[en] Purpose: To positively prevent levitation of a nuclear fuel assembly within a reactor container without involving a difficulty in disengagement of the assembly in a simple manner. Constitution: In an arrangement wherein a fuel assembly having fuel elements received within an outer bushing and having an entrance nozzle disposed at the tip thereof is inserted and supported within a connection pipe provided with an orifice between partitions defining a low pressure coolant chamber and a high pressure coolant chamber, the orifice formed in the entrance nozzle is disposed obliquely towards the tip of the nozzle from the outer periphery of the entrance nozzle. When the pump is started to cause coolant within the chamber to flow into the nozzle through the orifice, the assembly receives a downward pressing force to prevent levitation thereof because the orifice is disposed inclined. (Yoshino, Y.)