The aim of this project is to improve and refine our understanding of the behaviour of plutonium, americium and other long lived radionuclides in the marine environment.
A dual isotopic trace technique to separate the oxidation states of plutonium in seawater was successfully tested.
The distriubtions of plutonium and americium between filtrate and suspended solids in near surface and near bottom water throughout the Irish Sea were examined and Kd coefficients determined for both elements. Measured plutonium-238 to plutonium-239, 240 quotients in filtered seawater, suspended particulate and surface sediment in the Western Irish Sea were clearly indicative of releases from Sellafield. There was a clear difference between the americium-241 to plutonium-239, 240 quotient in filtered seawater and that for the suspended load, reflecting the stronger particle reactivity of americium.
The data showed that proportionately more of the plutonium and americium in the water column close to the outfall was associated with suspended solid. Throughout the open waters of the Irish Sea the percentage of plutonium-239, 240 (V, VI) in filtered water lay in the range 77 to 94. No systematic variation of Kd with depth at given location was observed, but there was a clear difference between mean Kd values in the eastern and western zones, for plutonium and americium.
The the Almanzora River, samples were taken of surface sediments in the river bed and beach, river sediment cures, river trenches and biota. The samples were analysed for plutonium and caesium-137 content and geochemical composition. The concentration ratios of caesium and plutonium between river and marine sediment gave an idea of the magnitude of transfer processes. The ratios ranged from 10 to 20 in Palomares and were similar to those obtained from the Italian coast and the Mediterranean continental shelf. The concentration levels of caesium and plutonium were similar to those in fallout from Chernobyl.
A study was made of gamma emitters (including americium-241) in slowly accumulated subtidal sediment. A suitable site for obtaining undisturbed sediment cores was identified. The radionuclide record was confirmed to be continous and unaffected by postdepositional processes. Preliminary analysis showed that the vertical profiles of long lived radionuclides matched neither the instantaneous released activity versus time, nor the cumulated released activity versus time. Instead, activities increased towards the sediment to water interface, and the interelement ratios reamined constant. It was concluded that the signal recorded in the sediment core was strongly modulated by natural processes, such as tides.
An investigation was made of the complex formation of americium with organic matter in river estuaries with reference to americium of marine origin. Levels of organic carbon were measured in the estuarine waters of the Seine, Rhine, Escaunt and Vire. Americium-241 and cobalt-60 were introducd into samples of river water and complex formation measured. It was shown that complex formation was a factor of some importance within the estuaries of large rivers, and might be very variable according to the radionuclide involved. The development of complex formation as a function salinity and time has also been investigated.
A study has been made of the time evolution of radioactivity levels in the North Adriatic Sea. Chernobyl radionuclides were used as tracers of sedimentation and erosionprocesses. Concentrations and inventories of caesium-134 and caesium-137 in sediments were higher in the pelitic arcas and in the terminal tract of major rivers. Preliminary measurements were carried out on the distribution of natural radionuclides in the water column, for the study of gas fluxes between sea and atmosphere.
Scavenging of particle reactive nuclides in the Ligurian Sea was studied. The disequilibrium of uranium-238 to thorium-234 has been used to determine the rates of removal processes, in the framework of a general programme on biogeochemical fluxes.
The study will embrace five distinct marine zones, namely the Irish sea; the Channel and the Seine Estuary; the Almanzora river bed, mouth and adjacent shelf; the Gulf of Taranto; and the Ligurian Sea. Although these domains differ widely in their physical oceanography, many of the fundamental process governing the behaviour of transuranics and other long lived nuclides are common to them all and, as such, are the main focus of the work proposed below. A feature of this collaboration is the application of compatible and, in some case, identical analytical techniques to the study of physical and chemical speciation, dispersion, sediment transport and organic complexation of transuranium nuclides under a wide range of marine (and riverine) conditions. It has been agreed that the programmes of the participating laboratories will be closely coordinated with the aim of enhancing the value and universality of the results obtained.
Funding SchemeCSC - Cost-sharing contracts
19100 La Spezia