Patent Number: 
Section: claims

1. A steel composition comprising:Cr at between about 10.0 wt% and about 13.0 wt%;C at between about 0.17 wt% and about 0.23 wt%;Mo at between about 0.80 wt% and about 1.2 wt%;Si less than or equal to about 0.5 wt%;Mn less than or equal to about 1.0 wt%;V at between about 0.25 wt% and about 0.35 wt%;W at between about 0.40 wt% and about 0.60 wt%; andFe at least 80 wt%;wherein the processing of the steel composition includes transforming at least some of the steel composition into an austenite phase by heating the steel composition to a temperature from 1100° C. to 1300° C. for 40-60 hours. 2. The steel composition of claim 1,wherein the steel composition has been processed so that it exhibits a swelling of less than 0.9% by volume at a depth between 500-700 nm below the surface after dual-beam Fe++ and He++ irradiation to doses of 188 displacements per atom (dpa) with 0.2 appm He/dpa, as calculated using the Stopping Range in Matter simulation with the K-P option for damage cascades and a 40 eV displacement energy, created by irradiating the steel composition at 460° C. with a defocused beam of 5 MeV Fe++ ions and a raster-scanned beam of ˜2 MeV He++ ions transmitted through a thin Al foil for scattering and energy reduction to create a uniform He profile at the irradiation depth of a sample of the steel composition. 3. The steel composition of claim 2, wherein the steel composition exhibits a swelling of less than 0.75% by volume. 4. The steel composition of claim 2, wherein the steel composition exhibits a swelling of less than 0.5% by volume. 5. The steel composition of claim 2, wherein the steel composition exhibits a swelling of less than 0.3% by volume. 6. The steel composition of claim 1, wherein the steel composition is an HT9 steel. 7. A fuel element made of the steel composition of claim 1. 8. A component of a fuel assembly made of the steel composition of claim 1. 9. A steel composition comprising:(Fe)a(Cr)b(Mo, Ni, Mn, W, V)cNd;whereina, b, c, and d are each a number greater than zero representing a weight percentage;b is between 11 and 13;c is between about 0.25 and about 0.9;d is between about 0.01 and about 0.04; andbalanced by a; andwherein the processing of the steel composition includes transforming at least some of the steel composition into an austenite phase by heating the steel composition to a temperature from 1100° C. to 1300° C. for 40-60 hours. 10. The steel composition of claim 9, wherein b is between 11.5 and 12.5. 11. The steel composition of claim 9,wherein the steel composition has been processed so that it exhibits a swelling of less than 0.9% by volume at a depth between 500-700 nm below the surface after dual-beam Fe++ and He++ irradiation to doses of 188 displacements per atom (dpa) with 0.2 appm He/dpa, as calculated using the Stopping Range in Matter simulation with the K-P option for damage cascades and a 40 eV displacement energy, created by irradiating the steel composition at 460° C. with a defocused beam of 5 MeV Fe++ ions and a raster-scanned beam of ˜2 MeV He++ ions transmitted through a thin Al foil for scattering and energy reduction to create a uniform He profile at the irradiation depth of a sample of the steel composition. 12. The steel composition of claim 11, wherein the steel composition exhibits a swelling of less than 0.75% by volume. 13. The steel composition of claim 11, wherein the steel composition exhibits a swelling of less than 0.5% by volume. 14. The steel composition of claim 11, wherein the steel composition exhibits a swelling of less than 0.3% by volume. 15. The steel composition of claim 9, wherein the steel composition is an HT9 steel. 16. A fuel element made of the steel composition of claim 9. 17. A component of a fuel assembly made of the steel composition of claim 9. 18. The steel composition of claim 1, wherein:Cr is at between about 10.0 wt% and about 12.5 wt%;C at between about 0.17 wt% and about 0.22 wt%;Mo at between about 0.80 wt% and about 1.2 wt%;Si less than or equal to about 0.5 wt%;Mn less than or equal to about 1.0 wt%;V at between about 0.25 wt% and about 0.35 wt%;W at between about 0.40 wt% and about 0.60 wt%;P less than or equal to about 0.5 wt%;S less than or equal to about 0.5 wt%; andFe at least 80 wt%. 19. The steel composition of claim 1, further comprising:Ni at between about 0.3 wt% and about 0.7 wt%. 20. The steel composition of claim 1, wherein at least substantially all of the composition is in the martensite phase.