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Description
During operation of nuclear power plants, corrosion products are activated in the active zone, transported by the coolant, and contaminate the inner walls of primary circuit components by adsorption/incorporation into corrosion layers formed on the material. To ensure safe operation and reduce radiation hazard for working personnel, it is essential that decontamination is carried out on regular basis. The principle of decontamination is to remove corrosion layers and release incorporated radionuclides. Corrosion layers formed on stainless steel surfaces (used in primary circuit components of Czech NPPs) consist of insoluble spinel-type compounds of Fe, Cr and Ni. In chemical decontamination methods, most efficient removal is achieved by oxidation of the compounds into higher states to produce more soluble species. Efficiency of decontamination media is usually further increased by application at elevated temperatures (70-90 °C). However, this increases the overall energy consumption of the process and, in some cases, complicates transportation of the medium. In this context, there is a strong demand for decontamination media that could achieve sufficient decontamination factors even under lower temperatures.
This work is aimed at the development of low-temperature medium for decontamination of primary circuit of Czech NPPs, which is based on previously patented medium developed for decommissioning purposes [1]. Composition of the patented medium was modified for the purposes of operational decontamination, and its efficiency was tested and confirmed on model substrates (Cr2O3, Fe3O4, Fe2NiO4). Currently, dissolution of inactive samples of corrosion layers on stainless steel materials is being assessed. In parallel, real samples from the primary circuit are being characterized and will be subjected to decontamination. Results from dissolution/decontamination of inactive and active samples will be presented.