[en] Dynamical models and numerical methods for a digital simulation of protected transients in loop-type LMFBRs resulting in EPRI-CURL code are presented. The model is capable of simulating operational transients, anticipated incidents, and postulated accidents which do not lead to sodium boiling. The dynamical models include: point reactor kinetics, primary, intermediate, and tertiary system heat transfer and coolant flow dynamics governed by forced and natural convection effects; and plant protection and control systems. A numerical method is incorporated which calculated the characteristic times of the 489 state variables modeling the entire system, and compares them with a variable preset integration timestep. A Runge-Kutta algorithm is applied to those state variables with moderate and slow response, and a quasistatic approximation is applied to those with rapid response; i.e., the stiff equations. This assures numerical stability and is shown to greatly reduce the computation time requirements without much sacrifice in accuracy. The steady state (quasistatic) equations are further utilized to determine the unperturbed state of the system prior to transient initiation. The system response to a complete loss-of-electric power leading to buoyancy-induced natural circulation is calculated and compared to parallel calculations using DEMO and SSC-L simulation models. (orig.)