A preconceptual design has been developed for the3He Target/Blanket System for the Accelerator Production of Tritium Project. The design use tungsten wire‐wrapped rods to produce neutrons when the rods are struck by a proton beam. The rods are contained in bundles inside hexagonal Inconel ducts and cooled by D2O. Rod bundles are grouped in patterns in the proton beam inside a chamber filled with3He that is transmuted to tritium by the neutrons coming from the tungsten rods.Additional3He is transmuted in a blanket region surrounding the helium chamber. This paper describes the initial thermal‐hydraulic design and testing that has been completed to confirm the designed calculations for pressure drop through the bundle and heat transfer in the bundle. Heat transfer tests were run to verify steady‐state operation. These tests were followed by increasing power until nucleate boiling occurs to determine operating margins. Changes that improve the initial design are described. ©American Institute of Physics 1995