and the additional element than the core, the first region comprising a greater than stoichiometric amount of the additional element than uranium silicide (U 3 Si 2 ) and a greater concentration of the additional element than the core;

a second region surrounding the first region and comprising a metal and the additional element, the metal comprising from 30 atomic percent to 70 atomic percent of the second region; and

an outer region of the protective structure around the second region and comprising the metal.

2. The nuclear fuel element of claim 1 , further comprising a cladding material around the outer region.

3. The nuclear fuel element of claim 1 , wherein the metal comprises one or more of zirconium, yttrium, thorium, and hafnium.

4. The nuclear fuel element of claim 1 , wherein the protective structure exhibits a gradient of the fissile element, a concentration of the fissile element decreasing with an increasing distance from the core.

5. The nuclear fuel element of claim 1 , wherein the protective structure exhibits a gradient of the additional element.

6. The nuclear fuel element of claim 1 , wherein the metal comprises one or more elements selected from zirconium, molybdenum, beryllium, plutonium, hafnium, cerium, tungsten, thorium, chromium, tantalum, niobium, titanium, yttrium, silicon, aluminum, nickel, cobalt, scandium, bismuth, and copper.

7. The nuclear fuel element of claim 1 , wherein the metal comprises zirconium silicide.

8. The nuclear fuel element of claim 1 , wherein the metal comprises thorium oxide.

9. The nuclear fuel element of claim 1 , wherein the metal comprises a metal nitride, a metal oxide, or a metal carbide.

10. The nuclear fuel element of claim 1 , wherein the additional element comprises a remaining portion of the second region.

11. The nuclear fuel element of claim 1 , wherein the second region further comprises at least one of carbon, nitrogen, and oxygen.

12. The nuclear fuel element of claim 1 , wherein the protective structure further comprises a third region adjacent to the second region, the third region comprising the metal and the additional element and comprising a higher atomic percent of the metal than the second region.

13. The nuclear fuel element of claim 12 , wherein the third region comprises from 51 atomic percent to 99 atomic percent of the metal.

14. The nuclear fuel element of claim 12 , wherein a concentration of the additional element is greater in the first region than in the second region and greater in the second region than in the third region.

15. The nuclear fuel element of claim 12 , wherein:

the third region comprises from 51 atomic percent to 99 atomic percent of the metal; and

remaining portions of the third region comprise the additional element.

16. The nuclear fuel element of claim 1 , wherein the protective structure comprises one or more additives selected from the group consisting of carbon nanotubes, carbon black, and graphene.

17. A method of forming a nuclear fuel element, the method comprising:

providing a first feed material in a reaction vessel, the first feed material comprising a fissile element comprising uranium and an additional element comprising silicon;

exposing the first feed material to energy from an energy source to form a core of the nuclear fuel element, the core comprising uranium silicide (U 3 Si 2 ) formed from the fissile element and the additional element;

providing a second feed material comprising the fissile element, the additional element, and at least a metal around an outer portion of the core; and

exposing the second feed material to energy from the energy source to form a protective structure around the core and to form inter granular bonds between the core and the protective structure, the protective structure comprising:

a first region comprising a different concentration of the fissile element and the additional element than the core, the first region comprising a greater than stoichiometric amount of the additional element than uranium silicide (U 3 Si 2 ) and a greater concentration of the additional element than the core;

a second region surrounding the first region and comprising the metal and the additional element, the metal comprising from 30 atomic percent to 70 atomic percent of the second region; and

an outer region of the protective structure around the second region and comprising the metal.

18. The method of claim 17 , wherein the metal is selected from zirconium, molybdenum, beryllium, plutonium, hafnium, cerium, tungsten, thorium, chromium, tantalum, niobium, titanium, yttrium, silicon, aluminum, nickel, cobalt, scandium, bismuth, and copper.

19. The method of claim 17 , further comprising forming the nuclear fuel element to comprise an increasing concentration of the metal with an increasing distance from a center of the nuclear fuel element.

20. The method of claim 17 , further comprising forming a third region comprising the metal and the additional element between the second region and the outer region.