Kinetic Monte Carlo simulation of hydrogen diffusion in tungsten

- Kinetics Monte Carlo (KMC) method is developed to model H diffusion in W.
- KMC determined diffusion coefficient for H in W is = 8.45 × 10−7 exp(−0.440/kBT) [m2/s].
- KMC result matches experiment value very well.
- KMC result is much more accurate than other simulation methods.

This research developed a Kinetic Monte Carlo (KMC) method for simulating hydrogen diffusion in tungsten bulk. The KMC inputs such as diffusion paths and energy barriers are based on the first principle calculations in the literatures. In this simulation model, stable hydrogen interstitial sites in tungsten are the tetrahedral sites on each surface of the bcc lattice, and each site has four tetrahedral neighboring sites. A numerical program has been developed to perform the diffusion simulation for any hydrogen concentration and tungsten temperature combination. The KMC calculated diffusion coefficients fitted to the Arrhenius equation is D [m2/s] = 8.45 × 10−7 exp(−0.440/kBT), which match the experiment data very well. The pre-exponential factor D0 is found to be proportional to the hydrogen concentration, and a more general diffusion coefficient equation is derived for other concentrations. At last, the neighbor condition as a function of the concentration is analyzed.