In the past, most of nuclear power plants in the world were constructed with 30 or 40 years of design-life. But some nuclear power plants are still operating beyond their design lives through regulatory permission to extend its operation. To extend designlife of nuclear power plant, it needs additional design and replacement for equipment and piping. It has also to meet the regulatory requirements under the approval of the regulatory body. Therefore, the original design life of 60 years has been applied to safety class 1 equipment and piping of some nuclear power plants. One of the methods to confirm whether safety class 2&3 equipment and piping can also operate up to 60 years is to perform the fatigue evaluation based on ASME B&PV Code. In consideration of the effects of load increase by extending their lifespan from 40 to 60 years, the equipment and piping should be evaluated the structural integrity by performing the heat transfer analysis and structural analysis. In this paper, the fatigue evaluation for the Safety Class 2 FW piping with 40-year design life was performed based on Subsection NB/NC of ASME B&PV Section III and Reg. Guide 1.207 to show that its fatigue integrity can be secured under 60-year operation even in the PWR environmental conditions.

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