The Hole in Fukushima's Reactor Was Always There. A 95-Gram Drone Finally Saw It.
Fifteen years after the Fukushima Daiichi meltdown, robots are finally seeing what happened inside the reactor vessels — and what they found is worse than the models predicted.
Micro-drones deployed by Tokyo Electric Power Company into the Unit 3 reactor captured the first close-up footage of a hole in the bottom of the pressure vessel, the thick-walled steel container that originally housed the nuclear core. Lumps of what engineers believe to be melted fuel debris were visible hanging from the opening, according to reporting by the Associated Press. It is the first visual confirmation of a pressure vessel breach in any of the three reactors that melted down in March 2011.
The drones, built specifically for this mission, measure just 13 by 12 centimeters and weigh 95 grams with battery, camera, and LED lights attached. Two were flown separately over a two-week mission beginning March 5, each managing roughly eight minutes inside the primary containment vessel before communications constraints forced them back. The footage showed ruptured tubes, damaged structures, and brown and gray deposits hanging like giant icicles from the vessel bottom.
Masaki Kuwajima, a TEPCO spokesperson, confirmed the hole at the pressure vessel bottom and said the hanging material is consistent with melted fuel debris, according to the AP. The drones also collected radiation readings and data to build a detailed three-dimensional map of the reactor interior.
The finding matters because it refines the timeline of how the meltdowns unfolded. When the March 2011 earthquake and tsunami knocked out cooling systems at the plant, the fuel rods in three reactors overheated, melted through their cladding, and relocated within and in some cases through the pressure vessel. Knowing where the debris ended up — and where the vessel was breached — changes what the removal process will have to contend with.
TEPCO previously extracted tiny samples of melted fuel from the Unit 2 reactor in November 2024 and April 2025, a milestone that took years of robot development. But internal conditions in Unit 3 appear more degraded. Full-scale debris removal across all three reactors is not currently scheduled until fiscal 2037 at the earliest. TEPCO has said it expects the decommissioning process to extend into the second half of the century.
The robotics involved in this mission represent a genuine advance in hazardous environment autonomy. Sending a sub-100-gram vehicle into a space riddled with obstacles, radiation hot spots, and unpredictable debris — and getting it back with usable footage — requires navigation, fault tolerance, and real-time decision-making that failed earlier generations of inspection robots. The communications limitations that cut the original flight plan short underscore how much the drones still have to operate on borrowed time: eight minutes does not allow for a leisurely survey.
The micro-drones used here are a far cry from the underwater robot that provided a murkier picture of Unit 3 nearly a decade ago. They are smaller, more maneuverable, and designed for this specific geometry. TEPCO says the data will inform the access strategy for debris retrieval, which remains one of the most technically demanding engineering projects in human history.
There are 880 tons of fuel debris spread across Units 1, 2, and 3. Nobody has ever removed melted fuel from a shattered reactor core. The hole in Unit 3's pressure vessel is a data point — not just a milestone, but a constraint. It tells engineers that whatever retrieval tools eventually go in will need to work around a breach that changes how debris may be distributed, how radiation flows, and how tight the operating envelope actually is.