[en] Scaling criteria for a natural- and forced-convection circulation loop under single-phase and two-phase flow conditions are derived from the fluid-balance equations, boundary conditions, and solid energy equations. For a single-phase-flow case the continuity, integral momentum, and energy equations in one-dimensional area-averaged forms are used. For a two-phase flow case, the one-dimensional drift-flux model obtained from the short-time temporal averaging and the sectional area averaging is used. The scaling criteria are applied to a conceptual design of a 2 x 4 loop facility for simulating the Babcock and Wilcox 177 NSSS design. Feasibility of practical solutions are studied and some conclusions on this proposed facility in terms of the proper scaling are obtained