Patent Number: 
Section: claims

1. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a current of coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel with the current of coolant flow being separated into streams which collide as said fluid flows to said outlet nozzles, and provided with a flow stabilizing member being lower than one of said outlet nozzles, said member being supported on or above a portion of the upper core plate that is not perforated for fluid flow, disposed in the vicinity of a core barrel in a region outside of said fuel region and positioned to separate said streams thereby preventing the streams from colliding to suppress temperature fluctuations of said coolant flow. 2. An internal structure of a nuclear reactor according to  claim 1 , wherein said flow stabilizing member is disposed beneath an outlet of said outlet nozzle. claim 1 3. An internal structure of a nuclear reactor according to  claim 2 , wherein said flow stabilizing member is disposed directly underneath a center portion of said outlet of said outlet nozzle. claim 2 4. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel, said upper plenum being shaped to define several separate streams for said coolant which collide; and a flow stabilizing member being lower than said outlet nozzle, said member being supported on or above a portion of the upper core plate that is not perforated for fluid flow, disposed in the vicinity of a core barrel in a region outside of said fuel region, wherein said flow stabilizing member is disposed at positions midway between said two adjacent outlet nozzles to prevent said separate streams from colliding to prevent temperature fluctuations of said coolant. 5. An internal structure of a nuclear reactor according to  claim 4 , wherein said flow stabilizing member is dimensioned so that a top end thereof is positioned at a height level within a range from a position midway between an upper surface of said upper core plate and a lowermost portion of said outlet of said outlet nozzle to a position lower than said lowermost portion of said outlet. claim 4 6. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel, and provided with a flow stabilizing member being lower than said outlet nozzles, said coolant flowing along at least two streams which collide toward said outlet nozzles, said member being supported on or above a portion of the upper core plate that is not perforated for fluid flow, disposed in the vicinity of a core barrel in a region outside of said fuel region, wherein said flow stabilizing member is disposed directly underneath a center portion of said outlet of said outlet nozzle and dimensioned so that a top end thereof is positioned at a height level within a range from a position midway between an upper surface of said upper core plate and a lowermost portion of said outlet of said outlet nozzle to a position lower than said lowermost portion of said outlet to thereby prevent said streams from colliding. 7. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a current of coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel with the current of coolant flow being separated into streams which collide as said fluid flows to said outlet nozzles, and provided with a flow stabilizing member being lower than one of said outlet nozzles, said member being constructed to impede fluid flow therethrough, disposed in the vicinity of a core barrel in a region outside of said fuel region and positioned to separate said streams thereby preventing the streams from colliding to suppress temperature fluctuations of said coolant flow. 8. An internal structure of a nuclear reactor according to  claim 7 , wherein said flow stabilizing member is disposed beneath an outlet of said outlet nozzle. claim 7 9. An internal structure of a nuclear reactor according to  claim 8 , wherein said flow stabilizing member is disposed directly underneath a center portion of said outlet of said outlet nozzle. claim 8 10. The internal structure of a nuclear reactor according to  claim 9  wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 9 11. The internal structure of a nuclear reactor according to  claim 8  wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 8 12. The internal structure of a nuclear reactor according to  claim 7  wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 7 13. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel, said upper plenum being shaped to define several separate streams for said coolant which collide; and a flow stabilizing member being lower than said outlet nozzle, said member being constructed to impede fluid flow therethrough, disposed in the vicinity of a core barrel in a region outside of said fuel region, wherein said flow stabilizing member is disposed at positions midway between said two adjacent outlet nozzles to prevent said separate streams from colliding to prevent temperature fluctuations of said coolant. 14. An internal structure of a nuclear reactor according to  claim 13 , wherein said flow stabilizing member is dimensioned so that a top end thereof is positioned at a height level within a range from a position midway between an upper surface of said upper core plate and a lowermost portion of said outlet of said outlet nozzle to a position lower than said lowermost portion of said outlet. claim 13 15. The internal structure of a nuclear reactor according to  claim 14  wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 14 16. The internal structure of a nuclear reactor according to  claim 13  wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 13 17. An internal structure of a nuclear reactor including an upper plenum which is defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles mounted on a side wall of a nuclear reactor vessel, and provided with a flow stabilizing member being lower than said outlet nozzles, said coolant flowing along at least two streams which collide toward said outlet nozzles, said member being constructed to impede fluid flow therethrough, disposed in the vicinity of a core barrel in a region outside of said fuel region, wherein said flow stabilizing member is disposed directly underneath a center portion of said outlet of said outlet nozzle and dimensioned so that a top end thereof is positioned at a height level within a range from a position midway between an upper surface of said upper core plate and a lowermost portion of said outlet of said outlet nozzle to a position lower than said lowermost portion of said outlet to thereby prevent said streams from colliding. 18. The internal structure of a nuclear reactor according to  claim 17  wherein said flow stabilizing member is solid so as to prevent the flow of liquid therethrough. claim 17