Electrochemistry and the Performance Assessment of Nuclear Waste under Permanent Disposal Conditions
by David Shoesmith
Sunday, October 4, 2009 | Vienna, Austria
All national programs for the permanent disposal of high level nuclear waste involve its containment within a deep geological repository. These repository concepts are based on multiple barriers to radionuclide release with no common mode of failure. Within this sequence, the waste form itself (most commonly the spent fuel discharged from a reactor) and the metallic container within which it is sealed are the key engineered (as opposed to natural geologic) barriers. The key geological property controlling container corrosion, and waste form corrosion inside a failed container, will be the groundwater redox condition that will evolve with time as environmental oxidants in the groundwater are consumed and the radiation fields that produce radiolytic oxidants (via the decomposition of water primarily within a failed container) decay. Models must be capable of assessing with reasonable certainty the evolution of repository behaviour from the initial excavated damaged state to the original undisturbed state. Given the long time frames involved (103 to 106 years) this is a unique challenge for engineered structures.
Electrochemical approaches, coupled to a wide range of supplementary analytical and spectroscopic methods, have been applied to this task. This presentation will illustrate how electrochemical methods have been used to, (1.) develop the mechanistic understanding of materials corrosion processes; (2.) generate the databases essential for model development; (3.) provide the framework for the computational models capable of predicting the evolution of corrosion damage with time and estimate the lifetimes of waste containers and the release rates of radionuclides; and (4.) provide the essential feedback required for the engineering design of optimized barriers able to provide adequate performance at reasonable cost.
David Shoesmith is a professor in the Department of Chemistry at the University of Western Ontario (London, ON, Canada) and specializes in research on the electrochemistry, surface analysis, and corrosion of materials. He has held this appointment since June 1, 1998, and is the Canadian Natural Sciences and Engineering Research Council and Nuclear Waste Management Organization (NSERC/NWMO) Industrial Research Chair holder in Nuclear Fuel Disposal Chemistry (since November 2000). Initially a five year appointment, this chair was renewed for a further five years in November 2005. Previously, he worked for Atomic Energy of Canada Ltd for 25 years, achieving the rank of principal scientist. Since 1980 he has been an active researcher in the Canadian Nuclear Waste Disposal Program, and is a recognized international expert on waste form and waste container issues. He is an elected fellow of the National Association of Corrosion Engineers (NACE International) (1996) and the Canadian Society for Chemistry (1985). He has won awards from The Electrochemical Society (Lash Miller), the Canadian Society for Chemistry, the Canadian Institute of Mining and Metallurgy (Cohen Award), Atomic Energy of Canada (Discovery Award), and a University of Western Ontario Distinguished Professorship. He is currently funded by waste management organizations in Canada, Sweden, and Switzerland. He has served on program review boards in Switzerland, USA, and France, and as a consultant on corrosion issues for many nuclear and non-nuclear companies. He has written over 350 publications, 210 of which are in refereed journals and conference proceedings.