[en] Sodium boiling and dryout behavior behind planar blockages were examined with three 37-pin bundle experiments of different spacer and blockage type. Boiling inception within the grid spacer cells, closed on one side by the blockage, caused vigorous sodium boiling and subsequent dryout due to the restricted freedom of coolant movement. Local boiling behind the central blockage in the wire-wrapped pin bundle usually resulted in an oscillatory boiling pattern, while the transition to the stable boiling pattern was identified in one case. The edge blockage in the similar wire-wrapped bundle produced oscillatory or stable boiling patterns depending on the flow rates. The difference and transition in the flow patterns were analyzed from the viewpoint of the volume balance of the vapor cavity to adjust the thermal and hydraulic boundary conditions at the two-phase interface region. The dryout data were intercompared to account for the location of the dryout position and the critical condition of the onset of local dryout. This study led to a model in which the liquid film on the pins within the vapor cavity varies in quantity mainly through the entrainment generation and the deposition of the entrained droplets. (author)