Patent Number: 
Section: claims

1. A shroud segment for a nuclear reactor vessel, the shroud segment comprising:an elongated inner shell;an elongated outer shell;a plurality of elongated intermediate shells disposed between the inner and outer shells;the inner shell, outer shell, and intermediate shells being radially spaced apart forming a plurality of annular cavities for holding water;a top closure plate attached to the top of the shroud segment; anda bottom closure plate attached to the bottom of the shroud segment;wherein the top and bottom closure plates are configured for detachable coupling to adjoining shroud segments to form a stacked array of shroud segments;a mounting clamp pivotably attached to the bottom closure plate, the mounting clamp movable between an open unlocked position and a closed locked position; andan elastically deformable and arcuately shaped seismic restraint fixedly attached to the shroud segment;wherein the seismic restraint is a leaf spring fixedly attached to the clamp and pivotable with the clamp. 2. The shroud segment of claim 1, wherein the annular cavities extend from the top closure plate to the bottom closure plate. 3. The shroud segment of claim 1, wherein the annular cavities are fluidly interconnected by a plurality of drain holes extending through the intermediate shells. 4. The shroud segment of claim 3, wherein the drain holes are radially staggered between adjacent intermediate shells. 5. The shroud segment of claim 3, wherein the outer shell includes drains holes to fluidly connect the annular cavities to an exterior of the shell segment. 6. The shroud segment of claim 1, wherein the intermediate shells have a length that is coextensive with the length of the shroud. 7. The shroud segment of claim 1, wherein the mounting clamp is attached to a radially extending mounting lug on the bottom closure plate. 8. The shroud segment of claim 1, wherein the mounting clamp includes a recess configured to receive a mounting lug on a top closure plate of a second shroud segment. 9. The shroud segment of claim 1, wherein the mounting clamp includes a locking fastener for holding the mounting clamp in the closed locked position. 10. A shroud segment for a nuclear reactor vessel, the shroud segment comprising:an elongated inner shell;an elongated outer shell;a plurality of elongated intermediate shells disposed between the inner and outer shells;the inner shell, outer shell, and intermediate shells being radially spaced apart forming a plurality of annular cavities for holding water;a top closure plate attached to the top of the shroud segment;a bottom closure plate attached to the bottom of the shroud segment;wherein the top and bottom closure plates are configured for detachable coupling to adjoining shroud segments to form a stacked array of shroud segments;a mounting clamp pivotably attached to the bottom closure plate, the mounting clamp movable between an open unlocked position and a closed locked position; andan elastically deformable and arcuately shaped seismic restraint fixedly attached to the shroud segment;wherein the seismic restraint defines an outward facing concave recess, the seismic restraint configured to engage an interior of the reactor vessel when the shroud segment is mounted therein. 11. The shroud segment according to claim 1, wherein the intermediate shells each have a length that is coextensive with respective lengths of the inner and outer shells, and wherein the shroud segment forms a riser region inside the shroud segment. 12. The shroud segment of claim 11, wherein the inner, outer, and intermediate shells of the shroud segment are seal welded to the top and bottom closure plates collectively forming a self-supporting shroud segment structure. 13. The shroud segment of claim 1, wherein the top closure plate includes radially extending lifting lugs configured for rigging. 14. A shroud segment for a nuclear reactor vessel, the shroud segment comprising:an elongated inner shell;an elongated outer shell;a plurality of elongated intermediate shells disposed between the inner and outer shells;the inner shell, outer shell, and intermediate shells being radially spaced apart forming a plurality of annular cavities between the inner shell, outer shell, and intermediate shells configured for holding water;a top closure plate attached to the top of the shroud segment; anda bottom closure plate attached to the bottom of the shroud segment;wherein the annular cavities are fluidly interconnected by a plurality of drain holes formed through the outer shell and intermediate shells, the drain holes in the outer shell spaced longitudinally apart along a length of the outer shell, and the drain holes in the intermediate shells being spaced longitudinally apart along a respective length of each intermediate shell;the top and bottom closure plates configured for detachable coupling to adjoining shroud segments to form a stacked array of shroud segments;a mounting clamp configured to detachably couple to a top closure plate of an adjoining shroud segment;the mounting clamp pivotably coupled to the bottom closure plate via a pivot pin extending through the bottom closure plate and defining a stationary pivot axis, the mounting clamp movable about the pivot axis between an open unlocked position and a closed locked position; anda locking fastener rotatably mounted to the bottom closure plate and operable to retain the mounting claim in the closed locked position. 15. The shroud segment of claim 14, wherein the inner shell does not include drain holes. 16. A shroud segment for a nuclear reactor vessel, the shroud segment comprising:an elongated inner shell;an elongated outer shell;a plurality of radially spaced apart elongated intermediate shells disposed between the inner and outer shells;a top closure plate attached to the top of the shroud segment and having an outer circumferentially-extending peripheral edge which is substantially flush in radial direction with the outer shell;a bottom closure plate attached to the bottom of the shroud segment and having an outer circumferentially-extending peripheral edge which is substantially flush in radial direction with the outer shell;wherein the top and bottom closure plates each comprise a plurality of mounting tabs protruding radially outwards beyond their respective peripheral edges, the mounting tabs being configured for coupling to mounting tabs of adjoining shroud segments to form a stacked array of shroud segments;an outer annular cavity formed between the intermediate shells and the outer shell;an inner annular cavity formed between the intermediate shells and the inner shell;a plurality of intermediate annular cavities formed between the intermediate shells; anda mounting clamp pivotably attached to each of the mounting tabs of the bottom closure plate, the mounting clamps movable between an open unlocked position and a closed locked position;wherein the inner, outer, and intermediate shells of each shroud segment is seal welded to their respective top and bottom closure plates collectively forming a self-supporting shroud segment structure, each shroud segment detachably coupled to an adjoining shroud segment.