[en] Sensitivity studies have shown that during the blowdown phase of a hypothetical loss-of-coolant accident (LOCA) in a pressurised water reactor (PWR), the maximum temperature predicted for the cladding of a nuclear fuel element is highly dependent on the heat transfer relationships assumed to describe the onset of dryout and the subsequent post-dryout heat transfer at the relevant coolant conditions. In the present work, power transient experiments were performed using vertical round tube test sections to determine the heat transfer characteristics associated with a change from pre-dryout to post-dryout flow boiling conditions. Because of the availability of rig and instrumentation, tests were conducted using Freon-12 as the coolant and electrically heated tubes as the heat dissipating surfaces