EXTERNAL REPORT SCK•CEN-ER-120 10/PDC/P-9 Behaviour of Selenium in Boom Clay Pierre De Cannière1, André Maes2, Steve Williams3, Christophe Bruggeman2, Thomas Beauwens1, Norbert Maes1, and Mark Cowper3 1 SCK•CEN 2 KULeuven 3 AEA Technology SCK•CEN ref: CO 90 01 1467.01 1467 RP.W&D.037 NIROND ref: CCHO2004/00/00 DS251-A44/2.1 May, 2010 SCK•CEN RDD Boeretang 200 BE-2400 Mol Belgium EXTERNAL REPORT OF THE BELGIAN NUCLEAR RESEARCH CENTRE SCK•CEN-ER-120 10/PDC/P-9 Behaviour of Selenium in Boom Clay Pierre De Cannière1, André Maes2, Steve Williams3, Christophe Bruggeman2, Thomas Beauwens1, Norbert Maes1, and Mark Cowper3 1 SCK•CEN 2 KULeuven 3 AEA Technology SCK•CEN ref: CO 90 01 1467.01 1467 RP.W&D.037 NIROND ref: CCHO2004/00/00 DS251- A44/2.1 May, 2010 Status: Unclassified ISSN 1782-2335 SCK•CEN Boeretang 200 BE-2400 Mol Belgium This report can be cited as follows: De Cannière P., Maes A., Williams S., Bruggeman C., Beauwens T., Maes N., and Cowper M. (2010) Behaviour of selenium in Boom Clay. Work performed under contract: SCK•CEN ref: CO 90 01 1467.01 1467 RP.W&D.037 – NIROND ref: CCHO2004/00/00 DS251-A44/2.1. External Report of the Belgian Nuclear Research Centre, SCK•CEN-ER-120. May 2010. PDF file available at: http://publications.sckcen.be/dspace/ http://publications.sckcen.be/dspace/simple-search © SCK•CEN Studiecentrum voor Kernenergie Centre d’étude de l’énergie Nucléaire Boeretang 200 BE-2400 Mol Belgium Phone +32 14 33 21 11 Fax +32 14 31 50 21 http://www.sckcen.be Contact: Knowledge Centre [email protected] RESTRICTED All property rights and copyright are reserved. Any communication or reproduction of this document, and any communication or use of its content without explicit authorization is prohibited. Any infringement to this rule is illegal and entitles to claim damages from the infringer, without prejudice to any other right in case of granting a patent or registration in the field of intellectual property. SCK•CEN, Studiecentrum voor Kernenergie/Centre d'Etude de l'Energie Nucléaire Stichting van Openbaar Nut – Fondation d'Utilité Publique - Foundation of Public Utility Registered Office: Avenue Herrmann Debroux 40 – BE-1160 BRUSSEL Operational Office: Boeretang 200 – BE-2400 MOL 5/328 6/328 Table of Contents Executive Summary .................................................................................................................................................11 Foreword ............................................................................................................................................................11 Summary ............................................................................................................................................................11 Redox disequilibrium..............................................................................................................................12 79 Unknown initial speciation of Se in the source term............................................................................13 79 Migration parameters selected for Se...................................................................................................13 Abstract.....................................................................................................................................................................17 1. Introduction......................................................................................................................................................21 1.1. Background.............................................................................................................................................21 1.2. Objective.................................................................................................................................................22 1.3. Main uncertainties and research strategy ................................................................................................22 1.3.1 Complexity and uncertainties affecting the experiments with selenium ..................................23 1.3.2 Objectives and research strategy ..............................................................................................24 2. Thermodynamic calculations – AEAT ...........................................................................................................29 2.1. Overview.................................................................................................................................................29 2.2. Applied geochemical codes and reference database – AEAT.................................................................29 2.3. In situ Boom Clay conditions – AEAT...................................................................................................29 2.4. Expected speciation of selenium under Boom Clay conditions – AEAT................................................30 2.5. Calculated thermodynamical solubility of selenium under Boom Clay conditions – AEAT..................32 3. Geochemical behaviour of selenium in Boom Clay .......................................................................................37 3.1. Introduction.............................................................................................................................................37 3.2. Sorption of selenium on Boom Clay and its components .......................................................................37 3.3. Kinetics of reduction of selenite .............................................................................................................41 3.4. Solubility of selenium compounds under reducing conditions ...............................................................42 3.5. Association of selenium with Boom Clay organic matter.......................................................................43 3.6. Conclusions.............................................................................................................................................45 4. Determination of migration parameters of selenium in Boom Clay............................................................49 4.1. Introduction.............................................................................................................................................49 4.2. Experimental...........................................................................................................................................50 4.3. Results.....................................................................................................................................................51 4.4. Discussion...............................................................................................................................................54 4.4.1 Pore diffusion coefficient (Dp) .................................................................................................56 4.4.2 Porosity (η) ..............................................................................................................................56 4.4.3 Sorption – retardation (R) ........................................................................................................57 4.5. Conclusion ..............................................................................................................................................58 4.5.1 Summary of the migration parameters for 79Se in Boom Clay.................................................59 5. Summary and conclusions...............................................................................................................................63 5.1. Overview.................................................................................................................................................63 5.2. Key uncertainties and abstraction for performance assessment..............................................................64 5.3. Summary of the transport parameters for the selenium species considered............................................68 7/328 5.4. Recommendations and future works.......................................................................................................71 6. Acknowledgments ............................................................................................................................................75 7. References.........................................................................................................................................................79 APPENDICES..........................................................................................................................................................149 A1 General information on selenium ...................................................................................................................153 A1.1 Overview.................................................................................................................................................153 A1.2 Inventory and isotopic composition........................................................................................................153 A1.3 Uncertainties related to the value of selenium-79 half-life and recent changes......................................154 79 75 A1.4 Nuclear decay mode of Se and Se......................................................................................................157 A1.5 Selenium inorganic and organic chemistry .............................................................................................157