Molecular dynamics simulations have been performed to investigate the structural and dynamical properties of the second hydration shell of Th4+ ion at various chloride concentrations and temperatures. When the concentration increases (ca. 5 M), the hydration of Th4+ ion involves the displacement of the water molecules by Cl- ligand and slightly decreases the total coordination number. The residence time of water molecules in the second hydration shell decreases as a function of increasing solution temperature. (C) 2002 Elsevier Science B.V. All rights reserved.