Modeling electrochemical deactivation of the graphite surface
Irradiated graphite of uranium:graphite reactors, which is a radioactive waste, is formed during the decommissioning of nuclear reactors. The paper presents the results of modeling performed to assess the potential and basic parameters of the electrochemical decontamination method for processing irradiated graphite parts. This treatment makes it possible to reduce activity by removing radionuclides from the most contaminated surface layer. Graphite is proposed to be used as an anode for electrochemical decontamination from radioactive metals. This approach ensures processing a part of graphite waste in the form of bushings or rings without significant additional generation of radioactive waste.
A one:dimensional mathematical model of electrolytic decontamination is proposed, which describes the oxidation processes of metal radionuclides in the surface layer of irradiated reactor graphite, diffusion and electric migration of radionuclide ions from the anode to the cathode. The rate of removing radioactive cesium from irradiated graphite is calculated depending on the anode voltage, the interelectrode gap and the temperature inside the electrolytic cell. The optimal parameters of electrolytic deactivation of irradiated graphite are determined for removing 137Cs radionuclide. It has been shown that it is advisable to carry out the processing at the minimum possible interelectrode gap, the temperature close to the boiling point of the electrolyte and the maximum possible voltage. In particular, at L = 0.5 cm, T = 90°C, E = 10 V removal rate of 137Cs is 0.6 min. The obtained results could be used in conducting experiments aimed at creating a technology for electrolytic deactivation of irradiated graphite and developing electrolysis units for processing radioactive waste.
After experimental verification of the calculation results, this mathematical model can be used for determining the efficiency of existing technological systems for electrochemical decontamination of metallic radioactive waste using various design options for irradiated graphite anodes.
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