The tritium recovery technique at the steam generator in fast breeder reactor under the double pipe concept was studied by both of experiment and simulation. The permeation of tritium was lowered at ~1000ppm oxygen in Ar as a recovery gas. But tritium is easily converted to water form by adding 10ppm oxygen. To explain these experimental results and expand the tritium behavior at double pipe concept, DFT and Monte Carlo simulations were applied. The surface oxide layer mode was developed and stability of tritium was evaluated. It was found that most stable structure was formed in the oxide layer although tritium is unstable at the surface of oxide layer. Tritium permeation rate was almost the same even if the oxide layer was formed, but the tritium retention is enhanced by adding the oxide layer. To expand these results to tritium permeation and recovery model, numerical analysis was performed as a function of sweep rate, material thickness and thickness of surface oxide layer. It was found that control of sweep rate is one of key factors. But the design restriction, control of oxide layer thickness by flowing O2+Ar gas will be potential option for the recovery of tritium at steam generator.