ABSTRACT
The organic coatings used in the reactor building of nuclear power plant protect not only the structure metal from the oxidation and radiation, but also the sealing performance and metal separator and walls from the corrosion of the radioactive particles during LOCA. Therefore a good
anti-oxidation, good adhesion, radiation absorption and the good mechanical properties should be possessed by the coating in NPP. The ordinary conditions are 50℃ with the amount of radiation 0.1 Gy/h,while during the accident conditions the temperature maybe rise to 150℃ with a large number of radiation particles. So during the service of the nuclear power plant, the coatings will suffer the aging of oxidation and radiation, which maybe makes the coatings lose their safe functions during the accident conditions. For the moment organic coatings, such as epoxy resins, polyurethanes, rubber resins and phenolic resins, are largely used in the nuclear power plant, due to their antioxidant properties. In China and abroad the study of the aging and the degradation of epoxy have been implemented for years, but also there are a lot of questions for the mechanism of aging and degradation aspects. Additionally, the study on the lifetime of coatings was not conducted in depth.
This dissertation conducted a study on the mechanism of oxidation and lifetime of the epoxy coatings, by the experimental simulation of the internal environment in nuclear power plants, including the oxidative aging and the radiant aging.
The results of the experiments on the MMS system and the 3D cross linking system showed the same properties under the oxidation and the radiant aging. Amide and acid were detected as the main products among the three materials during the processes of oxidation. The results of the Infrared Spectroscopy and the Gel permeation chromatography showed that the amide may be produced by the oxidative degradation, while the carboxylic acid may be the result of the cut of crosslinking.
The main oxidative products, carboxylic acid and amide, were also found by the analysis corresponding the industrial application. During the oxidation, three different systems reflected the same property.
The modulus of Young and the elongation at break are two main physical characters of the epoxy coatings. The increase of the modulus of Young and the decrease of the elongation at break were found due to the development of oxidation. The performance of three systems was similar.
Comparing the concentration of acid and the elongation at break, a proportional relation was found between them. The lifetime of epoxy therefore could be predicted by setting the threshold of lost functionality of epoxy coatings.
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Keywords: Epoxy resin, Coating, Thermal aging, Radiation aging,chemical structure analysis, Lifetime
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