COBRA-TF Analysis of the High Flux Reactor Hot Channel for a Postulated Large-Break Loss-of-Coolant Accident

In this study, calculations were performed to simulate a postulated large-break loss-of-coolant accident for the High Flux Reactor (HFR) cooling system using the COBRA-TF computer code. COBRA-TF has been chosen for this analysis since it has suitable and validated two-phase flow models and critical heat flux (CHF) correlations for channels having small hydraulic diameters. Calculations have been performed to determine the CHF margins for the HFR. Six types of calculations were performed to provide a range of CHF margins. All COBRA-TF calculations indicate that margin does exist to the CHF limit for the small-hydraulic-diameter highest-power HFR channel. The range of margin is 2.1 to 1.3 times the nominal power of the highest power channel, depending on the boundary conditions and CHF correlation used. The range of margin identified in the HFR analysis is consistent with the margin values used in commercial nuclear power plants.