In the most challenging nuclear power plant accidents, transient critical heat flux (CHF) is a primary phenomenon that drives peak cladding temperature and ultimately fuel failure. It is not yet determined whether the use of steady-state CHF methods can accurately predict transient CHF under the conditions of a blowdown due to a loss of coolant accident. There are limited comprehensive experiments at prototypic conditions. Moreover, complex multi-physics makes it difficult to mechanistically quantify hysteresis.
To address this deficiency, a quality separate-effects test facility was built to simulate an electrically heated rod under blowdown conditions. The test facility reached pressurized water reactor thermal-hydraulic conditions. CHF was repeatedly measured with depressurization rates ranging from 7 MPa s-1 to 17 MPa s-1. From the gathered literature, these measurements at prototypic conditions acquired in a controlled methodology are novel to the body of knowledge. Finally, steady-state CHF methods were evaluated using RELAP5-3D simulations. The results showed many steady-state CHF methods performed inadequately, but wide-ranged look-up table methods had the most acceptable results. Moreover, there was no significant correlation between prediction accuracy and depressurization rates tested.