A novel efficient "soft" chemical decontamination technology has been developed - supported by the Paks Nuclear Power Plant - at the Institute of Radiochemistry and Radioecology of the University of Pannonia. The present work gives a brief overview on the corrosion and dissolution processes of austenitic stainless steel and carbon steel specimens that occur in the oxidative pretreatment step (mixture of 1.0 g·dm^-3 HMnO4 + 0.2 mol·dm^-3 HNO3, pH = 0.8-1.0) of the novel base-technology. The oxidative pretreatment of steel specimens was performed under laboratory conditions in an electrochemical cell, and the open circuit (corrosion) potential of treated surfaces was studied by a VoltaLab 40 (RADIOMETER) type electrochemical measuring system controlled by PC. In addition, the redoxi potential in the decontamination solution was measured on-line by Consort C861 type electrochemistry meter. In the course of the chemical procedure the concentration of the main alloying components (stainless steel: Fe, Cr, Ni, carbon steel: Fe) dissolved from the surface oxide layer into the decontamination solutions was determined by ICP-OES method. The morphology and chemical composition of the oxide layer formed on the surfaces of steel specimens were studied by scanning electron microscopy (SEM), equipped with an energy dispersive X-ray microanalyzer (EDX). The results of our laboratory experiments have revealed that the acidic dissolution of austenitic stainless steel surfaces by nitric acid is negligible (at room temperature), while that the carbon steel surface is significant and intensive. After addition of permanganic acid, a moderate dissolution of the protective oxide layer of the austenitic stainless steel surface was observed; however, the reaction is blocked by MnO2 formed on the steel surface. On the other hand, the dissolution rate of carbon steel surface is not increased following the addition of permanganic acid into nitric acid solution, and the formation of surface MnO2 is marginal.