Thermal stratification is a common phenomenon in the surge line of Pressurized Water Reactors (PWR). The stratification temperature difference (ΔT) and cyclic behavior severities are the most prevalent during heat-up and cool-down operations of a PWR, when temperature difference between the pressurizer and the hot leg in the Reactor Coolant System (RCS) becomes the largest and inventory fluctuations in RCS are the highest. These behaviors cause cyclic damages and deformations of the pipe. In addition, USNRC recommended integrity evaluations of the piping system submitted to thermal stratified flow in USNRC Bulletin 88–11. In this reason, the importance of monitoring the fatigue induced by the thermal stratified flow in thick-wall pipes rises more and more. To raise the accuracy of solutions for the fatigue damage induced by thermal stratification, the exact global temperature profile is needed to be derived. Many studies have been performed to obtain these profiles. The purpose of this paper is to predict the global temperature profiles in the piping systems submitted to thermal-stratified flow from measured temperatures on the outside wall. It presents both the inverse transfer function method and the numerical-analysis method.

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