An experiment on a heat transfer and a natural-circulation performance for an integral-type reactor have been carried out using the VISTA facility, and the calculated results using the TASS/SMR and MARS codes have been compared with the experimental results. The VISTA is an experimental facility that consists of a primary system, a secondary system, and a passive residual heat removal system (PRHRS), to simulate the SMART (SysteM integrated modular Advanced ReacTor) plant. The experimental results show that the fluid is stabilized well in the primary system and the PRHRS under natural-circulation conditions. The TASS/SMR and MARS codes predict the overall characteristics of the natural circulation in the primary system and the PRHRS well. From the calculation results, most of the heat transferred from the primary system is removed at the PRHRS heat exchanger by a condensation heat transfer. Under natural-circulation conditions in the integral reactor, a smoothing function at the transition region between different heat transfer modes will be adopted in the TASS/SMR code and a pressure-loss model needs to be improved on the cross-flow bundle geometry in the MARS code.