During the first full-scale survey inside the containment vessel of the plant's No. 1 reactor, damaged in the March 2011 earthquake and tsunami, a maximum radiation level of 11.1 sieverts per hour was detected, The Asahi Shimbun reported Thursday.
Exposure to that level of radiation for less than an hour could be fatal.
However, plant operator Tokyo Electric Power Co. said the figure was lower than the 73 sieverts per hour detected in the No. 2 reactor's containment vessel in March, a level that would be fatal to humans in just minutes.
Tepco inserted a camera into the No. 1 reactor's containment vessel Oct. 9 for the first time since the plant was damaged in the earthquake and tsunami.
More than 9 feet of water was seen in the containment vessel, and Tepco officials said the melted nuclear fuel lying under the water is being cooled.
"Some data on radiation levels and water levels have become available," said Masayuki Ono, acting general manager of Tepco's Nuclear Power and Plant Siting Division. "We think we have obtained important information in planning future responses."