Conceptual design and analysis of a combined passive cooling system for both reactor and spent fuel of the pool-vessel reactor system

A novel combined long-term passive cooling system is proposed for the pool-type reactor, aiming to enhance the safety and reliability of the entire system during extended station blackout accidents (SBO). This passive cooling system primarily consists of a natural circulation primary loop, a C-type heat exchanger submerged in the pool, the reactor pool (RP) and the spent fuel pool (SFP), and a two-phase loop thermosyphon (TPLT) cooling subsystem. The TPLT cooling subsystem comprises a separated evaporator and condenser, with the evaporation bundle immersed in the SFP and the condensation bundle placed within a dry air cooling tower. Three typical design configurations were selected for numerical simulation and performance evaluation, including C-type tube bundles placed inside the RP and TPLT evaporation bundles placed inside the SFP, C-type tube bundles and TPLT evaporation bundles both placed inside the SFP, and C-type tube bundles and TPLT evaporation bundles both placed inside the RP. The analysis results demonstrate that this combined passive cooling system can effectively achieve passive cooling of the reactor and spent fuel under accident conditions, mitigate the rise in reactor coolant temperature, and prevent saturation boiling in the RP and SFP. Furthermore, different system layout configurations have a significant impact on its operational characteristics, allowing for rational optimization and improvement based on specific safety requirements of the system.