I've been developing & applying the nuclear safety analysis codes & methodologies to typical PWRs.I performed safety or performance analysis of typical Westinghouse-type nuclear power plants and OPR1000 nuclear power plants in Korea using computer codes, such as LOFTRAN, CESEC-III, RETRAN-3D, RELAP-5, THINC, CETP-D, TORC, VIPRE, etc., and safety analysis methodologies received from Westinghouse, ABB-CE, EPRI or NRC in the United States.Based on these experiences, I’ve been actively involved in the development of the safety analysis codes and methodologies since 2001.I've been participated in the "SPACE" code development project, which is the two-phase three-field thermal-hydraulic best-estimated safety analysis code for typical LWRs. The code has been verified and validated using various analytical, experimental or operational data. Through the successful V&V works, the topical reports have been prepared about the code and the safety analysis methodologies for DBAs. The licenses (SERs) of the code and methodologies for the safety analysis of NPPs in Korea had been issued in 2017. I’ve also been interested in applications of thermal hydraulics technology, which is mainly used in the safety analysis of nuclear power plants. I’ve reviewed or verified SMRs (small modular reactors) or else other advanced reactors, and participated in research to produce hydrogen using electricity or and waste heat generated from nuclear power plants.Until recently, I was also involved in various research tasks ranging from research administration to research strategy while developing & planning research policies.On July 1, 2018, I returned to the safety analysis group to verify the safety of nuclear power plants when a postulated accidents or multiple cause accidents occur. Recently, the researches have been being made on ways to improve the safety of nuclear power plants by using technologies of the 4th industrial revolution such as artificial intelligence, big data or else other technologies.I will continue to work to help my company and societies by utilizing nuclear power and thermal hydraulics technologies.