Development of a thermal striping spectrum for use in evaluating pressurizer surge line fatigue

Data taken from the German HDR test facility have been evaluated to understand the thermal-hydraulic phenomena which occur during conditions of stratified flow in a pressurizer surge line. The temperature oscillations in the fluid layer between the hot and cold fluids can approach the maximum possible top-to-bottom temperature differential. The temperature oscillation at the pipe wall is considerably less than that in the fluid, being no more than about 50 percent of the maximum possible temperature difference. The location of this fluid interface changes with changing flow rate in the pipe. At lower flow rates, the magnitude of the temperature fluctuations decrease significantly. The ordered overall range pair cycle counting approach was used to determine pipe surface temperature fluctuation spectra. Stress analysis was conducted to determine the fatigue usage resulting from the developed spectra. This evaluation, conducted for typical plant startup operating conditions (surge line temperatures and flows), shows that thermal striping fatigue usage will be minimal