Patent Number: 
Section: claims

1. A nuclear reactor lower internals structure having an axial and a circumferential dimension comprising:a tubular core barrel supported coaxially within the lower internals and having an inside vertically extending surface and an upper and lower end; anda reflector having a plurality of axial and circumferential segments and an outside curvature that substantially matches a curvature of the inside surface of the core barrel and contacts at least a substantial portion of the inside surface of the core barrel covered by the reflector, is supported substantially over at least a central axial length of the core barrel that extends substantially from or above the lower end toward the upper end and over at least a portion of the circumferential dimension covered by the reflector, the reflector further has an inside contour that matches an outside contour of an abutting array of a plurality of nuclear fuel assemblies that are designed to be supported within the core barrel to form a nuclear core and the axial and circumferential reflector segments are separately, fixedly connected to and respectively supported by the inside vertically extending surface of the core barrel at a plurality of axial and circumferential locations and wherein the reflector does not extend substantially continuously from the lower end to the upper end of the core barrel and is divided into axial sections that interface with each other at an acute angle with the inside surface of the core barrel. 2. The nuclear reactor lower internals structure of claim 1 wherein the circumferential sections have a stepped interface with each other formed from alternating angles wherein adjacent alternating angles are bent in opposite directions. 3. The nuclear reactor lower internals structure of claim 2 wherein the alternating angles are substantially right angles. 4. The nuclear reactor lower internals structure of claim 1 wherein at least two of the circumferential sections are spaced from each other and are separated by a baffle and former structure. 5. The nuclear reactor lower internals structure of claim 1 wherein the acute angle is approximately between 25° and 45°. 6. The nuclear reactor lower internals structure of claim 5 wherein the acute angle is approximately thirty degrees. 7. The nuclear reactor lower internals structure of claim 1 wherein the number of axial sections is either three or four. 8. The nuclear reactor lower internals structure of claim 1 wherein there is a space provided between interfacing axial sections. 9. The nuclear reactor lower internals structure of claim 1 wherein at least two of the circumferential sections are spaced from each other and are separated by a baffle and former structure, wherein a former plate is positioned to cover substantially each circumferential end of the interface of the axial sections. 10. The nuclear reactor lower internals structure of claim 1 wherein the circumferential sections are not contiguous. 11. The nuclear reactor lower internals structure of claim 1 including a plurality of axially extending coolant channels between the outside curvature of the reflector and the inside surface of the core barrel. 12. The nuclear reactor lower internals structure of claim 1 wherein the reflector does not extend substantially continuously from the lower end to the upper end of the core barrel and is divided into axial sections that interface with each other including axial coolant channels through the reflector that extend across the interface and tubular sleeves inserted and closely received within at least some of the coolant channels in the vicinity of the interface that span the interface. 13. The nuclear reactor lower internals structure of claim 1 wherein the core barrel is attached to a reactor vessel at a plurality of spaced circumferential locations by a plurality of attachment bracket arrangements that maintain a space between the reactor vessel and an outside of the core barrel, wherein at least two of the attachment bracket arrangements are positioned circumferentially around and affixed to an outside surface of the core barrel at substantially different axial elevations. 14. The nuclear reactor lower internals structure of claim 13 wherein adjacent attachment bracket arrangements are positioned at the substantially different axial elevations. 15. The nuclear reactor lower internals structure of claim 13 wherein the space between the reactor vessel and the outside of the core barrel forms a coolant path and the substantially different axial elevations are spaced far enough apart so that coolant blocked by one of the attachment bracket arrangements at an upper elevation is reformed directly below the one of the attachment bracket arrangement before the coolant reaches a lower axial elevation of the next attachment bracket arrangement at the substantially different axial elevation. 16. The nuclear reactor lower internals structure of claim 1 wherein the reflector includes a specimen basket for supporting a radiation specimen. 17. The nuclear reactor lower internals structure of claim 16 wherein the specimen basket is positioned within a hollowed out portion of the reflector. 18. The nuclear reactor lower internals structure of claim 17 wherein the hollowed out portion extends from a top surface of the reflector.