Critical Heat Flux in TRIGA-Fueled Reactors Cooled by Natural Convection

An experimental study of low-pressure, natural convection critical heat flux (CHF) has been carried out with full-scale fuel pins, simulating typical Training, Research, Isotopes, and General Atomics (TRIGA) reactor conditions. The test section is an annular upwardly flowing channel formed by a round tube and a simulated fuel pin heater rod with a chopped-cosine power profile, located in the center of the tube. Experiments were performed under the following conditions: inlet water subcooling varying from 10 to 70 K, pressure varying from 110 to 200 kPa, and natural circulation mass flux up to 400 kg/m²s. CHF was observed, and associated data have been compared with selected CHF correlations. It has been found that the CHF increases as the pressure or mass flux increases, but does not significantly depend on the inlet subcooling. Among the numerous presented CHF data and correlations, few data exist, and no specific correlations have been developed for TRIGA reactor conditions. Because of the lack of specific correlation, the correlations of Bernath, El-Genk et al., Mishima and Ishii, and Block and Wallis have been used to estimate the TRIGA CHF outside of their intended ranges of applicability. These correlations are evaluated against the current experimental data.