[en] Experimental studies are being conducted in ¹/₁₅-scale models of a four-loop pressurized water reactor at pressures to 60 psig to extend the understanding of steam-water interaction phenomena and processes associated with a loss-of-coolant accident. Penetration studies were undertaken in the ¹/₁₅-scale, steel vessel model with a 1.0-inch downcomer gap width to investigate the effect of gap width variation on ECC penetration. Preliminary analysis of these data indicates that a larger downcomer gap width does not alter the effects of model operating pressure level, injection water flow rate, and injection water subcooling that have been observed in previous penetration studies conducted with a 0.59-inch gap