FUNMIG Integrated Project results and conclusions from a safety case perspective

Abstract

Abstract The scope of the FUNMIG Integrated Project (IP) was to improve the knowledge base on biogeochemical processes in the geosphere which are relevant for the safety of radioactive waste repositories. An important part of this project involved the interaction between data producers (research) and data users (radioactive waste management organisations in Europe). The aim thereof was to foster the benefits of the research work for performance assessment (PA), and in a broader sense, for the safety case of radioactive waste repositories. For this purpose a specifically adapted procedure was elaborated. Thus, relevant features, events and processes (FEPs) for the three host rock types, clay, crystalline and salt, were taken from internationally accepted catalogues and mapped onto each of the 108 research tasks conducted during the FUNMIG project by a standardised procedure. The main outcome thereof was a host-rock specific tool (Task Evaluation Table) in which the relevance and benefits of the research results were evaluated both from the PA and research perspective. Virtually all generated data within FUNMIG are related to the safety-relevant FEP-groups “transport mechanisms” and “retardation”. Generally speaking, much of the work within FUNMIG helped to support and to increase confidence in the simplified PA transport and retardation models used for calculating radionuclide (RN) transport through the host rock. Some of the studies on retardation processes (e.g. coupled sorption-redox processes at the mineral–water interface) yielded valuable data for all three rock types dealt within the IP. However, most of the studies provided improved insight regarding host-rock specific features and processes, the majority of this work being dedicated to clay-rich and crystalline host rocks. For both of these host rock types, FUNMIG has significantly contributed to improving understanding on a conceptual level, both by providing new experimental data at different spatial scales and by developing improved modelling approaches. The disposal concept in salt host rocks differs from those in other host rock types in that the host rock is, at least in part, regarded as near-field from which under normal scenarios no release of radionuclides is possible. Corresponding investigations in FUNMIG concerned therefore not salt host rocks but an example of an overburden under the premise of radionuclide escape from the salt barrier. Selected highlights with regard to FUNMIG’s achievements include: For argillaceous host rocks, the systematic effort of investigating and comparing diffusion and sorption processes at different scales in different clay rocks using a variety of methods has substantially increased the knowledge basis for future safety cases. For crystalline host rocks, valuable data on the generation, transport and filtration of clay colloids from the near-field and their impact on RN transport under realistic conditions have been obtained. The results from studies on organic colloids and on biofilms, including their interaction with radionuclides, have been shown to be of interest for future safety cases of salt-host rocks. Among the main research issues from a PA perspective that need to be addressed in the future, the following are noted: (i) the question of irreversibility of RN sorption to colloids in fractures of crystalline rocks, (ii) a comprehensive model for cation and anion diffusion in clays for different scales and (iii) the applicability of mechanistic retardation models for strongly sorbing radionuclides in intact clay and crystalline host rocks. An important lesson learnt from the interaction between research and PA is that it would be desirable to apply a similar evaluation procedure for proposed research tasks before the start of the research work. In this regard, the procedures developed within FUNMIG are a useful tool for planning future Integrated Projects.