A new approach for reconstructing the 131I-spreading due to the 2011 Fukushima nuclear accident by means of measuring 129I in airborne particulate matter

Chemical species of cesium and iodine in condensed vaporized microparticles formed by melting nuclear fuel components with concrete materials

In this study, we report chemical species of Cs and I in condensed vaporized particles (CVPs) produced by melting experiments using nuclear fuel components containing CsI with concrete. Analyses of CVPs by SEM with EDX showed the formation of many round particles containing Cs and I of diameters less than ∼20 μm. X-ray absorption near-edge-structure and SEM-EDX analyses showed two kinds of particles: one containing large amounts of Cs and I, suggesting the presence of CsI, and the other containing small amounts of Cs and I with large Si content. When CVSs were placed in contact with deionized water, most of the CsI from both particles was dissolved. In contrast, some fractions of Cs remained from the latter particles and possessed different chemical species from CsI. In addition, the remaining Cs was concomitantly present with Si, resembling chemical components in the highly radioactive cesium-rich microparticles (CsMPs) released by nuclear plant accidents into the surrounding environments. These results strongly suggest that Cs was incorporated in CVSs along with Si by melting nuclear fuel components to form sparingly-soluble CVMPs.

A summary of environmental radioactivity research studies by members of the Japan Society of Nuclear and Radiochemical Sciences

Many scientists who are members of the Japan Society of Nuclear and Radiochemical Sciences have been involved in academic activities in response to the Fukushima Daiichi Nuclear Power Plant accident. Projects had been implemented that include determining radionuclides in environmental samples, identifying the distribution of radionuclides by large-scale soil monitoring, tracing radionuclide discharge time series, clarifying environmental dynamics of radionuclides, etc. For the last 10 years, these results have been shared and discussed in annual workshops partly sponsored by the society. This review summarizes the studies yielding these results, and they include reconstruction of the 131I distribution on soil by long-lived 129I analysis, reconstruction of the radioactive plume transport, identification of biological resuspension sources, discovery and characterization of cesium particles, and parameterization of the environmental behavior of radiocesium for dose assessment.

Radiochemical analysis of the drain water sampled at the exhaust stack shared by Units 1 and 2 of the Fukushima Daiichi Nuclear Power Station

Radioactive gas of Unit 1 of the Fukushima Daiichi Nuclear Power Station was released from the exhaust stack shared by Units 1 and 2 through the venting line on March 12th, 2011. In the present study, radiochemical analysis of drain water sampled at the drain pit of the exhaust stack was conducted to study radionuclides released during venting of the Unit 1. Not only volatile ¹²⁹I, ¹³⁴Cs and ¹³⁷Cs but also ⁶⁰Co, ⁹⁰Sr, ¹²⁵Sb and Unit 1-originated stable Mo isotopes were detected. Although Unit 1-originated stable Mo isotopes were clearly detected, their amounts were quite low compared to Cs, suggesting that the formation of Cs₂MoO₄ was suppressed under the accident condition. Approximately 90% of iodine existed as I⁻ and 10% as IO₃⁻ in November 2020. Furthermore, larger amount of ¹²⁹I than ¹³⁷Cs was observed, suggesting major chemical form of ¹³¹I was molecular iodine rather than CsI at the accident time. The ¹³⁴Cs/¹³⁷Cs radioactivity ratio decay-corrected to March 11th, 2011 was 0.86, supported the results that Unit 1 originated radiocesium in environment has smaller ¹³⁴Cs/¹³⁷Cs radioactivity ratio than Unit 2 and 3 originated radiocesium.

129I in a sediment core offshore Fukushima: Distribution, source and its implication

¹²⁹I released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident has been observed in the atmospheric, terrestrial and oceanic environments, and it also entered the marine sediments via dispersion by sea water movement and deposition around Japan. However, there have been few studies of marine sediment cores in contrast to the large number of studies on seawater. In this work, a sediment core collected near FDNPP was analyzed for ¹²⁹I. It is observed that the ¹²⁹I/¹²⁷I atomic ratios in this sediment core are comparable to those in the seawater and sediments collected from offshore Fukushima after the accident, but 2 orders of magnitude higher than those in seawater in this region before the accident, suggesting the significant amount of ¹²⁹I has been transferred and incorporated to the offshore shallow sediments. The difference in environmental behavior between ¹²⁹I and ¹³⁷Cs is discussed based on their depth distributions in the sediment core in comparison with the grain size distribution of sediments. The peak concentrations of iodine isotopes were found in a relatively deeper layer than radiocesium. Radiocesium follows the distribution of fine grains in the sediment core, implying its high association to fine grains.

Reassessment of early 131I inhalation doses by the Fukushima nuclear accident based on atmospheric 137Cs and 131I/137Cs observation data and multi-ensemble of atmospheric transport and deposition models

The Fukushima Dai-ichi Nuclear Power Plant accidents following the March 11, 2011 Tohoku earthquake, and subsequent tsunami released radioactive materials into the atmosphere and caused significant public health concerns, particularly thyroid cancers in children. However, the lack of measurement data for atmospheric concentrations of ¹³¹I has caused persistent and widespread uncertainty. This study estimated the maximum potential thyroid doses of inhaled ¹³¹I in the early post-accident phase between March 12 and 23, 2011 by using the hourly measured data of the ¹³⁷Cs concentrations at 101 suspended particulate matter (SPM) monitoring sites, a new multi-model ensemble (MME) method of simulating ¹³⁷Cs concentrations using two Atmospheric Transport and Deposition Models (ATDMs), the ¹³¹I/¹³⁷Cs ratio obtained from measurement data analysis, and the internal exposure model. Based on the measurements, the maximum potential thyroid doses were estimated at 3.1-160 mSv at 5 sites in the Fukushima-Hamadori area for 1-year-old children assumed to remain outdoors, whereas they were less than 4.3 mSv at the other sites in the base case of the ¹³¹I/¹³⁷Cs ratio. The spatial distribution of the maximum potential of early inhalation doses was estimated by using the MME and measurements. The inhalation thyroid doses in the evacuation scenarios were compared to the estimates reported by previous studies. The results of the present study were almost congruent with the outcomes of previous investigations except for thyroid doses contributed by highly contaminated plumes on March 12 and 15. The sensitivity analysis for the ¹³¹I/¹³⁷Cs ratio indicated that these plumes carried the potential to significantly increase the thyroid doses of residents.