Sensing and Sampling of Trace Contaminations by a Dexterous Hexrotor UAV at Nuclear Facilities-18600

Safe and efficient cleanups are a priority for decontamination and decommissioning of nuclear facilities. The contaminations of byproducts and wastes in such nuclear facilities pose a serious problems while decommissioning, to both the operators and public. Sensing these contaminations and cleaning them is an essential part of the safety procedures. The contaminations might range from low-energy to high-energy byproducts. Sensing these byproducts would require contact based or non-contact based sensing, based on its energy levels. Byproducts such as americium, are low-energy which makes it difficult to sense and sample without contact. Therefore, the workers need to physically swab the surfaces to collect the samples of these contaminations. These tasks pose a great danger for the safety of the human workers which includes the risk to reach greater heights, exposure to the radiation and sampling the entire building. A robotic solution is much more desirable in these cases, where the worker can safely handle the contaminations from a safe area. Use of robotic technologies inside these hazardous environments ensures the safety and enhances the performance. The more suitable robotic solution for reaching great heights and covering large areas of nuclear facilities, are aerial vehicles. Multirotor unmanned aerial vehicle (UAV) are chosen for their ability to hover at a position and also fly around in confined spaces. Quadrotors are a common choice of multirotor UAVs both research and industry because of its ease to fly and commercial availability. For the applications during the cleanups we need the UAV to not only hover and fly in confined spaces, but also interact with the physical world. Despite of quadrotor’s advantages, they are not a best suit as they can’t interact with the physical world. The tasks involving physical interactions would require the UAV to apply arbitrary forces & torques in all six degrees of freedom (DOF). As quadrotors are under-actuated and nonholonomic in motion, they cannot exert all the required forces. At Collaborative Robotics Lab, Purdue University, we developed a novel multirotor UAV solution, Dexterous Hexrotor, which can exert arbitrary forces & torques in all six DOF, independently and instantaneously. This enables the UAV platform to quickly respond to the external disturbances and precisely hold its position during the mission. The Dexterous Hexrotor serves as a robotic tool for the workers to perform sensing and sampling during the cleanups. Workers can operate Dexterous Hexrotor manually and/or semi-autonomously with human intervention. Manual control requires the worker to fly the Dexterous Hexrotor using a remote control. So the workers should possess knowledge on flying the UAV and to perform physical interaction. A semiautonomous Dexterous Hexrotor requires human input to some extent and requires very less knowledge of flying. The autonomy is designed to operate in flight mode and sampling mode. In flight mode, Dexterous Hexrotor takes off from a “safe” area, reaches the desired altitude, and fly autonomously towards a sampling point. This sampling point is the target position specified on the 2D reference map. This mode also includes navigation towards the sampling point, avoiding the obstacles in the constrained environment. After reaching a stopping point, Dexterous Hexrotor waits for the human input for a target location to swab and collect samples. The Dexterous hexrotor is now in sampling mode and waits for the human input. The human operator selects the swabbing location through the live streaming video from onboard camera. WM2018 Conference, March 18 22, 2018, Phoenix, Arizona, USA 2 Through visual servoing, aided by the map, the UAV will move closer towards the target position. It then transitions to the impact control scheme to perform physical interaction with the wall and collects samples. Once the sample is collected, it autonomously returns back to the takeoff position in “safe” area for the analysis by mass spectrometry. In this paper, we majorly focus on the physical interaction strategy and the required components which enables the autonomy. Decommissioning of nuclear facilities requires decontamination inside the entire buildings. Decontamination of nuclear facilities involves sensing and sampling the huge buildings, long shafts, etc. Sampling the entire facility is not possible due to the limitation in Dexterous Hexrotor’s flight time. But this can be achieved by using a swarm of Dexterous Hexrotors to cover larger areas. The onboard robotic arm can be designed based on the applications such as cleaning, applying sealants, etc. The modularity of the design allows us to switch components as per the requirements of the task. These kind of robotic solutions functioning as tools for the workers, aims to make the work environment safer and playful. INTRODUCTION Managing the nuclear waste from nuclear