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Temporal absences in observation records lead to release losses during the source term inversions of atmospheric radionuclide emissions. Consequently, objectively-estimated source terms for the Fukushima accident contain fewer release details and present large discrepancies when compared with the expert-judged one. This paper describes an objective method that can adaptively recover the missing releases caused by the temporal absences of observations. The proposed method assumes that the accident releases of radionuclides are piecewise-constant and comprise both peaks and constant releases. The missing releases are adaptively recovered as either peaks or constant releases by minimizing the total variation of the estimated source term. The proposed method is applied to the Fukushima accident and evaluated against regional airborne and deposited 137Cs observations. The results demonstrate that this method effectively recovers the missing releases, producing a source term that matches the timing of both on-site gamma dose rate peaks and accident events. The retrieved source term improves the simulation of air concentrations and reproduces most of the deposition patterns. This is the first time that an objective method has independently reproduced the details in the expert-judged one for the Fukushima accident. [Display omitted] • Recovery of missing releases caused by temporal absences of observations. • Preservation of both sharp peaks and constant releases. • First independent objective source term matching the expert-judged one. • Agreement with on-site gamma dose rate peak timing and accident events. • Improved spatiotemporal simulation of airborne 137Cs for the Fukushima accident. [ABSTRACT FROM AUTHOR]

The Fukushima Daiichi Nuclear Plant (FDNPP) accident resulted in huge environmental and socioeconomic impacts to Japan. To document the actual environmental and socioeconomic effects of the FDNPP accident, we describe here atmospheric and marine contamination due to radionuclides released from the FDNPP accident using papers published during past five years, in which temporal and spatial variations of FDNPP-derived radionuclides in air, deposition and seawater and their mapping are recorded by local, regional and global monitoring activities. High radioactivity-contaminated area in land were formed by the dispersion of the radioactive cloud and precipitation, depending on land topography and local meteorological conditions, whereas extremely high concentrations of 131 I and radiocesium in seawater occurred due to direct release of radioactivity-contaminated stagnant water in addition to atmospheric deposition. For both of atmosphere and ocean, numerical model simulations, including local, regional and global-scale modeling, were extensively employed to evaluate source terms of the FDNPP-derived radionuclides from the monitoring data. These models also provided predictions of the dispersion and high deposition areas of the FDNPP-derived radionuclides. However, there are significant differences between the observed and simulated values. Then, the monitoring data would give a good opportunity to improve numerical modeling. [ABSTRACT FROM AUTHOR]

In March 2011, severe nuclear accident happened at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) after the gigantic earthquake and following huge tsunami wave. A lot of investigations to assess environmental and radiological impacts of released radionuclides have been conducted by domestic and international organizations. Environmental radioactivity research related to the FDNPP accident has spread widely over different scientific fields due to specific features of the accident, and specifically its impact on the marine environment. The present paper summarizes major lessons learned from the environmental investigations of the FDNPP accident. Environmental radioactivity studies have typical interdisciplinary character; especially physics and chemistry are fundamental as a base of process studies in the environment. In this sight, we review chemical aspects regarding FDNPP-derived radiocesium transfer within and between compartments (atmosphere, ocean and land). We also discuss future trends in investigations of behavior of anthropogenic radionuclides in the environment, important not only for a better understanding of impacts of the FDNPP accident on the environment, but also for improving our general knowledge of the total environment in the Anthropocene era and its protection for the future. • 10 years after the FDNPP accident, the environment has been contaminated mainly by Cs-137. • Understanding of Cs-transfer within and between compartments has considerably improved. • Chemical processes are a key factor of Cs-transfer between aquatic and solid phases. • Migration of Cs-137 in terrestrial and marine ecosystems will dominate in future studies. [ABSTRACT FROM AUTHOR]

A transfer coefficient matrix (TCM) was created in a previous study using a Lagrangian dispersion model to provide plume predictions under different emission scenarios. The TCM estimates the contribution of each emission period to all sampling locations and can be used to estimate source terms by adjusting emission rates to match the model prediction with the measurements. In this paper, the TCM is used to formulate a cost functional that measures the differences between the model predictions and the actual air concentration measurements. The cost functional also includes a background term which adds the differences between a first guess and the updated emission estimates. Uncertainties of the measurements, as well as those for the first guess of source terms are both considered in the cost functional. In addition, a penalty term is added to create a smooth temporal change in the release rate. The method is first tested with pseudo observations generated using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model at the same location and time as the actual observations. The inverse estimation system is able to accurately recover the release rates and performs better than a direct solution using singular value decomposition (SVD). It is found that computing ln ( c ) differences between model and observations is better than using the original concentration c differences in the cost functional. The inverse estimation results are not sensitive to artificially introduced observational errors or different first guesses. To further test the method, daily average cesium-137 air concentration measurements around the globe from the Fukushima nuclear accident are used to estimate the release of the radionuclide. Compared with the latest estimates by Katata et al. (2014), the recovered release rates successfully capture the main temporal variations. When using subsets of the measured data, the inverse estimation method still manages to identify most of the major events in the temporal profile of the release. [ABSTRACT FROM AUTHOR]

