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Summary Near-Field Processes - The Challenge of Integration into Performance Assessment Lawrence Johnson 1 , Delphine Pellegrini 2 , Jesús Alonso 3 , Frédéric Plas 4 and Maarten Van Geet 5 Nagra 1 , Switzerland; IRSN 2 , France; Enresa 3 , Spain; Andra 4 , France; SCK.CEN 5 , Belgium Over the past decade, the EU has strongly promoted coordination of R&D in relation to nuclear waste disposal. In the area of engineered barrier (EB) processes there have been numerous focused projects dealing with waste form processes (SF and HLW), canister corrosion, and bentonite behaviour, as well as system-wide process-related projects such as gas production and transport and coupled heat and moisture transport in the EBS. The NF-PRO project dealt with all of these aspects together in a single large project for EB systems in crystalline, clay and salt host rock repositories. Furthermore, one component of NF-PRO focused on performance assessment (PA), which was a daunting challenge given the diversity of systems and EBS design concepts. The PA-related work was focused on providing context for the experimental and modelling studies in the sense of defining expected in situ conditions and boundary conditions, as well as giving a frame of reference for the contributions of the different parts of the system to overall repository performance. In the end, the PA specialists were able to bring back to their own national programmes useful data and process level models for integration into their future integrated PA studies. In addition, the incorporation of a PA group within the project helped to build some bridges between specialist groups. Some lessons from the project work are outlined from the perspective of the PA Component of NF-PRO. 1. Introduction A fundamental objective of all disposal systems for nuclear waste is to provide safety by minimizing the release of radionuclides from the disposal system. This is done by designing a disposal system in which the waste is completely contained for some suitable period and, following breaching of containment, is largely retained within the disposal system as a result of slow radionuclide transport and strong chemical retention processes. Many processes can influence, either positively or negatively, the effectiveness of these safety functions of isolation and retardation. The objective of the EU NF-PRO project is to improve the understanding of and the technical basis for the contribution to these safety functions provided by the near-field system. The near field is considered to comprise the engineered barrier system (EBS) and the region of rock immediately surrounding the repository excavations (i.e. mainly the excavation-disturbed zone). NF-PRO builds on a strong foundation of previous related EU projects (note the following is a partial list) in the areas of waste form processes [1, 2], canister corrosion [3], bentonite behaviour [4, 5], and system-wide processrelated projects such as gas production and transport [6] and safety assessment [7], in addition to 213
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