power plants and nuclear weapons development has been a major issues over the decades. Several facilities containing the nuclear reactors, chemical processing buildings, laboratories are involved in this process. The nuclear wastes from such facilities are processed in processing facilities and are stored in underground storage facilities. Many of such facilities are set for decontamination and decommissioning and some facilities would require constant inspections for contaminations. Fig. 1. Carlsbad Waste Isolation pilot plant (WIPP) The Department of Energy and the office of Environmental Management has being assigned to perform nuclear waste cleanups in 107 sites across the United States. There are still 16 active sites which are yet to be cleaned up [1]. These active sites include Savannah River site, Hanford site, Portsmouth Gaseous diffusion plant, Sandia National Laboratories, CarlsbadWIPP, etc. The Carlsbad –WIPP is a permanent storage facility for Transuranic (TRU) radioactive waste which contains alpha-emitting isotopes with an atomic number greater than uranium. WM2018 Conference, March 18 22, 2018, Phoenix, Arizona, USA 3 The facility occupies a space of 16 square miles at 2150 feet underground. Vertical shafts circulate air from the surface as shown in fig 1. Performing cleanup tasks safely in such facilities is not an easy task for humans. Especially the vertical shaft pose a serious challenge for inspection in terms of reachability and sensing. Savannah River site and Hanford site has facilities such as reactor building, support facilities, auxiliary structures, etc., which need regular cleanups. DOE has signed up to decontamination and decommission (D&D) 415 facilities and structures at Portsmouth site where uranium enrichment operations were held. Demolition of 36 inactive facilities and building larger than 700,000 square feet has been accomplished by safely eliminating the contaminations. An aerial view of Portsmouth gaseous diffusion plant is shown in fig 2. Fig. 2. Portsmouth Gaseous Diffusion Plant The nuclear sites mentioned above, always poses safety hazard for the workers and also to the general public. Considering the harsh environment in such facilities, it is safer to use robots to assist humans rather than sending humans. Robots have been an integral part of some of the cleanups, D&D activities. Most of these robots have been developed to perform a specific task, at specific locations. This doesn’t yield an efficient approach for robotic solutions towards the existing problems, as it requires time and resources to build newer robots. Modular design is much desirable to yield efficiency in serving multiple purposes by reconfiguration. Mothership is one such ground robot, designed to serve multiple purposes because of its ease of configurability [2]. It is built in a modular fashion which allows the engineers to create a new robot from the same modules depending on the tasks and terrains. Another important factor to be considered in developing a robot is the ease to control them. The workers on site should be able to control the robot rather than a highly paid engineers. These two factors provides an effective robot which acts as a tools for the workers to enhance their tasks performance in D&D. DEXTEROUS HEXROTOR FOR SENSING AND SAMPLING We propose Dexterous Hexrotor as a tool for the workers in nuclear facilities to perform their job tasks with safety and efficiency. The tasks would require the UAVs to cover the large facilities and physically interact with the contaminated surfaces to collect samples and perform cleanups. Commercially available multirotor UAVs have the ability to hover and fly in confined spaces by avoiding obstacles. But they can’t physically interact with the contaminated locations. WM2018 Conference, March 18 22, 2018, Phoenix, Arizona, USA 4 Dexterous Hexrotor is capable of flying in confined spaces and physically interact with surfaces to collect samples or perform cleanups, autonomously [3] [4]. Dexterous Hexrotor is built from a hexrotor platform with propellers tilted at an optimized angle, called cant. Common multirotor UAVs such as quadrotor, have parallel actuators which enables the actuation in 4 DOF. The remaining 2 DOF, which are forces in horizontal plane, are achieved through torques around horizontal axes. This makes the UAV under actuated, non-holonomic and not suitable for physical interactions or flying close to the physical structures. The cant angle in Dexterous Hexrotor enables forces and torques in all six DOF independently, providing instantaneous forces in the horizontal plane. The Dexterous Hexrotor is capable to fight external disturbances during the physical interactions and also disturbances associated with flying close to the structures [5]. Dexterous Hexrotor Prototypes A team of Dexterous Hexrotors are developed to perform the operations autonomously. Each Dexterous Hexrotor is configured according to the requirement of the task. A 1 DOF Robotic arm is installed on the UAV to perf