Analytical study of steam diffusion and chemical interaction with beryllium powder on hot surface inside the grooves

Tokamak reactor operation is accompanied by beryllium dust (powder) formation inside vacuum vessel as a result of plasma-facing armour erosion. This dust will be accumulated mainly within the grooves on armour hot surfaces. A significant safety problem associated with explosion hazard may be caused by hydrogen chemical production from overheated steam on beryllium dust at accident conditions of water in-leakage. However it is expected that this chemical reaction will become extinct due to limited diffusion of steam into narrow grooves. An analysis of the data on Be/steam chemical reaction rates at a temperature above 700degreesC has been carried out. Reaction features in porous medium (powder bulk) have been considered. The factors of steam/hydrogen binary diffusion have been determined. A calculation model for the reaction simulation is briefly described. The results of parametrical analysis are presented for various temperatures and pressures in the case of dust location on open surface and inside grooves. Hydrogen production rate in powder inside grooves is considerably less than that on open surface.