Abstract: Radionuclide aerosol sampling is a vital component in the detection of nuclear explosions, nuclear accidents, and other radiation releases. This was proven by the detection and tracking of emissions from the Fukushima Daiichi incident across the globe by IMS stations. Two separate aerosol samplers were operated in Richland, WA following the event and debris from the accident were measured at levels well above detection limits. While the atmospheric activity concentration of radionuclides generally compared well between the two stations, they did not agree within uncertainties. This paper includes a detailed study of the aerosol sample homogeneity of 134Cs and 137Cs, then relates it to the overall uncertainty of the original measurement. Our results show that sample inhomogeneity adds an additional 5−10% uncertainty to each aerosol measurement and that this uncertainty is in the same range as the discrepancies between the two aerosol sample measurements from Richland, WA. [Copyright &y& Elsevier]

A serious accident at Fukushima Dai-Ichi NPP triggered radioactive emission to the atmosphere on 12 March 2011. The results of gamma spectrometric measurements of both gaseous and aerosol fraction of the air, collected in Krakow over the period from March 21 till the end of May 2011, as well as wet and dry deposition recorded from March till the end of October 2011, are presented in this paper. Krakow happened to be the first Polish location where radioactive isotopes characteristic for reactor releases, such as 131I, 132I, 129mTe, 132Te, 134Cs, 136Cs, and 137Cs, were detected. The maximum activity for aerosols equal to (5.73 ± 0.35) mBq/m3, (0.461 ± 0.041) mBq/m3 and (0.436 ± 0.038) mBq/m3 for 131I, 134Cs and 137Cs, respectively, was recorded for March 29, 2011. The data on the fallout are also given. The results of the radiochemical analysis of aerosol samples showed no traces of plutonium or americium isotopes associated with the disaster to be detected. The results of air activity concentration from Fukushima accident observed in Central Europe, Poland, in comparison to those of Chernobyl accident observed in Japan are presented and discussed. The comparison has revealed a discrepancy in the recognized relative scale of both accidents, and important difference in long distance transport of contamination, to exist. An attempt to explain the variation in the activity ratios between the aerosol fraction for 131I and 137Cs as resulting from exchange between the gaseous and aerosol fractions of 131I while the contamination had been propagating, is made. [ABSTRACT FROM AUTHOR]

Abstract: A new TRS document on Transfer of radionuclides to Wildlife has compiled equilibrium CRwo-media values for a variety of radionuclides and ecosystems. Assessment tools such as the ERICA Tool use equilibrium whole organism concentration ratios (CRwo-media) to predict radionuclide activity concentrations in wildlife from those in media (e.g. water). The aim of this paper is to compare and contrast model predictions of doses from 137Cs to marine organisms using three different approaches: (i) the ERICA Tool utilising the new TRS values to estimate internal and external doses to reference organisms for the Black sea and the Aegean Sea and for the sea close to the Fukushima Dai-ichi plant. (ii) a hydrodynamic site specific model for seawater for parts of the Aegean Sea, Greece which estimates radionuclide concentrations using site specific data and (iii) a biokinetic model for fish applied to the Fukushima releases to the Pacific. The advantages and limitations of these approaches are discussed with respect to determining doses to pelagic fish. The applicability of the three approaches will vary with the objective of an assessment. The site specific model can predict variation in 137Cs with depth and uses site specific CR values. The application of the biokinetic model to predicted 137Cs activity concentrations in seawater and fish due to near coastal inputs from Fukushima Dai-ichi showed that the maximum internal dose-rates in fish attributable to 137Cs would be substantially lower than those determined using equilibrium assumptions in ERICA but the accumulative doses over 100 days were similar. [Copyright &y& Elsevier]

