“…Typically, the system dynamics of a reactor is simulated by the complex codes consisting of the one-dimensional or three-dimensional neutronics, the correlations of two-phase follow, critical flow and thermal properties, and the built in control system blocks. Those codes such as RELAP, RETRAN, and TRACE, are applied for safety analyses, plant design, and predictions of postulated tests [1,2,3]. Although those advanced codes are programmed to calculate the systematic parameters during significant transients, the computing time is proportional to the nodolization of reactor models and specific transients.…”