For the decommissioning of Fukushima Daiichi Nuclear Power Station (1F), defueling of the fuel debris in the reactor core of Units 1-3 is planned to start within 10 years. Preferential items in the characterization of the fuel debris were identified for this work, in which the procedure and handling tools were assumed on the basis of information on 1F and experience after the Three Mile Island Unit 2 (TMI-2) accident. The candidates for defueling tools for 1F were selected from among the TMI- 2 defueling tools. It was found that they could be categorized into six groups according to their operating principles. The important properties of the fuel debris for defueling were selected considering the effect of the target materials on the tool performance. The selected properties are shape, size, density, thermal conductivity, heat capacity, melting point, hardness, elastic modulus, and fracture toughness. Of these properties, the mechanical properties (hardness, elastic modulus, fracture toughness) were identified as preferential items, because too few data on these characteristics of fuel debris are available in past severe accident studies. (authors)