A fast-running simulator code for pressurized water reactors, called FISA-1 (Fully-Implicit Safety Analysis), is developed here to simulate operational transients. This simulator code is based on the homogeneous equilibrium mixture model and the fully-implicit method for thermal-hydraulic analysis is the primary side.
The nonlinear finite difference equations in the finite difference form are linearized by the Newton-Raphson method for quick convergence. First, the energy equation is solved, which is decoupled from mass and momentum equations. The spatial acceleration term in the momentum equation is manipulated with the mass equation so that the mass flow rate can be written as a function of pressure. Substituting the mass flow rate expressed in terms of pressure into the mass equation, we finally obtain the linearized equation with the pressure variables only. Several physical models, component models, and control and protection models are implemented in FISA-1 for the analysis of the plant. The flow model of the primary side is tested with analytical methods, experiments, and other codes. Two different PWR plant transients are analyzed to verify the simulator code by being compared with plant data and the results of RETRANO2. Not only fast-running capability but also reasonable accuracy and absolute stability are proved.