Washing processes impact on the decontamination of tiles and concrete contaminate by radioactive cesium and strontium

An accident on a nuclear reactor with a radionuclide deposition on urban surfaces could present a danger of external of irradiation for the populace. In order to evaluate this risk, and taking into account the few available data in the literature, it appeared essential to us to test in the laboratory the efficacy of decontamination techniques on judiciously selected urban surfaces before considering a feasibility study on a large scale. The originally of this work consisted in evaluating by the means of experiments in controlled environment the decontaminating efficiency of a rain event and washing with aggressive solutions on clay tiles and concrete contaminated with strontium and cesium aerosols. The rainwater proved not to be very effective in eliminating the radionuclides, the weaker its effect the higher its intensity. A greater efficiency was obtained after 2 h 30 of washing with the NH4Cl 0,1 mol l-1 solution applied directly after the contamination. The residual activity then amounts to 90 % on the tiles and 40 % on the concrete. The results obtained are average for the concrete but not very satisfactory for the tiles and confirm, under conditions of accidental deposit, the difficulty in moving such a contamination. (author)