Quantitative assessment of dissolved radiotracers in the English Channel: Sources, average impact of la Hague reprocessing plant and conservative behaviour (1983, 1986, 1988, 1994)

International audienceKnowledge of long-term movements of water-masses in the English Channel has been substantially improved using hydrodynamic modelling coupled with radio-tracers studies; nevertheless, the precision of results so obtained is still largely dependent on measurement precision. New tools are now available to make more accurate determinations of radio-tracer distribution: (1) Repositioning of station locations at the same tide reference-time, giving a homogeneous spatial data set, coupled with the possibility of interpolating and quantifying the amounts of dissolved radioactivity #owing through the English Channel; (2) the "rst measurements of tritium (H) in seawater on a large scale in the English Channel demonstrate that this fully conservative radionuclide is a clearly identi"able marker of industrial releases; (3) recent campaigns carried out during the FLUXMANCHE II CCE (1994) programme show the general distribution of dissolved radionuclides Cs, Cs, Co, Sb, Ru and H in the English Channel and the Irish Sea; and (4) the re-utilisation of data from previous campaigns (1983, 1986, 1988) provides indications, at any given location in the English Channel, about the average dilution and distribution of releases derived from the La Hague reprocessing plant. Excesses and losses of radionuclides are now quanti"ed with respect to known source terms; estimates of losses are provided for non-conservative radionuclides, while an excess of Cs was observed in the English Channel during the period 1983}1994. This excess, which has the same order of magnitude as the quantities released from La Hague plant in the English (P. Bailly du Bois) 0278-4343/99/$-see front matter 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 8-4 3 4 3 (9 9) 0 0 0 4 9-7 Channel, could be explained by about 1% of the Sella"eld reprocessing plant releases entering the Channel. These results con"rm and give a more detailed picture of the previously known distribution of water masses in the English Channel. They lead to clear information about transit times and dilution at this scale, and provide directly comparable data for the validation of hydrodynamic models

Percentage contribution of inputs from the Atlantic, Irish Sea, English Channel and Baltic into the North Sea during 1988: A tracer-based evaluation using artificial radionuclides

International audienceA sampling cruise carried out in the North Sea in July 1988 has enabled the construction of general maps showing the distribution of salinity and temperature as well as the activities of the radionuclides 125 Sb, 137 Cs and 134 Cs. An inspection of the raw data and the distribution patterns so obtained shows the important role of meteorological fluctuations in the movement of near-surface waters throughout the North Sea. A simple mixing model is used to interpret the North Sea dataset in terms of four contributory water-masses (the Atlantic, Irish Sea, English Channel and Baltic), each of which can be identified by its specific characteristics. Maps are drawn up which indicate the contribution factor in percentage of each of these water masses at all points in the North Sea to a precision better than 15%. Pt is also possible to extract the contribution of direct fallout resulting from the Chernobyl accident; comparison with previously obtained results allows an evaluation of the rate of renewal of surface waters in the North Sea over a period of two years. In all areas, this value appears to be better than 75%

Incidences des procédés d'épuration appliqués aux effluents industriels sur le comportement chimique du ruthénium 106 dans l'environnement marin. Cas des rejets de l'usine de retraitement des combustibles irradiés de La Hague

Depuis la mise en service de l'usine de retraitement des combustibles irradiés de la Hague en 1966, l'efficacité des moyens employés pour épurer les effluents radioactifs liquides a été multipliée par un facteur 600. Le comportement chimique du 106Ru déterminé dans les rejets déversés en mer et en deux stations d'observation proches de l'émissaire, a évolué parallèlement à l'évolution des procédés d'épuration. La méthodologie de type “voie humide” basée sur l'entraînement de l06Ru par le sulfure de cobalt a permis de répondre aux objectifs de protection de l'environnement et aux impératifs de production. Le comportement du radionucléide a alors été celui des complexes du nitrosylruthénium chimiquement peu réactifs, générés au cours de la mise en solution des combustibles en milieu nitrique. A partir de 1989, la vitrification des effluents les plus marqués par ce type de complexation et l'optimisation du procédé par voie humide ont permis de limiter les rejets liquides de 106Ru. Parallèlement, l'inertie chimique du radionucléide s'est atténuée. Les mesures de radioactivité de l'algue Fucus serratus déterminées in situ montrent que la disponibilité de 106Ru à partir de l'eau de mer dépend étroitement de l'hydrolyse des complexes du nitrosylruthénium. Les produits d'hydrolyse du radionucléide paraissent être les formes privilégiées des échanges avec l'algue pour laquelle le facteur de concentration est évalué à 500 ± 350

Spatial and Temporal Distribution (1987-91) of 125Sb Used to Trace Pathways and Transit Times of Waters Entering the North Sea from the English Channel

International audienceThe labelling of marine waters off north-western Europe by artificial radio-nuclides discharged by the nuclear fuel reprocessing plants at Sellafield and La Hague provides a potentially useful tool for the study of hydrodynamic processes. In this context, the present investigation introduces a tracer, 125 Sb, which is conservative within the watermass and which is characteristic of releases from La Hague. Analysis of the data collected between 1987 and 1991 shows that a large part of the Channel waters entering the North Sea follow a route along the Belgian, Dutch, German and Danish coasts, while undergoing a low degree of dilution with other marine waters circulating in the central North Sea. The westward extension of the Channel plume is variable with time, but the general distribution is in good agreement with the ICES box model. Estimates are given for the transit times from Cap de la Hague to various sectors of the North Sea; it takes 15-17 months for labelled waters to reach the Norwegian Channel