Rapid Environmental Mapping with Instrumented Unmanned Aerial Vehicle: Experience and Lessons Learned from the Commissioning and Trial Measurements in the Areas Affected by TEPCO Fukushima Daiichi Nuclear Power Plant Accident

Background A part of the International Atomic Energy Agency (IAEA)’s response to the accident at TEPCO Fukushima Daiichi nuclear power plant was the Action Plan on Nuclear Safety. One of its requirements was a need to urgently develop portable equipment, associated instrumentation, and validated methodologies for radiological mapping and radiation monitoring. As a result, a dedicated project was developed and implemented on the use of instrumented unmanned aerial vehicles (UAV) in areas that are not accessible on foot and where high radiation levels might exist. This report covers a 10-year period during which the UAV industry has matured immensely and there have been a number of significant developments in UAV technology and detector systems tested and deployed (e.g., see Ref. [1] and references therein). Use of UAV systems has become widely accepted by regulatory authorities in a number of sectors, even including the use of autonomous/semiautonomous systems within the nuclear industry [2, 3]. However, even in 2023, commercially available off-the-shelf systems to perform radiological mapping are few (e.g., Ref. [4, 5]) and practical operational experience remains limited. Herein, we describe the project and system developed and delivered to Fukushima Prefecture. Development of the UAV-Based System The UAV System The selected UAV system was an Aibotix X6 [6]. The intended market for the X6 at that time was for photographic inspection and thus came equipped with a centrally mounted stabilized camera gimbal. A more precise method of measuring height above ground level through a laser rangefinder system was added. The radiation detector systems developed by the IAEA Nuclear Science and Instrumentation Laboratory were mounted on the gimbal such that the radiation detectors and cameras could be exchanged. Data were collected at a frequency of 1 Hz and transferred to the main UAV processing unit, whereupon the measurement data were combined with flight parameters, especially position and altitude. These data were transmitted in real time on the pilot remote control and stored on both the UAV and detector systems, for later analysis.