[en] A redesigned beryllium reflector has been installed in the Advanced Test Reactor (ATR) at the Idaho National Engineering Laboratory. The main feature of the redesigned reflector was the introduction of horizontal sawcuts at 13 different elevations immediately adjacent to the fuel region of the core. Two other significant core design changes were made at the same time: (1) the hafnium plates on the outer shim control cylinders were reduced in arc length from 134⁰ to 122⁰, and (2) the inside diameter of the center flux trap baffle was reduced from 85.725 mm (3.375 in.) to 82.2325 mm (3.2375 in.) to increase the metal-to-water ratio in the center flux trap baffle region. Following installation of the redesigned components, zero power physics tests were made with a core of new fuel elements prior to resuming full power operation. The power distribution measurements were obtained in both the ATR and ATRC by irradiating U--Al flux wires in each of the forty fuel elements. The irradiated wires are counted for beta activity which is then converted to specific fission rate. The specific fission rate data are used to calculate point power densities and fuel element powers