Development of Unmanned Aerial Vehicle Technology for High-resolution Environmental Data Acquisition and an Investigation Method for Reactor Decommissioning at Fukushima Daiichi Nuclear Power Plant

We propose a survey method for accessing the interior of the reactor pressure vessel (RPV) in Unit 1 of the Fukushima Daiichi Nuclear Power Plant (1F-1) through a presumed bottom opening, aiming to collect crucial environmental data such as internal conditions, video imagery, and spatial dose rate maps to inform decommissioning strategies. To enable this, a prototype UAV was developed for stable flight under harsh conditions, including high radiation, darkness, confined spaces, high humidity, and fog. The UAV incorporates dual redundant sensors for position control and combines autonomous hovering with collision avoidance systems to enhance stability in narrow spaces. Performance evaluations demonstrated that the UAV met all requirements and achieved stable flight in fog-free environments, while stable operation was largely maintained even under foggy conditions, despite minor reductions in control precision. The bottom-access survey method proved to be safe and efficient, with no issues in data collection or communication. These findings confirm the feasibility of spatial dose rate mapping inside the RPV and highlight the potential for acquiring detailed internal data that had previously been difficult to obtain.