Transient analysis of the safety characteristics on a super carbon-dioxide cooled micro modular reactor.

• Transient analysis is performed on S-CO 2 cooled micro modular reactor using modified SYST-CO 2. • Safety characteristics under ULOFA, URIA, ULOHS, UOC and PLOFA are investigated. • The MMR core outlet temperature is to be the most constraining factor in the reactor safety. The supercritical CO 2 (S-CO 2) demonstrates great potential as a coolant for nuclear reactors due to its low critical pressure and temperature. It offers improved thermal efficiency and decreased requirements for structural materials. By incorporating core physics models and updated thermal–hydraulic models, the SYST-SCO 2 code developed in prior research has been enhanced and utilized for conducting transient safety analysis on the micro modular reactor (MMR) proposed by the Korea Advanced Institute of Science and Technology (KAIST). The analyzed transients include the Unprotected Loss of Flow Accident (ULOFA), Unprotected Reactivity Insertion Accident (URIA), Unprotected Loss of Heat Sink (ULOHS), Unprotected Over Cooling (UOC), and the Protected Loss of Flow Accident (PLOFA). It is found that the MMR experiences the exceeding of coolant outlet temperature limit of 676℃ in the ULOFA for over 155 s. With the reactor shutdown system put into operation, the reactor core can be maintained to operate with the fuel pellet, cladding and coolant temperatures below their limits respectively in the LOFA. Enough safety margin can be left for the MMR reactor core in URIA, ULOHS and UOC transients. Among the safety limits for the fuel and coolant, the core outlet temperature limit is the easiest to reach in the analyzed accidents. [ABSTRACT FROM AUTHOR]