Recent developments in ultra-wideband (UWB) technology have shown great promise in wireless transmission of sensor data in complex environments that are hostile to RF propagation, such as nuclear facilities. UWB RF communications is particularly important for reliable communications for its robust link despite the multipath phenomenon in heavy metallic environment of nuclear reactors, as well as in addressing penetration challenges through thick nuclear concrete walls. Although UWB signaling and unique data modulations are critical for successful communications in such harsh propagation environments, a fixed UWB radio hardware architecture, with fixed frequency and transmit power level, could still be expected to face difficulties in various nuclear facilities as their RF propagation environment might be different with unique and dynamic characteristics. In this paper we report on a newly developed UWB system based on softwaredefined- radio (SDR) that is capable of adapting its communications parameters to its propagation environment for optimized transmission/reception results in various nuclear facilities. This new UWB-SDR system has been successfully laboratory and field tested and is ready for testing and evaluation in commercial reactors. In this paper we briefly review the advantages of UWB communications for nuclear facilities and focus on details of the unique UWB-SDR architecture of the newly developed sensor communications system. Then we present experimental results conducted at the UC Davis McClellan Nuclear Center, and conclude the paper with a summary of the main observations and path for future research.