Patent Number: 039768341
Section: claims

1. A nuclear reactor system comprising: a reactor vessel having a nuclear core therein comprised of a plurality of fuel assemblies;  a guide structure supported in said vessel in vertically spaced relationship from said core, said guide structure including two vertically spaced plates each of which substantially overlies said core, said two plates being interconnected and vertically spaced by a plurality of control element guidance means;  a plurality of control elements situated within said control element guidance means and adapted for vertical reciprocal movement into and out of said core;  a main coolant flow path defined in said reactor vessel for directing coolant fluid during normal operation through said core and then through one of said plates of said guide structure into the region between said two spaced plates;  a third plate substantially overlying said core;  means for supporting said third plate in vertical spaced relation from one of said two plates of said guide structure to define a plenum therebetween;  means for substantially sealing said plenum from said main coolant flow path;  a source of emergency coolant fluid;  means for flow coupling said source to said plenum for introducing emergency coolant fluid into said plenum; and  means connected to said plenum for discharging emergency coolant therein into said core of said nuclear reactor. 2. The reactor system of claim 1 wherein said guide structure is supported above said core and wherein the lower of said two plates of said guide structure serves to maintain alignment of the upper ends of said fuel assemblies in said core, said lower plate of said guide structure having a plurality of flow holes therethrough forming a portion of said main coolant flow path. 3. The reactor system of claim 2 wherein said third plate has a plurality of holes therethrough, wherein said means for supporting said third plate supports said third plate above said lower plate of said guide structure to define said plenum between said third plate and said lower plate, said plurality of holes in said third plate being in alignment with said plurality of flow holes in said lower plate; and wherein said means for sealing includes a plurality of annular sleeves positioned between and in sealing relationship with said third plate and said lower plate, each of said annular sleeves being coaxially disposed with respect to one of said holes in said third plate. 4. The reactor system of claim 3 wherein said discharging means includes a plurality of discharge holes in said lower plate of said guide structure. 5. The reactor system of claim 4 wherein said discharge means further includes: longitudinally extending discharge channels within some of said fuel assemblies, each of said channels having openings in the side wall along the length thereof; and tubular connecting means for each of said channels, each of said tubular connecting means having one end in registry with said channel and the other end received within one of said discharge holes in said lower plate of said guide structure to communicate with said plenum. 6. The reactor system of claim 5 wherein there are a plurality of aligned openings in said third plate and said upper and lower plates of said guide structure to permit passage therethrough of said control elements; wherein said fuel assemblies include longitudinally extending control channels, and hollow alignment means affixed to the upper end of said fuel assemblies, said hollow alignment means having one end in registry with one of said control channels and the other end received in one of said aligned openings in said lower plate of guide structure, said control elements being telescopingly reciprocally movable within said alignment means and said control channels; and wherein said sealing means includes means positioned between said third plate and said lower plate for sealing said aligned openings from said plenum. 7. The reactor system of claim 6 wherein said control element guidance means comprises a plurality of longitudinally extending hollow tubes extending between and through said upper and lower plates and said third plate, said tubes being aligned with said aligned opening in said upper, lower and third plates, each of said hollow tubes being adapted to house only one of said control elements for telescoping movement therewithin; wherein said alignment means of said fuel assemblies are received within the lower end of said hollow tubes in said aligned openings in said lower plate; and wherein said means positioned between said third plate and said lower plate for sealing said aligned openings from said plenum comprises tubular spacers through which pass said hollow tubes, said tubular spacers having their opposite ends disposed in abutting relation to the lower surface of said third plate and the upper surface of said lower plate. 8. The reactor system of claim 7 wherein each of said hollow tubes has a flange on one end which engages one of said upper and lower plates and a threaded portion of the other end; wherein there is a concentric tube for each of said hollow tubes extending between said upper plate and said third plate and which surrounds said hollow tube, and a nut adapted to be threaded onto said threaded portion of each of said hollow tubes whereby each of said hollow tubes is placed in tension and each of said concentric tubes and each of said annular sleeves and tubular spacers are placed in compression. 