Enhancement of Zirconolite Dissolution Due to Water Radiolysis
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0985-NN09-04
Enhancement of Zirconolite Dissolution Due to Water Radiolysis Magaly Tribet1, Nelly Toulhoat1,2, Nathalie Moncoffre1, Pierre Toulhoat3, Christophe Jegou4, Catherine Corbel5, Isabelle Bardez4, and Gilles Leturcq6 1 CNRS/Universite Claude Bernard Lyon 1, Institut de Physique Nucleaire de Lyon, 4 rue Enrico Fermi, Villeurbanne, 69622, France 2 Commissariat ‡ l'Energie Atomique, DEN, CEN Saclay, Gif sur Yvette cedex, 91191, France 3 CNRS/ISA Universite Claude Bernard Lyon 1, UFR de Chimie Biochimie, Villeurbanne, 69622, France 4 Commissariat ‡ l'Energie Atomique, DEN/DTCD/SECM, CEN Valrho, Bagnols sur Ceze cedex, 30207, France 5 Commissariat ‡ l'Energie Atomique, DSM/DRECAM/LSI, Ecole Polytechnique, palaiseau, 91128, France 6 Commissariat ‡ l'Energie Atomique, DEN/DRCP/SCPS, CEN Valrho, Bagnols sur Ceze cedex, 30207, France ABSTRACT Zirconolite is a candidate host material for conditioning minor tri- and tetra-valent actinides arising from enhanced nuclear spent fuel reprocessing and partitioning, in the case of disposal of the nuclear waste. Its chemical durability has been studied here under charged particle-induced radiolysis (He2 + and proton external beams) to identify the possible effects of water radiolysis on the dissolution rates in pure water and to describe the alteration mechanisms. Two experimental geometries have been used in order to evaluate the influence of the following parameters: solid irradiation, water radiolysis. In the first geometry the beam gets through the sample before stopping at the surface/water interface. In the second one the beam stops before the surface/water interface. Results on the elemental releases due to the enhanced dissolution of the zirconolite surface during charged particle-induced irradiation of water are presented. Under radiolysis, an increase of one order of magnitude is observed in the Ti, Zr and Nd elemental releases. No difference in the total elemental releases can be noticed when the solid is also irradiated. INTRODUCTION Natural groundwater is believed to act as the principal vector for the transport of radioactive elements from a nuclear waste geological repository. Minor actinides resulting from enhanced reprocessing of the spent fuel could be contained in a specific matrix, having a good stability over geologic periods of time. Zirconolite has been proposed for the incorporation of tri- and tetra-valent actinides because of its very high chemical durability [1-3]. The dissolution of both natural and synthetic zirconolites has been studied by several authors over the last fifteen years [4-6]. The aqueous-alteration is rapidly stopped by the formation at the interface of a very thin, insoluble, decalcified film. This passivation layer protects the surface from further alteration [5]. Concerning irradiation effects, leaching experiments performed on fully metamict natural Th-enriched zirconolite as well as leaching experiments performed on synthetic ceramics irradiated by external heavy-ion beams show that the chemical durability is not fundamentally
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