Insulation Failure Mechanism Of Epoxy Nanocomposites Under Simulated Loss Of Coolant Accident Condition In Nuclear Power Plant

When loss of coolant accident occurs,the electrical system of nuclear power plant should be required to operate stably in extreme accident environment.There is a great prospect for polymer-based nanocomposites in nuclear power plant due to their excellent insulation properties.The mechanism of insulation degradation in the environment of loss of coolant accidents is worthy of attention.The epoxy-based nanocomposites prepared were aged by high-energy gamma irradiation and acid-base solution which simulate the extreme conditions of loss of coolant accident.The effects of gamma radiation and chemical corrosion conditions on the trap distribution characteristics and surface charge accumulation behavior of epoxy nanocomposites with different total irradiation doses were studied.It reveals the characteristics of the physical and chemical structure changes of the sample and its correlation with the charge transport behavior,and provides a reference for in-depth understanding of the degradation and failure mechanism of polymer materials in extreme environments of water loss accidents and the development of materials that withstand that environment.The main work carried out as follows:1.Epoxy resin(ER)was selected as the based polymer and the average particle size of 60 nm?-Al₂O₃ was selected as nano-fillers.Mechanical blending method was used to prepare ER/Al₂O₃ nanocomposites.Firstly,the samples were irradiated with a Cobalt-60 source with the total radiation dose 0,500 and 1000 k Gy,respectively.Secondly,the samples were etched with a boric acid solution with a p H of 4.7 and a trisodium phosphate solution with a p H of 11.The corrosion temperatures were 60°C and 100°C,respectively,and the corrosion time was 48 h.The physicochemical properties of nanocomposites were investigated by means of broadband dielectric spectrometer,infrared spectroscopy and X-ray photoelectron spectroscopy.The results show that the ER mainly undergoes hydrolysis reaction in the corrosion solution at100?,and the amide group is more prone to hydrolysis in acidic than in the alkaline solution.The oxidation reaction mainly occurs in the acid-base solution at 60?;During the process,products such as hydroxyl and carboxyl groups were generated.2.The surface potential decay method was used to analyze the trap energy level distribution and carrier mobility of the material which reflect the behavior of charge transport.The results show that the corrosion causes the depth of the trap and the deep trap density to decrease,while the shallow trap density and the carrier mobility increase.The density of shallow trap decreases and the density of deep traps increased by the addition of nanoparticles.The total irradiation dose of?-rays increased from 0to 1000 k Gy,and the energy level of the shallow and deep traps increased,and the density of the shallow and deep traps decreased.The formation of hydroxyl and carboxyl groups during corrosion in ER,the interaction between the nanoparticles and the matrix,and the crosslinking reaction caused by irradiation are the important cause of charge transport behavior.3.The planar electrode structure and different polar DC voltages was applied in the experiment.The effects of voltage amplitude,nanoparticle addition,total irradiation dose,and acid-base corrosion conditions on surface charge accumulation was explored by different polar DC voltages charging.The results show that after the sample is immersed and etched by chemical solution,the surface of the sample is more likely to accumulate charge.With the increase of nanoparticle content,the surface charge density shows a increases and then decreases tendency.As the total irradiation dose increases,the surface charge density tends to decrease.The accumulation characteristics of surface charges are mainly related to the trap level and density of the sample surface.