Analysis of start-up and long-term operation characteristics of passive residual heat removal system

Highlights: • Different CMT operation modes in the process of residual heat removal are compared. • The influences of different start-up times of the PRHRS are compared. • Separate heat pipe is introduced to increase the effective time of the PRHRS. • Conjugate boundary method is verified and used to study the characteristics of the SPH. - Abstract: Since the passive residual heat removal system (PRHRS) can transfer the decay heat from the core through the passive form and increase the inherent reliability of the system, it has received the attention of many researchers. The present researches mainly focus on the analysis of heat removal characteristics and design optimization, but pay less attention to the start-up and long-term operation characteristics under different conditions. In this paper, the simulation models of the reactor and PRHRS on the secondary side of steam generator are established by the RELAP5/MOD4.0 computer code. The operating characteristics of the PRHRS under the station blackout accident are studied. The results show that the operation of the system is affected significantly by the water level of the pressurizer and the initial water volume of the water tank. Based on the results, the start-up and long-term operation characteristics of the PRHRS are further analyzed. The research results show that, when the injected flow rate of the CMT is large enough, the natural circulation in the primary loop would be interrupted because a lot of residual heat is absorbed by the cool water, but this phenomenon will not threaten the safety of reactor; the different start-up time of the PRHRS has certain influences on the primary loop parameters, with little effect on the final heat derivation; the effective operation time of the PRHRS is strongly dependent on the initial volume of the water in the tank and the introduction of separate heat pipe could greatly reduce the dependence. The research results in this paper have important reference values that are critical for the design and operation of the PRHRS on the secondary side of the steam generator.