Local scale marine modelling of Fukushima releases. Assessment of water and sediment contamination and sensitivity to water circulation description

The dispersion of 137Cs released from Fukushima nuclear power plant to the sea after the March 11th 2011 tsunami has been studied using numerical models. The 3D dispersion model consists of an advec tion/diffusion equation with terms describing uptake/release reactions between water and seabed sedi ments. The dispersion model has been fed with daily currents provided by HYCOM and JCOPE2 ocean models. Seabed sediment 137Cs patterns obtained using both current data set have been compared. The impact of tides and of atmospheric deposition has been evaluated as well. It has been also found that a 2-step kinetic model (two consecutive reversible reactions) for describing water/sediment interactions produces better results than a 1-step model (one single reversible reactio

Should we measure plutonium concentrations in marine sediments near Fukushima?

Pu contamination originating from Fukushima accident has not been detected in marine sediment samples collected outside a 30 km circle around the plant. It is shown, by means of numerical modelling, that if any impact from the accident has occurred, this would remain in a very close area to Fukushima because of the low Pu mobility in the marine environment. Since the situation inside the 30 km zone remains unknown, further studies on the determination of Pu isotopes in sediments within this area are required

Numerical analysis for 137CS on seabed sediment including atmospheric deposition near the Fukushima coastal area

Radionuclides were released into the atmosphere and ocean from the accident at the Fukushima Daiichi Nuclear Power Plant (NPP) in March 2011. Numerical simulations were performed to evaluate the distribution of 137Cs in the ocean with considering directly release and deposition from the atmosphere. Calculated concentrations of 137Cs in the sea water and seabed are compared with the measured data, and atmospheric transport model has been also used to calculate the rates of atmospheric deposition on the sea surface. Lots of atmospheric deposition was occurred on sea surface in northeast direction from Fukushima NPP due to westerly wind and precipitation on March 15-31, 2011. Most modelling for the marine dispersion of 137Cs after Fukushima accident was considered as a perfectly conservative radionuclide, thus scavenging processes and adsorption on seabed sediments are neglected. The processes of the non-conservative from the numerical simulations have been well described and the calculated results are also in agreement with the measured data. The concentrations of 137Cs in seabed sediments were mainly contributed by the atmospheric deposition and long residence time showed in northeast coastal area off Fukushima NPP

The behaviour of 236-U in the North Atlantic Ocean assessed from numerical modelling: A new evaluation of the input function into the Arctic

-A numerical model, previously validated with other radionuclides, was applied to simulate the dispersion of 236U released from European nuclear fuel reprocessing plants in the North Atlantic and Shelf Seas using a published reconstruction of Sellafield and La Hague releases. Model results are in better agreement with observations if the lowest estimation of such releases are used. This implies that approximately 40 kg of 236U has been discharged from Sellafield. It was found that adsorption of 236U on bed sediments of the shallow European Shelf Seas plays an essential role in its dispersion patterns. This contrasts strongly with the more conservative behaviour of 129I in the same area. This has two important implications in the use of 236U as oceanographic tracer; i) special care must be taken in coastal areas, as sediments might act as sinks and sources of 236U; ii) the annual input function of 236U into the Arctic is not directly controlled by the annual discharges from Sellafield and La Hague, since sediments from the Irish, Celtic and North Sea modulate and smooth the signal. Only 52% of the total releases enter into the Arctic Ocean

Assessment in marine environment for a hypothetic nuclear accident based on the database of tidal harmonic constants

The eleven nuclear power plants in operation, under construction and a well-planned plant in the east coast of China generally use seawater for reactor cooling. In this study, an oceanic dispersion assessment system based on a database of tidal harmonic constants is developed. This system can calculate the tidal current without a large computational cost, and it is possible to calculate real-time predictions of pollu-tant dispersions in the ocean. Calculated amplitudes and phases have maximum errors of 10% and 20%with observations, respectively. A number of hypothetical simulations were performed according to vary-ing of the release starting time and duration of pollutant for the six nuclear sites in China. The developed system requires a computational time of one hour for one month of real-time forecasting in Linux OS. Thus, it can use to evaluate rapidly the dispersion characteristics of the pollutants released into the sea from a nuclear accident.European Union FP7 EURATOM project PREPARE 32328

The behaviour of I-129 released from nuclear fuel reprocessing factories in the North Atlantic Ocean and transport to the Arctic assessed from numerical modelling

