Structural and Crystallization Study of a Simplified Aluminoborosilicate Nuclear Glass Containing Rare-Earths: Effect of
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1265-AA03-02
Structural and Crystallization Study of a Simplified Aluminoborosilicate Nuclear Glass Containing Rare-Earths: Effect of ZrO2 Concentration. Daniel Caurant1, Arnaud Quintas1,2, Odile Majérus1, Pascal Loiseau1, Thibault Charpentier3, P. Vermaut4 and Jean-Luc Dussossoy2 1 Laboratoire de Chimie de la Matière Condensée de Paris (UMR-CNRS 7574), ENSCP (ChimieParisTech), 11 rue Pierre et Marie Curie, 75005 Paris, France 2 CEA, DEN, DTCD, SECM, Laboratoire d’Etude et Développement des Matrices de Conditionnement, Marcoule, 30207 Bagnols-sur-Cèze, France 3 CEA, IRAMIS, Service Interdisciplinaire sur les Systèmes Moléculaires et Matériaux, CEA CNRS UMR 3299, Saclay, 91191 Gif-sur-Yvette, France 4 Laboratoire de Métallurgie Structurale (UMR-CNRS 7045), ENSCP, 75005 Paris, France ABSTRACT Zirconium is an abundant element in nuclear wastes. In this paper, we present structural and crystallization results for a simplified glass composition belonging to the SiO2-Al2O3-B2O3Na2O-CaO-ZrO2-RE2O3 system (RE = Nd or La) developed to immobilize highly concentrated waste solutions. The effect of varying ZrO2 content on the structure and the crystallization tendency of this glass was studied using a multi-spectroscopic approach. Zr was shown to be located in six-fold coordinated sites with preferential charge compensation by Na+ cations. Whereas a significant decrease of the proportion of BO4 units was observed with ZrO2 content, no effect was detected on the environment of AlO4 units. However, a significant structural evolution of the silicate network occurred due to the formation of Si-O-Zr bonds. Whatever ZrO2 concentration, the crystallization of only a rare earth silicate apatite phase was observed during either slow cooling from the melt or isothermal heat treatment. Whereas nucleation mainly occurred from the surface of the glass without ZrO2, the introduction of zirconium induced apatite crystallization in the bulk. It is proposed that this nucleating effect of ZrO2 is mainly due to changes induced in the neighborhood of Nd3+ cations in glass structure. INTRODUCTION ZrO2 is present in borosilicate glasses used to immobilize highly radioactive nuclear wastes arising from the reprocessing of spent nuclear fuels. Zirconium may originate both from the highly radioactive waste solutions (as fission product and as zirconium alloy cladding material used to enclose fuel in reactors) and from the glass frit added to the wastes for glass preparation. In order to reduce the volume of nuclear glass needed to immobilize radioactive wastes, new glass compositions able to immobilize higher concentrations of wastes than today are under development [1]. For instance, RE(rare earth)-rich aluminoborosilicate glasses are envisaged for the immobilization of the highly concentrated waste solutions that would arise from the reprocessing of high burn-up UO2 spent fuels [2]. In previous works, we investigated the effect of composition changes on the structure and thermal stability of a simplified 7-oxides version of such a glass (glass Zr1RE
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