UNCORRECTED PROOF 1 2 Behavior of thorium–uranium(IV) phosphate–diphosphate 3 sintered samples during leaching tests. 4 Part II. Saturation processes 5 N. Clavier a , E. du Fou de Kerdaniel a , N. Dacheux a, * , P. Le Coustumer b , 6 R. Drot a , J. Ravaux c , E. Simoni a 7 a Groupe de Radiochimie, Institut de Physique Nucle ´aire, Ba ˆt.100, Universite ´ Paris-Sud-11, 91406 Orsay, France 8 b CDGA, Universite ´ de Bordeaux I, BP 19, Avenue des faculte ´s, 33405 Talence, France 9 c LCSM, Universite ´ H. Poincare ´ – Nancy I, BP 239, 54506 Vandoeuvre le `s Nancy, France 10 Accepted 18 November 2005 11 12 Abstract 13 Sintered pellets of thorium-uranium(IV) phosphate–diphosphate solid solutions (b-Th 4x U x (PO 4 ) 4 P 2 O 7 , b-TUPD) 14 were altered in several acidic media. All the results reported in the first part of this paper confirmed the good chemical 15 durability of the samples. The evolution of the normalized weight loss showed that, in several media, thorium quickly pre- 16 cipitates in a neoformed phosphate-based phase while uranium(IV) is released in the leachate due to its oxidation into the 17 uranyl form. The characterization of neoformed phases was carried out through several techniques involving grazing 18 XRD, infrared and l-Raman spectroscopies, EPMA, SEM and TEM. SEM micrographies showed that the dissolution 19 mainly occurs at the grain boundaries, leading to the break away of the grains: only the first 15 lm are altered for 2 months 20 in 10 1 M HNO 3 . From EPMA and BET measurements, neither the chemical composition nor the specific surface area are 21 significantly modified. Near to equilibrium, two neoformed phases were observed and identified by grazing XRD and/or 22 l-Raman spectroscopy at the surface of the leached pellets: one is found to be amorphous and progressively turns into the 23 crystallized thorium phosphate–hydrogen phosphate hydrate (TPHPH). From the results obtained, a chemical scheme of 24 the dissolution of b-TUPD sintered samples is proposed. The behavior of the actinides in the gelatinous phase appears 25 mainly driven by their oxidation state: thorium remains in the tetrapositive state and is quickly and quantitatively precip- 26 itated while uranium(IV) is oxidized into uranyl then released in the leachate. The Th-precipitation as TPHPH first appears 27 scattered then covers the entire surface of the pellet, inducing a delay of the actinides release in the leachate. Both phases 28 act as protective layers and should induce the significant delay of the release of actinides (Th, U) to the biosphere. 29 Ó 2005 Published by Elsevier B.V. 30 IDT: C0300; C0800; R0900; T0700; S1300; U0200; W0100 31 32 1. Introduction 33 Several phosphate materials such as apatites 34 (Ca 10 (PO 4 ) 6 F 2 ) [1,2], monazites (LnPO 4 ) and associ- 0022-3115/$ - see front matter Ó 2005 Published by Elsevier B.V. doi:10.1016/j.jnucmat.2005.11.010 q DOI of original article: 10.1016/j.jnucmat.2005.11.009 * Corresponding author. Tel.: +33 1 69 15 73 46; fax: +33 1 69 15 71 50. E-mail address: dacheux@ipno.in2p3.fr (N. Dacheux). Journal of Nuclear Materials xxx (2005) xxx–xxx www.elsevier.com/locate/jnucmat NUMA 41954 No. of Pages 13, Model 3+ 21 December 2005 Disk Used ARTICLE IN PRESS