Nuclear Waste Disposal: The Interface between Performance Assessment and Research
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NUCLEAR WASTE DISPOSAL: RESEARCH
Inc.
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THE INTERFACE BETWEEN PERFORMANCE ASSESSMENT AND
R.B. LYON Whiteshell Nuclear Research Establishment, Pinawa, Manitoba ROE ILO
Atomic Energy of Canada Ltd.,
ABSTRACT The potential impact of the post-closure phase of a nuclear fuel waste disposal project is radiation dose to man. Radiation dose is estimated as the end product of a total systems analysis. Field and laboratory research must be assimilated in a form that can be accepted by the total systems analysis procedure. A central focus of this assimilation must be the consideration of uncertainties in the analysis and data used. Irreducible uncertainty arises because of the wide variability in natural systems and the unprecedented extrapolation into the distant future. The SYVAC computer program provides a framework for assimilation of the results of the field and laboratory research with a systematic treatment of uncertainty. A SYVAC assessment of the post-closure performance of a Canadian nuclear waste disposal facility is presented with particular illustrations of the interface between the assessment models and data and the field and laboratory research.
INTRODUCTION Performance assessment of the post-closure phase of a nuclear waste disposal facility has the objective of evaluating the potential radiation dose
to man due to the migration of radionuclides from the waste to man's
environment. The post-closure phase is taken to be that time period after the facility has been backfilled and sealed and the surface facilities have been decommissioned. In my discussion of the interface between performance assessment and research, I will make reference throughout to the Canadian disposal approach, which involves emplacement of the waste in rooms at a depth of a kilometre in an igneous intrusive rock formation, known as a pluton, in the Canadian Shield [1]. In principle, however, I believe the discussion will have equal relevance for other disposal concepts in other countries. To estimate the degree to which radionuclides could migrate from the waste to the environment, we must evaluate how water could reach and corrode the waste containers, to dissolve or leach out the radionuclides, how the solution could seep to the surface and, finally, how the radionuclides could disperse or concentrate in the biosphere to cause radiation dose to man. In addition, we must evaluate the extent to which natural phenomena, such as glacial episodes, could influence this process. Such a performance assessment has problems of complexity, magnitude, uncertainty, validation and demonstration. Complexity arises because the final result of our analysis, an estimate of radiation dose to man, requires simultaneous consideration of hydrogeological, chemical and natural processes. The magnitude of the problem is clear when we consider that an underground
474 waste vault could have an area of several square kilometres and the possible pathways to the biosphere could extend over several hundred kilometres. Detailed investigation of even a smal
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