Strontium-90 migration to water wells at the Chernobyl Nuclear Power Plant; re-evaluating of a decision model
Leslie Smith, and Petros Gaganis
University of British Columbia, Department of Earth and Ocean Sciences, Vancouver, BC, Canada
The decision model used by Bugai and others (1996) to evaluate the necessity of proposed protective measures for the Pripyat Town well field located near the Chernobyl Nuclear Power Plant is re-evaluated. The principal features of this re-evaluation are: a) a more comprehensive but computer-intensive simulation model is adopted in deriving estimates of the 90 Sr concentration at a well head, b) a greater number of parameters are treated as stochastic variables rather than as deterministic variables assigned conservative upper or lower bounds, and c) data unavailable to Bugai and others (1996) are used to update estimates of several of the model parameters. When judged against the updated model, Bugai and others (1996) overestimated the cumulative probability of well field contamination during the 70-yr planning horizon by a factor of about 20+ or -5. Elements that were precluded from consideration in the Bugai model that can lead to higher 90 Sr concentration at a well head (such as well interference effects and the duration of source loading at the water table) are outweighed by the relaxation of conservative approximations related to the regional hydraulic gradient, the ground-water recharge rate, the hydraulic conductivity estimates, and the updating of the estimated layer thicknesses. The Bugai model is not conservative with respect to well field contamination during the early years of the planning horizon, but the revised estimates of the probability of well field failure do not have a significant effect in the decision model. Model comparisons show that there can be an advantage in carrying out early sensitivity studies using a detailed model to guide the design of a simpler model that, because of its computational advantage, would be used in estimating the probability of well field contamination.
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