Building Stakeholder Confidence by Reducing the Gulf between Experimental Data and Model Predictions in Assessments of R
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Building Stakeholder Confidence by Reducing the Gulf between Experimental Data and Model Predictions in Assessments of Repository Performance Kaye P. Hart Australian Nuclear Science and Technology Organisation, Menai NSW 2234, Australia; [email protected] ABSTRACT Confidence in the ability of repository systems to isolate high level wastes from the environment can be strengthened by placing greater reliance on robust designs for the repository system, and by using multiple lines of evidence to demonstrate that parameters, models and predictions developed for the repository are relevant. A particularly useful approach is to demonstrate that models and predictions incorporate processes that have been shown to be important in existing natural systems. INTRODUCTION Disposal of high level waste (HLW) is being considered in a number of countries. Internationally, geological disposal is accepted as an ethically and environmentally sound waste management solution [1]. Granite, clay, salt, and tuff have been investigated in a number of countries as host formations for repositories. All of these geological materials provide the necessary setting to isolate wastes from the bio-sphere over geological time-scales. Generally, the OECD/NEA [2] notes that, for a well chosen site, the barrier systems and host rock are reasonably predictable over 105 to 106 years, and that shorter term uncertainties can be bounded with some confidence. The safety of the planned repository over geological time needs to be demonstrated for each site within a given country’s domestic regulatory requirements and legal framework, as well as under any international agreements [3]. However, to carry out such safety assessments it is necessary to extrapolate a wide range of data to predict the behaviour of these systems over long periods of time. Consequently, the basic data developed for all components of the repository system (i.e., waste packages, natural systems, and the host formations) underlie the viability of these predictions. One way to reduce stakeholder concerns associated with disposal of wastes in geological repositories is to demonstrate an understanding of the existing, complicated natural systems in which the waste is emplaced. This demonstrated understanding can then provide increased confidence in the baseline from which future projections are being made and is of critical importance to reducing stakeholder concerns. REPOSITORY SYSTEMS Simply, the constituents of a repository system include: the waste form, packaging, engineered and natural barriers, and the host geological system. Each component within the repository system is part of the multi-barrier system that provides its own integrity to the isolation of the HLW. Importantly, the performance of the system is not dependent on any one barrier instead, each operates to provide redundancy so that if there are deficiencies in any one barrier over time the other components of the system will mitigate any potential impacts. This
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scenario is usually referred to as the mul
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