Development of a thermalahydraulic system code, TAPINS, for 10 MW regional energy reactor

Small modular reactors (SMRs) with integral system layout have been drawing a great deal of attention as alternative options to branch out the utilization of nuclear energy as well as to offer the inherent safety features. Serving to confirm the design basis and analyze the transient behavior of an integral reactor such as REX-10, a thermalahydraulic system code named TAPINS (Thermalahydraulic Analysis Program for INtegral reactor System) is developed in this study. The TAPINS supports the simple pre-processing to build up the frameworks of node diagram for the typical integral reactor configuration. The TAPINS basically consists of mathematical models for the reactor coolant system, the core, the once-through helical-coil steam generator, and the built-in steamagas pressurizer. The hydrodynamic model of the TAPINS is formulated using the one-dimensional momentum integral model, which is based on the analytical integration of the momentum equation around the closed loop in the system. As a key contribution of the study, a dynamic model for the steamagas pressurizer with non-condensable gas present is newly proposed and incorporated into the code. The TAPINS is validated by comparing against the experimental data from the pressurizer insurge tests conducted at MIT (Massachusetts Institute of Technology) and natural circulation tests in the RTF (REX-10 Test Facility) at RERI (Regional Energy Reactor Institute). From the comparison results, it is demonstrated that, notwithstanding a few simplifying assumptions and the undemanding solution method to facilitate solutions for transients, the TAPINS can provide a reasonable prediction on the performances and the transients of an integral reactor system operating on natural circulation.