[en] Experiments designed to simulate certain types of postulated loss-of-coolant accidents in CANDU reactors show that, for some conditions, long time delays occur before the injected water is able to penetrate down the feeders to reach the horizontal fuel channels. The time delays are identified as a ''hot-wall'' effect, caused by countercurrent flow flooding in the feeders, due to the interaction between the water downflow and the upflow of steam generated by release of heat from the feeder pipe walls. This paper describes results of full-scale tests to measure the hot wall delays for the CANDU reactor core geometry. A theoretical model is described that predicts the measured time delays reasonably well. (orig.)