128 A Tribute to Rodney C. Ewing: Celebrating a Half-Century of Transformative Contributions to Geoscience, Mineralogy, and Material Science
Honoring Prof. Rodney C. Ewing (1946–2024), this session celebrates over 50 years of groundbreaking contributions to mineralogy, geoscience, and materials science, from atomic-scale processes to field-scale applications.
Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 217A
Cesium-rich Micro-particles: A Window Into the Meltdown Events at the Fukushima Daiichi Nuclear Power Plant
Paper number: 128-12
Program: Technical Sessions
Time: 4:30 PM – 4:45 PM
Authors
Abstract
In 2011, sparingly soluble cesium-rich microparticles (CsMPs) were released during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. CsMPs, typically a few microns in size, are mainly composed of Si, Fe, Zn, and Cs. They most likely formed through molten core–concrete interaction (MCCI), serving as microscale records of the reactor conditions during the meltdowns.
We were the first to report nanoscale fuel fragments associated with CsMPs, identified as ∼70 nm UO₂₊ₓ nanocrystals embedded in magnetite with technetium (Tc) and molybdenum (Mo), as well as isometric (U,Zr)O₂₊ₓ nanocrystals. One of the UO₂₊ₓ nanoparticles was enriched in plutonium (Pu), located adjacent to zirconium cladding fragments—likely due to Pu enrichment at the periphery of irradiated fuels.
Isotope ratios of ²³⁵U/²³⁸U (~0.0193), ²⁴⁰Pu/²³⁹Pu (~0.347), and ²⁴²Pu/²³⁹Pu (~0.065) in the CsMPs were consistent with those calculated for irradiated fuel fragments. These findings suggest that the long-distance dispersion of Pu from the FDNPP can be attributed to the transport of CsMPs that incorporated nanoscale fuel fragments prior to dispersion.
Additionally, direct imaging of radioactive Cs atoms was achieved using high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Some CsMPs contained inclusions of pollucite with high Cs contents (27–36 wt%, reported as Cs₂O). HAADF-STEM imaging along the [111] zone axis revealed an ordered array of Cs atoms, consistent with simulated images using the multi-slice method. The presence of pollucite indicates that locally enriched Cs reacted with siliceous materials during the meltdown, likely via volatilization and condensation processes.
The atomic-resolution imaging of radioactive Cs represents a significant advance in understanding the fate of radioactive cesium both inside and outside nuclear reactors affected by meltdown events. These results highlight the heterogeneous physical and chemical nature of nuclear debris at the nanoscale, reflecting the complex thermal processes that occurred during the Fukushima meltdown.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-411935
© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.