A quantitative estimate of English Channel water fluxes into the North Sea from 1987 to 1992 based on radiotracer distribution

Abstract

Seven oceanographic campaigns carried out in the North Sea between July 1987 and January 1992 by the Marine Radioecology Laboratory (LERFA) of La Hague have led to the drawing up of general maps showing the distribution of the radionuclides 125 Sb, 137 Cs, 134 Cs and 99 Tc 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 flow between the Straits of Dover and the Skagerrak. On this basis, it is possible to link the flux of radionuclides released from the nuclear fuel reprocessing plant at La Hague ( 125 Sb and 99 Tc) 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 97000-195000 m 3 /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.

Dissolved Radiotracers and Numerical Modeling in North European Continental Shelf Dispersion Studies (1982–2016): Databases, Methods and Applications

“…This method was particularly fruitful in 1988 in the North Sea, where it was possible to distinguish and map the distribution of the four main water masses entering the North Sea by using the simultaneous measurements of three radionuclides ( 125 Sb, 137 Cs, 134 Cs) and salinity ( Figure 11) [17]. As compared with another campaign performed two years before, the contribution of the direct fallout after the Chernobyl accident and the rate of renewing of North Sea waters were also calculated.…”

“…By accounting for all available measurements associated with their representative area and depth, it is possible to map the radionuclide distributions and calculate radionuclides quantities existing in specific areas. Such inventories give integrated values with a better precision than individual concentrations [17,20].…”

“…As regards criteria 3, 4 and 5, some radionuclides exhibit long term conservative behaviors in seawater, such as 125 Sb, 99 Tc and 3 H (tritium) [35], and to a lesser extent 90 Sr, 137 Cs and 134 Cs. Between 1970 and 1995 extensive measurements of these radionuclides were carried in the seas of north-western Europe [5,6,11,12,[14][15][16][17][18][19][20][21]24,36]. Reductions in fluxes released during the period from 1980 to 2000 have led to significant decreases in concentrations in the marine system.…”

“…Percentage origins of water masses entering the North Sea in 1988 deduced from dissolved radionuclides measurements (a); 134 Cs remaining fallout from the Chernobyl accident and rate of renewing of water masses in two years (b), adapted from[17].…”

The Alderney Race: general hydrodynamic and particular features

“…Many studies have been performed to investigate the behaviour of these dissolved radionuclide releases in the past 30 years. They involve several time and space scales, ranging from minutes and kilometres following an individual release [5,6] and up to years and thousands of kilometres [7][8][9][10]. As the dispersion of dissolved releases is governed by hydrodynamics, the measurements of radionuclide concentrations and plume dispersion reveal the cumulated effects of the current and diffusion effects at different scales.…”