Application of an improved WallDYN surface model to estimate ITER boronization layer lifetime

The WallDYN code was developed to model the coupled evolution of the impurity influx onto the first wall, the surface composition and the flux of impurities back into the plasma in fusion devices. It was recently shown that its default surface erosion/deposition model is poorly suited to describe cases where impurity sources deplete over time, causing net deposition zones to become net erosion zones, because it has a limited memory of previously deposited materials amounts. Therefore, the model was augmented by a dedicated deposition layer that records the deposited material allowing to re-erode it later and thus maintain a global material balance. The augmented surface model is compared to dynamic SDTrimSP calculations to verify its ability to model layer growth/recession and mixed material formation. Finally, recently published calculations on the B migration in ITER are repeated with the improved model and predictions on the B layer lifetime in the main chamber and layer deposition in divertor are refined. • The new three layer surface model for WallDYN allows to model complex transitions from net-deposition to net-erosion. • It compares well to dznamic SDTrimSP calculations. • The boronization life time estimates are unaffected by applying the new model. • BUT the B material balance is closed now. • The final location for B deposits at the inner target can be confirmed now.