[en] This study aims at identifying the plausible thermal-hydraulic (T-H) phenomena and processes during domestic Pressurized Water Reactors (PWRs) accidents, and ranking their relative importance against the respective safety criteria. Korea Institute of Nuclear Safety (KINS) is structuring the best-estimate REactor Thermal-hydraulic Analysis System (KINS-RETAS), to be used for a regulatory audit of the applicant's safety analysis results. The T-H system code MARS, originally developed by KAERI, is a pivot code in the KINS-RETAS, where the RCS T-H responses to postulated plant conditions are simulated. According to the Software Quality Assurance (SQA) guidance, the verification and validation (V and V) of MARS is required to confirm its adequacy to the targeted application, simulation of TH phenomena in the system to the component levels during the reactor conditions of normal operation to DBA in domestic PWRs. Consolidation of the previous LBLOCA PIRT results, compensated by the PIRTs for other transients except the LBLOCA, is needed to organize the part of the MARS code V and V matrices