9. The reactor system of claim 7 wherein said means for sealing further comprises: a flange on each of said hollow tubes at one end, a threaded portion on the other end of each of said hollow tubes, a concentric tube for each of said hollow tubes extending between said upper plate of said guide structure and said third plate and surrounding said hollow tube, and a nut adapted to be threaded onto the threaded portion of each of said hollow tubes to place said annular sleeves and tubular spacers in compression between said lower plate and said third plate. 10. The reactor system of claim 2 wherein said means for supporting said third plate supports said third plate below said upper plate of said guide structure to define said plenum between said third plate and said upper plate; and wherein said means for discharging comprises a plurality of hollow discharge tubes extending downward from said third plate and through said lower plate of said guide structure, said plenum being in fluid communication with the interior of said hollow discharge tubes at the upper end of said tubes to discharge emergency coolant into said discharge tubes and the lower end of said hollow tubes being in fluid communication with said core. 11. The reactor system of claim 10 wherein said discharge means further includes: longitudinally extending discharge channels within some of said fuel assemblies, each of said channels having openings in the side wall along the length thereof; and tubular connecting means for each of said channels, each of said tubular connecting means having one end in registry with said channel and the other end received within the lower end of one of said hollow discharge tubes to communicate therewith. 12. The reactor system of claim 11 wherein there are a plurality of aligned openings in said third plate and said upper and lower plates in said guide structure to permit passage therethrough of said control elements; and wherein said fuel assemblies include longitudinally extending control channels and hollow alignment means affixed to the upper end of said fuel assemblies, said hollow alignment means having one end in registry with one of said control channels and the other end received in one of said aligned openings in said lower plate of said guide structure, said control elements being telescopingly reciprocally movable within said alignment means and said control channels; and wherein said sealing means includes means positioned between said third plate and said upper plate for sealing said aligned openings from said plenum. 13. The reactor system of claim 12 wherein said control element guidance means comprises a plurality of longitudinally extending hollow tubes extending between and through said upper and lower plates and said third plate, said tubes being aligned with said aligned openings in said upper, lower and third plates, each of said hollow tubes being adapted to house only one of said control elements for telescoping movement therewithin; wherein said alignment means of said fuel assemblies are received within the lower end of said hollow tubes in said aligned openings in said lower plate; and wherein said means positioned between said third plate and said upper plate for sealing said aligned openings from said plenum comprises tubular spacers through which pass said hollow tubes, said tubular spacers having their opposite ends disposed in abutting relation to the upper surface of said third plate and the lower surface of said upper plate. 14. The reactor system of claim 13 wherein said means for sealing further comprises: a flange on one end of each of said hollow tubes extending between and through said plates which engages one of said upper and lower plates, a threaded portion on the other end of each of said hollow tubes, a concentric tube for each of said hollow tubes extending between said third plate and said lower plate and surrounding said hollow tube, and a nut adapted to be threaded onto said threaded portion of each of said hollow tubes to place said tubular spacers surrounding said hollow tubes in compression between said third plate and said upper plate. 15. The reactor system of claim 14 wherein each of said hollow discharge tubes for discharging coolant fluid to said core extends at its upper end through both said third plate and said upper plate of said guide structure, each of said discharge tubes being sealed at its upper end above said upper plate, and having an opening in the side wall thereof at a location between said upper plate and said third plate to provide communication between said plenum and the interior of said discharge tubes. 16. The reactor system of claim 2 wherein said source of emergency coolant fluid is positioned outside of said reactor vessel, and wherein said means for flow coupling said source to said plenum comprises a first conduit means extending from said source through the wall of said reactor vessel to the interior of said vessel and a second conduit means extending longitudinally downward and through at least said upper plate of said guide structure, said second conduit means being flow coupled at its upper end to said first conduit means and being in fluid communication with said plenum at its lower end.