Tokyo Electric Power Company Holdings released footage Thursday showing the interior of a damaged reactor at the Fukushima Daiichi nuclear power plant, marking the first visual confirmation of a hole in the pressure vessel since the 2011 disaster.

The images were captured by micro-drones measuring 12 by 13 centimeters and weighing 95 grams each during a two-week mission that began March 5. The drones documented a gaping hole in the steel container of the Unit 3 reactor core, with brown and gray objects resembling giant icicles hanging from the damaged structure.

TEPCO spokesperson Masaki Kuwajima confirmed the hanging objects are believed to be melted fuel debris. The footage also showed tubes with ruptures and other damaged structures that were originally enclosed within the pressure vessel. The drones collected radiation measurements and gathered data to create a detailed three-dimensional map of the reactor's interior.

The March 11, 2011 earthquake and tsunami destroyed cooling systems at Fukushima Daiichi, causing meltdowns in reactors 1, 2, and 3. The three reactors contain at least 880 tons of melted fuel debris with radiation levels that remain dangerously high 15 years later.

TEPCO successfully extracted small melted fuel samples from Unit 2 reactor last year, but internal details of the damaged reactors have remained largely unknown. The company plans additional remote-controlled probes and sampling missions to analyze the melted fuel and develop robots for future debris removal.

Experts estimate the complete removal of fuel debris could take several more decades. The latest drone mission represents a significant advancement from an underwater robot probe conducted nearly a decade ago that provided less clear imagery of the Unit 3 reactor's interior.