In the damaged reactors of the Fukushima Daiichi Nuclear Power Plant, groundwater microorganisms have continuously infiltrated contaminated water, potentially influencing the degradation of nuclear fuel debris. This study investigates the role of siderophore-releasing in altering fuel debris analogs under aerobic conditions. Fuel debris analog pellet samples (FDAPS) containing CeO₂-ZrO₂ solid solution and metallic Fe were exposed to a siderophore-producing bacterium (SB) for 50 days. SEM-EDX analyses revealed Fe-containing degradation products on the FDAPS surface, as well as Fe migration through the filter and precipitation in the surrounding medium. RBS and ERDA spectrometry identified these degradation products as Fe oxyhydroxides. While small amounts of Zr were detected in Fe-rich areas, its dissolution appeared limited.
Further experiments using melt and powder simulants composed of UO₂, Fe(0), and U-Zr-Fe mixtures demonstrated that Bacillus subtilis enhanced Fe and U dissolution, with aqueous U primarily existing as U(VI) and solid-phase U predominantly as U(IV). The bacterium oxidized Fe(0), leading to the formation of amorphous nano-sized solid Fe species. A fraction of dissolved Fe adsorbed or precipitated onto UO₂ particles, indicating microbial mediation in Fe-U interactions. These findings highlight the significant impact of microbial activity on fuel debris degradation, particularly in Fe-containing regions, which may influence radionuclide mobilization in nuclear accident environments.

Microorganism,uranium,degradation