Clays in Natural & Engineered Barriers for Radioactive Waste Confinement Montpellier October 21- 25, 2012 ©ANDRA – C.TR.ASTR.12-0065/A Behaviour of nitrate present in nuclear waste and impact on repository chemistry and safety A. Albrecht 1 , A. Bertron 2 , G. Berger 3 , N. Bleyen 4 , P. De Cannière 5 , B. Erable 6 , M. Libert 7 , H. Pauwels 8 , I. Pointeau 7 , C. Sergeant 9 , J. Small 10 , L. Truche 11 , E. Valcke 4 References Albrecht, A., Bertron, A. and Libert, M., 2012. Microbial catalysis of redox reactions in concrete cells of nuclear waste repositories: a review and introduction. In: F. Bert, C. Cau-dit-Coumes, F. Frizon and S. Lorette (Editors), Cement-based materials for nuclear waste storage. Springer, Berlin, pp. 147-159. Alquier, M., Jacquemet, N., Bertron, A., Erable, B., Sablayrolles, C., Albasi, C., Basseguy, R., Escadeillas, G., Strehaiano, P. and Vignoles, M., 2012. Etudes expérimentales de la réactivité des nitrates à l’interface bitume – eau cimentaire – ciment en conditions biotiques; Final Report. Report number: en vérification, LGC - LMDC - LCA, Université de Toulouse. Istok, J.D., Senko, J.M., Krumholz, L.R., Watson, D., Bogle, M.A., Peacock, A., Chang, Y.-J. and White, D.C., 2004. In Situ Bioreduction of Technetium and Uranium in a Nitrate-Contaminated Aquifer. Environ. Sci. Technol., 38(2): 468–475. Li, X. and Krumholz, L.R., 2008. Influence of Nitrate on Microbial Reduction of Pertechnetate. Environ. Sci. Technol., 42(6): 1910–1915. Miquel, S. and Basso, M., 2010. Considération d'une fluctuation du niveau de la nappe dans le modèle sol multicouche : Applications au Programme Scientifique FAVL-Radifère; Rapport final. Report number: F.RP.FSTR.10.0017.A, Société de Calcul Mathématique, S.A., Paris. Moors, H., Geissler, A., Boven, P., Selenska-Pobell, S. and Leys, N., 2012. BN Experiment: Intermediate results of the microbiolgical analyses; Technical Note. Report number: 2011-39, SCK•CEN and HZDR, Mol and Dresden. Nikitenko, S.I., Venault, L., Pflieger, R., Chave, T., Bisel, I. and Moisy, P., 2010. Potential applications of sonochemistry in spent nuclear fuel reprocessing: A short review. Ultrasonics Sonochemistry, 17(6): 1033-1040. Ollivier, P., Joulian, C., Parmentier, M., Crouzet, C. and Pauwels, H., 2011. Approche couplée des processus biologiques et géochimiques de la réduction des nitrates dans les argilites du Callovo-Oxfordien - Processus de dénitrification en milieux simples; Rapport final. Report number: RP-60105-FR / DRPFSTR120010A, BRGM, Orléans. Oremland, R.S., Blum, J.S., Bindi, A.B., Dowdle, P.R., Herbel, M. and Stolz, J.F., 1999. Simultaneous Reduction of Nitrate and Selenate by Cell Suspensions of Selenium-Respiring Bacteria. Appl. Environ. Microbiol., 65: 4385-4392. 1 Andra Châtenay-Malabry F, 2 LMDC Toulouse F, 3 IRAP Toulouse F, 4 SCK•CEN Mol B, 5 FANC Brussels B, 6 ENSIACET-LGC/LCA Toulouse F, 7 CEA Cadarache F, 8 BRGM Orléans F, 9 CENBG Bordeaux F, 10 NNL Warrington UK, 11 G2R Nancy F (I) Nitrate concentration, reactivity and performance assessment THIS STUDY: Nitrate reactivity and concen- tration in time and space FINAL OUTPUT: Solubility (C sat ) and sorption (Kd) of radionuclides (RN) SAFETY CALCULATIONS / PERFORMANCE ASSESSMENT INPUT: Industrial use of nitrate, i.e. the nuclear fuel cycle → nitrate in nuclear waste (II) The system: a clay-rich host rock with a concrete engineered barrier and metal waste containers From a complex geometry... e.g. an Andra waste cell for intermediate activity – long lived waste ...to a simpler representation Generic waste cell applicable for any repository in clay-rocks Concrete bloc Concrete plug Biological protection Concrete plug Clay seal Storage cell Concrete plug Clay groove Concrete plug Gallery O 2 O 2 O 2 Host rock EB Waste container After closure: Low degree of saturation, some free oxygen After partial re- saturation and breeching