Reductive immobilization of 79 Se by iron canister under simulated repository environment D. Cui Æ A. Puranen Æ J. Devoy Æ A. Scheidegger Æ O. X. Leupin Æ P. Wersin Æ R. Gens Æ K. Spahiu Received: 15 July 2009 / Published online: 12 August 2009 Ó Akade ´miai Kiado ´, Budapest, Hungary 2009 Abstract To understand the fate of 79 Se in a repository- like environment, the interactions between iron canister surface with dissolved selenite (SeO 3 2- ) and selenate (SeO 4 2- ) in anaerobic solutions have been investigated. Se(IV) immobilization on iron surface was observed to be about 100 times faster than that of Se(VI) at same conditions. An iron surface coated with a FeCO 3 layer corrosion product is more reactive than a polished iron to immobilize Se(IV) and Se(VI). The reacted iron surfaces were analysed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Raman spectrometry and micro-X-ray Absorption Spectroscopy (XAS). The result show that Se(IV) and Se(VI) were reduced and precipitated. The dominating phase was found to be FeSe 2. Keywords Reductive immobilization  Selenium  Iron canister  Nuclear waste  Repository Introduction For safety assessments for nuclear waste repositories, it is conservatively assumed that groundwater will enter through the engineered barrier system within a timeframe of [ 1,000 years [1]. After the canister have breached radionuclides will released from spent fuel and vitrified nuclear waste into groundwater. Among them, the fission product 79 Se (t 1/2 = 2.95 9 10 5 years) is one of important dose contributors due to its long half-life and high mobility of its oxidized anions SeO 3 2- and SeO 4 2- . Se(VI), Se(IV), Se(0) and Se(-I) (as FeSe 2 ) are more commonly observed in nature than Se(-II) (as FeSe). Se(0) and FeSe 2 are stable, poorly soluble and relatively resistant to re-oxidation [2]. Fe(II) and Fe(0) mediated redox reactions of Se, and the rate limiting steps have been examined using in situ X-ray absorption near-edge structure (XANES) [3]. It was shown that the reduction of Se(VI) in the presence of Fe(II) aq occurs in two steps, with rapid initial adsorption and conversion of Se(VI) to Se(IV) followed by a slow reduction of Se(IV) to Se(0). The rate of this reaction depends on both Fe(II) aq concentration and pH. At pH [ 5, Fe(II) and Fe(III) pre- cipitate as minerals such as green rust Fe II 4 Fe III 2 OH ð Þ 12 À CO 3 Þ, which can be more reductive than Fe(II) aq [4]. Se(VI) in a solution containing Cl - , SO 4 2- , NO 3 - , HCO 3 - , and PO 4 3- in a capped vessel was found to be rapidly reduced by Fe(0) to Se(-II) [5]. In another investigation [6], a rapid D. Cui (&) Studsvik Nuclear AB, 61182 Nykoping, Sweden e-mail: daqing.cui@studsvik.se D. Cui Department of Physical, Inorganic and Structural Chemistry, Stockholm University, 10691 Stockholm, Sweden A. Puranen Department of Chemistry, Royal Institute of Technology, 10044 Stockholm, Sweden J. Devoy IRSN/DPAM/SERCI/LE2C, 13115 Saint Paul-lez-Durance Cedex, France A. Scheidegger Paul Scherrer Institut, 5232 Villigen PSI, Switzerland O. X. Leupin  P. Wersin NAGRA, Hardstrasse 73, 5430 Wettingen, Switzerland R. Gens ONDRAF/NIRAS, 1210 Bruxelles, Belgium K. Spahiu SKB, 10240 Stockholm, Sweden 123 J Radioanal Nucl Chem (2009) 282:349–354 DOI 10.1007/s10967-009-0328-8