In estuaries, volatiles radionucleides (14C, 3H, 131I) originating from anthropogenic liquid waste release from nuclear reactor or hospitals are potentially transferable to the atmosphere. Due to the high biologic activity, the degradation of organic matter produce carbon dioxide fluxes to the atmosphere allowing transfer of 14CO2 released by nuclear industry. Similarly tritium is transfered to the atmosphere trough evaporation process. We present here, results obtained during FLORE-1 cruise in February 2003, a winter period when biological activity is supposed to be low. The first results of iodine 131 distribution and estimations of radiocarbon and tritium fluxes are presented.

This work aims to validate the dispersion parameters of hydrodynamic models for the short term (hour to week), and short distances (100 m - 30 km), by using high precision and high frequency measurements of tritium obtained in the release plume. An instantaneous 2D hydrodynamic model has been developed with a mesh size of 110m and an area of 50×50 km. More than 7,000 samples have been collected and measured for tritium concentrations in 2002 and 2003. Currents and bathymetric measurements, as well as drifters observations complete these measurements. Results confirm the efficiency of the hydrodynamic model, main differences being attributable to bathymetry incertitudes. After calibration, the model gives accurate results during six hours following a release. The obtained field database represents an exceptional tool for hydrodynamic models validation in realistic conditions of releases, tide and wind, in an area where the current dynamic is particularly strong (more than 5 m/s during high tides). The dispersion parameters obtained will be applied for other hydrodynamic models covering continental macro-tidal seas. Such models will be used to simulate soluble pollutants dispersion, with known uncertainties, in realistic chronic or accidental release conditions.

Radionuclides in the environment require regular monitoring to establish activity concentrations and make reliable dose estimates. This study examines the variability in selected radionuclide activity concentrations at a variety of spatial scales and assesses the resulting errors in dose estimates. The Ribble Estuary, UK provides an ideal location to conduct non-destructive tests (β-dose rate measurements) due to the discharge of 234Th and $^{234\textrm{\tiny{m}}}$Pa from the BNFL fuel fabrication plant at Springfields (Lancashire, UK). This estuary also receives Sellafield derived radionuclides after transport through the Irish Sea. Results indicate that significant errors in external beta and gamma dose assessments may result from the use of single sediment activity concentration or dose values to represent an area of contaminated sediment. For example, in an area only 1m × 1m square, a field coefficient of variation for beta dose may be as high as 25%, even when there are no visible textural or compositional variations to account for this, and this increased to 83% at the 100×100m scale. Erroneous conclusions on the nature of change in time-series measurements can be made if local field variability has not been assessed and allowed for when planning the monitoring programme.

TRANSMER hydrodynamic model simulates dispersion of dissolved substances in seawater at the scale of the English Channel and the south of the North Sea with a mesh size of one kilometre and a time step of 30 minutes. This model evaluates the medium- and long-term consequences of releases of soluble pollutants in the marine ecosystem under normal or accidental conditions, at a very low computation cost (it takes less than one hour to simulate one year). It has been qualitatively and quantitatively validated by 1400 measurements of 125Sb in seawater in the English Channel and the North Sea. Budgets of measured and simulated radionuclide quantities are balanced for theses seas. The correlation factor between individual measurements in seawater and calculation results is 0.88 with an average error of ± 54%, the error attributable to the measurement process being 15% on average. TRANSMER appears as a robust tool for modelling medium- and long-term consequences of releases of soluble pollutants in the marine ecosystem under normal or accidental conditions.

The quantification of radionuclides by direct gamma-X spectrometry with energy below 100 keV requires knowledge the elementary composition of the sample or the development of a device for determining the mass attenuation coefficients. This is especially true for 129I which is characterised by a 29.8 keV X-ray and 39.6 keV gamma ray. Experimental equipment has been developed in order to obtain this mass attenuation coefficient as a function of energy. 129I concentrations were measured in samples of seaweed (Fucus serratus and Laminaria digitata) collected monthly over a period of one year nearby La Hague reprocessing plant in France. This paper describes the measurement methodology used to determine 129I concentrations and variations in the two seaweeds over a one-year period. Mean mass attenuation coefficients for 129I energies were established in order to determine the self-attenuation corrective factor for both seaweed species, regardless of the sampling date.