of waste container: bathtub effect with dissolved NO 3 - present NO 3 - NO 3 - SO 4 2- SO 4 2- EDZ CDZ unaffected, saturated stainless steel C-steel -8 -4 0 4 8 12 pe°(W) O 2 /O 2- NO 3 - /N 2 NO 3 - /NO 2 - MnO 2 /MnCO 3 SO 4 2- /HS - FeOOH/FeCO 3 CO 2 /CH 4 SeO 4 2- /H 2 SeO 3 UO 2 2+ /U 4+ H + /H 2 NO 2 - /NH 4 + TcO 4 2- /TcO 2 ??? (III) Evolution in time (hydrology, redox potential, RN speciation) 0.01 0.1 1 10 100 nitrate (mM) Tc(VII) reduction inhibited * U(VI) reduction inhibited ** *Li & Krumholz, 2008; ** Istok et al., 2004 *** Senko et al., 2002; ****Oreland et al. 1999 Little impact on Tc(VII) reduction * U(VI) reduction inhibited **,*** Se(VI) reduction inhibited **** ...with a likely evolution in time Enhanced saturation and return to the natural redox potential of the clay rock Albrecht et al., 2012 oxidising reducing Host rock (i.e. COx) Concrete NO 3 - O 2 SO 4 2- ...and the crucial impact of nitrate on RN speciation Need to quantify the reactivity and the evolution of nitrate in space and time? (IV) Summary of experimental results All experimental results confirm the need of catalysis of the nitrate reduction, regardless of the type of electron donor (H 2 or organic acids); a clear distinction has been observed between surface catalysis, mostly producing ammonium (i.e. Truche et al., 2012, and this symposium) and microbial catalysis forming essentially N 2 or denitrification intermediates depending on the pH of the medium (concrete or clay-rich rock) or the type of microbes present, individual species (Ollivier et al., 2011; Pauwels et al., this symposium; Alquier et al., 2012) or naturally occurring / contamination consortia (Bleyen et al., this symposium, Sergeant et al. 2009). 150°C pH 2 =7.5 bar no H 2 added filings powder pH ini =7; carbon steel sterile Ollivier et al., 2011 Truche and Berger, 2912; Truche et al., 2012 Time (days) Time (hours) with crushed COx no COx (idem 90, 122, 150 et 182°C) no H 2 formation of NH 4 + in all cases of reactivity pH ini 7-8 Surface catalysis with H 2 as electron donor Carbon steel can act both as a catalyser as well as a carbon donor if its surface is highly reactive (i.e. powdered); in the presence of H 2 it readily acts as a catalyser regardless of its surface characteristics Microbial catalysis with acetate as electron donor: (1) at the waste – concrete interface no H 2 added Carbon steel filings cannot act as a catalyser if no additional electron donor is added Carbon steel can act as a catalyser even at low temperatures in the presence and absence of clay rock (i.e. COx), but not in a concrete environment In the absence of surface catalysis and in case of metabolic inhibition of microbial activity (i.e. initial pH 9 for Ps or pH 11 for Hd) nitrate does not react. pH 2 =7 bar with crushed cement ⇒ reactivity pH ini 12-13 Stainless steel can act as a catalyser and an electron source even at low temperatures at high pH (i.e. presence of concrete); in the presence of clay rock (neutral pH) it does neither serve as a catalyst not as an electron donor carbon steel stainless steel Halomonas desidera, Hd Pseudomonas stutzeri , Ps If metabolic activity is not inhibited, nitrate reduction is rapid and complete depending on the presence of the electron donor. The pH of the reaction is influenced by the reduction of nitrate and the oxidation of acetate; in the case of incomplete reduction to nitrite, the pH drops, in the case of complete reduction the pH increases. It is likely that microbes can influence the pH by influencing reaction kinetics. In a sterile solution containing acetate as an electron donor, nitrate does not react, and the nitrite concentration remains 0. In the presence of the single microbial species, Pm, nitrate reduction is measurable, but slow ; nitrite reduction is even slower. Pseudomonas mandellii, Pm First results form the Bitumen – Nitrate – Clay