Institute for Radiation Protection and Nuclear Safety (IRSN)
Not a member yet
7928 research outputs found
Sort by
FLUXMANCHE radiotracers measurements: A contribution to the dynamics of the English Channel and North Sea
No full textInternational audienceFrom 1986 to 1992, 125Sb released by the nuclear fuel reprocessing plant at La Hague has been used to study the transfer of waters from mid-Channel areas towards the Straits of Dover. Since 1940, these investigations have formed part of the MAST 53 FLUXMANCHE programme and have involved repeated measurements on a Straits of Dover transect. A discussion of the results is presented here which takes into account new information provided by a hydrodynamic model developed in the framework of FLUXMANCHE; it combines knowledge of the monthly fluxes of water trough the Straits of Dover and week-by-week simulation of the 125Sb activities of waters flowing in this aera. It is proposed that soluble radionuclides introduced into the central Channel are transferred towards the Straits of Dover over a time which varies from four to seven months depending on the route taken
A quantitative estimate of English Channel water fluxes into the North Sea from 1987 to 1992 based on radiotracer distribution
No full textInternational audienceSeven oceanographic campaigns carried out in the North Sea between July 1987 and January 1992 by the Marine Radioecology Laboratory (LRM) of La Hague have led to the drawing of general maps showing the distribution of the radionuclides 125Sb, 137Cs, 134Cs and 99Tc in seawater. In this way, the total amounts of radioactivity (inventories) present in the southern North Sea were evaluated from each separate campaign, thus leading to an assessment of the mean distribution of water masses, originating from the English Channel, which is siutated between the Straits of Dover and Skagerrak. On this basis, it is possible to link the flux of radionuclides released from the nuclear fuel reprocessing plant at La Hague (125Sb and99Tc) with the inventories of radiotracers observed in the southern North Sea. Hence, the most probable mean transit time of Channel waters entering the North Sea were calculated for each campaign; Channel waters take 110–152 days to flow from Cap de la Hague to the Straits of Dover and 170–250 days to travel from there to the entrance of the Baltic. The water flux through the Straits of Dover is estimated to lie in the range 97,000–195,000 m3/s for the period between January and July 1988. Very good agreement is found between the activities measured at different times and the results of a model simulating the hydrodynamic behaviour of the North Sea
The distribution of artificial radionuclides in the English Channel, southern North Sea, Skagerrak and Kattegat, 1990–1993
No full textInternational audienceThis paper presents the initial results concerning the distribution of artificial radionuclides from research cruises conducted in collaboration by three European institutes as part of an EEC MAST research project. Ten cruises were undertaken covering the English Channel, southern and eastern North Sea, Skagerrak and Kattegat over a period of 2.5 yr. A large number of analyses of four artificial radionuclides (13'Cs, "Tc, '*%b, !%r), which behave conservatively in seawater, provided information about the general distribution of water masses and circulation patterns as well as about single transport events in the study area. Controlled liquid releases from the La Hague nuclear fuel reprocessing plant are transported eastwards, forming a characteristic distribution pattern in the Channel and the southern North Sea. This includes a near-coastal "plume" and a distinct boundary between waters contaminated predominantly by La Hague and by Sellafield. Spatial and temporal distributions of radionuclide ratios were used, for the first time, to calculate transit times from the English Channel to the coast of Jutland. The data published herein provide an essential input to the calibration of numerical models simulating water transport processes. The results demonstrate the continuing usefulness of artificial radionuclides as oceanographic tracers, even at the very low concentrations observed at present in northwest European Shelf waters
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
No full textInternational 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
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
No full textInternational 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%
Effects of Coulomb interactions on the electronic structure of the Si(001) surface
No full textInternational audienceThe electronic structure of the Si(001) surface is obtained with a tight-binding method developed in the slab geometry. The effects of local Coulomb interactions on the stability of antiferromagnetic solutions and on the width of the gap in the surface states at the Si(001) surface reconstructed with symmetric dimers are first visualized with a two-orbital model Hamiltonian. It allows us to study the effect of the coupling between the dangling and the bonding orbitals. The calculation performed with the tight-binding method supports the results of the model and provides an explanation of the semiconducting character of the reconstructed Si(001) surface with symmetric dimers. For realistic parameters which include the atomic values of the interorbital exchange, an antiferromagnetic order of (2×2) symmetry is stable. It is argued that even if the long-range antiferromagnetic order is destabilized by quantum fluctuations in quasi-two-dimensional surface states, the short-range antiferromagnetic order induced in the dangling orbitals by Coulomb interactions is sufficient to explain the semiconducting behavior of symmetric dimers
