Nanoscale visualization of crack tips inside molten corium-concrete interaction debris using 3D-FIB-SEM with multiphase positional misalignment correction

Hotaka Miyata; Kenta Yoshida; Kenji Konashi; Yufeng Du; Toru Kitagaki; Takahisa Shobu; Yusuke Shimada

doi:10.1093/jmicro/dfaf005

Nanoscale visualization of crack tips inside molten corium-concrete interaction debris using 3D-FIB-SEM with multiphase positional misalignment correction

Microscopy (Oxf). 2025 Jan 25:dfaf005. doi: 10.1093/jmicro/dfaf005. Online ahead of print.

Authors

Hotaka Miyata¹, Kenta Yoshida¹, Kenji Konashi¹, Yufeng Du², Toru Kitagaki³, Takahisa Shobu⁴, Yusuke Shimada⁵

Affiliations

¹ Institute for Materials Research, Tohoku University, Ibaraki 311-1313, Japan.
² National Key Laboratory of Nuclear Reactor, Technology, Nuclear Power Institute of China, Chengdu, Sichuan, 610213, China.
³ Collaborative Laboratories for Advanced Decommissioning Science, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Ibaraki 319-1195, Japan.
⁴ Materials Sciences Research Center, Japan Atomic Energy Agency, 2-4 Shirakata, Tokai-mura, Ibaraki 319-1195, Japan.
⁵ Faculty of Engineering, Kyushu University, Fukuoka 819-0395, Japan.

PMID: 39864820
DOI: 10.1093/jmicro/dfaf005

Abstract

Characterizing molten corium-concrete interaction (MCCI) fuel debris in Fukushima reactors is essential to develop efficient methods for its removal. To enhance the accuracy of microscopic observation and focused ion beam (FIB) microsampling of MCCI fuel debris, we developed a three-dimentional FIB scanning electron microscopy (SEM) technique with a multiphase positional misalignment (MPPM) correction method. This system automatically aligns voxel positions, corrects contrast, and removes artifacts from a series of over 500 SEM images. The MPPM correction method, which focuses on time-modulated contrast, considerably reduces charge-up artifacts in glass phases, enabling 3D morphological observation and analytical transmission electron microscopy of crack tips in two types of MCCI debris at the 3D/nanoscale for the first time. In the Fe-ZrSiO4-based debris, metallic balls composed of Fe, Cr2O3, and ZrO2 with dimples on the surface of about 2-58 µm in diameter were observed at the crack tips. In the (Zr, U)SiO4 based debris, a core-shell structure composed of a (U, Zr)O2 core with a diameter of about 1-5 μm and a (Zr, U)SiO4 shell with a diameter of about 2-9 μm in complex molten corium-concrete interaction fuel debris at the crack tips.

Keywords: 3D analysis; Crack; FIB; Fuel debris; SEM.

Abstract

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