Oceans, seas, estuaries and rivers represent a vast sink for many substances of anthropic origin (metals, radionuclides, etc...). Depending on their chemical form, artificial radionuclides discharged into the sea by the nuclear industry can be carried onto land in marine aerosols, as well as by degassing seawater as is the case for tritium (3H) or for radiocarbon (14C). Three oceanographic cruises in the English Channel: TE-SEA, TRANSAT 1 and 2 have been performed on R.V. “Côtes de la Manche" to quantify the flux of 3H in gaseous form, from the sea into the atmosphere, following particular discharge into the sea from the COGEMA spent fuel reprocessing plant at La Hague (North West France). During cruises, the maximum concentration measured in the air was 10.6 Bq.L-1, which is distinctly higher than the background of 1$^{\circ}$Bq.L-1 thus demonstrating the transfer of 3H between water and atmosphere. The mean flux of 3H between the water and the atmosphere, calculated during these cruises was 2.4 107 Bq.km-2.d-1. For the Seine Bay area (4400 km2) this flux represents 39 TBq.yr-1 and hence less than 0.3 % of 3H discharged into the ocean from the COGEMA spent fuel reprocessing plant at La Hague.

COGEMA La Hague nuclear reprocessing plant is located in the North West of Cotentin peninsula near Cherbourg (France). This nuclear plant releases radioelements in atmosphere and in the English Channel. About 8.5 TBq.year-1 of radiocarbon are released as the liquid wastes through a pipe a few kilometres off sea shore, West of the reprocessing plant. Recent studies in the peninsula show anomalous higher radiocarbon contents in vegetation near the coast that have suggested a supplementary marine contribution through the degassing of the 14C excess supplied by liquid releases of the nuclear plant. Carbon dioxide partial pressure, 14C activities were measured in air and sea water in the Bay of Seine and around the COGEMA-La Hague nuclear reprocessing plant during three cruises in 2000 and 2002. Results show clearly that sea is a source of CO2 and 14C to the atmosphere. Higher 14C concentrations in air and water related to the La Hague liquid wastes are clearly recorded. The aim of this paper is to show results of these oceanographic campaigns. Flux between seawater and atmosphere are calculated in the North-West Cotentin and in Bay of Seine.

A numerical model has been developed to simulate the input of radionuclides into the Mediterranean Sea through the Rhone River plume. The model is fully 3D. It solves the hydrodynamic equations, which include baroclinic terms and a turbulence model, together with the suspended sediment equations and radionuclide dispersion equations. The suspended sediment sub-model includes four particle classes, settling and deposition. The radionuclide equations include the exchanges of radionuclides between water, suspended sediments and bed sediments, described using a kinetic model. The effect of salinity changes upon uptake kinetics has also been included. Computed water circulation, salinity pattern, suspended sediment distribution and sedimentation rates are in agreement with observations in the area. The model has been applied to simulate the dispersion of 137Cs and $^{239,240}$Pu through the plume. Computed specific activities in water, suspended matter and bottom sediments are in agreement with the measured distributions. The model can also be applied to calculate distribution coefficients. Although some water circulation models for the Rhone River plume exist in current literature, this is the first time in which a detailed hydrodynamic and suspended sediment model has been applied to simulate the dispersion of radionuclides in the plume.

Two models with different conceptual and numerical approaches have been used to simulate the dispersion of radionuclides released from Sellafield nuclear fuel reprocessing plant. The first is a long-term box-model for simulating dispersion from Sellafield to the Arctic environment in which water fluxes between boxes are obtained from basic oceanographic information. Water-sediment radionuclide exchanges are described through sedimentation and remobilisation processes on the basis of equilibrium distribution coefficients. The second model is a 3D high-resolution model that explicitly solves tidal mixing and suspended sediment transport in the Irish Sea. Exchanges of radionuclides between the liquid and solid phases are now described in terms of kinetic rates. Thus, this model has a general applicability and can be used in situations out from equilibrium. Both models have been used to simulate the dispersion of Cs and Pu in the Irish Sea. Results from the two models are comparable, being differences in the results smaller than should be expected from the very different modelling approaches.

