Patent Number: 
Section: claims

1. A nuclear waste cask with impact protection comprising:a longitudinal axis;a longitudinally elongated cask body including a top end, a bottom end, and a sidewall extending between the ends, and a cavity configured for holding a nuclear waste canister; andan impact limiter coupled to the top end of the cask body, the impact limiter comprising an annular perforated sleeve having a body including a central opening and a circumferential array of elongated longitudinal passages formed therethrough around the central opening. 2. The cask according to claim 1, wherein the longitudinal passages are oriented parallel to each other and extend between a top surface and a bottom surface of the perforated sleeve. 3. The cask according to claim 2, wherein the longitudinal passages are oriented parallel to the longitudinal axis of the cask. 4. The cask according to claim 2, wherein e longitudinal passages have a circular transverse cross section. 5. The cask according to claim 4, wherein the longitudinal passages each have a longitudinal length which is greater than their respective diameter. 6. The cask according to claim 5, wherein the longitudinal passages each have a length greater than at least two times their respective diameter. 7. The cask according to claim 4, wherein the array of longitudinal passages are dispersed in a full 360 degree pattern around an entirety of the perforated sleeve. 8. The cask according to claim 5, wherein the array of longitudinal passages comprises multiple concentric rings of longitudinal passages which extend circumferentially around the perforated sleeve. 9. The cask according to claim 8, wherein the longitudinal passages in each ring have progressively larger diameters moving outwardly from the central opening. 10. The cask according to claim 9, wherein the longitudinal passages of an outermost ring each have larger diameters than the longitudinal passages of an innermost ring. 11. The cask according to claim 8, wherein the longitudinal passages are arrayed in a staggered pitch pattern. 12. The cask according to claim 11, wherein the perforated sleeve includes at least three concentric rings of longitudinal passages. 13. The cask according to claim 11, wherein each longitudinal passage is separated by a solid web of material of the perforated sleeve which is smaller in radial thickness than a largest diameter of the longitudinal passages. 14. The cask according to claim 1, wherein the longitudinal passages are closely packed such that a radial reference line drawn outwards from a geometric center of the perforated sleeve through any portion of the perforated sleeve intersects at least one longitudinal passage. 15. The cask according to claim 1, wherein the body of the perforated sleeve has a solid monolithic unitary structure which defines the central opening and longitudinal passages. 16. The cask according to claim 15, wherein the body of the perforated sleeve is formed of metal. 17. The cask according to claim 16, wherein the body of the perforated sleeve is formed of a soft isotopic metallic material comprising aluminum or aluminum alloy. 18. The cask according to claim 16, wherein the body of the perforated sleeve is collectively formed by multiple metallic ring segments stacked together, each ring segment defining a portion of the central opening and longitudinal passages which are concentrically aligned in each ring segment. 19. The cask according to claim 1, wherein the impact limiter further comprises an outer cap shell including a circular end wall and a sidewall extending longitudinally from the end wall, the perforated sleeve being nested inside the cap shell. 20. The cask according to claim 19, wherein the impact limiter includes a centrally-located internal annular collar which defines a receptacle which slideably receives a top end forging on the top end of the cask. 21. The cask according to claim 20, wherein the collar is spaced radially inwards from the sidewall of the end cap to define an annulus, the perforated sleeve being nested in the annulus. 22. The cask according to claim 19, wherein the outer cap shell defines an end cavity of the impact limiter, the end cavity containing an energy absorbing material. 23. The cask according to claim 22, wherein the energy absorbing material is a corrugated aluminum panel honeycomb structure or a polymeric foam material. 24. The cask according to claim 1, wherein the perforated sleeve defines a longitudinally-extending annular load transfer surface arranged to transmit an external impact force on the impact limiter to a corresponding annular impact load bearing surface formed by a diametrically reduced stepped portion of the top end of the cask. 25. The cask according to claim 1, wherein the impact limiter protrudes radially outward beyond the sidewall of the cask. 26. The cask according to claim 1, further comprising a second impact limiter coupled to the bottom end of the cask body, the second impact limiter comprising an annular perforated sleeve having a body including a central opening and a circumferential array of elongated longitudinal passages formed therethrough. 27. The cask according to claim 1, wherein the perforated sleeve has a solidity ratio less than 0.5 resulting in an open area of the sleeve collectively formed by the longitudinal passages being greater than 50 percent. 28. The cask according to claim 1, wherein the longitudinal passages are arranged in a triangular staggered 60 degree hole pattern. 29. The cask according to claim 1, wherein the perforated sleeve comprises an outer circumferential wall and an inner circumferential wall extending longitudinally between opposing major end surfaces of the perforated sleeve. 30. The cask according to claim 1, wherein the top end of the cask comprises an end forging defining an outward facing annular bearing surface which is radially aligned with an inwardly facing annular load transfer surface of the perforated sleeve.