The current regulatory requirement that peak cladding temperatures (PCTs) never exceed 1204°C (2200°F) at any time during a loss-of-coolant accident (LOCA) is frequently the most limiting factor in setting core peaking factor limits. Of the many plant specific characteristics involved in predicting a fuel rod’s thermal response to a LOCA, the containment or “back” pressure plays a significant role, especially in pressure suppression pressurized water reactor (PWR) containments. The back pressure effect is studied by comparing the predicted PCT histories at back pressure levels of 138, 155, 172, and 207 kN/m2 (20, 22.5, 25.0, and 30 psia). A typical four-loop PWR with 15 × 15 fuel assemblies is analyzed. The analysis is performed using an in-house LOCA code named HEATUP-R/AEP, which calculates fuel thermal response during core reflood. In addition to temperature, the reflood rates, exit qualities, and cladding oxidation rates are studied. Results show significant increases in PCTs at lower pressure due to enhanced steam binding in the coolant loops.