Suggestion of typical phases of in-vessel fuel-debris by thermodynamic calculation for decommissioning technology of Fukushima-Daiichi Nuclear Power Station

福島第一原子力発電所の廃止措置に向けた熱力学計算による圧力容器内デブリの相状態評価

池内 宏知  ; 近藤 賀計*; 野口 芳宏*; 矢野 公彦 ; 鍛治 直也; 鷲谷 忠博 

Ikeuchi, Hirotomo; Kondo, Yoshikazu*; Noguchi, Yoshihiro*; Yano, Kimihiko; Kaji, Naoya; Washiya, Tadahiro

For the decommissioning of Fukushima-Daiichi Nuclear Power Station (1F), characterization of fuel-debris in cores of Unit 1-3 is necessary. In this study, typical phases of fuel-debris generated in reactor pressure vessel were suggested by means of thermodynamic calculation using compositions of core materials and core temperatures. At low ogygen potential where metallic zirconium remains, (U,Zr)O, UO, and ZrO were formed as oxides, and oxygen-dispersed Zr, Fe(Zr,U), and FeUZr were formed as metals. With an increase in zirconium oxidation, the mass of those metals, especially FeUZr, were decreased, but the other phases of metals hardly changed qualitatively. Consequently, (U,Zr)O is suggested as a typical phase of oxide, and Fe(Zr,U) is suggested as that of metal. This result can contribute to the characterization of debris in 1F, which will be also revised by considering the effect of iron content in RPV.