Detection method for fuel assemblies in a reactor core

Purposes: To enable exchange of a plurality of fuel assemblies arranged in the core of a LMFBR type reactor after exact detection of the fuel assemblies. Method: Upon fuel exchange for a LMFBR type reactor, ultrasonic waves are sent through liquid sodium and impinged onto the handling heads of fuel assemblies before taking out the fuel assemblies out of a reactor vessel into a fuel storage facility, to thereby judge whether the intended fuel assemblies to be discharged have been discharged by utilizing the reflection waves from the surface of the handling heads. (Aizawa, K.)