A quantitative evaluation of the fate of 129I, released from the European reprocessing plants of Sellafield (UK) and La Hague (France), has been made by means of a Lagrangian dispersion model. Transport of radionuclides to the Arctic Ocean has been determined. Thus, 5.1 and 16.6 TBq of 129I have been intro-duced in the Arctic from Sellafield and La Hague respectively from 1966 to 2012. These figures represent, respectively, 48% and 55% of the cumulative discharge to that time. Inventories in the North Atlantic, including shelf seas, are 4.4 and 13.8 TBq coming from Sellafield and La Hague respectively. These figures are significantly different from previous estimations based on field data. The distribution of these inven-tories among several shelf seas and regions has been evaluated as well. Mean ages of tracers have been finally obtained, making use of the age-averaging hypothesis. It has been found that mean ages for Sellafield releases are about 3.5 year larger than for La Hague releases.European Union FP7 EURATOM project PREPARE 323287Ministerio de Ciencia, Innovación y Universidades FIS2012–3185

The behaviour of Cs-137 in the North Atlantic Ocean assessed from numerical modelling: Releases from nuclear fuel reprocessing factories, redissolution from contaminated sediments and leakage from dumped nuclear wastes

A Lagrangian model which simulates the dispersion of 137Cs in the North Atlantic has been developed. The model includes water/sediment interactions. It has been tested comparing calculated and measured 137Cs concentrations in water and sediments of the European Shelf resulting after the releases from the nuclear fuel reprocessing plants of Sellafield and La Hague. Some additional numerical experiments have been carried out. First, the redissolution of 137Cs from contaminated sediments after the reduction in releases from the reprocessing plants has been studied. This allowed to calculate effective half-lives of 137Cs in several sub-basins. Later, potential leakage of 137Cs from dumped nuclear wastes in several locations of the Atlantic has been investigated. Even in worst-case scenarios, these leakages should not lead to any radiological implications.Ministerio de Economía y Competitividad FIS2015-69673-

Marine dispersion assessment of 137Cs released from the Fukushima nuclear accident

Radionuclides were released into the atmosphere and ocean due to an accident in the Fukushima Daiichi Nuclear Power Plant (NPP) in March 2011. Numerical simulations were carried out to evaluate the distribution of 137Cs in the ocean considering both direct releases to the sea and deposition from the atmosphere as source terms. A significant amount of atmospheric deposition occurred on the sea surface in the northeast direction from the Fukushima NPP, due to westerly winds and precipitations on March 15–31, 2011. In a previous study using local scale modeling, no significant differences in resulting 137Cs patterns in water and sediments with and without atmospheric deposition were found. However, this new research, on a regional scale, has pointed out meaningful differences in seabed sediment radionuclide concentrations in the Fukushima northeast area with and without atmospheric deposition.National Research Foundation of Korea (NRF) 2012M2A8A4025National Research Foundation of Korea (NRF) 2012M5A1A1029European Union FP7 EURATOM project PREPARE 32328

Numerical Modeling of the Releases of 90Sr from Fukushima to the Ocean: An Evaluation of the Source Term

A numerical model consisting of a 3D advection/diffusion equation, including uptake/release reactions between water and sediments described in a dynamic way, has been applied to simulate the marine releases of 90Sr from the Fukushima power plant after the March 2011 tsunami. This is a relevant issue since 90Sr releases are still occurring. The model used here had been successfully applied to simulate 137Cs releases. Assuming that the temporal trend of 90Sr releases was the same as for 137Cs during the four months after the accident simulated here, the source term could be evaluated, resulting in a total release of 80 TBq of 90Sr until the end of June, which is in the lower range of previous estimates. Computed vertical profiles of 90Sr in the water column have been compared with measured ones. The 90Sr inventories within the model domain have also been calculated for the water column and for bed sediments. Maximum dissolved inventory (obtained for April 10th, 2011) within the model domain results in about 58 TBq. Inventories in bed sediments are 3 orders of magnitude lower than in the water column due to the low reactivity of this radionuclide. 90Sr/137Cs ratios in the ocean have also been calculated and compared with measured values, showing both spatial and temporal variations.National Research Foundation of Korea (NRF) 2012M2A8A4025National Research Foundation of Korea (NRF) 2012M5A1A1029European Union FP7 EURATOM project PREPARE 323287Ministerio de Ciencia e Innovación CTM2011-15152-