[en] Transient natural convection in a lenticular shaped heat-generating layer of water has been studied experimentally as a model of a possible core melt configuration. The layer has an insulated lower boundary and an isothermal upper boundary. Correlations are developed for the flow development and decay time constants when internal heating is either suddenly started or stopped. Flow development times are found to be generally greater than those for similar processes in a horizontal layer. The results of the present study are supported by earlier steady-state measurements and numerical solutions of the governing partial differential equations. (author)