Limiting countercurrent flow phenomenon in small break LOCA transients

Countercurrent flow limit phenomena in the loops of a PWR affects small break LOCA transients significantly. This paper reviews the countercurrent flow at three different locations in the loop to identify a limiting phenomenon during a cold leg small break. It is believed that the limiting phenomenon occurs at the inclined pipe which connects the hot leg to the steam generator. Therefore this phenomenon must be simulated properly in any numerical of physical simulations of small break LOCA's. It is pointed out that data from any test loops with scaling have to be analyzed with caution. Distortions in the flow areas of the steam generator tubes and hot leg may result in nontypical transients. (orig.)