Transport Of Actinides Research Articles

The Speciation of Uranium and Thorium at the Broubster Natural Analogue Site, Caithness, Scotland

ABSTRACTAnomalously high concentrations of uranium, thorium and the rare earth elements (REE) are associated with peat-rich soils near Broubster, northern Scotland. The source of the anomaly has been traced to a hydrocarbon-containing mineralised zone within a uraniferous, calcareous Devonian sedimentary sequence. From there, the elements have been transported approximately 100 metres downslope and fixed within waterlogged peat deposits. The degree of concentration and fractionation accompanying actinide transport is extreme. This paper describes the results of a theoretical modelling exercise and complementary experimental study carried out to determine the chemical speciation of actinides at the Broubster site. Efforts made to identify mobilisation and retention mechanisms for uranium and thorium have led to the development of a simple model for actinide behaviour in the peat soils. The work, which forms part of an on-going programme of research into natural radionuclide migration, is primarily aimed at improving confidence in predictive models used for radiological assessment.

Thermodynamic properties of lanthanide and actinide ions in avueous solution

This paper reports systematics on the thermodynamic properties of lanthanides and actinides in avueous solution. It includes comparisons between the 4f and 5f series. We will limit our review to non-compleved avuo ions, mainly divalent, trivalent and tetravalent ions. Special attention is drawn to crystallographic radii since they are basic parameters in the interpretation of thermodynamic properties. A consistent set of data is presented for M 2+, M 3+ and M 4+ ions. Effect of coordination number is discussed and estimates are given for unusual ovidation states. The structure of trivalent avuo ions is described from different evperimental lanthanide data and actinide transport number determinations. Then entropies of avuo ions are re-estimated and the problem of hydration enthalpy calculations is discussed. Finally, we compare the stability of the different ovidation states of the actinides.

The transfer to land of actinide-bearing sediments from the Irish sea by spray

Since 1957, British Nuclear Fuels Ltd. have discharged to the Irish Sea about 18000 Ci of plutonium alpha activity, in addition to other actinides and fission products. Experiments are described which demonstrate that seaspray in the area is enriched with actinides relative to their concentration in bulk seawater. It has been shown that the actinides in spray are derived predominantly from sediment suspended in seawater in the surf zone, and enrichment factors of 3 to 50 for plutonium and americium in spray relative to unfiltered seawater have been observed. It has also been shown that the intertidal zone is a relatively insignificant source of airborne actinides. The transport and vertical distribution of actinides and seaspray has been determined at heights of up to 10 m above the beach and as far as 9 km inland. These measurements indicate that, in addition to the surf zone, a small but significant source of less enriched spray is present further out to sea, and possible mechanisms are discussed. It is estimated that about 2 Ci of 239+240Pu may have been transferred from the sea to land by seaspray during the last 15 years. The greatest concentration of 239+240Pu detected in air was 22 fCi m −3 and it is concluded that it is improbable that any member of the public would have been exposed to more than 1% of the ICRP dose limit.

Einfluss der brennstoffporösität und der brennstabparameter auf die radiale Uran-Plutonium-Entmischung in Reaktorbrennstäben

In fast breeder fuel pins a radial redistribution of the initially homogeneously distributed fuel components is observed. Since this effect can result in considerable fuel temperature rises, it must be calculable with respect to a safe fuel pin design. Experimental and theoretical results indicate that thermodiffusion and possibly pore migration are the mechanisms responsible for actinide transport. A theoretical model already exists for the redistribution effect of thermodiffusion, a model for the pore migration effect is given in the present paper. Superposition of the two models yields predictions about the influence of the fuel pin parameters on the radial U-Pu-redistribution, which is to be expected during the irradiation. On the other hand, the actinide redistribution can be controlled by a suitable choice of fuel pin parameters. The most important ones are the fuel stoichiometry, the fuel porosity and the linear pin power. The parameter combinations resulting in negligible redistribution effects are given.