Comparison of the Concepts and Assumptions in Five Recent HLW/Spent Fuel Performance Assessments
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COMPARISON OF THE CONCEPTS AND ASSUMPTIONS IN FIVE RECENT HLW/SPENT FUEL PERFORMANCE ASSESSMENTS 4 23 2 2 F.B. Nealll, P. Baertschi , I.G. McKinley , P.A. Smith , , T. Sumerling and H. Umeki
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1Paul Scherrer Institute, Switzerland 2 NAGRA, Wettingen, Switzerland 3Present address: Intera Information Technologies Ltd., Melton Mowbray, UK 4Safety Assessment Management, Reading, UK 5 Power Reactor and Nuclear Fuel Development Corporation, Japan
INTRODUCTION Integrated performance assessments of proposed repositories for HLW involve multidisciplinary studies which include identification of possible paths of future evolution of the repository system (scenario analysis) and quantification of the consequences of each scenario using deterministic or probabilistic modelling approaches. The results of such studies are commonly presented as estimates of consequence (e.g. dose to a representative individual) against time which extends into the distant future. Individual components of the model chains used can be tested to some extent, but how can the integrated assessment be evaluated to give additional confidence in the overall results? In order to address this issue, the Kristallin-l performance assessmentI has been compared with other HLW/spent fuel performance assessments. This technical comparison forms the basis of this paper which summarises the results from a more extensive comparison of a number of HLW/spent fuel disposal concepts, safety assessment methodologies and models 2. It is part of a wider study which attempted to put the results of the Kristallin-I performance assessment into perspective by use of both this technical comparison with other performance assessments and by consideration of other information (e.g. natural analogue studies, environmental radiation data and risk assessments for radiological and non-radiological hazards) which allows the reasonableness of the results and significance of the predicted doses to be illustrated. Due to limitations of space, this aspect of the study has not been included here and the reader is referred to the "Kristallin-I: Results in Perspective" report 2 for more details.
COMPARISON OF KRISTALLIN-1 WITH OTHER SAFETY ASSESSMENTS On the basis of some similarity of disposal concept (disposal of HLW or spent fuel in crystalline rock below the water table) and availability of recent documentation, a small number of state-of-the-art safety assessments were selected for comparison with Kristallin- I (Table I). Comparison of the results alone of these safety assessments and Kristallin-1 is not particularly illuminating as all the maximum doses predicted lie between 10-3 and 10-s mSv.y-' (Figure 1). Thus, a more detailed examination was made of the consequences of different disposal concepts and modelling approaches on individual results. Basis for comparison The methodological approaches differ between the five assessments. Most notably:
Mat. Res. Soc. Symp. Proc. Vol. 353 01995 Materials Research Society
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Table I: Key characteristics of the disposal systems consider
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