Patent Number: 
Section: abstract

Within an upper plenum of a nuclear reactor, a portion of a heated coolant flows radially outward from a central portion of a core barrel (30) towards outlet nozzles (12) in a region of an upper core plate (21) extending outside of an outer periphery of the core along an inner wall of a core barrel (30). Portions of the coolant flows beneath the outlet nozzles (12). Thus, streams of heated coolant flowing in opposite directions may collide with each other. After collision, the flow directions of the heated coolant are changed to flow upward. Due to the collision, the coolant flow behavior becomes complicated and unstable, making it difficult to measure the temperature of the heated coolant with an outlet pipe (42) connected to the outlet nozzle (12). Within an upper plenum (40) defined above a fuel region through which a coolant flows and which is hydraulically communicated with a plurality of outlet nozzles (12) mounted on a side wall of a nuclear reactor vessel (10), short flow stabilizing members (1) each being lower than the outlet nozzle (12) are disposed in the vicinity of a core barrel (30) in an region outside of the fuel region.