Characterization of fuel debris properties for decommissioning of Fukushima Daiichi Nuclear Power Stations

Washiya, Tadahiro ; Yano, Kimihiko ; Ikeuchi, Hirotomo  ; Kaji, Naoya; Takano, Masahide ; Morimoto, Kyoichi 

On March 11, 2011, the Great East Japan Earthquake caused the severe accident at Fukushima Daiichi NPS (F1). In the reactors of unit 1-3, large amount of fuel debris was generated. Thermodynamic equilibrium (TDE) calculations based on results of MAAP code analysis was carried out and typical debris phases were predicted. Experimental studies were also carried out using simulated fuel debris, and verify the expected properties. The F1 accident differs from the past severe accidents. Specific factors in the F1 accident to be considered in this study are fuel assembly and control rod materials, core configuration and accident sequence. Further specific factors are high zirconium and iron contents, BC and sea water effects and molten core concrete interaction (MCCI). Mechanical properties were identified as important properties. Mechanical properties have been obtained experimentally using simulated debris as based on (U,Zr)O and (U,Zr,Fe)O materials.