Assessment of TAPINS and TASS/SMR codes and application to overpower transients in REX-10

This paper presents numerical studies to assess the applicability of the TAPINS and the TASS/SMR codes for an integral reactor on natural circulation and to evaluate the new reactor design and the transient responses of REX-10 during overpower transients. REX-10 is a small pressurized water reactor with integral design which aims at providing the small-scale electricity generation and the nuclear district heating. For thermal-hydraulic analyses of an integral PWR such as REX-10, an in-house system code named TAPINS (Thermal-hydraulic Analysis Program for INtegral reactor System) is developed by Seoul National University. Based on the simple field equations formulated using the momentum integral model, TAPINS consists of component models for the core, the helical-coil steam generator, and the steam-gas pressurizer. In this study, the design assessment and transient simulations of REX-10 are carried out using TAPINS, and TASS/SMR selected as another thermalhydraulic code for independent calculations. As preliminary analyses to assess the applicability of these two codes to REX-10, a series of tests at RTF (REX-10 Test Facility) are simulated and the calculation results are compared with the data. Thereafter the prototypical REX-10 is modeled by TAPINS and TASS/SMR. The major design parameters of REX-10 are identified through the steady-state calculation, and the transient responses to overpower transients caused by a reactivity insertion accident and an increase in feedwater event are investigated. The thermal-hydraulic behavior and safety performance of REX-10 are evaluated from the prediction results.