This paper discusses the spatial controller design with periodic output feedback for a 540 MWe PHWR. the spatial model of the reactor developed in (Tiwari, 1999) is augmented with models for variation of coolant and fuel temperatures to form a 72 order model. This new model having 14 inputs and 29 outputs, is suitably reduced by aggregation method. Finally, a periodic output feedback control for the high order model is designed using the reduced model. the results of nonlinear simulations are presented. Copyright © 2004 IFAC