Abstract
In order to estimate the reliable risk and safety required for retrieval of the fuel debris from Fukushima Daiichi NPP damaged reactors, it is important to understand the degradation of the fuel debris. Because groundwater merges into the contaminated water through cracks caused by PCV damage, microorganisms in the groundwater were introduced into PCV. This fact indicates that the fuel debris is in contact with the microorganisms in groundwater until the dismantle and the retrieval. We investigated the effect of siderophore-releasing microorganisms (SBs) on fuel debris. Fuel debris analogue pellet samples (FDAPSs) were formed by melting and solidifying CeO2 (an alternative to UO2)-ZrO2 solid solution, and metallic iron. FDAPSs were contacted with two kinds of SBs on a membrane filter placed on agar medium for 50 days.The contacted pellet samples, the filter, and the precipitates deposited on the agar medium were analyzed by SEM-EDS, a secondary ion mass spectrometer (SIMS), Rutherford Backscattering Spectrometry (RBS), and Elastic Recoil Detection Spectrometry (ERDA). SEM-EDS analyses showed that the degradation products containing Fe were detected on the pellet samples, on the filter, and on the agar medium, indicating that Fe ions were dissolved, detached from the pellet samples, and migrated through the filter by the addition of SBs. Some portion of Fe were detected in the SBs cells. RBS and ERDA analyses showed that the degradation products were determined as Fe oxyhydroxides. Although Zr and Ce were detected in small amounts on the filter by SIMS analysis, dissolution of Zr and Ce may be limited. Therefore, presence of siderophore releasing microorganisms accelerate degradation of fuel debris in which Fe metal regions are preferentially degraded.
