Experimental and modelling study of artificial radionuclides (²³⁹Pu, ²⁴¹Am and ⁹⁹Tc) uptake by suspended matter in environmental waters located in the south of Spain

¹ Departamento de Fisica Atomica, Molecular y Nuclear, Facultad de Fisica, University of Seville, Apdo., 41060 Sevilla, Spain
² Departamento de Fisica Aplicada 1, University of Seville, EUITA, Carretera de Utrera km 1, 41013 Sevilla, Spain
³ Departamento de Fisica Aplicada 2, University of Seville, ETSA, Avda. Reina Mercedes s/n, 41012 Sevilla, Spain

Abstract

The interest on transfer coefficients studies have increased recently, since they are important parameters required understanding and reliably modelling the dispersion of conservative and non-conservative radionuclides in aquatic environments. The approaches, based in the implementation of the uptake kinetics of dissolved radionuclides by solid particles, are more appropriate than those based in the use of the distribution coefficients, k_d. In this work, we present a series of tracing experiments to study the uptake of Pu, Am and Tc in natural aqueous suspensions from three aquatic systems (Gergal reservoir, Guadalquivir river, and the estuary of Tinto river) located in the South of Spain. The kinetic transfer coefficient for direct sorption depends on the total available surface of particles and on the concentration of active sites in the surface layer (what depends on the mineral composition, free edges, pores, coatings, etc.). In order to compare results from different environments and to fix the conditions of applicability of the derived coefficients, it is necessary to handle the particle size spectra and the mineral composition of natural occurring suspended loads. The time dependent uptake curves, covering up to a large period, are fitted to the numerical solutions calculated with different models of the uptake kinetics.