Discussions on Tritiated Water Treatment for Fukushima Daiichi Nuclear Power Station

Analysis of environmental biological effects and OBT accumulation potential of microalgae in freshwater systems exposed to tritium pollution

The ecological risk of tritiated wastewater into the environment has attracted much attention. Assessing the ecological risk of tritium-containing pollution is crucial by studying low-activity tritium exposure's environmental and biological effects on freshwater micro-environment and the enrichment potential of organically bound tritium (OBT) in microalgae and aquatic plants. The impact of tritium-contaminated wastewater on the microenvironment of freshwater systems was analyzed using microcosm experiments to simulate tritium pollution in freshwater systems. Low activity tritium pollution (105 Bq/L) induced differences in microbial abundance, with Proteobacteria, Bacteroidota, and Desulfobacterota occupying important ecological niches in the water system. Low activity tritium (105-107 Bq/L) did not affect the growth of microalgae and aquatic plants, but OBT was significantly enriched in microalgae and two aquatic plants (Pistia stratiotes, Spirodela polyrrhiza), with the enrichment coefficients of 2.08-3.39 and 1.71-2.13, respectively. At the transcriptional level, low-activity tritium (105 Bq/L) has the risk of interfering with gene expression in aquatic plants. Four dominant cyanobacterial strains (Leptolyngbya sp., Synechococcus elongatus, Nostoc sp., and Anabaena sp.) were isolated and demonstrated good environmental adaptability to tritium pollution. Environmental factors can modify the tritium accumulation potential in cyanobacteria and microalgae, theoretically enhancing food chain transfer.

Current and emerging technologies for the remediation of difficult-to-measure radionuclides at nuclear sites

Difficult-to-measure radionuclides (DTMRs), defined by an absence of high energy gamma emissions during decay, are problematic in groundwaters at nuclear sites. DTMRs are common contaminants at many nuclear facilities, with (often) long half-lives and high radiotoxicities within the human body. Effective remediation is, therefore, essential if nuclear site end-state targets are to be met. However, due to a lack of techniques for in situ DTMR detection, technologies designed to remediate these nuclides are underdeveloped and tend to be environmentally invasive. With a growing agenda for sustainable remediation and reduction in nuclear decommissioning costs, there is renewed international focus on the development of less invasive technologies for DTMR clean-up. Here, we review recent developments for remediation of selected problem DTMRs (129I, 99Tc, 90Sr and 3H), with a focus on industrial and site-scale applications. We find that pump and treat (P&T) is the most used technique despite efficacy issues for 129I and 3H. Permeable reactive barriers (PRBs) are a less invasive alternative but have only been demonstrated for removal of 99Tc and 90Sr at scale. Phytoremediation shows promise for site-scale removal of 3H but is unsuitable for 129I and 99Tc due to biotoxicity and bioavailability hazards, respectively. No single technique can remediate all DTMRs of focus. Likewise, there has been no successful site-applied technology with high removal efficiencies for iodine species typically present in groundwaters (iodide/I-, iodate/IO3- and organoiodine). Further work is needed to adapt and improve current techniques to field scales, as well as further research into targeted application of emerging technologies.

Impact of the Fukushima Accident on 3H and 14C Environmental Levels: A Review of Ten Years of Investigation

The investigation of the impact of the Fukushima accident is still going on although more than ten years have passed since the disaster. The main goal of this paper was to summarize the results of tritium and radiocarbon determinations in different environmental samples, possibly connected with the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. A document containing compiled data may serve as a solid basis for further research in the selected fields. To accomplish such effort, we went through dozens of relevant published papers, reporting 3H and 14C activity concentrations in precipitations, groundwater, seawater, river systems, tree rings, and, in some more extraordinary samples, such as herbaceous plants or debris from the damaged reactor buildings. As the referenced results would not be obtainable without adequate analytical techniques, the most common methods for routine measurement of tritium and radiocarbon concentrations are discussed as well. We believe that the correct identification of the affected environmental compartments could help quantify the released 3H and 14C activities and track their following fate, which could be especially important for plans to discharge contaminated water from the FDNPP in the upcoming years.

TRITIUM CONCENTRATION IN MONTHLY PRECIPITATION NEAR THE FUSION TEST FACILITY IN JAPAN BEFORE AND AFTER THE DEUTERIUM PLASMA EXPERIMENT

In Japan, the deuterium plasma experiment using the Large Helical Device was started at the National Institute for Fusion Science (NIFS) in March 2017 to investigate high-temperature plasma physics and hydrogen isotope effects in research leading towards the realisation of fusion energy. The deuterium plasma experiment produces small amount of tritium by fusion reactions. To understand any impacts by the experiment to the surrounding environment, monthly precipitation samples have been collected at the NIFS site since November 2013 to assess the relationship between isotope composition and chemical species in precipitation including tritium. By comparing data before and after the deuterium plasma experiment start, it was found that tritium released from the main stack of the fusion test facility had no impact on the environment surrounding NIFS.

Trajectory and factors of radiation risk perception of students aged 10-12 years at the time of the Fukushima Daiichi Nuclear Power Station accident

Various studies have investigated radiation risk perceptions after the accident at the Fukushima Daiichi Nuclear Power Station. However, student surveys are limited. This study aimed to investigate the perception of radiation risk among students aged 18-20 years who were in the 5th and 6th grades of elementary school at the time of the accident. We surveyed students in the Fukushima Prefecture and outside the prefecture. Out of all the data, 59% of the respondents were living in the Fukushima Prefecture at the time of the accident and 41% outside the prefecture. Trajectory analysis showed that changes in anxiety levels over time since 2011 could be divided into five classes: (a) the anxiety was the highest, and this tendency persisted. (b) High at the beginning, but decreased more quickly than class 1. (c) High at the beginning, but it diminished quickly. (d) Not high, but did not diminish easily in later years. (e) Low from the beginning, and persisted. Multinomial logistic analysis showed that among students living outside the prefecture at the time of the accident, a significantly higher proportion was in groups 4 and 5 than in group 2. A significant proportion of boys were present in groups 3, 4 and 5. A significant proportion of students whose current educational institutions were inside the prefecture were present in group 3. The level of anxiety was associated with the academic course, but not with subjective knowledge of radiation. In contrast, in the qualitative analysis of the free text, 31% considered 'knowledge about radiation' as the reason for the reduction in anxiety level. At the time of the investigation, most young people were not anxious about radiation. However, approximately 20% still had strong anxiety. We established that continuous risk communication is necessary. Furthermore, that stabilization and support related to life in general is important.