Incorporation and testing of refrigerant fluids (R-134a) in the subchannel analysis code CTF (COBRA-TF)

The subchannel codes such as COBRA-TF (CTF) are often used in the simulation of thermal hydraulic parameters in a reactor core. Use of these codes for safety analysis requires extensive validation against experimental data. While typically validation is performed on experiments in water, a large number of experiments using refrigerant are available in literature and may be used to expand the validation range of these codes. This research is focused on the subchannel code CTF which has been modified to incorporate Refrigerant-134a fluid properties. Subsequently the modified code was tested against several experimental results available for R-134a. Evaluation of the Heat Balance Method (HBM) and Direct Substitution Method (DSM) for CHF was carried out. In the case of the CHF Look-Up Table (LUT), fluid-to-fluid scaling was performed to predict the local CHF phenomena. Overall the HBM predictions show better agreement (with the exception of Katto's correlation when applied to test section with a cold-wall) as compared to the CHF LUT results which tended to significantly overpredict dryout under high qualities.