Highly radioactive cesium-rich microparticles (CsMPs) were released from the Fukushima Daiichi nuclear power plant (FDNPP) to the surrounding environment at an early stage of the nuclear disaster in March of 2011; however, the quantity of released CsMPs remains undetermined. Here, we report a novel method to quantify the number of CsMPs in surface soils at or around Fukushima and the fraction of radioactivity they contribute, which we call "quantification of CsMPs" (QCP) and is based on autoradiography. Here, photostimulated luminescence (PSL) is linearly correlated to the radioactivity of various microparticles, with a regression coefficient of 0.0523 becquerel/PSL/h (Bq/PSL/h). In soil collected from Nagadoro, Fukushima, Japan, CsMPs were detected in soil sieved with a 114 μm mesh. There was no overlap between the radioactivities of CsMPs and clay particles adsorbing Cs. Based on the distribution of radioactivity of CsMPs, the threshold radioactivity of CsMPs in the size fraction of <114 μm was determined to be 0.06 Bq. Based on this method, the number and radioactivity fraction of CsMPs in four surface soils collected from the vicinity of the FDNPP were determined to be 48-318 particles per gram and 8.53-31.8%, respectively. The QCP method is applicable to soils with a total radioactivity as high as ∼10 Bq/kg. This novel method is critically important and can be used to quantitatively understand the distribution and migration of the highly radioactive CsMPs in near-surface environments surrounding Fukushima.

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Laser Induced Breakdown Spectroscopy (LIBS) has the potential to allow direct, standoff measurement of contaminants on nuclear plant. Here, LIBS is evaluated as an analytical tool for measurement of Sr and Cs contamination on type 304 stainless steel surfaces. Samples were reacted in model acidic (PUREX reprocessing) and alkaline (spent fuel ponds) Sr and Cs bearing liquors, with LIBS multi-pulse ablation also explored to measure contaminant penetration. The Sr II (407.77nm) and Cs I (894.35nm) emission lines could be separated from the bulk emission spectra, though only Sr could be reliably detected at surface loadings >0.5mgcm. Depth profiling showed decay of the Sr signal with time, but importantly, elemental analysis indicated that material expelled from LIBS craters is redistributed and may interfere in later laser shot analyses.

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Metaschoepite is commonly found in U-contaminated environments and metaschoepite-bearing wastes may be managed via shallow or deep disposal. Understanding metaschoepite dissolution and tracking the fate of any liberated U is thus important. Here, discrete horizons of metaschoepite (UO 3 • nH 2 O) particles were emplaced in flowing sediment/groundwater columns representative of the UK Sellafield Ltd. site. The column systems either remained oxic or became anoxic due to electron donor additions, and the columns were sacrificed after 6-and 12-months for analysis. Solution chemistry, extractions, and bulk and micro/nano-focus X-ray spectroscopies were used to track changes in U distribution and behavior. In the oxic columns, U migration was extensive, with UO 2 2+ identified in effluents after 6-months of reaction using fluorescence spectroscopy. Unusually, in the electron-donor amended columns, during microbially mediated sulfate reduction, significant amounts of UO 2 -like colloids (>60% of the added U) were found in the effluents using TEM. XAS analysis of the U remaining associated with the reduced sediments confirmed the presence of trace U(VI), noncrystalline U(IV), and biogenic UO 2 , with UO 2 becoming more dominant with time. This study highlights the potential for U(IV) colloid production from U(VI) solids under reducing conditions and the complexity of U biogeochemistry in dynamic systems.