Uranium leaching from simulated fuel debris prepared from UO and stainless steel

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

Fuel debris generated due to nuclear severe accidents is expected to contain a wide variety of uranium compounds. In this project, we have investigated chemical stability of simulated fuel debris containing elements from stainless steel (Fe, Cr, and Ni) against exposure to water. The simulated debris was prepared from the powders of UO and SUS304 by heating the mixed powder at 1200 C for 1 h under continuous gas flow of 2% O in Ar. The produced powder was characterized by XRD, SEM-EDX, Raman micro-spectroscopy, and Mssbauer spectroscopy. The series of characterization revealed that the simulated debris comprised U(Fe,Cr)O, UO, and Fe(III) oxides. Then, the simulated debris was exposed to pure water for 30 days. The same leaching test of UO was performed for comparison. The chemical analysis of leached metals demonstrated that the U elution from the simulated debris was significantly lower than that from UO. In addition, Fe, Cr, and Ni were under quantitation limit as well. The Raman spectra showed that the exposure to water induced insignificant change in the spectra of the simulated debris, while the Raman band structure of UO seemed to become slightly unclear after 30 days immersion.