Reactor fuel assembly with a fluid passage control element

Object: To accurately detect a malfunction in a reactor fuel assembly. Structure: A fuel assembly has a neutron shield block positioned on the internal surface at the upper part thereof, and a fluid passage control element is inserted into the assembly. The fluid passage control element is formed with an axial central passage at the core portion thereof along the length abount one half of said element, and the central passage is radially formed with a plurality of radial passages at the upper part thereof so that said radial passages come in communication with the leading end of the central passage. The element is further peripherally formed with a plurality of axially extended-through peripheral passages as communicating passages. On the other hand, it is designed so that a plurality of thermocouples are embedded on an extended line of the radial passages located upwardly of the fuel assembly. Accordingly, variation of temperature of each thermocouple may be measured to accurately detect a closed position of fuel rod flux. (Kamimura, M.)