Estimation of RPV damage and fuel debris relocation behavior in the PCV at Fukushima Daiichi Nuclear Power Station, 8; Numerical simulation of core material relocation behavior in the RPV lower head region

Li, X. ; Yamaji, Akifumi*; Sato, Ikken*; Yamashita, Takuya  

This study presents a numerical evaluation of possible core material discharge behavior from the RPV lower head region including the penetrations (Control Rod Drive (CRD) Housing) in 1F Unit-2 with Lagrangian-based MPS method. Two-dimensional geometry is established to model CRD housing with simplified inner structures in the center of RPV, with surrounding RPV walls and RPV insulation below. The initial temperature distribution/boundary conditions referenced the results from accident progression and global RPV CFD analysis (Series presentations (2), (5), and (7)). The results show that local CRD housing melting assumed at 15%Zr-85%Fe eutectic temperature (1523 K) before global RPV failure could result in melt discharge into the pedestal, which is consistent with the accident progression analysis and plant internal investigation results.