A thermodynamic method of excited cellular automata is put forward for modeling mass transfer in an open multilevel system "surface layer-interface with chessboard-like distribution of normal tensile and compressive stresses-substrate with stochastic distribution of atomic nanoclusters having excess atomic volume". Under excess pressure in the bulk of the irradiated material one can see the formation of nanocluster flows along the conjugate directions of maximum tangential stresses. The outward material extrusion takes place in the local interface zones with normal tensile stresses. Such processes should underlie the swelling and growth of irradiated materials with close-packed structure