Evaluation of Residents’ Timing of Return to or New Settlement in Kawauchi Village, at 10 Years after the Fukushima Daiichi Nuclear Power Plant Accident

Kawauchi village in Fukushima prefecture was affected by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, and residents had to evacuate from their hometown in 2011. This study clarified the timing and related factors with regard to residents returning to or newly settling in Kawauchi. A survey was conducted using a questionnaire, from February to March 2021, with assistance from the Kawauchi village office and post office. Of the 374 residents, 170 (45.5%) had returned to or newly settled in Kawauchi within the past 2 years (group 1), 84 (22.5%) in the past 2–5 years (group 2), and 99 (26.5%) after more than 5 years (group 3) following the evacuation order. An additional 21 residents (5.5%) who had lived in Kawauchi at the time of the FDNPP had not yet returned (group 4). Compared with the other groups, residents in group 1 were more satisfied with their current lives and were coping better with stress. Even though they had experienced a serious nuclear disaster, residents of Kawauchi village who returned to their hometown in the early phase had a high sense of satisfaction with their current life one decade after the FDNPP accident.

Improved Wet Scavenging Schemes for Air Dispersion Modeling of Cs-137 in the Fukushima Accident

Wet scavenging process is critical for air dispersion modeling of Cs-137 in the Fukushima Daiichi Nuclear power plant (FDNPP) accident. Although intensively investigated, wet scavenging simulation is still subject to uncertainties caused by the biases in wet scavenging modeling and meteorological input. To reduce these uncertainties, the on-line coupled modeling feature of the Weather Research and Forecasting-Chemistry (WRF-Chem) model was utilized and both the in-cloud and below-cloud scavenging processes are considered. In this study, the in-cloud scheme Environ and below-cloud scheme Baklanov are combined with each other to form Environ-Bakla to simulate the wet deposition of Cs-137. The model is systematically compared with a previous WRF-Chem model with a single below-cloud scheme Baklanov, based on both the cumulative deposition and ambient concentration of Cs-137 based on the FDNPP accident observation. The results demonstrate that the in-cloud scavenging scheme substantially improves the cumulative deposition simulation in regions with light rain like Tochigi, Nakadori etc. With respect to the atmospheric concentration, the inclusion of in-cloud scavenging doesn’t necessarily improve the performances and the Environ-Bakla only shows fair performance under plume events with no rain or light rain.

Estimation of Effect of Radiation Dose Reduction for Internal Exposure by Food Regulations under the Current Criteria for Radionuclides in Foodstuff in Japan Using Monitoring Results

This study examined the effect of food regulations under the current criteria (e.g., 100 Bq/kg for general foods) established approximately a year after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Foods are monitored to ensure that foods exceeding the standard limit are not distributed; ~300,000 examinations per year have been performed especially since FY2014. This study comprehensively estimated the internal exposure dose resulting from the ingestion of foods containing radioactive cesium using the accumulated monitoring results. Committed effective dose was conservatively calculated as the product of the radioactive concentration randomly sampled from test results, food intake, and dose coefficient. The median, 95th, and 99th percentile of the dose were 0.0479, 0.207, and 10.6 mSv/y, respectively, in the estimation with all test results (without regulation), and 0.0430, 0.0790, and 0.233 mSv/y, respectively, in the estimation with results within the standard limits (with regulation) in FY2012. In FY2016, the dose with and without regulation were similar, except for high percentile, and those doses were significantly smaller than 1 mSv/y, which was adopted as the basis for the current criteria. The food regulation measures implemented in Japan after the FDNPP accident have been beneficial, and food safety against radionuclides has been ensured.

First isolation and analysis of caesium-bearing microparticles from marine samples in the Pacific coastal area near Fukushima Prefecture

A part of the radiocaesium from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident was emitted as glassy, water-resistant caesium-bearing microparticles (CsMPs). Here, we isolated and investigated seven CsMPs from marine particulate matter and sediment. From the elemental composition, the 134Cs/137Cs activity ratio, and the 137Cs activity per unit volume results, we inferred that the five CsMPs collected from particulate matter were emitted from Unit 2 of the FDNPP, whereas the two CsMPs collected from marine sediment were possibly emitted from Unit 3, as suggested by (i) the presence of calcium and absence of zinc and (ii) the direction of the atmospheric plume during the radionuclide emission event from Unit 3. The presence of CsMPs can cause overestimation of the solid–water distribution coefficient of Cs in marine sediments and particulate matter and a high apparent radiocaesium concentration factor for marine biota. CsMPs emitted from Unit 2, which were collected from the estuary of a river that flowed through a highly contaminated area, may have been deposited on land and then transported by the river. By contrast, CsMPs emitted from Unit 3 were possibly transported eastward by the wind and deposited directly onto the ocean surface.

Differentiating Fukushima and Nagasaki sourced plutonium from global fallout: Pu vs Cs in soils and biota