The post-depositional reactivity of the plutonium was investigated in bottom sediments collected in the central English Channel using an experimental approach. Medium to coarse grained surficial sediments and fine-grained undisturbed sediment cores were spiked with 238Pu. After a one-month incubation, pore waters were extracted under strictly anoxic conditions and dissolved plutonium was analysed by liquid scintillation techniques. Kd values ranged from 102 to 105 in surficial sediments undergoing oxic diagenesis, and were shown to be grain-size dependant. In fine-grained sediments undergoing anoxic diagenesis, Kd values ranged between 103 and 105. Kd profile suggests an active recycling of the plutonium in the topmost sediment layers, and subsequent efficient uptake process at depth, tentatively acido-volatile sulphide (AVS) precipitation. This hypothesis was further confirmed by a correlation between the AVS content and the loosely bound plutonium extracted using an oxidising/complexing solution from sediment subsamples. In surficial sediments, by contrast, loosely bound plutonium was likely to be associated with the carbonate phase as surface complexes.

Within the scope of a joint IRSN/EDF research program, it is possible to present a first status of free water tritium and organically bound tritium levels in the French coastal marine environment, from Concarneau to Gravelines. Seasonal sampling was conducted over two years, 2001 and 2002. The matrices selected for this specific survey include water, seaweed, molluscs, crustaceans and fish. The background concentration, estimated from the results obtained at two sites, Concarneau and Roscoff, remote from industrial sources, is close to the detection limit of 1,2 Bq.l-1. Along the Channel coast and the entrance of the North Sea, tritium is released in seawater by four nuclear power plants (14 reactors) and mainly by the reprocessing plant of La Hague. The concentrations measured are in good agreement with activities calculated with the hydrodynamic model of dispersion TRANSMER. The results confirm a dilution factor of two between the north Cotentin area and the Straits of Dover for soluble radionuclides. The concentrations are in the range of 2 to 20 Bq.l-1 for free and organically bound tritium in biota. Although isotopic fractionation is theoretically expected to be slight, the available results indicate a ratio between tritium bound to organic matter and tritium in free water greater than one.

The Radiological Protection Institute of Ireland has monitored levels of anthropogenic radionuclides in the Irish marine environment for over 20 years. While the primary objective of the monitoring programme is to assess the exposure of the Irish population resulting from the presence of these radionuclides in the marine environment, the programme also aims to assess the geographical distribution and temporal variations of the radionuclides. The programme involves the routine sampling of and testing for radioactivity in fish, shellfish, seaweed, sediments and seawater. The data generated in the course of this programme, as well as in a separate study of changing plutonium isotopic ratios in Fucus vesiculosus from the west coast of Ireland, were used to estimate transport times from the Sellafield nuclear fuel reprocessing plant to various locations on the Irish coastline. For conservative radionuclides, transit times of 5-6 months to the NE coast of Ireland, 1-3 years to the south coast of Ireland and 3-8 years to the west coast were calculated. In contrast, for plutonium, the Sellafield signal was not observed on the west coast until the late 1980s/early 1990s.

National Research Institute of Fisheries Science (NRIFS) has carried out the long term monitoring program for radioactive pollution in marine organisms caught around Japan in order to confirm the safety of marine organisms as food source. Recently, the effective ecological half-lives have been introduced to estimate the recovery time from radioactive pollution. In this study, the effective ecological half-lives of Cs-137 for some fishes were calculated from our monitoring data. It is known that fish species have each effective ecological half-lives. However, it has been unclear what change these half-lives of Cs-137 for fishes. Fishes intake Cs-137 through food chain and directly from their surrounding seawater. Therefore, the effective ecological half-lives of Cs-137 for some fishes would be controlled by the effective environment half-lives of Cs-137 for their surrounding seawater. There is difference in the effective environment half-lives between the open ocean and the coastal seawaters. Some fishes move between the open ocean and the coastal areas, and therefore their effective ecological half-lives are influenced by the effective environment half-lives for seawaters of both areas. Consequently, the rate of the influence by seawater in each area would produce the differences in the effective ecological half-lives among fish species.

