PWR Pressurizer Surge Line Thermal Stratification Calculator
Compute top-to-bottom temperature gradient (ΔT), thermal bowing curvature, bending stress, and cumulative fatigue usage factor per NRC Bulletin 88-11.
Surge Line Conditions & Stratification
Stratification Stress & Fatigue Output
Recommended Tools & Equipment
Tested hardware and components for high reliability
Thermal Stratification & NRC Bulletin 88-11
During low-velocity flow transients (such as insurges or outsurges during reactor startup or shutdown), hot water from the pressurizer and colder water from the Reactor Coolant System (RCS) hot leg flow through the horizontal surge line without turbulent mixing due to density differences. Hot water rides across the pipe crown while cold water settles along the pipe invert.
Thermal Bowing and Fatigue Consequences
The differential thermal expansion between the hot upper half and cooler lower half causes the pipe to bow downward like a bimetallic strip ("banana effect"). Restraint by pipe supports and terminal nozzles at the pressurizer and hot leg produces severe cyclic bending stresses, which caused pipe whip restraint lift-off and fatigue cracking documented in NRC Bulletin 88-11.