<p>The release of plutonium (Pu) from the 2011 Fukushima accident has raised questions on how prevalent it is in the environment and how its cycling into the biosphere compares with that from the previous Nagasaki and global-fallout sources.  Here, we report on systematic sampling and analysis of soils, earthworms, and wild boar as markers of Pu in the deposition areas near the Fukushima Daiichi Nuclear Power Station (FDNPS) and Nagasaki. Highly-sensitive Accelerator Mass Spectrometry (AMS) methods were used to distinguish the Pu sourced from the FDNPS accident, and Nagasaki-detonation, from worldwide fallout Pu. We primarily used <sup>241</sup>Pu/<sup>239</sup>Pu atom ratios, as the other typically-used Pu measures (<sup>240</sup>Pu/<sup>239</sup>Pu atom ratios, activity concentrations) were less sensitive and did not distinguish the FDNPS Pu from background in most study samples.</p><p> </p><p>Near the FDNPS, results indicate that five years after the accident, 0.4% – 2% of the Pu in the local soils (0-5cm) had originated from the FDNPS releases, the remainder being from global fallout.  The trace amounts of FDNPS Pu (e.g., 0.02-0.04 Bq kg<sup>-1</sup><sup>239</sup>Pu estimated in local ~3km deposition) contrasted sharply with the <sup>134+137</sup>Cs content which was about 10<sup>6</sup> times greater than background in the same samples. The accident also contributed new Pu of ~0.3% – 3% in earthworms and ~1% – 10% in wild boar near the FDNPS. The soil and wild boar data from across the study sites consistently indicate only low levels of new accident-Pu and do not support the concept of a substantial undiscovered deposit of Pu near the FDNPS. Unlike sparsely-taken individual soil samples that might miss a Pu hotspot, the wild boar samples represent the integration of uptake throughout their entire foraging areas.</p><p> </p><p>Near Nagasaki, our measurements in 2016 show a lasting legacy of Pu sourced from the 1945 detonation (~93% soils, ~88% earthworm, ~96% boar in samples <5km from the Nagasaki hypocentre; the remainder from global fallout). Even with these high percentages arising from the 1945 detonation,  the Pu amounts at all study sites in Japan are comparable  to background fallout levels elsewhere and are orders of magnitude lower than what remains near Chernobyl. At the study areas, the dose rates from Pu to organisms, as well as to potential human consumers of wild boar meat, have been only slightly elevated above background and are orders of magnitude lower than the dose potentials from the <sup>134,137</sup>Cs in samples from near the FDNPS.  </p><p> </p><p>The results demonstrate progress in increasing the sensitivity of AMS methods, including the use of <sup>241</sup>Pu/<sup>239</sup>Pu atom ratios, to compare recent and past nuclear contamination events and suggest that the Nagasaki-detonation Pu will be distinguishable in the environment long after the FDNPP-accident Pu is not.</p>

The impact and fate of fallout radionuclides by Fukushima Daiichi Nuclear Power Plant Accident in hydrological systems and post-accident environmental recovery

<p>The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released the largest quantity of radiocaesium into the terrestrial environment since the Chernobyl nuclear accident. The surrounding land received 2.7 PBq of radiocaesium to forests, agricultural lands, grasslands, and urban areas, from which the radionuclides migrated through soil and waterways. In this presentation, the deposition and distribution of radionuclides, especially radiocaesium, in the terrestrial environment as a result of the FDNPP accident are discussed based on the past 10 years' intensive dataset. Anthropogenic activities such as rice and vegetable cultivation and residential activities in the upstream area have led to a rapid decline in the activity concertation of 137Cs of suspended sediment (SS) transport in the river network, and these declines directly control the dissolved 137Cs concentration in the river water. We outline the environmental and anthropogenic factors that influenced the subsequent transport and impacts of radionuclides through the environment. The environmental aftermath of the accident at Fukushima is compared to Chernobyl, and the relatively rapid remediation of the Fukushima region relative to the region surrounding Chernobyl will be explained.</p>

Radiocesium-bearing microparticles cause a large variation in 137Cs concentration in the aquatic insect, Stenopsyche marmorata, in the Ota River, Fukushima, Japan

<p>Radiocesium-bearing microparticles (CsMPs), which are insoluble, Cs-bearing, silicate glass particles, have been found in terrestrial and freshwater environments after the TEPCO's Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in Japan. Few studies have investigated the distribution of CsMPs in freshwater ecosystems and their uptake by aquatic organisms. In this study, we determined the uptake of CsMPs by aquatic insects in the Ota River in Fukushima. Although aquatic insects are usually measured for radioactivity in bulk samples of several tens of insects, we investigated the variability of <sup>137</sup>Cs concentration in individual aquatic insects, and the influence of CsMPs on them. Measurement of <sup>137</sup>Cs concentrations in detritivorous caddisfly (Stenopsyche marmorata) larvae and carnivorous dragonfly larvae showed that 3 of 47 caddisfly larvae had considerably higher radioactivity, whereas no such outliers were observed in dragonfly larvae. These caddisfly larvae were confirmed to contain the CsMPs emitted from Unit 2 of the FDNPP, using a scanning electron microscope and radioactivity measurements after isolation of the CsMPs. CsMPs were also found in potential food sources of caddisfly larvae, such as periphyton and drifting particulate organic matter, indicating that larvae may ingest CsMPs along with food particles of similar size. Our study demonstrated that CsMPs could be taken up by aquatic insects and possibly by the fish consuming them. The existence of CsMPs can result in sporadic, extremely high <sup>137</sup>Cs concentrations, and large variations in samples, and consequently obscure the actual transfer and temporal trends of <sup>137</sup>Cs in freshwater ecosystems.</p>

Dissolution, Mechanical Properties, and Thermal Stability of Microparticles Containing Radioactive Cesium on Plant Litter Derived from the Fukushima Daiichi Nuclear Power Plant Accident, and Soil Decontamination Trials

<p>The radioactive cesium (<sup>134</sup>Cs and <sup>137</sup>Cs), which originated from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, has remained in the soil and on plants as water-insoluble microparticles (termed as CsMPs) to some extent, and maintained relatively high radioactivity levels in the district. However, it has been reported that the radioactive Cs has been absorbed by plants. To interpret this phenomenon, the authors investigated CsMPs to determine if they become soluble during filtration and dialysis experiments. Moreover, other physical properties, such as mechanical properties and thermal stability, were observed during the course of the relevant experiments. These properties can be obtained by using carbonized charcoal litter with CsMPs. And simple and economic decontamination trials of the soil were performed by sieving after drying and roughly crushing.</p>