Abstract
To obtain the knowledge that contributes to the safer operation of nuclear power plants and their prompt recovery and termination in the event of an accident, soft epoxy resins with rubber-based additives—used as insulators and airtight sealants in electrical penetrations in nuclear power plants—were aged under several simulated severe accident environments with different conditions of heat, gamma rays, and exposure to superheated steam containing no oxygen. Then, changes in structural, dynamic mechanical, mechanical, and dielectric properties were examined. It has been found that this resin becomes hard as a result of cross-linking if aged by irradiation with gamma rays. Since the cross-linking slows down the molecular motions, the glass transition temperature increases, whereas the dielectric permittivity and the dielectric loss factor decrease unless the steam penetrates the sample. Although the sample melts and disappears if directly exposed to superheated steam at 171 °C or 200 °C, the irradiation with gamma rays conducted prior to the steam exposure can mitigate the hydrolysis induced by the steam. Although the soft epoxy resin shows drastic changes in various properties, its properties after the aging approach or exceed the corresponding ones of the non-degraded ordinary hard epoxy resin. Therefore, it seems that using soft epoxy resin according to its purposes would not be a problem.
Highlights
Epoxy resin is widely used in industries and ordinary households as adhesives and electrical insulating materials because of its excellent heat resistance, electrical insulating properties, and durability [1,2]
Soft epoxy resin with a rubber-based additive provided by a Japanese supplier of electrical goods for nuclear power plants was used as samples
The above important fact clearly pressed if gamma rays were irradiated beforehand
Summary
Epoxy resin is widely used in industries and ordinary households as adhesives and electrical insulating materials because of its excellent heat resistance, electrical insulating properties, and durability [1,2]. On the other hand, when epoxy resin alone has a weak point, various additives or fillers are added to overcome such disadvantages while retaining its excellent properties [1,2]. The present study deals with epoxy resin being used as airtight sealants in electrical penetrations for cables in nuclear power plants. This material needs good electrical insulating performance as it is expected to work as electrical insulating materials for electric conductors penetrating through the electrical penetrations. Some manufacturer of nuclear power apparatus considers that ordinary epoxy resin alone might be too hard for sealants. A rubber-based additive is added to epoxy resin, which is called soft epoxy resin, to increase its softness and toughness [11,12]
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