The HPR1000 nuclear power unit in China utilizes a double-layer reinforced concrete containment and incorporates a safety design concept that combines both active and passive safety measures. This design significantly enhances the safety of the nuclear power system. However, the construction cost of HPR1000 is considerably higher compared to second-generation units, thereby impacting its economic competitiveness. In order to further improve the safety of nuclear power and to solve the contradiction between safety and economy, this paper proposes a new type of passive containment accident mitigation scheme based on HPR1000. A multifunctional pool (MP), which employs the condensation of steam jet injection in submerged condition to absorb the steam produced during a containment accident, serving as a means of pressure suppression. Furthermore, the water sources for the safety injection system, reactor cavity injection system, and core exchange system are all consolidated within the pool, resulting in significant simplification of the systems and equipment of the nuclear power unit. The performance of the scheme against large break loss-of-coolant accident (LBLOCA) is evaluated by the critical incident analysis program simulation. The results show that by appropriately compensating the volume of air space within the MP, it is possible to effectively impede the increase in pressure within the shell. Compared with HPR1000, the containment size can be reduced by nearly 47% and the total water capacity of the containment system is reduced by about 1 700 m³ while maintauning safety performance. The MP can store non-condensable gases in the containment after the accident, enhancing the heat transfer performance of the passive containment heat removal system (PCS). The core is adequately cooled, and the fuel cladding’s outer surface reaches a maximal temperature of 1 389 K, which is below the embrittlement failure temperature of 1 477 K, ensuring the integrity of the reactor core’s.