Thermal stratification of pressurizer surge line in nuclear power plant induced by the stratification of fluid results in additional stresses (system-dependent and system-independent stresses). These additional stresses are related to the thermal stratification distribution, such as temperature difference, stratification location, stratification length and boundary layer slope and thickness. This thermal stratification distribution is effected by several parameters such as turbulent penetration length and surge line slope. These influence factors are studied with numerical method. For the additional stresses, this study theoretically establishes the solution of the system-dependent stresses according to the thermal stratification distribution assumption. With the system-dependent and system-independent stresses, a complex three-dimension problem is simplified into a one-dimension. Using this effective one-dimension method, fatigue evaluation can be fast processed and accurate improved in engineering analyses.
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