One implementation of vented low pressure containment for HTR

Abstract As third layer of barrier for radioactive retention, and main structure for the fourth level of defense in depth requirement, containment is important for nuclear power plant. For modular HTR, the containment is normally designed as vented low pressure containment (VLPC), sometimes another name of confinement is also used. The main functions of VLPC include: to protect the power plant from external hazard, to provide suitable environment during normal operation, to reduce the radioactive release during and after accident by early direct release and later filtration. The basic requirement for the safety function of radioactive retention by VLPC is ALARA in the case of modular HTR. Even though, the detailed implementation of VLPC is different for different power plant, for example even in China, HTR-10, HTR-PM, and newly designed HTR-PM600 have slightly different implementation. This paper will discuss the different implementation of VLPC for modular HTR in China, especially the new implementation of VLPC for HTR-PM600. Corresponding to the fact that there are 6 NSSS modules in one building, the new implementation of VLPC for HTR-PM600 is to treat the whole reactor building as the VPLC, and sub-atmosphere ventilation is applied to the reactor building, instead of individual reactor cavity as in the case of HTR-PM and HTR-10. And the reactor building can have the capability to withstand the air craft crash. The auxiliary systems for VLPC in HTR-PM600 will also be changed from that of HTR-PM accordingly.