The aim of this study was to compare the indicator properties of Fucus vesiculosus and Ascophyllum nodosum. Activity concentrations of 137Cs, 40K, 7Be, 228Ra, 99Tc, 90Sr and $^{239,240}$Pu were measured in plants of the two species collected monthly in 2002 from one location at the southeastern coast of Norway. For 40K, 137Cs, 90Sr, 7Be and 228Ra the activity concentrations were significantly higher in Fucus vesiculosus than in Ascophyllum nodosum, whereas the opposite was the case for 99Tc. For 137Cs, 90Sr, 7Be and 228Ra the temporal variations in activity concentrations showed similar pattern for the two species, whereas for 99Tc the temporal pattern was different for the two species. The observed temporal variations in activity concentrations of 137Cs (both species) and 90Sr (only Fucus vesiculosus) correlate with expected variations in seawater concentrations. For 137Cs salinity, light conditions, temperature and growth rates seem to work in the same direction as the variations in seawater concentrations. A lack of correlation between salinity and 99Tc concentrations in the algae indicates a slower dynamic in uptake and/or secretion for technetium. The observed differences between the two species may partly be explained by the difference in growth rate and life length between the two species.

The deposition from Chernobyl in spring 1986 was most unevenly distributed in Finland and elevated the 137Cs contents of fishes in Finnish lakes significantly. High activity concentrations of 137Cs still occur in fish from certain lakes in the areas of the highest deposition. Activity concentrations of 137Cs in perch varied from 20 to 7 800 and those in lake water from 4 to 330 Bq/m3 in 1998 and 2002. Concentration factors (Bq/kg in perch / Bq/kg in lake water) ranged from 1 300 to 30 000 in the lakes studied. Ecological halftimes of 137Cs in perch in certain lakes, monitored regularly since 1986, and representing different types in terms of environmental transfer, were estimated as examples. The longest halftimes of 137Cs in perch were approximately 8 years and the shortest approximately 3 years determined for the time period of 1988-2002. Except for estimation of radiation doses to people eating fish, data on changes of activity concentrations in various parts of the aquatic system are also needed when estimating radiation doses to fish and other biota. Slow recovery of the habitat and feed from 137Cs results in higher exposure of biota than in case of rapid activity decrease.

Important historical informations on the temporal changes of anthropogenic pollution in marine environment can be assessed using sediment analysis. Dating is a crucial prerequisite to reconstruct pollution events, to calculate fluxes, and thus to allow comparison between different sites. This work presents estimates of accumulation rates of sediments in the Bay of Biscay. Fives cores were collected during RIKEAU 2002 cruise on board o/v Thalia in order to study temporal changes in PAH and organohalogens compounds content of sediment. We compare chronostratigraphic estimates on cores derived from the natural radionuclide 210Pb in excess with estimates from the known times of introduction of the artificial radionuclide 137Cs to the environment. 210Pb, 226Ra and 137Cs were measured directly by non-destructive gamma spectrometry using a well type γ-detector. Total 210Pb and 226Ra activities vary from 30 to 150 mBq g-1, and 20 to 36 mBq g-1 respectively; 137Cs presents lower levels (< 5 mBq g-1). Profiles of 210Pb$_{\scriptsize\textrm{xs}}$ in three cores present a well mixed layer, from 2-3 to 10 cm, in the uppermost sediments, followed by an exponential decrease of activities, suitable for the determination of sedimentation rates. Under constant flux and sedimentation rate assumptions, vertical accretion rates derived from 210Pb$_{\scriptsize\textrm{xs}}$ present a large range from nearly 0.1 cm yr-1 up to almost 0.3 cm yr-1. Differences are mainly due to relative position of studied cores regarding the muddy patch. Although the moderate level of 137Cs limits the accuracy of this dating method, profiles of 137Cs with depth strengthen mean rates derived from 210Pb$_{\scriptsize\textrm{xs}}$ data. The implication of this dating on pollutant inputs in sediments of the Bay of Biscay is briefly discussed.

