Numerical Investigation on Heat and Mass Transfer of Volatile Flammable Gases Within the Nuclear Reactor Containment

Abstract

Diffusion of volatile flammable species in the air can cause a fire risk within the nuclear reactor containment. However, computational prediction on species concentration distributions remains significantly difficult due to a shortage of multicomponent diffusion coefficients. In this work, considerable effort has been made to calculate concentration distributions of formaldehyde and benzene vapor volatilized from radiation-proof coatings of reactor containment walls. For this purpose, a numerical model is proposed to simulate species transport and concentration distributions due to full multicomponent diffusion and thermal diffusion. Meanwhile, the in-house UDFs' source code is programmed for solving diffusivities and essential thermophysical properties. After compiling and linking the source code with the numerical model, a pressure-based SIMPLE algorithm is imposed for pressure–velocity coupling calculations. Computational results indicate that concentration distributions are highly dependent on the fluid motion as well as potentially flammable areas decrease gradually with increased ventilation rates. Also, primary and secondary vortices are symmetrically distributed about the vertical centerline of the reactor containment as well as triangular secondary vortices can significantly suppress concentrations of formaldehyde and benzene vapor at the bottom portion of the containment. Finally, excellent agreement is observed between computational results and analytical solutions.