Many nuclear power plants in Japan and overseas have experienced stress corrosion cracking in the weld portion of the apparatus made from stainless steel. To deal with this problem, a preventive maintenance method, which covers welding parts with thermosetting resin, has been used. By this method working time for coating in the plant is so long that it has made a serious problem for the workers' health. Thus we have developed a new method to cover the welding part with resin. This method can reduce the working time in the plant by preparing the composite sheets in the factory. Two thermosetting resins, epoxy and vinyl ester, were used for this system. Adhesive strengths of the composite systems were measured under various conditions. Both composite materials showed the good adhesion against SUS (>2MPa) over the temperature range from 0 to 150°C in the air. The epoxy composites applied under water had the similar adhesion strength to that in the air. The adhesive strengths after gamma beam irradiation of 20MGy kept more than 2MPa, and it was revealed that these materials have the excellent irradiation proof properties. The arrenius plots made from the results of tensile tests after the heat treatment indicated the lifetime of more than 40years. These two materials could be coated well on the rough welding surfaces as well as the flat surface in the practical tests. This system is expected as an effective preventive maintenance method for covering over the weld due to the high performances in heat and radiation resistances and working time.

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