Spent Fuel Waste Disposal: Analyses of Model Uncertainty in the MICADO Project

Abstract

Abstract Direct geological disposal of spent fuel from nuclear energy production is a waste management strategy of many European member states. Disposal safety must be ensured for thousands to millions of years. If one wants to put the highly radioactive used nuclear fuel within a thick-walled metallic canister directly into a repository, corrosion of the canister will occur and access of deep groundwater will eventually take place. What happens if deep groundwater comes into contact with the fuel? Research has been ongoing for more than 25 years to create a large experimental data base to simulate the long-term performance of the waste thus disposed of. Further, there has been a substantial effort to develop descriptive and predictive modeling procedures. The evaluation of the long term performance of the spent fuel relies on the development of theoretical and sometimes semi-empirical models which can be combined with more general safety assessment models allowing repository barrier performance predictions for overall repository performance assessment (PA). The coordinated action MICADO has recently assessed the uncertainties in models describing the dissolution processes of spent nuclear fuel in a repository for geological time periods. Coordinated by SUBATECH/ARMINES, this international coordinated action combines the efforts of many European waste management agencies, technical support organisations for regulators, universities and research organisations. Participating organisations are CEA, ANDRA and IRSN from France, SCK.CEN and BEL-V form Belgium, KIT Karlsruhe (former FZK-INE), ITU and GRS from Germany, ENRESA, UPC, CIEMAT and AMPHOS21 from Spain, SKB, SSM, Studsvik and KTH from Sweden, NAGRA from Switzerland and Quintessa from the United Kingdom. Essentially most worldwide leading experts participate in the project, representing different approaches to the assessment of the performance of disposed spent fuel for very long times: based on electrochemical, geochemical and/or radiolytical modeling approaches. Based on inputs from such models and the associated experimental studies, simplified operational models for spent fuel dissolution are developed and used by waste management and regulating organisations for the safety assessments in more complex systems. The objective was to find out whether international research has now provided sufficiently reliable models to assess the corrosion behavior of spent fuel in groundwater and by this to contribute to answering the question whether the highly radioactive used fuel from nuclear reactors can be disposed of safely in a geological repository. Principal project results are described in the paper.