Autonomous Navigation and piloting of mobile robotic vehicles throughout complex structures such as a nuclear facility, without requiring the installation of special fixtures within the structure, is becoming increasingly important. This paper discusses the development and implementation of navigation algorithms which use the measurements from an on-board scanning range sensor. The navigation algorithms include a Global Path Planner, a Local Path Planner and a Location Identification System. The Global Path Planner selects the optimum path for the mobile robot, employing a stored database containing information about routes throughout the facility. The designated path is defined in terms of local goal coordinates. The Local Path Planner must navigate between the commanded local goal locations, detecting and circumventing any unexpected obstacles which impede the progression of the robot. The Transport Window Concept is employed to accomplish local path planning. The Location Identification System employs the facility database to correlate stored information with measurement data from the scanning range sensor to precisely position the robot and periodically update its on-board Inertial Navigation System. The Local Path Planning Algorithms have been implemented and functionally verified using the Odetics 3D Laser Imaging Radar mounted on a mobile robot navigating through a modelled portion of a nuclear power plant.