Numerical Investigation of Natural Convective Condensation with Noncondensable Gases in the Reactor Containment after Severe Accidents

Abstract EN

The heat and mass transfer processes of natural convective condensation with noncondensable gases are very important for the passive containment cooling system of water cooled reactors.

Numerical simulation of natural convective condensation with noncondensable gases was realized in the Fluent software by adding condensation models.

The scaled AP600 containment condensation experiment was simulated to verify the numerical method.

It was shown that the developed method can predict natural convective condensation with noncondensable gases well.

The velocity, species, and density fields in the scaled AP600 containment were presented.

The heat transfer rate distribution and the influences of the mass fraction of air on heat transfer rate were also analyzed.

It is found that the driving force of natural convective condensation with noncondensable gases is mainly caused by the mass fraction difference but not temperature difference.

The natural convective condensation with noncondensable gases in AP1000 containment was then simulated.

The temperature, species, velocity, and heat flux distributions were obtained and analyzed.

The upper head of the containment contributes to 35.1% of the total heat transfer rate, while its area only takes 25.4% of the total condensation area of the containment.

The influences of the mass fraction of low molecular weight noncondensable gas (hydrogen) on the natural convective condensation were also discussed based on the detailed species, density, and velocity fields.

The results show that addition of hydrogen (production of zirconium-water reaction after severe accident) will weaken the intensity of natural convection and the heat and mass transfer processes significantly.

When hydrogen contributes to 50% mole fraction of the noncondensable gases, the heat transfer coefficient will be reduced to 45%.