A model is developed that enables the determination of steady-state values of all system variables of the boiling water reactor simulator loop DESIRE. The model calculates natural-circulation mass flow rate, subcooling, carry-under, and feedwater flow rate from the three independent variables: power, feedwater temperature, and the setting of a controllable friction valve. The void fraction in the assembly is calculated using the drift-flux model with Dix's correlation. A submodel for the calculation of carry-under is derived on the basis of measurements. Comparison of the model with measurements shows an excellent agreement over a wide range of operating conditions.