Leaching and migration of Np, Pu, and Am from a-doped SON68 HLW glass in contact with dense clay
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Leaching and migration of Np, Pu, and Am from α-doped SON68 HLW glass in contact with dense clay Elie Valcke1, Mireille Gysemans1, Hugo Moors1, Pierre Van Iseghem1, Nicole Godon2, and Patrick Jollivet2 1 SCK•CEN, Boeretang 200, 2400 Mol, Belgium 2 CEA Valrhô, B.P. 17171, 30207 Bagnols-sur-Cèze, France ABSTRACT In the frame of an integrated in situ test on the alteration of the SON68 reference glass in realistic disposal conditions, the leaching of Np, Pu, and Am from α-doped SON68 glass samples and their migration in three clay-based backfill materials at high density was measured. The addition of powdered glass frit to a Ca-bentonite decreased the glass alteration by two orders of magnitude, and resulted in a concomitant decrease of the radionuclide leaching in comparison with dried Boom Clay, which is the more agressive backfill. All actinides were selectively retained in the alteration layer, but the retention degree was lower for Np than for Pu and Am. All backfill materials proved to be efficient barriers against radionuclide migration. For nearly all radionuclides and backfill materials, the migration profile showed a contribution of colloidal transport. INTRODUCTION As part of the studies on the long-term performance of the French R7T7 HLW glass in an underground repository in the Boom Clay, we have designed and operated during the last 10 years the CORALUS tests (CORrosion of alpha-Active gLass in Underground Storage). These are integrated in situ tests on the alteration of the SON68 reference glass1 in conditions that are representative for those expected to prevail in a disposal system with a clay-based backfill [1-3]. One of the objectives is to measure the leaching of the incorporated radionuclides from the αdoped SON68 glass, and their migration in the contacting compacted clays. The results are reported in this paper. The results on glass and clay alteration are discussed elsewhere in this volume [1]. EXPERIMENTAL ASPECTS The CORALUS in situ tests For a good understanding of the results, the CORALUS experiment is briefly summarised. A more detailed description is given in another publication in this volume [1]. 1
SON 68 is the abbreviation of SON 68 18 17 L1C2A2Z1, a reference glass with a composition simulating the nominal composition of the COGEMA R7T7 glass that is used for the vitrification of high-level and long-lived radioactive waste. Its main constituents are (wt%) 45.5 SiO2, 4.9 Al2O3, 14.0 B2O3, 11.8 Na2O + Li2O, 4.0 CaO, 2.9 Fe2O3, 2.65 ZrO2, 2.5 ZnO, 9.65 fission product oxides, 0.85 actinide oxides, 2.25 other elements.
The CORALUS in situ tests comprise four modular test tubes, placed in the Boom Clay through the underground research facility (URF) HADES (Mol, Belgium), for durations up to 10 years. Each tube consists of three modules. In each module, inactive and α-doped SON 68 glass samples, placed on an inner support tube, are in contact with a backfill exerting a design swelling pressure of 2 MPa. Built-in piezometers allow to sample interstitial solution. Within the inner support
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