Abstract: This paper presents measurements of the effect of the atmospheric radioactive release from the Fukushima Dai-ichi nuclear power station at three sites belonging to the Spanish environmental monitoring system. Measured values varied depending on the locations of the sites in Spain and their respective climatic characteristics. 134Cs, 136Cs, 137Cs, 131I, and 132Te activity concentrations in filter samples were studied and associated levels of 131I fallout were estimated from wet and dry deposition. Particulate aerosol activity concentrations ranges, in μBq/m3, were 1.63–3080 (131I), 2.8–690 (137Cs), 1.3–620 (134Cs) and 3.6–330 (132Te), while the associated 131I fallout was roughly estimated to be less than 20 Bq/m2, Gaseous 131I was also detected and the 131I-gaseous/131I-total ratio increased at the three stations from approximately 0.75 at the end of March to 0.85–0.9 during the first few days of April. Finally, the presence of 131I in some crucial parts of the food chain was also studied. 131I was detected in samples from goat''s and cow''s milk (maximum levels of 1.11 Bq/L) and in broadleaf plants (maximum level 1.42 Bq/kg). [Copyright &y& Elsevier]

Abstract: The radioactivity levels in the air of the radionuclides released by the Fukushima accident were measured at the Laboratoire Souterrain de Modane, in the South-East of France, during the period 25 March–18 April 2011. Air-filters from the ventilation system exposed for one or two days were measured using low-background gamma-ray spectrometry. In this paper we present the activity concentrations obtained for the radionuclides 131I, 132Te, 134Cs, 137Cs, 95Nb, 95Zr, 106Ru, 140Ba/La and 103Ru. The activity concentration of 131I was of the order of 100 μBq/m3, more than 100 times higher than the activities of other fission products. The highest activities of 131I were measured as a first peak on 30 March and a second peak on 3–4 April. The activity concentrations of 134Cs and 137Cs varied from 5 to 30 μBq/m3. The highest activity concentration recorded for Cs corresponded to the same period as for 131I, with a peak on 2–3 April. The results of the radioactivity concentration levels in grass and mushrooms exposed to the air in the Modane region were also measured. Activity concentrations of 131I of about 100 mBq/m2 were found in grass. [Copyright &y& Elsevier]

Abstract: The impact of the Fukushima accident on the nuclear fuel cycle back-end is obvious. In the present paper the various back-end options and their impact on the environment will be presented in view of this new perspective. The partitioning and transmutation (P&T) concept and the direct disposal of nuclear fuel including a very long intermediate storage will certainly be revisited with respect to safety considerations; here the instant release fraction (IRF) and the long-term stability of the fuel matrix under real repository conditions are highly relevant. Furthermore the impact of released radionuclides to the environment will have a higher attention. [Copyright &y& Elsevier]

The utilization of numerical atmospheric dispersion prediction (NDP) models for assisting the emergency response to emission of radionuclides has been recommended by a working group of the Meteorological Society of Japan. This paper verifies the feasibility of the recommendation through NDP model intercomparison with limited emission source information for the case of the Fukushima Dai-ichi Nuclear Power Plant accident caused by the Great East Japan Earthquake in 2011. According to the recommendation of the working group, the NDP models are run under the assumption of a constant rate of emission during the whole forecast period. This is the worst-case scenario when limited source information is available. Generally, no information is provided on the temporal variability and strength of the emissions, while the source location is known. Surface air radionuclide forecasts are utilized for providing warnings of the risk of inhaling radioactive substances suspended in the low-level atmosphere, whereas column-integrated radionuclide forecasts are utilized for estimating the potential maximum wet deposition of radioactive materials on the ground due to precipitation. The NDP model short-range forecasts were validated with observational data for three locations, at the times when the most serious contamination events occurred at each of the three monitoring stations. The NDP models successfully predicted the risk of surface air contamination and/or ground surface contamination caused by wet deposition in these cases. Particularly, the NDP model forecasts allow us to disseminate warnings at effective lead times before exposure to radiation. The different NDP models gradually deviate their forecasts as the lead time progresses. The deviations may indicate the magnitude of forecast errors. Thus, the use of multi-model forecasts is of greater benefit than the single model forecasts, because forecast error information is suggested. Image 1 • We propose the use of prediction models for environmental emergencies. • We performed model prediction experiments for atmospheric radionuclide dispersion. • The prediction models were validated with the Fukushima nuclear accident data. • Model prediction allows us to disseminate warnings at effective lead times. [ABSTRACT FROM AUTHOR]