The U.S. Nuclear Regulatory Commission pressurized thermal shock (PTS) study had previously identified small-break loss-of-coolant accidents (SBLOCAs) as a risk dominant accident scenario due to (numerically calculated) primary loop flow stagnation at high pressure. The objectives of the present effort were twofold: first, to develop a physically based understanding of controlling thermal-hydraulic phenomena producing such PTS SBLOCA stagnation scenarios and second, to use these insights in developing a simple (computationally efficient) “mapping” tool to quantify the occurrence and thermal behavior of such high-pressure flow stagnation regimes. Review of the previous [transient reactor analysis code (TRAC)] calculations revealed that inaccurate modeling of vapor condensation erroneously produced the flow stagnation and hence overly conservative (rapid) vessel cooldown rates. Using a corrected version of this code, our new calculations now exhibit flow circulation. However, parametric analysis of less likely (more equipment failure—power-operated relief valves/ high-pressure injection pumps) scenarios revealed that flow stagnation was indeed possible but could only occur at lower pressures. This simple mapping procedure has been favorably benchmarked against the (TRAC) system calculations. This tool is therefore useful for screening possible risk dominant SBLOCA scenarios in various pressurized water reactor designs.