Japan's nuclear regulator has released a video of the interior of the No.3 reactor building at the crippled Fukushima Daiichi nuclear power plant.
The reactor suffered a meltdown and a hydrogen explosion that blew off the upper part of the building.
Workers have finished removing debris from the fifth and highest floor of the building. They are now transferring nuclear fuel from a cooling pool in the building to a storage facility on the compound.
Members of a panel at the Nuclear Regulation Authority entered the building on December 12. They had reopened an investigation into the 2011 nuclear accident in the autumn.
The panel members walked from the first floor to the third, despite the scattered debris. But they could not get to the fourth floor as the stairway had been destroyed by the explosion.
On the third floor ceiling they found beams that had been badly bent, and air ducts that had been ripped off. The damage indicates that the hydrogen explosion on the fifth floor or adjacent area had an impact on the third floor.
The panel members observed high radiation levels in some spots on each floor. One section of the second floor had a level of 150 millisieverts per hour.
The panel says more decontamination work is needed in order to scrap the reactor. It plans to continue its investigation and compile a report as early as next year.