Engineers at Japan's tsunami-battered Fukushima-Daiichi nuclear power plant have reported seeing no serious damage to its inner walls and pipes during a camera inspection Thursday.

Plant operator Tokyo Electric Power Company is trying to determine the state of nuclear fuel inside three crippled reactors, after fuel melted through the walls of their core units and dropped to the bottom of their containment vessels.

The meltdowns and subsequent explosions last March spread contamination over wide swaths of northeastern Japan and forced mass evacuations from the region.

Engineers passed a fiber-optic camera through a hole in one of the facility's wrecked reactors Thursday to see inside. Some of the images were blurred, apparently due to vapor from contaminated cooling water.

Reactor temperatures were also found to be stable.