Modeling Swirl Penetration and Thermal Cycling in Un-Isolable Branch Lines of PWR Plants

Thermal cycling has been identified as a mechanism that can potentially lead to fatigue cracking in un-isolable branch lines attached to pressurized water reactor (PWR) primary coolant piping. A significant research and development program has been undertaken to understand the mechanisms causing thermal cycling and to model the thermal-hydraulic boundary conditions for use in piping structural analysis. This paper will describe test and modeling results, with primary emphasis on predicting swirl penetration in dead-ended branch lines. Swirl penetration refers to the establishment of an axial vortical structure within the branch line, which has been shown previously to be the primary driving mechanism for thermal cycling in dead-ended branch lines. Swirl penetration testing was performed in a high Reynolds number facility to investigate the fluid dynamic and geometric parameters affecting the formation and decay of branch line swirl. Test results and preliminary model development are presented.Copyright © 2003 by ASME