Radiation: what drones and robots have seen where people cannot go

Radiation — especially penetrating gamma rays — creates charge inside semiconductors much as it damages living cells. The damage comes in two kinds: gradual degradation as the accumulated dose builds up (total ionising dose), and instant bit flips or malfunctions when a particle strikes (single-event effects). Drones rely on commercial electronics to stay small and light, and those parts are vulnerable to radiation.

The largest site is the decommissioning of TEPCO’s Fukushima Daiichi Nuclear Power Station. After the 2011 accident, the first machines into the reactor buildings were remote-controlled ground robots. Since then the primary containment vessels have been explored step by step with crawling robots, telescopic probes and underwater vehicles, revealing deposits believed to be fuel debris. More recently, small drones have flown inside a containment vessel (in February 2024, two small drones imaged the area outside the pedestal in Unit 1). In November 2024, a very small amount of fuel debris was retrieved from Unit 2 on a trial basis.

You also meet it in inspections of operating and retired nuclear facilities, at accelerators and research sites, at radiographic testing where pipe welds are imaged with radiation sources, and in piping, storage tanks and process plants of oil and gas production — and some mines — where naturally occurring radioactive material (NORM) builds up as scale. Outdoors, unmanned helicopters and other uncrewed aircraft have long been used to measure air dose rates across wide areas after the accident (for example, JAEA surveyed the area within 5 km of the plant by unmanned helicopter in 2016).

• Start from a dose estimate: from dose rate and dwell time, estimate the accumulated dose the electronics can survive. The camera usually fails first.
• Accept “single-use” as an option: a contaminated aircraft may never be allowed out. Decide recovery, decontamination, storage and disposal at the outset.
• Plan for entry through small openings: containment vessels are entered through existing penetrations or small holes. Rehearse aircraft size, guards and tether handling on a mock-up before the real thing.
• Treat GNSS loss, darkness and link loss together: buildings block satellites and radio and are pitch dark. Decide lighting, relays, tethers and link-loss behaviour.
• Log dose and time with the imagery: so you can later tell whether degraded images reflect change in the object or degradation of the sensor.

In Japan, nuclear facilities are regulated by the Nuclear Regulation Authority under the Reactor Regulation Act, and worker exposure is managed under the Ordinance on Prevention of Ionizing Radiation Hazards and related rules. The dose limit for radiation workers is 100 mSv over five years and 50 mSv in any one year. Drones reduce human exposure, but the exposure of pilots and recovery staff still belongs in the plan. Equipment brought into a controlled area is checked for contamination before it can leave.

Flight over and around nuclear facilities is often restricted because they are designated critical sites, and outdoor flights also fall under aviation flight rules. Related: GNSS-denied, darkness, confined spaces, world regulations.

• Long work under high dose: cameras and boards lose life with every unit of dose absorbed. Aircraft that loiter for hours remain hard.
• Handling heavy objects in flight: tasks like debris retrieval are out of reach for flying machines. Drones remain “look and measure” tools.
• Cleaning up contaminated aircraft: an aircraft that cannot be recovered becomes an obstacle for the next job.
• Tying dose accurately to position: in dark buildings without satellites, the positional accuracy of the dose map itself is a challenge.

Small radiation-tolerant cameras and boards have become affordable, and each entry into a building updates a dose map and 3D model. The day before workers go in, a drone always measures “today’s dose” and marks the route. Debris retrieval, though, is still done by heavy arms and ground robots; flying machines keep working as the eyes of people and robots. Decommissioning lasts decades, and that accumulated record becomes the most valuable asset. That is the editors’ outlook.