Characterization of the VULCANO test products for fuel debris removal from the Fukushima Daiichi Nuclear Power Plant

Kitagaki, Toru ; Ikeuchi, Hirotomo ; Yano, Kimihiko ; Ogino, Hideki; Haquet, J.-F.*; Brissonneau, L.*; Tormos, B.*; Piluso, P.*; Washiya, Tadahiro 

Characterization of the fuel debris is required to develop fuel debris removal tools for the decommissioning of Fukushima Daiichi Nuclear Power Plant (1F). In this study, the VULCANO MCCI test, VBS-U4, was selected as 1F similar conditions and the characteristics of the samples were examined. In the molten pool sample, the round-edged corium-rich oxides region, with diameters of 1-10 mm, is surrounded by a concrete-rich oxide region. It shows convection of the molten pool. Other samples also show the features of the MCCI progression. The main chemical forms of the samples are SiO, (U,Zr)O, Fe and so on. The microstructure of the samples is heterogeneous structure composed of these phases. The difference in Vickers hardness between the metallic phases and the oxide phases is a distinctive characteristic. It can be noted that the heterogeneous distribution of metallic phases in 1F MCCI products interrupt with the removal operation such as by damaging the core-boring bit.