Evaluation on CAP1400 Passive Containment Cooling System Capability

CAP1400 is the large advanced passive demonstration plant, which is one of the National Science and Technology Major Projects. CAP1400 is an innovative design and development based on AP1000 advanced design philosophy with passive safety features. While keeping the same safety level as AP1000, CAP1400 aims to improve plant economy by means of enlargement of reactor core, increase of unit power output and optimization of plant overall design. The CAP1400 nuclear power plant uses the passive containment cooling system (PCS) to remove heat from the containment after accidents when high mass and energy fluid is released from primary or secondary systems. On account of the more mass and energy release and the internal structures design changes of CAP1400, the operating parameters may exceed the range of AP600 and AP1000 containment tests. In order to further study the performance of the CAP1400 PCS system, a series of verification tests have been carried out in the National PWR Project. This paper describes the background of the test setup, the really focused issues of the experiment and the main test results. The experimental data from separate effect tests and large scaled test were analyzed and evaluated in depth. The performance of the PCS was studied, including water film coverage outside the containment shell, water film evaporation and heat transfer characteristics, air natural circulation and convection outside the containment vessel, convection and condensation of the air / steam mixture on the inner surface of the containment vessel, as well as the overall performance of PCS systems. The results show that the important correlations applied in CAP1400 containment pressure and temperature response analysis could predict the heat and mass transfer reasonably and the envelope factors used for safety analysis are conservative. Parameters affecting the containment pressure and temperature have been investigated, and the reasonability and conservation of containment thermal and hydraulic analysis code has been evaluated by comparing the calculated results with the measured results. The results show that containment analysis code could simulate the important heat transfer phenomena of the test containment well and predict the temperature and pressure response reasonably with some conservation. Containment pressure and temperature response analysis after typical design basis accident analysis have been preformed, and the results show that the CAP1400 PCS is sufficient to remove the heat from the containment which ensure the safety of the plant. All of the results provide firm basis for the development of CAP1400 and sufficient support for the safety review. This work also lays the foundation for the further development of relevant analytical tools and the development of advanced and passive technologies with higher power levels.