Modelling of a Generic Near-Surface Disposal System
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Modelling of a Generic Near-Surface Disposal System Noelia R. Sileo1, Néstor O. Fuentes2,3 U. A. Materiales – GIDAT, GAEN, CNEA 2 Programa Nacional de Gestión de Residuos Radiactivos, GASNyA 3 Instituto Sabato – UNSAM / CNEA Av. Gral. Paz 1499, B1650KNA – San Martín, Buenos Aires, Argentina. 1
ABSTRACT Development of numerical tools for performance assessment studies of radioactive waste disposal facilities, must address the management of the wide-ranging uncertainties associated with the long-term behaviour of these complex systems. Different approaches and assumptions are made in order to identify and describe relationships between the disposal system and its environment. They take into account, among other factors, the uncertainties associated with temporal evolution of the system within a proposed scenario; the landscape changes arising from future human actions, climate and geological events and processes; the relationships between components of the disposal system and its immediate environment; the behaviour and characteristics of radionuclides within the system and their role in contributing to radiation exposure. In all cases, the different scenario-based models are typically used to determine the radiological significance of potential future discharges from waste disposal facilities. However, it is important to keep always in mind that in any specific case, the purpose of developing and/or applying a model may vary from a simple calculation (e.g. to support concept development) to detailed site-specific performance assessment in support of a disposal license application. The assumptions and modelling simplifications that are appropriate to one type of calculation may not be so easily justified in different circumstances. In order to develop the capability of modelling different long-term scenarios for a generic disposal site for low and intermediate level radioactive wastes, implementation of models of both the near-field/geosphere and biosphere were performed using general approaches for geosphere-biosphere interface, with sub-models for the whole system. INTRODUCTION The present work is a first approach to develop a generic evolution scenario system comprised both of the near surface disposal system and the geosphere formed by the rock and unconsolidated material that lies between the near-field and the biosphere. It can consist of both the unsaturated or vadose zone, which is above the groundwater table, and the saturated zone which is below the groundwater table. In order to develop a conceptual model for a given scenario, it is necessary to consider [1]: x The source of contaminants – i.e. the disposal facility; x The release mechanisms – the processes affecting in the release of radionuclides from the source; x The transport media - the media through which the radionuclides are transported; x The transport mechanisms - the processes affecting the transport of radionuclides; x The exposure media - the media in which humans are exposed to the radionuclides; and
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x The exposure mechanisms - the pr
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