Critical heat flux during reflood transients in small hydraulic diameter geometries

Critical Heat Flux (CHF) at a low flow condition in a small hydraulic diameter duct is an important phenomenon for a MTR/ATR (Materials Test Reactor/Advanced Test Reactor) design under a number of accident conditions including reflood transients. Current CHF models in the literature, such as the Mishima/Nishihara and Oh/Englert CHF models, are based on macroscopic system parameters and not local thermal hydraulic conditions. These macroscopic parameter-based models cannot be readily used for analysis in transient best-estimate thermal hydraulic codes. This investigation focuses on developing a low flow rate CHF correlation, based on local conditions, that is amenable to implementation into a best-estimate transient thermal hydraulic code for a small hydraulic diameter channel. The model development proceeds with a means of correlating CHF data to local conditions parameters and then applying a correction factor to the resulting correlation, that permits accurate predictions over a range of pressures. An evaluation of the proposed local conditions-based CHF model is conducted by predicting independent sets of CHF experimental results over a range of flow rate, pressure, and sub cooling conditions. Conclusions on the viability of the proposed CHF model and suggestions for future efforts in improving the reflood heat transfer CHF models for small hydraulic diameter ducts are provided with an evaluation of the model results.