Because of high marketability of SMR, although many countries are trying to develop SMR, the SMR market is not formed yet. For early dominance of SMR market, the SMR. system should be fail-safe, simple and economical. In order to develop FAil-safe Simple Economical SMR (FASES) system we applied the design characteristics of HTGRs into water-cooled reactors. In this study, we performed conceptual design and feasibility study for the FASES system. The feasibility study is focused on a thermal-hydraulic aspect in normal operating conditions and several accident conditions. The key design characteristic of the FASES system obtained from design concepts is to have sufficient decay heat removal capability even in the accidents involving extended station blackout (SBO), failure of passive decay heat removal system (PDHRS), and failure of emergency core cooling system (ECCS). Based on the design concepts, we could define several thermal-hydraulic design requirements. Then, we performed thermal-hydraulic analysis for feasibility study and proposed the specific design of the FASES system satisfying several design requirements.