Numerical study of transient diffusion behavior of SF6 and He in a nuclear power plant condenser

When leakage occurs in the titanium tubes of a nuclear power plant condenser, the ability to quickly and accurately locate the position of the leaking tubes holds significant importance for the safe and stable operation of the condenser. SF6 and He are commonly used tracer gases for pinpointing the location of leaking titanium tubes in large condensers. In order to investigate the diffusion behavior of these two different tracer gases in the condenser of a nuclear power unit, a three-dimensional computational fluid dynamics (CFD) model of the condenser was established based on the porous media. Concentration distribution characteristics and diffusion rate differences of SF6 and He inside the condenser are analyzed through transient analyses. The results indicate that the amount of tracer gas leakage significantly influences the time it takes for the tracer gas to diffuse to the suction port, and the location of tracer gas leakage has a significant impact on the concentration distribution pattern at the suction port. He exhibits a faster diffusion rate compared to SF6. When a leak occurs at location 1 of the B4 module with a leak rate of 0.007 kg/s, the mass concentration of He peaks at the suction port of the A3 module after ∼2.2 s, whereas the mass concentration of SF6 reaches its maximum at the suction port of the A3 module after around 9.5 s.