Revisiting the TMI-2 core melt specimens to verify the simulated corium for Fukushima Daiichi NPS

Takano, Masahide ; Onozawa, Atsushi ; Suzuki, Miho; Obata, Hiroki

For the decommissioning of damaged cores of Fukushima Daiichi NPS, the retrieval operation of solidified core melt (corium) and its safe management are essential tasks. To understand characteristics of corium specific to the 1F cores, we have prepared and analyzed various types of simulated corium specimens in laboratory scale. To verify the effect of cooling condition found on the simulated corium, we revisit the actual corium specimens collected from the TMI-2 accident core, which have been stored at the Reactor Fuel Examination Facility (RFEF) in JAEA Tokai since 1991. Comparing the phases and microstructure, rapid-cooled specimens have dense microstructure and consist of single phase of cubic structure. On the other hand, the slow-cooled specimens consist of U-rich cubic and Zr-rich tetragonal phases distributed minutely. From these observations we have confirmed the similar dependence of microstructure and mechanical property on the cooling condition.