Photo Special: Radiation level at Fukushima reactor highest since 2011 disaster

An about 1-square-meter hole is seen in a walkway in the containment vessel of the No. 2 reactor at Tokyo Electric Power Co.'s Fukushima No. 1 nuclear plant. It is thought that the heat of the melted nuclear fuel caused the walkway to give way. (Image courtesy of Tokyo Electric Power Co.)

The inside of the containment vessel of the No. 2 reactor at the Fukushima No. 1 nuclear plant is seen in this composite image provided by Tokyo Electric Power Co.

Material believed to be melted nuclear fuel is seen on a grate, in the containment vessel of the No. 2 rector at the Fukushima No. 1 nuclear plant. (Image courtesy of Tokyo Electric Power Co.)

Tokyo Electric Power Co.'s Fukushima No. 1 nuclear plant is seen from the air in this Nov. 22, 2016 file photo. (Mainichi)