Interaction in situ underground rock laboratory experiments (BN – Mont Terri) are more complex in their interpretation because surface and microbial reduction may coexist and because of naturally occurring / contamination consortia (see Bleyen et al this symposium). From microbiological analysis of samples from URL’s to in situ nitrate reduction experiments e.g. at the Bure site: from sampling and observation... to DNA sequencing and characterisation Hymerobacter riigui Pseudomonas stutzeri Didymella exigua Sergeant et al., 2009 see also: Moors et al., 2011; Schwyn et al., Moors et al., both this symposium (2) in a clay-rock (COx) setting Alquier et al., 2012 (V) Synthesis of results and integration into transfer / reactivity simulations All experimental results can be used to quantify reaction kinetics for nitrate reduction (λ of a 1 st order reaction). Many codes allow coupling of transport and (radioactive /) chemical decay. A code used at Andra (SAMM, Miquel and Basso, 2010) can be used as an illustration clay rock (COx) 10000 years of release The nitrate concentration at any point in space and time can be used for RN speciation assessment 4M mol/kg λ=0.0008 /yr; T½=866 yrs z=7 concrete distance to waste canister (m) time (years) For more comprehensive modelling approaches see Small et al. and Pointeau et al., both this symposium and Small and Abrahamsen, 2012 (VI) The use of nitrate concentration to assess RN speciation – Future research (1) The impact of various nitrate concentrations on RN speciation has already been studied for neutral pH, natural settings (see III). A detailed analysis of this type of work is required, in particular in view of possible regular behaviour. To test the nitrate impact on RN speciation in near-field settings in situ experiments with nitrate and RN (or stable analogues) will have to be carried out ( i.e. selenium – nitrate planned at Mont Terri BN). (2) Microbial activity and surface catalysis also control RN redox kinetics; it will be necessary to find a way to evaluate their mutual impact, to allow a better phenomenological understanding and applied simulations. (3) It will be necessary to gain a better understanding of the above reactivity/ catalysis of both nitrate and RN in various concrete settings (fresh vs. fully carbonated) at different initial nitrate concentrations (mM to M). Nikitenko et al. 2010) Senko, J.M., Istok, J.D., Suflita, J.M. and Krumholz, L.R., 2002. In-Situ Evidence for Uranium Immobilization and Remobilization. Environ. Sci. Technol., 36(7): 1491–1496. Sergeant, C., Vesvres, M.-H., Nèble, S., Barsotti, V., Poulain, S., Hadi, J. and Marrec, C.L., 2009. Caractérisation microbiologique à l’état zéro des argilites du site de Meuse/Haute-Marne (souches autochtones) et de souches allochtones isolées des milieux argileux; Rapport FORPRO. Report number, CNRS - GDR FORPRO, Bordeaux. Small, J. and Abrahamsen, L., 2012. BN Experiment: Biogeochemical modelling of the 2nd nitrate injection in Interval 2; Mont Terri Technical Note. Report number: 2012-95, National Nuclear Laboratory, Warrington. Truche, L. and Berger, G., 2012. Effet catalytique des aciers et produits de corrosion sur la réduction abiotique des nitrates et sulfates par H 2 en condition de stockage MAVL; Rapport final. Report number: CRPFSTR120027, GR2 - IRAP, Nancy - Toulouse. Truche, L., Berger, G., Albrecht, A. and Domergue, L., 2012. Abiotic nitrate reduction induced by carbon steel and hydrogen: Implications for environmental processes in waste repositories. Appl.Geochem., in press. After more complete re- saturation and disappearance of NO 3 - , sulphate (carbonate) may become the dominant electron acceptor see also companion presentations The Log scale is indicative for the large natural variation in nitrate, which is likely more remarkable in the waste cells View publication stats View publication stats