Analysis of core flooding capability and containment vessel pressure during LOCA on advanced marine reactor MRX

Using a light water reactor transient analysis code RELAP5/MOD2, LOCA analyses in relatively early phase including a pressure balance phase between the pressure vessel and the containment were carried out on an Advanced Marine Reactor (MRX) which employs a water filled containment vessel and a natural convection type decay heat removal system as a passive safety system. The changed parameters of the analyses were a location of pipe rupture, the initial gaseous volume of the containment vessel and so forth in order to survey the operable range of the water level in the containment to keep the core flooding and suppress the containment vessel pressure under a design pressure during LOCAs. The analytical results showed that the operable range of initial gaseous volume of the containment vessel was 26-37 m3 (water level of the containment: 11.5 to 11.8 m) around the reference volume 30 m3. As for the long term cooling, it is confirmed that the capabilities of EDRS (Emergency Decay Heat Removal System) and CWCS (Containment Water Cooling System) are suitable to keep the core flooding and suppress the containment vessel pressure even during the long term cooling after LOCA. (author)