Analysis of ex-vessel debris-pedestal structure interactions and debris cooling in Fukushima Daiichi Nuclear Power Station Unit-3

Li, X. ; Yamaji, Akifumi*; Sato, Ikken ; Furuya, Masahiro*; Oishi, Yuji*; Nagae, Yuji 

To facilitate the fuel debris retrieval as part of the decommissioning of Fukushima Daiichi Nuclear Power Station (1F), it is necessary to grasp the in-depth debris distribution and status in the pedestal regions of the damaged units. For 1F Unit-3, it has been confirmed that the deposits in the pedestal region can be up to 2-3 meters high from the PCV internal investigations performed with remotely operated vehicles by TEPCO HD. This study will focus on the detailed evaluation of radiative heat transfer and convective vapor cooling boundaries applied on the free surfaces of debris and structures in the pedestal. Sensitivity analysis with different debris distributions, environment temperature, and emissivities was performed. The results show that remelting of debris and melting of pedestal structures are not expected during the re-heating phase if the pedestal background temperature is less than 1300 K.