Radioactive Waste Management and Decommissioning 2018 Microbial Influence Microbial Influence on the Performance of Subsurface, Salt-Based Radioactive Waste Repositories Salt-Based Radioactive Waste of Subsurface, Microbial Influence on the Performance on the Performance of Subsurface, Salt-Based Radioactive Waste Repositories An Evaluation Based on Microbial Ecology, Bioenergetics and Projected Repository Conditions Radioactive Waste Management and Decommissioning Microbial Influence on the Performance of Subsurface, Salt-Based Radioactive Waste Repositories An Evaluation Based on Microbial Ecology, Bioenergetics and Projected Repository Conditions © OECD 2018 NEA No. 7387 NUCLEAR ENERGY AGENCY ORGANISATION FOR ECONOMIC CO-OPERATION AND DEVELOPMENT ORGANISATION FOR ECONOMIC CO-OPERATION AND DEVELOPMENT The OECD is a unique forum where the governments of 35 democracies work together to address the economic, social and environmental challenges of globalisation. The OECD is also at the forefront of efforts to understand and to help governments respond to new developments and concerns, such as corporate governance, the information economy and the challenges of an ageing population. The Organisation provides a setting where governments can compare policy experiences, seek answers to common problems, identify good practice and work to co-ordinate domestic and international policies. The OECD member countries are: Australia, Austria, Belgium, Canada, Chile, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Israel, Italy, Japan, Korea, Latvia, Luxembourg, Mexico, Netherlands, New Zealand, Norway, Poland, Portugal, Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Turkey, the United Kingdom and the United States. The European Commission takes part in the work of the OECD. OECD Publishing disseminates widely the results of the Organisation’s statistics gathering and research on economic, social and environmental issues, as well as the conventions, guidelines and standards agreed by its members. This work is published on the responsibility of the OECD Secretary-General. NUCLEAR ENERGY AGENCY The OECD Nuclear Energy Agency (NEA) was established on 1 February 1958. Current NEA membership consists of 33 countries: Argentina, Australia, Austria, Belgium, Canada, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Korea, Luxembourg, Mexico, the Netherlands, Norway, Poland, Portugal, Romania, Russia, the Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Turkey, the United Kingdom and the United States. The European Commission also takes part in the work of the Agency. The mission of the NEA is: – to assist its member countries in maintaining and further developing, through international co-operation, the scientific, technological and legal bases required for a safe, environmentally sound and economical use of nuclear energy for peaceful purposes; – to provide authoritative assessments and to forge common understandings on key issues as input to government decisions on nuclear energy policy and to broader OECD analyses in areas such as energy and the sustainable development of low-carbon economies. Specific areas of competence of the NEA include the safety and regulation of nuclear activities, radioactive waste management and decommissioning, radiological protection, nuclear science, economic and technical analyses of the nuclear fuel cycle, nuclear law and liability, and public information. The NEA Data Bank provides nuclear data and computer program services for participating countries. This document, as well as any data and map included herein, are without prejudice to the status of or sovereignty over any territory, to the delimitation of international frontiers and boundaries and to the name of any territory, city or area. Corrigenda to OECD publications may be found online at: www.oecd.org/publishing/corrigenda. © OECD 2018 You can copy, download or print OECD content for your own use, and you can include excerpts from OECD publications, databases and multimedia products in your own documents, presentations, blogs, websites and teaching materials, provided that suitable acknowledgement of the OECD as source and copyright owner is given. All requests for public or commercial use and translation rights should be submitted to [email protected]. Requests for permission to photocopy portions of this material for public or commercial use shall be addressed directly to the Copyright Clearance Center (CCC) at [email protected] or the Centre français d'exploitation du droit de copie (CFC) [email protected]. Cover photos: Geological salt beds deep underground in New Mexico (Courtesy of Carlsbad Department of Development); Halobacterium sp. (noricense) isolated from Salado halite in the Waste Isolation Pilot Plant (United States). FOREWORD Foreword Because of their ability to effectively isolate radioactive waste from the environment and the public, deep geological formations are considered the optimal choice for the disposal of hazardous waste. Granitic rock, basalt, clay, tuff and evaporite salt beds are among the different types of sites that are being considered for radioactive waste repositories. Since it was determined that organisms are active even in deep geological settings, a great deal of research has been undertaken to determine the influence of microorganisms on repository performance (i.e. safety cases). Nonetheless, few data are available on the microbiology of subterranean salt formations in proposed and active locations for radioactive waste repositories. Because the biogeochemistry of other deep geological settings differs significantly from that of subterranean salt, it is not always possible to extrapolate microbial activity from one type of site to another. In lieu of directly applicable data, repository scientists rely on “indirect” information – such as microbial ecology, genomics and the thermodynamic feasibility of certain types of metabolism in hypersaline environments – to predict microbial activity and the potential impact on the performance of the repository. The lack of data and the resulting uncertainty surrounding microbial processes in high ionic strength repository settings has meant that performance assessments and safety cases must be conservative in their predictions of potential microbial impact. While such a conservative approach can be defended in a regulatory process, a better understanding of the system would nonetheless alleviate the need to spend engineering resources on what may only be perceived problems. Microorganisms are predicted to have diverse effects on radioactive waste repository performance. These effects are linked to activities that may affect radionuclide speciation and solubility, or that may enhance mobility and thus the source term used in evaluating repository performance. MICROBIAL INFLUENCE ON THE PERFORMANCE OF SUBSURFACE, SALT-BASED RADIOACTIVE WASTE REPOSITORIES, NEA No. 7387, OECD 2018 3 ACKNOWLEDGEMENTS Acknowledgements The NEA would like to express its appreciation to the principal authors of this report: J.S. Swanson,1 A. Cherkouk,2 T. Arnold,2 A. Meleshyn3 and D.T. Reed.1 The Los Alamos National Laboratory (LANL) – Carlsbad Operations Actinide Chemistry and Repository Science Program in Carlsbad, New Mexico – the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) Centre for Resource Ecology in Rossendorf, Germany; and the Gesellschaft für Anlagen und Reaktorsicherheit in Braunschweig, Germany helped in compiling this report. The NEA also wishes to acknowledge the support of Russ Patterson, the US Department of Energy (DOE) programme manager. LANL research described herein was funded by the Department of Energy-Carlsbad Field Office (DOE-CBFO) as part of the ongoing recertification of the Waste Isolation Pilot Plant (WIPP) transuranic repository. HZDR research described herein was funded by the Young Investigators Grant, MicroSALT, and by the German Federal Ministry for Economic Affairs and Energy (BMWi). 1. Los Alamos National Laboratory – Carlsbad Operations; Carlsbad, New Mexico, United States. 2. Helmholtz-Zentrum Dresden-Rossendorf; Dresden, Germany. 3. Gesellschaft für Anlagen und Reaktorsicherheit; Braunschweig, Germany. 4 MICROBIAL INFLUENCE ON THE PERFORMANCE OF SUBSURFACE, SALT-BASED RADIOACTIVE WASTE REPOSITORIES, NEA No. 7387, OECD 2018 TABLE OF CONTENTS Table of contents List of abbreviations and acronyms ................................................................................ 7 Executive summary ............................................................................................................ 9 Chapter 1. Repository performance and the possible effects of microbial activity ............................................................................................................. 11 Chapter 2. Background .................................................................................................... 13 The subterranean salt environment and the potential for microbial life ............ 13 The microbiology of hypersaline systems and the subterranean salt biosphere ....................................................................................................................... 14 Chapter 3. The potential for microbial activity under projected repository conditions ....................................................................................................... 19 Expected conditions ...................................................................................................