Research on the stability of fuel debris consisting of oxides and alloys, 8; Dissolution of uranium from simulated fuel debris in the UO-Zr-SS system and formation of alteration layer

Kumagai, Yuta   ; Watanabe, Masayuki   ; Kusaka, Ryoji  ; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Sasaki, Takayuki*

Fuel debris generated during the 1F accident is expected to remain in contact with water. The contact with water has possibility to cause long-term degradation of the fuel debris. One of the causes of the degradation is oxidation of the debris matrix by hydrogen peroxide (HO) due to the water radiolysis. In this study, we performed 30-day immersion tests in aqueous HO solution using simulated fuel debris samples prepared from uranium oxide (UO), stainless steel (SUS304), and zirconium metal (Zr) or oxide (ZrO). The U dissolution by the immersion was much lower than the HO consumed. Moreover, the HO reaction with UO sample once induced dissolution of U but the U concentration decreased with immersion time. Also, in the results of the simulated debris samples, increasing trend of dissolved U concentration was not clearly observed. These results indicate formation of solid uranyl peroxides as alteration layer, as it was reported in the similar immersion studies of UO.