Alteration of fuel debris simulants by Bacillus subtilis

Liu, J. ; Dotsuta, Yuma; Kitagaki, Toru  ; Aoyagi, Noboru   ; Mei, H.  ; Takano, Masahide ; Kozai, Naofumi   

This study aims to reveal the potential bacterial alteration of nuclear fuel debris. A melt simulant composed of UZrO and Fe(0), and three powder simulants (UO, Fe(0), and their mixed powder) were prepared and exposed to Bacillus subtilis in a Fe-deficient medium under aerobic conditions. B. subtilis could not dissolve Zr from the melt simulant but enhanced the dissolution of U and Fe, although the change of the melt simulant was too small to evaluate. Experiments using powder simulants were performed to investigate the bacterial influence in detail. B. subtilis enhanced the dissolution of U from the UO powder and Fe from the Fe(0) powder, although the dissolution of U was low. Most aqueous U species were probably U(VI), while the U that remained as a solid phase was mostly U(IV). The Fe(0) powder was oxidized by this bacterium, transforming it into an aqueous and solid Fe species. The stable species consisted of amorphous nano-sized particles. A fraction of the dissolved Fe was adsorbed or precipitated onto the UO particles and remained undissolved. These results strongly suggest that bacteria can degrade nuclear fuel debris, although this study did not elucidate the mechanism of oxidative dissolution.