A parametric thermohydraulic study for an advanced pressurized water reactor (APWR) with a tight fuel rod lattice has been performed. The APWR improves uranium utilization. It has been assumed that the APWR core should be placed in a modern German pressurized water reactor (PWR) plant. Within this study ∼200 different reactors have been calculated. The tightening of the fuel rod lattice implies a decrease of the net electrical output of the plant. APWR cores mean higher core pressure drops and higher water velocities in the core region. The cores tend to be shorter and the number of fuel rods higher than for the PWR. In the range of interest, homogeneous and heterogeneous reactors are about equivalent (same net electrical output of the plant for the same ratio between water and fuel rod volume). For homogeneous reactors the optimum designs are for H/d = 20 (H= axial pitch of the integral spiral ribs on fuel rod surface, d = diameter of the fuel rod) and for heterogeneous reactors for H/d = 35.