To optimize containment design and enhance the passive safety characteristics of nuclear power systems, this study proposes a passive containment heat absorption system based on phase change energy storage principles, aiming to achieve peak suppression and delay of containment pressure during the early stage of post-accident scenarios. The specific heat capacities of two phase change materials (PCMs), paraffin 56–58 and PEG6000, were measured using the sapphire method. A visual experimental loop was also constructed to investigate PCM behavior under nuclear reactor accident conditions, and the overall heat storage performances of paraffin 56–58, PEG6000, and conventional water were comparatively evaluated. The results indicate that when the heating fluid temperature is 100 °C and the flow velocity is 0.86 m/s, the thermal equilibrium times of paraffin 56–58 and PEG6000 were approximately 12900 s and 48000 s, respectively. After solidification, PEG6000 formed a porous-like structure, resulting in inferior cyclic heat transfer performance. As the heating fluid temperature increases, both PCMs show accelerated thermal response; however, the heat storage rate per unit time of paraffin 56–58 is higher than that of PEG6000. Paraffin 56–58 demonstrates greater potential for application in storing decay heat released from the reactor core after an accident within the containment. The findings of this study provide a theoretical basis for the development and application of phase change energy storage systems. 

severe accident mitigation,passive safety,containment,latent heat storage,PCM,thermal storage performance