We report detailed depth profiles of the particle-reactive radionuclides 234Th (24.1 days) and 7Be (53.3 days) in sediment cores collected at different seasons in the Thau Lagoon, located in the south of France. Two sites with contrasting characteristics were selected: C4 in the middle of the lagoon and C5 nearby oyster farming. Both sites were visited six times between December 2001 and May 2003. 234Th in excess (234Th$_{\mathrm{xs}}$; i.e. supplied to sediment by settling particles) and 7Be both show seasonal variations in activities and in penetration within sediment. With their very short half-lives and moderate sedimentation rates at both sites (around 0.1 - 0.3 cm per year), 234Th$_{\mathrm{xs}}$ and 7Be should be present only at the water-sediment interface. However all the profiles show penetration of both short-lived radionuclides to variable depths, from 1 up to 8 cm, that indicates efficient biological mixing of upper sediments. Such a mixing is usually described as a biodiffusive transport defined by bioturbation coefficient (D$_{\mathrm{b}}$). The simplest way to calculate D$_{\mathrm{b}}$ from radionuclide profiles is to assume steady-state within the mixed layer. For site C4, steady-state bioturbation rates (D$_{\mathrm{b}}$-SS) range between 1 and 12 cm2 yr-1, with a weak seasonal signal. The mixing of surface sediments at site C5 presents a greater range (1 - 31 cm2 yr-1) with the highest values observed in summer. Radionuclide fluxes at the water-sediment interface show too seasonal variations, particularly marked at site C5 in relation with its position. Such a time-series of short radionuclides at the water-sediment is most unusual. It provides the opportunity to develop a non-steady state modelling in order to test the significance of bioturbation rates based on steady state assumption. These tests allow to figure out how variations (seasonal, episodic) of radionuclide fluxes could induce errors on D$_{\mathrm{b}}$-SS determinations.

Assessment of the future radioactive environmental contamination threat by releases from dumped submarine and ship reactors with Spent Nuclear Fuel (SNF) is a project goal. The methodology of detection of traces of 85Kr and 3H (which the first are leaking from the SNF) in sea water is advanced. Search of ship nuclear reactors on a bottom in dumpsites on 85K plume is proposed. Investigation of releases from the dumped ship reactors with SNF of icebreaker “Lenin" in Kara Sea is launched (September 2003). Research has complex character: experiments with SNF, creation of techniques located on R/V “Ak. B. Petrov" and expedition works. Preliminary observation of hydrological characteristics in zone of marked dumpsites has been fulfilled. The first results on the 85Kr concentration in near-bottom layer of Kara and the Barents Seas also Tritium and Radiocesium during August 2003 were obtained.

The development and application of a new detection system is described for autonomously working radioactivity measurements, usable in seawater and river environment. The system is based on a NaI scintillator with specifications for use in the marine environment and for real time acquisition. It is simple, stable for long-term monitoring, and of low consumption. The sensor was energy and efficiency calibrated in the laboratory. Many tests were made for the linearity and the stability of the electronics. The energy resolution calibration of the sensor was performed prior to its location into the tank, using various reference point sources. The system was deployed in open sea in order to measure background and low volumetric activity of 137Cs (19 Bq/m3). The field measurements in the Aegean Sea offer very promising results concerning the use of the whole system in the marine environment to be used as continuous monitoring and alarm system.

Assimilation of observations is a powerful tool to improve the predictive capabilities of models for radionuclide transport and fate. We describe results of numerical experiments on assimilation of the data on radionuclide contamination of the Black Sea in the result of Chernobyl accident using the three-dimensional model of circulation and radionuclide transport THREETOX. Data assimilation can be formulated as a procedure that contains two steps: update and forecast. On the update step THREETOX is run from the time of release or deposition to the time of the forecast using the updated input from all the measured data available at this period to be assimilated. On the forecast step THREETOX is run from the forecast time to the end of the modeling period using the results of the update step to produce the forecast of radionuclide transport. The data assimilation method called “method of iterations to optimal solution" (IOS) was used at the update step. The approach has been applied to the assimilation of the observational data of 137Cs concentration measured in the “Typhoon" surveys for the period June 1986 to September 1990. From the results of numerical experiments we conclude that usage of a data assimilation procedure can essentially improve predictive capability of the models for radionuclide transport. The computational time for the data assimilation method chosen is small in comparison with the general time of calculations. Results from the study will provide a better understanding of the processes of radionuclide transport in the seas. This novel approach was implemented in the EU DSS RODOS for the real-time simulation of radioactivity transport in the marine environment.