[en] The passive containment cooling capability provides an ultimate heat sink in accident situations. Among various proposed design concepts, the most commonly adopted is the concept of buoyancy driven air flow for passive cooling. The governing parameters, which can be used either in experimental facility design or constitutive relation development, are derived by applying the zonal estimation concept, which treats the boundary layer and core region separately. In this work, the steady state governing equations, which incorporate the effects of turbulence, are employed and the estimations of physical quantities related in this problem are made and verified. The relative importances among governing parameters are carefully investigated, and the balances of the physical quantities in the system are evaluated. Through this procedure, the number of governing parameters is reduced. The estimated magnitude of each governing parameter is verified through predicting the boundary, layer thickness. The results of this study show that the most important parameters are found to be Grashof and Reynolds numbers in the heated region and Reynolds number and length ratio in the core region. (author)