Critical heat flux (CHF) tests have been performed for a vertically upward R134a flow in a 5 x 5 rod bundle in the following parameter ranges: outlet pressure 1.5-3.0 MPa, mass flux 50-2500 kg m(-2) s(-1), inlet quality -0.08 to -0.75 and critical quality -0.17 to 1.58. Parametric trends of the CHF data agree well with the general understanding. Water equivalent CHF data is generated using a set of well-established modeling parameters, then compared with (a) the EPRI/Colombia University's water CHF database for similar geometry and experimental conditions and (b) commonly used CHF prediction methods. The water equivalent CHF data generated from the present tests shows a good agreement with the actual water CHF data for both Katto's and Ahmad's modeling methods when considering the differences in the detailed geometric and flow conditions. They are also predicted well by the 1995 CHF look-up table. These results indicate that R134a can be a good modeling fluid for the CHF of water in rod bundles at least in the investigated parameter ranges. (c) 2005 Elsevier Ltd. All rights reserved.