Degradation of nuclear fuel debris analog by siderophore-releasing microorganisms

Abstract

ABSTRACT In damaged Fukushima Daiichi NPP reactors, groundwater microorganisms have continuously seeped into contaminated water. We investigated the effect of a siderophore-releasing microorganism (SB) on fuel debris analogs. Fuel debris analog pellet samples (FDAPS) and powder samples containing CeO2 (an alternative to UO2)-ZrO2 solid solution and metallic iron were formed. FDAPSs were contacted with SB on a membrane filter placed on agar medium for 50 days. With the addition of SB, Fe-containing degradation products were detected by SEM-EDX analyses on FDAPSs, on the filter, and on the agar medium, revealing that some fractions of Fe ions were dissolved and precipitated on FDAPSs, and the rest became detached from FDAPSs and migrated through the filter. The SB-derived degradation differed from those by P. fluorescens and Na-citrate solution. The RBS and ERDA spectrometry analyses identified the degradation products as Fe oxyhydroxides. Although Zr was detected in small amounts in the Fe area by SEM-EDX and by SIMS analyses, the dissolution of Zr may be limited. These results clarify that the presence of SB accelerates the degradation of fuel debris in which Fe metal regions are preferentially degraded, and some fraction of Fe were detached and migrated from the fuel debris analog.