NATURAL AND ENGINEERED BARRIERS IN A ROMANIAN DISPOSAL SITE FOR LOW AND INTERMEDIATE LEVEL WASTE

摘要

The operational waste generated by the Cernavoda Nuclear Power Plant will be disposed in a near-surface facility. The low and intermediate level wastes, containing particularly large concentrations of C-14 and H-3, are treated and conditioned in steel drums, which will be placed in the disposal cells and then immobilized in concrete. The Saligny site has been proposed for LIL waste disposal. Geologically, the main components of this site are the quaternary loess, the Precambrian and pre-quaternary clays, and the Eocene and Barremian limestones. Hydrologically, the site can be divided into a vadose zone down to 45-50m and three distinct aquifers, two of them in the limestone beds and the third into the lenses of sand and limestone existing in the pre-quatemary clay layer. Preliminary performance assessments, presented in this paper, indicate that the geologic layers are efficient natural barriers against water flow and radionuclide migration from the vadose zone to the Barremian aquifer. The semi-arid climate and the low precipitation rate prevent contaminant transport from the disposal site to the Eocene aquifer. FEHM simulations of transient groundwater flow showed that seasonal variations influence the moisture content profile in the top of the vadose zone, but the influence over the long term is not significant for contaminant transport. The Danube River level variations control water movement in the Barremian aquifer, especially in the upper part where the limestone is highly fractured and water moves toward the river when its level is low and toward the site when the river level is high. The disposal concept tries to combine the natural and engineered barriers in order to ensure the safety of the environment and population. Therefore, the concrete filling the disposal cells surrounds the waste with a medium that facilitates C-14 retention by precipitation, thus reducing the C-14 releases in the atmosphere and geosphere.