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Validation of the global model for ⁹⁰Sr migration from the waste burial in the Chernobyl exclusion zone

Abstract
The reported work aimed at modeling process of radionuclide migration from the near-surface waste burial (trench no.22) containing nuclear fuel particles to the unsaturated zone and aquifer. The developed global model of the waste site accounts for dissolution of reactor fuel particles, vertical radionuclide transport in the unsaturated zone, and horizontal transport in the underlying aquifer by advection-dispersion mechanisms. It is based on the following sub-models: the geostatistical model for radioactivity distribution in trench; the radionuclide source term model describing dissolution of fuel particles, radionuclide redistribution in the trench body and unsaturated zone (STERM1D) and the two- and three-dimensional contaminant transport in the aquifer (MODFLOW - MT3D). Modeling work included sensitivity analyses, calibrations and eventually validation tests for the global model by means of comparison of model predictions to experimental data. In addition, a preliminary step by step validation process was applied to "elementary" sub-models. The developed modeling methodology is mostly suited for producing spatially averaged parameter values (such as radionuclide concentrations in trench porous solution, integral radionuclide release to aquifer) and is applicable for long-term predictions on a scale of decades assuming that hydrological and geochemical conditions remain steady state.